Patent Application
20160145685
Technology provided herein relates in part to methods, processes and apparatuses for non-invasive assessment of genetic variations.
Genetic information of living organisms (e.g., animals, plants and microorganisms) and other forms of replicating genetic information (e.g., viruses) is encoded in deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). Genetic information is a succession of nucleotides or modified nucleotides representing the primary structure of chemical or hypothetical nucleic acids. In humans, the complete genome contains about 30,000 genes located on twenty-four (24) chromosomes (see The Human Genome, T. Strachan, BIOS Scientific Publishers, 1992). Each gene encodes a specific protein, which after expression via transcription and translation fulfills a specific biochemical function within a living cell.
Many medical conditions are caused by one or more genetic variations. Certain genetic variations cause medical conditions that include, for example, hemophilia, thalassemia, Duchenne Muscular Dystrophy (DMD), Huntington's Disease (HD), Alzheimer's Disease and Cystic Fibrosis (CF) (Human Genome Mutations, D. N. Cooper and M. Krawczak, BIOS Publishers, 1993). Such genetic diseases can result from an addition, substitution, or deletion of a single nucleotide in DNA of a particular gene. Certain birth defects are caused by a chromosomal abnormality, also referred to as an aneuploidy, such as Trisomy 21 (Down's Syndrome), Trisomy 13 (Patau Syndrome), Trisomy 18 (Edward's Syndrome), Monosomy X (Turner's Syndrome) and certain sex chromosome aneuploidies such as Klinefelter's Syndrome (XXY), for example. Another genetic variation is fetal gender, which can often be determined based on sex chromosomes X and Y. Some genetic variations may predispose an individual to, or cause, any of a number of diseases such as, for example, diabetes, arteriosclerosis, obesity, various autoimmune diseases and cancer (e.g., colorectal, breast, ovarian, lung).
Identifying one or more genetic variations or variances can lead to diagnosis of, or determining predisposition to, a particular medical condition. Identifying a genetic variance can result in facilitating a medical decision and/or employing a helpful medical procedure. Identification of one or more genetic variations or variances sometimes involves the analysis of cell-free DNA.
Cell-free DNA (CF-DNA) is composed of DNA fragments that originate from cell death and circulate in peripheral blood. High concentrations of CF-DNA can be indicative of certain clinical conditions such as cancer, trauma, burns, myocardial infarction, stroke, sepsis, infection, and other illnesses. Additionally, cell-free fetal DNA (CFF-DNA) can be detected in the maternal bloodstream and used for various noninvasive prenatal diagnostics.
The presence of fetal nucleic acid in maternal plasma allows for non-invasive prenatal diagnosis through the analysis of a maternal blood sample. For example, quantitative abnormalities of fetal DNA in maternal plasma can be associated with a number of pregnancy-associated disorders, including preeclampsia, preterm labor, antepartum hemorrhage, invasive placentation, fetal Down syndrome, and other fetal chromosomal aneuploidies. Hence, fetal nucleic acid analysis in maternal plasma can be a useful mechanism for the monitoring of fetomaternal well-being.
Provided in some aspects herein are methods for analyzing fetal nucleic acid in a sample, comprising digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments, and analyzing the digested nucleic acid fragments. In some aspects the analyzing comprises determining the presence or absence of one or more polynucleotides in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid. In certain aspects the one or more loci are chosen from loci in Table 2AB, Table 2CB, Table 3 and Table 4.
Provided in some aspects herein are methods for analyzing nucleic acid in a sample, comprising: enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, thereby generating enriched hypomethylated nucleic acid and analyzing the enriched hypomethylated nucleic acid, which analyzing comprises determining the presence, absence or amount of a polynucleotide in one or more loci chosen from loci of Table 4.
Provided in some aspects herein are methods for enriching for a minority nucleic acid species in a sample, comprising digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments and analyzing the digested nucleic acid fragments.
Provided in some aspects herein are methods for enriching for a minority nucleic acid species in a sample, comprising digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments and enriching the digested nucleic acid fragments relative to non-digested nucleic acid, thereby generating nucleic acid enriched for the minority nucleic acid species.
In some aspects provided herein are methods for analyzing nucleic acid in a sample, comprising enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, thereby generating enriched hypomethylated nucleic acid and analyzing the enriched hypomethylated nucleic acid, which analyzing comprises determining the presence, absence or amount of a polynucleotide in one or more loci chosen from loci of Table 4.
In some aspects provided herein are methods for preparing a collection of amplification primers, comprising (a) selecting one or more genomic loci, wherein each of the loci comprises three or more or all features selected from: (i) a locus length of about 5000 contiguous base pairs, or less, (ii) a CpG density of 16 CpG methylation sites per 1000 base pairs, or less, (iii) a gene density of 0.1 genes per 1000 base pair, or less, (iv) at least 5 CpG methylation sites, (v) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (vi) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition site can be specifically digested by a methylation sensitive cleavage agent, (vii) a locus comprising a methylation status of 40% or less in fetal nucleic acid, (viii) a locus comprising a methylation status of 60% or more in maternal nucleic acid, and (ix) a locus comprising a difference in methylation status of 5% or more between fetal nucleic acid and maternal nucleic acid, and (b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared. Any suitable combination of three or more (e.g., 3, 4, 5, 6, 7 or 8) of features (i), (ii), (iii), (iv), (v), (vi), (vii), (viii) and/or (ix) can be utilized in a suitable order for the selection in (a). In some aspects, each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a). In some embodiments, amplification primer pairs are prepared that amplify a target polynucleotide in one or more loci provided in Table 4.
In certain aspects provided herein is a collection of oligonucleotide primer pairs for identifying the presence or absence of a hypomethylated locus prepared by a process comprising (a) selecting one or more genomic loci wherein each locus comprises three or more or all features selected from (i) 5000 contiguous base pairs, or less, (ii) a CpG density of 16 CpG methylation sites per 1000 base pairs, or less, (iii) a gene density of 0.1 genes per 1000 base pair, or less, (iv) at least 5 CpG methylation sites, (v) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (vi) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition sites can be specifically digested by a methylation sensitive cleavage agent, (vii) a locus comprising a methylation status of 40% or less in fetal nucleic acid, (viii) a locus comprising a methylation status of 60% or more in maternal nucleic acid, and (ix) a locus comprising a difference in methylation status of 5% or more between fetal nucleic acid and maternal nucleic acid and (b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared. Any suitable combination of three or more (e.g., 3, 4, 5, 6, 7 or 8) of features (i), (ii), (iii), (iv), (v), (vi), (vii), (viii) and/or (ix) can be utilized in a suitable order for the selection in (a). In some aspects of the foregoing, each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a). In some embodiments, amplification primer pairs are provided that amplify a target polynucleotide in one or more loci provided in Table 4.
In certain aspects presented herein is a collection of amplification primer pairs for identifying the presence or absence of a hypermethylated locus prepared by a process comprising (a) selecting one or more genomic loci wherein each locus comprises three or more or all features selected from: (i) a locus length of about 5000 contiguous base pairs, or less, (ii) at least 5 CpG methylation sites, (iii) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (iv) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition sites can be specifically digested by a methylation sensitive restriction endonuclease, (v) a locus comprising a methylation status of 60% or more in a minority nucleic acid species, (vi) a locus comprising a methylation status of 40% or less in a majority nucleic acid species, and (vii) a locus comprising a difference in methylation status of 5% or more between a minority nucleic acid species and a majority nucleic acid species and (b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared. Any suitable combination of three or more (e.g., 3, 4, 5 or 6) of features (i), (ii), (iii), (iv), (v), (vi) and/or (vii) can be utilized in a suitable order for the selection in (a). In certain aspects of the foregoing, each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a). In some embodiments, amplification primer pairs are prepared that amplify a target polynucleotide in one or more loci provided in Table 5.
Also, presented herein, in some aspects, is a method of preparing a collection of amplification primers, comprising (a) selecting one or more genomic loci wherein each locus comprises three or more features selected from (i) a locus length of about 5000 contiguous base pairs, or less, (ii) at least 5 CpG methylation sites, (iii) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (iv) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition site can be specifically digested by a methylation sensitive restriction endonuclease, (v) a locus comprising a methylation status of 60% or more in fetal nucleic acid, (vi) a locus comprising a methylation status of 40% or less in maternal nucleic acid, and (vii) a locus comprising a difference in methylation status of 5% or more between fetal nucleic acid and maternal nucleic acid and (b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared. Any suitable combination of three or more (e.g., 3, 4, 5 or 6) of features (i), (ii), (iii), (iv), (v), (vi) and/or (vii) can be utilized in a suitable order for the selection in (a). In some embodiments, amplification primer pairs are provided that amplify a target polynucleotide in one or more loci provided in Table 5.
Certain aspects of the technology are described further in the following description, examples, drawings and claims.
The drawings illustrate aspects of the technology and are not limiting. For clarity and ease of illustration, the drawings are not made to scale and, in some instances, various aspects may be shown exaggerated or enlarged to facilitate an understanding of particular embodiments.
Provided herein are methods for enriching and/or analyzing a sub-population of cell-free nucleic acid from a larger pool of cell-free nucleic acid in a sample nucleic acid. Cell-free nucleic acid sometimes comprises a mixture of nucleic acids from different sources (e.g., fetal versus maternal tissue, tumor cells versus normal cells). Nucleic acid from different sources sometimes can be differentially methylated. Such differential methylation of certain subpopulations of cell free nucleic acid can be useful for enriching and/or analyzing a particular subpopulation of nucleic acid. Provided herein are methods for enriching and/or analyzing a particular subpopulation of nucleic acid (e.g., fetal nucleic acid) in a sample comprising circulating cell-free (ccf) nucleic acid.
Provided also are methods, processes and apparatuses useful for identifying a genetic variation. Identifying a genetic variation sometimes comprises detecting a copy number variation and/or sometimes comprises adjusting an elevation comprising a copy number variation. In some embodiments, identifying a genetic variation by a method described herein can lead to a diagnosis of, or determining a predisposition to, a particular medical condition. Identifying a genetic variance can result in facilitating a medical decision and/or employing a helpful medical procedure.
Samples
Provided herein are methods and compositions for analyzing nucleic acid. In some embodiments, nucleic acid fragments in a mixture of nucleic acid fragments are analyzed. A mixture of nucleic acids can comprise two or more nucleic acid fragment species having different nucleotide sequences, different fragment lengths, different origins (e.g., genomic origins, fetal vs. maternal origins, cell or tissue origins, sample origins, subject origins, and the like), or combinations thereof.
Nucleic acid or a nucleic acid mixture utilized in methods and apparatuses described herein often is isolated from a sample obtained from a subject (e.g., a test subject). A subject can be any living or non-living organism, including but not limited to a human, a non-human animal, a plant, a bacterium, a fungus or a protist. Any human or non-human animal can be selected, including but not limited to mammal, reptile, avian, amphibian, fish, ungulate, ruminant, bovine (e.g., cattle), equine (e.g., horse), caprine and ovine (e.g., sheep, goat), swine (e.g., pig), camelid (e.g., camel, llama, alpaca), monkey, ape (e.g., gorilla, chimpanzee), ursid (e.g., bear), poultry, dog, cat, mouse, rat, fish, dolphin, whale and shark. A subject may be a male or female (e.g., woman). In some embodiments a subject is a pregnant human female.
Nucleic acid may be isolated from any type of suitable biological specimen or sample (e.g., a test sample). A sample or test sample can be any specimen that is isolated or obtained from a subject (e.g., a test subject, a human subject, a pregnant female). Non-limiting examples of specimens include fluid or tissue from a subject, including, without limitation, umbilical cord blood, chorionic villi, amniotic fluid, cerebrospinal fluid, spinal fluid, lavage fluid (e.g., bronchoalveolar, gastric, peritoneal, ductal, ear, arthroscopic), biopsy sample (e.g., from pre-implantation embryo), celocentesis sample, fetal nucleated cells or fetal cellular remnants, washings of female reproductive tract, urine, feces, sputum, saliva, nasal mucous, prostate fluid, lavage, semen, lymphatic fluid, bile, tears, sweat, breast milk, breast fluid, embryonic cells and fetal cells (e.g. placental cells). In some embodiments, a biological sample is a cervical swab from a subject. In some embodiments, a biological sample may be blood and sometimes plasma or serum. As used herein, the term “blood” encompasses whole blood or any fractions of blood, such as serum and plasma as conventionally defined, for example. Blood or fractions thereof often comprise nucleosomes (e.g., maternal and/or fetal nucleosomes). Nucleosomes comprise nucleic acids and are sometimes cell-free or intracellular. Blood also comprises buffy coats. Buffy coats are sometimes isolated by utilizing a ficoll gradient. Buffy coats can comprise white blood cells (e.g., leukocytes, T-cells, B-cells, platelets, and the like). In certain instances, buffy coats comprise maternal and/or fetal nucleic acid. Blood plasma refers to the fraction of whole blood resulting from centrifugation of blood treated with anticoagulants. Blood serum refers to the watery portion of fluid remaining after a blood sample has coagulated. Fluid or tissue samples often are collected in accordance with standard protocols hospitals or clinics generally follow. For blood, an appropriate amount of peripheral blood (e.g., between 3-40 milliliters) often is collected and can be stored according to standard procedures prior to or after preparation. A fluid or tissue sample from which nucleic acid is extracted may be a cellular (e.g., cell-free). In some embodiments, a fluid or tissue sample may contain cellular elements or cellular remnants. In some embodiments fetal cells or cancer cells may be included in the sample.
A sample often is heterogeneous, by which is meant that more than one type of nucleic acid species is present in the sample. For example, heterogeneous nucleic acid can include, but is not limited to, (i) fetal derived and maternal derived nucleic acid, (ii) cancer and non-cancer nucleic acid, (iii) pathogen and host nucleic acid, and more generally, (iv) mutated and wild-type nucleic acid. A sample may be heterogeneous because more than one cell type is present, such as a fetal cell and a maternal cell, a cancer and non-cancer cell, or a pathogenic and host cell. In some embodiments, a minority nucleic acid species and a majority nucleic acid species are present. The term “minority nucleic acid species” as used herein refers to a nucleic acid species in a sample that is present in an amount that is less than 50%, less than 40%, less than 30%, less than 20% or less than 10% of the total amount of nucleic acid present in the sample. The term “majority nucleic acid species” as used herein refers to a nucleic acid species in a sample that is present in an amount that is greater than greater than 50%, greater than 60%, greater than 70%, or greater than 80% of the total amount of nucleic acid present in the sample. In some embodiments a minority nucleic acid species comprises fetal nucleic acid. In some embodiments a minority nucleic acid species comprises placental nucleic acid. In some embodiments a minority nucleic acid comprises nucleic acid derived from a tumor or malignant cell-type. In some embodiments a minority nucleic acid species comprises hypomethylated nucleic acid, one or more hypomethylated loci or unmethylated nucleic acid. In some embodiments a minority nucleic acid species comprises hypomethylated fetal nucleic acid. In some embodiments a minority nucleic acid species comprises methylated nucleic acid, hypermethylated nucleic acid or one or more hypermethylated loci. In some embodiments a minority nucleic acid species comprises hypermethylated fetal nucleic acid. In some embodiments a majority nucleic acid species comprises maternal nucleic acid. In some embodiments a majority nucleic acid species is derived from normal healthy tissue of a test subject (e.g., non cancerous tissue, non-malignant tissue, non-infected tissue).
For prenatal applications of technology described herein, fluid or tissue sample may be collected from a female (e.g., a pregnant female) at a gestational age suitable for testing, or from a female who is being tested for possible pregnancy. Suitable gestational age may vary depending on the prenatal test being performed. In certain embodiments, a pregnant female subject sometimes is in the first trimester of pregnancy, at times in the second trimester of pregnancy, or sometimes in the third trimester of pregnancy. In certain embodiments, a fluid or tissue is collected from a pregnant female between about 1 to about 45 weeks of fetal gestation (e.g., at 1-4, 4-8, 8-12, 12-16, 16-20, 20-24, 24-28, 28-32, 32-36, 36-40 or 40-44 weeks of fetal gestation), and sometimes between about 5 to about 28 weeks of fetal gestation (e.g., at 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or 27 weeks of fetal gestation). In some embodiments, a fluid or tissue sample is collected from a pregnant female during or just after (e.g., 0 to 72 hours after) giving birth (e.g., vaginal or non-vaginal birth (e.g., surgical delivery)).
Nucleic Acid Isolation and Processing
Nucleic acid may be derived from one or more sources (e.g., cells, serum, plasma, buffy coat, lymphatic fluid, skin, soil, and the like) by methods known in the art. Cell lysis procedures and reagents are known in the art and may generally be performed by chemical (e.g., detergent, hypotonic solutions, enzymatic procedures, and the like, or combination thereof), physical (e.g., French press, sonication, and the like), or electrolytic lysis methods. Any suitable lysis procedure can be utilized. For example, chemical methods generally employ lysing agents to disrupt cells and extract the nucleic acids from the cells, followed by treatment with chaotropic salts. Physical methods such as freeze/thaw followed by grinding, the use of cell presses and the like also are useful. High salt lysis procedures also are commonly used. For example, an alkaline lysis procedure may be utilized. The latter procedure traditionally incorporates the use of phenol-chloroform solutions, and an alternative phenol-chloroform-free procedure involving three solutions can be utilized. In the latter procedures, one solution can contain 15 mM Tris, pH 8.0; 10 mM EDTA and 100 ug/ml Rnase A; a second solution can contain 0.2N NaOH and 1% SDS; and a third solution can contain 3M KOAc, pH 5.5. These procedures can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y., 6.3.1-6.3.6 (1989), incorporated herein in its entirety.
The terms “nucleic acid” and “nucleic acid molecule” are used interchangeably. The terms refer to nucleic acids of any composition form, such as deoxyribonucleic acid (DNA, e.g., complementary DNA (cDNA), genomic DNA (gDNA) and the like), ribonucleic acid (RNA, e.g., message RNA (mRNA), short inhibitory RNA (siRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), microRNA, RNA highly expressed by the fetus or placenta, and the like), and/or DNA or RNA analogs (e.g., containing base analogs, sugar analogs and/or a non-native backbone and the like), RNA/DNA hybrids and polyamide nucleic acids (PNAs), all of which can be in single- or double-stranded form. Unless otherwise limited, a nucleic acid can comprise known analogs of natural nucleotides, some of which can function in a similar manner as naturally occurring nucleotides. A nucleic acid can be in any form useful for conducting processes herein (e.g., linear, circular, supercoiled, single-stranded, double-stranded and the like). A nucleic acid can be a polynucleotide and/or a nucleic acid fragment. A nucleic acid may be, or may be from, a plasmid, phage, autonomously replicating sequence (ARS), centromere, artificial chromosome, chromosome, or other nucleic acid able to replicate or be replicated in vitro or in a host cell, a cell, a cell nucleus or cytoplasm of a cell in certain embodiments. A nucleic acid in some embodiments can be from a single chromosome or fragment thereof (e.g., a nucleic acid sample may be from one chromosome of a sample obtained from a diploid organism). Nucleic acids sometimes comprise nucleosomes, fragments or parts of nucleosomes or nucleosome-like structures. Nucleic acids sometimes comprise protein (e.g., histones, DNA binding proteins, and the like). Nucleic acids analyzed by processes described herein sometimes are substantially isolated and are not substantially associated with protein or other molecules. Nucleic acids also include derivatives, variants and analogs of RNA or DNA synthesized, replicated or amplified from single-stranded (“sense” or “antisense”, “plus” strand or “minus” strand, “forward” reading frame or “reverse” reading frame) and double-stranded polynucleotides. Deoxyribonucleotides include deoxyadenosine, deoxycytidine, deoxyguanosine and deoxythymidine. For RNA, the base cytosine is replaced with uracil and the sugar 2′ position includes a hydroxyl moiety. A nucleic acid may be prepared using a nucleic acid obtained from a subject as a template.
Nucleic acid may be isolated at a different time point as compared to another nucleic acid, where each of the samples is from the same or a different source. A nucleic acid may be from a nucleic acid library, such as a cDNA or RNA library, for example. A nucleic acid may be a result of nucleic acid purification or isolation and/or amplification of nucleic acid molecules from the sample. Nucleic acid provided for processes described herein may contain nucleic acid from one sample or from two or more samples (e.g., from 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, or 20 or more samples).
Nucleic acids can include extracellular nucleic acid in certain embodiments. The term “extracellular nucleic acid” as used herein can refer to nucleic acid isolated from a source having substantially no cells and also is referred to as “cell-free” nucleic acid and/or “cell-free circulating” nucleic acid. Extracellular nucleic acid can be present in and obtained from blood (e.g., from the blood of a pregnant female). Extracellular nucleic acid often includes no detectable cells and may contain cellular elements or cellular remnants. Non-limiting examples of a cellular sources for extracellular nucleic acid are blood, blood plasma, blood serum and urine. As used herein, the term “obtain cell-free circulating sample nucleic acid” includes obtaining a sample directly (e.g., collecting a sample, e.g., a test sample) or obtaining a sample from another who has collected a sample. Without being limited by theory, extracellular nucleic acid may be a product of cell apoptosis and cell breakdown, which provides basis for extracellular nucleic acid often having a series of lengths across a spectrum (e.g., a “ladder”).
Extracellular nucleic acid can include different nucleic acid species, and therefore is referred to herein as “heterogeneous” in certain embodiments. For example, blood serum or plasma from a person having cancer can include nucleic acid from cancer cells and nucleic acid from non-cancer cells. In another example, blood serum or plasma from a pregnant female can include maternal nucleic acid and fetal nucleic acid. In some instances, fetal nucleic acid sometimes is about 5% to about 50% of the overall nucleic acid (e.g., about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, or 49% of the total nucleic acid is fetal nucleic acid). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 500 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 500 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 250 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 250 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 200 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 200 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 150 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 150 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 100 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 100 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 50 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 50 base pairs or less). In some embodiments, the majority of fetal nucleic acid in nucleic acid is of a length of about 25 base pairs or less (e.g., about 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% of fetal nucleic acid is of a length of about 25 base pairs or less). The term “fetal nucleic acid” as referred to herein means any nucleic acid (e.g., polynucleotide) derived from a tissue, cell or fluid originating from a human embryo, fetus, or unborn human child. Non-limiting examples of fetal tissue include umbilical cord, portions of the placenta, fetal organs, fetal skin, fetal hair, fetal blood (e.g., fetal plasma, fetal blood cells), fetal lymphatic fluid, amniotic fluid, the like or combinations thereof).
A nucleic acid sample obtained from blood, serum, plasma or urine often comprises circulating cell free (ccf) DNA (e.g., circulating cell free nucleic acids). Circulating cell free DNA from a pregnant female often comprise fetal nucleic acid and maternal nucleic acid. In some embodiments ccf DNA isolated from a test subject comprises a nucleic acid derived from one or more tumors and nucleic acid derived from normal healthy (e.g., non-cancerous) tissues or cells. Circulating cell free DNA often comprises nucleic acid fragments ranging from about 1000 nucleotides in length or less. In some embodiments the mean, average, median, mode or absolute size of ccf fragments is about 700 nucleotides (nt) or less, 600 nt or less, 500 nt or less, 400 nt or less, 350 nt or less, 300 nt or less, 250 nt or less, 200 nt or less, 190 nt or less, 180 nt or less, 170 nt or less, 160 nt or less, 150 nt or less, 140 nt or less, 130 nt or less, 120 nt or less, 110 nt or less or 100 nt or less. In some embodiments the mean, average, median, mode or absolute size of ccf fragments is associated with a methylation status. For example, in some embodiments ccf fragments of about 250 nt or less, 225 nt or less, 200 nt or less, 190 nt or less, 180 nt or less, 170 nt or less, 160 nt or less, 150 nt or less, 140 nt or less, 130 nt or less, 120 nt or less, 110 nt or less or 100 nt or less in length are derived from a locus that is hypomethylated. In some embodiments ccf fragments of about 150 nt or more, 160 nt or more, 170 nt or more, 180 nt or more, 190 nt or more, 200 nt or more, 250 nt or more, or 300 nt or more are derived from a locus that is hypermethylated.
Nucleic acid may be provided for conducting methods described herein without processing of the sample(s) containing the nucleic acid, in certain embodiments. In some embodiments, nucleic acid is provided for conducting methods described herein after processing of the sample(s) containing the nucleic acid. For example, a nucleic acid can be extracted, isolated, purified, partially purified or amplified from the sample(s). The term “isolated” as used herein refers to nucleic acid removed from its original environment (e.g., the natural environment if it is naturally occurring, or a host cell if expressed exogenously), and thus is altered by human intervention (e.g., “by the hand of man”) from its original environment. The term “isolated nucleic acid” as used herein can refer to a nucleic acid removed from a subject (e.g., a human subject). An isolated nucleic acid can be provided with fewer non-nucleic acid components (e.g., protein, lipid) than the amount of components present in a source sample. A composition comprising isolated nucleic acid can be about 50% to greater than 99% free of non-nucleic acid components. A composition comprising isolated nucleic acid can be about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% free of non-nucleic acid components. The term “purified” as used herein can refer to a nucleic acid provided that contains fewer non-nucleic acid components (e.g., protein, lipid, carbohydrate) than the amount of non-nucleic acid components present prior to subjecting the nucleic acid to a purification procedure. A composition comprising purified nucleic acid may be about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% free of other non-nucleic acid components. The term “purified” as used herein can refer to a nucleic acid provided that contains fewer nucleic acid species than in the sample source from which the nucleic acid is derived. A composition comprising purified nucleic acid may be about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% free of other nucleic acid species. For example, fetal nucleic acid can be purified from a mixture comprising maternal and fetal nucleic acid. In certain examples, nucleosomes comprising small fragments of fetal nucleic acid can be purified from a mixture of larger nucleosome complexes comprising larger fragments of maternal nucleic acid.
The term “amplified” as used herein refers to subjecting a target polynucleotide in a sample to a process that linearly or exponentially generates amplicon nucleic acids having the same or substantially the same nucleotide sequence as the target polynucleotide, or segment thereof. A target polynucleotide is often a portion of a genome or portion of a locus represented in a sample as a polynucleotide fragment. In some embodiments a nucleotide sequence, or portion thereof, of a target polynucleotide is known. The term “amplified” as used herein can refer to subjecting a target polynucleotide (e.g., in a sample comprising other nucleic acids) to a process that selectively and linearly or exponentially generates amplicon nucleic acids having the same or substantially the same nucleotide sequence as the target polynucleotide, or segment thereof. Amplicons that are generated from, and have the same or substantially the same nucleotide sequence as a target polynucleotide, are referred to herein as target specific amplicons. The term “amplified” as used herein can refer to subjecting a population of nucleic acids to a process that non-selectively and linearly or exponentially generates amplicon nucleic acids having the same or substantially the same nucleotide sequence as nucleic acids, or portions thereof, that were present in the sample prior to amplification. In some embodiments, the term “amplified” refers to a method that comprises a polymerase chain reaction (PCR).
Nucleic acid also may be processed by subjecting nucleic acid to a method that generates nucleic acid fragments, in certain embodiments, before providing nucleic acid for a process described herein. In some embodiments, nucleic acid subjected to fragmentation or cleavage may have a nominal, average or mean length of about 5 to about 10,000 base pairs, about 100 to about 1,000 base pairs, about 100 to about 500 base pairs, or about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000 or 9000 base pairs. Fragments can be generated by a suitable method known in the art, and the average, mean or nominal length of nucleic acid fragments can be controlled by selecting an appropriate fragment-generating procedure. In certain embodiments, nucleic acid of a relatively shorter length can be utilized to analyze sequences that contain little sequence variation and/or contain relatively large amounts of known nucleotide sequence information. In some embodiments, nucleic acid of a relatively longer length can be utilized to analyze sequences that contain greater sequence variation and/or contain relatively small amounts of nucleotide sequence information.
Nucleic acid fragments may contain overlapping nucleotide sequences, and such overlapping sequences can facilitate construction of a nucleotide sequence of the non-fragmented counterpart nucleic acid, or a segment thereof. For example, one fragment may have subsequences x and y and another fragment may have subsequences y and z, where x, y and z are nucleotide sequences that can be 5 nucleotides in length or greater. Overlap sequence y can be utilized to facilitate construction of the x-y-z nucleotide sequence in nucleic acid from a sample in certain embodiments. Nucleic acid may be partially fragmented (e.g., from an incomplete or terminated specific cleavage reaction) or fully fragmented in certain embodiments.
Nucleic acid can be fragmented by various methods known in the art, which include without limitation, physical, chemical and enzymatic processes. Non-limiting examples of such processes are described in U.S. Patent Application Publication No. 20050112590 (published on May 26, 2005, entitled “Fragmentation-based methods and systems for sequence variation detection and discovery,” naming Van Den Boom et al.). Certain processes can be selected to generate non-specifically cleaved fragments or specifically cleaved fragments. Non-limiting examples of processes that can generate non-specifically cleaved fragment nucleic acid include, without limitation, contacting nucleic acid with apparatus that expose nucleic acid to shearing force (e.g., passing nucleic acid through a syringe needle; use of a French press); exposing nucleic acid to irradiation (e.g., gamma, x-ray, UV irradiation; fragment sizes can be controlled by irradiation intensity); boiling nucleic acid in water (e.g., yields about 500 base pair fragments) and exposing nucleic acid to an acid and base hydrolysis process.
As used herein, “fragmentation” or “cleavage” refers to a procedure or conditions in which a nucleic acid molecule, such as a nucleic acid template gene molecule or amplified product thereof, may be severed into two or more smaller nucleic acid molecules. Such fragmentation or cleavage can be sequence specific, base specific, or nonspecific, and can be accomplished by any of a variety of methods, reagents or conditions, including, for example, chemical, enzymatic, physical fragmentation.
As used herein, “fragments”, “cleavage products”, “cleaved products” or grammatical variants thereof, refers to nucleic acid molecules resultant from a fragmentation or cleavage of a nucleic acid template gene molecule or amplified product thereof. While such fragments or cleaved products can refer to all nucleic acid molecules resultant from a cleavage reaction, typically such fragments or cleaved products refer only to nucleic acid molecules resultant from a fragmentation or cleavage of a nucleic acid template gene molecule or the segment of an amplified product thereof containing the corresponding nucleotide sequence of a nucleic acid template gene molecule. For example, an amplified product can contain one or more nucleotides more than the amplified nucleotide region of a nucleic acid template sequence (e.g., a primer can contain “extra” nucleotides such as a transcriptional initiation sequence, in addition to nucleotides complementary to a nucleic acid template gene molecule, resulting in an amplified product containing “extra” nucleotides or nucleotides not corresponding to the amplified nucleotide region of the nucleic acid template gene molecule). Accordingly, fragments can include fragments arising from portions of amplified nucleic acid molecules containing, at least in part, nucleotide sequence information from or based on the representative nucleic acid template molecule.
As used herein, the term “complementary cleavage reactions” refers to cleavage reactions that are carried out on the same nucleic acid using different cleavage reagents or by altering the cleavage specificity of the same cleavage reagent such that alternate cleavage patterns of the same target or reference nucleic acid or protein are generated. In certain embodiments, nucleic acid may be treated with one or more specific cleavage agents (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more specific cleavage agents) in one or more reaction vessels (e.g., nucleic acid is treated with each specific cleavage agent in a separate vessel).
Nucleic acid may be specifically cleaved or non-specifically cleaved by contacting the nucleic acid with one or more enzymatic cleavage agents (e.g., nucleases, restriction enzymes). The term “specific cleavage agent” as used herein refers to an agent, sometimes a chemical or an enzyme that can cleave a nucleic acid at one or more specific sites. Specific cleavage agents often cleave specifically according to a particular nucleotide sequence at a particular site. Non-specific cleavage agents often cleave nucleic acids at non-specific sites or degrade nucleic acids. Non-specific cleavage agents often degrade nucleic acids by removal of nucleotides from the end (either the 5′ end, 3′ end or both) of a nucleic acid strand.
Any suitable non-specific or specific enzymatic cleavage agent can be used to cleave or fragment nucleic acids. A suitable restriction enzyme can be used to cleave nucleic acids, in some embodiments. Examples of enzymatic cleavage agents include without limitation endonucleases (e.g., DNase (e.g., DNase I, II); RNase (e.g., RNase E, F, H, P); Cleavase™ enzyme; Taq DNA polymerase; E. coli DNA polymerase I and eukaryotic structure-specific endonucleases; murine FEN-1 endonucleases; type I, II or III restriction endonucleases such as Acc I, Afl III, Alu I, Alw44 I, Apa I, Asn I, Ava I, Ava II, BamH I, Ban II, Bcl I, Bgl I. Bgl II, Bln I, Bsm I, BssH II, BstE II, Cfo I, Cla I, Dde I, Dpn I, Dra I, EcIX I, EcoR I, EcoR I, EcoR II, EcoR V, Hae II, Hae II, Hind II, Hind III, Hpa I, Hpa II, Kpn I, Ksp I, Mlu I, MIuN I, Msp I, Nci I, Nco I, Nde I, Nde II, Nhe I, Not I, Nru I, Nsi I, Pst I, Pvu I, Pvu II, Rsa I, Sac I, Sal I, Sau3A I, Sca I, ScrF I, Sfi I, Sma I, Spe I, Sph I, Ssp I, Stu I, Sty I, Swa I, Taq I, Xba I, Xho I; glycosylases (e.g., uracil-DNA glycosylase (UDG), 3-methyladenine DNA glycosylase, 3-methyladenine DNA glycosylase II, pyrimidine hydrate-DNA glycosylase, FaPy-DNA glycosylase, thymine mismatch-DNA glycosylase, hypoxanthine-DNA glycosylase, 5-Hydroxymethyluracil DNA glycosylase (HmUDG), 5-Hydroxymethylcytosine DNA glycosylase, or 1,N6-etheno-adenine DNA glycosylase); exonucleases (e.g., exonuclease III); ribozymes, and DNAzymes. Nucleic acid in a sample or mixture can be treated with an agent that modifies a methylated nucleotide to another moiety. In some embodiments nucleic acid in a sample or mixture may be treated with an agent (e.g., a chemical agent), and a modified nucleic acid may be cleaved. Non-limiting examples of nucleic acid modifying agents include (i) alkylating agents such as methylnitrosourea that generate several alkylated bases, including N3-methyladenine and N3-methylguanine, which are recognized and cleaved by alkyl purine DNA-glycosylase; (ii) sodium bisulfite (i.e., bisulfite), which causes deamination of cytosine residues in DNA to form uracil residues that can be cleaved by uracil N-glycosylase; and (iii) a chemical agent that converts guanine to its oxidized form, 8-hydroxyguanine, which can be cleaved by formamidopyrimidine DNA N-glycosylase. Examples of chemical cleavage processes include without limitation alkylation, (e.g., alkylation of phosphorothioate-modified nucleic acid); cleavage of acid lability of P3′-N5′-phosphoroamidate-containing nucleic acid; and osmium tetroxide and piperidine treatment of nucleic acid.
Nucleic acid also may be exposed to a process that modifies certain nucleotides in the nucleic acid before providing nucleic acid for a method described herein. A process that selectively modifies nucleic acid based upon the methylation state of nucleotides therein can be applied to nucleic acid, for example. In addition, conditions such as high temperature, ultraviolet radiation, x-radiation, can induce changes in the sequence of a nucleic acid molecule. Nucleic acid may be provided in any form useful for conducting a sequence analysis or manufacture process described herein, such as solid or liquid form, for example. In certain embodiments, nucleic acid may be provided in a liquid form optionally comprising one or more other components, including without limitation one or more buffers or salts.
Nucleic acid may be single or double stranded. Single stranded DNA, for example, can be generated by denaturing double stranded DNA by heating or by treatment with alkali, for example. Nucleic acid sometimes is in a D-loop structure, formed by strand invasion of a duplex DNA molecule by an oligonucleotide or a DNA-like molecule such as peptide nucleic acid (PNA). D loop formation can be facilitated by addition of E. Coli RecA protein and/or by alteration of salt concentration, for example, using methods known in the art.
The term “polynucleotide” as used herein refers to all or a portion of a nucleic acid. The term “polynucleotide” as used herein can refer to a portion or all of a genome, chromosome, gene or locus. A polynucleotide is sometimes a nucleic acid fragment (e.g., a fragment of nucleic acid produced from shearing or an enzymatic reaction, a ccf nucleic acid fragment, an amplicon, an extension product, or the like). A polynucleotide can be single or double stranded.
Methylation-Sensitive Cleavage
In some embodiments, a sample nucleic acid (e.g., a sample comprising maternal nucleic acids, fetal nucleic acids or a mixture thereof, (e.g., ccf DNA)) is digested with one or more methylation sensitive cleavage agents. Any suitable sample nucleic acid can be contacted with or digested with a methylation sensitive cleavage agent. Non-limiting examples of sample nucleic acid that can be contacted with or digested with a methylation sensitive cleavage agent include nucleic acid isolated from the blood, serum, plasma or urine of a test subject (e.g., a pregnant female, a cancer patient), nucleic acid enriched for a minority species, nucleic acid enriched for fetal nucleic acid, maternal nucleic acid, or a sample enriched for unmethylated nucleic acid, hypomethylated nucleic acid, methylated nucleic acid or hypermethylated nucleic acid, the like or combinations thereof. In some embodiments sample nucleic acid is contacted with one or more methylation sensitive cleavage agents under suitable conditions (e.g., using a suitable buffer, enzyme concentration, DNA concentration, pH, temperature and/or incubation duration) which often results in digested nucleic acid fragments and/or undigested nucleic acid fragments. Digested nucleic acid fragments can comprise any suitable subset of nucleic acid fragments or target polynucleotides. In some embodiments undigested nucleic acid fragments can comprise any suitable subset of nucleic acid fragments or target polynucleotides. Non-limiting examples of digested or undigested subsets of nucleic acid fragments include fetal nucleic acid, maternal nucleic acid, unmethylated nucleic acid, hypomethylated nucleic acid, methylated nucleic acid, hypermethylated nucleic acid, minority nucleic acid, majority nucleic acid, the like, fragments thereof or combinations thereof. Digested and/or undigested nucleic acid fragments are often enriched, separated and/or analyzed by a method described herein.
In some embodiments, one or more methylation sensitive cleavage agents are methylation sensitive restriction enzymes (e.g., methylation sensitive restriction endonucleases). Methylation sensitive cleavage agents and methylation sensitive restriction enzymes are agents that cleave nucleic acid depending on the methylation state of their recognition site. For example, methylation sensitive DNA restriction endonucleases are generally dependent on the methylation state of their DNA recognition site for activity. In some instances, certain methylation sensitive endonucleases cleave or digest nucleic acid only if it is not methylated at their DNA recognition sequence. Some methylation sensitive endonucleases cleave or digest nucleic acid only if it is methylated at their DNA recognition sequence. Some methylation sensitive endonucleases cleave or digest nucleic acid at their or near their recognition sequence. (i.e. digest at unmethylated or hypomethylated sites). Some methylation sensitive endonucleases cleave or digest nucleic acid 5′ and/or 3′ of their recognition sequence. Sometimes methylation sensitive endonucleases cleave or digest nucleic acids at random distances (e.g., 5, 10, 20, 50, 100, or 150 base pairs or more) at a site located 5′ and/or 3′ of their recognition sequences. In some embodiments an unmethylated or hypomethylated DNA fragment can be cut into smaller fragments compared to a methylated or hypermethylated DNA fragment that is not digested. In some embodiments a methylated or hypermethylated DNA fragment can be cut into smaller fragments compared to an unmethylated or hypomethylated DNA fragment that is not digested. For example, the average, mean, median or nominal length of certain digested nucleic acid fragments can be about 20 bases to about 200 bases (e.g., about 30, 40, 50, 60, 70, 80, 90, 100, 150 bases). In certain embodiments nucleic acids in a sample (e.g., genomic DNA or ccf DNA) are digested with an enzyme to produce digested nucleic acid fragments with an average, mean, median or nominal length of about 1000 bases or less, about 500 bases or less, about 250 bases or less, about 200 bases or less, about 150 bases or less or about 100 bases (e.g., 100 base pairs) or less. In some embodiments nucleic acids in a sample are digested to produce nucleic acid fragments with an average, mean, median or nominal length between about 25 bases and about 500 bases, between about 25 bases and about 250 bases, between about 25 bases and about 200 bases, between about 25 bases and about 150 bases, between about 40 bases and about 100 bases, or between about 40 bases and about 80 bases. In some embodiments nucleic acids in a sample are digested to produce nucleic acid fragments with an average, mean, median or nominal length between about 500 bases, about 450 bases, about 400 bases, about 350 bases, about 300 bases, about 250 bases, about 200 bases, about 190 bases, about 180 bases, about 170 bases, about 160 bases, about 150 bases, about 140 bases, about 130 bases, about 120 bases, about 110 bases or about 100 bases.
In some embodiments sample nucleic acids are digested with one or more methylation sensitive cleavage agents resulting in an enrichment of a subset of nucleic acid species (e.g., hypermethylated nucleic acid, hypomethylated nucleic acid, fetal nucleic acid, a minority nucleic acid species, the like or a combination thereof). In some instances, digestion of ccf DNA at certain hypomethylated regions in a genome can provide a mixture enriched for undigested nucleic acid fragments (e.g., enriched for hypermethylated polynucleotides) comprising an average, mean, median or nominal length of 100 bases or more, 120 bases or more, 140 bases or more, 160 bases or more, 180 bases or more, 200 bases or more, 250 bases or more, 300 bases or more, 400 bases or more or 500 bases or more in length. In some instances, digestion of ccf DNA at certain restriction enzyme recognition sequences that are unmethylated can provide a mixture enriched for undigested nucleic acid fragments comprising one or more restriction enzyme recognition sequences that are methylated. In some embodiments, digestion of ccf DNA at certain hypermethylated regions in a genome can provide a mixture enriched for undigested nucleic acid fragments (e.g., enriched for hypomethylated polynucleotides) comprising an average, mean, median or nominal length of 100 bases or more, 120 bases or more, 140 bases or more, 160 bases or more, 180 bases or more, 200 bases or more, 250 bases or more, 300 bases or more, 400 bases or more or 500 bases or more in length. In some embodiments undigested fragments are enriched for fetal nucleic acids. In some instances, digestion of ccf DNA at certain methylated restriction enzyme recognition sequences can provide a mixture enriched for undigested nucleic acid fragments comprising one or more restriction sites that are unmethylated.
The terms “cleave”, “cut” and “digest” are used interchangeably herein.
In some embodiments the expected average fragment size of digested fragments for a given restriction enzyme can be estimated based, in part, on the length of the recognition sequence of the restriction enzyme. For example, without being limited to theory, in a genome with 50% GC content and no dinucleotide bias, a four-cutter (e.g., an endonuclease having a 4 base recognition sequence) can be estimated to cut at about every 256 bases, a six-cutter (e.g., an endonuclease having a 6 base recognition sequence) can be expected to cut at about every 4,096 bases, and an eight-cutter (e.g., an endonuclease having a 8 base recognition sequence) should cut at about every 65,536 bases. The expected average fragment size of digested fragments for a given enzyme reaction can be reduced (e.g., frequency of cutting can be increased) by including additional restriction endonucleases in a digestion reaction where each restriction endonuclease has a different recognitions sequence and/or specificity. Sometimes the expected average fragment size of digested fragments for a given restriction enzyme or for a given digestion can be determined empirically for a given sample or sample type (e.g., genomic DNA, ccf DNA). In some embodiments nucleic acid is digested with one or more restriction endonucleases comprising a recognition sequence of 16 bases pairs or less, 12 base pairs or less, 8 base pairs or less, 6 base pairs or less or 4 base pairs or less. In some embodiments nucleic acid is digested with one or more restriction endonucleases comprising a recognition sequence of 4 base pairs or less.
Methylation sensitive restriction enzymes can include any suitable methylation sensitive restriction enzyme described herein or known in the art. For example, a methylation sensitive restriction enzyme can include any suitable Type I, Type II, Type III, Type IV or Type V restriction endonuclease. Type I enzymes are generally complex, multi-subunit, combination restriction-and-modification enzymes that cut DNA at random sites far from their recognition sequences. Type II enzymes generally cut DNA at defined positions close to or within their recognition sequences. Type II enzymes generally recognize DNA sequences that are symmetric, because they often bind to DNA as homodimers, but a some recognize asymmetric DNA sequences, because they bind as heterodimers. Some Type II enzymes recognize continuous sequences in which the two half-sites of the recognition sequence are adjacent, while others recognize discontinuous sequences in which the half-sites are separated. Type II enzymes generally leaves a 3″-hydroxyl on one side of each cut and a 5″-phosphate on the other. Sometimes Type II enzymes (e.g., Type IIS) cleave outside of their recognition sequence to one side. These enzymes generally recognize sequences that are continuous and asymmetric. Some Type II enzymes (e.g., Type IIG) cleave outside of their recognition sequences, recognize continuous sequences and cleave on just one side. Other Type II enzymes cleave outside of their recognition sequences, recognize discontinuous sequences and cleave on both sides releasing a small fragment containing the recognition sequence. Type III enzymes generally cleave outside of their recognition sequences and require two such sequences in opposite orientations within the same DNA molecule to accomplish cleavage. Type IV enzymes generally recognize modified, typically methylated DNA and are generally exemplified by the McrBC and Mrr systems of E. coli. Non-limiting examples of restriction enzymes that can be used for a method described herein include AatII, AccII, ACiI, AcII, AfeI, AgeI, AgeI-HF, Aor13HI, Aor51HI, AscI, AseI, BceAI, BmgBI, BsaAI, BsaHI, BsiEI, BspDI, BsrFI, BspT104I, BssHII, BstBI, BstUI, Cfr10I, ClaI, CpoI, EagI, Eco52I, FauI, FseI, FspI, DpnI, DpnII, HaeII, HaeIII, HapII, HfaI, HgaI, HhaI, HinP1I, HPAII, Hpy99I, HpyCH4IV, KasI, MaeII, McrBC, MluI, MspI, NaeI, NgoMIV, NotI, NotI-HF, NruI, NsbI, NtBsmAI, NtCviPII, PaeR7I, PIuTI, PmII, PmaCI, Psp1406I, PvuI, RsrII, SacII, SaII, SaII-HF, ScrFI, SfoI, SfrAI, SmaI, SnaBI, TspMI, ZraI, the like, isoschizomers thereof, or combinations thereof. Non-limiting examples of enzymes that digest nucleic acid according to a non-methylated recognition sequence include HpaII, HinP1I, HhaI, MaeII, BstUI and AciI. In some embodiments, one or more of the restriction enzymes are selected from HHAI, HinP1I and HPAII. In some embodiments, an enzyme that can be used is HpaII that cuts only the unmethylated sequence CCGG. In some embodiments, an enzyme that can be used is HhaI that cuts only the unmethylated sequence GCGC. In some embodiments, an enzyme that can be used is HinP1I that cuts only the unmethylated sequence GCGC. Such enzymes are available from New England BioLabs®, Inc. and from other suitable sources. In some embodiments combinations of two or more methyl-sensitive enzymes can be used. In some embodiments combinations of two or more methyl-sensitive enzymes that digest only unmethylated DNA also can be used. In some embodiments combinations of two or more methyl-sensitive enzymes that digest only methylated DNA also can be used. Suitable enzymes that digest only methylated DNA include, but are not limited to, DpnI, which cuts at a recognition sequence GATC, and McrBC, which belongs to the family of AAA+ proteins and cuts DNA containing modified cytosines and cuts at recognition site 5′ . . . PumC(N40-3000) PumC . . . 3′ (New England BioLabs®, Inc., Beverly, Mass.).
In some embodiments, one or more restriction enzymes are selected according to the overhangs (i.e., one or more unpaired nucleotides) that result from digestion with a restriction endonuclease. An overhang is generally one or more unpaired nucleotides at the end of a double stranded polynucleotide fragment. In some embodiment, one or more unpaired nucleotides of an overhang extend from the 3′ end or 5′ end of a polynucleotide strand. Such overhangs sometimes can be referred to as “sticky ends” and can be used, for example, for ligating to an oligonucleotide, adaptor or other molecule as described herein. In some embodiments overhangs are utilizes for hybridization of a primer sequence or part thereof, often for a subsequent amplification process. In some embodiments, one or more restriction enzymes are selected that produce blunt ends (e.g., no overhang). Blunt ends can also be utilized for ligating an adaptor (i.e., adapter). In some embodiment, a restriction enzyme digest produces digested fragments comprising sticky ends, blunt ends and/or a combination thereof. For example, sometimes a digested fragment includes an overhang at both ends, a blunt end at both ends, or an overhang and a blunt end. In some embodiments an overhang can be produced as a result of a polymerase extension (e.g., as a result of a PCR reaction).
Oligonucleotide Ligation
Any suitable overhang or blunt end can be used to ligate an oligonucleotide or adaptor to one end or both ends of a nucleic acid fragment. In some embodiments, digestion of nucleic acid (e.g., methylation sensitive digestion of hypomethylated nucleic acid) generates digested nucleic acid fragments having blunt ends and/or overhangs (i.e., one or more unpaired nucleotides) at the 3′ and/or 5′ ends of the digested fragments. Such blunt ends and/or overhangs can be ligated to an oligonucleotide, adaptor or other molecule having a complementary overhang sequence (e.g., ligation sequence). For example, a digested fragment having a 5′-CG-3′ overhang can be ligated (e.g., using a DNA ligase) to an oligonucleotide having a 3′-GC-S′ overhang. Oligonucleotides comprising an overhang used for ligation are often double-stranded. In some embodiments, the oligonucleotide can ligate to substantially all fragments produced by a particular cleavage agent. For example, an oligonucleotide can ligate to at least 90%, 95%, 96%, 97%, 98%, 99%, 99.9% or 100% of the fragments produced by a particular cleavage agent in some embodiments. In some embodiments, different oligonucleotides are used.
In some embodiments ligation is not required for amplification and/or enrichment of nucleic acids digested by a methylation sensitive restriction enzyme. Digested nucleic acid can be amplified by one or more primer sets, often added in excess, comprising a 3′ end that is complementary to overhangs produced as a result of a restriction digest or extension. In some embodiments digested nucleic acid can be amplified using target specific primer sets directed to hybridize to nucleic acid sequences (e.g., target polynucleotide sequences) of hypomethylated or hypermethylated loci. In some embodiments, hypomethylated or hypermethylated nucleic acid can be enriched prior to or after restriction digest by a suitable size selection method (e.g., size selection by PEG precipitation, size selection by column chromatograph, size selection by bridge amplification, the like or combinations thereof). In some embodiments, hypomethylated nucleic acid can be enriched prior to, during or after amplification of restriction digested products by a suitable method (e.g., size selection by PEG precipitation, size selection by column chromatograph, size selection by bridge amplification, the like or combinations thereof).
In some embodiment an overhang is not required for enrichment and/or amplification of hypomethylated nucleic acids. For example, hypomethylated nucleic acid can be enriched by precipitation using a methyl-specific binding agent (e.g., an antibody, a methyl binding protein), or by another suitable method followed by digestion of the hypomethylated nucleic acid by a restriction enzyme that produces blunt-ends or overhang ends. In either embodiment, oligonucleotides (e.g., double stranded oligonucleotides) can be ligated to the digested fragments and the ligated sequences can be captured, enriched, amplified, and/or sequenced by using nucleic acid sequences, or a portion thereof, of the newly ligated oligonucleotides.
In some embodiments, an oligonucleotide comprises an element useful for enrichment and/or analysis of the digested nucleic acid fragments. Elements useful for enrichment and/or analysis of the digested nucleic acid fragments may include, for example, binding agents, capture agents (e.g., binding pairs), affinity ligands, antibodies, antigens, primer hybridization sequences (e.g., a sequence configured for a primer to specifically anneal), a suitable predetermined sequence that can be used for enrichment and/or capture (e.g., a sequence that can hybridize to a complementary nucleic acid comprising a binding agent, e.g., biotin), adaptor sequences, identifier sequences, detectable labels and the like, some of which are described in further detail below. For example, an oligonucleotide may be biotinylated such that it can be captured onto a streptavidin-coated bead. In some embodiments, an oligonucleotide comprises an element useful for a targeted enrichment and/or analysis of the digested nucleic acid fragments. For example, certain nucleotide sequences in a sample may be targeted for enrichment and/or analysis (e.g., using oligonucleotides comprising sequence-specific amplification primers). In some embodiments, an oligonucleotide comprises an element useful for global (i.e., non-targeted) enrichment and/or analysis of the digested nucleic acid fragments. For example, certain oligonucleotides may comprise universal amplification hybridization sequences useful for global (e.g., non-target sequence dependent) enrichment and/or analysis of digested nucleotide sequence fragments.
Oligonucleotides can be designed and synthesized using a suitable process, and may be of any length suitable for ligating to certain nucleic acid fragments (e.g., digested nucleic acid fragments) and performing enrichment and/or analysis processes described herein. Oligonucleotides may be designed based upon a nucleotide sequence of interest (e.g., target fragment sequence, target polynucleotides, reference fragment sequence) or may be non-sequence specific (e.g., for a global enrichment process described herein) and/or may be sample-specific (e.g., may comprise a sample-specific identifier as described below). An oligonucleotide, in some embodiments, may be about 10 to about 300 nucleotides, about 10 to about 100 nucleotides, about 10 to about 70 nucleotides, about 10 to about 50 nucleotides, about 15 to about 30 nucleotides, or about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 nucleotides in length. An oligonucleotide may be composed of naturally occurring and/or non-naturally occurring nucleotides (e.g., labeled nucleotides), or a mixture thereof. Oligonucleotides suitable for use with embodiments described herein, may be synthesized and labeled using known techniques. Oligonucleotides may be chemically synthesized according to the solid phase phosphoramidite triester method first described by Beaucage and Caruthers (1981) Tetrahedron Letts. 22:1859-1862, using an automated synthesizer, and/or as described in Needham-VanDevanter et al. (1984) Nucleic Acids Res. 12:6159-6168. Purification of oligonucleotides can be effected by native acrylamide gel electrophoresis or by anion-exchange high-performance liquid chromatography (HPLC), for example, as described in Pearson and Regnier (1983) J. Chrom. 255:137-149.
Primers
A primer is often a strand of nucleic acid (e.g., an oligonucleotide, an oligonucleotide primer) that serves as a starting point for nucleic acid synthesis. The terms “primer” and “oligonucleotide primer” are used interchangeably herein. A primer is often used for nucleic acid sequencing, amplification, fill-in reactions and extension reactions. A portion of a primer is often complementary to, and can hybridize to, a portion of a nucleic acid template (e.g., a target polynucleotide). A portion of a primer that is complimentary to a portion of a target sequence which the primer pair is configured to amplify is sometimes referred to herein as a hybridization sequence. In some embodiments, an oligonucleotide primer comprises a hybridization sequence (e.g., a sequence complementary to a portion of a target sequence or template nucleic acid). All or a portion of a primer hybridization sequence can be complementary to a portion of a target polynucleotide or template nucleic acid. In some embodiments a primer, or portion thereof is complementary to an adaptor that was previously ligated to a target polynucleotide or template nucleic acid. In some embodiments a primer, or portion thereof is complementary to an overhang generated by a restriction enzyme cleavage reaction. In some embodiments, a primer is useful for amplification (unidirectional amplification, bi-directional amplification) of certain nucleic acid fragments (e.g., digested nucleic acid fragments). In some embodiments, oligonucleotides comprise hybridization sequences that are specific for certain genomic target sequences (e.g., target polynucleotides). An oligonucleotide primer, primer pair or nucleic acid that is specific for a target polynucleotide often hybridized specifically to the target polynucleotide or a portion thereof under suitable hybridization conditions. In some embodiments, oligonucleotides comprise primer hybridization sequences that are not specific for certain genomic target sequences (e.g., universal primer hybridization sequences configured to anneal to a universal adaptor or linker that is ligated or attached to one or more target polynucleotides). Universal primer hybridization sequences may be useful for global (i.e., non-targeted) amplification of certain nucleic acid fragments (e.g., digested nucleic acid fragments). The term “primer” as used herein refers to a nucleic acid that includes a nucleotide sequence capable of hybridizing or annealing to a target polynucleotide, at or near (e.g., adjacent to) a specific region of interest or universal primer site (e.g., a ligated adaptor, an overhang). Primers can allow for specific determination of a target polynucleotide nucleotide sequence or detection of the target polynucleotide (e.g., presence or absence of a sequence or copy number of a sequence), or feature thereof, for example. A primer may be naturally occurring or synthetic. The term “specific” or “specificity”, as used herein, refers to the binding or hybridization of one molecule to another molecule, such as a primer for a target polynucleotide or universal primer for a universal primer hybridization sequence. That is, “specific” or “specificity” refers to the recognition, contact, and formation of a stable complex between two molecules, as compared to substantially less recognition, contact, or complex formation of either of those two molecules with other molecules. As used herein, the term “anneal” refers to the formation of a stable complex between two molecules. The terms “primer”, “oligo”, or “oligonucleotide” may be used interchangeably throughout the document, when referring to primers.
A primer or primer pair can be designed and synthesized using suitable processes, and may be of any length suitable for hybridizing to a nucleotide sequence of interest (e.g., where the nucleic acid is in liquid phase or bound to a solid support) and performing analysis processes described herein. Primers may be designed based upon a target nucleotide sequence. A primer in some embodiments may be about 10 to about 100 nucleotides, about 10 to about 70 nucleotides, about 10 to about 50 nucleotides, about 15 to about 30 nucleotides, or about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 nucleotides in length. A primer may be composed of naturally occurring and/or non-naturally occurring nucleotides (e.g., labeled nucleotides), or a mixture thereof. Primers suitable for use with embodiments described herein, may be synthesized and labeled using known techniques. Primers may be chemically synthesized according to the solid phase phosphoramidite triester method first described by Beaucage and Caruthers, Tetrahedron Letts., 22:1859-1862, 1981, using an automated synthesizer, as described in Needham-VanDevanter et al., Nucleic Acids Res. 12:6159-6168, 1984. Purification of primers can be effected by native acrylamide gel electrophoresis or by anion-exchange high-performance liquid chromatography (HPLC), for example, as described in Pearson and Regnier, J. Chrom., 255:137-149, 1983.
A primer pair refers to a pair of two oligonucleotide primers, oriented in opposite directions and configured for amplifying (e.g., by PCR) a nucleic acid template (e.g., a specific target polynucleotides). A nucleic acid template (e.g., target polynucleotide) can be single and/or double stranded. A primer pair or a collection of primer pairs can be designed by a suitable method that often optimizes or matches various features of each primer of a primer pair. In some embodiments where a collection of primer pairs is used in an amplification reaction, various features of each primer pair in a collection are optimized. Algorithms and methods for designing and optimizing primer pairs, as well as collections of primer pairs for an amplification (e.g., an amplification reaction) are well known. Any suitable method of designing and optimizing primer pairs or collections of primer pairs can be used to design primer pairs or collections of primer pairs for amplification of target polynucleotides. Non-limiting examples of features of oligonucleotide primers that are often used for design and optimization of primer pairs include primer length, GC content and Tm. Primers of a primer pair often comprise a similar Tm. In some embodiments a primer pair is optimized for amplification of a specific target polynucleotide.
All or a portion of a primer nucleic acid sequence (e.g., where a primer comprises naturally occurring, synthetic or modified nucleotides, and/or an identifier) may be substantially complementary to a target polynucleotide, or to an adaptor or linker of a target polynucleotide, in some embodiments. As referred to herein, “substantially complementary” with respect to sequences, refers to nucleotide sequences that will hybridize with each other. The stringency of the hybridization conditions can be altered to tolerate varying amounts of sequence mismatch. Included are target and primer hybridization sequences that are 55% or more, 56% or more, 57% or more, 58% or more, 59% or more, 60% or more, 61% or more, 62% or more, 63% or more, 64% or more, 65% or more, 66% or more, 67% or more, 68% or more, 69% or more, 70% or more, 71% or more, 72% or more, 73% or more, 74% or more, 75% or more, 76% or more, 77% or more, 78% or more, 79% or more, 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more or 99% or more complementary to each other.
Primers that are substantially complementary to a target polynucleotide sequence or portion thereof (e.g., linker or adaptor thereof) are also substantially identical to the complement of a target polynucleotide sequence or portion thereof. That is, sometimes primers are substantially identical to the anti-sense strand of a target polynucleotide. As referred to herein, “substantially identical” with respect to sequences refers to nucleotide sequences that are 55% or more, 56% or more, 57% or more, 58% or more, 59% or more, 60% or more, 61% or more, 62% or more, 63% or more, 64% or more, 65% or more, 66% or more, 67% or more, 68% or more, 69% or more, 70% or more, 71% or more, 72% or more, 73% or more, 74% or more, 75% or more, 76% or more, 77% or more, 78% or more, 79% or more, 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more or 99% or more identical to each other. One test for determining whether two nucleotide sequences are substantially identical is to determine the percent of identical nucleotide sequences shared.
Primer hybridization sequences and lengths thereof may affect hybridization of a primer to a target polynucleotide sequence, or portion thereof. Depending on the degree of mismatch between the primer and target polynucleotide, low, medium or high stringency conditions may be used to effect primer/target annealing. As used herein, the term “stringent conditions” refers to conditions for hybridization and washing. Methods for hybridization reaction temperature condition optimization are known to those of skill in the art, and may be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y., 6.3.1-6.3.6 (1989) or in chapter 11 of Sambrook et al., MOLECULAR CLONING: A LABORATORY MANUAL, second edition, Cold Spring Harbor Laboratory Press, New York (1990), both of which are incorporated by reference herein. Aqueous and non-aqueous methods are described in that reference and either can be used. Non-limiting examples of stringent hybridization conditions are hybridization in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 50° C. Another example of stringent hybridization conditions are hybridization in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 55° C. A further example of stringent hybridization conditions is hybridization in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 60° C. Often, stringent hybridization conditions are hybridization in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 65° C. More often, stringency conditions are 0.5M sodium phosphate, 7% SDS at 65° C., followed by one or more washes at 0.2×SSC, 1% SDS at 65° C. Stringent hybridization temperatures can also be altered (i.e. lowered) with the addition of certain organic solvents, formamide for example. Organic solvents, like formamide, reduce the thermal stability of double-stranded polynucleotides, so that hybridization can be performed at lower temperatures, while still maintaining stringent conditions and extending the useful life of nucleic acids that may be heat labile.
As used herein, the phrase “hybridizing” or grammatical variations thereof, refers to binding of a first nucleic acid molecule to a second nucleic acid molecule under low, medium or high stringency conditions, or under nucleic acid synthesis conditions. Hybridizing can include instances where a first nucleic acid molecule binds to a second nucleic acid molecule, where the first and second nucleic acid molecules are complementary. As used herein, “specifically hybridizes” refers to preferential hybridization under nucleic acid synthesis conditions of a primer, to a nucleic acid molecule having a sequence complementary to the primer compared to hybridization to a nucleic acid molecule not having a complementary sequence. For example, specific hybridization includes the hybridization of a primer to a target polynucleotide sequence that is complementary to the primer.
A primer, in certain embodiments, may contain a modification such as one or more inosines, abasic sites, locked nucleic acids, minor groove binders, duplex stabilizers (e.g., acridine, spermidine), Tm modifiers or any modifier that changes the binding properties of the primers. A primer, in certain embodiments, may contain a detectable molecule or entity (e.g., a fluorophore, radioisotope, colorimetric agent, particle, enzyme and the like).
A primer also may refer to a polynucleotide sequence that hybridizes to a subsequence of a target polynucleotide or another primer and facilitates the detection of a primer, a target polynucleotide or both, as with molecular beacons, for example. The term “molecular beacon” as used herein refers to detectable molecule, where the detectable property of the molecule is detectable only under certain specific conditions, thereby enabling it to function as a specific and informative signal. Non-limiting examples of detectable properties are, optical properties, electrical properties, magnetic properties, chemical properties and time or speed through an opening of known size.
A primer often comprises one or more non-native elements. A non-native element can be any feature of an oligonucleotide primer that is made by the hand of a person. A non-native element associated with an oligonucleotide is often not associated with an oligonucleotide (e.g., DNA or RNA) in nature (e.g., not found in nature). In some embodiments, a non-native element comprises an identifier. Non-limiting examples of an identifier include sequence tags, labels (e.g., a radiolabel (e.g., an isotope), a metallic label, a fluorescent label, a fluorophore, a chemiluminescent label, an electrochemiluminescent label (e.g., Origen™), a phosphorescent label, a light scattering molecule, a quencher (e.g., a fluorophore quencher), a fluorescence resonance energy transfer (FRET) pair (e.g., donor and acceptor), a dye, a protein (e.g., an enzyme (e.g., alkaline phosphatase and horseradish peroxidase), an antibody (e.g., a suitable binding agent) or part thereof, a linker, a member of a binding pair), an enzyme substrate (e.g., any moiety capable of participating in an enzyme reaction), a small molecule (e.g., biotin, avidin), a mass tag, quantum dots, nanoparticles, the like or combinations thereof), an amino acid, protein, carbohydrate, fatty acid, lipid, a modified nucleotide (e.g., a non-native nucleotide, e.g., a nucleotide comprising an additional element (e.g., an element of the periodic table of elements), molecule, or a secondary group not found associated with a nucleotide of a DNA or RNA oligonucleotide found in nature), the like, or a combination thereof. For embodiments in which the identifier is a detectable label, the identifier often is a molecule that emits a detectable signal having an intensity different than the intensity of a signal emitted by a naturally occurring nucleotide base under the same conditions (e.g., at the same emission wavelength for a fluorophore). In some embodiments a non-native element comprises or consists of a heterologous nucleotide sequence. A heterologous nucleotide sequence sometimes is synthetic and sometime originates from a type of organism (e.g., a non-human organism or non-mammalian organism) different than the organism from which a sample is derived from. A primer sometimes is a chimeric molecule comprising a hybridization sequence and a heterologous polynucleotide (e.g., heterologous to the hybridization sequence) made by the hand of a person or by a machine and not found in nature. A non-native element can be attached or associated with a primer by any suitable method. In some embodiments a non-native element is attached to a primer by a covalent bond. In some embodiments a non-native element is associated or bound to a primer by a non-covalent bond.
Adaptors
In some embodiments, an oligonucleotide comprises an adaptor sequence and/or complement thereof. Adaptor sequences often are useful for certain sequencing methods such as, for example, a sequencing-by-synthesis process described herein. Adaptors sometimes are referred to as sequencing adaptors or adaptor oligonucleotides. Adaptor sequences typically include one or more sites useful for attachment to a solid support (e.g., flow cell). In some embodiments adaptors comprises one or more binding and/or capture agents. Adaptors also may include sequencing primer hybridization sites (i.e. sequences complementary to primers used in a sequencing reaction) and identifiers (e.g., indices) as described below. Adaptor sequences can be located at the 5′ and/or 3′ end of a nucleic acid and sometimes can be located within a larger nucleic acid sequence. Adaptors can be any length and any sequence, and may be selected based on standard methods in the art for adaptor design.
One or more adaptor sequences may be incorporated into a nucleic acid (e.g. oligonucleotide) by any method suitable for incorporating adaptor sequences into a nucleic acid. For example, PCR primers used for generating PCR amplicons (i.e., amplification products) may comprise adaptor sequences or complements thereof. Thus, PCR amplicons that comprise one or more adaptor sequences can be generated during an amplification process. In some instances, one or more adaptor sequences can be ligated to a nucleic acid by any ligation method suitable for attaching adaptor sequences to a nucleic acid. In some embodiments an adaptor, or portion thereof, is ligated to one or both ends of a nucleic acid fragment. Sometimes one or more adaptors are ligated to one or more unpaired nucleotides at the 5′ and 3′ end of a digested nucleic acid fragment. In some embodiments the sequence of an adaptor ligated to one end of a nucleic acid fragment is different that the sequence of an adaptor ligated at the other end of a nucleic acid fragment. In some embodiments a portion of an adaptor is complementary to a sticky end that remains after digestion of a nucleic acid by a restriction endonuclease. Adaptors used for ligation are often initially double stranded. Sometimes after ligation an unligated strand of an adaptor is removed, discarded or displaced leaving a single strand of the adaptor ligated to its target. Ligation processes may include, for example, blunt-end ligations, ligations that exploit 3′ adenine (A) overhangs generated by Taq polymerase during an amplification process and ligate adaptors having 3′ thymine (T) overhangs, and other “sticky-end” ligations. Ligation processes can be optimized such that adaptor sequences hybridize to each end of a nucleic acid and not to each other.
The term “modified variant” as used herein refers to a nucleic acid (e.g., a digested nucleic acid fragment) comprising any suitable modification or combination of modifications. Non-limiting examples of suitable modifications of nucleic acids include chemically modified residues, enzymatically modified residues, cleaved fragments of a nucleic acid, a nucleic acid comprising one or more ligated adaptors or linkers, a nucleic acid comprising an identifier, binding agent or capture agent, amplicons or extension products of a nucleic acid or a modified variant thereof, amplicons or extension products comprising a portion of a nucleic acid, amplicons or extension products comprising additional nucleotides and/or modified sequences (e.g., additions, deletions, and/or mutations), the like or combinations thereof.
Identifiers
In some embodiments, a nucleic acid (e.g., an oligonucleotide), protein or binding agent comprises an identifier. An identifier can be any feature that can identify a particular origin or aspect of a nucleic acid fragment (e.g., digested nucleic acid fragment), protein and/or binding agent. An identifier may be referred to herein as a tag, label, index, barcode, identification tag, sequence tag, index primer, and the like. An identifier can be a suitable detectable label or sequence tag incorporated into or attached to a nucleic acid (e.g., a polynucleotide) that allows detection, identification and/or quantitation of nucleic acids and/or nucleic acid targets that comprise the identifier. In some embodiments an identifier allows detection, identification and/or quantitation of nucleic acids and/or nucleic acid targets that are associated with an identifier. For example, in some embodiments a first nucleic acid (e.g., a target) is associated with a second nucleic acid comprising an identifier, the first nucleic acid can hybridized to the second nucleic acid and the first nucleic can be identified, quantified or characterized according to the identifier on the second nucleic acid. An identifier (e.g., a sample identifier) can identify the sample from which a particular fragment originated. For example, an identifier (e.g., a sample aliquot identifier) can identify the sample aliquot from which a particular fragment originated. In another example, an identifier (e.g., chromosome identifier) can identify the chromosome from which a particular fragment originated. A nucleic acid comprising an identifier is sometimes referred to herein as “labeled” (e.g., for a nucleic acid comprising a suitable label) or “tagged” (e.g., for a nucleic acid comprising a sequence tag). In some embodiments an identifier is distinguishable from another identifier. A “distinguishable identifier” as used herein means that a signal from one identifier can be distinguished and/or differentiated from the signal from another identifier. A “signal” as referred to herein can be a suitable detectable read-out and/or change thereof, non-limiting example of which include nucleotide sequence, mass, any detectable electromagnetic radiation (e.g., visible light (e.g., fluorescence, phosphorescence, chemiluminescence), infrared, ultraviolet, radiation (e.g., X-rays, gamma, beta or alpha), anions and ions (e.g., ionization, pH), the like or combinations thereof. In some embodiments a presence, absence or change in a signal can be detected and/or quantified. For example, a change in wavelength or a change in the intensity (e.g., a loss or a gain) of a wavelength of electromagnetic radiation may be a detectable and/or quantifiable read-out. In some embodiments of nucleic acid sequencing, a signal may comprise the detection and/or quantitation of a collection of signals.
Non-limiting examples of detectable labels include a radiolabel (e.g., an isotope), a metallic label, a fluorescent label, a fluorophore, a chemiluminescent label, an electrochemiluminescent label (e.g., Origen™), a phosphorescent label, a light scattering molecule, a quencher (e.g., a fluorophore quencher), a fluorescence resonance energy transfer (FRET) pair (e.g., donor and acceptor), a dye, a protein (e.g., an enzyme (e.g., alkaline phosphatase and horseradish peroxidase), an antibody or part thereof, a linker, a member of a binding pair), an enzyme substrate (e.g., any moiety capable of participating in an enzyme reaction), a small molecule (e.g., biotin, avidin), a mass tag, quantum dots, nanoparticles, the like or combinations thereof.
An identifier may be a unique sequence of nucleotides (e.g., sequence-based identifiers) and/or a particular length of polynucleotide (e.g., length-based identifiers; size-based identifiers, a stuffer sequence). Identifiers for a collection of samples or plurality of chromosomes, for example, may each comprise a unique sequence of nucleotides (e.g., a sequence tag). As used herein, the term “sequence tag” or “tag” refers to any suitable sequence of nucleotides in a nucleic acid (e.g., a polynucleotide, a nucleic acid fragment). A sequence tag is sometimes a polynucleotide label. A sequence tag sometimes comprises a heterologous or artificial nucleotide sequence. A sequence tag may comprise a nucleic acid index, barcode and/or one or more nucleotide analogues. A nucleic acid sequence of a sequence tag is often known. In some embodiments a “sequence tag” is a known and/or identifiable sequence of nucleotides and/or nucleotide analogues. In some embodiments a “sequence tag” is a unique sequence. A unique sequence may be a nucleotide sequence (e.g., a “sequence tag”), or reverse complement thereof, that is not present in a sample of nucleic acids where the sequence tag is used. In some embodiments a unique sequence does not hybridize directly, under hybridization conditions, to sample nucleic acids or target polynucleotides.
In some embodiments a sequence tag is configured to hybridize to a target sequence (e.g., a sequence complementary to a sequence tag). In some embodiments a sequence tag is a probe. A probe is often a nucleic acid comprising one or more identifiers that is configured to hybridize to a specific sequence of a target polynucleotide. In some embodiments a sequence tag is a primer or portion thereof. In some embodiments a primer comprises a sequence tag. A primer is often a polynucleotide configured to bind in a sequence-specific manner to a target polynucleotide where the primer is configured for extension by a polymerase while using a portion of the target as a template. In some embodiments a target polynucleotide comprises a sequence tag.
A sequence tag sometimes is incorporated into a target polynucleotide species using a method known in the art. In some embodiments, a sequence tag is incorporated into a target polynucleotide species as part of library preparation. In some embodiments, a sequence tag is native to sample nucleic acid, is predetermined and/or pre-exists within a target polynucleotide. In some embodiments target specific oligonucleotides are designed to hybridize near or adjacent to a predetermined and/or pre-existing sequence tag. For example, a predetermined sequence tag may be a suitable four nucleotide sequence (e.g., ATGC) where the location of the sequence tag within a target polynucleotide (e.g., a chromosome) is known. In certain embodiments one or more target specific oligonucleotides are designed to hybridize to one or more locations on a target polynucleotide (e.g., a chromosome) adjacent to a predetermined and/or pre-existing sequence tag (e.g., ATGC). In such embodiments, the sequence tag (e.g., ATGC) is detected and/or quantified by using the target specific oligonucleotides as a primer and by sequencing the next four nucleotides (e.g., ATGC). In certain embodiments, complementary nucleotides (e.g., or nucleotide analogues, labeled nucleotides) are added by a suitable polymerase. In some embodiments, sequence tags may be detected directly or indirectly by a mass spectrometry method (e.g., using MALDI-TOF). In embodiments where a 3 nucleotide sequence tag is used, 9 potential target polynucleotides may be detected by a suitable DNA sequencing method. Likewise, a 4 nucleotide sequence tag may permit detection of 16 targets, a 5 nucleotide sequence tag may permit detection of 25 targets and so on.
A sequence tag identifier (e.g., sequence-based identifiers, length-based identifiers) may be of any length suitable to distinguish certain nucleic acid fragments from other nucleic acid fragments. In some embodiments, identifiers may be from about one to about 100 nucleotides in length. A sequence tag may comprise 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 20 or more, 30 or more or 50 or more contiguous nucleotides. In some embodiments a sequence tag comprises about 1 to about 50, about 2 to about 30, about 2 to about 20 or about 2 to about 10 contiguous nucleotides. For example, sequence tag identifiers independently may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50, 60, 70, 80, 90 or 100 nucleotides (e.g., contiguous nucleotides) in length. In some embodiments, an identifier contains a sequence of six nucleotides. In some instances, an identifier is part of an adaptor sequence for a sequencing process, such as, for example, a sequencing-by-synthesis process described in further detail herein. In some instances, an identifier may be a repeated sequence of a single nucleotide (e.g., poly-A, poly-T, poly-G, poly-C). Such sequence tag identifiers may be detected and distinguished from each other by any suitable method, for example, by using a suitable sequencing method, mass spectrometry, a nanopore technology, the like or combinations thereof.
An identifier may be directly attached (e.g., by a covalent bond, e.g., by a phosphodiester linkage) or indirectly attached and/or associated with a nucleic acid. Indirect attachment may comprise use of one or more binding pairs (e.g., antibody/antigen, biotin/avidin, the like). Indirect attachment may comprise hybridization (e.g., sequence-specific, non-covalent, base-pairing interactions). An identifier may be covalently bound or non-covalently bound to a nucleic acid. An identifier may be permanently or reversibly attached. In some embodiments an identifier is incorporated into or attached to a nucleic acid during a sequencing method (e.g., by a polymerase). In some embodiments, an identifier is located within or adjacent to an adaptor sequence. In some embodiments, an identifier is located within a portion of one or more primer hybridization sequences. A identifier may permit the detection, identification, quantitation and/or tracing of (i) polynucleotides to which the identifier is attached or incorporated (e.g., a labeled or tagged oligonucleotide, a labeled or tagged primer or extension product thereof), (ii) a polynucleotide to which a labeled or tagged polynucleotide hybridizes, and/or (iii) a polynucleotide to which a labeled or tagged polynucleotide is ligated to.
Any suitable type and/or number of identifiers can be used (e.g., for multiplexing). In some embodiments 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 20 or more, 30 or more or 50 or more different (e.g., distinguishable) identifiers are utilized in a method described herein (e.g., a nucleic acid detection, quantitation and/or sequencing method). In some embodiments, one, two, three or more identifies are associated with a nucleic acid or a subset of nucleic acids.
In some embodiments identifiers (e.g., sequence tags, labels) are chromosome-specific, locus specific, or gene specific. In some embodiments a locus-specific identifier is used to analyze (e.g., identify, quantify, or the like) a suitable locus (e.g., hypomethylated region, hypomethylated nucleotides, SNPs, the like or a combination thereof) or a collection of loci that are the same or different. For example, a locus-specific sequence tag sometimes is a sequence of nucleic acids that is configured to selectively identify one specific target locus. In some embodiments a locus-specific identifier is configured to selectively identify two or more specific target loci.
In some embodiments, an analysis comprises analyzing (e.g., detecting, counting, sequencing, quantifying, processing counts, the like or combinations thereof) one or more identifiers. In some embodiments, a detection process includes detecting an identifier and sometimes not detecting other features (e.g., sequences) of a nucleic acid. In some embodiments, a counting process includes counting each identifier. In some embodiments, an identifier is the only feature of a nucleic acid that is detected, analyzed and/or counted.
Binding/Capture Agents
In some embodiments a method described herein involves the use of a binding agent and/or a capture agent (e.g., a binding pair). The term “binding agent” as used herein refers to any molecule (e.g., nucleic acid, protein, carbohydrate, lipid, the like or combination thereof) that specifically binds another molecule (e.g., a target molecule (e.g., an antigen), a binding partner). An binding agent “specifically binds” to a corresponding binding partner where the binding agent often has less than about 30%, 20%, 10%, 5% or 1% cross-reactivity with another agent. A binding agent and it's corresponding binding partner are often referred to collectively herein as a binding pair. A binding agent often specifically binds a target molecule or binding partner with a dissociation constant (Kd) on the order of 10−6, 10−7, 10−8, 10−9, or less. In some embodiments a capture agent comprises a binding agent. In some embodiments a capture agent comprises a binding agent immobilized on a solid support or a binding agent configured to bind a solid support. In some embodiments a capture agent comprises a member of a binding pair immobilized on a solid support or a member of a binding pair configured to bind a solid support. In some embodiments a binding agent binds to a capture agent. In certain embodiments a binding agent is covalently linked to a capture agent or a member of a binding pair. For example, a binding agent may comprise an antibody covalently linked to biotin and a capture agent can comprise avidin immobilized on a solid support where the binding agent is configured to bind to the solid support. Non-limiting examples of binding pairs include, without limitation: avidin/biotin; an antibody/antigen; antibody/epitope; antibody/hapten; operator/repressor; nuclease/nucleotide; lectin/polysaccharide; steroid/steroid-binding protein; ligand/receptor; enzyme/substrate; Ig/protein A; Fc/protein A; Ig/protein G; Fc/protein G; Histidine polymers (e.g., a His tag) and heavy metals; a polynucleotide and its corresponding complement; the like or combinations thereof.
A binding agent and/or corresponding partners can be directly or indirectly coupled to a substrate or solid support. In some embodiments, a substrate or solid support is used to separate certain nucleic acid fragments (e.g., species of nucleic acid fragments, digested nucleic acid fragments) in a sample. Some methods involve binding partners where one partner is associated with an oligonucleotide and the other partner is associated with a solid support. In some instances, a single binding agent can be employed for the enrichment of certain nucleic acid fragments (e.g., digested nucleic acid fragments). In some instances, a combination of different binding agents may be employed for the enrichment of certain nucleic acid fragments (e.g., digested nucleic acid fragments). For example, at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 50, 75 or 100 different binding agents may be used for the enrichment of certain nucleic acid fragments (e.g., digested nucleic acid fragments).
Methods of separation are known in the art. Any suitable method of separation can be used. Non-limiting examples of separation methods include adsorption, centrifugation, chromatography (e.g., affinity chromatography, flow cytometry, various fluid separation methods (e.g., chip based separation), molecular size exclusion, the like or combinations thereof), crystallization, decantation, drying, electrophoresis, flotation, flocculation, filtration, dialysis, magnetic separation, precipitation (e.g., nucleic acid precipitation, immuno-precipitation, solid phase or solid support precipitation, or the like), sedimentation, gravity separation, sieving, the like or combinations thereof. A sample is often subjected to a separation process resulting in one or more separation products. In some embodiments a separation product comprises a minority nucleic acid species. In some embodiments a separation process generates a separation product enriched for minority nucleic acid species (e.g., hypomethylated nucleic acid, fetal nucleic acid, target polynucleotides, tumor nucleic acid). In some embodiments two or more nucleic acid species (e.g., nucleic acid species fragments) are separated by an enrichment process. Non-limiting examples of a separation product comprises an isolated product, a purified or partially purified product, a fractionated product (e.g., an elution fraction, a flow though fraction), an immobilized product, an enriched product, the like or a combination thereof.
In some embodiments, a binding/capture agent is an antibody or a portion thereof, naturally occurring or synthetic (e.g., genetically engineered). Antibodies can be immunoglobulin molecules or immunologically active portions (e.g., binding fragments) of immunoglobulin molecules (e.g., molecules that contain an antigen binding site that specifically binds an antigen). Antibodies, portions thereof (e.g., binding portions), mutants or chimeras thereof can be expressed and/or isolated from any suitable biological organism or source. Non-limiting examples of binding/capture agents include monoclonal antibodies, polyclonal antibodies, Fabs, Fab′, single chain antibodies, synthetic antibodies, DNA, RNA, aptamers (DNA/RNA), peptoids, zDNA, peptide nucleic acids (PNAs), locked nucleic acids (LNAs), lectins, synthetic or naturally occurring chemical compounds (including but not limited to drugs, labeling reagents), dendrimers, peptides, polypeptides, biotin, streptavidin, or combinations thereof. A variety of antibodies and antibody fragments can be generated for use as a specific binding agent. Antibodies sometimes are IgG, IgM, IgA, IgE, or an isotype thereof (e.g., IgG1, IgG2a, IgG2b or IgG3), sometimes are polyclonal or monoclonal, and sometimes are chimeric, humanized or bispecific versions of such antibodies. In some embodiments a binding/capture agent used herein is an antibody, or fragment thereof that specifically binds 5-methylcytosine. Polyclonal antibodies, monoclonal antibodies, fragments thereof, and variants thereof that bind specific antigens are commercially available, and methods for generating such antibodies are known.
A binding agent also can be a polypeptide or peptide. A polypeptide may include a sequence of amino acids, amino acid analogs, or peptidomimetics, typically linked by peptide bonds. The polypeptides may be naturally occurring, processed forms of naturally occurring polypeptides (such as by enzymatic digestion), chemically synthesized, or recombinant expressed. The polypeptides for use in a method herein may be chemically synthesized using standard techniques. Polypeptides may comprise D-amino acids (which are resistant to L-amino acid-specific proteases), a combination of D- and L-amino acids, beta amino acids, or various other designer or non-naturally occurring amino acids (e.g., beta-methyl amino acids, C alpha-methyl amino acids, N alpha-methyl amino acids, and the like) to convey special properties. Synthetic amino acids may include ornithine for lysine, and norleucine for leucine or isoleucine. In some instances, polypeptides can have peptidomimetic bonds, such as ester bonds, to prepare polypeptides with novel properties. Polypeptides also may include peptoids (N-substituted glycines), in which the side chains are appended to nitrogen atoms along the molecule's backbone, rather than to the alpha-carbons, as in amino acids.
In some embodiments a binding agent is a methyl-specific binding agent. In some embodiments a methyl-specific binding agent selectively and/or specifically (e.g., with high affinity) binds a methylated nucleotide (e.g., 5-methyl cytosine). In some embodiments a methyl-specific binding agent selectively and/or specifically binds a methylation site or locus that is unmethylated (e.g., unmethylated cytosine, unmethylated CpG). In some embodiments a methyl-specific binding agent is an antibody or portion thereof (e.g., a binding fragment thereof). In some embodiments a methyl-specific binding agent comprises a portion of an antibody (e.g., an Fc portion of an immunoglobulin). A methyl-specific binding agent can be an antibody that specifically binds a methylation site or locus that is methylated. A methyl-specific binding agent can be an antibody that specifically binds a hypermethylated locus. Non-limiting examples of antibodies that specifically bind methylated nucleic acid, hypermethylated nucleic acid and/or hypermethylated loci include anti-5-methylcytosine antibody, clone 33D3; anti-5-hydroxymethylcytosine (5hmC) antibody, clone HMC-MA01; anti-5-hydroxymethylcytosine antibody, clone AB3/63.3; anti-5-hydroxymethylcytosine (5hmC) antibody, clone HMC 31, the like or a combination thereof. In certain embodiments, a methyl-specific binding agent can be an antibody that specifically binds a methylation site that is not methylated (e.g., an unmethylated CpG). Often, a methyl-specific binding agent that specifically binds a methylation site that is unmethylated does not substantially bind to a methylation site that is methylated. In some embodiments a methyl-specific binding agent is not an antibody or binding fragment thereof. In some embodiments a methyl-specific binding agent comprises a methyl-specific binding protein (e.g., a methyl-binding domain protein) or a portion thereof. Any suitable methyl-specific binding protein, or portion thereof, can be used for a method described herein. Non-limiting examples of methyl-specific binding proteins include methyl CpG Binding Protein 2 (Rett Syndrome)(MECP2), Methyl-CpG-binding domain protein 1 (MBD1), Methyl-CpG-binding domain protein 2 (MBD2), Methyl-CpG-binding domain protein 4 (MBD4) and Methyl-CpG-binding domain proteins 5-12. Methyl-CpG-binding domain proteins that specifically bind methylated CpG can be isolated, purified or cloned and expressed from a suitable plant, animal, insect, yeast or prokaryote.
In some embodiments a methyl-specific binding agent is an antibody that specifically binds a methylated histone or methylated histone subunit. Antibodies that specifically bind methylated histone proteins, where the histone is associated with a nucleic acid fragment, can be used to enrich for certain nucleic acid species. For example, as shown in Example 2 methylation sites in placenta that are associated with H3K9me3 comprise an intermediate to low amount of methylation (e.g., <75%, <80% methylated) compared to ccf DNA in non-pregnant females. In some embodiments methyl-specific binding agents that specifically bind methylated histones can be used to immunoprecipitate and enrich hypomethylated nucleic acid from a sample (e.g., sample nucleic acid from a pregnant female). For example, methyl-specific binding agents that specifically bind H3K9me3 can be used to immunoprecipitate and enrich hypomethylated nucleic acid from a sample (e.g., sample nucleic acid from a pregnant female). In some embodiments methyl-specific binding agents that specifically bind H3K9me3 can be used to immunoprecipitate and enrich for fetal nucleic acid.
Solid Support
In some embodiments, a binding/capture agent can be linked directly or indirectly to a solid support (e.g., a substrate). In some embodiments, nucleic acid fragments are associated with a solid support, such as the solid supports described below, by one or more binding agents, such as the binding agents described herein. A solid support or substrate can be any physically separable solid to which a nucleic acid, protein, carbohydrate or binding agent can be directly or indirectly attached.
A solid support can be any shape (e.g., flat, concave, convex, a groove, a channel, a cylinder, a tube, a sphere (e.g., a bead)) or size, and can exist as a separate entity or as an integral part of an apparatus or machine (e.g., a collection of beads (e.g., beads in a column), membrane, microwell, matrix, cuvette, plate, vessel, plate, centrifuge tube, slide, chip, wafer, flow cell, the like, or combinations thereof. In some embodiments a solid support comprises a suitable surface, for example as provided by a suitable substrate (e.g., a microarray substrate, a chip). In some embodiments a solid support is a flow cell configured for use in a DNA sequencer. In some embodiments a solid support is configured for a massively parallel sequencing (MPS) method or configured for use in a massively parallel sequencing (MPS) apparatus, machine or device.
A solid support can comprise a suitable material, non-limiting examples of which include glass, borosilicate glass, silica, quartz, fused quartz, mica, silicon (Si), carbon (e.g., diamond) modified silicon, a suitable metal (e.g., gold, titanium, silver, brass, aluminum and the like), steel (e.g., a steel alloy), ceramic, germanium, graphite, plastic, dextran, semiconductor fabrics, high refractive index dielectrics, crystals, a suitable polymer such as (poly)tetrafluoroethylene, (poly)vinylidenedifluoride, polymethacrylate (PMA), polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), polystyrene, polycarbonate, polyacrylamide, nylon, latex, cellulose (e.g., activated cellulose), the like or combinations thereof. In some embodiments a solid support comprises particles such as beads (e.g., paramagnetic beads, magnetic beads, microbeads, nanobeads), microparticles, and nanoparticles. Solid supports also can include, for example, chips, columns, optical fibers, wipes, filters (e.g., flat surface filters), one or more capillaries, glass and modified or functionalized glass (e.g., controlled-pore glass (CPG)), quartz, mica, diazotized membranes (paper or nylon), polyformaldehyde, cellulose, cellulose acetate, paper, ceramics, metals, metalloids, semiconductive materials, quantum dots, coated beads or particles, other suitable chromatographic materials, magnetic particles; plastics (including acrylics, polystyrene, copolymers of styrene or other materials, polybutylene, polyurethanes, TEFLON™, polyethylene, polypropylene, polyamide, polyester, polyvinylidene difluoride (PVDF), and the like), polysaccharides, nylon or nitrocellulose, resins, silica or silica-based materials including silicon, silica gel, and modified silicon, Sephadex®, Sepharose®, agarose, carbon, metals (e.g., steel, gold, silver, aluminum, silicon and copper), inorganic glasses, conducting polymers (including polymers such as polypyrole and polyindole); micro or nanostructured surfaces such as nucleic acid tiling arrays, nanotube, nanowire, or nanoparticulate decorated surfaces; or porous surfaces or gels such as methacrylates, acrylamides, sugar polymers, cellulose, silicates, other fibrous or stranded polymers, the like or combinations thereof. In some embodiments a solid support is a collection of particles. In some instances, the solid support or substrate may be coated using passive or chemically-derivatized coatings with any number of materials, including polymers, such as dextrans, acrylamides, gelatins or agarose. Beads and/or particles may be free or in connection with one another (e.g., sintered). In some embodiments, the solid phase can be a collection of particles. In certain embodiments, the particles can comprise silica, and the silica may comprise silica dioxide. In some embodiments the silica can be porous, and in certain embodiments the silica can be non-porous. In some embodiments, the particles further comprise an agent that confers a paramagnetic property to the particles. In certain embodiments, the agent comprises a metal, and in certain embodiments the agent is a metal oxide, (e.g., iron or iron oxides, where the iron oxide contains a mixture of Fe2+ and Fe3+).
In some embodiments a solid support is configured to immobilize a nucleic acid, protein, carbohydrate, a nucleic acid library, a reagent, binding agent, analyte, the like, combination thereof or portion thereof. In some embodiments a solid support comprises a plurality of molecules (e.g., proteins, nucleic acids, functional groups, binding agents, one or members of a binding pair, reactive chemical moieties, the like or combinations thereof). In certain embodiments a solid support comprises a plurality of oligonucleotides (e.g., primers) configured to capture a nucleic acid library or part thereof. In certain embodiments oligonucleotides are attached to a solid support at their 5′ ends or at their 3′ends. In some embodiments attachment of an oligonucleotide to a solid support is reversible (e.g., by cleavage with a nuclease or restriction endonuclease). In some embodiments, a plurality of primers are attached or immobilized to a support at their 5′ ends. In some embodiments, the 5′ end of one or more primers immobilized on a support comprise a single stranded region of about 5 nucleotides to about 30 nucleotides.
In some embodiments a solid support comprises discrete locations (e.g., addresses, mapped locations) where target polynucleotide species are disposed. For example, in some embodiments a solid support may comprises target-specific oligonucleotides immobilized at discrete locations where the target-specific oligonucleotides are configured to capture and/or amplify specific target sequences (e.g., target polynucleotides). In some embodiments target polynucleotides may be amplified at discrete locations on a solid support and the location of the specific amplicons is known (e.g., mapped, e.g., identifiable with a suitable imaging device). In some embodiments amplifying target polynucleotides on a solid support generates cluster of amplified target polynucleotide species at discrete locations on the solid phase.
In some embodiments a nucleic acid library, or portion thereof is immobilized to a suitable solid support. The term “immobilized” as used herein means direct or indirect attachment to a solid support. In some embodiments the term “capture” as used herein refers to immobilization of a nucleic acid, protein, carbohydrate, analyte or reagent. Immobilization can be covalent or non-covalent. Immobilization can be permanent or reversible. In some embodiments immobilization comprises hybridization of complementary nucleic acid sequences. In some embodiments a plurality of oligonucleotides is complementary to one or more universal sequences or sequence tags integrated into a library of nucleic acids. In some embodiments a plurality of nucleic acids comprises specific nucleic acid sequences configured to hybridize, immobilize and/or capture nucleic acids comprising one or more specific loci (e.g., a hyper or hypo methylated locus). In some embodiments nucleic acids are immobilized by use of one or more binding agents (e.g., a binding protein or antibody) that bind specifically to a nucleic acid sequence, protein, carbohydrate, reagent, analyte or portion thereof. For example, a binding agent can specifically bind to and/or immobilize (e.g., capture) polynucleotides comprising specific nucleic acid sequences. In some embodiments a binding agent can specifically bind to and/or immobilize (e.g., capture) polynucleotides comprising specific nucleic acid sequences (e.g., CpG) with a specific methylation status (e.g., a methylated, unmethylated or partially methylated sequence).
Methylated Nucleotides, Sites and Loci
A methylated nucleotide or a methylated nucleotide base refers to the presence of a methyl moiety (e.g., a methyl group) on a nucleotide base, where the methyl moiety is not normally present in the nucleotide base. For example, cytosine can comprise a methyl moiety at position 5 of its pyrimidine ring and can be referred to herein as methylated or as methyl cytosine. Cytosine, in the absence of a 5-methyl group is not a methylated nucleotide and can be referred to herein as unmethylated. In another example, thymine contains a methyl moiety at position 5 of its pyrimidine ring, however, for purposes herein, thymine is not considered a methylated nucleotide. A “methylation site” as used herein refers to a location of a nucleotide (e.g., a cytosine) within a nucleic acid where the nucleotide is methylated or has the possibility of being methylated. For example the nucleic acid sequence CpG is a methylation site where the cytosine may or may not be methylated. Cytosine methylation may also occur at the methylation sites CHG and/or CHH (e.g., where H=A, T or C). Where the particular methylated or unmethylated nucleotide is not specified, “methylation status” (e.g., unmethylated, methylated, hypomethylated, hypermethylated) often refers to cytosine methylation. A CpG island refers to a genomic region that comprises a high frequency of CpG methylation sites that may or may not be methylated.
The term “methylation profile” “methylation state” or “methylation status,” are used interchangeably herein and refer to the state of methylation (e.g., methylated, unmethylated, hypermethylated, hypomethylated; percent methylated, or the like) of one or more methylation sites on a polynucleotide (e.g., a nucleic acid, a target polynucleotide), a nucleic acid species or subset, or a genetic locus (e.g., a defined region on a chromosome). A methylation status can refer to a frequency of methylation, relative methylation, differential methylation, absolute methylation, a ratio or percentage of methylation, the like or a combination thereof. A genetic locus comprising one or more methylation sites is sometimes referred to herein as a methylation locus or loci. The term “methylation profile” or “methylation status” refers to the amount or relative amount of methylated or unmethylated methylation sites on a polynucleotide, a nucleic acid species or subset, or locus. A “methylation profile” or “methylation status” sometimes refers to a relative state of methylation for a polynucleotide, a nucleic acid species or subset, or locus between two nucleic acid subsets or samples. For example, a locus can be relatively less methylated in fetal than in maternal nucleic acid. The term “amount” as used herein can refer to a mean, average, median, mode or absolute amount (e.g., quantity, number, count, total, aggregate, sum, quota, group, size, mass, weight, volume, bulk, lot, quantum, moles, concentration, percentage, or the like).
A methylation status of a methylation site can be referred to as unmethylated, methylated, hypomethylated or hypermethylated, for example. Methylation status can be determined by any suitable method. A methylation site comprising a methylated nucleotide is referred to herein as methylated. A methylation site comprising an unmethylated nucleotide is referred to herein as unmethylated. Methylation status of a methylation site is often provided as a percent or ratio. In some embodiments a methylation status of a first methylation site in a sample is a ratio of the quantity of first methylation sites that are methylated to the quantity of first methylation sites that are unmethylated. In some embodiments a methylation status of a first methylation site in a sample is a percentage of the quantity of first methylation sites that are methylated to the quantity of total methylation sites present in a sample or population of nucleic acid. For example, for a given sample, the methylation status for a first methylation site can be 0.3 (e.g., 30%) indicating that 30% of the nucleic acid fragments containing the first methylation site are methylated at the first methylation site, and 70% of the nucleic acids in the sample containing the first site are not methylated at the first methylation site. A hypomethylated site, for example, often refers to a methylation site present on a plurality of nucleic acid fragments in a sample, where the methylation site is methylated on less than 60% (e.g., 0.60), less than 50% (e.g., 0.50), less than 40%, less than 30%, less than 20%, less than 15%, less than 10%, less than 5% or less than 3% of the nucleic acid fragments in the sample that comprise the methylation site. A hypermethylated site, for example, often refers to a methylation site present on a plurality of nucleic acids fragments in a sample, where the methylation site is methylated in greater than 95%, greater than 90%, greater than 85%, greater than 80%, greater than 75%, greater than 70%, greater than 60% or greater than 50% of the nucleic acids fragments in the sample that comprise the methylation site.
In some embodiments the methylation status of a locus is determined. A locus (e.g., a locus targeted for analysis, a methylation locus, a differentially methylated locus) can be any suitable length. A locus often comprises an average, mean, median or absolute length of about 5,000 bp or more, 10,000 bp or more, 15,000 bp or more, 20,000 bp or more, 30,000 bp or more, 40,000 bp or more, 50,000 bp or more, 75,000 bp or more, or 100,000 bp or more. In some embodiments a locus is about 20,000 to about 100,000 bp, or about 20,000 to about 50,000 bp in length. In some embodiments a locus comprises a minimum amount of CpG sites. In some embodiments a locus (e.g., DMR) comprises at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, or at least 20 CpG methylation sites.
The methylation status of a methylation locus (e.g. locus, loci, polynucleotide, region comprising one or more methylation sites) can be referred to as unmethylated, methylated, hypomethylated (e.g., less methylated), hypermethylated (e.g., more methylated), or differentially methylated, for example. A methylation locus comprising one or more methylated nucleotides can be referred to herein as methylated. For example methylated nucleic acids often comprise one or more methylated nucleotides. A methylation locus that does not contain any methylated nucleotides is referred to herein as unmethylated. The methylation status of a locus can be determined by any suitable method. In some embodiments the methylation status of a methylation locus is determined as an average, mean or median of the methylation status of all methylation sites within a locus for a given sample or population of nucleic acid. For example, for a given sample, the methylation status for a first site in a locus can be 0.3 (e.g., 30% of the nucleic acid fragments containing the site are methylated), a second site within the locus can be 0.4 (e.g., 40%), a third site within the locus can be 0.45 (45%) and the mean methylation status of the locus can be calculated as the mean of the methylation status of all sites within the locus (e.g., in the foregoing example, the mean methylation status of the locus is 0.4 or 40%). A hypomethylated nucleic acid or locus often refers to a locus comprising a mean methylation status of less than about 0.75, less than about 0.7, less than about 0.65, less than about 0.6, less than about 0.5, less than about 0.4, less than about 0.3, less than about 0.2, less than about 0.15, less than about 0.10, less than about 0.05 or less than about 0.03 for a given sample. A hypermethylated nucleic acid or locus often refers to a locus comprising a mean methylation status of greater than about 0.95, greater than about 0.90, greater than about 0.85, greater than about 0.80, greater than about 0.75, greater than about 0.70, greater than about 0.65, greater than about 0.60 or greater than about 0.50 for a given sample.
In some embodiments a methylation site, polynucleotide (e.g., target polynucleotide) or locus (e.g., region) is differentially methylated between two or more samples (e.g., sources) or subsets of nucleic acids. A differentially methylated site or locus (e.g., a differentially methylated region (e.g., DMR)), sometimes refers to a difference in the methylation status of a methylation site, region or locus between two or more samples or subsets of nucleic acids (e.g., fetal derived ccf DNA verse maternal derived ccf DNA). In some embodiments a methylation status of a locus is determined as an average, mean or median of the methylation status of a locus obtained from multiple test subjects (e.g., multiple samples) derived from the same source (e.g., enriched fetal nucleic acid). For example a methylation status for a methylation locus can be determined as an average, mean or median of the methylation status of a locus of a first sample, second sample and third sample where all three samples were derived from a different test subject and all three samples were derived from the same source (e.g., enriched fetal nucleic acid). In the foregoing example the presence or absence of a differentially methylated locus can be determined by comparing the methylation status of the first methylation locus derived from multiple samples of a first source (e.g., multiple samples of enriched fetal nucleic acid) to the methylation status of the same methylation locus derived from multiple samples of a second source (e.g., maternal nucleic acid).
In some embodiments a differentially methylated locus comprises a difference in methylation status between two samples or subsets of nucleic acids of about 0.1% or more, about 0.5% or more, 1% or more, about 5% or more, about 7% or more, about 10% or more, about 15% or more, about 20% or more, about 30% or more, about 40% or more, about 50% or more, or about 60% or more. For example a locus in fetal nucleic acid may comprise a methylation status of about 85%, the same locus in maternal nucleic acid may comprise a methylation status of about 90% and the difference in methylation status is about 5%. In some embodiments differentially methylated refers to a statistical difference (e.g., a statistically significant difference) in methylation status of a methylation site or locus between two or more samples or subsets of nucleic acids. In some embodiments methylation sites or loci are determined as differentially methylated or not differentially methylated by a t-test (e.g., a t statistic) or by a suitable statistical method.
In some embodiments analysis (e.g., an analysis of digested nucleic acid fragments, an analysis of enriched fetal nucleic acid) comprises determining the presence, absence or amount of a polynucleotide (e.g., a target polynucleotide) in a locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid. The term “a polynucleotide in a locus” means a polynucleotide comprising a sequence that is present within a particular locus. A locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid can, in some embodiments, refer to a locus that is less methylated in fetal nucleic acid relative to maternal nucleic acid by a difference in methylation status of about 0.1% or more, about 0.5% or more, about 1% or more, about 2% or more, about 3% or more, about 4% or more, about 5% or more, about 6% or more, about 7% or more, about 8% or more, about 9% or more, about 10% or more, about 15% or more, about 20% or more, about 30% or more, about 40% or more, about 50% or more, or about 60% or more. In some embodiments a locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid can refers to a locus that is about 75% or less, about 70% or less, about 65% or less, about 60% or less, about 55% or less, about 50% or less, about 40% or less, about 30% or less, about 20% or less, or about 10% or less methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments a locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid can refers to a locus that is about 55% or more, about 60% or more, about 65% or more, about 70% or more, about 75% or more, about 80% or more, about 85% or more or about 90% or more methylated in maternal nucleic acid relative to fetal nucleic acid. In some embodiments a locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid is about 60% or more methylated in maternal nucleic acid relative to fetal nucleic acid and about 60% or less methylated in fetal nucleic acid relative to maternal nucleic acid.
In some embodiments the terms “hypomethylated” and “hypermethylated” are relative terms and compare the methylation status of a methylation site, region or locus of different samples, samples obtained at different time points or subsets of nucleic acids derived from different sources (e.g., different cells, different tissues (e.g., fetal vs. maternal, tumor vs. non-tumor, placenta vs. maternal liver)). The term “hypomethylated” is sometimes a relative term and refers to a first subpopulation or subset of nucleic acids that is relatively less methylated when compared to a second subpopulation or subset of nucleic acids. A locus that is hypomethylated in a first subset of nucleic acid relative to a second subset of nucleic acid is, in some embodiments, a locus that is relatively less methylated in the first subset relative to the second subset of nucleic acid. In some embodiments a locus that is hypomethylated in a first subset of nucleic acid relative to a second subset of nucleic acid is relatively less methylated in the first subset compared to the second subset and comprises a difference in methylation status between the first and second subsets of about 0.1% or more, about 0.5% or more, about 1% or more, about 5% or more, about 7% or more, about 10% or more, about 15% or more, about 20% or more, about 30% or more, about 40% or more, about 50% or more, about 60% or more, about 70% or more, about 80% or more, or about 90% or more.
In some embodiments a differentially methylated site or locus of a first sample or subset of nucleic acid is hypermethylated relative to a second sample or subset of nucleic acid. The term “hypermethylated” is sometimes a relative term and refers to a first subpopulation or subset of nucleic acids that is relatively more methylated when compared to a second subpopulation or subset of nucleic acids. A locus that is hypermethylated in a first subset of nucleic acid relative to a second subset of nucleic acid is, in some embodiments, a locus that is relatively more methylated in the first subset relative to the second subset of nucleic acid. In some embodiments a locus that is hypermethylated in a first subset of nucleic acid relative to a second subset of nucleic acid is relatively more methylated in the first subset compared to the second subset and comprises a difference in methylation status between the first and second subsets of about 0.1% or more, about 0.5% or more, about 1% or more, about 5% or more, about 7% or more, about 10% or more, about 15% or more, about 20% or more, about 30% or more, about 40% or more, about 50% or more, about 60% or more, about 70% or more, about 80% or more, or about 90% or more.
Examples of methylation sites and loci that are hypomethylated in placenta relative to nucleic acid of a non-pregnant female (e.g., buffy coats or ccf DNA from a non-pregnant female) are provided in TABLE 2AB, TABLE 2CB, TABLE 3 (e.g., SEQ ID NOs: 1-84) and/or TABLE 4. Methylation sites and loci shown in TABLE 2AB, TABLE 2CB, TABLE 3 (e.g., SEQ ID NOs: 1-84) and/or TABLE 4 are expected to be hypomethylated in fetal nucleic acid (e.g., ccf DNA derived from fetal tissue) relative to maternal nucleic acid (e.g., ccf DNA derived from maternal tissue) in a sample of nucleic acid obtained from a pregnant female subject. Examples of methylation sites and loci that are hypermethylated in placenta relative to nucleic acid of a non-pregnant female (e.g., buffy coats or ccf DNA from a non-pregnant female) are provided in TABLE 2AA, 2B, 2CA and TABLE 5. Information in TABLE 5 is based on the human reference sequence (UCSC Ver. hg19, NCBI Build GRCh37), which was produced by the International Human Genome Sequencing Consortium. Methylation sites and loci shown in TABLE 2AA, 2B, 2CA and TABLE 5 are expected to be hypermethylated in fetal nucleic acid (e.g., ccf DNA derived from fetal tissue) relative to maternal nucleic acid (e.g., ccf DNA derived from maternal tissue) in a sample of nucleic acid obtained from a pregnant female subject.
In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment, a target polynucleotide) in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments an analysis comprises quantifying (e.g., determining an amount of) a polynucleotide in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment) in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid where the loci are chosen from the loci in TABLE 2AB, TABLE 2CB, TABLE 3 (e.g., SEQ ID NOs: 1-84), TABLE 4 or a combination thereof. In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment) in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid where the loci are chosen from a suitable chromosome. For example, the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid can be chosen from chromosome 13, chromosome 18 and/or chromosome 21. In some embodiments the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are chosen from one or more suitable chromosomes in TABLE 4 (e.g., one or more loci in chromosome 13, chromosome 18 and/or chromosome 21). In some embodiments differentially methylated regions or loci are determined according to a suitable statistical test that compares the methylation status of a region or locus between two or more sample or sources. In some embodiments a locus is a differentially methylated region (e.g., DMR) when the methylation status of the locus is statistically different (e.g., a significant statistical difference) between two different samples or sources (e.g., maternal vs fetal). A statistical difference (e.g., a significant difference) can be determined by any suitable statistical method. Non-limiting examples of suitable statistical tests or methods that can compare two or more samples and/or determine a statistical difference include a T-test (e.g., a mean, median, or absolute t-statistic), a student's T-test, a Z-test, an F-test, Chi-squared test, Wilcox test, ANOVA, MANOVA, MANCOVA, logistic regression, maximum likelihood, p-values, the like, combinations or variations thereof. In some embodiments one or more loci relatively less methylated in a minority nucleic acid species (e.g., fetal nucleic acid) than in a majority nucleic acid species (e.g., maternal nucleic acid) are chosen according to a suitable statistical test. In some embodiments one or more loci relatively less methylated in a minority nucleic acid species than in a majority nucleic acid species are chosen according to a suitable t-statistic (e.g., a mean, median or average t-statistic).
In certain embodiments a locus in a first sample is differentially methylated compared to the same locus in a second sample when the methylation status of the locus in the first sample is significantly different from the methylation status of the same locus in the second sample. In some embodiments a differentially methylated locus is a DMR (e.g., a locus relatively less methylated in a minority nucleic acid species than in a majority nucleic acid species (e.g., a locus relatively less methylated in fetal nucleic acid than in maternal nucleic acid)). In some embodiments a DMR comprises a t-statistic less than about −1, less than about −2, less than about −3, less than about −4, less than about −5, less than about −6, less than about −7, less than about −8, less than about −9, less than about −10, less than about −11, less than about −12, less than about −13, less than about −14, less than about −14.10, less than about −14.90, less than about −15, or less than about −16. In some embodiments a DMR comprises a t-statistic (e.g., a median t-statistic (e.g., median.tstat)) between about −18 and −2, between about −18 and −3, between about −18 and −4, between about −18 and −5, between about −18 and −6, between about −18 and −7, between about −18 and −8, between about −18 and −9, between about −18 and −10, between about −18 and −11, between about −18 and −12, between about −18 and −13, between about −18 and −14 or between about −17 and about −14. In some embodiments a DMR comprises a t-statistic (e.g., a median t-statistic (e.g., median.tstat)) between about −18.0 and −14.90 or between about −18.0 and −14.10. A locus that is differentially methylated can be determined according to a comparison between two different samples or sources by any suitable method that generates a statistical value that is comparable to, or that can be converted to a t-statistic (e.g., a p-value, Z-score, or the like). A statistical value that can be converted to and/or compared to a certain t-statistic herein, and is determined equal to, or within 5%, 10% or 20% of the value of a certain t-statistic herein, is considered the same as (e.g., equivalent to) the certain t-statistic herein to which it was compared.
In some embodiments a DMR comprises one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 4 where the one or more loci comprise a median t-statistic (e.g., median.tstat) less than about −2, less than about −3, less than about −4, less than about −5, less than about −6, less than about −7, less than about −8, less than about −9, less than about −10, less than about −11, less than about −12, less than about −13, less than about −14, less than about −14.10, less than about −14.90, less than about −15, or less than about −16. In some embodiments the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 4 where the one or more loci comprise a median t-statistic (e.g., median.tstat) between about −18 and −2, between about −18 and −3, between about −18 and −4, between about −18 and −5, between about −18 and −6, between about −18 and −7, between about −18 and −8, between about −18 and −9, between about −18 and −10, between about −18 and −11, between about −18 and −12, between about −18 and −13, between about −18 and −14 or between about −17 and about −14. In some embodiments the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 4 where the one or more loci comprise a median t-statistic (e.g., median.tstat) between about −18.0 and −14.90 or between about −18.0 and −14.10.
In some embodiments a DMR comprises one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 5 where the one or more loci comprise a median t-statistic (e.g., median.tstat) less than about −2, less than about −3, less than about −4, less than about −5, less than about −6, less than about −7, less than about −8, less than about −9, less than about −10, less than about −11, less than about −12, less than about −13, less than about −14, less than about −14.10, less than about −14.90, less than about −15, or less than about −16. In some embodiments the one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 5 where the one or more loci comprise a median t-statistic (e.g., median.tstat) between about −18 and −2, between about −18 and −3, between about −18 and −4, between about −18 and −5, between about −18 and −6, between about −18 and −7, between about −18 and −8, between about −18 and −9, between about −18 and −10, between about −18 and −11, between about −18 and −12, between about −18 and −13, between about −18 and −14 or between about −17 and about −14. In some embodiments the one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid are chosen from TABLE 5 where the one or more loci comprise a median t-statistic (e.g., median.tstat) between about −18.0 and −14.90 or between about −18.0 and −14.10.
Large contiguous genomic regions (e.g., locus) that are differentially methylated (e.g., hypomethylated) in fetal nucleic acid relative to maternal nucleic acid are sometimes associated with gene deserts. In some embodiments a DMR comprises a low gene density. In some embodiments a hypomethylated locus comprises a low gene density. In some embodiments a locus that is hypomethylated in fetal nucleic acid comprises a low gene density. In some embodiments a locus comprising a low gene density comprises a gene density of about 10 genes or less, 9 genes or less, 8 genes or less, 7 genes or less, 6 genes or less, 5 genes or less, 4 genes or less, 3 genes or less, 2 genes or less, 1 genes or less or 0 genes per 50,000 contiguous base pairs. The gene densities provided herein can be scaled according to the size of a particular locus. For example, sometimes a locus comprising a low gene density comprises a gene density of about 0.02 genes/kb or less which is equivalent to about 0.2 genes/10 kb or less or about 2 genes/100 kb or less.
In certain embodiments a DMR or locus (e.g., a differentially methylated locus, a selected locus (e.g., a locus selected for analysis)) is selected and/or analyzed according to a CpG density of the region or locus. In some embodiments a DMR or locus comprises a relatively low CpG density. In some embodiments a hypomethylated locus comprises a relatively low CpG density. In some embodiments a locus that is hypomethylated in fetal nucleic acid comprises a relatively low CpG density. A CpG density can be an absolute, average, mean, median or mode CpG density. In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, or 150 CpG methylation sites, or less, per 50,000 base pairs (i.e., which base pairs are contiguous nucleotides in genomic nucleic acid). In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, or 30 CpG methylation sites or less per 10,000 base pairs (i.e., which base pairs are contiguous nucleotides in genomic nucleic acid). In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, or 3 CpG methylation sites or less per 1000 base pairs (i.e., which base pairs are contiguous nucleotides in genomic nucleic acid). In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3 CpG methylation sites or less per 100 base pairs (i.e., which base pairs are contiguous nucleotides in genomic nucleic acid). In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 0.2, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04 or 0.03 CpG methylation sites or less per 10 base pairs (i.e., which base pairs are contiguous nucleotides in genomic nucleic acid). In some embodiments a locus comprising a relatively low CpG density comprises a CpG density of about 0.02, 0.019, 0.018, 0.017, 0.016, 0.015, 0.014, 0.013, 0.012, 0.011, 0.010, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, or 0.003 CpG methylation sites or less per base pair in a stretch of contiguous nucleotides in genomic nucleic acid (e.g., a stretch of 10 contiguous nucleotides or more, a stretch of 100 contiguous nucleotides or more, a stretch of 10,000 contiguous nucleotides or more, a stretch of about 50,000 contiguous nucleotides or more. For example, one or more loci relatively less methylated in a minority nucleic acid species (e.g., fetal nucleic acid) than in a majority nucleic acid species (e.g., maternal nucleic acid) sometimes comprise a relatively low CpG density.
In certain embodiments a DMR or locus (e.g., a differentially methylated locus, a selected locus (e.g., a locus selected for analysis)) is selected and/or analyzed according to the number and/or spacing (e.g., frequency) of methylation sensitive restrictions sites within a DMR or locus. In certain embodiments a locus (e.g., a locus targeted for analysis, a differentially methylated locus) comprises one or more restriction endonuclease recognition sequence(s) (restriction site(s)) where each restriction site can be cleaved, either in a methylated state or unmethylated state, by a methylation sensitive restriction endonuclease. A restriction endonuclease recognition sequence is often referred to herein as a restriction endonuclease recognition site. A restriction site that can be specifically cleaved, either in a methylated state or unmethylated state, by a methylation sensitive restriction endonuclease is sometimes referred to herein as a “methylation sensitive restriction site”. In some embodiments all of the methylation sensitive restriction sites in a locus can be cleaved by the same methylation sensitive restriction endonuclease. In some embodiments a locus comprises methylation sensitive restriction sites that can be cleaved by two or more different methylation sensitive restriction endonuclease. In some embodiments a locus comprises a plurality of methylation sensitive restriction sites. A locus can comprise, on average, one or at least one methylation sensitive restriction site for every 10 bp, every 20 bp, every 30 bp, every 40 bp, every 50 bp, every 60 bp, every 70 bp, every 80 bp, every 90 bp, every 100 bp, every 110 bp, every 120 bp, every 130 bp, every 140 bp, every 150 bp, every 160 bp, every 170 bp, every 180 bp, every 190 or about every 200 bp. In certain embodiments a locus comprises, on average, one or at least one methylation sensitive restriction site for every 30 to about 200 bp, every 40 to about 200 bp, every 50 bp to about 200 bp, every 60 bp to about 200 bp, every 30 to about 150 bp, every 40 to about 150 bp, every 50 bp to about 150 bp, every 60 bp to about 150 bp, every 30 to about 100 bp, every 40 to about 100 bp, every 50 bp to about 100 bp, or every 60 bp to about 100 bp. In some embodiments the average, mean, median or absolute distance between each methylation sensitive restriction site within a locus is about 10 bp, 20 bp, 30 bp, 40 bp, 50 bp, 60 bp, 70 bp, 80 bp, 90 bp, 100 bp, 110 bp, 120 bp, 130 bp, 140 bp, 150 bp, 160 bp, 170 bp, 180 bp, 190 or about 200 bp. In some embodiments the average, mean, median or absolute distance between each methylation sensitive restriction site within a locus is about 30 to about 200 bp, 40 to about 200 bp, 50 bp to about 200 bp, 60 bp to about 200 bp, 30 to about 150 bp, 40 to about 150 bp, 50 bp to about 150 bp, 60 bp to about 150 bp, 30 to about 100 bp, 40 to about 100 bp, 50 bp to about 100 bp, or 60 bp to about 100 bp. Often, for determining the presence or absence of a differentially methylated locus, one or more methylation sensitive restriction endonucleases are selected according to the desired number and/or spacing of corresponding methylation sensitive restrictions sites within a genome or locus. In some embodiments one or more methylation sensitive restriction endonucleases are selected according a the average, mean, median or absolute length of digested fragments that are desired (e.g., digested ccf fragments).
In some embodiments a polynucleotide, comprising one or more methylation sites or methylation loci (e.g., hypermethylated loci), is relatively more methylated in fetal nucleic acid than maternal nucleic. In some embodiments an analysis comprises analyzing enriched methylated nucleic acid and/or enriched hypermethylated nucleic acid. The term “enriched methylated nucleic acid” as used herein refers to one or more polynucleotides in a first sample comprising more methylated nucleotides than polynucleotides of a second sample (e.g., a sample prior to an enrichment process), where the first sample comprises enriched methyl nucleic acid. In some embodiments a first sample comprising enriched methylated nucleic acid comprises 1% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more or 70% or more methylated nucleotides relative to a second sample. In some embodiments enriched methylated nucleic acid is enriched hypermethylated nucleic acid. In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment) in one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments an analysis comprises quantifying a polynucleotide in one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid. In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment) in one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid where the loci are chosen from the loci in TABLE 2AA, TABLE 2B, TABLE 2CA, TABLE 5 or a combination thereof. In some embodiments an analysis comprises determining the presence or absence of a polynucleotide (e.g., a nucleic acid fragment) in one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid where the loci are chosen from a suitable chromosome. For example, the one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid can be chosen from chromosome 13, chromosome 18 and/or chromosome 21. In some embodiments the one or more loci relatively more methylated in fetal nucleic acid than in maternal nucleic acid can be chosen from one or more suitable chromosomes in TABLE 5 (e.g., one or more loci in chromosome 13, chromosome 18 and/or chromosome 21).
Identifying a Differentially Methylated Locus
In some embodiments one or more differentially methylated loci are identified by a method described herein. In some embodiments a differentially methylated locus is identified, in part, by digesting a nucleic acid sample with one or more methylation sensitive restriction endonucleases, amplifying the nucleic acid (e.g., specific target polynucleotides within in a locus) after digestion, where amplicons (e.g., target specific amplicons) are generated, and analyzing and/or comparing the amount of amplicons from two or more samples or sources. In certain embodiments sample nucleic are digested by one or more selected methylation sensitive restriction endonucleases at one or more methylation sensitive restriction sites that are unmethylated. In certain embodiment sample nucleic are digested by one or more selected methylation sensitive restriction endonucleases at one or more methylation sensitive restriction sites that are methylated. In some embodiments target polynucleotides in a nucleic acid sample are amplified after a restriction enzyme digestion reaction. Often, target polynucleotides that are left uncut by a methylation sensitive restriction endonuclease are amplified and target polynucleotides that are cleaved a not amplified.
In some embodiments one or more differentially methylated loci (e.g., hypomethylated loci, hypermethylated loci) can be identified, in part, by designing one or more oligonucleotide primer pairs capable of amplifying certain target polynucleotides after a restriction enzyme digestion of sample nucleic acid. A locus often comprises a plurality of target polynucleotides where each target nucleic comprises one or more methylation sensitive restriction sites and where each target polynucleotide can be amplified by a primer pair. In some embodiments a collection of oligonucleotide primer pairs is designed for use in an amplification reaction wherein each primer pair is specific for a target polynucleotide. A primer that is specific for a target polynucleotide can specifically hybridize, under suitable hybridization conditions, to a portion of the target polynucleotide. Each primer of a primer pair that is specific for a target polynucleotide can specifically hybridize, under suitable hybridization conditions, to a portion of a target polynucleotide. Each primer of a pair often hybridizes to opposite strands and at opposite ends of a target polynucleotide. For example, primer pairs are often designed to flank a target polynucleotide of interest. In some embodiments a differentially methylated locus is identified, in part, by designing an oligonucleotide primer pair capable of amplifying a target polynucleotide, where the target polynucleotide comprises at least one restriction endonuclease recognition sequence (e.g., a methylation sensitive restriction site). For example, in some embodiments a collection of oligonucleotide primer pairs is designed for use in an amplification, where (i) each of the primer pairs is specific for a target polynucleotide located within a locus, wherein the locus comprises two or more target polynucleotides, (ii) each of the two or more target polynucleotides comprise at least one restriction endonuclease recognition sequence, and (iii) each of the primer pairs flank the at least one restriction endonuclease recognition sequence. Often a primer pair is designed to flank a methylation sensitive restriction site of a target polynucleotide so that cleavage of the target polynucleotide by a methylation sensitive restriction enzyme inhibits or prevents amplification of the target polynucleotide. For example, in certain embodiments, prior to amplification, nucleic acid of a first sample and a second sample are digested with a methylation sensitive restriction endonuclease that specifically digest the nucleic acid at one or more selected restriction endonuclease recognition sequences. In some embodiments the methylation sensitive restriction endonuclease cleaves only unmethylated recognition sequences. Alternatively, a methylation sensitive restriction endonuclease can be used that only cleaves at methylated recognition sequences. After a restriction digest, samples are often contacted with a collection of oligonucleotide primer pairs designed as described herein, under amplification conditions, thereby providing target specific amplicons. Often amplicons from two samples are analyzed and/or compared and one or more differentially methylated loci can be identified according to the analysis and/or comparison. An analysis sometimes comprises determining an amount of the target specific amplicons from each of two or more samples (e.g., samples comprising nucleic acids derived from different sources). In some embodiments a differentially methylated locus is identified where the amount of target specific amplicons of a locus of a first sample is significantly different from the amount of target specific amplicons of a locus of a second sample. For example, where a methylation sensitive restriction enzyme is used that cuts at unmethylated recognitions sequences, a locus of a first sample that comprises significantly more target specific amplicons than a second sample, is often identified as a hypermethylated locus relative to the same locus in the second sample.
Differentially methylated loci are often identified using sample nucleic acid comprising ccf DNA of an average, mean, median or absolute length 300 bp or less, 250 bp or less or 200 bp or less. In some embodiments the average, mean, median or absolute length of target polynucleotides in a sample nucleic acid is about 40 to 2000, 40 to 1500, 40 to 1000, 40 to 500, or 40 to 250 base pairs.
In certain embodiments a DMR or locus (e.g., a differentially methylated locus, a selected locus (e.g., a locus selected for analysis)) is selected and/or analyzed according to one or more features, non-limiting examples of which include: a size of a locus (e.g., mean, median, average, size range or absolute size); methylation status of a minority species of nucleic acid (e.g., in fetal nucleic acid; e.g., mean, median, average, limit of, span of, range of, or absolute methylation status); a mean, median, average, absolute or relative methylation status of a majority nucleic acid species (e.g., in maternal nucleic acid; e.g., mean, median, average, limit of, span of, range of, or absolute methylation status); a difference in methylation status between a minority nucleic acid species and a majority nucleic acid species; CpG density; number of CpG sites; gene density; number of restriction sites; distance and/or spacing between restriction sites for loci having two or more restriction sites; and amplicon size (e.g., mean, median, average, absolute or range of amplicon size; e.g., amplicon sizes ranging from 40-125 nucleotides in length); the like; or combinations thereof. A differentially methylated locus sometimes is selected and/or analyzed according to 2, 3, 4, 5, 6, 7, 8 or more features described herein.
In certain embodiments a DMR or locus (e.g., a differentially methylated locus, a selected locus (e.g., a locus selected for analysis)) is selected and/or analyzed according to size. For example, a size of a DMR or locus (e.g., mean, median, average, size range or absolute size) can comprise about 50,000, 40,000, 30,000, 20,000, 10,000, 7500, 5000, 2500, 2000, 1750, 1500, 1250, 1000, 750, 500, 250, 200, 150, or 100 contiguous base pairs, or less.
A differentially methylated locus sometimes comprises a CpG density of 0.016, 0.012, 0.008, 0.004, or 0.002 CpG methylation sites per base pair, or less. A CpG density can be provided in any suitable scale and may comprise any suitable units of measure. For example, a differentially methylated locus sometimes comprises a CpG density of 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1, CpG methylation sites per 1000 base pairs, or less. A differentially methylated locus sometimes comprises a CpG density of 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20 or 10 CpG methylation sites per 10,000 base pairs, or less. A differentially methylated locus sometimes comprises a CpG density of 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100 or 50 CpG methylation sites per 50,000 base pairs, or less.
A differentially methylated locus sometimes comprises a gene density of 0.5, 0.4, 0.3, 0.2, 0.1, 0.08, 0.06, 0.04, 0.02, 0.01 or 0.008 genes per 1000 base pairs, or less. In some embodiments a differentially methylated locus comprises no genes. A gene density can be provided in any suitable scale and may comprise any suitable units of measure. For example, a differentially methylated locus sometimes comprises a gene density of 5, 4, 3, 2, 1, 0.8, 0.6, 0.4, 0.2, 0.1 or 0.08 genes per 10,000 base pairs, or less. A differentially methylated locus sometimes comprises a gene density of 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5 or 0.4 genes per 50,000 base pairs, or less.
A differentially methylated locus sometimes comprises at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or at least 20 CpG methylation sites. In some embodiments a differentially methylated locus comprises one restriction endonuclease recognition site, or a plurality of restriction endonuclease recognition sites where the average, mean, median or absolute distance between each restriction endonuclease recognition site in the locus is about 20 to about 500, about 20 to about 400, about 20 to about 350, about 20 to about 200, about 20 to about 150, about 30 to about 150, about 40 to about 150, about 20 to about 100 or about 40 to about 100 base pairs. For embodiments in which a locus includes one or more restriction endonuclease recognition sites, each of the one or more restriction endonuclease recognition sites can be recognized and/or digested, depending on the methylation status of the site, by one or more methylation sensitive restriction endonucleases. In some embodiments the average, mean, median or absolute distance between each methylation sensitive restriction endonuclease recognition site on a locus is about 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 125, 130, 135, 140, 145 or about 150 base pairs. Methylation sensitive restriction endonuclease recognition sites on a locus may be recognized by the same, or two or more different methylation sensitive restriction enzymes. A differentially methylated locus sometimes comprises an average, mean, median or absolute number of at least 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 methylation sensitive restriction endonuclease recognition sites per 1000 base pairs, wherein each of restriction endonuclease recognition sites can be specifically recognized and/or digested by a methylation sensitive cleavage agent.
A differentially methylated locus sometimes comprises a methylation status of about 75% or less, about 70% or less, about 65% or less, about 60% or less, about 55% or less, about 50% or less, about 40% or less, about 35% or less, about 30% or less, about 25% or less, about 20% or less, about 15% or less, or about 10% or less in fetal nucleic acid.
A differentially methylated locus sometimes comprises a methylation status of about 55% or more, about 60% or more, about 65% or more, about 70% or more, about 75% or more, about 80% or more, about 85% or more or about 90% or more in maternal nucleic acid.
A differentially methylated locus sometimes comprises a difference in methylation status between two nucleic acid species or subgroups (e.g., between a minority nucleic acid and a majority nucleic acid, e.g., between fetal nucleic acid and maternal nucleic acid) of about 0.1% or more, about 0.5% or more, about 1% or more, about 2% or more, about 3% or more, about 4% or more, about 5% or more, about 6% or more, about 7% or more, about 8% or more, about 9% or more, about 10% or more, about 15% or more, about 20% or more, about 30% or more, about 40% or more, about 50% or more, or about 60% or more. In some embodiments a difference in methylation status between two nucleic acid species or subgroups can be a statistical difference (e.g., a statistically significant difference) as determined by a suitable statistical test (e.g., a t-test).
Identifying a differentially methylated locus sometimes comprises determining and/or analyzing a methylation status of a locus of a first and a second nucleic acid species or subgroup. In some embodiments, a differentially methylated locus is about 20, 15, 10, or 5% or less methylated in a first nucleic acid species or subgroup (e.g., fetal nucleic acid) and about 50, 60, 65, 70, or 75% or more methylated in a second nucleic acid species or subgroup (e.g., maternal nucleic acid).
Methylation-Sensitive Enrichment, Detection and Quantification
Non-limiting examples of processes for analyzing, detecting and/or quantifying a methylation state of a marker are described in International Application Publication No. WO 2012/149339 published on Nov. 1, 2012 (International Application No. PCT/US2012/035479 filed on Apr. 27, 2012) and in International Application Publication No. WO 2011/034631 published on Mar. 24, 2011 (International Application No. PCT/US2010/027879 filed on Mar. 18, 2010), the entire content of which is incorporated herein by reference, including all text, tables and drawings. In some embodiments, a methylation sensitive procedure is utilized as part of detecting and/or quantifying a marker. Non-limiting examples of methylation sensitive procedures include bisulfite treatment of DNA, bisulfite sequencing, methylation specific PCR (MSP), quantitative methylation specific PCR (QPSP), combined bisulfite restriction analysis (COBRA), methylation-sensitive single nucleotide primer extension (Ms-SNuPE), MethylLight, methylation pyrosequencing, immunoprecipitation with 5-Methyl Cytosine (MeDIP), Methyl CpG Immunoprecipitation (MCIp; e.g., use of an antibody that specifically binds to a methyl-CpG binding domain (MBD) of a MBD2 methyl binding protein (MBD-Fc) for immunoprecipitation of methylated or unmethylated DNA), and methyl-dependent enzyme digestion with McrBC.
Enrichment of a certain nucleic acid subset or species sometimes comprises selectively separating a subset (e.g., subpopulation or species) of nucleic acids from a mixture. In some embodiments a selective separation comprises a method or process that separates, enriches or partially purifies a target subset based on one or more physical characteristics (e.g., methylated or unmethylated nucleotides, a sequence of nucleotides, molecular weight, size, charge, polarity, binding characteristics (e.g., affinity, Kd, on-off rate), an identifier, the like or combinations thereof) unique to, or more predominant in, the target group relative to other components, subsets or species in a mixture. Selectively separating a subset (e.g., subpopulation or species) of nucleic acids from a mixture often results in one or more separation products. A process comprising a selective separation is sometimes not a complete or 100% separation. In some embodiments a selective separation comprises a partial separation where some portion of the target species or components being selectively separated are not separated. In some embodiments the efficiency of a selective separation separates about 60% or more, about 70% or more, about 80% or more, about 85% or more, about 90% or more, about 95% or more, about 97% or more, about 98% or more, about 99% or more or about 100% of the targeted species from a mixture. Methods provided herein can generate separation products that are enriched for a subpopulation of nucleic acid (e.g., enriched for a sub-population of cell-free nucleic acid). In certain embodiments, separation products can be enriched for fetal nucleic acid. In certain embodiments, separation products can be enriched for hypomethylated nucleic acids, hypermethylated nucleic acids, digested nucleic acid fragments, undigested nucleic acid fragments or a minority nucleic acid species. In some embodiments nucleic acid (e.g., a separation product) enriched for hypomethylated loci are often enriched for fetal nucleic acids (e.g., as described herein, e.g., as per Example 2). In some embodiments nucleic acid (e.g., a separation product) enriched for hypomethylated loci are often enriched for a minority nucleic acid species.
In some embodiments enrichment of a certain nucleic acid subset or species comprises exposing nucleic acids (e.g., sample nucleic acid) to conditions that separate certain nucleic acid subsets or species. Enrichment of a certain nucleic acid subset or species sometimes comprises selectively separating digested nucleic acid fragments from non-digested nucleic acid fragments. Digested nucleic acids can be selectively separated from non-digested nucleic acids by any suitable method. Digested nucleic acid fragments are generally shorter polynucleotide fragments of lower molecular weight than undigested nucleic acid in a sample. In some embodiments, undigested nucleic acids can be separated (e.g., selectively separated) from digested nucleic acid fragments by a suitable size or mass-based separation method. Non-limiting examples of size-based and/or mass-based separation methods include size exclusion chromatography, density gradient centrifugation, precipitation, sedimentation, equilibrium sedimentation, polyethylene glycol precipitation, gel filtration, electrophoresis (e.g., gel electrophoresis), the like or a combination thereof. In some embodiments digested nucleic acid are ligated to an adaptor or linker and can be selectively separated from non-digested nucleic acids by certain characteristics of the adaptor or linker. For example, digested fragments comprising a linker or adaptor can be selectively separated according to an identifier (e.g., a fluorescent identifier) or capture agent that is associated with an adaptor or linker. In some embodiments digested fragments comprising a linker or adaptor can be selectively separated according to a nucleic acid sequence of the adaptor or linker, for example by hybridization to a capture agent, where the capture agent is a nucleic acid complementary to a portion of the linker or adaptor.
In some embodiments, selective separation of digested nucleic acids from undigested nucleic acids generates a separation product comprising about 50% or greater digested nucleic acid. For example, a separation product can comprise about 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% digested nucleic acid. In some embodiments, some or substantially all undigested nucleic acid in a sample are separated from digested nucleic acid in the sample, thereby generating a separation product enriched for digested nucleic acid. In certain embodiments, digested nucleic acid fragments are enriched for fragments from fetal origin.
In some embodiments, fetal nucleic acid is enriched without generating of a separation product. In certain embodiments, a separation product can be enriched for fetal nucleic acid by enrichment of digested nucleic acid (e.g., digested hypomethylated nucleic acid, e.g., followed by specific amplification of hypomethylated nucleic acid) and/or by another suitable method. In some embodiments, a separation product comprises about 5%, 10%, 15%, 20% or greater fetal nucleic acid. For example, a separation product can comprise about 25%, 30% 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% fetal nucleic acid. In some embodiments, some or substantially all undigested nucleic acid is separated from sample nucleic acid, thereby generating a separation product enriched for fetal nucleic acid.
A sample of nucleic acid can be enriched for a nucleic acid species (e.g., a subset or subpopulation of nucleic acids (e.g., a minority nucleic acid species, one or more loci, one or more target polynucleotides, hypomethylated nucleic acid, fetal nucleic acid)) by methods described herein thereby providing or generating nucleic acid enriched for a nucleic acid species. A nucleic acid sample enriched for a nucleic acid species often comprises a greater amount (e.g., concentration, absolute amount, percentage, the like) of the nucleic acid species when compared to the same nucleic acid sample prior to enrichment. In some embodiments the amount of a nucleic acid species in a nucleic acid sample enriched for a nucleic acid species comprises about a 1.5-fold to 1,000-fold increase in the nucleic acid species compared to an amount of the nucleic acid species in a sample prior to an enrichment method. In some embodiments the amount of a nucleic acid species in a nucleic acid sample is increased about 1.5 fold or more, 2 fold or more, 3 fold or more, 4 fold or more, 5 fold or more, 6 fold or more, 7 fold or more, 8 fold or more, 9 fold or more, or about 10 fold or more (e.g., 20, 30, 40, 50, 60, 70, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800 or 900-fold or more). A nucleic acid species in a separation product sometimes is enriched 1.5-fold to 1,000-fold (e.g., 20, 30, 40, 50, 60, 70, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800 or 900-fold enriched) relative to a nucleic acid species in a sample nucleic acid prior to enrichment. In certain embodiments, the relative proportion of (i) fetal nucleic acid to (ii) non-fetal nucleic acid is greater (e.g., enriched) in the separation product than in the sample nucleic acid. For determining such a proportion, non-fetal nucleic acid sometimes is maternal nucleic acid. Fetal nucleic acid sometimes is enriched 1.5-fold to 1,000-fold relative to fetal nucleic acid in sample nucleic acid (e.g., 20, 30, 40, 50, 60, 70, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800 or 900-fold enriched). In some embodiments, fetal nucleic acid can be enriched about 1.5-fold to about 200-fold relative to fetal nucleic acid in sample nucleic acid. For example, fetal nucleic acid can be enriched about 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 120, 140, 160, 180 or 200-fold (e.g.,
A separation and/or enrichment product containing enriched fetal nucleic acid often contains fetal nucleic acid fragments. Fetal nucleic acid fragments in a separation and/or enrichment product often range in size from about 50 base pairs to about 200 base pairs. The entire fetal genome or significant fraction of the fetal genome (e.g., 70% or more of the fetal genome) sometimes is represented in a separation product. Fetal nucleic acid fragments having the same length (e.g., 149 base pair fragment length or 150 base pair fragment length) in a separation product often represent a large number of sequences. There often are many fetal nucleic acid fragments having the same length but different sequences in a separation product. In some embodiments, about 1/15th of the fetal genome is represented by fetal nucleic acid fragments having the same length (e.g., 1/12th to 1/18th (e.g., 1/13th, 1/14th, 1/16th, 1/17th, 1/18th)). Fetal nucleic acid fragments having a particular length in a separation product often are from multiple and distinct regions of the genome. Some or all fetal nucleic acid fragments in a separation product often have sizes separated by one base pair (1-bp), where each fragment is 1-bp larger than the next shorter fragment.
In some embodiments, nucleic acid (e.g., extracellular nucleic acid) is enriched or relatively enriched for a subpopulation or species of nucleic acid using a method described herein and/or one or more additional enrichment methods. Non-limiting examples of nucleic acid species or subpopulations include fetal nucleic acid, maternal nucleic acid, nucleic acid comprising fragments of a particular length or range of lengths, hypermethylated nucleic acid, methylated nucleic acid, hypomethylated nucleic acid, unmethylated nucleic acid, or nucleic acid from a particular genome region (e.g., locus (e.g., hypomethylated locus, hypermethylated locus), a single chromosome, a set of chromosomes, and/or certain chromosome regions). Such enriched samples can be used in conjunction with a method provided herein. Thus, in certain embodiments, methods of the technology comprise a step of enriching and/or analyzing a subpopulation of nucleic acid in a sample, such as, for example, fetal nucleic acid. In some embodiments, certain methods for determining fetal fraction described below also can be used to enrich for fetal nucleic acid. In certain embodiments, maternal nucleic acid is selectively removed (partially, substantially, almost completely or completely) from the sample. In some embodiments, enriching and/or analyzing a particular low copy number species nucleic acid (e.g., a minority species, fetal nucleic acid) may improve quantitative sensitivity. Methods for enriching a sample for a particular species of nucleic acid are described, for example, in U.S. Pat. No. 6,927,028, International Patent Application Publication No. WO2007/140417, International Patent Application Publication No. WO2007/147063, International Patent Application Publication No. WO2009/032779, International Patent Application Publication No. WO2009/032781, International Patent Application Publication No. WO2010/033639, International Patent Application Publication No. WO2011/034631, International Patent Application Publication No. WO2006/056480, and International Patent Application Publication No. WO2011/143659, all of which are incorporated by reference herein.
In some embodiments, nucleic acid is enriched for certain target fragment species and/or reference fragment species. In some embodiments, nucleic acid is enriched for a specific nucleic acid fragment length or range of fragment lengths using one or more length-based separation methods described below. In some embodiments, nucleic acid is enriched for fragments from a select genomic region (e.g., chromosome) using one or more sequence-based separation methods described herein and/or known in the art. Certain methods for enriching and/or analyzing a nucleic acid subpopulation (e.g., fetal nucleic acid) in a sample are described in detail below.
In some embodiments a nucleic acid subpopulation (e.g., fetal nucleic acid, tumor nucleic acid) can be enriched by exploiting epigenetic differences (e.g., methylation differences) between two or more nucleic acid subpopulations (e.g., fetal nucleic acid and maternal nucleic acid). For example, fetal nucleic acid can be differentiated and separated from maternal nucleic acid based on methylation differences. Methylation-based fetal nucleic acid enrichment methods are described in U.S. Patent Application Publication No. 2010/0105049, which is incorporated by reference herein. Separation and/or enrichment methods sometimes involve contacting a sample nucleic acid with a methyl-specific binding agent (e.g., methyl-CpG binding protein (MBD), methylation specific binding antibodies, the like, portions thereof or combinations thereof). In some embodiments digested nucleic acid fragments or modified variants thereof are selectively separated by a process comprising a methyl-specific binding agent.
In some embodiments a methyl-specific binding agent specifically binds and/or associates with methylated nucleic acid and/or hypermethylated nucleic acid. For example a methyl-specific antibody can specifically bind a methylated portion (e.g., a methylated CpG) of a nucleic acid fragment. In some embodiments a methyl-specific binding agent specifically binds hypermethylated nucleic acid (e.g., hypermethylated locus) comprising one or more methylation sites that are methylated. In certain embodiments a methyl-specific binding agent binds methylated nucleic acid and/or hypermethylated nucleic acid with a higher affinity than it binds unmethylated or hypomethylated nucleic acid.
In some embodiments a methyl-specific binding agent specifically binds and/or associates with unmethylated nucleic acid and/or hypomethylated nucleic acid. For example a methyl-specific antibody can specifically bind an unmethylated portion (e.g., a unmethylated CpG) of a nucleic acid fragment (e.g., a digested nucleic acid fragment). In some embodiments a methyl-specific binding agent specifically binds and/or associates with hypomethylated nucleic acid (e.g., hypomethylated locus) comprising one or more methylation sites on the nucleic acid that are unmethylated. In certain embodiments a methyl-specific binding agent binds unmethylated nucleic acid and/or hypomethylated nucleic acid with a higher affinity than it binds methylated or hypermethylated nucleic acid.
In some embodiments nucleic acid in a sample is contacted with one or more methyl-specific binding agents. In some embodiments enriching for a particular species or subset of nucleic acid comprises contacting nucleic acid in a sample with a methyl-specific binding agent. Specific nucleic acid species, subsets or subpopulations in a sample can be selectively separated by a process comprising contacting the nucleic acid in the sample with one or more methyl-specific binding agents. Non-limiting examples of nucleic acids and/or nucleic acid species that can be selectively separated by a process described herein include fetal nucleic acid, maternal nucleic acid, tumor derived nucleic acid, nucleic acid from healthy tissue, unmethylated nucleic acid, hypomethylated nucleic acid, hypomethylated loci, methylated nucleic acid, hypermethylated nucleic acid, hypermethylated loci, size fractionated nucleic acids (e.g., size fractionated separation products), cleaved nucleic acid (e.g., nucleic acid cleaved by a restriction endonuclease), uncleaved nucleic acid, modified nucleic acid (e.g., chemically treated nucleic acid, sheared nucleic acid, nucleic acid comprising adaptors, linkers, the like, or combinations thereof), amplification or extension products of nucleic acids, the like, combinations thereof or mixtures thereof. Enrichment of a certain nucleic acid subset or species sometimes comprises selectively separating hypomethylated and/or unmethylated nucleic acid from methylated and/or hypermethylated nucleic acid. Enrichment of hypomethylated and/or unmethylated nucleic acid or methylated and/or hypermethylated nucleic acid sometimes comprises exposing nucleic acid in a sample to conditions that separate hypomethylated and/or unmethylated nucleic acid from methylated and/or hypermethylated nucleic acid.
Contacting a mixture of nucleic acid species or a mixture comprising two or more subpopulations with a methyl-specific binding agent often results in bound and unbound nucleic acids. Bound nucleic acids often are non-covalently associated with a binding agent (e.g., a methyl-specific binding agent) with a moderate to high affinity (e.g., Kd≦10−6 M). Unbound nucleic acids (e.g., free nucleic acids) are often not substantially associated with a methyl-specific binding agent. A sample can be contacted with a binding agent under one or more different conditions (e.g., binding conditions) that determine which subpopulations of nucleic acids in a sample associate or do not associate with a binding agent. In some embodiments a sample of nucleic acid is contacted with a binding agent under conditions where substantially all of the nucleic acids in a sample associate and/or binds to the binding agent. For example, substantially all of the nucleic acids in a sample may comprise at least 90%, 95%, 96%, 97%, 98%, 99%, 99.9% or 100% of the nucleic acids in a sample. In certain embodiments a sample of nucleic acid is contacted with a binding agent under conditions where a portion of the nucleic acids in a sample associate and/or bind to the binding agent. Conditions that determine binding of a particular nucleic acid species to a specific binding agent are often known or can be determined empirically.
In some embodiments a methyl-specific binding agent is soluble in a solution. In some embodiments, a methyl-specific binding agent is immobilized on a solid support or substrate. For example, a methyl-specific binding agent can be immobilized on a bead, chip or flow cells. Sometimes a methyl-specific binding agent is reversibly immobilized on a solid support or substrate. In some embodiments a methyl-specific binding agent is reversibly immobilized on a solid support comprising a capture agent. Sometimes a methyl-specific binding agent comprises a capture agent (e.g., a member of a binding pair, e.g., biotin).
In some embodiments nucleic acid in a sample is contacted with one or more methyl-specific binding agents that specifically bind nucleic acid (e.g., methylated, hypermethylated, unmethylated or hypomethylated nucleic acid), thereby generating bound nucleic acid fragments and unbound nucleic acid fragments. In some embodiments nucleic acids in a sample that are associated with a methyl-specific binding agent (e.g., bound nucleic acids) can be selectively separated from nucleic acids in the sample that are not substantially associated with a methyl-specific binding agent thereby generating one or more separation products. In some embodiments a portion of nucleic acid in a sample that is associated with a binding agent (e.g., a methyl-specific binding agent) can be disassociated and/or selectively eluted from a binding agent using a suitable method, thereby generating one or more separation products. For example, a portion of nucleic acid in a sample that is associated with a binding agent (e.g., bound nucleic acids) can be disassociated or selectively eluted by altering binding and/or elution conditions. Non-limiting examples of elution conditions that can be altered include salt concentration (monovalent or divalent salt concentrations), temperature, pH, volume, flow rate, addition of a competitor that competes for binding to the binding agent, the like or combinations thereof. For example, bound nucleic acids can sometimes be selectively eluted by increasing salt concentration from about 50 mM to about 800 mM. In some embodiments a salt gradient can be used to selectively elute fractions (e.g., separation products) from a binding agent. For example, nucleic acid fragments comprising methylated nucleotides (e.g., methylated nucleic acid, hypermethylated polynucleotides) that are associated with a methyl-specific binding agent (e.g., a methyl-specific binding agent immobilized on a solid support) can be separated (e.g., eluted, step-wise eluted) from a methyl-specific binding agent thereby providing one or more separation products. In the foregoing example, two or more nucleic acids species, where each species comprises different amounts of methylated nucleotides, can be separated and/or fractionated into one or more separation products using a suitable elution process. In some embodiments, generating a separation product does not comprise an elution process. For example, nucleic acids in a sample can be contacted with one or more methyl-specific binding agents thereby generating a separation product comprising unbound nucleic acid fragments. In the foregoing example, the unbound nucleic acids may comprise an enriched minority species of nucleic acid. In some embodiments enrichment comprises contacting a mixture of methylated (e.g., hypermethylated) and hypomethylated nucleic acids with a methyl-specific binding agent that specifically associated with methylated nucleic acid, under conditions that do not permit binding of hypomethylated nucleic acid, and the unbound portion (e.g., unbound nucleic acid) comprises separated and enriched hypomethylated nucleic acid. In the foregoing example the bound fraction of nucleic acid may comprise separated and enriched methylated nucleic acid (e.g., hypermethylated nucleic acid). In some embodiments enrichment comprises contacting a mixture of methylated (e.g., hypermethylated) and hypomethylated nucleic acids with a methyl-specific binding agent that specifically associated with unmethylated nucleotides (e.g., polynucleotides comprising one or more unmethylated nucleotides), under conditions that do not permit binding of methylated nucleic acid (e.g., hypermethylated nucleic acid), and the unbound portion (e.g., unbound nucleic acid) comprises separated and enriched hypermethylated nucleic acid. In the foregoing example the bound fraction of nucleic acid may comprise separated and enriched hypomethylated nucleic acid.
A separation product can be generated before, during or after any step of a method described herein. A separation product can be generated before, during or after a digestion or cleavage reaction. A separation product can be generated before, during or after modification or amplification of nucleic acids in a sample. A separation product can be generated before, during or after an enrichment method. A separation product can be generated before, during or after a process comprising nucleic acid sequencing.
Methods herein also can include the use of methylation-sensitive restriction enzymes (as described above; e.g., HhaI and HpaII), which allow for the enrichment of fetal nucleic acid regions in a maternal sample by selectively digesting nucleic acid from the maternal sample with an enzyme that selectively and completely or substantially digests the maternal nucleic acid to enrich the sample for at least one fetal nucleic acid region.
Another method for enriching for a nucleic acid subpopulation (e.g., fetal nucleic acid) that can be used with a method described herein is a restriction endonuclease enhanced polymorphic sequence approach, such as a method described in U.S. Patent Application Publication No. 2009/0317818, which is incorporated by reference herein. Such methods include cleavage of nucleic acid comprising a non-target allele with a restriction endonuclease that recognizes the nucleic acid comprising the non-target allele but not the target allele; and amplification of uncleaved nucleic acid but not cleaved nucleic acid, where the uncleaved, amplified nucleic acid represents enriched target polynucleotides (e.g., fetal nucleic acid) relative to non-target polynucleotides (e.g., maternal nucleic acid). In some embodiments, nucleic acid may be selected such that it comprises an allele having a polymorphic site that is susceptible to selective digestion by a cleavage agent, for example. In some embodiments, nucleic acid may be selected such that it comprises an allele having a polymorphic site that is susceptible to selective digestion by a cleavage agent, for example.
In some embodiments digested nucleic acid comprising one or more target loci (e.g., hypomethylated or hypermethylated loci) is selectively enriched and/or amplified. For example, a nucleic acid comprising a target allele (e.g., an unmethylated CpG) is sometimes cleaved with a restriction endonuclease (e.g., a methylation sensitive cleavage agent) that recognizes a nucleic acid comprising a target locus, but generally not a non-target locus; optionally, one or more adaptors is ligated to the cleaved nucleic acid; and cleaved nucleic acid, but not uncleaved nucleic acid, is amplified, where the cleaved, amplified nucleic acid represents enriched target polynucleotides (e.g., fetal nucleic acid) relative to non-target polynucleotides (e.g., maternal nucleic acid). In some embodiments digested nucleic acid fragments comprising linkers or adaptors can be amplified using one or more primers that a complementary to a portion of the ligated linkers or adaptors. Sometimes, for example, where only fragments comprising one or more ligated adaptors are amplified using adaptor specific-primers, the amplification process is referred to as a non-target-based approach. Sometimes amplification comprises a target-based approach, where target specific primers are utilized to selectively amplify specific loci, genes or subsets of nucleic acids (e.g., nucleic acids derived from one or more specific chromosomes). In some embodiments amplification comprises a targeted and non-targeted approached. In some embodiments an analysis of nucleic acids (e.g., an analysis of digested nucleic acid fragments, an analysis of enriched nucleic acid (e.g., enriched fetal nucleic acid, enriched hypomethylated nucleic acid, enriched methylated nucleic acid, enriched hypermethylated nucleic acid)) comprises selective amplification by a targeted and/or a non-targeted approach. For example, digested fragments can be selectively amplified using an adaptor-specific primer and a target specific primer. Some methods for enriching for a nucleic acid subpopulation (e.g., fetal nucleic acid) that can be used with a method described herein include selective enzymatic degradation approaches. Such methods involve protecting target sequences (e.g., target polynucleotides) from exonuclease digestion thereby facilitating the elimination in a sample of undesired sequences (e.g., maternal DNA). For example, in one approach, sample nucleic acid is denatured to generate single stranded nucleic acid, single stranded nucleic acid is contacted with at least one target-specific primer pair under suitable annealing conditions, annealed primers are extended by nucleotide polymerization generating double stranded target sequences, and digesting single stranded nucleic acid using a nuclease that digests single stranded (i.e., non-target) nucleic acid. In some embodiments, the method can be repeated for at least one additional cycle. In some embodiments, the same target-specific primer pair is used to prime each of the first and second cycles of extension, and in some embodiments, different target-specific primer pairs are used for the first and second cycles.
Some methods for enriching and/or analyzing a nucleic acid subpopulation (e.g., fetal nucleic acid) that can be used with a method described herein include massively parallel signature sequencing (MPSS) approaches. MPSS typically is a solid phase method that uses adaptor (i.e., tag) ligation, followed by adaptor decoding, and reading of the nucleic acid sequence in small increments. Tagged PCR products are typically amplified such that each nucleic acid generates a PCR product with a unique tag. Tags are often used to attach the PCR products to microbeads. After several rounds of ligation-based sequence determination, for example, a sequence signature can be identified from each bead. Each signature sequence (MPSS tag) in a MPSS dataset is analyzed, compared with all other signatures, and all identical signatures are counted.
In some embodiments, certain MPSS-based enrichment methods can include amplification (e.g., PCR)-based approaches. In some embodiments, locus-specific amplification methods can be used (e.g., using locus-specific amplification primers). In some embodiments, a multiplex SNP allele PCR approach can be used. In some embodiments, a multiplex SNP allele PCR approach can be used in combination with uniplex sequencing. For example, such an approach can involve the use of multiplex PCR (e.g., MASSARRAY system) and incorporation of capture probe sequences into the amplicons followed by sequencing using, for example, the Illumina MPSS system. In some embodiments, a multiplex SNP allele PCR approach can be used in combination with a three-primer system and indexed sequencing. For example, such an approach can involve the use of multiplex PCR (e.g., MASSARRAY system) with primers having a first capture probe incorporated into certain locus-specific forward PCR primers and adaptor sequences incorporated into locus-specific reverse PCR primers, to thereby generate amplicons, followed by a secondary PCR to incorporate reverse capture sequences and molecular index barcodes for sequencing using, for example, the Illumina MPSS system. In some embodiments, a multiplex SNP allele PCR approach can be used in combination with a four-primer system and indexed sequencing. For example, such an approach can involve the use of multiplex PCR (e.g., MASSARRAY system) with primers having adaptor sequences incorporated into both locus-specific forward and locus-specific reverse PCR primers, followed by a secondary PCR to incorporate both forward and reverse capture sequences and molecular index barcodes for sequencing using, for example, the Illumina MPSS system. In some embodiments, a microfluidics approach can be used. In some embodiments, an array-based microfluidics approach can be used. For example, such an approach can involve the use of a microfluidics array (e.g., Fluidigm) for amplification at low plex and incorporation of index and capture probes, followed by sequencing. In some embodiments, an emulsion microfluidics approach can be used, such as, for example, digital droplet PCR.
In some embodiments, universal amplification methods can be used (e.g., using universal or non-locus-specific amplification primers). In some embodiments, universal amplification methods can be used in combination with pull-down approaches. In some embodiments, a method can include biotinylated ultramer pull-down (e.g., biotinylated pull-down assays from Agilent or IDT) from a universally amplified sequencing library. For example, such an approach can involve preparation of a standard library, enrichment for selected regions by a pull-down assay, and a secondary universal amplification step. In some embodiments, pull-down approaches can be used in combination with ligation-based methods. In some embodiments, a method can include biotinylated ultramer pull down with sequence specific adaptor ligation (e.g., HALOPLEX PCR, Halo Genomics). For example, such an approach can involve the use of selector probes to capture restriction enzyme-digested fragments, followed by ligation of captured products to an adaptor, and universal amplification followed by sequencing. In some embodiments, pull-down approaches can be used in combination with extension and ligation-based methods. In some embodiments, a method can include molecular inversion probe (MIP) extension and ligation. For example, such an approach can involve the use of molecular inversion probes in combination with sequence adaptors followed by universal amplification and sequencing. In some embodiments, complementary DNA can be synthesized and sequenced without amplification.
In some embodiments, extension and ligation approaches can be performed without a pull-down component. In some embodiments, a method can include locus-specific forward and reverse primer hybridization, extension and ligation. Such methods can further include universal amplification or complementary DNA synthesis without amplification, followed by sequencing. Such methods can reduce or exclude background sequences during analysis, in some embodiments.
In some embodiments, pull-down approaches can be used with an optional amplification component or with no amplification component. In some embodiments, a method can include a modified pull-down assay and ligation with full incorporation of capture probes without universal amplification. For example, such an approach can involve the use of modified selector probes to capture restriction enzyme-digested fragments, followed by ligation of captured products to an adaptor, optional amplification, and sequencing. In some embodiments, a method can include a biotinylated pull-down assay with extension and ligation of adaptor sequence in combination with circular single stranded ligation. For example, such an approach can involve the use of selector probes to capture regions of interest (i.e., target sequences), extension of the probes, adaptor ligation, single stranded circular ligation, optional amplification, and sequencing. In some embodiments, the analysis of the sequencing result can separate target sequences form background.
In some embodiments, nucleic acid is enriched for fragments from a select genomic region (e.g., chromosome) using one or more sequence-based separation methods described herein. Sequence-based separation generally is based on nucleotide sequences present in the fragments of interest (e.g., target and/or reference fragments) and substantially not present in other fragments of the sample or present in an insubstantial amount of the other fragments (e.g., 5% or less). In some embodiments, sequence-based separation can generate separated target fragments and/or separated reference fragments. Separated target fragments and/or separated reference fragments typically are isolated away from the remaining fragments in the nucleic acid sample. In some embodiments, the separated target fragments and the separated reference fragments also are isolated away from each other (e.g., isolated in separate assay compartments). In some embodiments, the separated target fragments and the separated reference fragments are isolated together (e.g., isolated in the same assay compartment). In some embodiments, unbound fragments can be differentially removed or degraded or digested.
In some embodiments, a selective nucleic acid capture process is used to separate target and/or reference fragments away from the nucleic acid sample. Commercially available nucleic acid capture systems include, for example, Nimblegen sequence capture system (Roche NimbleGen, Madison, Wis.); Illumina BEADARRAY platform (Illumina, San Diego, Calif.); Affymetrix GENECHIP platform (Affymetrix, Santa Clara, Calif.); Agilent SureSelect Target Enrichment System (Agilent Technologies, Santa Clara, Calif.); and related platforms. Such methods typically involve hybridization of a capture oligonucleotide to a segment or all of the nucleotide sequence of a target or reference fragment and can include use of a solid phase (e.g., solid phase array) and/or a solution based platform. Capture oligonucleotides (sometimes referred to as “bait”) can be selected or designed such that they preferentially hybridize to nucleic acid fragments from selected genomic regions or loci (e.g., one of chromosomes 21, 18, 13, X or Y, or a reference chromosome).
In some embodiments, nucleic acid is enriched for a particular nucleic acid fragment length, range of lengths, or lengths under or over a particular threshold or cutoff using one or more length-based separation methods. For example, isolated cell-free nucleic having fragment lengths of about 300 base pairs or less, about 200 base pairs or less, about 150 base pairs or less, about 100 base pairs or less, about 75 base pairs or less or about 50 base pairs or less can be enriched for fetal nucleic acid, in certain instances. Nucleic acid fragment length typically refers to the number of nucleotides in the fragment. Nucleic acid fragment length also is sometimes referred to as nucleic acid fragment size. In some embodiments, a length-based separation method is performed without measuring lengths of individual fragments. In some embodiments, a length based separation method is performed in conjunction with a method for determining length of individual fragments. In some embodiments, length-based separation refers to a size fractionation procedure where all or part of the fractionated pool can be isolated (e.g., retained) and/or analyzed. Size fractionation procedures are known in the art (e.g., separation on an array, separation by a molecular sieve, separation by gel electrophoresis, separation by column chromatography (e.g., size-exclusion columns), and microfluidics-based approaches). In some embodiments, length-based separation approaches can include fragment circularization, chemical treatment (e.g., formaldehyde, polyethylene glycol (PEG)), mass spectrometry and/or size-specific nucleic acid amplification, for example.
Certain length-based separation methods that can be used with methods described herein employ a selective sequence tagging approach, for example. The term “sequence tagging” refers to incorporating a recognizable and distinct sequence into a nucleic acid or population of nucleic acids. The term “sequence tagging” as used herein has a different meaning than the term “sequence tag” described later herein. In such sequence tagging methods, a fragment size species (e.g., short fragments) nucleic acids are subjected to selective sequence tagging in a sample that includes long and short nucleic acids. Such methods typically involve performing a nucleic acid amplification reaction using a set of nested primers which include inner primers and outer primers. In some embodiments, one or both of the inner can be tagged to thereby introduce a tag onto the target amplification product. The outer primers generally do not anneal to the short fragments that carry the (inner) target sequence. The inner primers can anneal to the short fragments and generate an amplification product that carries a tag and the target sequence. Typically, tagging of the long fragments is inhibited through a combination of mechanisms which include, for example, blocked extension of the inner primers by the prior annealing and extension of the outer primers. Enrichment for tagged fragments can be accomplished by any of a variety of methods, including for example, exonuclease digestion of single stranded nucleic acid and amplification of the tagged fragments using amplification primers specific for at least one tag.
Another length-based separation method that can be used with methods described herein involves subjecting a nucleic acid sample to polyethylene glycol (PEG) precipitation. Examples of methods include those described in International Patent Application Publication Nos. WO2007/140417 and WO2010/115016. This method in general entails contacting a nucleic acid sample with PEG in the presence of one or more monovalent salts under conditions sufficient to substantially precipitate large nucleic acids without substantially precipitating small (e.g., less than 300 nucleotides) nucleic acids.
Another size-based enrichment method that can be used with methods described herein involves circularization by ligation, for example, using circligase. Short nucleic acid fragments typically can be circularized with higher efficiency than long fragments. Non-circularized sequences can be separated from circularized sequences, and the enriched short fragments can be used for further analysis.
Determining Fetal Nucleic Acid Content
In some embodiments an analysis (e.g., an analysis of nucleic acids) comprises determining an amount of fetal nucleic acid in a nucleic acid sample. An amount of fetal nucleic acid (e.g., concentration, relative amount, ratio, absolute amount, copy number, and the like) in nucleic acid (e.g., a nucleic acid sample or mixture) is determined in some embodiments. In some embodiments, the amount of fetal nucleic acid in a sample is referred to as “fetal fraction”. In some embodiments, “fetal fraction” refers to the fraction of fetal nucleic acid in circulating cell-free nucleic acid in a sample (e.g., a blood sample, a serum sample, a plasma sample) obtained from a pregnant female. In some embodiments determining an amount of fetal nucleic acid comprises determining a ratio (e.g., percentage, a percent representation) of fetal nucleic acid to a total amount of nucleic acid in a sample. In some embodiments determining an amount of fetal nucleic acid comprises determining a ratio (e.g., percentage) of the amount of fetal nucleic acid to the amount of maternal nucleic acid in a sample. In some embodiments, a method in which a genetic variation is determined also can comprise determining fetal fraction. Determining fetal fraction can be performed in a suitable manner, non-limiting examples of which include methods described below.
In some embodiments, the amount of fetal nucleic acid is determined according to markers specific to a male fetus (e.g., Y-chromosome STR markers (e.g., DYS 19, DYS 385, DYS 392 markers); RhD marker in RhD-negative females), allelic ratios of polymorphic sequences, or according to one or more markers specific to fetal nucleic acid and not maternal nucleic acid (e.g., differential epigenetic biomarkers (e.g., methylation; described in further detail below) between mother and fetus, or fetal RNA markers in maternal blood plasma (see e.g., Lo, 2005, Journal of Histochemistry and Cytochemistry 53 (3): 293-296)).
Determination of fetal nucleic acid content (e.g., fetal fraction) sometimes is performed using a fetal quantifier assay (FQA) as described, for example, in U.S. Patent Application Publication No. 2010/0105049, which is hereby incorporated by reference. This type of assay allows for the detection and quantification of fetal nucleic acid in a maternal sample based on the methylation status of the nucleic acid in the sample. The amount of fetal nucleic acid from a maternal sample sometimes can be determined relative to the total amount of nucleic acid present, thereby providing the percentage of fetal nucleic acid in the sample. The copy number of fetal nucleic acid sometimes can be determined in a maternal sample. The amount of fetal nucleic acid sometimes can be determined in a sequence-specific (or locus-specific) manner and sometimes with sufficient sensitivity to allow for accurate chromosomal dosage analysis (for example, to detect the presence or absence of a fetal aneuploidy or other genetic variation).
A fetal quantifier assay (FQA) can be performed in conjunction with any method described herein. Such an assay can be performed by any method known in the art and/or described in U.S. Patent Application Publication No. 2010/0105049, such as, for example, by a method that can distinguish between maternal and fetal DNA based on differential methylation status, and quantify (i.e. determine the amount of) the fetal DNA. Methods for differentiating nucleic acid based on methylation status include, but are not limited to, methylation sensitive capture, for example, using a MBD2-Fc fragment in which the methyl binding domain of MBD2 is fused to the Fc fragment of an antibody (MBD-FC) (Gebhard et al. (2006) Cancer Res. 66(12):6118-28); methylation specific antibodies; bisulfite conversion methods, for example, MSP (methylation-sensitive PCR), COBRA, methylation-sensitive single nucleotide primer extension (Ms-SNuPE) or Sequenom MassCLEAVE™ technology; and the use of methylation sensitive restriction enzymes (e.g., digestion of maternal DNA in a maternal sample using one or more methylation sensitive restriction enzymes thereby enriching for fetal DNA). Methyl-sensitive enzymes also can be used to differentiate nucleic acid based on methylation status, which, for example, can preferentially or substantially cleave or digest at their DNA recognition sequence if the latter is non-methylated. Thus, an unmethylated DNA sample will be cut into smaller fragments than a methylated DNA sample and a hypermethylated DNA sample will not be cleaved. Except where explicitly stated, any method for differentiating nucleic acid based on methylation status can be used with the compositions and methods of the technology herein. The amount of fetal DNA can be determined, for example, by introducing one or more competitors at known concentrations during an amplification reaction. Determining the amount of fetal DNA also can be done, for example, by RT-PCR, primer extension, sequencing and/or counting. In certain instances, the amount of nucleic acid can be determined using BEAMing technology as described in U.S. Patent Application Publication No. 2007/0065823. In some embodiments, the restriction efficiency can be determined and the efficiency rate is used to further determine the amount of fetal DNA.
A fetal quantifier assay (FQA) sometimes can be used to determine the concentration of fetal DNA in a maternal sample, for example, by the following method: a) determine the total amount of DNA present in a maternal sample; b) selectively digest the maternal DNA in a maternal sample using one or more methylation sensitive restriction enzymes thereby enriching the fetal DNA; c) determine the amount of fetal DNA from step b); and d) compare the amount of fetal DNA from step c) to the total amount of DNA from step a), thereby determining the concentration of fetal DNA in the maternal sample. The absolute copy number of fetal nucleic acid in a maternal sample sometimes can be determined, for example, using mass spectrometry and/or a system that uses a competitive PCR approach for absolute copy number measurements. See for example, Ding and Cantor (2003) Proc. Natl. Acad. Sci. USA 100:3059-3064, and U.S. Patent Application Publication No. 2004/0081993, both of which are hereby incorporated by reference.
Fetal fraction sometimes can be determined based on allelic ratios of polymorphic sequences (e.g., single nucleotide polymorphisms (SNPs)), such as, for example, using a method described in U.S. Patent Application Publication No. 2011/0224087, which is hereby incorporated by reference. In such a method, nucleotide sequence reads are obtained for a maternal sample and fetal fraction is determined by comparing the total number of nucleotide sequence reads that map to a first allele and the total number of nucleotide sequence reads that map to a second allele at an informative polymorphic site (e.g., SNP) in a reference genome. Fetal alleles can be identified, for example, by their relative minor contribution to the mixture of fetal and maternal nucleic acids in the sample when compared to the major contribution to the mixture by the maternal nucleic acids. Accordingly, the relative abundance of fetal nucleic acid in a maternal sample can be determined as a parameter of the total number of unique sequence reads mapped to a target polynucleotide sequence on a reference genome for each of the two alleles of a polymorphic site.
The amount of fetal nucleic acid in extracellular nucleic acid can be quantified and used in conjunction with a method provided herein. Thus, in certain embodiments, methods of the technology described herein comprise an additional step of determining the amount of fetal nucleic acid. The amount of fetal nucleic acid can be determined in a nucleic acid sample from a subject before or after processing to prepare sample nucleic acid. In certain embodiments, the amount of fetal nucleic acid is determined in a sample after sample nucleic acid is processed and prepared, which amount is utilized for further assessment. In some embodiments, an outcome comprises factoring the fraction of fetal nucleic acid in the sample nucleic acid (e.g., adjusting counts, removing samples, making a call or not making a call).
The determination step can be performed before, during, at any one point in a method described herein, or after certain (e.g., aneuploidy detection) methods described herein. For example, to achieve an aneuploidy determination method with a given sensitivity or specificity, a fetal nucleic acid quantification method may be implemented prior to, during or after aneuploidy determination to identify those samples with greater than about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or more fetal nucleic acid. In some embodiments, samples determined as having a certain threshold amount of fetal nucleic acid (e.g., about 15% or more fetal nucleic acid; about 4% or more fetal nucleic acid) are further analyzed for the presence or absence of aneuploidy or genetic variation, for example. In certain embodiments, determinations of, for example, the presence or absence of aneuploidy are selected (e.g., selected and communicated to a patient) only for samples having a certain threshold amount of fetal nucleic acid (e.g., about 15% or more fetal nucleic acid; about 4% or more fetal nucleic acid).
In some embodiments, the determination of fetal fraction or determining the amount of fetal nucleic acid is not required or necessary for identifying the presence or absence of a chromosome aneuploidy. In some embodiments, identifying the presence or absence of a chromosome aneuploidy does not require the sequence differentiation of fetal versus maternal DNA. This is because the summed contribution of both maternal and fetal sequences in a particular chromosome, chromosome portion or segment thereof is analyzed, in some embodiments. In some embodiments, identifying the presence or absence of a chromosome aneuploidy does not rely on a priori sequence information that would distinguish fetal DNA from maternal DNA.
Nucleic Acid Amplification and Detection
In some embodiments, nucleic acid fragments (e.g., digested nucleic acid fragments) may be amplified and/or subjected to a analysis and/or detection process (e.g., sequence-based analysis, mass spectrometry). In some embodiments, nucleic acid fragments are (e.g., digested nucleic acid fragments) subjected to a detection process (e.g., sequencing) without amplification. Such methods without amplification typically have less starting material (e.g., less input nucleic acid resulting from an enrichment process herein) for downstream analysis. In some embodiments a nucleic acid or a subset (e.g., subpopulation, species) of nucleic acid is enriched by a process comprising nucleic acid amplification. For example, fetal nucleic acid can be enriched by a process comprising nucleic acid amplification.
Nucleic acid fragments (e.g., digested nucleic acid fragments), or amplified nucleic acid fragment sequences, or detectable products prepared from the foregoing, can be detected by a suitable detection process. Non-limiting examples of methods of detection, quantification, sequencing and the like include mass detection of mass modified amplicons (e.g., matrix-assisted laser desorption ionization (MALDI) mass spectrometry and electrospray (ES) mass spectrometry), a primer extension method (e.g., iPLEX™; Sequenom, Inc.), direct DNA sequencing, Molecular Inversion Probe (MIP) technology from Affymetrix, restriction fragment length polymorphism (RFLP analysis), allele specific oligonucleotide (ASO) analysis, methyl-specific PCR (MSPCR), pyrosequencing analysis, acycloprime analysis, Reverse dot blot, GeneChip microarrays, Dynamic allele-specific hybridization (DASH), Peptide nucleic acid (PNA) and locked nucleic acids (LNA) probes, TaqMan, Molecular Beacons, Intercalating dye, FRET primers, AlphaScreen, SNPstream, genetic bit analysis (GBA), Multiplex minisequencing, SNaPshot, GOOD assay, Microarray miniseq, arrayed primer extension (APEX), Microarray primer extension, Tag arrays, Coded microspheres, Template-directed incorporation (TDI), fluorescence polarization, Colorimetric oligonucleotide ligation assay (OLA), Sequence-coded OLA, Microarray ligation, Ligase chain reaction, Padlock probes, Invader assay, hybridization using at least one probe, hybridization using at least one fluorescently labeled probe, cloning and sequencing, electrophoresis, the use of hybridization probes and quantitative real time polymerase chain reaction (QRT-PCR), digital PCR, nanopore sequencing, chips and combinations thereof. In some embodiments the amount of each nucleic acid species is determined by mass spectrometry, primer extension, sequencing (e.g., any suitable method, for example nanopore or pyrosequencing), Quantitative PCR (Q-PCR or QRT-PCR), digital PCR, combinations thereof, and the like.
Nucleic acid detection and/or quantification also may include, for example, solid support array based detection of fluorescently labeled nucleic acid with fluorescent labels incorporated during or after PCR, single molecule detection of fluorescently labeled molecules in solution or captured on a solid phase, or other sequencing technologies such as, for example, sequencing using ION TORRENT or MISEQ platforms or single molecule sequencing technologies using instrumentation such as, for example, PACBIO sequencers, HELICOS sequencer, or nanopore sequencing technologies.
Nucleic Acid Amplification
In many instances, it is desirable to amplify a nucleic acid sequence or a subset of nucleic acids of the technology herein using any of several nucleic acid amplification procedures which are well known in the art, some of which are listed or described herein. Specifically, nucleic acid amplification is the enzymatic synthesis of nucleic acid amplicons (copies) which contain a sequence that is complementary to a nucleic acid sequence being amplified. In some embodiments amplification comprises ligating one or more adaptors to a nucleic acid target or target subset of nucleic acids (e.g., digested nucleic acid, enriched nucleic acid, separated nucleic acid). Nucleic acid amplification is especially beneficial when the amount of target sequence present in a sample is very low. By amplifying the target sequences and detecting the amplicon synthesized, the sensitivity of an assay can be vastly improved, since fewer target sequences are needed at the beginning of the assay to better ensure detection of nucleic acid in the sample belonging to the organism or virus of interest. One or more nucleic acids can be amplified in solution or while immobilized on a solid phase. One or more nucleic acids can be amplified prior to and/or after immobilization on a solid support (e.g., a solid support in a flow cell). In some embodiments one or more nucleic acids can be amplified after release from a solid phase.
A variety of polynucleotide amplification methods are well established and frequently used in research. For instance, the general methods of polymerase chain reaction (PCR) for polynucleotide sequence amplification are well known in the art and are thus not described in detail herein. For a review of PCR methods, protocols, and principles in designing primers, see, e.g., Innis, et al., PCR Protocols: A Guide to Methods and Applications, Academic Press, Inc. N.Y., 1990. PCR reagents and protocols are also available from commercial vendors, such as Roche Molecular Systems.
PCR is most usually carried out as an automated process with a thermostable enzyme. In this process, the temperature of the reaction mixture is cycled through a denaturing region, a primer annealing region, and an extension reaction region automatically. Machines specifically adapted for this purpose are commercially available.
Although PCR amplification of a polynucleotide sequence (e.g., a target polynucleotide) is typically used in practicing the present technology, one of skill in the art will recognize that the amplification of a genomic sequence found in a maternal blood sample may be accomplished by any known method, such as ligase chain reaction (LCR), transcription-mediated amplification, and self-sustained sequence replication or nucleic acid sequence-based amplification (NASBA), each of which provides sufficient amplification. More recently developed branched-DNA technology may also be used to qualitatively demonstrate the presence of a particular genomic sequence of the technology herein, which represents a particular methylation pattern, or to quantitatively determine the amount of this particular genomic sequence in the maternal blood. For a review of branched-DNA signal amplification for direct quantitation of nucleic acid sequences in clinical samples, see Nolte, Adv. Clin. Chem. 33:201-235, 1998.
The compositions and processes of the technology herein are also particularly useful when practiced with digital PCR. Digital PCR was first developed by Kalinina and colleagues (Kalinina et al., “Nanoliter scale PCR with TaqMan detection.” Nucleic Acids Research. 25; 1999-2004, (1997)) and further developed by Vogelstein and Kinzler (Digital PCR. Proc Natl Acad Sci USA. 96; 9236-41, (1999)). The application of digital PCR for use with fetal diagnostics was first described by Cantor et al. (PCT Patent Publication No. WO05023091A2) and subsequently described by Quake et al. (US Patent Publication No. US 20070202525), which are both hereby incorporated by reference. Digital PCR takes advantage of nucleic acid (DNA, cDNA or RNA) amplification on a single molecule level, and offers a highly sensitive method for quantifying low copy number nucleic acid. Fluidigm® Corporation offers systems for the digital analysis of nucleic acids.
The terms “amplify”, “amplification”, “selective amplification”, “amplification reaction”, or “amplifying” refer to any in vitro process for multiplying the copies of a nucleic acid. Amplification sometimes refers to an “exponential” increase in nucleic acid. However, “amplifying” as used herein can also refer to linear increases in the numbers of a select nucleic acid, but is different than a one-time, single primer extension step. In some embodiments a limited amplification reaction, also known as pre-amplification, can be performed. Pre-amplification is a method in which a limited amount of amplification occurs due to a small number of cycles, for example 10 cycles, being performed. Pre-amplification can allow some amplification, but stops amplification prior to the exponential phase, and typically produces about 500 copies of the desired nucleotide sequence(s). Use of pre-amplification may also limit inaccuracies associated with depleted reactants in standard PCR reactions, for example, and also may reduce amplification biases due to nucleotide sequence or abundance of the nucleic acid. In some embodiments a one-time primer extension may be performed as a prelude to linear or exponential amplification.
Any suitable amplification technique can be utilized. Amplification of polynucleotides include, but are not limited to, polymerase chain reaction (PCR); ligation amplification (or ligase chain reaction (LCR)); amplification methods based on the use of Q-beta replicase or template-dependent polymerase (see US Patent Publication Number US20050287592); helicase-dependent isothermal amplification (Vincent et al., “Helicase-dependent isothermal DNA amplification”. EMBO reports 5 (8): 795-800 (2004)); strand displacement amplification (SDA); thermophilic SDA nucleic acid sequence based amplification (3SR or NASBA) and transcription-associated amplification (TAA). Non-limiting examples of PCR amplification methods include standard PCR, AFLP-PCR, Allele-specific PCR, Alu-PCR, Asymmetric PCR, Colony PCR, Hot start PCR, Inverse PCR (IPCR), In situ PCR (ISH), Intersequence-specific PCR (ISSR-PCR), Long PCR, Multiplex PCR, Nested PCR, Quantitative PCR, Reverse Transcriptase PCR (RT-PCR), Real Time PCR, Single cell PCR, Solid phase PCR, digital PCR, combinations thereof, and the like. For example, amplification can be accomplished using digital PCR, in certain embodiments (see e.g. Kalinina et al., “Nanoliter scale PCR with TaqMan detection.” Nucleic Acids Research. 25; 1999-2004, (1997); Vogelstein and Kinzler (Digital PCR. Proc Natl Acad Sci USA. 96; 9236-41, (1999); PCT Patent Publication No. WO05023091A2; US Patent Publication No. US 20070202525). Digital PCR takes advantage of nucleic acid (DNA, cDNA or RNA) amplification on a single molecule level, and offers a highly sensitive method for quantifying low copy number nucleic acid. Systems for digital amplification and analysis of nucleic acids are available (e.g., Fluidigm® Corporation). Reagents and hardware for conducting PCR are commercially available.
A generalized description of a selective amplification process is presented herein. Primers (e.g., a primer pair, a collection of primer pairs) and nucleic acid (e.g., target polynucleotides) are contacted under suitable hybridization conditions, and complementary sequences anneal to one another, for example. Primers can anneal to a nucleic acid, at or near (e.g., adjacent to, abutting, and the like) a sequence of interest. In some embodiments, a primer pair hybridizes within about 10 to 30 nucleotides from a nucleic acid sequence of interest and, under amplification conditions can produce amplified products (e.g., amplicons). In some embodiments, the primers hybridize within a nucleic acid sequence of interest (e.g., a target polynucleotide).
Any suitable amplification conditions can be used to perform an amplification resulting in the production of amplicons. In some embodiments a sample comprising target polynucleotides is contacted with one or more target specific primer pairs (e.g., a collection of primers) under amplification conditions where target specific amplicons are generated. Amplification conditions often comprise a reaction mixture containing a polymerase, at least one primer (e.g., a primer pair), at least one target polynucleotide and additional components (e.g., buffers, salts and nucleotide triphosphates) necessary for polymerase activity. Non-limiting examples of components of an amplification reaction may include, but are not limited to, e.g., primers (e.g., individual primers, primer pairs, a collection of primer pairs and the like) a polynucleotide template, polymerase, nucleotides, dNTPs and the like. In some embodiments, non-naturally occurring nucleotides or nucleotide analogs, such as analogs containing a detectable label (e.g., fluorescent or colorimetric label), may be used for example. Polymerases can be selected by a person of ordinary skill and include polymerases for thermocycle amplification (e.g., Taq DNA Polymerase; Q-Bio™ Taq DNA Polymerase (recombinant truncated form of Taq DNA Polymerase lacking 5′-3′exo activity); SurePrime™ Polymerase (chemically modified Taq DNA polymerase for “hot start” PCR); Arrow™ Taq DNA Polymerase (high sensitivity and long template amplification)) and polymerases for thermostable amplification (e.g., RNA polymerase for transcription-mediated amplification (TMA) described at World Wide Web URL “gen-probe.com/pdfs/tma_whiteppr.pdf”). Other enzyme components can be added, such as reverse transcriptase for transcription mediated amplification (TMA) reactions, for example.
Amplification conditions can be dependent upon primer sequences (e.g., primer hybridization sequences), abundance of nucleic acid, and the desired amount of amplification, and therefore, one of skill in the art may choose from a number of PCR protocols available (see, e.g., U.S. Pat. Nos. 4,683,195 and 4,683,202; and PCR Protocols: A Guide to Methods and Applications, Innis et al., eds, 1990. Digital PCR is also known in the art; see, e.g., United States Patent Application Publication no. 20070202525, filed Feb. 2, 2007, which is hereby incorporated by reference). Amplification conditions often comprise a plurality of suitable temperature changes (e.g., temperature cycles) and incubation times (e.g., an incubation time for annealing, melting and extension). Amplification is typically carried out as an automated process, often in a thermocycler with a thermostable enzyme. In this process, the temperature of the reaction mixture is cycled multiple times through a denaturing step, a primer-annealing step, and an extension reaction step automatically. Some amplification protocols also include an activation step and a final extension step. Machines specifically adapted for this purpose are commercially available. A non-limiting example of a amplification protocol that may be suitable for embodiments described herein is, treating the sample at 95° C. for 5 minutes; repeating thirty-five cycles of 95° C. for 45 seconds and 68° C. for 30 seconds; and then treating the sample at 72° C. for 3 minutes. A completed amplification reaction can optionally be kept at 4° C. until further action is desired. Multiple cycles frequently are performed using a commercially available thermal cycler. Suitable isothermal amplification processes known and selected by the person of ordinary skill in the art also may be applied, in certain embodiments.
In some embodiments, an amplification product (e.g., an amplicon) may include naturally occurring nucleotides, non-naturally occurring nucleotides, nucleotide analogs and the like and combinations of the foregoing. An amplicon often has a nucleotide sequence that is identical to or substantially identical to a nucleic acid sequence herein, or complement thereof. A “substantially identical” nucleotide sequence in an amplification product will generally have a high degree of sequence identity to the nucleotide sequence species being amplified or complement thereof (e.g., about 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% sequence identity), and variations sometimes are a result of infidelity of the polymerase used for extension and/or amplification, or additional nucleotide sequence(s) added to the primers used for amplification. Nucleic acids in a sample can be enriched by an amplification method described herein. An amplification product (e.g., amplicons) can be generated before, during or after any step of a method described herein. An amplification product can be generated before, during or after a digestion or cleavage reaction. An amplification product can be generated before, during or after a modification of nucleic acids in a sample. An amplification product can be generated before, during or after an enrichment method. An amplification product can be generated before, during or after a separation or purifications step. An amplification product can be generated before, during or after a process comprising nucleic acid sequencing. In some embodiments digested nucleic acids or undigested nucleic acids are enriched by an amplification. In some embodiments enriched and/or separated nucleic acid are further enriched by an amplification. In some embodiments enriched and/or separated methylated, hypermethylated and/or hypomethylated nucleic acid are further enriched by an amplification.
Collection of Primers
In some embodiments a collection of oligonucleotide primers or primer pairs is provided herein for identifying the presence or absence of one or more differentially methylated loci (e.g., hypermethylated loci. hypomethylated loci). In some embodiments a collection of oligonucleotide primers or primer pairs is provided herein for analyzing one or more differentially methylated loci (e.g., hypermethylated loci. hypomethylated loci). In certain embodiments, a collection of primers or primer pairs is provided in a kit. In some embodiments provided herein is a method of preparing a collection of oligonucleotide primers or primer pairs for analyzing or identifying the presence or absence of one or more differentially methylated loci (e.g., hypermethylated loci. hypomethylated loci).
A collection of oligonucleotide primers or primer pairs for analyzing or identifying the presence or absence of a differentially methylated locus (e.g., a hypomethylated locus, a hypermethylated locus) can be prepared by a process comprising selecting one or more genomic loci wherein each locus comprises one or more features, non-limiting examples of which include: a size of a locus (e.g., mean, median, average, size range or absolute size); methylation status of a minority species of nucleic acid (e.g., in fetal nucleic acid; e.g., mean, median, average, limit of, span of, range of, or absolute methylation status); a mean, median, average, absolute or relative methylation status of a majority nucleic acid species (e.g., in maternal nucleic acid; e.g., mean, median, average, limit of, span of, range of, or absolute methylation status); a difference in methylation status between a minority nucleic acid species and a majority nucleic acid species; CpG density; number of CpG sites; gene density; number of restriction sites; distance and/or spacing between restriction sites for loci having two or more restriction sites; and amplicon size (e.g., mean, median, average, absolute or range of amplicon size; e.g., amplicon sizes ranging from 40-125 nucleotides in length); the like; or combinations thereof. A differentially methylated locus sometimes is selected and/or analyzed according to 2, 3, 4, 5, 6, 7, 8 or more features described herein.
For example, in some embodiments a collection of amplification primer pairs for identifying the presence or absence of a hypomethylated locus are prepared by a process comprising selecting one or more genomic loci wherein each locus comprises three or more features selected from: (i) a locus length of about 5000 contiguous base pairs, or less, (ii) a CpG density of 16 CpG methylation sites per 1000 base pairs, or less, (iii) a gene density of 0.1 genes per 1000 base pair, or less, (iv) at least 5 CpG methylation sites, (v) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (vi) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition sites can be specifically digested by a methylation sensitive cleavage agent, (vii) a locus comprising a methylation status of 40% or less in fetal nucleic acid, (viii) a locus comprising a methylation status of 60% or more in maternal nucleic acid, and (ix) a locus comprising a difference in methylation status of 5% or more between fetal nucleic acid and maternal nucleic acid. In some embodiments a collection of amplification primer pairs for identifying the presence or absence of a hypermethylated locus are prepared by a process comprising selecting one or more genomic loci wherein each locus comprises three or more features selected from: (i) a locus length of about 5000 contiguous base pairs, or less, (ii) at least 5 CpG methylation sites, (iii) a plurality of restriction endonuclease recognition sites wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site on the locus is about 20 to about 125 base pairs, and each of the restriction endonuclease recognition sites is recognized by one or more methylation sensitive restriction endonucleases, (iv) at least 1 restriction endonuclease recognition site per 1000 base pairs, wherein the at least one restriction endonuclease recognition sites can be specifically digested by a methylation sensitive restriction endonuclease, (v) a locus comprising a methylation status of 60% or more in a minority nucleic acid species, (vi) a locus comprising a methylation status of 40% or less in a majority nucleic acid species, and (vii) a locus comprising a difference in methylation status of 5% or more between a minority nucleic acid species and a majority nucleic acid species.
Primer pairs are sometimes configured for use in an amplification, where each primer or primer pair is specific for a target polynucleotide located within a loci. Often a locus comprises 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 or more target polynucleotides. In some embodiments a primer pair is configured to amplify one or more target polynucleotides. In some embodiments a primer comprises a hybridization sequence that is complimentary to a portion of the target sequence which the primer is configured to amplify. In certain embodiments both of the oligonucleotide primers of a primer pair comprises a hybridization sequence that is complimentary to a portion of the target sequence which the primer pair is configured to amplify. In some embodiments a primer comprises a hybridization sequence that is complimentary to a linker (e.g., a universal linker or adapter) or portion thereof that is ligated to a target sequence which the primer is configured to amplify. In some embodiments each of the oligonucleotide primers of a primer pair comprise a different hybridization sequence. In some embodiments each of the oligonucleotide primers of a primer pair comprise the same hybridization sequence, for example, where universal linkers are ligated to a target sequence. Sometimes a target sequence, which a primer pair is configured to amplify, is longer than the combined length of the hybridization sequences of a target specific primer pair.
Target polynucleotides can be single stranded or double stranded. In some embodiments a target polynucleotide comprises a length of about 1000 nucleotides to about 20 nucleotides, about 500 nucleotides to about 30 nucleotides, about 400 nucleotides to about 30 nucleotides, about 400 nucleotides to about 40 nucleotides, about 360 nucleotides to about 40 nucleotides or about 180 nucleotides to about 40 nucleotides. In some embodiments a target polynucleotide is about 1000 base pairs (bp) or less, about 900 base pairs or less, about 800 bp or less, about 700 bp or less, about 600 bp or less, about 500 bp or less, about 400 bp or less, about 300 bp or less, or about 200 bp or less. Target polynucleotides, or portions thereof are sometimes present in circulating cell free DNA. In some embodiments a target polynucleotide is circulating cell free DNA. Circulating cell free DNA sometimes comprises a length of about 1000 nucleotides to about 20 nucleotides, about 500 nucleotides to about 30 nucleotides, about 400 nucleotides to about 30 nucleotides, about 400 nucleotides to about 40 nucleotides, about 360 nucleotides to about 40 nucleotides or about 180 nucleotides to about 40 nucleotides.
In some embodiments each target polynucleotide comprises at least one methylation sensitive restriction site. In some embodiments a collection of oligonucleotide primer pairs is configured for amplification of one or more target polynucleotides where each target polynucleotide comprises at least one methylation sensitive restriction site. In some embodiments each primer pair hybridizes to a portion of a target polynucleotide that flanks at least one methylation sensitive restriction site.
In some embodiments a collection of oligonucleotides primers or primer pairs comprises one or more oligonucleotide primers that comprise a non-native element. A primer of a collection sometimes comprises one or more non-native elements. In some embodiments a non-native element is a heterologous nucleotide sequence. In some embodiments a non-native element is an identifier. In some embodiments a non-native element is or comprises a binding agent (e.g., a member of a binding pair). In certain embodiments a non-native element is a non-native nucleotide or a nucleotide comprising a chemical modification.
In some embodiments a differentially methylated locus is identified by a process comprising (a) digesting one or more target polynucleotides of a first sample and a second sample with one or more methylation sensitive restriction endonucleases that specifically digest a target polynucleotide at restriction endonuclease sites that are unmethylated, where each of the samples comprise one or more selected loci, (b) contacting each sample with a collection of oligonucleotide primers prepared by a method described herein, under amplification conditions, thereby providing target specific amplicons of undigested target polynucleotides and analyzing the target specific amplicons from each sample. In some embodiments a differentially methylated locus is identified according to an analysis comprises comparing and/or determining an amount of target specific amplicons from each sample. The identity (e.g., nucleic acid sequence, detection of an identifier, tag or label) or amount of an amplicon can be by any suitable method (e.g., by nucleic acid sequencing, mass spectrometry, spectrophotometry, the like or combinations thereof). In some embodiments a differentially methylated locus is identified where the amount of target specific amplicons of a first sample are significantly different from an amount of target specific amplicons of a second sample. In certain embodiments nucleic acids of a first sample and a second sample are from different sources (e.g., fetal and maternal sources). Sometimes a first sample and/or a second sample comprise circulating cell free nucleic acid. Sometimes an analysis comprises comparing and/or determining a methylation status of one or more selected loci in a first sample and/or one or more selected loci in a second sample. In some embodiments a first sample comprises a minority nucleic acid species (e.g., fetal nucleic acid). In some embodiments a first sample comprises enriched fetal nucleic acid. In some embodiments a second sample comprises a majority nucleic acid species (e.g., maternal nucleic acid).
In some embodiments a differentially methylated locus (e.g., a locus hypomethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci 60% or more, 65% or more, 70% or more, 75% or more, 80% or more or 85% or more methylated in a majority nucleic acid species (e.g., maternal nucleic acid) relative to a minority nucleic acid species (e.g., fetal nucleic acid). In some embodiments a differentially methylated locus (e.g., a locus hypomethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less, 15% or less, 10% or less or 5% or less methylated in a minority nucleic acid species relative to a majority nucleic acid species. In some embodiments a differentially methylated locus (e.g., a locus hypomethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more selected loci is 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more or 40% or more.
In some embodiments a differentially methylated locus (e.g., a locus hypermethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci 60% or more, 65% or more, 70% or more, 75% or more, 80% or more or 85% or more methylated in a minority nucleic acid species (e.g., fetal nucleic acid) relative to a majority nucleic acid species (e.g., maternal nucleic acid). In some embodiments a differentially methylated locus (e.g., a locus hypermethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less, 15% or less, 10% or less or 5% or less methylated in a majority nucleic acid species relative to a minority nucleic acid species. In some embodiments a differentially methylated locus (e.g., a locus hypermethylated in a minority species relative to a majority nucleic acid species) is identified where an analysis comprises identifying one or more selected loci, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more selected loci is 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more or 40% or more.
Obtaining Sequence Reads
In some embodiments analyzing nucleic acids or nucleic acid fragments comprises sequencing. In some embodiments, nucleic acids (e.g., nucleic acid fragments, digested nucleic acid fragments, sample nucleic acid, cell-free nucleic acid, enriched nucleic acid fragments, fetal nucleic acid fragments, maternal nucleic acid fragments) may be sequenced. In some embodiments, a full or substantially full sequence is obtained and sometimes a partial sequence is obtained. In some embodiments, a nucleic acid is not sequenced, and the sequence of a nucleic acid is not determined by a sequencing method, when performing a method described herein. In some embodiments, nucleic acid fragments (e.g., digested nucleic acid fragments) are sequenced with or without prior amplification as described above. In some embodiments, digested nucleic acid fragments are sequenced via ligated adaptor sequences (e.g., adaptor nucleic acids) as described above. Sequencing, mapping and related analytical methods are known in the art (e.g., United States Patent Application Publication US200910029377, incorporated by reference). Certain aspects of such processes are described hereafter.
As used herein, “reads” (i.e., “a read”, “a sequence read”) are short nucleotide sequences produced by any sequencing process described herein or known in the art. Reads can be generated from one end of nucleic acid fragments (“single-end reads”), and sometimes are generated from both ends of nucleic acids (e.g., paired-end reads, double-end reads).
In some embodiments the nominal, average, mean or absolute length of single-end reads sometimes is about 20 contiguous nucleotides to about 50 contiguous nucleotides, sometimes about 30 contiguous nucleotides to about 40 contiguous nucleotides, and sometimes about 35 contiguous nucleotides or about 36 contiguous nucleotides. In some embodiments, the nominal, average, mean or absolute length of single-end reads is about 20 to about 30 bases in length. In some embodiments, the nominal, average, mean or absolute length of single-end reads is about 24 to about 28 bases in length. In some embodiments, the nominal, average, mean or absolute length of single-end reads is about 21, 22, 23, 24, 25, 26, 27, 28 or about 29 bases in length.
In certain embodiments, the nominal, average, mean or absolute length of the paired-end reads sometimes is about 10 contiguous nucleotides to about 50 contiguous nucleotides (e.g., about 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 or 49 nucleotides in length), sometimes is about 15 contiguous nucleotides to about 25 contiguous nucleotides, and sometimes is about 17 contiguous nucleotides, about 18 contiguous nucleotides, about 20 contiguous nucleotides, about 25 contiguous nucleotides, about 36 contiguous nucleotides or about 45 contiguous nucleotides.
Reads generally are representations of nucleotide sequences in a physical nucleic acid. For example, in a read containing an ATGC depiction of a sequence, “A” represents an adenine nucleotide, “T” represents a thymine nucleotide, “G” represents a guanine nucleotide and “C” represents a cytosine nucleotide, in a physical nucleic acid. Sequence reads obtained from the blood of a pregnant female can be reads from a mixture of fetal and maternal nucleic acid. A mixture of relatively short reads can be transformed by processes described herein into a representation of a genomic nucleic acid present in the pregnant female and/or in the fetus. A mixture of relatively short reads can be transformed into a representation of a copy number variation (e.g., a maternal and/or fetal copy number variation), genetic variation or an aneuploidy, for example. Reads of a mixture of maternal and fetal nucleic acid can be transformed into a representation of a composite chromosome or a segment thereof comprising features of one or both maternal and fetal chromosomes. In certain embodiments, “obtaining” nucleic acid sequence reads of a sample from a subject and/or “obtaining” nucleic acid sequence reads of a biological specimen from one or more reference persons can involve directly sequencing nucleic acid to obtain the sequence information. In some embodiments, “obtaining” can involve receiving sequence information obtained directly from a nucleic acid by another.
Sequence reads can be mapped and the number of reads or sequence tags mapping to a specified nucleic acid region (e.g., a chromosome, a bin, a genomic section) are referred to as counts. In some embodiments, counts can be manipulated or transformed (e.g., normalized, combined, added, filtered, selected, averaged, derived as a mean, the like, or a combination thereof). In some embodiments, counts can be transformed to produce normalized counts. Normalized counts for multiple genomic sections can be provided in a profile (e.g., a genomic profile, a chromosome profile, a profile of a segment of a chromosome). One or more different elevations in a profile also can be manipulated or transformed (e.g., counts associated with elevations can be normalized) and elevations can be adjusted.
In some embodiments, one nucleic acid sample from one individual is sequenced. In certain embodiments, nucleic acid samples from two or more biological samples, where each biological sample is from one individual or two or more individuals, are pooled and the pool is sequenced. In the latter embodiments, a nucleic acid sample from each biological sample often is identified by one or more unique identification tags.
In some embodiments, a fraction of the genome is sequenced, which sometimes is expressed in the amount of the genome covered by the determined nucleotide sequences (e.g., “fold” coverage less than 1). When a genome is sequenced with about 1-fold coverage, roughly 100% of the nucleotide sequence of the genome is represented by reads. A genome also can be sequenced with redundancy, where a given region of the genome can be covered by two or more reads or overlapping reads (e.g., “fold” coverage greater than 1). In some embodiments, a genome is sequenced with about 0.01-fold to about 100-fold coverage, about 0.2-fold to 20-fold coverage, or about 0.2-fold to about 1-fold coverage (e.g., about 0.02-, 0.03-, 0.04-, 0.05-, 0.06-, 0.07-, 0.08-, 0.09-, 0.1-, 0.2-, 0.3-, 0.4-, 0.5-, 0.6-, 0.7-, 0.8-, 0.9-, 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 15-, 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90-fold coverage).
In some embodiments an analysis comprises sequencing a portion of nucleic acids in a test sample and sometimes an analysis comprises sequencing substantially all of the nucleic acids in a test sample. In some embodiments a portion of nucleic acids in test sample comprises fetal nucleic acids (e.g., enriched fetal nucleic acids), maternal nucleic acids (e.g., enriched maternal nucleic acids), placental nucleic acids (e.g., enriched placental nucleic acids), tumor nucleic acids (e.g., enriched tumor nucleic acids), hypomethylated nucleic acids (e.g., enriched hypomethylated nucleic acids, hypomethylated loci), hypermethylated nucleic acids (e.g., enriched hypermethylated nucleic acids, hypermethylated loci), minority nucleic acids, majority nucleic acids, the like or a combination thereof. In some embodiments substantially all of an enriched nucleic acid species (e.g., enriched fetal, maternal, placental, hypomethylated, hypermethylated, or tumor nucleic acids) is sequenced. In some embodiments a portion of an enriched nucleic acid species (e.g., enriched fetal, maternal, placental, hypomethylated, hypermethylated, or tumor nucleic acids) is sequenced. In some embodiments an analysis of nucleic acids (e.g., an analysis of digested nucleic acid fragments, an analysis of enriched fetal nucleic acid) comprises targeted sequencing and/or non-targeted sequencing of nucleic acids (e.g., digested and/or enriched nucleic acids). For example, where a targeted sequencing or amplification approach is used, sometimes a portion (e.g., a selected portion) of an enriched nucleic acid species is sequenced. A selected portion can be one or more selected genes, exons, introns, promoters, loci (e.g., hypermethylated loci, hypomethylated loci, polymorphisms, alleles), chromosomes, the like, portions thereof or combinations thereof. In some embodiments modified variants of nucleic acids (e.g., modified variants of digested nucleic acids) are analyzed by targeted sequencing and/or by non-targeted sequencing.
In certain embodiments, a subset of nucleic acid fragments is selected prior to sequencing. In certain embodiments, hybridization-based techniques (e.g., using oligonucleotide arrays) can be used to first select for nucleic acid sequences from certain chromosomes (e.g., a potentially aneuploid chromosome and other chromosome(s) not involved in the aneuploidy tested). In some embodiments, nucleic acid can be fractionated by size (e.g., by gel electrophoresis, size exclusion chromatography or by microfluidics-based approach) and in certain instances, fetal nucleic acid can be enriched by selecting for nucleic acid having a lower molecular weight (e.g., less than 300 base pairs, less than 200 base pairs, less than 150 base pairs, less than 100 base pairs). In some embodiments, fetal nucleic acid can be enriched by suppressing maternal background nucleic acid, such as by the addition of formaldehyde. In some embodiments, a portion or subset of a pre-selected set of nucleic acid fragments is sequenced randomly. In some embodiments, the nucleic acid is amplified prior to sequencing. In some embodiments, a portion or subset of the nucleic acid is amplified prior to sequencing.
In some embodiments, a sequencing library is prepared prior to or during a sequencing process. Methods for preparing a sequencing library are known in the art and commercially available platforms may be used for certain applications. Certain commercially available library platforms may be compatible with certain nucleotide sequencing processes described herein. For example, one or more commercially available library platforms may be compatible with a sequencing by synthesis process. In some embodiments, a ligation-based library preparation method is used (e.g., ILLUMINA TRUSEQ, Illumina, San Diego Calif.). Ligation-based library preparation methods typically use a methylated adaptor design which can incorporate an index sequence at the initial ligation step and often can be used to prepare samples for single-read sequencing, paired-end sequencing and multiplexed sequencing. In some embodiments, a transposon-based library preparation method is used (e.g., EPICENTRE NEXTERA, Epicentre, Madison Wis.). Transposon-based methods typically use in vitro transposition to simultaneously fragment and tag DNA in a single-tube reaction (often allowing incorporation of platform-specific tags and optional barcodes), and prepare sequencer-ready libraries.
Any sequencing method suitable for conducting methods described herein can be utilized. In some embodiments, a high-throughput sequencing method is used. High-throughput sequencing methods generally involve clonally amplified DNA templates or single DNA molecules that are sequenced in a massively parallel fashion within a flow cell (e.g. as described in Metzker M Nature Rev 11:31-46 (2010); Volkerding et al. Clin Chem 55:641-658 (2009)). Such sequencing methods also can provide digital quantitative information, where each sequence read is a countable “sequence tag” or “count” representing an individual clonal DNA template, a single DNA molecule, bin or chromosome. Next generation sequencing techniques capable of sequencing DNA in a massively parallel fashion are collectively referred to herein as “massively parallel sequencing” (MPS). High-throughput sequencing technologies include, for example, sequencing-by-synthesis with reversible dye terminators, sequencing by oligonucleotide probe ligation, pyrosequencing and real time sequencing. Non-limiting examples of MPS include Massively Parallel Signature Sequencing (MPSS), Polony sequencing, Pyrosequencing, Illumina (Solexa) sequencing, SOLiD sequencing, Ion semiconductor sequencing, DNA nanoball sequencing, Helioscope single molecule sequencing, single molecule real time (SMRT) sequencing, nanopore sequencing, ION Torrent and RNA polymerase (RNAP) sequencing.
Systems utilized for high-throughput sequencing methods are commercially available and include, for example, the Roche 454 platform, the Applied Biosystems SOLID platform, the Helicos True Single Molecule DNA sequencing technology, the sequencing-by-hybridization platform from Affymetrix Inc., the single molecule, real-time (SMRT) technology of Pacific Biosciences, the sequencing-by-synthesis platforms from 454 Life Sciences, Illumina/Solexa and Helicos Biosciences, and the sequencing-by-ligation platform from Applied Biosystems. The ION TORRENT technology from Life technologies and nanopore sequencing also can be used in high-throughput sequencing approaches.
In some embodiments, first generation technology, such as, for example, Sanger sequencing including the automated Sanger sequencing, can be used in a method provided herein. Additional sequencing technologies that include the use of developing nucleic acid imaging technologies (e.g. transmission electron microscopy (TEM) and atomic force microscopy (AFM)), also are contemplated herein. Examples of various sequencing technologies are described below.
A nucleic acid sequencing technology that may be used in a method described herein is sequencing-by-synthesis and reversible terminator-based sequencing (e.g. Illumina's Genome Analyzer; Genome Analyzer II; HISEQ 2000; HISEQ 2500 (Illumina, San Diego Calif.)). With this technology, millions of nucleic acid (e.g. DNA) fragments can be sequenced in parallel. In one example of this type of sequencing technology, a flow cell is used which contains an optically transparent slide with 8 individual lanes on the surfaces of which are bound oligonucleotide anchors (e.g., adaptor primers). A flow cell often is a solid support that can be configured to retain and/or allow the orderly passage of reagent solutions over bound analytes. Flow cells frequently are planar in shape, optically transparent, generally in the millimeter or sub-millimeter scale, and often have channels or lanes in which the analyte/reagent interaction occurs.
In certain sequencing by synthesis procedures, for example, template DNA (e.g., circulating cell-free DNA (ccfDNA)) sometimes can be fragmented into lengths of several hundred base pairs in preparation for library generation. In some embodiments, library preparation can be performed without further fragmentation or size selection of the template DNA (e.g., ccfDNA). Sample isolation and library generation may be performed using automated methods and apparatus, in certain embodiments. Briefly, template DNA is end repaired by a fill-in reaction, exonuclease reaction or a combination of a fill-in reaction and exonuclease reaction. The resulting blunt-end repaired template DNA is extended by a single nucleotide, which is complementary to a single nucleotide overhang on the 3′ end of an adaptor primer, and often increases ligation efficiency. Any complementary nucleotides can be used for the extension/overhang nucleotides (e.g., A/T, C/G), however adenine frequently is used to extend the end-repaired DNA, and thymine often is used as the 3′ end overhang nucleotide.
In certain sequencing by synthesis procedures, for example, adaptor oligonucleotides are complementary to the flow-cell anchors, and sometimes are utilized to associate the modified template DNA (e.g., end-repaired and single nucleotide extended) with a solid support, such as the inside surface of a flow cell, for example. In some embodiments, the adaptor also includes identifiers (i.e., indexing nucleotides, or “barcode” nucleotides (e.g., a unique sequence of nucleotides usable as an identifier to allow unambiguous identification of a sample and/or chromosome)), one or more sequencing primer hybridization sites (e.g., sequences complementary to universal sequencing primers, single end sequencing primers, paired end sequencing primers, multiplexed sequencing primers, and the like), or combinations thereof (e.g., adaptor/sequencing, adaptor/identifier, adaptor/identifier/sequencing). Identifiers or nucleotides contained in an adaptor often are six or more nucleotides in length, and frequently are positioned in the adaptor such that the identifier nucleotides are the first nucleotides sequenced during the sequencing reaction. In certain embodiments, identifier nucleotides are associated with a sample but are sequenced in a separate sequencing reaction to avoid compromising the quality of sequence reads. Subsequently, the reads from the identifier sequencing and the DNA template sequencing are linked together and the reads de-multiplexed. After linking and de-multiplexing the sequence reads and/or identifiers can be further adjusted or processed as described herein.
In certain sequencing by synthesis procedures, utilization of identifiers allows multiplexing of sequence reactions in a flow cell lane, thereby allowing analysis of multiple samples per flow cell lane. The number of samples that can be analyzed in a given flow cell lane often is dependent on the number of unique identifiers utilized during library preparation and/or probe design. Non limiting examples of commercially available multiplex sequencing kits include Illumina's multiplexing sample preparation oligonucleotide kit and multiplexing sequencing primers and PhiX control kit (e.g., Illumina's catalog numbers PE-400-1001 and PE-400-1002, respectively). A method described herein can be performed using any number of unique identifiers (e.g., 4, 8, 12, 24, 48, 96, or more). The greater the number of unique identifiers, the greater the number of samples and/or chromosomes, for example, that can be multiplexed in a single flow cell lane. Multiplexing using 12 identifiers, for example, allows simultaneous analysis of 96 samples (e.g., equal to the number of wells in a 96 well microwell plate) in an 8 lane flow cell. Similarly, multiplexing using 48 identifiers, for example, allows simultaneous analysis of 384 samples (e.g., equal to the number of wells in a 384 well microwell plate) in an 8 lane flow cell.
In certain sequencing by synthesis procedures, adaptor-modified, single-stranded template DNA is added to the flow cell and immobilized by hybridization to the anchors under limiting-dilution conditions. In contrast to emulsion PCR, DNA templates can be selectively amplified in a flow cell by “bridge” amplification, which relies on captured DNA strands “arching” over and hybridizing to an adjacent anchor oligonucleotide. In some embodiments digested nucleic acid fragments are amplified by a process comprising bridge amplification. Multiple amplification cycles convert the single-molecule DNA template to a clonally amplified arching “cluster,” with each cluster containing approximately 1000 clonal molecules. Approximately 50×106 separate clusters can be generated per flow cell. For sequencing, the clusters are denatured, and a subsequent chemical cleavage reaction and wash leave only forward strands for single-end sequencing. Sequencing of the forward strands is initiated by hybridizing a primer complementary to the adaptor sequences, which is followed by addition of polymerase and a mixture of four differently colored fluorescent reversible dye terminators. The terminators are incorporated according to sequence complementarity in each strand in a clonal cluster. After incorporation, excess reagents are washed away, the clusters are optically interrogated, and the fluorescence is recorded. With successive chemical steps, the reversible dye terminators are unblocked, the fluorescent labels are cleaved and washed away, and the next sequencing cycle is performed. This iterative, sequencing-by-synthesis process sometimes requires approximately 2.5 days to generate read lengths of 36 bases. With 50×106 clusters per flow cell, the overall sequence output can be greater than 1 billion base pairs (Gb) per analytical run.
Another nucleic acid sequencing technology that may be used with a method described herein is 454 sequencing (Roche). 454 sequencing uses a large-scale parallel pyrosequencing system capable of sequencing about 400-600 megabases of DNA per run. The process typically involves two steps. In the first step, sample nucleic acid (e.g. DNA) is sometimes fractionated into smaller fragments (300-800 base pairs) and polished (made blunt at each end). Short adaptors are then ligated onto the ends of the fragments. These adaptors provide priming sequences for both amplification and sequencing of the sample-library fragments. One adaptor (Adaptor B) contains a 5′-biotin tag for immobilization of the DNA library onto streptavidin-coated beads. After nick repair, the non-biotinylated strand is released and used as a single-stranded template DNA (sstDNA) library. The sstDNA library is assessed for its quality and the optimal amount (DNA copies per bead) needed for emPCR is determined by titration. The sstDNA library is immobilized onto beads. The beads containing a library fragment carry a single sstDNA molecule. The bead-bound library is emulsified with the amplification reagents in a water-in-oil mixture. Each bead is captured within its own microreactor where PCR amplification occurs. This results in bead-immobilized, clonally amplified DNA fragments.
In the second step of 454 sequencing, single-stranded template DNA library beads are added to an incubation mix containing DNA polymerase and are layered with beads containing sulfurylase and luciferase onto a device containing pico-liter sized wells. Pyrosequencing is performed on each DNA fragment in parallel. Addition of one or more nucleotides generates a light signal that is recorded by a CCD camera in a sequencing instrument. The signal strength is proportional to the number of nucleotides incorporated. Pyrosequencing exploits the release of pyrophosphate (PPi) upon nucleotide addition. PPi is converted to ATP by ATP sulfurylase in the presence of adenosine 5′ phosphosulfate. Luciferase uses ATP to convert luciferin to oxyluciferin, and this reaction generates light that is discerned and analyzed (see, for example, Margulies, M. et al. Nature 437:376-380 (2005)).
Another nucleic acid sequencing technology that may be used in a method provided herein is Applied Biosystems' SOLiD™ technology. In SOLiD™ sequencing-by-ligation, a library of nucleic acid fragments is prepared from the sample and is used to prepare clonal bead populations. With this method, one species of nucleic acid fragment will be present on the surface of each bead (e.g. magnetic bead). Sample nucleic acid (e.g. genomic DNA) is sheared into fragments, and adaptors are subsequently attached to the 5′ and 3′ ends of the fragments to generate a fragment library. The adaptors are typically universal adaptor sequences so that the starting sequence of every fragment is both known and identical. Emulsion PCR takes place in microreactors containing all the necessary reagents for PCR. The resulting PCR products attached to the beads are then covalently bound to a glass slide. Primers then hybridize to the adaptor sequence within the library template. A set of four fluorescently labeled di-base probes compete for ligation to the sequencing primer. Specificity of the di-base probe is achieved by interrogating every 1st and 2nd base in each ligation reaction. Multiple cycles of ligation, detection and cleavage are performed with the number of cycles determining the eventual read length. Following a series of ligation cycles, the extension product is removed and the template is reset with a primer complementary to the n−1 position for a second round of ligation cycles. Often, five rounds of primer reset are completed for each sequence tag. Through the primer reset process, each base is interrogated in two independent ligation reactions by two different primers. For example, the base at read position 5 is assayed by primer number 2 in ligation cycle 2 and by primer number 3 in ligation cycle 1. Another nucleic acid sequencing technology that may be used in a method described herein is the Helicos True Single Molecule Sequencing (tSMS). In the tSMS technique, a poly-A sequence is added to the 3′ end of each nucleic acid (e.g. DNA) strand from the sample. Each strand is labeled by the addition of a fluorescently labeled adenosine nucleotide. The DNA strands are then hybridized to a flow cell, which contains millions of oligo-T capture sites that are immobilized to the flow cell surface. The templates can be at a density of about 100 million templates/cm2. The flow cell is then loaded into a sequencing apparatus and a laser illuminates the surface of the flow cell, revealing the position of each template. A CCD camera can map the position of the templates on the flow cell surface. The template fluorescent label is then cleaved and washed away. The sequencing reaction begins by introducing a DNA polymerase and a fluorescently labeled nucleotide. The oligo-T nucleic acid serves as a primer. The polymerase incorporates the labeled nucleotides to the primer in a template directed manner. The polymerase and unincorporated nucleotides are removed. The templates that have directed incorporation of the fluorescently labeled nucleotide are detected by imaging the flow cell surface. After imaging, a cleavage step removes the fluorescent label, and the process is repeated with other fluorescently labeled nucleotides until the desired read length is achieved. Sequence information is collected with each nucleotide addition step (see, for example, Harris T. D. et al., Science 320:106-109 (2008)).
Another nucleic acid sequencing technology that may be used in a method provided herein is the single molecule, real-time (SMRT™) sequencing technology of Pacific Biosciences. With this method, each of the four DNA bases is attached to one of four different fluorescent dyes. These dyes are phospholinked. A single DNA polymerase is immobilized with a single molecule of template single stranded DNA at the bottom of a zero-mode waveguide (ZMW). A ZMW is a confinement structure which enables observation of incorporation of a single nucleotide by DNA polymerase against the background of fluorescent nucleotides that rapidly diffuse in an out of the ZMW (in microseconds). It takes several milliseconds to incorporate a nucleotide into a growing strand. During this time, the fluorescent label is excited and produces a fluorescent signal, and the fluorescent tag is cleaved off. Detection of the corresponding fluorescence of the dye indicates which base was incorporated. The process is then repeated.
Additional non-limiting examples of a nucleic acid sequencing technology and/or nucleic acid amplification method that may be used herein include Avalanche™ (Life Technologies) and WildFire (e.g., Life Technologies, US patent publication US20130012399). Avalanche and WildFire are examples of sequencing technologies that utilize solid phase nucleic acid amplification reactions. In some embodiments solid phase nucleic acid amplification methods (e.g., Avalanche™ and Wildfire) produce clusters of like amplicons on a solid phase that are sometimes referred to herein as cluster generation methods.
Another nucleic acid sequencing technology that may be used in a method described herein is ION TORRENT (Life Technologies) single molecule sequencing which pairs semiconductor technology with a simple sequencing chemistry to directly translate chemically encoded information (A, C, G, T) into digital information (0, 1) on a semiconductor chip. ION TORRENT uses a high-density array of micro-machined wells to perform nucleic acid sequencing in a massively parallel way. Each well holds a different DNA molecule. Beneath the wells is an ion-sensitive layer and beneath that an ion sensor. Typically, when a nucleotide is incorporated into a strand of DNA by a polymerase, a hydrogen ion is released as a byproduct. If a nucleotide, for example a C, is added to a DNA template and is then incorporated into a strand of DNA, a hydrogen ion will be released. The charge from that ion will change the pH of the solution, which can be detected by an ion sensor. A sequencer can call the base, going directly from chemical information to digital information. The sequencer then sequentially floods the chip with one nucleotide after another. If the next nucleotide that floods the chip is not a match, no voltage change will be recorded and no base will be called. If there are two identical bases on the DNA strand, the voltage will be double, and the chip will record two identical bases called. Because this is direct detection (i.e. detection without scanning, cameras or light), each nucleotide incorporation is recorded in seconds.
Another nucleic acid sequencing technology that may be used in a method described herein is the chemical-sensitive field effect transistor (CHEMFET) array. In one example of this sequencing technique, DNA molecules are placed into reaction chambers, and the template molecules can be hybridized to a sequencing primer bound to a polymerase. Incorporation of one or more triphosphates into a new nucleic acid strand at the 3′ end of the sequencing primer can be detected by a change in current by a CHEMFET sensor. An array can have multiple CHEMFET sensors. In another example, single nucleic acids are attached to beads, and the nucleic acids can be amplified on the bead, and the individual beads can be transferred to individual reaction chambers on a CHEMFET array, with each chamber having a CHEMFET sensor, and the nucleic acids can be sequenced (see, for example, U.S. Patent Application Publication No. 2009/0026082).
Another nucleic acid sequencing technology that may be used in a method described herein is electron microscopy. In one example of this sequencing technique, individual nucleic acid (e.g. DNA) molecules are labeled using metallic labels that are distinguishable using an electron microscope. These molecules are then stretched on a flat surface and imaged using an electron microscope to measure sequences (see, for example, Moudrianakis E. N. and Beer M., PNAS USA. 1965 March; 53:564-71). In some embodiments, transmission electron microscopy (TEM) is used (e.g. Halcyon Molecular's TEM method). This method, termed Individual Molecule Placement Rapid Nano Transfer (IMPRNT), includes utilizing single atom resolution transmission electron microscope imaging of high-molecular weight (e.g. about 150 kb or greater) DNA selectively labeled with heavy atom markers and arranging these molecules on ultra-thin films in ultra-dense (3 nm strand-to-strand) parallel arrays with consistent base-to-base spacing. The electron microscope is used to image the molecules on the films to determine the position of the heavy atom markers and to extract base sequence information from the DNA (see, for example, International Patent Application No. WO 2009/046445).
Other sequencing methods that may be used to conduct methods herein include digital PCR and sequencing by hybridization. Digital polymerase chain reaction (digital PCR or dPCR) can be used to directly identify and quantify nucleic acids in a sample. Digital PCR can be performed in an emulsion, in some embodiments. For example, individual nucleic acids are separated, e.g., in a microfluidic chamber device, and each nucleic acid is individually amplified by PCR. Nucleic acids can be separated such that there is no more than one nucleic acid per well. In some embodiments, different probes can be used to distinguish various alleles (e.g. fetal alleles and maternal alleles). Alleles can be enumerated to determine copy number. In sequencing by hybridization, the method involves contacting a plurality of polynucleotide sequences with a plurality of polynucleotide probes, where each of the plurality of polynucleotide probes can be optionally tethered to a substrate. The substrate can be a flat surface with an array of known nucleotide sequences, in some embodiments. The pattern of hybridization to the array can be used to determine the polynucleotide sequences present in the sample. In some embodiments, each probe is tethered to a bead, e.g., a magnetic bead or the like. Hybridization to the beads can be identified and used to identify the plurality of polynucleotide sequences within the sample.
In some embodiments, nanopore sequencing can be used in a method described herein. Nanopore sequencing is a single-molecule sequencing technology whereby a single nucleic acid molecule (e.g. DNA) is sequenced directly as it passes through a nanopore. A nanopore is a small hole or channel, of the order of 1 nanometer in diameter. Certain transmembrane cellular proteins can act as nanopores (e.g. alpha-hemolysin). Nanopores sometimes can be synthesized (e.g. using a silicon platform). Immersion of a nanopore in a conducting fluid and application of a potential across it results in a slight electrical current due to conduction of ions through the nanopore. The amount of current which flows is sensitive to the size of the nanopore. As a DNA molecule passes through a nanopore, each nucleotide on the DNA molecule obstructs the nanopore to a different degree and generates characteristic changes to the current. The amount of current which can pass through the nanopore at any given moment therefore varies depending on whether the nanopore is blocked by an A, a C, a G, a T, or in some instances, methyl-C. The change in the current through the nanopore as the DNA molecule passes through the nanopore represents a direct reading of the DNA sequence. A nanopore sometimes can be used to identify individual DNA bases as they pass through the nanopore in the correct order (see, for example, Soni G V and Meller A. Clin. Chem. 53: 1996-2001 (2007); International Patent Application No. WO2010/004265).
There are a number of ways that nanopores can be used to sequence nucleic acid molecules. In some embodiments, an exonuclease enzyme, such as a deoxyribonuclease, is used. In this case, the exonuclease enzyme is used to sequentially detach nucleotides from a nucleic acid (e.g. DNA) molecule. The nucleotides are then detected and discriminated by the nanopore in order of their release, thus reading the sequence of the original strand. For such an embodiment, the exonuclease enzyme can be attached to the nanopore such that a proportion of the nucleotides released from the DNA molecule is capable of entering and interacting with the channel of the nanopore. The exonuclease can be attached to the nanopore structure at a site in close proximity to the part of the nanopore that forms the opening of the channel. The exonuclease enzyme sometimes can be attached to the nanopore structure such that its nucleotide exit trajectory site is orientated towards the part of the nanopore that forms part of the opening.
In some embodiments, nanopore sequencing of nucleic acids involves the use of an enzyme that pushes or pulls the nucleic acid (e.g. DNA) molecule through the pore. In this case, the ionic current fluctuates as a nucleotide in the DNA molecule passes through the pore. The fluctuations in the current are indicative of the DNA sequence. For such an embodiment, the enzyme can be attached to the nanopore structure such that it is capable of pushing or pulling a target polynucleotide through the channel of a nanopore without interfering with the flow of ionic current through the pore. The enzyme can be attached to the nanopore structure at a site in close proximity to the part of the structure that forms part of the opening. The enzyme can be attached to the subunit, for example, such that its active site is orientated towards the part of the structure that forms part of the opening.
In some embodiments, nanopore sequencing of nucleic acids involves detection of polymerase bi-products in close proximity to a nanopore detector. In this case, nucleoside phosphates (nucleotides) are labeled so that a phosphate labeled species is released upon the addition of a polymerase to the nucleotide strand and the phosphate labeled species is detected by the pore. Typically, the phosphate species contains a specific label for each nucleotide. As nucleotides are sequentially added to the nucleic acid strand, the bi-products of the base addition are detected. The order that the phosphate labeled species are detected can be used to determine the sequence of the nucleic acid strand.
The length of the sequence read is often associated with the particular sequencing technology. High-throughput methods, for example, provide sequence reads that can vary in size from tens to hundreds of base pairs (bp). Nanopore sequencing, for example, can provide sequence reads that can vary in size from tens to hundreds to thousands of base pairs. In some embodiments, the sequence reads are of a mean, median or average length of about 15 bp to 900 bp long (e.g. about 20 bp, about 25 bp, about 30 bp, about 35 bp, about 40 bp, about 45 bp, about 50 bp, about 55 bp, about 60 bp, about 65 bp, about 70 bp, about 75 bp, about 80 bp, about 85 bp, about 90 bp, about 95 bp, about 100 bp, about 110 bp, about 120 bp, about 130, about 140 bp, about 150 bp, about 200 bp, about 250 bp, about 300 bp, about 350 bp, about 400 bp, about 450 bp, or about 500 bp. In some embodiments, the sequence reads are of a mean, median, mode or average length of about 1000 bp or more.
In some embodiments, chromosome-specific sequencing is performed. In some embodiments, chromosome-specific sequencing is performed utilizing DANSR (digital analysis of selected regions). Digital analysis of selected regions enables simultaneous quantification of hundreds of loci by cfDNA-dependent catenation of two locus-specific oligonucleotides via an intervening ‘bridge’ oligo to form a PCR template. In some embodiments, chromosome-specific sequencing is performed by generating a library enriched in chromosome-specific sequences. In some embodiments, sequence reads are obtained only for a selected set of chromosomes. In some embodiments, sequence reads are obtained only for chromosomes 21, 18 and 13.
In some embodiments, nucleic acids may include a fluorescent signal or sequence tag information. Quantification of the signal or tag may be used in a variety of techniques such as, for example, flow cytometry, quantitative polymerase chain reaction (qPCR), gel electrophoresis, gene-chip analysis, microarray, mass spectrometry, cytofluorimetric analysis, fluorescence microscopy, confocal laser scanning microscopy, laser scanning cytometry, affinity chromatography, manual batch mode separation, electric field suspension, sequencing, and combination thereof.
Mapping Reads
Mapping nucleotide sequence reads (i.e., sequence information from a fragment whose physical genomic position is unknown) can be performed in a number of ways, and often comprises alignment of the obtained sequence reads with a matching sequence in a reference genome (e.g., Li et al., “Mapping short DNA sequencing reads and calling variants using mapping quality score,” Genome Res., 2008 Aug. 19.) In such alignments, sequence reads generally are aligned to a reference sequence and those that align are designated as being “mapped” or a “sequence tag.” In some embodiments, a mapped sequence read is referred to as a “hit”. In some embodiments, mapped sequence reads are grouped together according to various parameters and assigned to particular genome sections, which are discussed in further detail below.
Various computational methods can be used to map each sequence read to a genome section. Non-limiting examples of computer algorithms that can be used to align sequences include BLAST, BLITZ, and FASTA, or variations thereof. In some embodiments, the sequence reads can be found and/or aligned with sequences in nucleic acid databases known in the art including, for example, GenBank, dbEST, dbSTS, EMBL (European Molecular Biology Laboratory) and DDBJ (DNA Databank of Japan). BLAST or similar tools can be used to search the identified sequences against a sequence database. Search hits can then be used to sort the identified sequences into appropriate genome sections (described hereafter), for example.
A “sequence tag” is a nucleic acid (e.g. DNA) sequence (i.e. read) assigned specifically to a particular genome section and/or chromosome (i.e. one of chromosomes 1-22, X or Y for a human subject). A sequence tag may be repetitive or non-repetitive within a single portion of the reference genome (e.g., a chromosome). In some embodiments, repetitive sequence tags are eliminated from further analysis (e.g. quantification). In some embodiments, a read may uniquely or non-uniquely map to portions in the reference genome. A read is considered “uniquely mapped” if it aligns with a single sequence in the reference genome. A read is considered “non-uniquely mapped” if it aligns with two or more sequences in the reference genome. In some embodiments, non-uniquely mapped reads are eliminated from further analysis (e.g. quantification). A certain, small degree of mismatch (0-1) may be allowed to account for single nucleotide polymorphisms that may exist between the reference genome and the reads from individual samples being mapped, in certain embodiments. In some embodiments, no degree of mismatch is allowed for a read mapped to a reference sequence.
As used herein, a reference sequence or reference genome often is an assembled or partially assembled genomic sequence from an individual or multiple individuals. In certain embodiments, where a sample nucleic acid is from a pregnant female, a reference sequence sometimes is not from the fetus, the mother of the fetus or the father of the fetus, and is referred to herein as an “external reference.” A maternal reference may be prepared and used in some embodiments. When a reference from the pregnant female is prepared (“maternal reference sequence”) based on an external reference, reads from DNA of the pregnant female that contains substantially no fetal DNA often are mapped to the external reference sequence and assembled. In certain embodiments the external reference is from DNA of an individual having substantially the same ethnicity as the pregnant female. A maternal reference sequence may not completely cover the maternal genomic DNA (e.g., it may cover about 50%, 60%, 70%, 80%, 90% or more of the maternal genomic DNA), and the maternal reference may not perfectly match the maternal genomic DNA sequence (e.g., the maternal reference sequence may include multiple mismatches).
Genomic Sections
In some embodiments, mapped sequence reads (i.e. sequence tags) are grouped together according to various parameters and assigned to particular genomic sections. Often, the individual mapped sequence reads can be used to identify an amount of a genomic section present in a sample. In some embodiments, the amount of a genomic section can be indicative of the amount of a larger sequence (e.g. a chromosome) in the sample. The term “genomic section” can also be referred to herein as a “sequence window”, “section”, “bin”, “locus”, “region”, “partition”, “portion” (e.g., portion of a reference genome, portion of a chromosome) or “genomic portion.” In some embodiments, a genomic section is an entire chromosome, portion of a chromosome, portion of a reference genome, multiple chromosome portions, multiple chromosomes, portions from multiple chromosomes, and/or combinations thereof. In some embodiments, a genomic section is predefined based on specific parameters. In some embodiments, a genomic section is arbitrarily defined based on partitioning of a genome (e.g., partitioned by size, portions, contiguous regions, contiguous regions of an arbitrarily defined size, and the like).
In some embodiments, a genomic section is delineated based on one or more parameters which include, for example, length or a particular feature or features of the sequence. Genomic sections can be selected, filtered and/or removed from consideration using any suitable criteria know in the art or described herein. In some embodiments, a genomic section is based on a particular length of genomic sequence. In some embodiments, a method can include analysis of multiple mapped sequence reads to a plurality of genomic sections. Genomic sections can be approximately the same length or the genomic sections can be different lengths. In some embodiments, genomic sections are of about equal length. In some embodiments genomic sections of different lengths are adjusted or weighted. In some embodiments, a genomic section is about 10 kilobases (kb) to about 100 kb, about 20 kb to about 80 kb, about 30 kb to about 70 kb, about 40 kb to about 60 kb, and sometimes about 50 kb. In some embodiments, a genomic section is about 10 kb to about 20 kb. A genomic section is not limited to contiguous runs of sequence. Thus, genomic sections can be made up of contiguous and/or non-contiguous sequences. A genomic section is not limited to a single chromosome. In some embodiments, a genomic section includes all or part of one chromosome or all or part of two or more chromosomes. In some embodiments, genomic sections may span one, two, or more entire chromosomes. In addition, the genomic sections may span joint or disjointed portions of multiple chromosomes.
In some embodiments, genomic sections can be particular chromosome portion in a chromosome of interest, such as, for example, chromosomes where a genetic variation is assessed (e.g. an aneuploidy of chromosomes 13, 18 and/or 21 or a sex chromosome). A genomic section can also be a pathogenic genome (e.g. bacterial, fungal or viral) or fragment thereof. Genomic sections can be genes, gene fragments, regulatory sequences, introns, exons, and the like.
In some embodiments, a genome (e.g. human genome) is partitioned into genomic sections based on the information content of the regions. The resulting genomic regions may contain sequences for multiple chromosomes and/or may contain sequences for portions of multiple chromosomes. In some embodiments, the partitioning may eliminate similar locations across the genome and only keep unique regions. The eliminated regions may be within a single chromosome or may span multiple chromosomes. The resulting genome is thus trimmed down and optimized for faster alignment, often allowing for focus on uniquely identifiable sequences.
In some embodiments, the partitioning may down weight similar regions. The process for down weighting a genomic section is discussed in further detail below. In some embodiments, the partitioning of the genome into regions transcending chromosomes may be based on information gain produced in the context of classification. For example, the information content may be quantified using the p-value profile measuring the significance of particular genomic locations for distinguishing between groups of confirmed normal and abnormal subjects (e.g. euploid and trisomy subjects, respectively). In some embodiments, the partitioning of the genome into regions transcending chromosomes may be based on any other criterion, such as, for example, speed/convenience while aligning tags, high or low GC content, uniformity of GC content, other measures of sequence content (e.g. fraction of individual nucleotides, fraction of pyrimidines or purines, fraction of natural vs. non-natural nucleic acids, fraction of methylated nucleotides, and CpG content), methylation state, duplex melting temperature, amenability to sequencing or PCR, uncertainty value assigned to individual bins, and/or a targeted search for particular features. A “segment” of a chromosome generally is part of a chromosome, and typically is a different part of a chromosome than a genomic section (e.g., bin). A segment of a chromosome sometimes is in a different region of a chromosome than a genomic section, sometimes does not share a polynucleotide with a genomic section, and sometimes includes a polynucleotide that is in a genomic section. A segment of a chromosome often contains a larger number of nucleotides than a genomic section (e.g., a segment sometimes includes a genomic section), and sometimes a segment of a chromosome contains a smaller number of nucleotides than a genomic section (e.g., a segment sometimes is within a genomic section).
Outcomes and Determination of the Presence or Absence of a Genetic Variation
Some genetic variations are associated with medical conditions. Genetic variations often include a gain, a loss, and/or alteration (e.g., reorganization or substitution) of genetic information (e.g., chromosomes, portions of chromosomes, polymorphic regions, translocated regions, altered nucleotide sequence, the like or combinations of the foregoing) that result in a detectable change in the genome or genetic information of a test subject with respect to a reference subject free of the genetic variation. The presence or absence of a genetic variation can be determined by analyzing and/or manipulating enriched nucleic acids. In some embodiments, the presence or absence of a genetic variation can be determined by analyzing and/or manipulating sequence reads that have been mapped to genomic sections (e.g., genomic bins) as described herein.
An analysis can be a target-based analysis (e.g., targeted analysis) or a non-target-based analysis (e.g., non-targeted). A target-based analysis generally comprises analysis (e.g., sequencing, quantitation) of selected nucleic acids or a selected subset of nucleic acids (e.g., a subpopulation of nucleic acids). In some embodiments a selective nucleic acid subset comprises selected genes, selected loci (e.g., hypomethylated loci, hypermethylated loci), selected alleles (e.g., selected polymorphisms), nucleic acids derived from one or more selected chromosomes, selected fetal nucleic acids, the like or combinations thereof. In some embodiments a target-bases analysis comprises a suitable target specific amplification or sequencing method. A target-based analysis generally comprises use of one or more sequence-specific oligonucleotides (e.g., primers or capture agents) that hybridize to specific selected nucleic acid sequences that are expected and/or known to exist in a test sample (e.g., an unmanipulated sample isolated from a test subject). A non-target-based analysis generally does not comprise a sequence-specific selection process or utilizes oligonucleotides that hybridize to specific selected nucleic acid sequences that are expected and/or known to exist in a test sample. In some embodiments a non-target-based analysis utilizes adaptors and/or adaptor specific primers to amplify and/or sequence nucleic acids or a subset of nucleic acids in a test sample. For example, a non-target-based analysis sometimes comprises ligation of adaptors and/or hybridization of primers to sticky ends that results from restriction enzyme cleavage followed by a suitable capture, primer extension, amplification and/or sequencing method.
Sequence reads that have been mapped or partitioned based on a selected feature or variable can be quantified to determine the number of reads that were mapped to each genomic section (e.g., bin, partition, genomic segment and the like), in some embodiments. In certain embodiments, the total number of mapped sequence reads is determined by counting all mapped sequence reads, and in some embodiments the total number of mapped sequence reads is determined by summing counts mapped to each bin or partition. In certain embodiments, a subset of mapped sequence reads is determined by counting a predetermined subset of mapped sequence reads, and in some embodiments a predetermined subset of mapped sequence reads is determined by summing counts mapped to each predetermined bin or partition. In some embodiments, predetermined subsets of mapped sequence reads can include from 1 to n−1 sequence reads, where n represents a number equal to the sum of all sequence reads generated from a test subject or reference subject sample. In certain embodiments, predetermined subsets of mapped sequence reads can be selected utilizing any suitable feature or variable.
Quantifying or counting sequence reads can be done in any suitable manner including but not limited to manual counting methods and automated counting methods. In some embodiments, an automated counting method can be embodied in software that determines or counts the number of sequence reads or sequence tags mapping to each chromosome and/or one or more selected genomic sections. As used herein, software refers to computer readable program instructions that, when executed by a computer, perform computer operations.
The number of sequence reads mapped to each bin and the total number of sequence reads for samples derived from test subject and/or reference subjects can be further analyzed and processed to provide an outcome determinative of the presence or absence of a genetic variation. Mapped sequence reads that have been counted sometimes are referred to as “data” or “data sets”. In some embodiments, data or data sets can be characterized by one or more features or variables (e.g., sequence based [e.g., GC content, specific nucleotide sequence, the like], function specific [e.g., expressed genes, cancer genes, the like], location based [genome specific, chromosome specific, genomic section or bin specific], the like and combinations thereof). In certain embodiments, data or data sets can be organized into a matrix having two or more dimensions based on one or more features of variables. Data organized into matrices can be stratified using any suitable features or variables. A non-limiting example of data organized into a matrix includes data that is stratified by maternal age, maternal ploidy, and fetal contribution. In certain embodiments, data sets characterized by one or more features or variables sometimes are processed after counting.
In some embodiments nucleic acids are analyzed. Sometimes enriched nucleic acids, digested nucleic acids, ligated nucleic acids and/or amplified nucleic acids are analyzed. In some embodiments analyzing nucleic acids comprises generating sequencing reads, mapping sequence reads, counting sequencing reads, processing sequencing reads, processing sequencing counts or a combination thereof.
Data Processing
Mapped sequence reads that have been counted are referred to herein as raw data, since the data represent unmanipulated counts (e.g., raw counts). In some embodiments, sequence read data in a data set can be processed further (e.g., mathematically and/or statistically manipulated) and/or displayed to facilitate providing an outcome. In certain embodiments, data sets, including larger data sets, may benefit from pre-processing to facilitate further analysis. Pre-processing of data sets sometimes involves removal of redundant and/or uninformative genomic sections or bins (e.g., bins with uninformative data, redundant mapped reads, genomic sections or bins with zero median counts, over represented or under represented sequences). Without being limited by theory, data processing and/or preprocessing may (i) remove noisy data, (ii) remove uninformative data, (iii) remove redundant data, (iv) reduce the complexity of larger data sets, and/or (v) facilitate transformation of the data from one form into one or more other forms. The terms “pre-processing” and “processing” when utilized with respect to data or data sets are collectively referred to herein as “processing”. Processing can render data more amenable to further analysis, and can generate an outcome in some embodiments.
The term “noisy data” as used herein refers to (a) data that has a significant variance between data points when analyzed or plotted, (b) data that has a significant standard deviation, (c) data that has a significant standard error of the mean, the like, and combinations of the foregoing. Noisy data sometimes occurs due to the quantity and/or quality of starting material (e.g., nucleic acid sample), and sometimes occurs as part of processes for preparing or replicating DNA used to generate sequence reads. In certain embodiments, noise results from certain sequences being over represented when prepared using PCR-based methods. Methods described herein can reduce or eliminate the contribution of noisy data, and therefore reduce the effect of noisy data on the provided outcome.
The terms “uninformative data”, “uninformative bins”, and “uninformative genomic sections” as used herein refer to genomic sections, or data derived therefrom, having a numerical value that is significantly different from a predetermined cutoff threshold value or falls outside a predetermined cutoff range of values. A cutoff threshold value or range of values often is calculated by mathematically and/or statistically manipulating sequence read data (e.g., from a reference and/or subject), in some embodiments, and in certain embodiments, sequence read data manipulated to generate a threshold cutoff value or range of values is sequence read data (e.g., from a reference and/or subject). In some embodiments, a threshold cutoff value is obtained by calculating the standard deviation and/or median absolute deviation (e.g., MAD) of a raw or normalized count profile and multiplying the standard deviation for the profile by a constant representing the number of standard deviations chosen as a cutoff threshold (e.g., multiply by 3 for 3 standard deviations), whereby a value for an uncertainty is generated. In certain embodiments, a portion or all of the genomic sections exceeding the calculated uncertainty threshold cutoff value, or outside the range of threshold cutoff values, are removed as part of, prior to, or after the normalization process. In some embodiments, a portion or all of the genomic sections exceeding the calculated uncertainty threshold cutoff value, or outside the range of threshold cutoff values or raw data points, are weighted as part of, or prior to the normalization or classification process. Examples of weighting are described herein. The terms “redundant data”, and “redundant mapped reads” as used herein refer to sample derived sequences reads that are identified as having already been assigned to a genomic location (e.g., base position) and/or counted for a genomic section.
Any suitable procedure can be utilized for processing data sets described herein. Non-limiting examples of procedures suitable for use for processing data sets include filtering, normalizing, weighting, monitoring peak heights, monitoring peak areas, monitoring peak edges, determining area ratios, mathematical processing of data, statistical processing of data, application of statistical algorithms, analysis with fixed variables, analysis with optimized variables, plotting data to identify patterns or trends for additional processing, the like and combinations of the foregoing. In some embodiments, data sets are processed based on various features (e.g., GC content, redundant mapped reads, centromere regions, telomere regions, the like and combinations thereof) and/or variables (e.g., fetal gender, maternal age, maternal ploidy, percent contribution of fetal nucleic acid, the like or combinations thereof). In certain embodiments, processing data sets as described herein can reduce the complexity and/or dimensionality of large and/or complex data sets. A non-limiting example of a complex data set includes sequence read data generated from one or more test subjects and a plurality of reference subjects of different ages and ethnic backgrounds. In some embodiments, data sets can include from thousands to millions of sequence reads for each test and/or reference subject.
Data processing can be performed in any number of steps, in certain embodiments. For example, data may be processed using only a single processing procedure in some embodiments, and in certain embodiments data may be processed using 1 or more, 5 or more, 10 or more or 20 or more processing steps (e.g., 1 or more processing steps, 2 or more processing steps, 3 or more processing steps, 4 or more processing steps, 5 or more processing steps, 6 or more processing steps, 7 or more processing steps, 8 or more processing steps, 9 or more processing steps, 10 or more processing steps, 11 or more processing steps, 12 or more processing steps, 13 or more processing steps, 14 or more processing steps, 15 or more processing steps, 16 or more processing steps, 17 or more processing steps, 18 or more processing steps, 19 or more processing steps, or 20 or more processing steps). In some embodiments, processing steps may be the same step repeated two or more times (e.g., filtering two or more times, normalizing two or more times), and in certain embodiments, processing steps may be two or more different processing steps (e.g., filtering, normalizing; normalizing, monitoring peak heights and edges; filtering, normalizing, normalizing to a reference, statistical manipulation to determine p-values, and the like), carried out simultaneously or sequentially. In some embodiments, any suitable number and/or combination of the same or different processing steps can be utilized to process sequence read data to facilitate providing an outcome. In certain embodiments, processing data sets by the criteria described herein may reduce the complexity and/or dimensionality of a data set. In some embodiments, one or more processing steps can comprise one or more filtering steps. The term “filtering” as used herein refers to removing genomic sections or bins from consideration. Bins can be selected for removal based on any suitable criteria, including but not limited to redundant data (e.g., redundant or overlapping mapped reads), non-informative data (e.g., bins with zero median counts), bins with over represented or under represented sequences, noisy data, the like, or combinations of the foregoing. A filtering process often involves removing one or more bins from consideration and subtracting the counts in the one or more bins selected for removal from the counted or summed counts for the bins, chromosome or chromosomes, or genome under consideration. In some embodiments, bins can be removed successively (e.g., one at a time to allow evaluation of the effect of removal of each individual bin), and in certain embodiments all bins marked for removal can be removed at the same time.
In some embodiments, one or more processing steps can comprise one or more normalization steps. The term “normalization” as used herein refers to division of one or more data sets by a predetermined variable. Any suitable number of normalizations can be used. In some embodiments, data sets can be normalized 1 or more, 5 or more, 10 or more or even 20 or more times. Data sets can be normalized to values (e.g., normalizing value) representative of any suitable feature or variable (e.g., sample data, reference data, or both). Non-limiting examples of types of data normalizations that can be used include normalizing raw count data for one or more selected test or reference genomic sections to the total number of counts mapped to the chromosome or the entire genome on which the selected genomic section or sections are mapped; normalizing raw count data for one or more selected genomic segments to a median reference count for one or more genomic sections or the chromosome on which a selected genomic segment or segments is mapped; normalizing raw count data to previously normalized data or derivatives thereof; and normalizing previously normalized data to one or more other predetermined normalization variables. Normalizing a data set sometimes has the effect of isolating statistical error, depending on the feature or property selected as the predetermined normalization variable. Normalizing a data set sometimes also allows comparison of data characteristics of data having different scales, by bringing the data to a common scale (e.g., predetermined normalization variable). In some embodiments, one or more normalizations to a statistically derived value can be utilized to minimize data differences and diminish the importance of outlying data.
In some embodiments, a processing step comprises a weighting. The terms “weighted”, “weighting” or “weight function” or grammatical derivatives or equivalents thereof, as used herein, refer to a mathematical manipulation of a portion or all of a data set sometimes utilized to alter the influence of certain data set features or variables with respect to other data set features or variables (e.g., increase or decrease the significance and/or contribution of data contained in one or more genomic sections or bins, based on the quality or usefulness of the data in the selected bin or bins). A weighting function can be used to increase the influence of data with a relatively small measurement variance, and/or to decrease the influence of data with a relatively large measurement variance, in some embodiments. For example, bins with under represented or low quality sequence data can be “down weighted” to minimize the influence on a data set, whereas selected bins can be “up weighted” to increase the influence on a data set. A non-limiting example of a weighting function is [1/(standard deviation)2]. A weighting step sometimes is performed in a manner substantially similar to a normalizing step. In some embodiments, a data set is divided by a predetermined variable (e.g., weighting variable). A predetermined variable (e.g., minimized target function, Phi) often is selected to weigh different parts of a data set differently (e.g., increase the influence of certain data types while decreasing the influence of other data types).
In certain embodiments, a processing step can comprise one or more mathematical and/or statistical manipulations. Any suitable mathematical and/or statistical manipulation, alone or in combination, may be used to analyze and/or manipulate a data set described herein. Any suitable number of mathematical and/or statistical manipulations can be used. In some embodiments, a data set can be mathematically and/or statistically manipulated 1 or more, 5 or more, 10 or more or 20 or more times. Non-limiting examples of mathematical and statistical manipulations that can be used include addition, subtraction, multiplication, division, algebraic functions, least squares estimators, curve fitting, differential equations, rational polynomials, double polynomials, orthogonal polynomials, z-scores, p-values, chi values, phi values, analysis of peak elevations, determination of peak edge locations, calculation of peak area ratios, analysis of median chromosomal elevation, calculation of mean absolute deviation, sum of squared residuals, mean, standard deviation, standard error, the like or combinations thereof. A mathematical and/or statistical manipulation can be performed on all or a portion of sequence read data, or processed products thereof. Non-limiting examples of data set variables or features that can be statistically manipulated include raw counts, filtered counts, normalized counts, peak heights, peak widths, peak areas, peak edges, lateral tolerances, P-values, median elevations, mean elevations, count distribution within a genomic region, relative representation of nucleic acid species, the like or combinations thereof.
In some embodiments, a processing step can include the use of one or more statistical algorithms. Any suitable statistical algorithm, alone or in combination, may be used to analyze and/or manipulate a data set described herein. Any suitable number of statistical algorithms can be used. In some embodiments, a data set can be analyzed using 1 or more, 5 or more, 10 or more or 20 or more statistical algorithms. Non-limiting examples of statistical algorithms suitable for use with methods described herein include decision trees, counternulls, multiple comparisons, omnibus test, Behrens-Fisher problem, bootstrapping, Fisher's method for combining independent tests of significance, null hypothesis, type I error, type II error, exact test, one-sample Z test, two-sample Z test, one-sample t-test, paired t-test, two-sample pooled t-test having equal variances, two-sample unpooled t-test having unequal variances, one-proportion z-test, two-proportion z-test pooled, two-proportion z-test unpooled, one-sample chi-square test, two-sample F test for equality of variances, confidence interval, credible interval, significance, meta analysis, simple linear regression, robust linear regression, the like or combinations of the foregoing. Non-limiting examples of data set variables or features that can be analyzed using statistical algorithms include raw counts, filtered counts, normalized counts, peak heights, peak widths, peak edges, lateral tolerances, P-values, median elevations, mean elevations, count distribution within a genomic region, relative representation of nucleic acid species, the like or combinations thereof.
In certain embodiments, a data set can be analyzed by utilizing multiple (e.g., 2 or more) statistical algorithms (e.g., least squares regression, principle component analysis, linear discriminant analysis, quadratic discriminant analysis, bagging, neural networks, support vector machine models, random forests, classification tree models, K-nearest neighbors, logistic regression and/or loss smoothing) and/or mathematical and/or statistical manipulations (e.g., referred to herein as manipulations). The use of multiple manipulations can generate an N-dimensional space that can be used to provide an outcome, in some embodiments. In certain embodiments, analysis of a data set by utilizing multiple manipulations can reduce the complexity and/or dimensionality of the data set. For example, the use of multiple manipulations on a reference data set can generate an N-dimensional space (e.g., probability plot) that can be used to represent the presence or absence of a genetic variation, depending on the genetic status of the reference samples (e.g., positive or negative for a selected genetic variation). Analysis of test samples using a substantially similar set of manipulations can be used to generate an N-dimensional point for each of the test samples. The complexity and/or dimensionality of a test subject data set sometimes is reduced to a single value or N-dimensional point that can be readily compared to the N-dimensional space generated from the reference data. Test sample data that fall within the N-dimensional space populated by the reference subject data are indicative of a genetic status substantially similar to that of the reference subjects. Test sample data that fall outside of the N-dimensional space populated by the reference subject data are indicative of a genetic status substantially dissimilar to that of the reference subjects. In some embodiments, references are euploid or do not otherwise have a genetic variation or medical condition.
In some embodiments, a processing step can comprise generating one or more profiles (e.g., profile plot) from various aspects of a data set or derivation thereof (e.g., product of one or more mathematical and/or statistical data processing steps known in the art and/or described herein). The term “profile” as used herein refers to mathematical and/or statistical manipulation of data that facilitates identification of patterns and/or correlations in large quantities of data. Thus, the term “profile” as used herein often refers to values resulting from one or more manipulations of data or data sets, based on one or more criteria. A profile often includes multiple data points. Any suitable number of data points may be included in a profile depending on the nature and/or complexity of a data set. In certain embodiments, profiles may include 2 or more data points, 3 or more data points, 5 or more data points, 10 or more data points, 24 or more data points, 25 or more data points, 50 or more data points, 100 or more data points, 500 or more data points, 1000 or more data points, 5000 or more data points, 10,000 or more data points, or 100,000 or more data points.
In some embodiments, a profile is representative of the entirety of a data set, and in certain embodiments, a profile is representative of a portion or subset of a data set. That is, a profile sometimes includes or is generated from data points representative of data that has not been filtered to remove any data, and sometimes a profile includes or is generated from data points representative of data that has been filtered to remove unwanted data. In some embodiments, a data point in a profile represents the results of data manipulation for a genomic section. In certain embodiments, a data point in a profile represents the results of data manipulation for groups of genomic sections. In some embodiments, groups of genomic sections may be adjacent to one another, and in certain embodiments, groups of genomic sections may be from different parts of a chromosome or genome.
Data points in a profile derived from a data set can be representative of any suitable data categorization. Non-limiting examples of categories into which data can be grouped to generate profile data points include: genomic sections based on sized, genomic sections based on sequence features (e.g., GC content, AT content, position on a chromosome (e.g., short arm, long arm, centromere, telomere), and the like), levels of expression, chromosome, the like or combinations thereof. In some embodiments, a profile may be generated from data points obtained from another profile (e.g., normalized data profile renormalized to a different normalizing value to generate a renormalized data profile). In certain embodiments, a profile generated from data points obtained from another profile reduces the number of data points and/or complexity of the data set. Reducing the number of data points and/or complexity of a data set often facilitates interpretation of data and/or facilitates providing an outcome.
A profile frequently is presented as a plot, and non-limiting examples of profile plots that can be generated include raw count (e.g., raw count profile or raw profile), normalized count (e.g., normalized count profile or normalized profile), bin-weighted, z-score, p-value, area ratio versus fitted ploidy, median elevation versus ratio between fitted and measured fetal fraction, principle components, the like, or combinations thereof. Profile plots allow visualization of the manipulated data, in some embodiments. In certain embodiments, a profile plot can be utilized to provide an outcome (e.g., area ratio versus fitted ploidy, median elevation versus ratio between fitted and measured fetal fraction, principle components). The terms “raw count profile plot” or “raw profile plot” as used herein refer to a plot of counts in each genomic section in a region normalized to total counts in a region (e.g., genome, chromosome, portion of chromosome).
A profile generated for a test subject sometimes is compared to a profile generated for one or more reference subjects, to facilitate interpretation of mathematical and/or statistical manipulations of a data set and/or to provide an outcome. In some embodiments, a profile is generated based on one or more starting assumptions (e.g., maternal contribution of nucleic acid (e.g., maternal fraction), fetal contribution of nucleic acid (e.g., fetal fraction), ploidy of reference sample, the like or combinations thereof). In certain embodiments, a test profile often centers around a predetermined value representative of the absence of a genetic variation, and often deviates from a predetermined value in areas corresponding to the genomic location in which the genetic variation is located in the test subject, if the test subject possessed the genetic variation. In test subjects at risk for, or suffering from a medical condition associated with a genetic variation, the numerical value for a selected genomic section is expected to vary significantly from the predetermined value for non-affected genomic locations. Depending on starting assumptions (e.g., fixed ploidy or optimized ploidy, fixed fetal fraction or optimized fetal fraction or combinations thereof) the predetermined threshold or cutoff value or range of values indicative of the presence or absence of a genetic variation can vary while still providing an outcome useful for determining the presence or absence of a genetic variation. In some embodiments, a profile is indicative of and/or representative of a phenotype.
By way of a non-limiting example, normalized sample and/or reference count profiles can be obtained from raw sequence read data by (a) calculating reference median counts for selected chromosomes, genomic sections or portions thereof from a set of references known not to carry a genetic variation, (b) removal of uninformative genomic sections from the reference sample raw counts (e.g., filtering); (c) normalizing the reference counts for all remaining bins to the total residual number of counts (e.g., sum of remaining counts after removal of uninformative bins) for the reference sample selected chromosome or selected genomic location, thereby generating a normalized reference subject profile; (d) removing the corresponding genomic sections from the test subject sample; and (e) normalizing the remaining test subject counts for one or more selected genomic locations to the sum of the residual reference median counts for the chromosome or chromosomes containing the selected genomic locations, thereby generating a normalized test subject profile. In certain embodiments, an additional normalizing step with respect to the entire genome, reduced by the filtered genomic sections in (b), can be included between (c) and (d).
In some embodiments, the use of one or more reference samples known to be free of a genetic variation in question can be used to generate a reference median count profile, which may result in a predetermined value representative of the absence of the genetic variation, and often deviates from a predetermined value in areas corresponding to the genomic location in which the genetic variation is located in the test subject, if the test subject possessed the genetic variation. In test subjects at risk for, or suffering from a medical condition associated with a genetic variation, the numerical value for the selected genomic section or sections is expected to vary significantly from the predetermined value for non-affected genomic locations. In certain embodiments, the use of one or more reference samples known to carry the genetic variation in question can be used to generate a reference median count profile, which may result in a predetermined value representative of the presence of the genetic variation, and often deviates from a predetermined value in areas corresponding to the genomic location in which a test subject does not carry the genetic variation. In test subjects not at risk for, or suffering from a medical condition associated with a genetic variation, the numerical value for the selected genomic section or sections is expected to vary significantly from the predetermined value for affected genomic locations.
In some embodiments, analysis and processing of data can include the use of one or more assumptions. Any suitable number or type of assumptions can be utilized to analyze or process a data set. Non-limiting examples of assumptions that can be used for data processing and/or analysis include maternal ploidy, fetal contribution, prevalence of certain sequences in a reference population, ethnic background, prevalence of a selected medical condition in related family members, parallelism between raw count profiles from different patients and/or runs after GC-normalization and repeat masking (e.g., GCRM), identical matches represent PCR artifacts (e.g., identical base position), assumptions inherent in a fetal quantifier assay (e.g., FQA), assumptions regarding twins (e.g., if 2 twins and only 1 is affected the effective fetal fraction is only 50% of the total measured fetal fraction (similarly for triplets, quadruplets and the like)), fetal cell free DNA (e.g., cfDNA) uniformly covers the entire genome, the like and combinations thereof.
In those instances where the quality and/or depth of mapped sequence reads does not permit an outcome prediction of the presence or absence of a genetic variation at a desired confidence level (e.g., 95% or higher confidence level), based on the normalized count profiles, one or more additional mathematical manipulation algorithms and/or statistical prediction algorithms, can be utilized to generate additional numerical values useful for data analysis and/or providing an outcome. The term “normalized count profile” as used herein refers to a profile generated using normalized counts. Examples of methods that can be used to generate normalized counts and normalized count profiles are described herein. As noted, mapped sequence reads that have been counted can be normalized with respect to test sample counts or reference sample counts. In some embodiments, a normalized count profile can be presented as a plot.
As noted above, data sometimes is transformed from one form into another form. The terms “transformed”, “transformation”, and grammatical derivations or equivalents thereof, as used herein refer to an alteration of data from a physical starting material (e.g., test subject and/or reference subject sample nucleic acid) into a digital representation of the physical starting material (e.g., sequence read data), and in some embodiments includes a further transformation into one or more numerical values or graphical representations of the digital representation that can be utilized to provide an outcome. In certain embodiments, the one or more numerical values and/or graphical representations of digitally represented data can be utilized to represent the appearance of a test subject's physical genome (e.g., virtually represent or visually represent the presence or absence of a genomic insertion or genomic deletion; represent the presence or absence of a variation in the physical amount of a sequence associated with medical conditions). A virtual representation sometimes is further transformed into one or more numerical values or graphical representations of the digital representation of the starting material. These procedures can transform physical starting material into a numerical value or graphical representation, or a representation of the physical appearance of a test subject's genome.
In some embodiments, transformation of a data set facilitates providing an outcome by reducing data complexity and/or data dimensionality. Data set complexity sometimes is reduced during the process of transforming a physical starting material into a virtual representation of the starting material (e.g., sequence reads representative of physical starting material). Any suitable feature or variable can be utilized to reduce data set complexity and/or dimensionality. Non-limiting examples of features that can be chosen for use as a target feature for data processing include GC content, fetal gender prediction, identification of chromosomal aneuploidy, identification of particular genes or proteins, identification of cancer, diseases, inherited genes/traits, chromosomal abnormalities, a biological category, a chemical category, a biochemical category, a category of genes or proteins, a gene ontology, a protein ontology, co-regulated genes, cell signaling genes, cell cycle genes, proteins pertaining to the foregoing genes, gene variants, protein variants, co-regulated genes, co-regulated proteins, amino acid sequence, nucleotide sequence, protein structure data and the like, and combinations of the foregoing. Non-limiting examples of data set complexity and/or dimensionality reduction include; reduction of a plurality of sequence reads to profile plots, reduction of a plurality of sequence reads to numerical values (e.g., normalized values, Z-scores, p-values); reduction of multiple analysis methods to probability plots or single points; principle component analysis of derived quantities; and the like or combinations thereof.
Mass Spectrometry
In some embodiments a mass spectrometer is used to analyze nucleic acids and/or enriched nucleic acids (e.g., enriched fetal or maternal nucleic acids). Analysis of nucleic acids by a mass spectrometer can be a target-based analysis or a non-target based analysis. In some embodiments a mass spectrometer is used quantify nucleic acids and/or specific subsets (e.g., subpopulations) of nucleic acids. In some embodiments a mass spectrometer is used to detect, measure and/or quantify an identifier (e.g., a sequence tag, a label, a mass tag) associated with a selected subset or subpopulation of nucleic acids or associated with a specific target polynucleotide. In some embodiments detection, identification and/or quantitation of a target polynucleotide (e.g., a specific polynucleotide, a target comprising a tag) is determined by mass spectrometry (e.g., by a target-based analysis). In certain embodiments, a sequence of an oligonucleotide or polynucleotide is determined by a mass spectrometer. Mass spectrometry methods typically are used to determine the mass of a molecule, such as a nucleic acid fragment, sequence tag or an identifier. In some embodiments, the length and/or the sequence of a nucleic acid fragment (e.g., a sequence tag) can be extrapolated from the mass of a fragment, tag or a fragment comprising a tag. In some embodiments, the length and/or the sequence of a first nucleic acid fragment and/or a first sequence tag can be extrapolated from the mass of a second nucleic acid fragment that hybridizes to the first fragment or tag. In some embodiments, presence of a target and/or reference nucleic acid of a given length and/or sequence can be verified by comparing the mass of the detected signal with the expected mass of the target and/or a reference fragment. The relative signal strength, e.g., mass peak on a spectra, for a particular nucleic acid fragment and/or fragment length sometimes can indicate the relative population of the fragment species amongst other nucleic acids in a sample (see e.g., Jurinke et al. (2004) Mol. Biotechnol. 26, 147-164).
Mass spectrometry generally works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios. A typical mass spectrometry procedure involves several steps, including (1) loading a sample onto the mass spectrometry instrument followed by vaporization, (2) ionization of the sample components by any one of a variety of methods (e.g., impacting with an electron beam), resulting in charged particles (ions), (3) separation of ions according to their mass-to-charge ratio in an analyzer by electromagnetic fields, (4) detection of ions (e.g., by a quantitative method), and (5) processing of the ion signal into mass spectra.
Mass spectrometry methods are well known in the art (see, e.g., Burlingame et al. Anal. Chem. 70:647R-716R (1998)), and include, for example, quadrupole mass spectrometry, ion trap mass spectrometry, time-of-flight mass spectrometry, gas chromatography mass spectrometry and tandem mass spectrometry can be used with the methods described herein. The basic processes associated with a mass spectrometry method are the generation of gas-phase ions derived from the sample, and the measurement of their mass. The movement of gas-phase ions can be precisely controlled using electromagnetic fields generated in the mass spectrometer. The movement of ions in these electromagnetic fields is proportional to the m/z (mass to charge ratio) of the ion and this forms the basis of measuring the m/z and therefore the mass of a sample. The movement of ions in these electromagnetic fields allows for the containment and focusing of the ions which accounts for the high sensitivity of mass spectrometry. During the course of m/z measurement, ions are transmitted with high efficiency to particle detectors that record the arrival of these ions. The quantity of ions at each m/z is demonstrated by peaks on a graph where the x axis is m/z and the y axis is relative abundance. Different mass spectrometers have different levels of resolution, that is, the ability to resolve peaks between ions closely related in mass. The resolution is defined as R=m/delta m, where m is the ion mass and delta m is the difference in mass between two peaks in a mass spectrum. For example, a mass spectrometer with a resolution of 1000 can resolve an ion with a m/z of 100.0 from an ion with a m/z of 100.1. Certain mass spectrometry methods can utilize various combinations of ion sources and mass analyzers which allows for flexibility in designing customized detection protocols. In some embodiments, mass spectrometers can be programmed to transmit all ions from the ion source into the mass spectrometer either sequentially or at the same time. In some embodiments, a mass spectrometer can be programmed to select ions of a particular mass for transmission into the mass spectrometer while blocking other ions.
Several types of mass spectrometers are available or can be produced with various configurations. In general, a mass spectrometer has the following major components: a sample inlet, an ion source, a mass analyzer, a detector, a vacuum system, and instrument-control system, and a data system. Difference in the sample inlet, ion source, and mass analyzer generally define the type of instrument and its capabilities. For example, an inlet can be a capillary-column liquid chromatography source or can be a direct probe or stage such as used in matrix-assisted laser desorption. Common ion sources are, for example, electrospray, including nanospray and microspray or matrix-assisted laser desorption. Mass analyzers include, for example, a quadrupole mass filter, ion trap mass analyzer and time-of-flight mass analyzer.
The ion formation process is a starting point for mass spectrum analysis. Several ionization methods are available and the choice of ionization method depends on the sample used for analysis. For example, for the analysis of polypeptides a relatively gentle ionization procedure such as electrospray ionization (ESI) can be desirable. For ESI, a solution containing the sample is passed through a fine needle at high potential which creates a strong electrical field resulting in a fine spray of highly charged droplets that is directed into the mass spectrometer. Other ionization procedures include, for example, fast-atom bombardment (FAB) which uses a high-energy beam of neutral atoms to strike a solid sample causing desorption and ionization. Matrix-assisted laser desorption ionization (MALDI) is a method in which a laser pulse is used to strike a sample that has been crystallized in an UV-absorbing compound matrix (e.g., 2,5-dihydroxybenzoic acid, alpha-cyano-4-hydroxycinammic acid, 3-hydroxypicolinic acid (3-HPA), di-ammoniumcitrate (DAC) and combinations thereof). Other ionization procedures known in the art include, for example, plasma and glow discharge, plasma desorption ionization, resonance ionization, and secondary ionization.
A variety of mass analyzers are available that can be paired with different ion sources. Different mass analyzers have different advantages as known in the art and as described herein. The mass spectrometer and methods chosen for detection depends on the particular assay, for example, a more sensitive mass analyzer can be used when a small amount of ions are generated for detection. Several types of mass analyzers and mass spectrometry methods are described below.
Ion mobility mass (IM) spectrometry is a gas-phase separation method. IM separates gas-phase ions based on their collision cross-section and can be coupled with time-of-flight (TOF) mass spectrometry. IM-MS is discussed in more detail by Verbeck et al. in the Journal of Biomolecular Techniques (Vol 13, Issue 2, 56-61).
Quadrupole mass spectrometry utilizes a quadrupole mass filter or analyzer. This type of mass analyzer is composed of four rods arranged as two sets of two electrically connected rods. A combination of rf and dc voltages are applied to each pair of rods which produces fields that cause an oscillating movement of the ions as they move from the beginning of the mass filter to the end. The result of these fields is the production of a high-pass mass filter in one pair of rods and a low-pass filter in the other pair of rods. Overlap between the high-pass and low-pass filter leaves a defined m/z that can pass both filters and traverse the length of the quadrupole. This m/z is selected and remains stable in the quadrupole mass filter while all other m/z have unstable trajectories and do not remain in the mass filter. A mass spectrum results by ramping the applied fields such that an increasing m/z is selected to pass through the mass filter and reach the detector. In addition, quadrupoles can also be set up to contain and transmit ions of all m/z by applying a rf-only field. This allows quadrupoles to function as a lens or focusing system in regions of the mass spectrometer where ion transmission is needed without mass filtering.
A quadrupole mass analyzer, as well as the other mass analyzers described herein, can be programmed to analyze a defined m/z or mass range. Since the desired mass range of nucleic acid fragment is known, in some instances, a mass spectrometer can be programmed to transmit ions of the projected correct mass range while excluding ions of a higher or lower mass range. The ability to select a mass range can decrease the background noise in the assay and thus increase the signal-to-noise ratio. Thus, in some instances, a mass spectrometer can accomplish a separation step as well as detection and identification of certain mass-distinguishable nucleic acid fragments.
Ion trap mass spectrometry utilizes an ion trap mass analyzer. Typically, fields are applied such that ions of all m/z are initially trapped and oscillate in the mass analyzer. Ions enter the ion trap from the ion source through a focusing device such as an octapole lens system. Ion trapping takes place in the trapping region before excitation and ejection through an electrode to the detector.
Mass analysis can be accomplished by sequentially applying voltages that increase the amplitude of the oscillations in a way that ejects ions of increasing m/z out of the trap and into the detector. In contrast to quadrupole mass spectrometry, all ions are retained in the fields of the mass analyzer except those with the selected m/z. Control of the number of ions can be accomplished by varying the time over which ions are injected into the trap.
Time-of-flight mass spectrometry utilizes a time-of-flight mass analyzer. Typically, an ion is first given a fixed amount of kinetic energy by acceleration in an electric field (generated by high voltage). Following acceleration, the ion enters a field-free or “drift” region where it travels at a velocity that is inversely proportional to its m/z. Therefore, ions with low m/z travel more rapidly than ions with high m/z. The time required for ions to travel the length of the field-free region is measured and used to calculate the m/z of the ion.
Gas chromatography mass spectrometry often can analyze a target in real-time. The gas chromatography (GC) portion of the system separates the chemical mixture into pulses of analyte and the mass spectrometer (MS) identifies and quantifies the analyte.
Tandem mass spectrometry can utilize combinations of the mass analyzers described above. Tandem mass spectrometers can use a first mass analyzer to separate ions according to their m/z in order to isolate an ion of interest for further analysis. The isolated ion of interest is then broken into fragment ions (called collisionally activated dissociation or collisionally induced dissociation) and the fragment ions are analyzed by the second mass analyzer. These types of tandem mass spectrometer systems are called tandem in space systems because the two mass analyzers are separated in space, usually by a collision cell. Tandem mass spectrometer systems also include tandem in time systems where one mass analyzer is used, however the mass analyzer is used sequentially to isolate an ion, induce fragmentation, and then perform mass analysis.
Mass spectrometers in the tandem in space category have more than one mass analyzer. For example, a tandem quadrupole mass spectrometer system can have a first quadrupole mass filter, followed by a collision cell, followed by a second quadrupole mass filter and then the detector. Another arrangement is to use a quadrupole mass filter for the first mass analyzer and a time-of-flight mass analyzer for the second mass analyzer with a collision cell separating the two mass analyzers. Other tandem systems are known in the art including reflectron-time-of-flight, tandem sector and sector-quadrupole mass spectrometry.
Mass spectrometers in the tandem in time category have one mass analyzer that performs different functions at different times. For example, an ion trap mass spectrometer can be used to trap ions of all m/z. A series of rf scan functions are applied which ejects ions of all m/z from the trap except the m/z of ions of interest. After the m/z of interest has been isolated, an rf pulse is applied to produce collisions with gas molecules in the trap to induce fragmentation of the ions. Then the m/z values of the fragmented ions are measured by the mass analyzer. Ion cyclotron resonance instruments, also known as Fourier transform mass spectrometers, are an example of tandem-in-time systems.
Several types of tandem mass spectrometry experiments can be performed by controlling the ions that are selected in each stage of the experiment. The different types of experiments utilize different modes of operation, sometimes called “scans,” of the mass analyzers. In a first example, called a mass spectrum scan, the first mass analyzer and the collision cell transmit all ions for mass analysis into the second mass analyzer. In a second example, called a product ion scan, the ions of interest are mass-selected in the first mass analyzer and then fragmented in the collision cell. The ions formed are then mass analyzed by scanning the second mass analyzer. In a third example, called a precursor ion scan, the first mass analyzer is scanned to sequentially transmit the mass analyzed ions into the collision cell for fragmentation. The second mass analyzer mass-selects the product ion of interest for transmission to the detector. Therefore, the detector signal is the result of all precursor ions that can be fragmented into a common product ion. Other experimental formats include neutral loss scans where a constant mass difference is accounted for in the mass scans.
Any suitable mass spectrometer, mass spectrometer format, configuration or technology described herein or known in the art can be used to perform a method described herein, non-limiting examples of which include Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry (MS), Laser Desorption Mass Spectrometry (LDMS), Electrospray (ES) MS, Ion Cyclotron Resonance (ICR) MS, Fourier Transform MS, inductively coupled plasma-mass spectrometry (ICP-MS), accelerator mass spectrometry (AMS), thermal ionization-mass spectrometry (TIMS), spark source mass spectrometry (SSMS) and the like.
For quantification, controls may be used which can provide a signal in relation to the amount of the nucleic acid fragment, for example, that is present or is introduced. A control to allow conversion of relative mass signals into absolute quantities can be accomplished by addition of a known quantity of a mass tag or mass label to each sample before detection of the nucleic acid fragments. See for example, Ding and Cantor (2003) PNAS USA March 18; 100(6):3059-64. Any mass tag that does not interfere with detection of the fragments can be used for normalizing the mass signal. Such standards typically have separation properties that are different from those of any of the molecular tags in the sample, and could have the same or different mass signatures.
A separation step sometimes can be used to remove salts, enzymes, or other buffer components from the nucleic acid sample. Several methods well known in the art, such as chromatography, gel electrophoresis, or precipitation, can be used to clean up the sample. For example, size exclusion chromatography or affinity chromatography can be used to remove salt from a sample. The choice of separation method can depend on the amount of a sample. For example, when small amounts of sample are available or a miniaturized apparatus is used, a micro-affinity chromatography separation step can be used. In addition, whether a separation step is desired, and the choice of separation method, can depend on the detection method used. Salts sometimes can absorb energy from the laser in matrix-assisted laser desorption/ionization and result in lower ionization efficiency. Thus, the efficiency of matrix-assisted laser desorption/ionization and electrospray ionization sometimes can be improved by removing salts from a sample.
Enriched Nucleic Acids
Nucleic acid subsets or subpopulations (e.g., enriched nucleic acid (e.g., an enriched minority nucleic acid species, enriched hypomethylated nucleic acid, enriched fetal nucleic acid, the like or combinations thereof)) that are enriched and/or separated by a method described herein can be analyzed by any suitable analytical method. Non-limiting examples of an analytical methods that can use or analyze enriched nucleic acid include sequencing (e.g., any suitable type of nucleic acid sequencing (e.g., nanopore sequencing), any suitable method of obtaining sequence reads), genetic testing (e.g., gene detection, mutation detection, SNP detection, fetal screening, gender determination and the like), promoter analysis, pathogen analysis (e.g., viral detection and analysis), hybridization studies, cancer analysis (e.g., cancer screening), personalized medicine, cloning, gene therapy, genetic comparison studies (e.g., comparing SNPs between samples), the like or combinations thereof.
Outcome
Enriched nucleic acid (e.g., an enriched minority nucleic acid species, enriched hypomethylated nucleic acid, enriched fetal nucleic acid, the like or combinations thereof) can be used to determine the presence or absence of a genetic variation. A determination of the presence or absence of a genetic variation (e.g., fetal aneuploidy) can be generated for a sample (e.g., for an enriched nucleic acid), thereby providing an outcome (e.g., thereby providing an outcome determinative of the presence or absence of a genetic variation (e.g., fetal aneuploidy)) by a suitable method or by a method described here. Methods of determining the presence or absence of a genetic variation (e.g., a fetal aneuploidy) from sequence reads of ccf DNA obtained from a pregnant female are described, for example, in U.S. Patent Application Publication No. 20130085681 (published on Apr. 4, 2013, entitled “METHODS AND PROCESSES FOR NON-INVASIVE ASSESSMENT OF GENETIC VARIATIONS” naming Cosmin Deciu, Zeljko Dzakula, Mathias Ehrich and Sung Kyun Kim as inventors). A genetic variation often includes a gain, a loss and/or alteration (e.g., duplication, deletion, fusion, insertion, mutation, reorganization, substitution or aberrant methylation) of genetic information (e.g., chromosomes, segments of chromosomes, polymorphic regions, translocated regions, altered nucleotide sequence, the like or combinations of the foregoing) that results in a detectable change in the genome or genetic information of a test subject with respect to a reference. Presence or absence of a genetic variation can be determined by transforming, analyzing and/or manipulating sequence reads that have been mapped to genomic sections (e.g., genomic bins).
Methods described herein sometimes determine presence or absence of a fetal aneuploidy (e.g., full chromosome aneuploidy, partial chromosome aneuploidy or segmental chromosomal aberration (e.g., mosaicism, deletion and/or insertion)) for a test sample from a pregnant female bearing a fetus. Sometimes methods described herein detect euploidy or lack of euploidy (non-euploidy) for a sample from a pregnant female bearing a fetus. Methods described herein sometimes detect trisomy for one or more chromosomes (e.g., chromosome 13, chromosome 18, chromosome 21 or combination thereof) or segment thereof.
In some embodiments, presence or absence of a genetic variation (e.g., a fetal aneuploidy) is determined by a method described herein, by a method known in the art or by a combination thereof. Presence or absence of a genetic variation generally is determined from counts of sequence reads mapped to genomic sections of a reference genome. Counts of sequence reads utilized to determine presence or absence of a genetic variation sometimes are raw counts and/or filtered counts, and often are normalized counts. A suitable normalization process or processes can be used to generate normalized counts, non-limiting examples of which include bin-wise normalization, normalization by GC content, linear and nonlinear least squares regression, LOESS, GC LOESS, LOWESS, PERUN, RM, GCRM and combinations thereof. Normalized counts sometimes are expressed as one or more levels or elevations in a profile for a particular set or sets of genomic sections. Normalized counts sometimes are adjusted or padded prior to determining presence or absence of a genetic variation.
Presence or absence of a genetic variation (e.g., fetal aneuploidy) sometimes is determined without comparing counts for a set of genomic sections to a reference. Counts measured for a test sample and are in a test region (e.g., a set of genomic sections of interest) are referred to as “test counts” herein. Test counts sometimes are processed counts, averaged or summed counts, a representation, normalized counts, or one or more levels or elevations, as described herein. Sometimes test counts are averaged or summed (e.g., an average, mean, median, mode or sum is calculated) for a set of genomic sections, and the averaged or summed counts are compared to a threshold or range. Test counts sometimes are expressed as a representation, which can be expressed as a ratio or percentage of counts for a first set of genomic sections to counts for a second set of genomic sections. Sometimes the first set of genomic sections is for one or more test chromosomes (e.g., chromosome 13, chromosome 18, chromosome 21, or combination thereof) and sometimes the second set of genomic sections is for the genome or a part of the genome (e.g., autosomes or autosomes and sex chromosomes). Sometimes a representation is compared to a threshold or range. Sometimes test counts are expressed as one or more levels or elevations for normalized counts over a set of genomic sections, and the one or more levels or elevations are compared to a threshold or range. Test counts (e.g., averaged or summed counts, representation, normalized counts, one or more levels or elevations) above or below a particular threshold, in a particular range or outside a particular range sometimes are determinative of the presence of a genetic variation or lack of euploidy (e.g., not euploidy). Test counts (e.g., averaged or summed counts, representation, normalized counts, one or more levels or elevations) below or above a particular threshold, in a particular range or outside a particular range sometimes are determinative of the absence of a genetic variation or euploidy.
Presence or absence of a genetic variation (e.g., fetal aneuploidy) sometimes is determined by comparing test counts (e.g., raw counts, filtered counts, averaged or summed counts, representation, normalized counts, one or more levels or elevations, for a set of genomic sections) to a reference. A reference can be a suitable determination of counts. Counts for a reference sometimes are raw counts, filtered counts, averaged or summed counts, representation, normalized counts, one or more levels or elevations, for a set of genomic sections. Reference counts often are counts for a euploid test region.
In certain embodiments, test counts sometimes are for a first set of genomic sections and a reference includes counts for a second set of genomic sections different than the first set of genomic sections. Reference counts sometimes are for a nucleic acid sample from the same pregnant female from which the test sample is obtained. Sometimes reference counts are for a nucleic acid sample from one or more pregnant females different than the female from which the test sample was obtained. In some embodiments, a first set of genomic sections is in chromosome 13, chromosome 18, chromosome 21, segment thereof or combination of the foregoing, and the second set of genomic sections is in another chromosome or chromosomes or segment thereof. In a non-limiting example, where a first set of genomic sections is in chromosome 21 or segment thereof, a second set of genomic sections often is in another chromosome (e.g., chromosome 1, chromosome 13, chromosome 14, chromosome 18, chromosome 19, segment thereof or combination of the foregoing). A reference often is located in a chromosome or segment thereof that is typically euploid. For example, chromosome 1 and chromosome 19 often are euploid in fetuses owing to a high rate of early fetal mortality associated with chromosome 1 and chromosome 19 aneuploidies. A measure of deviation between the test counts and the reference counts can be generated.
Sometimes a reference comprises counts for the same set of genomic sections as for the test counts, where the counts for the reference are from one or more reference samples (e.g., often multiple reference samples from multiple reference subjects). A reference sample often is from one or more pregnant females different than the female from which a test sample is obtained. A measure of deviation between the test counts and the reference counts can be generated.
A suitable measure of deviation between test counts and reference counts can be selected, non-limiting examples of which include standard deviation, average absolute deviation, median absolute deviation, maximum absolute deviation, standard score (e.g., z-value, z-score, normal score, standardized variable) and the like. In some embodiments, reference samples are euploid for a test region and deviation between the test counts and the reference counts is assessed. A deviation of less than three between test counts and reference counts (e.g., 3-sigma for standard deviation) often is indicative of a euploid test region (e.g., absence of a genetic variation). A deviation of greater than three between test counts and reference counts often is indicative of a non-euploid test region (e.g., presence of a genetic variation). Test counts significantly below reference counts, which reference counts are indicative of euploidy, sometimes are determinative of a monosomy. Test counts significantly above reference counts, which reference counts are indicative of euploidy, sometimes are determinative of a trisomy. A measure of deviation between test counts for a test sample and reference counts for multiple reference subjects can be plotted and visualized (e.g., z-score plot).
Any other suitable reference can be factored with test counts for determining presence or absence of a genetic variation (or determination of euploid or non-euploid) for a test region of a test sample. For example, a fetal fraction determination can be factored with test counts to determine the presence or absence of a genetic variation. A suitable process for quantifying fetal fraction can be utilized, non-limiting examples of which include a mass spectrometric process, sequencing process or combination thereof.
Laboratory personnel (e.g., a laboratory manager) can analyze values (e.g., test counts, reference counts, level of deviation) underlying a determination of the presence or absence of a genetic variation (or determination of euploid or non-euploid for a test region). For calls pertaining to presence or absence of a genetic variation that are close or questionable, laboratory personnel can re-order the same test, and/or order a different test (e.g., karyotyping and/or amniocentesis in the case of fetal aneuploidy determinations), that makes use of the same or different sample nucleic acid from a test subject.
A genetic variation sometimes is associated with medical condition. An outcome determinative of a genetic variation is sometimes an outcome determinative of the presence or absence of a condition (e.g., a medical condition), disease, syndrome or abnormality, or includes, detection of a condition, disease, syndrome or abnormality (e.g., non-limiting examples listed in Table 1). In some cases a diagnosis comprises assessment of an outcome. An outcome determinative of the presence or absence of a condition (e.g., a medical condition), disease, syndrome or abnormality by methods described herein can sometimes be independently verified by further testing (e.g., by karyotyping and/or amniocentesis).
Analysis and processing of data can provide one or more outcomes. In some embodiments an analysis (e.g., an analysis of nucleic acids) comprises determining an outcome. The term “outcome” as used herein refers to a result of data processing that facilitates determining whether a subject was, or is at risk of having, a genetic variation. An outcome often comprises one or more numerical values generated using a processing method described herein in the context of one or more considerations of probability. A consideration of probability includes but is not limited to: measure of variability, confidence level, sensitivity, specificity, standard deviation, coefficient of variation (CV) and/or confidence level, Z-scores, Chi values, Phi values, ploidy values, fitted fetal fraction, area ratios, median elevation, the like or combinations thereof. A consideration of probability can facilitate determining whether a subject is at risk of having, or has, a genetic variation, and an outcome determinative of a presence or absence of a genetic disorder often includes such a consideration.
An outcome often is a phenotype with an associated level of confidence (e.g., fetus is positive for trisomy 21 with a confidence level of 99%, test subject is negative for a cancer associated with a genetic variation at a confidence level of 95%). Different methods of generating outcome values sometimes can produce different types of results. Generally, there are four types of possible scores or calls that can be made based on outcome values generated using methods described herein: true positive, false positive, true negative and false negative. The terms “score”, “scores”, “call” and “calls” as used herein refer to calculating the probability that a particular genetic variation is present or absent in a subject/sample. The value of a score may be used to determine, for example, a variation, difference, or ratio of mapped sequence reads that may correspond to a genetic variation. For example, calculating a positive score for a selected genetic variation or genomic section from a data set, with respect to a reference genome can lead to an identification of the presence or absence of a genetic variation, which genetic variation sometimes is associated with a medical condition (e.g., cancer, preeclampsia, trisomy, monosomy, and the like). In some embodiments, an outcome comprises a profile. In those embodiments in which an outcome comprises a profile, any suitable profile or combination of profiles can be used for an outcome. Non-limiting examples of profiles that can be used for an outcome include z-score profiles, p-value profiles, chi value profiles, phi value profiles, the like, and combinations thereof
An outcome generated for determining the presence or absence of a genetic variation sometimes includes a null result (e.g., a data point between two clusters, a numerical value with a standard deviation that encompasses values for both the presence and absence of a genetic variation, a data set with a profile plot that is not similar to profile plots for subjects having or free from the genetic variation being investigated). In some embodiments, an outcome indicative of a null result still is a determinative result, and the determination can include the need for additional information and/or a repeat of the data generation and/or analysis for determining the presence or absence of a genetic variation.
An outcome can be generated after performing one or more processing steps described herein, in some embodiments. In certain embodiments, an outcome is generated as a result of one of the processing steps described herein, and in some embodiments, an outcome can be generated after each statistical and/or mathematical manipulation of a data set is performed. An outcome pertaining to the determination of the presence or absence of a genetic variation can be expressed in any suitable form, which form comprises without limitation, a probability (e.g., odds ratio, p-value), likelihood, value in or out of a cluster, value over or under a threshold value, value with a measure of variance or confidence, or risk factor, associated with the presence or absence of a genetic variation for a subject or sample. In certain embodiments, comparison between samples allows confirmation of sample identity (e.g., allows identification of repeated samples and/or samples that have been mixed up (e.g., mislabeled, combined, and the like)).
In some embodiments, an outcome comprises a value above or below a predetermined threshold or cutoff value (e.g., greater than 1, less than 1), and an uncertainty or confidence level associated with the value. An outcome also can describe any assumptions used in data processing. In certain embodiments, an outcome comprises a value that falls within or outside a predetermined range of values and the associated uncertainty or confidence level for that value being inside or outside the range. In some embodiments, an outcome comprises a value that is equal to a predetermined value (e.g., equal to 1, equal to zero), or is equal to a value within a predetermined value range, and its associated uncertainty or confidence level for that value being equal or within or outside a range. An outcome sometimes is graphically represented as a plot (e.g., profile plot).
As noted above, an outcome can be characterized as a true positive, true negative, false positive or false negative. The term “true positive” as used herein refers to a subject correctly diagnosed as having a genetic variation. The term “false positive” as used herein refers to a subject wrongly identified as having a genetic variation. The term “true negative” as used herein refers to a subject correctly identified as not having a genetic variation. The term “false negative” as used herein refers to a subject wrongly identified as not having a genetic variation. Two measures of performance for any given method can be calculated based on the ratios of these occurrences: (i) a sensitivity value, which generally is the fraction of predicted positives that are correctly identified as being positives; and (ii) a specificity value, which generally is the fraction of predicted negatives correctly identified as being negative. The term “sensitivity” as used herein refers to the number of true positives divided by the number of true positives plus the number of false negatives, where sensitivity (sens) may be within the range of 0≦sens≦1. Ideally, the number of false negatives equal zero or close to zero, so that no subject is wrongly identified as not having at least one genetic variation when they indeed have at least one genetic variation. Conversely, an assessment often is made of the ability of a prediction algorithm to classify negatives correctly, a complementary measurement to sensitivity. The term “specificity” as used herein refers to the number of true negatives divided by the number of true negatives plus the number of false positives, where sensitivity (spec) may be within the range of 0≦spec≦1. Ideally, the number of false positives equal zero or close to zero, so that no subject is wrongly identified as having at least one genetic variation when they do not have the genetic variation being assessed.
In certain embodiments, one or more of sensitivity, specificity and/or confidence level are expressed as a percentage. In some embodiments, the percentage, independently for each variable, is greater than about 90% (e.g., about 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99%, or greater than 99% (e.g., about 99.5%, or greater, about 99.9% or greater, about 99.95% or greater, about 99.99% or greater)). Coefficient of variation (CV) in some embodiments is expressed as a percentage, and sometimes the percentage is about 10% or less (e.g., about 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1%, or less than 1% (e.g., about 0.5% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less)). A probability (e.g., that a particular outcome is not due to chance) in certain embodiments is expressed as a Z-score, a p-value, or the results of a t-test. In some embodiments, a measured variance, confidence interval, sensitivity, specificity and the like (e.g., referred to collectively as confidence parameters) for an outcome can be generated using one or more data processing manipulations described herein.
A method that has sensitivity and specificity equaling one, or 100%, or near one (e.g., between about 90% to about 99%) sometimes is selected. In some embodiments, a method having a sensitivity equaling 1, or 100% is selected, and in certain embodiments, a method having a sensitivity near 1 is selected (e.g., a sensitivity of about 90%, a sensitivity of about 91%, a sensitivity of about 92%, a sensitivity of about 93%, a sensitivity of about 94%, a sensitivity of about 95%, a sensitivity of about 96%, a sensitivity of about 97%, a sensitivity of about 98%, or a sensitivity of about 99%). In some embodiments, a method having a specificity equaling 1, or 100% is selected, and in certain embodiments, a method having a specificity near 1 is selected (e.g., a specificity of about 90%, a specificity of about 91%, a specificity of about 92%, a specificity of about 93%, a specificity of about 94%, a specificity of about 95%, a specificity of about 96%, a specificity of about 97%, a specificity of about 98%, or a specificity of about 99%).
After one or more outcomes have been generated, an outcome often is used to provide a determination of the presence or absence of a genetic variation and/or associated medical condition. An outcome typically is provided to a health care professional (e.g., laboratory technician or manager; physician or assistant). In some embodiments, an outcome determinative of the presence or absence of a genetic variation is provided to a healthcare professional in the form of a report, and in certain embodiments the report comprises a display of an outcome value and an associated confidence parameter. Generally, an outcome can be displayed in any suitable format that facilitates determination of the presence or absence of a genetic variation and/or medical condition. Non-limiting examples of formats suitable for use for reporting and/or displaying data sets or reporting an outcome include digital data, a graph, a 2D graph, a 3D graph, and 4D graph, a picture, a pictograph, a chart, a bar graph, a pie graph, a diagram, a flow chart, a scatter plot, a map, a histogram, a density chart, a function graph, a circuit diagram, a block diagram, a bubble map, a constellation diagram, a contour diagram, a cartogram, spider chart, Venn diagram, nomogram, and the like, and combination of the foregoing.
In some embodiments, presence or absence of a genetic variation (e.g., chromosome aneuploidy) is determined for a fetus. In such embodiments, presence or absence of a fetal genetic variation (e.g., fetal chromosome aneuploidy) is determined. In some embodiments an analysis (e.g., an analysis of nucleic acids) comprises determining the presence or absence of one or more genetic variations (e.g., in a fetus). In some embodiments an analysis comprises determining the presence or absence of one or more chromosome aneuploidies (e.g., a fetal aneuploidy). In some embodiments a fetal aneuploidy is a trisomy. In some embodiments a fetal trisomy is a trisomy of chromosome 13, 18, and/or 21.
In certain embodiments, presence or absence of a genetic variation (e.g., chromosome aneuploidy) is determined for a sample. In such embodiments, presence or absence of a genetic variation in sample nucleic acid (e.g., chromosome aneuploidy) is determined. In some embodiments, a variation detected or not detected resides in sample nucleic acid from one source but not in sample nucleic acid from another source. Non-limiting examples of sources include placental nucleic acid, fetal nucleic acid, maternal nucleic acid, cancer cell nucleic acid, non-cancer cell nucleic acid, the like and combinations thereof. In non-limiting examples, a particular genetic variation detected or not detected (i) resides in placental nucleic acid but not in fetal nucleic acid and not in maternal nucleic acid; (ii) resides in fetal nucleic acid but not maternal nucleic acid; or (iii) resides in maternal nucleic acid but not fetal nucleic acid.
Use of Outcomes
A health care professional, or other qualified individual, receiving a report comprising one or more outcomes determinative of the presence or absence of a genetic variation can use the displayed data in the report to make a call regarding the status of the test subject or patient. The healthcare professional can make a recommendation based on the provided outcome, in some embodiments. A health care professional or qualified individual can provide a test subject or patient with a call or score with regards to the presence or absence of the genetic variation based on the outcome value or values and associated confidence parameters provided in a report, in some embodiments. In certain embodiments, a score or call is made manually by a healthcare professional or qualified individual, using visual observation of the provided report. In certain embodiments, a score or call is made by an automated routine, sometimes embedded in software, and reviewed by a healthcare professional or qualified individual for accuracy prior to providing information to a test subject or patient. The term “receiving a report” as used herein refers to obtaining, by any communication means, a written and/or graphical representation comprising an outcome, which upon review allows a healthcare professional or other qualified individual to make a determination as to the presence or absence of a genetic variation in a test subject or patient. The report may be generated by a computer or by human data entry, and can be communicated using electronic means (e.g., over the internet, via computer, via fax, from one network location to another location at the same or different physical sites), or by any other method of sending or receiving data (e.g., mail service, courier service and the like). In some embodiments the outcome is transmitted to a health care professional in a suitable medium, including, without limitation, in verbal, document, or file form. The file may be, for example, but not limited to, an auditory file, a computer readable file, a paper file, a laboratory file or a medical record file.
The term “providing an outcome” and grammatical equivalents thereof, as used herein also can refer to any method for obtaining such information, including, without limitation, obtaining the information from a laboratory file. A laboratory file can be generated by a laboratory that carried out one or more assays or one or more data processing steps to determine the presence or absence of the medical condition. The laboratory may be in the same location or different location (e.g., in another country) as the personnel identifying the presence or absence of the medical condition from the laboratory file. For example, the laboratory file can be generated in one location and transmitted to another location in which the information therein will be transmitted to the pregnant female subject. The laboratory file may be in tangible form or electronic form (e.g., computer readable form), in certain embodiments.
A healthcare professional or qualified individual, can provide any suitable recommendation based on the outcome or outcomes provided in the report. Non-limiting examples of recommendations that can be provided based on the provided outcome report includes, surgery, radiation therapy, chemotherapy, genetic counseling, after birth treatment solutions (e.g., life planning, long term assisted care, medicaments, symptomatic treatments), pregnancy termination, organ transplant, blood transfusion, the like or combinations of the foregoing. In some embodiments the recommendation is dependent on the outcome based classification provided (e.g., Down's syndrome, Turner syndrome, medical conditions associated with genetic variations in T13, medical conditions associated with genetic variations in T18).
Software can be used to perform one or more steps in the process described herein, including but not limited to; counting, data processing, generating an outcome, and/or providing one or more recommendations based on generated outcomes.
Machines, Software and Interfaces
Apparatuses, software and interfaces may be used to conduct methods described herein. Using apparatuses, software and interfaces, a user may enter, request, query or determine options for using particular information, programs or processes (e.g., mapping sequence reads, processing mapped data and/or providing an outcome), which can involve implementing statistical analysis algorithms, statistical significance algorithms, statistical algorithms, iterative steps, validation algorithms, and graphical representations, for example. In some embodiments, a data set may be entered by a user as input information, a user may download one or more data sets by any suitable hardware media (e.g., flash drive), and/or a user may send a data set from one system to another for subsequent processing and/or providing an outcome (e.g., send sequence read data from a sequencer to a computer system for sequence read mapping; send mapped sequence data to a computer system for processing and yielding an outcome and/or report).
A user may, for example, place a query to software which then may acquire a data set via internet access, and in certain embodiments, a programmable processor may be prompted to acquire a suitable data set based on given parameters. A programmable processor also may prompt a user to select one or more data set options selected by the processor based on given parameters. A programmable processor may prompt a user to select one or more data set options selected by the processor based on information found via the internet, other internal or external information, or the like. Options may be chosen for selecting one or more data feature selections, one or more statistical algorithms, one or more statistical analysis algorithms, one or more statistical significance algorithms, iterative steps, one or more validation algorithms, and one or more graphical representations of methods, apparatuses, or computer programs.
Systems addressed herein may comprise general components of computer systems, such as, for example, network servers, laptop systems, desktop systems, handheld systems, personal digital assistants, computing kiosks, and the like. A computer system may comprise one or more input means such as a keyboard, touch screen, mouse, voice recognition or other means to allow the user to enter data into the system. A system may further comprise one or more outputs, including, but not limited to, a display screen (e.g., CRT or LCD), speaker, FAX machine, printer (e.g., laser, ink jet, impact, black and white or color printer), or other output useful for providing visual, auditory and/or hardcopy output of information (e.g., outcome and/or report).
In a system, input and output means may be connected to a central processing unit which may comprise among other components, a microprocessor for executing program instructions and memory for storing program code and data. In some embodiments, processes may be implemented as a single user system located in a single geographical site. In certain embodiments, processes may be implemented as a multi-user system. In the case of a multi-user implementation, multiple central processing units may be connected by means of a network. The network may be local, encompassing a single department in one portion of a building, an entire building, span multiple buildings, span a region, span an entire country or be worldwide. The network may be private, being owned and controlled by a provider, or it may be implemented as an internet based service where the user accesses a web page to enter and retrieve information. Accordingly, in certain embodiments, a system includes one or more machines, which may be local or remote with respect to a user. More than one machine in one location or multiple locations may be accessed by a user, and data may be mapped and/or processed in series and/or in parallel. Thus, any suitable configuration and control may be utilized for mapping and/or processing data using multiple machines, such as in local network, remote network and/or “cloud” computing platforms.
A system can include a communications interface in some embodiments. A communications interface allows for transfer of software and data between a computer system and one or more external devices. Non-limiting examples of communications interfaces include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, and the like. Software and data transferred via a communications interface generally are in the form of signals, which can be electronic, electromagnetic, optical and/or other signals capable of being received by a communications interface. Signals often are provided to a communications interface via a channel. A channel often carries signals and can be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and/or other communications channels. Thus, in an example, a communications interface may be used to receive signal information that can be detected by a signal detection module.
Data may be input by any suitable device and/or method, including, but not limited to, manual input devices or direct data entry devices (DDEs). Non-limiting examples of manual devices include keyboards, concept keyboards, touch sensitive screens, light pens, mouse, tracker balls, joysticks, graphic tablets, scanners, digital cameras, video digitizers and voice recognition devices. Non-limiting examples of DDEs include bar code readers, magnetic strip codes, smart cards, magnetic ink character recognition, optical character recognition, optical mark recognition, and turnaround documents.
In some embodiments, output from a sequencing apparatus may serve as data that can be input via an input device. In certain embodiments, mapped sequence reads may serve as data that can be input via an input device. In certain embodiments, simulated data is generated by an in silico process and the simulated data serves as data that can be input via an input device. The term “in silico” refers to research and experiments performed using a computer. In silico processes include, but are not limited to, mapping sequence reads and processing mapped sequence reads according to processes described herein.
A system may include software useful for performing a process described herein, and software can include one or more modules for performing such processes (e.g., data acquisition module, data processing module, data display module). The term “software” refers to computer readable program instructions that, when executed by a computer, perform computer operations. The term “module” refers to a self-contained functional unit that can be used in a larger software system. For example, a software module is a part of a program that performs a particular process or task.
Software often is provided on a program product containing program instructions recorded on a computer readable medium, including, but not limited to, magnetic media including floppy disks, hard disks, and magnetic tape; and optical media including CD-ROM discs, DVD discs, magneto-optical discs, flash drives, RAM, floppy discs, the like, and other such media on which the program instructions can be recorded. In online implementation, a server and web site maintained by an organization can be configured to provide software downloads to remote users, or remote users may access a remote system maintained by an organization to remotely access software.
Software may obtain or receive input information. Software may include a module that specifically obtains or receives data (e.g., a data receiving module that receives sequence read data and/or mapped read data) and may include a module that specifically processes the data (e.g., a processing module that processes received data (e.g., filters, normalizes, provides an outcome and/or report). The terms “obtaining” and “receiving” input information refers to receiving data (e.g., sequence reads, mapped reads) by computer communication means from a local, or remote site, human data entry, or any other method of receiving data. The input information may be generated in the same location at which it is received, or it may be generated in a different location and transmitted to the receiving location. In some embodiments, input information is modified before it is processed (e.g., placed into a format amenable to processing (e.g., tabulated)).
In some embodiments, provided are computer program products, such as, for example, a computer program product comprising a computer usable medium (e.g., a non-transitory storage medium) having a computer readable program code embodied therein, the computer readable program code adapted to be executed to implement a method comprising: (a) obtaining nucleotide sequence reads from a sample comprising circulating, cell-free nucleic acid from a pregnant female, where the sample has been enriched for fetal nucleic acid, (b) mapping the nucleotide sequence reads to reference genome sections, (c) counting the number of nucleotide sequence reads mapped to each reference genome section, (d) comparing the number of counts of the nucleotide sequence reads mapped in (c), or derivative thereof, to a reference, or portion thereof, thereby making a comparison, and (e) determining the presence or absence of a fetal aneuploidy based on the comparison.
Software can include one or more algorithms in certain embodiments. An algorithm may be used for processing data and/or providing an outcome or report according to a finite sequence of instructions. An algorithm often is a list of defined instructions for completing a task. Starting from an initial state, the instructions may describe a computation that proceeds through a defined series of successive states, eventually terminating in a final ending state. The transition from one state to the next is not necessarily deterministic (e.g., some algorithms incorporate randomness). By way of example, and without limitation, an algorithm can be a search algorithm, sorting algorithm, merge algorithm, numerical algorithm, graph algorithm, string algorithm, modeling algorithm, computational genometric algorithm, combinatorial algorithm, machine learning algorithm, cryptography algorithm, data compression algorithm, parsing algorithm and the like. An algorithm can include one algorithm or two or more algorithms working in combination. An algorithm can be of any suitable complexity class and/or parameterized complexity. An algorithm can be used for calculation and/or data processing, and in some embodiments, can be used in a deterministic or probabilistic/predictive approach. An algorithm can be implemented in a computing environment by use of a suitable programming language, non-limiting examples of which are C, C++, Java, Pen, Python, Fortran, and the like. In some embodiments, an algorithm can be configured or modified to include margin of errors, statistical analysis, statistical significance, and/or comparison to other information or data sets (e.g., applicable when using a neural net or clustering algorithm).
In certain embodiments, several algorithms may be implemented for use in software. These algorithms can be trained with raw data in some embodiments. For each new raw data sample, the trained algorithms may produce a representative processed data set or outcome. A processed data set sometimes is of reduced complexity compared to the parent data set that was processed. Based on a processed set, the performance of a trained algorithm may be assessed based on sensitivity and specificity, in some embodiments. An algorithm with the highest sensitivity and/or specificity may be identified and utilized, in certain embodiments.
In certain embodiments, simulated (or simulation) data can aid data processing, for example, by training an algorithm or testing an algorithm. In some embodiments, simulated data includes hypothetical various samplings of different groupings of sequence reads. Simulated data may be based on what might be expected from a real population or may be skewed to test an algorithm and/or to assign a correct classification. Simulated data also is referred to herein as “virtual” data. Simulations can be performed by a computer program in certain embodiments. One possible step in using a simulated data set is to evaluate the confidence of an identified results, e.g., how well a random sampling matches or best represents the original data. One approach is to calculate a probability value (p-value), which estimates the probability of a random sample having better score than the selected samples. In some embodiments, an empirical model may be assessed, in which it is assumed that at least one sample matches a reference sample (with or without resolved variations). In some embodiments, another distribution, such as a Poisson distribution for example, can be used to define the probability distribution.
A system may include one or more processors in certain embodiments. A processor can be connected to a communication bus. A computer system may include a main memory, often random access memory (RAM), and can also include a secondary memory. Secondary memory can include, for example, a hard disk drive and/or a removable storage drive, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, memory card and the like. A removable storage drive often reads from and/or writes to a removable storage unit. Non-limiting examples of removable storage units include a floppy disk, magnetic tape, optical disk, and the like, which can be read by and written to by, for example, a removable storage drive. A removable storage unit can include a computer-usable storage medium having stored therein computer software and/or data.
A processor may implement software in a system. In some embodiments, a processor may be programmed to automatically perform a task described herein that a user could perform. Accordingly, a processor, or algorithm conducted by such a processor, can require little to no supervision or input from a user (e.g., software may be programmed to implement a function automatically). In some embodiments, the complexity of a process is so large that a single person or group of persons could not perform the process in a timeframe short enough for providing an outcome determinative of the presence or absence of a genetic variation.
In some embodiments, secondary memory may include other similar means for allowing computer programs or other instructions to be loaded into a computer system. For example, a system can include a removable storage unit and an interface device. Non-limiting examples of such systems include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to a computer system.
Genetic Variations and Medical Conditions
The presence or absence of a genetic variance can be determined using a method or apparatus described herein. In certain embodiments, the presence or absence of one or more genetic variations is determined according to an outcome provided by methods and apparatuses described herein. A genetic variation generally is a particular genetic phenotype present in certain individuals, and often a genetic variation is present in a statistically significant sub-population of individuals. In some embodiments, a genetic variation is a chromosome abnormality (e.g., aneuploidy), partial chromosome abnormality or mosaicism, each of which is described in greater detail herein. Non-limiting examples of genetic variations include one or more deletions (e.g., micro-deletions), duplications (e.g., micro-duplications), insertions, mutations, polymorphisms (e.g., single-nucleotide polymorphisms (SNPs)), fusions, repeats (e.g., short tandem repeats), distinct methylation sites, distinct methylation patterns, the like and combinations thereof. An insertion, repeat, deletion, duplication, mutation or polymorphism can be of any length, and in some embodiments, is about 1 base or base pair (bp) to about 250 megabases (Mb) in length. In some embodiments, an insertion, repeat, deletion, duplication, mutation or polymorphism is about 1 base or base pair (bp) to about 1,000 kilobases (kb) in length (e.g., about 10 bp, 50 bp, 100 bp, 500 bp, 1 kb, 5 kb, 10 kb, 50 kb, 100 kb, 500 kb, or 1000 kb in length).
A genetic variation is sometime a deletion. In some embodiments, a deletion is a mutation (e.g., a genetic aberration) in which a part of a chromosome or a sequence of DNA is missing. A deletion is often the loss of genetic material. Any number of nucleotides can be deleted. A deletion can comprise the deletion of one or more entire chromosomes, a segment of a chromosome, an allele, a gene, an intron, an exon, any non-coding region, any coding region, a segment thereof or combination thereof. A deletion can comprise a microdeletion. A deletion can comprise the deletion of a single base.
A genetic variation is sometimes a genetic duplication. In some embodiments, a duplication is a mutation (e.g., a genetic aberration) in which a part of a chromosome or a sequence of DNA is copied and inserted back into the genome. In some embodiments, a genetic duplication (i.e. duplication) is any duplication of a region of DNA. In some embodiments a duplication is a nucleic acid sequence that is repeated, often in tandem, within a genome or chromosome. In some embodiments a duplication can comprise a copy of one or more entire chromosomes, a segment of a chromosome, an allele, a gene, an intron, an exon, any non-coding region, any coding region, segment thereof or combination thereof. A duplication can comprise a microduplication. A duplication sometimes comprises one or more copies of a duplicated nucleic acid. A duplication sometimes is characterized as a genetic region repeated one or more times (e.g., repeated 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 times). Duplications can range from small regions (thousands of base pairs) to whole chromosomes in some instances. Duplications frequently occur as the result of an error in homologous recombination or due to a retrotransposon event. Duplications have been associated with certain types of proliferative diseases. Duplications can be characterized using genomic microarrays or comparative genetic hybridization (CGH).
A genetic variation is sometimes an insertion. An insertion is sometimes the addition of one or more nucleotide base pairs into a nucleic acid sequence. An insertion is sometimes a microinsertion. In some embodiments, an insertion comprises the addition of a segment of a chromosome into a genome, chromosome, or segment thereof. In some embodiments, an insertion comprises the addition of an allele, a gene, an intron, an exon, any non-coding region, any coding region, segment thereof or combination thereof into a genome or segment thereof. In some embodiments, an insertion comprises the addition (i.e., insertion) of nucleic acid of unknown origin into a genome, chromosome, or segment thereof. In some embodiments, an insertion comprises the addition (i.e. insertion) of a single base.
As used herein a “copy number variation” generally is a class or type of genetic variation or chromosomal aberration. A copy number variation can be a deletion (e.g. micro-deletion), duplication (e.g., a micro-duplication) or insertion (e.g., a micro-insertion). Often, the prefix “micro” as used herein sometimes is a segment of nucleic acid less than 5 Mb in length. A copy number variation can include one or more deletions (e.g. micro-deletion), duplications and/or insertions (e.g., a micro-duplication, micro-insertion) of a segment of a chromosome. In some embodiments, a duplication comprises an insertion. In some embodiments, an insertion is a duplication. In some embodiments, an insertion is not a duplication. For example, often a duplication of a sequence in a genomic section increases the counts for a genomic section in which the duplication is found. Often a duplication of a sequence in a genomic section increases the elevation. In some embodiments, a duplication present in genomic sections making up a first elevation increases the elevation relative to a second elevation where a duplication is absent. In some embodiments, an insertion increases the counts of a genomic section and a sequence representing the insertion is present (i.e., duplicated) at another location within the same genomic section. In some embodiments, an insertion does not significantly increase the counts of a genomic section or elevation and the sequence that is inserted is not a duplication of a sequence within the same genomic section. In some embodiments, an insertion is not detected or represented as a duplication and a duplicate sequence representing the insertion is not present in the same genomic section.
In some embodiments a copy number variation is a fetal copy number variation. Often, a fetal copy number variation is a copy number variation in the genome of a fetus. In some embodiments a copy number variation is a maternal copy number variation. In some embodiments, a maternal and/or fetal copy number variation is a copy number variation within the genome of a pregnant female (e.g., a female subject bearing a fetus), a female subject that gave birth or a female capable of bearing a fetus. A copy number variation can be a heterozygous copy number variation where the variation (e.g., a duplication or deletion) is present on one allele of a genome. A copy number variation can be a homozygous copy number variation where the variation is present on both alleles of a genome. In some embodiments a copy number variation is a heterozygous or homozygous fetal copy number variation. In some embodiments a copy number variation is a heterozygous or homozygous maternal and/or fetal copy number variation. A copy number variation sometimes is present in a maternal genome and a fetal genome, a maternal genome and not a fetal genome, or a fetal genome and not a maternal genome.
“Ploidy” refers to the number of chromosomes present in a fetus or mother. In some embodiments, “Ploidy” is the same as “chromosome ploidy”. In humans, for example, autosomal chromosomes are often present in pairs. For example, in the absence of a genetic variation, most humans have two of each autosomal chromosome (e.g., chromosomes 1-22). The presence of the normal complement of 2 autosomal chromosomes in a human is often referred to as euploid. “Microploidy” is similar in meaning to ploidy. “Microploidy” often refers to the ploidy of a segment of a chromosome. The term “microploidy” sometimes refers to the presence or absence of a copy number variation (e.g., a deletion, duplication and/or an insertion) within a chromosome (e.g., a homozygous or heterozygous deletion, duplication, or insertion, the like or absence thereof). “Ploidy” and “microploidy” sometimes are determined after normalization of counts of an elevation in a profile (e.g., after normalizing counts of an elevation to an NRV of 1). Thus, an elevation representing an autosomal chromosome pair (e.g., a euploid) is often normalized to an NRV of 1 and is referred to as a ploidy of 1. Similarly, an elevation within a segment of a chromosome representing the absence of a duplication, deletion or insertion is often normalized to an NRV of 1 and is referred to as a microploidy of 1. Ploidy and microploidy are often bin-specific (e.g., genomic section specific) and sample-specific. Ploidy is often defined as integral multiples of ½, with the values of 1, ½, 0, 3/2, and 2 representing euploidy (e.g., 2 chromosomes), 1 chromosome present (e.g., a chromosome deletion), no chromosome present, 3 chromosomes (e.g., a trisomy) and 4 chromosomes, respectively. Likewise, microploidy is often defined as integral multiples of ½, with the values of 1, ½, 0, 3/2, and 2 representing euploidy (e.g., no copy number variation), a heterozygous deletion, homozygous deletion, heterozygous duplication and homozygous duplication, respectively.
In some embodiments, the microploidy of a fetus matches the microploidy of the mother of the fetus (i.e., the pregnant female subject). In some embodiments, the microploidy of a fetus matches the microploidy of the mother of the fetus and both the mother and fetus carry the same heterozygous copy number variation, homozygous copy number variation or both are euploid. In some embodiments, the microploidy of a fetus is different than the microploidy of the mother of the fetus. For example, sometimes the microploidy of a fetus is heterozygous for a copy number variation, the mother is homozygous for a copy number variation and the microploidy of the fetus does not match (e.g., does not equal) the microploidy of the mother for the specified copy number variation.
A microploidy is often associated with an expected elevation. For example, sometimes an elevation (e.g., an elevation in a profile, sometimes an elevation that includes substantially no copy number variation) is normalized to an NRV of 1 and the microploidy of a homozygous duplication is 2, a heterozygous duplication is 1.5, a heterozygous deletion is 0.5 and a homozygous deletion is zero.
A genetic variation for which the presence or absence is identified for a subject is associated with a medical condition in certain embodiments. Thus, technology described herein can be used to identify the presence or absence of one or more genetic variations that are associated with a medical condition or medical state. Non-limiting examples of medical conditions include those associated with intellectual disability (e.g., Down Syndrome), aberrant cell-proliferation (e.g., cancer), presence of a micro-organism nucleic acid (e.g., virus, bacterium, fungus, yeast), and preeclampsia.
Non-limiting examples of genetic variations, medical conditions and states are described hereafter.
Fetal Gender
In some embodiments, the prediction of a fetal gender or gender related disorder (e.g., sex chromosome aneuploidy) can be determined by a method or apparatus described herein. In some embodiments, a method in which fetal gender is determined can also comprise determining fetal fraction and/or presence or absence of a fetal genetic variation (e.g., fetal chromosome aneuploidy). Determining presence or absence of a fetal genetic variation can be performed in a suitable manner, non-limiting examples of which include karyotype analysis, amniocentesis, circulating cell-free nucleic acid analysis, cell-free fetal DNA analysis, nucleotide sequence analysis, sequence read quantification, targeted approaches, amplification-based approaches, mass spectrometry-based approaches, differential methylation-based approaches, differential digestion-based approaches, polymorphism-based approaches, hybridization-based approaches (e.g., using probes), and the like.
Gender determination generally is based on a sex chromosome. In humans, there are two sex chromosomes, the X and Y chromosomes. The Y chromosome contains a gene, SRY, which triggers embryonic development as a male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production. Individuals with XX are female and XY are male and non-limiting variations, often referred to as sex chromosome aneuploidies, include X0, XYY, XXX and XXY. In some instances, males have two X chromosomes and one Y chromosome (XXY; Klinefelter's Syndrome), or one X chromosome and two Y chromosomes (XYY syndrome; Jacobs Syndrome), and some females have three X chromosomes (XXX; Triple X Syndrome) or a single X chromosome instead of two (X0; Turner Syndrome). In some instances, only a portion of cells in an individual are affected by a sex chromosome aneuploidy which may be referred to as a mosaicism (e.g., Turner mosaicism). Other cases include those where SRY is damaged (leading to an XY female), or copied to the X (leading to an XX male).
In certain cases, it can be beneficial to determine the gender of a fetus in utero. For example, a patient (e.g., pregnant female) with a family history of one or more sex-linked disorders may wish to determine the gender of the fetus she is carrying to help assess the risk of the fetus inheriting such a disorder. Sex-linked disorders include, without limitation, X-linked and Y-linked disorders. X-linked disorders include X-linked recessive and X-linked dominant disorders. Examples of X-linked recessive disorders include, without limitation, immune disorders (e.g., chronic granulomatous disease (CYBB), Wiskott-Aldrich syndrome, X-linked severe combined immunodeficiency, X-linked agammaglobulinemia, hyper-IgM syndrome type 1, IPEX, X-linked lymphoproliferative disease, Properdin deficiency), hematologic disorders (e.g., Hemophilia A, Hemophilia B, X-linked sideroblastic anemia), endocrine disorders (e.g., androgen insensitivity syndrome/Kennedy disease, KAL1 Kallmann syndrome, X-linked adrenal hypoplasia congenital), metabolic disorders (e.g., ornithine transcarbamylase deficiency, oculocerebrorenal syndrome, adrenoleukodystrophy, glucose-6-phosphate dehydrogenase deficiency, pyruvate dehydrogenase deficiency, Danon disease/glycogen storage disease Type IIb, Fabry's disease, Hunter syndrome, Lesch-Nyhan syndrome, Menkes disease/occipital horn syndrome), nervous system disorders (e.g., Coffin-Lowry syndrome, MASA syndrome, X-linked alpha thalassemia mental retardation syndrome, Siderius X-linked mental retardation syndrome, color blindness, ocular albinism, Norrie disease, choroideremia, Charcot-Marie-Tooth disease (CMTX2-3), Pelizaeus-Merzbacher disease, SMAX2), skin and related tissue disorders (e.g., dyskeratosis congenital, hypohidrotic ectodermal dysplasia (EDA), X-linked ichthyosis, X-linked endothelial corneal dystrophy), neuromuscular disorders (e.g., Becker's muscular dystrophy/Duchenne, centronuclear myopathy (MTM1), Conradi-Hünermann syndrome, Emery-Dreifuss muscular dystrophy 1), urologic disorders (e.g., Alport syndrome, Dent's disease, X-linked nephrogenic diabetes insipidus), bone/tooth disorders (e.g., AMELX Amelogenesis imperfecta), and other disorders (e.g., Barth syndrome, McLeod syndrome, Smith-Fineman-Myers syndrome, Simpson-Golabi-Behmel syndrome, Mohr-Tranebjrg syndrome, Nasodigitoacoustic syndrome). Examples of X-linked dominant disorders include, without limitation, X-linked hypophosphatemia, Focal dermal hypoplasia, Fragile X syndrome, Aicardi syndrome, Incontinentia pigmenti, Rett syndrome, CHILD syndrome, Lujan-Fryns syndrome, and Orofaciodigital syndrome 1. Examples of Y-linked disorders include, without limitation, male infertility, retinits pigmentosa, and azoospermia.
Chromosome Abnormalities
In some embodiments, the presence or absence of a fetal chromosome abnormality can be determined by using a method or apparatus described herein. Chromosome abnormalities include, without limitation, a gain or loss of an entire chromosome or a region of a chromosome comprising one or more genes. Chromosome abnormalities include monosomies, trisomies, polysomies, loss of heterozygosity, deletions and/or duplications of one or more nucleotide sequences (e.g., one or more genes), including deletions and duplications caused by unbalanced translocations. The terms “aneuploidy” and “aneuploid” as used herein refer to an abnormal number of chromosomes in cells of an organism. As different organisms have widely varying chromosome complements, the term “aneuploidy” does not refer to a particular number of chromosomes, but rather to the situation in which the chromosome content within a given cell or cells of an organism is abnormal. In some embodiments, the term “aneuploidy” herein refers to an imbalance of genetic material caused by a loss or gain of a whole chromosome, or part of a chromosome. An “aneuploidy” can refer to one or more deletions and/or insertions of a segment of a chromosome.
The term “monosomy” as used herein refers to lack of one chromosome of the normal complement. Partial monosomy can occur in unbalanced translocations or deletions, in which only a segment of the chromosome is present in a single copy. Monosomy of sex chromosomes (45, X) causes Turner syndrome, for example.
The term “disomy” refers to the presence of two copies of a chromosome. For organisms such as humans that have two copies of each chromosome (those that are diploid or “euploid”), disomy is the normal condition. For organisms that normally have three or more copies of each chromosome (those that are triploid or above), disomy is an aneuploid chromosome state. In uniparental disomy, both copies of a chromosome come from the same parent (with no contribution from the other parent).
The term “euploid”, in some embodiments, refers a normal complement of chromosomes.
The term “trisomy” as used herein refers to the presence of three copies, instead of two copies, of a particular chromosome. The presence of an extra chromosome 21, which is found in human Down syndrome, is referred to as “Trisomy 21.” Trisomy 18 and Trisomy 13 are two other human autosomal trisomies. Trisomy of sex chromosomes can be seen in females (e.g., 47, XXX in Triple X Syndrome) or males (e.g., 47, XXY in Klinefelter's Syndrome; or 47, XYY in Jacobs Syndrome).
The terms “tetrasomy” and “pentasomy” as used herein refer to the presence of four or five copies of a chromosome, respectively. Although rarely seen with autosomes, sex chromosome tetrasomy and pentasomy have been reported in humans, including XXXX, XXXY, XXYY, XYYY, XXXXX, XXXXY, XXXYY, XXYYY and XYYYY.
Chromosome abnormalities can be caused by a variety of mechanisms. Mechanisms include, but are not limited to (i) nondisjunction occurring as the result of a weakened mitotic checkpoint, (ii) inactive mitotic checkpoints causing non-disjunction at multiple chromosomes, (iii) merotelic attachment occurring when one kinetochore is attached to both mitotic spindle poles, (iv) a multipolar spindle forming when more than two spindle poles form, (v) a monopolar spindle forming when only a single spindle pole forms, and (vi) a tetraploid intermediate occurring as an end result of the monopolar spindle mechanism.
The terms “partial monosomy” and “partial trisomy” as used herein refer to an imbalance of genetic material caused by loss or gain of part of a chromosome. A partial monosomy or partial trisomy can result from an unbalanced translocation, where an individual carries a derivative chromosome formed through the breakage and fusion of two different chromosomes. In this situation, the individual would have three copies of part of one chromosome (two normal copies and the segment that exists on the derivative chromosome) and only one copy of part of the other chromosome involved in the derivative chromosome.
The term “mosaicism” as used herein refers to aneuploidy in some cells, but not all cells, of an organism. Certain chromosome abnormalities can exist as mosaic and non-mosaic chromosome abnormalities. For example, certain trisomy 21 individuals have mosaic Down syndrome and some have non-mosaic Down syndrome. Different mechanisms can lead to mosaicism. For example, (i) an initial zygote may have three 21st chromosomes, which normally would result in simple trisomy 21, but during the course of cell division one or more cell lines lost one of the 21st chromosomes; and (ii) an initial zygote may have two 21st chromosomes, but during the course of cell division one of the 21st chromosomes were duplicated. Somatic mosaicism likely occurs through mechanisms distinct from those typically associated with genetic syndromes involving complete or mosaic aneuploidy. Somatic mosaicism has been identified in certain types of cancers and in neurons, for example. In certain instances, trisomy 12 has been identified in chronic lymphocytic leukemia (CLL) and trisomy 8 has been identified in acute myeloid leukemia (AML). Also, genetic syndromes in which an individual is predisposed to breakage of chromosomes (chromosome instability syndromes) are frequently associated with increased risk for various types of cancer, thus highlighting the role of somatic aneuploidy in carcinogenesis. Methods and protocols described herein can identify presence or absence of non-mosaic and mosaic chromosome abnormalities.
Tables 1A and 1B present a non-limiting list of chromosome conditions, syndromes and/or abnormalities that can be potentially identified by methods and apparatus described herein. Table 1B is from the DECIPHER database as of Oct. 6, 2011 (e.g., version 5.1, based on positions mapped to GRCh37; available at uniform resource locator (URL) dechipher.sanger.ac.uk).
Grade 1 conditions often have one or more of the following characteristics; pathogenic anomaly; strong agreement amongst geneticists; highly penetrant; may still have variable phenotype but some common features; all cases in the literature have a clinical phenotype; no cases of healthy individuals with the anomaly; not reported on DVG databases or found in healthy population; functional data confirming single gene or multi-gene dosage effect; confirmed or strong candidate genes; clinical management implications defined; known cancer risk with implication for surveillance; multiple sources of information (OMIM, GeneReviews, Orphanet, Unique, Wikipedia); and/or available for diagnostic use (reproductive counseling).
Grade 2 conditions often have one or more of the following characteristics; likely pathogenic anomaly; highly penetrant; variable phenotype with no consistent features other than DD; small number of cases/reports in the literature; all reported cases have a clinical phenotype; no functional data or confirmed pathogenic genes; multiple sources of information (OMIM, Genereviews, Orphanet, Unique, Wikipedia); and/or may be used for diagnostic purposes and reproductive counseling.
Grade 3 conditions often have one or more of the following characteristics; susceptibility locus; healthy individuals or unaffected parents of a proband described; present in control populations; non penetrant; phenotype mild and not specific; features less consistent; no functional data or confirmed pathogenic genes; more limited sources of data; possibility of second diagnosis remains a possibility for cases deviating from the majority or if novel clinical finding present; and/or caution when using for diagnostic purposes and guarded advice for reproductive counseling.
Preeclampsia
In some embodiments, the presence or absence of preeclampsia is determined by using a method or apparatus described herein. Preeclampsia is a condition in which hypertension arises in pregnancy (i.e. pregnancy-induced hypertension) and is associated with significant amounts of protein in the urine. In some instances, preeclampsia also is associated with elevated levels of extracellular nucleic acid and/or alterations in methylation patterns. For example, a positive correlation between extracellular fetal-derived hypermethylated RASSF1A levels and the severity of pre-eclampsia has been observed. In certain examples, increased DNA methylation is observed for the H19 gene in preeclamptic placentas compared to normal controls.
Preeclampsia is one of the leading causes of maternal and fetal/neonatal mortality and morbidity worldwide. Circulating cell-free nucleic acids in plasma and serum are novel biomarkers with promising clinical applications in different medical fields, including prenatal diagnosis. Quantitative changes of cell-free fetal (cff) DNA in maternal plasma as an indicator for impending preeclampsia have been reported in different studies, for example, using real-time quantitative PCR for the male-specific SRY or DYS 14 loci. In cases of early onset preeclampsia, elevated levels may be seen in the first trimester. The increased levels of cffDNA before the onset of symptoms may be due to hypoxia/reoxygenation within the intervillous space leading to tissue oxidative stress and increased placental apoptosis and necrosis. In addition to the evidence for increased shedding of cffDNA into the maternal circulation, there is also evidence for reduced renal clearance of cffDNA in preeclampsia. As the amount of fetal DNA is currently determined by quantifying Y-chromosome specific sequences, alternative approaches such as measurement of total cell-free DNA or the use of gender-independent fetal epigenetic markers, such as DNA methylation, offer an alternative. Cell-free RNA of placental origin is another alternative biomarker that may be used for screening and diagnosing preeclampsia in clinical practice. Fetal RNA is associated with subcellular placental particles that protect it from degradation. Fetal RNA levels sometimes are ten-fold higher in pregnant females with preeclampsia compared to controls, and therefore is an alternative biomarker that may be used for screening and diagnosing preeclampsia in clinical practice.
Pathogens
In some embodiments, the presence or absence of a pathogenic condition is determined by a method or apparatus described herein. A pathogenic condition can be caused by infection of a host by a pathogen including, but not limited to, a bacterium, virus or fungus. Since pathogens typically possess nucleic acid (e.g., genomic DNA, genomic RNA, mRNA) that can be distinguishable from host nucleic acid, methods and apparatus provided herein can be used to determine the presence or absence of a pathogen. Often, pathogens possess nucleic acid with characteristics unique to a particular pathogen such as, for example, epigenetic state and/or one or more sequence variations, duplications and/or deletions. Thus, methods provided herein may be used to identify a particular pathogen or pathogen variant (e.g. strain).
Cancers
In some embodiments, the presence or absence of a cell proliferation disorder (e.g., a cancer) is determined by using a method or apparatus described herein. For example, levels of cell-free nucleic acid in serum can be elevated in patients with various types of cancer compared with healthy patients. Patients with metastatic diseases, for example, can sometimes have serum DNA levels approximately twice as high as non-metastatic patients. Patients with metastatic diseases may also be identified by cancer-specific markers and/or certain single nucleotide polymorphisms or short tandem repeats, for example. Non-limiting examples of cancer types that may be positively correlated with elevated levels of circulating DNA include breast cancer, colorectal cancer, gastrointestinal cancer, hepatocellular cancer, lung cancer, melanoma, non-Hodgkin lymphoma, leukemia, multiple myeloma, bladder cancer, hepatoma, cervical cancer, esophageal cancer, pancreatic cancer, and prostate cancer. Various cancers can possess, and can sometimes release into the bloodstream, nucleic acids with characteristics that are distinguishable from nucleic acids from non-cancerous healthy cells, such as, for example, epigenetic state and/or sequence variations, duplications and/or deletions. Such characteristics can, for example, be specific to a particular type of cancer. Thus, it is further contemplated that a method provided herein can be used to identify a particular type of cancer.
Placenta hypomethylated domains (PHDs), as described herein, show characteristics consistent with the partially methylated domains and/or global hypomethylation of certain tumors and cancer subtypes. Thus, methods, systems and processes described herein can be directly applied to non-invasive detection and monitoring of various tumors and cancers. The term “tumor nucleic acid” as used herein refers to nucleic acid derived or originating from a tumor or cancerous tissue.
The examples set forth below illustrate certain embodiments and do not limit the technology.
In this example, genome-wide differences in DNA methylation are leveraged to enrich for fetal DNA through methylation-specific restriction digestion. Often, there is a direct relationship between fetal fraction and the ability to detect genetic variations in the fetus (fetal aneuploidies) using cell free DNA analysis. The purpose of this technology is to use the global differences in DNA methylation between maternal and fetal/placental ccf DNA to enrich for fetal DNA.
Differences in DNA methylation generally exist between certain contributors to maternal (e.g., buffy coat or PBMC-derived) ccf DNA and fetal (e.g., placenta-derived) ccf DNA. A whole genome bisulfite sequencing experiment was designed to sequence and determine DNA methylation patterns of maternal buffy coat, placenta tissue, non-pregnant female ccf DNA, and pregnant female ccf DNA. The results showed that the placenta was strikingly hypomethylated relative to the buffy coat or maternal plasma (
Such differential methylation is used to enrich for fetal ccf DNA. To perform such a method, the following steps are performed:
Because these enzymes generally are inhibited by DNA methylation, methylated DNA fragments (higher proportion of maternal relative to fetal) remain unaffected while unmethylated DNA fragments (higher proportion of fetal relative to maternal) are digested by the restriction endonucleases. Such a method results in a population of DNA fragments enriched for fetal DNA. Such enrichment sometimes leaves fewer input DNA molecules for downstream processing.
To examine the feasibility of a method described above, the frequency of certain restriction sites was evaluated. Based on the hg19 human genome sequence, a total of 3,953,090 recognition sequences were identified in the human genome for one of the enzymes (
Next, the distance between restriction enzyme recognition sequences was calculated. Since ccf DNA generally is present in maternal plasma within a narrow size window (e.g., typically less than 200 bp in length), the distance between sites is considered when selecting one or more restriction endonucleases. Using the CpG sites for which data was obtained in both non-pregnant ccf DNA and placenta (n=3,562,431), the median distance between adjacent CpG sites was 184 bp. In evaluating the distribution of distances, these analyses show approximately 529,000 fragments generated with a length between 40 bp and 100 bp (
Next, the mean methylation level of each CpG site within the restriction enzyme recognition sequence was compared between buffy coat and placenta (n=3,566,125). Within these sites, the median methylation level was significantly reduced in placenta relative to buffy coat (
A more direct comparison of the methylation level at each targeted CpG site revealed that the mean methylation of those sites in buffy coat was greater than the mean methylation in placenta for 80.8% of sites, although there was a large proportion that were unchanged (
Taken together, these data indicate that selective digestion and ligation of unmethylated fragments globally enriches for placental/fetal DNA in a sample comprising maternal and fetal ccf DNA. Tables 2AA, 2AB, 2B, 2CA and 2CB below present differentially methylated human genomic regions.
Information in Table 2AA, 2AB, 2B, 2CA, 2CB and Table 3 is based on the March 2006 human reference sequence (UCSC Ver. hg18, NCBI Build 36.1), which was produced by the International Human Genome Sequencing Consortium.
Additional hypomethylated loci are presented in TABLE 4, which includes genomic regions in chromosomes 13, 18 and 21 that are significantly hypomethylated in the placenta when compared to non-pregnant circulating cell free DNA. Additional hypermethylated loci are presented in TABLE 5, which includes genomic regions in chromosomes 13, 18 and 21 that are significantly hypermethylated in the placenta when compared to non-pregnant circulating cell free DNA. Chromosome numbers in TABLE 4 and TABLE 5 are indicated in the column labeled “chr”. In TABLE 4 and TABLE 5 chromosome-specific start (“start.pos” in TABLE 4 or “DMR Start” in TABLE 5) and end positions (“end.pos” in TABLE 4 or “DMR End” in TABLE 5)) reference nucleotide base positions from the hg19/GRCh37 build of the human reference genome. Each start and end position marks a specific chromosome region or locus. The data for these regions were obtained by performing whole genome bisulfite sequencing on 5 placenta and 9 non-pregnant ccf DNA samples. The regions are ranked according to the median t-statistic (median.tstat) or mean t-statistic (mean.tstat) of the region when comparing the methylation status of placenta nucleic acid to non-pregnant ccf DNA. In TABLE 4, a negative median t-statistic value indicates a locus that is less methylated in placenta relative to non-pregnant ccf DNA. In TABLE 5, a negative mean t-statistic value indicates a locus that is more methylated in placenta relative to non-pregnant ccf DNA. In TABLE 4 and TABLE 5 a large negative value (e.g., −17) indicates a greater significant difference in methylation status than a smaller negative value (e.g., −5) for mean or median t-statistic. In TABLE 5, each value in the “mean.diff” column is the difference between a first value and a second value: (i) the first value is the mean of mean methylation levels for CpG sites in the specified region for placenta, and (ii) the second value is the mean of mean methylation levels for CpG sites in the specified region for non-pregnant female plasma samples. The number of CpG sites in each locus is indicated by the column labeled “num.cg” in TABLE 4. The length of each locus is indicated in the column labeled “dmr.size” (TABLE 4) or “size” (TABLE 5). The first column on the left of the table is an internal identifier of each locus.
Whole genome bisulfite sequencing (WGBS) was performed, in part to characterize the methylome of ccf DNA from eight non-pregnant and seven pregnant female donors. In addition, seven genomic DNA samples isolated from buffy coat and five placenta samples were sequenced at single base resolution. This produced single-base resolution DNA methylome maps of ccf DNA for each sample type. This analysis demonstrated a link between local DNA methylation levels and ccf DNA fragment size and showed large, continuous regions of hypomethylation in the placenta (Placenta Hypomethylated Domains or PHDs), an epigenetic phenomenon, until recently, only described in tumor samples. Hypomethylated DMRs identified are provided in Table 4 and hypermethylated DMRs identified are provided in Table 5.
Whole genome bisulfite sequencing was performed on a set of unmatched samples including ccf DNA from 8 non-pregnant ((NP; n=8) and 7 pregnant (n=7) female donors and genomic DNA from 7 buffy coat (n=7) and 5 placenta (n=5) samples. CpG cytosines within longer fragments were determined more likely to be methylated, linking DNA methylation and fragment size in ccf DNA. Comparison of the methylomes of placenta and NP ccf DNA revealed many of the 51,259 identified differentially methylated regions (DMRs) were located in domains exhibiting consistent placenta hypomethylation across millions of consecutive bases. These regions were termed placenta hypomethylated domains. DMRs identified when comparing placenta to NP ccf DNA were recapitulated in pregnant ccf DNA, which confirmed the ability to detect differential methylation in ccf DNA mixtures.
Results
Single base resolution methylome maps of ccf DNA isolated from the plasma of 8 non-pregnant female donors were produced using WGBS. About 269-551 million paired monoclonal reads per sample were generated, enabling >10× coverage of 74-92% of the ˜28 million genomic CpG sites. Cytosine methylation was evaluated in each of the previously identified genomic contexts (CpG, CHG, and CHH). Almost all cytosine methylation occurred in the CpG context with 74.5-75.3% of all CpG cytosines being methylated; methylation in each of the other contexts was minimal (<0.25%). This data generated eight comprehensive genome-wide CpG cytosine methylation maps of ccf DNA which served as a foundation for subsequent comparisons within this study.
WGBS was performed on DNA obtained from buffy coat cells obtained from 7 distinct female donors. Methylation levels at 37775 CpG sites were confirmed by MassARRAY in an independent cohort of 8 buffy coat samples (Pearson correlation=0.953). Nearly all CpG sites in buffy coat showed either low (9.7%) or high (79.8%) levels of methylation, similar to the distribution in non-pregnant ccf DNA.
Next, the link between histone tail modifications and DNA methylation was examined. Using publically available PBMC ChIP-Seq data from the ENCODE project, CpG methylation in non-pregnant ccf DNA was examined within regions enriched for four distinct histone H3 modifications. In regions enriched for H3K4me3, 89.9% of cytosines showed less than 20% methylation while only 5.2% of unenriched sites were similarly unmethylated. Conversely, 84.9% of CpG sites were methylated (>75%) in H3K9me3 enriched regions as compared to 76.3% in unenriched regions. Distinct differences were also observed when comparing H3K4me1 and H3K27me3 enriched regions to corresponding unenriched CpG sites. Taken together, these data suggested a link between particular histone marks and CpG methylation in buffy coat. Comparison of the methylomes of buffy coat and non-pregnant ccf DNA indicated high similarity (Pearson correlation=0.954)); however, 152 differentially methylated regions (DMRs) (139 more methylated in buffy coat) were detected, suggesting there are additional sources of cell free DNA distinct from buffy coat present in circulation. This data linked histone modifications to CpG methylation in buffy coat and suggested that the majority of ccf DNA is derived from the hematopoetic compartment with minimal contributions from alternative tissues.
Since the fetal portion of ccf DNA in pregnant plasma is derived from the placenta, WGBS of 5 placenta samples was performed to identify placenta specific DMRs. Methylation levels of 37775 CpG sites were also measured using MassARRAY in a separate sample cohort and showed high concordance (Pearson correlation=0.897). Comparison of the distribution of methylation in placenta to the distribution in non-pregnant ccf DNA or buffy coat revealed a significant difference (p<2.2e-16; Kolmogorov-Smirnov Test). While only 15.5% and 10.5% of CpG sites exhibited intermediate methylation (20%-75%) in non-pregnant ccf DNA and buffy coat, respectively, 46.6% of CpG sites showed intermediate methylation in placenta tissue. Comparison of CpG sites between placenta and buffy coat revealed that the majority of the intermediate methylated regions in placenta were highly methylated in both non-pregnant ccf DNA and buffy coat. CpG methylation was compared to gene expression determined by microarray analysis on an independent cohort of 8 placenta samples. Transcription start sites (TSS) were generally unmethylated independent of gene expression level, while promoter and intragenic regions were linked to gene expression.
Differential methylation between placenta and each of the aforementioned sample types was then analyzed. The analysis identified 51,259 DMRs between placenta and non-pregnant ccf DNA, of which 89.5% were more methylated in ccf DNA, consistent with the observed distribution differences (
Examination of the genomic distribution of differential methylation uncovered large contiguous genomic regions with significant placenta hypomethylation relative to non-pregnant ccf DNA, termed placenta hypomethylated domains (PHDs). PHDs were typically located in gene deserts and were characterized by high, largely invariant levels of DNA methylation in non-pregnant ccf DNA and placenta hypomethylation, often approaching 50%. Using a window size of 50 kbp, PHDs were detected on each autosome that covered as many as ˜10 million bases. A number of these regions were located on chromosome 16 with particular focus upon a 10 Mbp PHD located on chromosome 16q. Since the presence of a PHD was consistently observed in regions of relatively low CpG density, the link between CpG density and methylation levels was further examined. Indeed, the magnitude of placenta hypomethylation in relatively low CpG density regions far surpasses that observed in more dense regions. A similar pattern was observed when comparing CpG methylation to gene density. Moreover, the magnitude of differential methylation was linked to the local CpG Density. This data identified large genomic regions which were consistently hypomethylated in the placenta and linked these regions to low CpG and gene density, perhaps underscoring a lack of heterochromatin formation during early placenta development or allele specific methylation of regions with relatively low CpG density in the placenta.
The methylome of ccf DNA derived from the plasma of seven pregnant female donors was measured to determine if the DMRs identified between placenta and non-pregnant ccf DNA could be detected. Overall methylation levels in pregnant and non-pregnant ccf DNA were similar for non-CpG cytosines (<0.25%); however, overall methylation within a CpG context was significantly reduced from 74.5-75.3% to 71.0-74.0% (p=3e-04, Wilcoxon rank-sum). Since pregnant ccf DNA comprises maternal and fetal ccf DNA, different methylation patterns were expected between non-pregnant ccf DNA and placenta tissue. To address this, the mean methylation level of each CpG site within DMRs identified between non-pregnant ccf DNA and placenta was evaluated. CpG sites within identified DMRs exhibited significantly (p<2e-16; Wilcoxon rank-sum) different methylation levels in pregnant ccf DNA relative to non-pregnant ccf DNA. Hierarchical clustering confirmed these results by clustering pregnant and non-pregnant ccf DNA samples as single branches on a dendrogram. Overall, these data confirmed the differential methylation identified when comparing non-pregnant ccf DNA and placenta tissue.
Previous reports have indicated that fetal ccf DNA is shorter than its maternal counterpart. Since hypomethylation is linked to an open chromatin structure and thus increased accessibility to native endonucleases during apoptosis, the relationship between CpG methylation and ccf DNA length in non-pregnant plasma was assessed to determine if this contributed to the observed size difference. In each of the samples analyzed, the most prominent length was about 168 bp. After accounting for the differences in the number of analyzed bases for each size fraction, CpG cytosines within longer fragments (>200 bp) were found, on average, 12.3-fold more likely to be methylated. Interestingly, a similar pattern was also found for cytosines in the CHG (31.5-fold) and CHH (95.5-fold) contexts, although their overall occurrence was much lower than methylated CpG cytosines. Methyl-CpG immunoprecipitation (MCIp)-Seq was performed on an independent set of two non-pregnant ccf DNA samples to confirm the observed size differences for CpG cytosines. MCIp enabled the separation and collection of both the unmethylated and methylated fractions of a sample. Sequencing both fractions from each sample revealed a distinct size difference with the most striking difference between fractions occurring at ˜320 bp, roughly the size of two nucleosomes.
Non-invasive prenatal aneuploidy detection is sometimes linked to the fraction of fetal (placental) DNA in a sample. It was hypothesized that the global hypomethylation of the placenta may allow enrichment of fetal DNA. ccf DNA was isolated from the plasma of 12 pregnant donors, three of which were confirmed to be carrying a fetus affected with trisomy 21, and measured each sample with and without enriching for unmethylated DNA. Data from a subset of placenta hypomethylated regions showed that enriching for unmethylated DNA resulted in a 3.99-fold (range: 2.9-5.9 fold) increase in chromosome 21 z-scores in trisomy 21 samples relative to the same samples without enrichment; one sample from a euploid pregnancy showed a similar level of enrichment (
Discussion
Whole genome methylome maps were created for a total of 27 samples from 4 distinct sample types, enabling a comprehensive characterization of the methylome of ccf DNA from pregnant plasma and each of its primary cellular and non-cellular contributors. A total of 152 DMRs were identified when comparing non-pregnant ccf DNA to DNA isolated from buffy coat, thought to be the primary cellular contributor to this nucleic acid pool. While the DNA methylation patterns were similar (Pearson correlation=0.954), the differences identified were consistent with additional minority contributors to non-pregnant ccf DNA. Sources of additional contributors may include organ systems with extensive bloodstream contact including the kidneys, liver, or endothelium. By comparing placenta to non-pregnant ccf DNA, 51,259 DMRs were identified. While placenta hypermethylated regions were identified across the entire genome, this study also suggested that leveraging the global hypomethylation of the placenta has utility.
While evaluating the genomic distribution of DMRs, large regions of placenta hypomethylation were unexpectedly observed. Further characterization of hypomethylated regions indicated that they were present in regions with low CpG and gene density. Regions with these characteristics were often located within heterochromatin domains, pointing to a reduction in the formation or re-distribution of heterochromatin in the developing placenta. This was supported by the observed decrease in CpG methylation in the placenta within regions containing the H3K9me3 mark in PBMC. The identified PHDs showed characteristics consistent with the partially methylated domains and/or global hypomethylation previously described in cancer subtypes. Commonalities between the placenta and tumors were previously described and included an increased proliferation rate, the ability to migrate, and invasive potential. These data indicated that the parallels between cancer and the placenta extend to their epigenomes and may provide an experimental opportunity for elucidating the molecular source of these similarities. In addition, the similarities suggested that lessons learned from this study may be directly applicable to non-invasive tumor detection and monitoring.
Methods
Blood Processing and DNA Extraction.
Plasma samples were collected under two separate Investigational Review Board (IRB) approved clinical protocols (BioMed IRB 301-01 and Western IRB 20090444). Buffy coat and placenta tissue was collected from consented subjects under a Western IRB approved protocol (20111833, study #1128724) and in accordance with the FDA Guidance on Informed Consent for in vitro Diagnostic Device Studies Using Leftover Human Specimens that are Not Individually Identifiable (Apr. 25, 2006). All subjects provided written informed consent prior to undergoing any study related procedures. All information was anonymized prior to processing. Blood was processed and DNA extracted as previously described (Ehrich M, et al., Am J Obstet Gynecol (2011) 204:205 e201-211; Palomaki G E, et al., Genet Med (2011) 13:913-920; Jensen T J, et al., Clin Chem (2012) 58:1148-1151).
Library Preparation of Ccf DNA
For libraries created from ccf DNA, DNA was subjected to end repair, mono-adenylation, and ligation as previously described (Jensen T J, et al., PLoS One (2013) 8:e57381, Jensen T J, et al., Clin Chem (2012) 58:1148-1151). Since ccf DNA exists as small fragments, no size selection was required prior to sequencing and the length of each library insert represents a native DNA fragment length. Ligated products were treated with sodium bisulfite (EpiTect; Qiagen) using a cycling incubation of 95° C. for 5 minutes, 60° C. for 25 minutes, 95° C. for 5 minutes, 60° C. for 85 minutes, 95° C. for 5 minutes, and 60° C. for 175 minutes followed by 3 cycles of 95° C. for 5 minutes, 60° C. for 180 minutes. Each reaction was purified according to the manufacturer's instructions (Qiagen). Converted product was amplified using Pfu Turbo Cx Hotstart DNA polymerase (Agilent) and the TruSeq primer cocktail (Illumina) using the following cycling parameters: 95° C. for 5 minutes; 98° C. for 30 seconds; 14 cycles of 98° C. for 10 seconds, 65° C. for 30 seconds, 72° C. for 30 seconds; and 95° C. for 5 minutes.
Library Preparation of Genomic DNA
For libraries created from buffy coat or placenta tissue, genomic DNA (10 μg) was fragmented by sonication and column purified (Qiagen). Three ligated products were prepared from each sample (2.5 μg each) by performing end repair, mono-adenylation, and adaptor ligation according to the manufacturer's protocol (TruSeq; Illumina). Bead-based purification (AMPure XP; Beckman Coulter) was performed after the end repair and ligation processes. Ligated products were pooled and 2 distinct bisulfite conversion reactions were performed as described above. Eluted products from each sample were pooled and concentrated using a column-based method (Qiagen). Finally, 40% of each converted sample was amplified as described above. PCR products were purified using magnetic beads (AMPure XP; Beckman Coulter).
Methyl-CpG Immunoprecipitation (MCIp) Library Preparation
Ccf DNA was isolated from the plasma of either two non-pregnant female donors or twelve pregnant female donors and subjected to methyl-CpG immunoprecipitation according to the manufacturer's instructions (EpiMark; New England Biolabs). Briefly, DNA was incubated with the MBD-Fc protein in the presence of 150 mM NaCl. DNA which did not bind to the protein was collected and characterized as the unmethylated fraction. The protein-DNA complex was washed three times with 150 mM NaCl and DNA was eluted by heating to 65° C. for 15 minutes. Resultant unmethylated and methylated fractions from each donor sample were subjected to library preparation using a modified version of the manufacturer's protocol. Due to low input amounts, adaptor ligation was performed using a diluted adaptor oligonucleotide (1:10 for unmethylated; 1:100 for methylated). Resultant ligated ccf DNA was amplified using TruSeq PCR Master Mix and TruSeq primer cocktail (Illumina) using the following cycling parameters: 98° C. for 30 seconds; 10 cycles of 98° C. for 10 seconds, 65° C. for 30 seconds, 72° C. for 30 seconds; and 72° C. for 5 minutes.
Massively Parallel Sequencing
Library quantification and flow cell clustering were performed as previously described (Ehrich M, et al., Am J Obstet Gynecol (2011) 204:205 e201-211; Palomaki G E, et al, Genet Med (2011) 13:913-920; Jensen T J, et al., Clin Chem (2012) 58:1148-1151). Paired end sequencing was performed for 100 cycles for all whole genome bisulfite samples and 36 cycles for all MCIp-seq samples.
Whole Genome Bisulfite Sequencing Analysis
Libraries prepared from Phi-X were sequenced upon each flow cell to ensure accurate base calling. All methylation analysis was performed using v0.9.0 of the Illumina bisulfite sequencing analysis program. Bismark v.06.3 (Krueger F, Andrews S R, Bioinformatics (2011), 27:1571-1572) was utilized to align each sequenced read to a bisulfite converted human genome (hg19) using Bowtie v.0.12.7 (Langmead B, et al., Genome Biol. (2009), 10:R25) and simultaneously perform cytosine methylation calls. Prior to alignment, each read was trimmed to remove contaminating adaptor sequences. Each trimmed sequence read was then aligned to each of four bisulfite converted genomes, each derived from the conversion of each strand and the corresponding complement. Alignment was determined by the single best alignment score to one genome. Methylation was subsequently called for each covered cytosine and summary statistics calculated using the Bismark methylation_extractor script.
MCIp Sequencing Analysis
Data were aligned to a February, 2009 build of the human genome (hg19) allowing for only perfect matches within the seed sequence using Bowtie. All paired reads with an insert size greater than 500 bp or with discordant chromosome mapping results were discarded prior to analysis. Size was calculated as the distance between the start site of each of the two paired end reads.
Post Analysis Processing
Post analysis processing was performed using custom scripts in an R or Perl programming environment. Under the assumption that strand specific methylation is uncommon in ccf DNA, methylation calls mapped to the reverse strand were converted to their corresponding forward strand positions and methylation levels recalculated prior to all analyses. The location of each genomic region was obtained from the hg19 build of the UCSC genome browser. Length of each read was calculated by subtracting the distance of the start position of each paired read. The ENCODE data for the four histone tail modifications in PBMC samples was downloaded as narrowPeak files from the UCSC genome ENCODE site.
DMR Identification
The mean and standard deviation were calculated for each covered CpG site for each sample type. A t-statistic was then calculated for each CpG site for all comparisons. All sites with a t-statistic with an absolute value less than 5 were removed. CpG sites were grouped if there was less than 300 bp between them after t-statistic filtering. A region was then considered a DMR if there were 9 or more CpG sites present.
EpiTYPER (MassARRAY) Analysis
EpiTYPER analysis was performed as previously described (Novak P, et al., PLoS One (2012) 7:e52299). Primers were designed to regions of interest using EpiDesigner software (http://epidesigner.com). Briefly, genomic DNA sequences were obtained from the UCSC genome browser and loaded in to EpiDesigner. Primer sequences were exported from EpiDesigner and primers were ordered from Integrated DNA Technologies (Coralville, Iowa) and were received after standard desalting at a concentration of 100 μM. Genomic DNA was subjected to sodium bisulfite conversion using the Zymo EZ DNA Methylation Kit (Zymo, Orange, Calif.). EpiTYPER biochemistry was then performed as previously described [29]. Methylation values were exported from EpiTYPER and analysis performed in an R programming environment. Poor quality data were removed prior to further analysis.
Gene Expression Analysis
RNA was extracted from placenta villi according to manufacturer's protocol (Qiagen) and hybridized to Affymetrix Human Exon 1.0 ST microarrays. All raw data files (.CEL) were subjected to rma-sketch normalization using Affymetrix Power Tools scripts. Specifically, expression level was calculated at the whole gene level using the “apt-probeset-summarize” command. Subsequent to normalization, results were merged with the annotation information resulting in a total of 22011 gene expression values. Results were subsequently filtered to remove all transcripts which were not included as part of the main array design (4219) and transcripts without a defined gene (329), leaving a final set of 17,463 genes. Gene positions were downloaded from the UCSC genome browser for both refseq and Ensembl genes and transcription start sites from these tables were used to reflect the TSS of the expressed gene. All genes without a defined TSS as part of the refseq or Ensembl gene lists or those not located on autosomes were discarded, leaving a final set of 16,231 genes. These genes were subsequently tiered into the high (5,410), low (5,411), and intermediate (5,410) expressing genes.
MCIp Trisomy Evaluation
Ccf DNA was extracted from two aliquots of plasma (4 mL each) collected from 12 pregnant female donors, three of which were carrying a fetus affected with trisomy 21. The ccf DNA from each sample was then pooled to minimize any collection bias and subsequently separated into two aliquots. Aliquots were then either left untreated or subjected to MCIp to enrich for unmethylated DNA. Sequencing libraries were prepared and sequenced as described above. All data which aligned within a subset of the identified placenta hypomethylated regions were used for downstream analysis. The median and median absolute deviation (MAD) were calculated using data from known euploid samples only for both unenriched and enriched samples independently. Depending on the group (unenriched vs. enriched), chromosome 21 z-scores were calculated using a robust method as follows: Z=(Chr 21 Fractionsample-Chr 21 FractionMedian)/Chr 21 FractionMAD.
Nucleic acids containing unmethylated and methylated cytosine residues can be distinguished in a number of ways including, but not limited to, methylation sensitive or methylation specific restriction enzyme treatment, sodium bisulfite conversion, and incubation with a protein, substrate, or other moiety capable of binding methylated or unmethylated DNA with differing affinity, for example an antibody to methylated cytosine or a protein containing a methyl binding domain (MBD).
As described herein, placenta nucleic acid (e.g., fetal nucleic acid derived from placenta) generally is hypomethylated relative to most tissues in the body. This feature of fetal nucleic acid is exploited to enrich a sample of nucleic acid obtained from maternal blood for fetal nucleic acid. A protein capable of distinguishing between methylated and unmethylated DNA can be used to differentially bind to methylated nucleic acid or hypomethylated nucleic acid. A non-limiting example of such a protein is MBD-Fc, which comprises the methyl binding domain of MBD2 fused to the Fc domain of human IgG1 (Gebhard C, et al., (2006) Cancer Res 66:6118-6128).
In a particular enrichment method, circulating cell-free (ccf) DNA is isolated from the plasma of non-pregnant female donors or pregnant female donors and subjected to methyl-CpG immunoprecipitation (e.g., EpiMark; New England Biolabs). Briefly, DNA is incubated with MBD-Fc protein in the presence of 150 mM NaCl. DNA that does not bind to the protein is collected and characterized as the unmethylated fraction. The protein-DNA complex can be washed three times with 150 mM NaCl and DNA can be eluted by heating to 65° C. for 15 minutes, yielding methylated nucleic acid.
Since it has been shown that fetal fraction enhances the ability to discriminate euploid from aneuploid samples in ccf DNA, it stands to reason that such a method would act to increase the discriminatory power of various non-invasive prenatal testing assays, thereby increasing test accuracy. Resultant unmethylated and methylated fractions from each donor sample may be subjected to further biochemical modifications (e.g., library preparation for massively parallel sequencing). Enriched and separated subsets of nucleic acids (e.g., generated as described above), can be analyzed using a number of methods including, but not limited to, massively parallel sequencing, digital PCR, or mass spectrometry.
Listed hereafter are non-limiting examples of certain embodiments of the technology.
A1. A method for analyzing fetal nucleic acid in a sample, comprising:
(a) digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments; and
(b) analyzing the digested nucleic acid fragments.
A2. The method of embodiment A1, which comprises prior to (b) enriching the digested nucleic acid fragments relative to non-digested nucleic acid, thereby generating nucleic acid enriched for the fetal nucleic acid.
A3. A method for enriching for fetal nucleic acid in a sample, comprising:
(a) digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments; and
(b) enriching the digested nucleic acid fragments relative to non-digested nucleic acid, thereby generating nucleic acid enriched for the fetal nucleic acid.
A4. The method of embodiment A3, comprising (c) analyzing the enriched fetal nucleic acid.
A4.1. The method of embodiment A1, A2 or A4, wherein the analyzing comprises a target-based analysis.
A4.2. The method of embodiment A1, A2 or A4, wherein the analyzing comprises a non-target-based analysis.
A4.3. The method of any one of embodiments A1, A2 and A4 to A4.2, wherein the analysis comprises sequencing.
A4.4. The method of embodiment A4.3, wherein the sequencing comprises sequencing a portion of the enriched fetal nucleic acid.
A4.5. The method of embodiment A4.4, comprising sequencing a portion of the enriched fetal nucleic acid that is hypomethylated.
A4.6. The method of embodiment A4.4, comprising sequencing a portion of the enriched fetal nucleic acid that is hypermethylated.
A4.7. The method of embodiment A4.3, comprising sequencing substantially all of the enriched fetal nucleic acid.
A4.8. The method of embodiment A4.3, wherein the sequencing method comprises sequencing by synthesis.
A4.9. The method of any one of embodiments A1, A2 and A4 to A4.2, wherein the analyzing comprises mass spectrometry.
A4.10. The method of embodiment A4.9, wherein the mass spectrometry analysis comprises a targeted-mass spectrometry.
A5. The method of any one of embodiments A1, A2 and A4 to A4.10, wherein the analyzing comprises determining the presence or absence of one or more polynucleotides in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid.
A5.1. The method of any one of embodiments A1, A2 and A4 to A5, wherein the analyzing comprises determining the amount of one or more polynucleotides in one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid.
A5.2. The method of any one of embodiments A1, A2 and A4 to A5, wherein a difference in methylation status between fetal nucleic acid and maternal nucleic acid for the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid is 5% or more.
A5.2.1. The method of embodiment A5.2, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid is determined by a statistical method chosen from a t-test, Z-test, Chi-square, Wilcox, ANOVA, MANOVA, MANCOVA and logistic regression.
A5.2.2. The method of embodiment A5.2.1, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid is determined by a t-test.
A5.2.3. The method of embodiment A5.2.2, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid for the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a median t-statistic between −18.0 and −7.0 or comprise a statistical difference comparable to a t-statistic between −18.0 and −7.0.
A5.3. The method of any one of embodiments A2 to A5.2.3, wherein the nucleic acid enriched for fetal nucleic acid comprise one or more polynucleotides in one or more loci that are 60% or less methylated in fetal nucleic acid and 61% or greater methylated in maternal nucleic acid.
A6. The method of any one of embodiments A5 to A5.3, wherein the one or more loci are chosen from loci in Table 2AB, Table 2CB, Table 3 and Table 4.
A6.1. The method of embodiment A6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg18, NCBI Build 36.1 of: chr13: 19290394-19290768, chr13: 19887090-19887336; chr13: 20193675-20193897; chr13: 109232856-109235065; chr13: 109716455-109716604; chr13: 112724910-112725742; chr13: 112799123-112799379; chr18: 6919797-6919981; chr18: 13377536-13377654; chr18: 41671477-41673011; chr18: 58203013-58203282; chr18: 70133945-70134397; chr18: 71128742-71128974; chr18: 72664454-72664736; chr18: 74170347-74170489; chr18: 75596358-75596579; chr18: 75760343-75760820; chr21: 33327593-33328334; chr21: 35180938-35185436; chr21: 44529935-44530388; chr21: 45061293-45061853; chr21: 45202815-45202972; chr21: 45671984-45672098; chr21: 45754383-45754487; chr3: 9963364-9964023; chr5: 138757911-138758724; chr6: 35561812-35562252; chr12: 1642456-1642708; chr12: 56406249-56407788; and chr12: 56416146-56418794.
A6.2. The method of embodiment A6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg18, NCBI Build 36.1 of: chr21: 9906600-9906800; chr21: 9907000-9907400; chr21: 9917800-9918450; chr21: 10010000-10015000; chr21: 13974500-13976000; chr21: 13989500-13992000; chr21: 13998500-14000100; chr21: 14017000-14018500; chr21: 14056400-14058100; chr21: 14070250-14070550; chr21: 14119800-14120400; chr21: 14304800-14306100; chr21: 16881500-16883000; chr21: 17905300-17905500; chr21: 23574000-23574600; chr21: 24366920-24367060; chr21: 25656000-25656900; chr21: 26830750-26830950; chr21: 26938800-26939200; chr21: 30176500-30176750; chr21: 31955000-31955300; chr21: 33272200-33273300; chr21: 33328000-33328500; chr21: 35185000-35186000; chr21: 36589000-36590500; chr21: 42399200-42399900; chr21: 42528400-42528600; chr21: 42598300-42599600; chr21: 42910000-42911000; chr21: 42945500-42946000; chr21: 42961400-42962700; chr21: 42978200-42979800; chr21: 43130800-43131500; chr21: 43446600-43447600; chr21: 43463000-43466100; chr21: 43545000-43546000; chr21: 43606000-43606500; chr21: 43902500-43903800; chr21: 44446500-44447500; chr21: 44614500-44615000; chr21: 44750400-44751000; chr21: 45145500-45146100; chr21: 45501000-45503000; chr21: 45571500-45573700; chr21: 45609000-45610600; chr21: 45670000-45677000; chr21: 45700500-45702000; chr21: 45753000-45755000; chr21: 45885000-45887000; chr21: 46111000-46114000; chr21: 46142000-46144500; chr21: 46227000-46233000; chr21: 46245000-46252000; chr21: 46280500-46283000; chr21: 46343500-46344200; chr21: 46368000-46378000; chr21: 46426700-46427500; and chr21: 46546914-46547404.
A6.3. The method of embodiment A6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; chr1: 209819233-209819714; chr15: 99270658-99271954; chr9: 110581951-110582676; chr11: 76039765-76040736; chr21: 37607430-37607980; chr2: 100226464-100227140; chr21: 40278885-40279778; chr20: 40125800-40126325; chr14: 96964341-96965236; chr1: 94566367-94567508; chr6: 32120324-32121235; chr6: 2158961-2159107; chr2: 85833089-85833413; chr4: 147936346-147936831; chr2: 33107594-33108530; chr22: 43407118-43407581; chr21: 39492468-39494149; chr9: 124359818-124360534; chr6: 164167085-164167560; chr4: 4674762-4675733; chr1: 23890894-23891476; chr15: 57844015-57844457; chr16: 68766035-68766853; chr1: 234961714-234962041; chr10: 32703471-32704423; chr13: 31100912-31101535; chr2: 216808192-216808391; chr12: 18476876-18477436; chr12: 120818881-120819190; chr19: 38673641-38674608; chr17: 36605585-36606403; chr7: 65736314-65736453; chr13: 51058670-51059041; chr11: 113766137-113766643; chr12: 26265265-26266147; chr5: 109673723-109674226; chr8: 10618285-10618795; chr19: 53244844-53245458; chr11: 105386196-105387277; chr21: 16248092-16248889; chr18: 55795530-55795975; chr3: 64598707-64599348; chr1: 196659363-196660153; chr4: 165952537-165954234; chr12: 124773668-124774705; chr6: 41666010-41666469; chr6: 159237124-159238595; chr9: 108544124-108545341; chr6: 13014688-13016135; chr16: 11443167-11443469; and chr9: 101265123-101265817.
A6.4. The method of embodiment A6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; and chr1: 209819233-209819714.
A6.5. The method of embodiment A6.5, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −9.0.
A6.6. The method of embodiment A6, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −10.0.
A6.7. The method of any one of embodiments A1 to A6 and A6.5 to A6.6, wherein the one or more loci are chosen from loci in chromosome 21, 18 or 13.
A6.8. The method of any one of embodiments A5 to A6.7, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 800 CpG methylation sites per 50,000 base pairs, or less.
A6.9. The method of embodiment A6.8, wherein the CpG density is about 600 CpG methylation sites per 50,000 base pairs, or less.
A6.10. The method of embodiment A6.9, wherein the CpG density is about 400 CpG methylation sites per 50,000 base pairs, or less.
A6.11. The method of embodiment A6.9, wherein the CpG density is about 200 CpG methylation sites per 50,000 base pairs, or less.
A6.12. The method of any one of embodiments A5 to A6.11, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 16 CpG methylation sites per 1,000 base pairs, or less.
A6.13. The method of embodiment A6.12, wherein the CpG density is about 12 CpG methylation sites per 1,000 base pairs, or less.
A6.14. The method of embodiment A6.13, wherein the CpG density is about 8 CpG methylation sites per 1,000 base pairs, or less.
A6.15. The method of embodiment A6.14, wherein the CpG density is about 4 CpG methylation sites per 1,000 base pairs, or less.
A6.16. The method of any one of embodiments A5 to A6.15, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 0.016 CpG methylation sites per base pair, or less.
A6.17. The method of embodiment A6.16, wherein the CpG density is about 0.012 CpG methylation sites per base pair, or less.
A6.18. The method of embodiment A6.17, wherein the CpG density is about 0.008 CpG methylation sites per base pair, or less.
A6.19. The method of embodiment A6.19, wherein the CpG density is about 0.004 CpG methylation sites per base pair, or less.
A6.20. The method of any one of embodiments A5 to A6.19, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 5 CpG methylation sites.
A6.21. The method of embodiment 6.20, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 9 CpG methylation sites.
A6.22. The method of embodiment 6.22, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 12 CpG methylation sites.
A6.23. The method of any one of embodiments A5 to A6.22, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 5,000 base pairs or less.
A6.24. The method of embodiment A6.23, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 2,000 base pairs or less.
A6.25. The method of embodiment A6.24, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 1,000 base pairs or less.
A6.26. The method of embodiment A6.25, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 750 base pairs or less.
A6.27. The method of embodiment A6.26, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 500 base pairs or less.
A6.28. The method of embodiment A6.27, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 250 base pairs or less.
A6.29. The method of any one of embodiments A5 to A6.28, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.1 genes per 1000 base pair, or less.
A6.30. The method of any one of embodiments A5 to A6.28, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.08 genes per 1000 base pair, or less.
A6.31. The method of any one of embodiments A5 to A6.28, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.06 genes per 1000 base pair, or less.
A6.32. The method of any one of embodiments A5 to A6.28, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.04 genes per 1000 base pair, or less.
A6.33. The method of any one of embodiments A5 to A6.28, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.02 genes per 1000 base pair, or less.
A6.34. The method of any one of embodiments A5 to A6.33, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 1 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition sites can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
A6.35. The method of any one of embodiments A5 to A6.33, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 10 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition site can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
A6.36. The method of any one of embodiments A5 to A6.33, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 20 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition site can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
A6.37. The method of any one of embodiments A5 to A6.33, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 30 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition site can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
A7. The method of embodiment A6.8, wherein the one or more loci are chosen from chromosome 13 in TABLE 4.
A7.1. The method of embodiment A6.8, wherein the one or more loci are chosen from chromosome 18 in TABLE 4.
A7.2. The method of embodiment A6.8, wherein the one or more loci are chosen from chromosome 21 in TABLE 4.
A7.3. The method of any one of embodiments A5 to A7.2, wherein the one or more loci one or more loci that are 60% or less methylated in fetal nucleic acid and 61% or greater methylated in maternal nucleic acid.
A7.4. The method of embodiment A7.3, wherein the loci are 70% or more methylated in the maternal nucleic acid.
A7.5. The method of embodiment A7.4, wherein the loci are 75% or more methylated in the maternal nucleic acid.
A7.6. The method of embodiment A7.5, wherein the loci are 80% or more methylated in the maternal nucleic acid.
A7.7. The method of any one of embodiments A5 to A7.6, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are 40% or less methylated in the fetal nucleic acid.
A7.8. The method of embodiment A7.7, wherein the loci are 30% or less methylated in the fetal nucleic acid.
A7.9. The method of embodiment A7.8, wherein the loci are 20% or less methylated in the fetal nucleic acid.
A7.10. The method of embodiment A7.9, wherein the loci are 10% or less methylated in the fetal nucleic acid.
A7.11. The method of any one of embodiments A5 to A7.10, wherein a difference in methylation status between fetal nucleic acid and maternal nucleic acid for the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid is 5% or more.
A7.12. The method of embodiment A7.11, wherein a difference in methylation status is 10% or more.
A7.13. The method of embodiment A7.12, wherein a difference in methylation status is 20% or more.
A7.14. The method of embodiment A7.13, wherein a difference in methylation status is 40% or more.
A8. The method of any one of embodiments A2 to A7.10, wherein the enriching comprises selectively separating the digested nucleic acid fragments from non-digested nucleic acid.
A9. The method of embodiment A8, wherein the digested nucleic acid fragments are selectively separated according to molecular weight.
A9.1. The method of embodiment A8, wherein the digested nucleic acid fragments are selectively separated according to size.
A10. The method of any one of embodiments A8 to A9.1, wherein the digested nucleic acid fragments are selectively separated by a process comprising polyethylene glycol mediated precipitation.
A11. The method of any one of embodiments A8 to A9.1, wherein the digested nucleic acid fragments are selectively separated by a process comprising size exclusion chromatography.
A12. The method of embodiment A8, wherein the digested nucleic acid fragments are selectively separated by a process comprising contacting the fragments with a methyl-specific binding agent.
A12.1. The method of embodiment A12, wherein the contacting the fragments with the methyl-specific binding agent provides bound nucleic acid fragments and unbound nucleic acid fragments.
A12.2. The method of embodiment A12.1, wherein the bound nucleic acid fragments are selectively separated from the unbound nucleic acid fragments.
A12.3. The method of embodiments A12.1, comprising exposing the bound nucleic acid fragments, or a portion thereof, to conditions that dissociate the bound nucleic acids from the methyl-specific binding agent thereby providing one or more elution products.
A13. The method of any one of embodiments A12 to A12.3, wherein the methyl-specific binding agent comprises an antibody or a portion thereof
A14. The method of embodiment A13, wherein the antibody specifically binds an unmethylated portion of one or more nucleic acid fragments in the sample.
A15. The method of embodiment A13, wherein the antibody specifically binds a methylated portion of one or more nucleic acid fragments in the sample.
A16. The method of any one of embodiments A12 to A12.2, wherein the methyl-specific binding agent comprises a methyl-CpG binding domain protein or a portion thereof.
A17. The method of embodiment A16, wherein the methyl-CpG binding domain protein is chosen from MeCP2, MBD1, MBD2, MBD3 and MBD4.
A18. The method of any one of embodiments A1 to A17, wherein the one or more methylation sensitive cleavage agents comprise one or more restriction endonucleases.
A19. The method of embodiment A18, wherein the one or more restriction endonucleases are selected from a Type I, Type II, Type III, Type IV or Type V restriction endonuclease.
A20. The method of embodiment A18 or A19, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 6 base pairs or less.
A21. The method of embodiment A18 or A19, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 4 base pairs or less.
A22. The method of any one of embodiments A18 to A21, wherein the one or more restriction endonucleases produce overhangs.
A23. The method of any one of embodiments A22, wherein each of the digested nucleic acid fragments comprises one or more unpaired nucleotides at the 5′ or 3′ end of the fragment.
A24. The method of any one of embodiments A18 to A21, wherein the one or more restriction endonucleases produce blunt ends.
A25 The method of any one of embodiments A18 to A23, wherein one or more of the restriction endonucleases are selected from HHAI, HinP11 and HPAII.
A26 The method of any one of embodiments A18 to A25, wherein the average, mean, median or nominal length of the digested nucleic acid fragments is about 40 bases to about 100 bases.
A27. The method of any one of embodiments A2 to A26, wherein the enriching in (b) comprises amplifying the digested nucleic acid fragments relative to the non-digested nucleic acid.
A28. The method of any one of embodiments A1 to A27, wherein the digested nucleic acid fragments are amplified by a process comprising ligating one or more adaptors to one or both ends of each of the digested nucleic acid fragments.
A29. The method of embodiment A28, wherein the ligating comprises a blunt end ligation.
A30. The method of embodiment A28 or A29, comprising ligating the one or more adaptors to one or more unpaired nucleotides at the 5′ or 3′ end of the digested nucleic acid fragments.
A31. The method of any one of embodiments A28 to A30, wherein the one or more adaptors comprise one or more capture agents.
A32. The method of embodiment A31, wherein the one or more capture agents are selected from an antibody, an antigen and a member of a binding pair.
A33. The method of embodiment A31 or A32, wherein the one or more capture agents comprise biotin.
A34. The method of any one of embodiments A27 to A33, wherein the digested nucleic acid fragments are amplified by a process comprising a bridge amplification.
A35. The method of any one of embodiments A1 to A34, wherein the nucleic acid from the pregnant female comprises cell-free circulating nucleic acid.
A36. The method of embodiment A35, wherein the nucleic acid is from blood serum, blood plasma or urine.
A37. The method of any one of embodiments A1, A2 and A4 to A36, wherein the analyzing comprises determining an amount of fetal nucleic acid in the nucleic acid sample.
A38. The method of embodiment A37, wherein determining the amount of fetal nucleic acid comprises determining a ratio of fetal nucleic acid to a total amount of nucleic acid in the sample.
A39. The method of embodiment A38, wherein the ratio is a percent representation.
A40. The method of any one of embodiments A1, A2 and A4 to A39, wherein the analyzing comprises determining the presence of absence of a fetal aneuploidy.
A41. The method of embodiment A40, wherein the fetal aneuploidy is a trisomy.
A42. The method of embodiment A41, wherein the trisomy is a trisomy of chromosome 13, 18 or 21.
A43. The method of any one of embodiments A1, A2 and A4 to A42, wherein the analyzing comprises non-targeted sequencing of the digested nucleic acid fragments or modified variant thereof.
A44. The method of any one of embodiments A1, A2 and A4 to A42, wherein the analyzing comprises targeted sequencing of the digested nucleic acid fragments or a modified variant thereof.
A45. The method of any one of embodiments A1 to A44, which comprises contacting the digested nucleic acid fragments with an agent that modifies a methylated nucleotide to another moiety.
A46. The method of any one of embodiments A40 to A45, wherein determining the presence or absence of a fetal aneuploidy comprises obtaining counts of sequence reads mapped to portions of a reference genome, which sequence reads are normalized and which sequence reads are from the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid.
A47. The method of embodiment A46, wherein determining the presence or absence of a fetal aneuploidy comprises comparing the normalized counts of sequence reads for a target chromosome to the normalized counts of sequence reads for the reference chromosome, whereby a statistically significant difference between the counts for the target chromosome and the counts for the reference chromosome determines the presence of a fetal aneuploidy.
A48. The method of embodiment A47, wherein counts of sequence reads of about 3 to about 15 loci on the target chromosome and the reference chromosome is determined.
A49. The method of embodiment A47, wherein counts of sequence reads of about 16 or more loci on the target chromosome and the reference chromosome is determined.
A50. The method of any one of embodiments A37 to A49, wherein determining the amount of fetal nucleic acid comprises use of a mass spectrometry method.
A51. The method of any one of embodiments A37 to A49, wherein determining the amount of fetal nucleic acid comprises use of a sequencing method.
B1. A method for analyzing nucleic acid in a sample, comprising:
(a) enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, thereby generating enriched hypomethylated nucleic acid; and
(b) analyzing the enriched hypomethylated nucleic acid, which analyzing comprises determining the presence, absence or amount of a polynucleotide in one or more loci chosen from loci of Table 4.
B2. The method of embodiment B1, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; chr1: 209819233-209819714; chr15: 99270658-99271954; chr9: 110581951-110582676; chr11: 76039765-76040736; chr21: 37607430-37607980; chr2: 100226464-100227140; chr21: 40278885-40279778; chr20: 40125800-40126325; chr14: 96964341-96965236; chr1: 94566367-94567508; chr6: 32120324-32121235; chr6: 2158961-2159107; chr2: 85833089-85833413; chr4: 147936346-147936831; chr2: 33107594-33108530; chr22: 43407118-43407581; chr21: 39492468-39494149; chr9: 124359818-124360534; chr6: 164167085-164167560; chr4: 4674762-4675733; chr1: 23890894-23891476; chr15: 57844015-57844457; chr16: 68766035-68766853; chr1: 234961714-234962041; chr10: 32703471-32704423; chr13: 31100912-31101535; chr2: 216808192-216808391; chr12: 18476876-18477436; chr12: 120818881-120819190; chr19: 38673641-38674608; chr17: 36605585-36606403; chr7: 65736314-65736453; chr13: 51058670-51059041; chr11: 113766137-113766643; chr12: 26265265-26266147; chr5: 109673723-109674226; chr8: 10618285-10618795; chr19: 53244844-53245458; chr11: 105386196-105387277; chr21: 16248092-16248889; chr18: 55795530-55795975; chr3: 64598707-64599348; chr1: 196659363-196660153; chr4: 165952537-165954234; chr12: 124773668-124774705; chr6: 41666010-41666469; chr6: 159237124-159238595; chr9: 108544124-108545341; chr6: 13014688-13016135; chr16: 11443167-11443469; and chr9: 101265123-101265817.
B3. The method of embodiment B1, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; and chr1: 209819233-209819714.
B4. The method of embodiment B1, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −7.0.
B5. The method of embodiment B1, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −9.0.
B6. The method of embodiment B1, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −10.0.
B6.1. The method of any one of embodiments B4 to B6, wherein the median t-statistic is determined by a t-test.
B7. The method of any one of embodiments B1 to B6.1, wherein the one or more loci are chosen from loci in chromosome 21, 18 or 13.
B8. The method of embodiment B7, wherein the one or more loci are chosen from chromosome 13 in TABLE 4.
B9. The method of embodiment B7, wherein the one or more loci are chosen from chromosome 18 in TABLE 4.
B10. The method of embodiment B7, wherein the one or more loci are chosen from chromosome 21 in TABLE 4.
B11. The method of any one of embodiments B1 to B10.2, wherein the one or more loci are relatively less methylated in fetal nucleic acid than in maternal nucleic acid.
B11.1. The method of any one of embodiments B11, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 800 CpG methylation sites per 50,000 base pairs, or less.
B11.2. The method of embodiment B11.1, wherein the CpG density is about 600 CpG methylation sites per 50,000 base pairs, or less.
B11.3. The method of embodiment B11.2, wherein the CpG density is about 400 CpG methylation sites per 50,000 base pairs, or less.
B11.4. The method of embodiment B11.3, wherein the CpG density is about 200 CpG methylation sites per 50,000 base pairs, or less.
B11.5. The method of any one of embodiments B11 to B11.4, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 16 CpG methylation sites per 1,000 base pairs, or less.
B11.6. The method of embodiment B11.5, wherein the CpG density is about 12 CpG methylation sites per 1,000 base pairs, or less.
B11.7. The method of embodiment B11.6, wherein the CpG density is about 8 CpG methylation sites per 1,000 base pairs, or less.
B11.8. The method of embodiment B11.7, wherein the CpG density is about 4 CpG methylation sites per 1,000 base pairs, or less.
B11.9. The method of any one of embodiments B11 to B11.8, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a CpG density of about 0.016 CpG methylation sites per base pair, or less.
B11.10. The method of embodiment B11.9, wherein the CpG density is about 0.012 CpG methylation sites per base pair, or less.
B11.11. The method of embodiment B11.10, wherein the CpG density is about 0.008 CpG methylation sites per base pair, or less.
B11.12. The method of embodiment B11.11, wherein the CpG density is about 0.004 CpG methylation sites per base pair, or less.
B11.13. The method of any one of embodiments B11 to B11.12, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 5 CpG methylation sites.
B11.14. The method of embodiment B11.13, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 9 CpG methylation sites.
B11.15. The method of embodiment B11.14, wherein the one or more loci relatively less methylated in fetal nucleic acid contain at least 12 CpG methylation sites.
B11.16. The method of any one of embodiments B11 to B11.15, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 5,000 base pairs or less.
B11.17. The method of embodiment B11.16, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 2,000 base pairs or less.
B11.18. The method of embodiment B11.17, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 1,000 base pairs or less.
B11.19. The method of embodiment B11.18, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 750 base pairs or less.
B11.20. The method of embodiment B11.19, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 500 base pairs or less.
B11.21. The method of embodiment B11.20, wherein the one or more loci relatively less methylated in fetal nucleic acid are about 250 base pairs or less.
B11.22. The method of any one of embodiments B11 to B11.21, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.1 genes per 1000 base pair, or less.
B11.23. The method of embodiment B11.22, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.08 genes per 1000 base pair, or less.
B11.24. The method of embodiment B11.23, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.06 genes per 1000 base pair, or less.
B11.25. The method of embodiment B11.24, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.04 genes per 1000 base pair, or less.
B11.26. The method of embodiment B11.25, wherein the one or more loci relatively less methylated in fetal nucleic acid comprise 0.02 genes per 1000 base pair, or less.
B11.27. The method of any one of embodiments B11 to B11.26, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 1 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition sites can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
B11.28. The method of embodiment B11.27, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 10 restriction endonuclease recognition sites per 1000 bp.
B11.29. The method of embodiment B11.28, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 20 restriction endonuclease recognition sites per 1000 bp.
B11.30. The method of embodiment B11.29, wherein each of the one or more loci relatively less methylated in fetal nucleic acid comprise at least 30 restriction endonuclease recognition sites per 1000 bp.
B12. The method of any one of embodiments B1 to B11.30, wherein the analyzing comprises determining the presence or absence of one or more polynucleotides in the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid.
B13. The method of any one of embodiments B1 to B12, wherein the analyzing comprises determining the amount of one or more polynucleotides in the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid.
B14. The method of any one of embodiments B11 to B13, wherein a difference in methylation status between fetal nucleic acid and maternal nucleic acid for the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid is 5% or more.
B14.1. The method of embodiment B14, wherein a difference in methylation status is 10% or more.
B14.2. The method of embodiment B14.1, wherein a difference in methylation status is 20% or more.
B14.3. The method of embodiment B14.2, wherein a difference in methylation status is 40% or more.
B14.4. The method of any one of embodiments B14 to B14.3, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid is determined by a statistical method chosen from a t-test, Z-test, Chi-square, Wilcox, ANOVA, MANOVA, MANCOVA and logistic regression.
B14.5. The method of embodiment B14.4, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid is determined by a t-test.
B14.6. The method of embodiment B14.5, wherein the difference in methylation status between fetal nucleic acid and maternal nucleic acid for the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid comprise a median t-statistic between −18.0 and −7.0 or comprise a statistical difference comparable to a t-statistic between −18.0 and −7.0.
B15. The method of any one of embodiments B1 to B14.6, wherein the nucleic acid enriched for hypomethylated nucleic acid comprise one or more polynucleotides in one or more loci that are 60% or less methylated in fetal nucleic acid than in maternal nucleic acid.
B16. The method of any one of embodiments B11 to B15, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are 60% or more methylated in the maternal nucleic acid.
B16.1. The method of embodiment B16, wherein the loci are 70% or more methylated in maternal nucleic acid.
B16.2. The method of embodiment B16.1, wherein the loci are 75% or more methylated in maternal nucleic acid.
B16.3. The method of embodiment B16.2, wherein the loci are 80% or more methylated in maternal nucleic acid.
B16.4. The method of any one of embodiments B11 to B16.3, wherein the one or more loci relatively less methylated in fetal nucleic acid than in maternal nucleic acid are 40% or less methylated in fetal nucleic acid.
B16.5. The method of embodiment B16.4, wherein the loci are 30% or less methylated in fetal nucleic acid.
B16.6. The method of embodiment B16.5, wherein the loci are 20% or less methylated in fetal nucleic acid.
B16.7. The method of embodiment B16.6, wherein the loci are 10% or less methylated in fetal nucleic acid.
B17. A method for analyzing nucleic acid in a sample, comprising:
(a) enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises fetal nucleic acid and maternal nucleic acid, thereby generating enriched hypomethylated nucleic acid; and
(b) analyzing the enriched hypomethylated nucleic acid, which analyzing comprises non-targeted analysis of substantially all of the hypomethylated nucleic acid.
B18. The method of any one of embodiments B1 to B17, wherein the enriching comprises exposing the nucleic acid sample to conditions that selectively separate the hypomethylated nucleic acid from methylated nucleic acid.
B19. The method of embodiment B18, wherein the enriching comprises contacting the nucleic acid in the nucleic acid sample with a binding agent that specifically associates with methylated nucleic acid, thereby generating separated and enriched hypomethylated nucleic acid.
B19.1. The method of embodiment B19, wherein the contacting the fragments with the binding agent provides bound nucleic acid fragments and unbound nucleic acid fragments.
B19.2. The method of embodiment B19.1, wherein the bound nucleic acid fragments are selectively separated from the unbound nucleic acid fragments.
B19.3. The method of embodiments B19.1, comprising exposing the bound nucleic acid fragments, or a portion thereof, to conditions that dissociate the bound nucleic acids from the binding agent thereby providing one or more elution products.
B20. The method of any one of embodiments B19 to B19.3, comprising amplifying the separated and enriched hypomethylated nucleic acid.
B21. The method of embodiment B20, wherein the amplification comprises ligating one or more adaptors to the enriched hypomethylated nucleic acid.
B22. The method of embodiment B20 or B21, wherein the amplifying comprises a targeted amplification.
B23. The method of embodiment B21 or B22, wherein the one or more adaptors comprise a capture agent.
B24. The method of any one of embodiments B20 to B23, wherein the enriched nucleic acid is amplified by a process comprising a bridge amplification.
B25. The method of any one of embodiments B18 to B24, wherein the conditions that separate hypomethylated nucleic acid from methylated nucleic acid comprise binding substantially all of the nucleic acid in the nucleic acid sample and selectively eluting the hypomethylated nucleic acid.
B26. The method of any one of embodiments B19.1 to B24, wherein the conditions that separate hypomethylated nucleic acid from methylated nucleic acid comprise binding substantially all of the methylated nucleic acid in the nucleic acid sample, wherein the unbound nucleic acid fragments comprises enriched hypomethylated nucleic acid.
B27. The method of any one of embodiments B19 to B26, wherein the binding agent, or a portion thereof, comprises a methyl-specific binding agent.
B28. The method of embodiment B27, wherein the methyl-specific binding agent comprises an antibody or a portion thereof.
B29. The method of embodiment B28, wherein the antibody, or portion thereof, specifically binds an unmethylated portion of one or more nucleic acid in the sample.
B30. The method of embodiment B28, wherein the antibody, or portion thereof, specifically binds a methylated portion of one or more nucleic acids in the sample.
B31. The method of embodiment B27, wherein the methyl-specific binding agent comprises a methyl-CpG binding domain protein or a portion thereof.
B32. The method of embodiments B27 or B31, wherein the methyl-CpG binding domain protein is chosen from MeCP2, MBD1, MBD2, MBD3 and MBD4.
B33. The method of any one of embodiments B1 to B32, wherein the enriching comprises digesting the nucleic acid sample with one or more methylation sensitive cleavage agents that specifically digest the nucleic acids at a recognition site comprising a methylation site.
B34. The method of B32 or B33, wherein the digesting produces digested nucleic acid fragment and non-digested nucleic acid fragments.
B35. The method of embodiment B34, wherein the enriching comprises selectively separating the digested nucleic acid fragments from non-digested nucleic acid.
B36. The method of any one of embodiments B33 to B35, wherein the one or more methylation sensitive cleavage agents comprise one or more restriction endonucleases.
B36.1. The method of embodiment B36, wherein the one or more restriction endonucleases digest the nucleic acids at an unmethylated methylation site.
B36.2. The method of embodiment B36, wherein the one or more restriction endonucleases digest the nucleic acids at a methylated methylation site.
B37. The method of any one of embodiments B36 to B36.2, wherein the one or more restriction endonucleases are selected from a Type I, Type II, Type III, Type IV or Type V restriction endonuclease.
B38. The method of any one of embodiments B36 to B37, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 6 base pairs or less.
B39. The method of any one of embodiments B36 to B38, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 4 base pairs or less.
B40. The method of any one of embodiments B36 to B39, wherein the one or more restriction endonucleases produce overhangs.
B41. The method of embodiment B40, wherein each of the digested nucleic acid fragments comprises one or more unpaired nucleotides at the 5′ or 3′ end of the fragment.
B42. The method of any one of embodiments B36 to B41, wherein one or more of the restriction endonucleases are selected from HHAI, HinP1I and HPAII.
B43. The method of any one of embodiments B36 to B39, wherein the one or more restriction endonucleases produce blunt ends.
B44. The method of any one of embodiments B36 to B43, wherein the average, mean, median or nominal length of the digested nucleic acid fragments is about 40 bases to about 100 bases.
B45. The method of any one of embodiments B34 to B44, wherein the enriching comprises amplifying the digested nucleic acid fragments relative to the non-digested nucleic acid.
B46. The method of embodiment B45, wherein the digested nucleic acid fragments are amplified by a process comprising ligating one or more adaptors to one or both ends of each of the digested nucleic acid fragments.
B47. The method of embodiment B46, wherein the ligating comprises a blunt end ligation.
B48. The method of embodiment B46 or B47, comprising ligating the one or more adaptors to one or more unpaired nucleotides at the 5′ or 3′ end of the digested nucleic acid fragments.
B49. The method of any one of embodiments B46 to B48, wherein the one or more adaptors comprise one or more capture agents.
B50. The method of embodiment B49, wherein the one or more capture agents are selected from an antibody, an antigen and a member of a binding pair.
B51. The method of embodiment B49 or B50, wherein the one or more capture agents comprise biotin.
B52. The method of any one of embodiments B45 to B51, wherein the digested nucleic acid fragments are amplified by a process comprising a bridge amplification.
B53. The method of any one of embodiments B1 to B52, wherein the nucleic acid from the pregnant female comprises cell-free circulating nucleic acid.
B54. The method of embodiment B53, wherein the nucleic acid is from blood serum, blood plasma or urine.
B55. The method of any one of embodiments B1 to B54, wherein the analyzing comprises determining an amount of fetal nucleic acid in the nucleic acid sample.
B56. The method of embodiment B55, wherein determining the amount of fetal nucleic acid comprises determining a ratio of fetal nucleic acid to a total amount of nucleic acid in the sample.
B57. The method of embodiment B56, wherein the ratio is a percent representation.
B58. The method of any one of embodiments B1 to B57, wherein the analyzing comprises determining the presence of absence of a fetal aneuploidy.
B59. The method of embodiment B58, wherein the fetal aneuploidy is a trisomy.
B60. The method of embodiment B59, wherein the trisomy is a trisomy of chromosome 13, 18 or 21.
B61. The method of any one of embodiments B1 to B60, wherein the analyzing comprises a target-based approach.
B62. The method of any one of embodiments B1 to B60, wherein the analyzing comprises a non-target-based approach.
B63. The method of any one of embodiments B1 to B62, wherein the analyzing comprises sequencing the enriched hypomethylated nucleic acid, or a portion thereof or sequencing the enriched hypermethylated nucleic acid, or a portion thereof.
B64. The method of embodiment B63, where the sequencing comprises non-targeted sequencing.
B65. The method of embodiment B63, where the sequencing comprises targeted sequencing.
B66. The method of any one of embodiments B1 to B65, which comprises contacting the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid with an agent that modifies a methylated nucleotide to another moiety.
B67. The method of any one of embodiments B58 to B66, wherein determining the presence or absence of a fetal aneuploidy comprises obtaining counts of sequence reads mapped to portions of a reference genome, which sequence reads are normalized and which sequence reads are from the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid.
B68. The method of embodiment B67, wherein determining the presence or absence of a fetal aneuploidy comprises comparing the normalized counts of sequence reads for a target chromosome to the normalized counts of sequence reads for the reference chromosome, whereby a statistically significant difference between the counts for the target chromosome and the counts for the reference chromosome determines the presence of a fetal aneuploidy.
B69. The method of embodiment B68, wherein counts of sequence reads of about 3 to about 15 loci on the target chromosome and the reference chromosome is determined.
B70. The method of embodiment B68, wherein counts of sequence reads of about 16 or more loci on the target chromosome and the reference chromosome is determined.
B71. The method of any one of embodiments B55 to B70, wherein determining the amount of fetal nucleic acid comprises use of a mass spectrometry method.
B72. The method of any one of embodiments B55 to B70, wherein determining the amount of fetal nucleic acid comprises use of a sequencing method.
B73. The method of embodiment B72, wherein the sequencing method comprises sequencing by synthesis.
B74. The method of any one of embodiments B1 to B73, wherein the analyzing comprises mass spectrometry.
B75. The method of embodiment B74, wherein the mass spectrometry analysis comprises a targeted-mass spectrometry.
C1. A method for enriching for a minority nucleic acid species in a sample, comprising:
(a) digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments; and
(b) analyzing the digested nucleic acid fragments.
C2. The method of embodiment C1, which comprises prior to (b) enriching the digested nucleic acid fragments relative to non-digested nucleic acid, thereby generating nucleic acid enriched for the minority nucleic acid species.
C3. A method for enriching for a minority nucleic acid species in a sample, comprising:
(a) digesting nucleic acid in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, with one or more methylation sensitive cleavage agents that specifically digest the nucleic acid at non-methylated recognition sites, thereby generating digested nucleic acid fragments; and
(b) enriching the digested nucleic acid fragments relative to non-digested nucleic acid, thereby generating nucleic acid enriched for the minority nucleic acid species.
C4. The method of embodiment C3, comprising (c) analyzing the enriched minority nucleic acid species.
C4.1. The method of embodiment C1, C2 or C4, wherein the analyzing comprises a target-based analysis.
C4.2. The method of embodiment C1, C2 or C4, wherein the analyzing comprises a non-target-based analysis.
C4.3. The method of any one of embodiments C1, C2 and C4 to C4.2, wherein the analysis comprises sequencing.
C4.4. The method of embodiment C4.3, wherein the sequencing comprises sequencing a portion of the enriched minority nucleic acid species.
C4.5. The method of embodiment C4.4, comprising sequencing a portion of the enriched minority nucleic acid species that is hypomethylated.
C4.6. The method of embodiment C4.4, comprising sequencing a portion of the enriched minority nucleic acid species that is hypermethylated.
C4.7. The method of embodiment C4.3, comprising sequencing substantially all of the enriched minority nucleic acid species.
C4.8. The method of embodiment C4.3, wherein the sequencing method comprises sequencing by synthesis.
C4.9. The method of any one of embodiments C1, C2 and C4 to C4.2, wherein the analyzing comprises mass spectrometry.
C4.10. The method of embodiment C4.9, wherein the mass spectrometry analysis comprises a targeted-mass spectrometry.
C5. The method of any one of embodiments C1, C2 and C4 to C4.10, wherein the analyzing comprises determining the presence or absence of one or more polynucleotides in one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species.
C5.1. The method of any one of embodiments C1, C2 and C4 to C5, wherein the analyzing comprises determining the amount of one or more polynucleotides in one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species.
C5.2. The method of any one of embodiments C1, C2 and C4 to C5, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species is 5% or more.
C5.2.1. The method of embodiment C5.2, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species is determined by a statistical method chosen from a t-test, Z-test, Chi-square, Wilcox, ANOVA, MANOVA, MANCOVA and logistic regression.
C5.2.2. The method of embodiment C5.2.1, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species is determined by a t-test.
C5.2.3. The method of embodiment C5.2.2, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species comprise a median t-statistic between −18.0 and −7.0 or comprise a statistical difference comparable to a t-statistic between −18.0 and −7.0.
C5.3. The method of any one of embodiments C2 to C5.2.3, wherein the nucleic acid enriched for the minority nucleic acid species comprise one or more polynucleotides in one or more loci that are 60% or less methylated in the minority nucleic acid species and about 61% or greater methylated in the majority nucleic acid species.
C6. The method of embodiment C5, wherein the one or more loci are chosen from loci in Table 2AB, Table 2CB, Table 3 and Table 4.
C6.1. The method of embodiment C6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg18, NCBI Build 36.1 of: chr13: 19290394-19290768, chr13: 19887090-19887336; chr13: 20193675-20193897; chr13: 109232856-109235065; chr13: 109716455-109716604; chr13: 112724910-112725742; chr13: 112799123-112799379; chr18: 6919797-6919981; chr18: 13377536-13377654; chr18: 41671477-41673011; chr18: 58203013-58203282; chr18: 70133945-70134397; chr18: 71128742-71128974; chr18: 72664454-72664736; chr18: 74170347-74170489; chr18: 75596358-75596579; chr18: 75760343-75760820; chr21: 33327593-33328334; chr21: 35180938-35185436; chr21: 44529935-44530388; chr21: 45061293-45061853; chr21: 45202815-45202972; chr21: 45671984-45672098; chr21: 45754383-45754487; chr3: 9963364-9964023; chr5: 138757911-138758724; chr6: 35561812-35562252; chr12: 1642456-1642708; chr12: 56406249-56407788; and chr12: 56416146-56418794.
C6.2. The method of embodiment C6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg18, NCBI Build 36.1 of: chr21: 9906600-9906800; chr21: 9907000-9907400; chr21: 9917800-9918450; chr21: 10010000-10015000; chr21: 13974500-13976000; chr21: 13989500-13992000; chr21: 13998500-14000100; chr21: 14017000-14018500; chr21: 14056400-14058100; chr21: 14070250-14070550; chr21: 14119800-14120400; chr21: 14304800-14306100; chr21: 16881500-16883000; chr21: 17905300-17905500; chr21: 23574000-23574600; chr21: 24366920-24367060; chr21: 25656000-25656900; chr21: 26830750-26830950; chr21: 26938800-26939200; chr21: 30176500-30176750; chr21: 31955000-31955300; chr21: 33272200-33273300; chr21: 33328000-33328500; chr21: 35185000-35186000; chr21: 36589000-36590500; chr21: 42399200-42399900; chr21: 42528400-42528600; chr21: 42598300-42599600; chr21: 42910000-42911000; chr21: 42945500-42946000; chr21: 42961400-42962700; chr21: 42978200-42979800; chr21: 43130800-43131500; chr21: 43446600-43447600; chr21: 43463000-43466100; chr21: 43545000-43546000; chr21: 43606000-43606500; chr21: 43902500-43903800; chr21: 44446500-44447500; chr21: 44614500-44615000; chr21: 44750400-44751000; chr21: 45145500-45146100; chr21: 45501000-45503000; chr21: 45571500-45573700; chr21: 45609000-45610600; chr21: 45670000-45677000; chr21: 45700500-45702000; chr21: 45753000-45755000; chr21: 45885000-45887000; chr21: 46111000-46114000; chr21: 46142000-46144500; chr21: 46227000-46233000; chr21: 46245000-46252000; chr21: 46280500-46283000; chr21: 46343500-46344200; chr21: 46368000-46378000; chr21: 46426700-46427500; and chr21: 46546914-46547404.
C6.3. The method of embodiment C6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; chr1: 209819233-209819714; chr15: 99270658-99271954; chr9: 110581951-110582676; chr11: 76039765-76040736; chr21: 37607430-37607980; chr2: 100226464-100227140; chr21: 40278885-40279778; chr20: 40125800-40126325; chr14: 96964341-96965236; chr1: 94566367-94567508; chr6: 32120324-32121235; chr6: 2158961-2159107; chr2: 85833089-85833413; chr4: 147936346-147936831; chr2: 33107594-33108530; chr22: 43407118-43407581; chr21: 39492468-39494149; chr9: 124359818-124360534; chr6: 164167085-164167560; chr4: 4674762-4675733; chr1: 23890894-23891476; chr15: 57844015-57844457; chr16: 68766035-68766853; chr1: 234961714-234962041; chr10: 32703471-32704423; chr13: 31100912-31101535; chr2: 216808192-216808391; chr12: 18476876-18477436; chr12: 120818881-120819190; chr19: 38673641-38674608; chr17: 36605585-36606403; chr7: 65736314-65736453; chr13: 51058670-51059041; chr11: 113766137-113766643; chr12: 26265265-26266147; chr5: 109673723-109674226; chr8: 10618285-10618795; chr19: 53244844-53245458; chr11: 105386196-105387277; chr21: 16248092-16248889; chr18: 55795530-55795975; chr3: 64598707-64599348; chr1: 196659363-196660153; chr4: 165952537-165954234; chr12: 124773668-124774705; chr6: 41666010-41666469; chr6: 159237124-159238595; chr9: 108544124-108545341; chr6: 13014688-13016135; chr16: 11443167-11443469; and chr9: 101265123-101265817.
C6.4. The method of embodiment C6, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; and chr1: 209819233-209819714.
C6.5. The method of embodiment C6, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −7.0.
C6.6. The method of embodiment C6, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −9.0.
C6.7. The method of embodiment C6, wherein the one or more loci are chosen from TABLE 4 having a median t-statistic between −18.0 and −10.0.
C6.7.1. The method of any one of embodiments C6.5 to C6.7, wherein the median t-statistic is determined by a t-test.
C6.8. The method of any one of embodiments C1 to A6 and C6.5 to A6.7.1, wherein the one or more loci are chosen from loci in chromosome 21, 18 or 13.
C6.9. The method of any one of embodiments C5 to C6.8, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid comprise a CpG density of about 800 CpG methylation sites per 50,000 base pairs, or less.
C6.10. The method of embodiment C6.9, wherein the CpG density is about 600 CpG methylation sites per 50,000 base pairs, or less.
C6.11. The method of embodiment C6.10, wherein the CpG density is about 400 CpG methylation sites per 50,000 base pairs, or less.
C6.12. The method of embodiment C6.11, wherein the CpG density is about 200 CpG methylation sites per 50,000 base pairs, or less.
C6.13. The method of any one of embodiments C5 to C6.12, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid comprise a CpG density of about 16 CpG methylation sites per 1,000 base pairs, or less.
C6.14. The method of embodiment C6.13, wherein the CpG density is about 12 CpG methylation sites per 1,000 base pairs, or less.
C6.15. The method of embodiment C6.14, wherein the CpG density is about 8 CpG methylation sites per 1,000 base pairs, or less.
C6.16. The method of embodiment C6.15, wherein the CpG density is about 4 CpG methylation sites per 1,000 base pairs, or less.
C6.17. The method of any one of embodiments C5 to C6.16, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid comprise a CpG density of about 0.016 CpG methylation sites per base pair, or less.
C6.18. The method of embodiment C6.17, wherein the CpG density is about 0.012 CpG methylation sites per base pair, or less.
C6.19. The method of embodiment C6.18, wherein the CpG density is about 0.008 CpG methylation sites per base pair, or less.
C6.20. The method of embodiment C6.19, wherein the CpG density is about 0.004 CpG methylation sites per base pair, or less.
C6.21. The method of any one of embodiments C5 to C6.20, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 5 CpG methylation sites.
C6.22. The method of embodiment C6.21, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 9 CpG methylation sites.
C6.23. The method of embodiment 6.22, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 12 CpG methylation sites.
C6.24. The method of any one of embodiments C5 to C6.23, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 5,000 base pairs or less.
C6.25. The method of embodiment C6.24, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 2,000 base pairs or less.
C6.26. The method of embodiment C6.25, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 1,000 base pairs or less.
C6.27. The method of embodiment C6.26, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 750 base pairs or less.
C6.28. The method of embodiment C6.27, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 500 base pairs or less.
C6.29. The method of embodiment C6.28, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 250 base pairs or less.
C6.30. The method of any one of embodiments C5 to C6.29, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.1 genes per 1000 base pair, or less.
C6.31. The method of embodiment C6.30, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.08 genes per 1000 base pair, or less.
C6.32. The method of embodiment C6.31, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.06 genes per 1000 base pair, or less.
C6.33. The method of embodiment C6.32, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.04 genes per 1000 base pair, or less.
C6.34. The method of embodiment C6.33, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.02 genes per 1000 base pair, or less.
C6.35. The method of any one of embodiments C5 to C6.34, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 1 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition sites can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
C6.36. The method of embodiment C6.35, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 10 restriction endonuclease recognition sites per 1000 bp.
C6.37. The method of embodiment C6.36, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 20 restriction endonuclease recognition sites per 1000 bp.
C6.38. The method of embodiment C6.37, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 30 restriction endonuclease recognition sites per 1000 bp.
C7. The method of embodiment C6.8, wherein the one or more loci are chosen from chromosome 13 in TABLE 4.
C7.1. The method of embodiment C6.8, wherein the one or more loci are chosen from chromosome 18 in TABLE 4.
C7.2. The method of embodiment C6.8, wherein the one or more loci are chosen from chromosome 21 in TABLE 4.
C7.3. The method of any one of embodiments C5 to C7.2, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species are 60% or more methylated in the majority nucleic acid species.
C7.4. The method of embodiment C7.3, wherein the loci are 70% or more methylated in the majority nucleic acid species.
C7.5. The method of embodiment C7.4, wherein the loci are 75% or more methylated in the majority nucleic acid species.
C7.6. The method of embodiment C7.5, wherein the loci are 80% or more methylated in the majority nucleic acid species.
C7.7. The method of any one of embodiments C5 to C7.6, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species are 40% or less methylated in the minority nucleic acid species.
C7.8. The method of embodiment C7.7, wherein the loci are 30% or less methylated in the minority nucleic acid species.
C7.9. The method of embodiment C7.8, wherein the loci are 20% or less methylated in the minority nucleic acid species.
C7.10. The method of embodiment C7.9, wherein the loci are 10% or less methylated in the minority nucleic acid species.
C7.11. The method of any one of embodiments C5 to C7.10, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species is 5% or more.
C7.12. The method of embodiment C7.11, wherein a difference in methylation status is 10% or more.
C7.13. The method of embodiment C7.12, wherein a difference in methylation status is 20% or more.
C7.14. The method of embodiment C7.13, wherein a difference in methylation status is 40% or more.
C8. The method of any one of embodiments C2 to C7.14, wherein the enriching comprises selectively separating the digested nucleic acid fragments from non-digested nucleic acid.
C9. The method of embodiment C8, wherein the digested nucleic acid fragments are selectively separated according to molecular weight.
C9.1. The method of embodiment C8, wherein the digested nucleic acid fragments are selectively separated according to size.
C10. The method of any one of embodiments C8 to C9.1, wherein the digested nucleic acid fragments are selectively separated by a process comprising polyethylene glycol mediated precipitation.
C11. The method of any one of embodiments C8 to C9.1, wherein the digested nucleic acid fragments are selectively separated by a process comprising size exclusion chromatography.
C12. The method of embodiment C8, wherein the digested nucleic acid fragments are selectively separated by a process comprising contacting the fragments with a methyl-specific binding agent.
C12.1. The method of embodiment C12, wherein the contacting the fragments with the methyl-specific binding agent provides bound nucleic acid fragments and unbound nucleic acid fragments.
C12.2. The method of embodiment C12.1, wherein the bound nucleic acid fragments are selectively separated from the unbound nucleic acid fragments.
C12.3. The method of embodiments C12.1, comprising exposing the bound nucleic acid fragments, or a portion thereof, to conditions that dissociate the bound nucleic acids from the methyl-specific binding agent thereby providing one or more elution products.
C13. The method of any one of embodiments C12 to C12.3, wherein the methyl-specific binding agent comprises an antibody or a portion thereof
C14. The method of embodiment C13, wherein the antibody specifically binds an unmethylated portion of one or more nucleic acid fragments in the sample.
C15. The method of embodiment C13, wherein the antibody specifically binds a methylated portion of one or more nucleic acid fragments in the sample.
C16. The method of any one of embodiments C12 to C12.2, wherein the methyl-specific binding agent comprises a methyl-CpG binding domain protein or a portion thereof.
C17. The method of embodiment C16, wherein the methyl-CpG binding domain protein is chosen from MeCP2, MBD1, MBD2, MBD3 and MBD4.
C18. The method of any one of embodiments C1 to C17, wherein the one or more methylation sensitive cleavage agents comprise one or more restriction endonucleases.
C19. The method of embodiment C18, wherein the one or more restriction endonucleases are selected from a Type I, Type II, Type III, Type IV or Type V restriction endonuclease.
C20. The method of embodiment C18 or C19, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 6 base pairs or less.
C21. The method of embodiment C18 or C19, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 4 base pairs or less.
C22. The method of any one of embodiments C18 to C21, wherein the one or more restriction endonucleases produce overhangs.
C23. The method of any one of embodiments C18 to C22, wherein each of the digested nucleic acid fragments comprises one or more unpaired nucleotides at the 5′ or 3′ end of the fragment.
C24. The method of any one of embodiments C18 to C21, wherein the one or more restriction endonucleases produce blunt ends.
C25. The method of any one of embodiments C18 to C23, wherein one or more of the restriction endonucleases are selected from HHAI, HinP1I and HPAII.
C26. The method of any one of embodiments C18 to C25, wherein the average, mean, median or nominal length of the digested nucleic acid fragments is about 40 bases to about 100 bases.
C27. The method of any one of embodiments C2 to C26, wherein the enriching in (b) comprises amplifying the digested nucleic acid fragments relative to the non-digested nucleic acid.
C28. The method of any one of embodiments C1 to C27, wherein the digested nucleic acid fragments are amplified by a process comprising ligating one or more adaptors to one or both ends of each of the digested nucleic acid fragments.
C29. The method of embodiment C28, wherein the ligating comprises a blunt end ligation.
C30. The method of embodiment C28 or C29, comprising ligating the one or more adaptors to one or more unpaired nucleotides at the 5′ or 3′ end of the digested nucleic acid fragments.
C31. The method of any one of embodiments C28 to C30, wherein the one or more adaptors comprise one or more capture agents.
C32. The method of embodiment C31, wherein the one or more capture agents are selected from an antibody, an antigen and a member of a binding pair.
C33. The method of embodiment C31 or C32, wherein the one or more capture agents comprise biotin.
C34. The method of any one of embodiments C27 to C33, wherein the digested nucleic acid fragments are amplified by a process comprising a bridge amplification.
C35. The method of any one of embodiments C1 to C34, wherein the nucleic acid from the pregnant female comprises cell-free circulating nucleic acid.
C36. The method of embodiment C35, wherein the nucleic acid is from blood serum, blood plasma or urine.
C37. The method of any one of embodiments C1, C2 and C4 to C36, wherein the analyzing comprises determining an amount of the minority nucleic acid species in the nucleic acid sample.
C38. The method of embodiment C37, wherein determining the amount of the minority nucleic acid species comprises determining a ratio of the minority nucleic acid species to a total amount of nucleic acid in the sample.
C39. The method of embodiment C38, wherein the ratio is a percent representation.
C40. The method of any one of embodiments C1, C2 and C4 to C39, wherein the analyzing comprises determining the presence of absence of a fetal aneuploidy.
C41. The method of embodiment C40, wherein the fetal aneuploidy is a trisomy.
C42. The method of embodiment C41, wherein the trisomy is a trisomy of chromosome 13, 18 or 21.
C43. The method of any one of embodiments C1, C2 and C4 to C42, wherein the analyzing comprises non-targeted sequencing of the digested nucleic acid fragments or modified variant thereof.
C44. The method of any one of embodiments C1, C2 and C4 to C42, wherein the analyzing comprises targeted sequencing of the digested nucleic acid fragments or a modified variant thereof.
C45. The method of any one of embodiments C1 to C44, which comprises contacting the digested nucleic acid fragments with an agent that modifies a methylated nucleotide to another moiety.
C46. The method of any one of embodiments C40 to C45, wherein determining the presence or absence of a fetal aneuploidy comprises obtaining counts of sequence reads mapped to portions of a reference genome, which sequence reads are normalized and which sequence reads are from the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid.
C47. The method of embodiment C46, wherein determining the presence or absence of a fetal aneuploidy comprises comparing the normalized counts of sequence reads for a target chromosome to the normalized counts of sequence reads for the reference chromosome, whereby a statistically significant difference between the counts for the target chromosome and the counts for the reference chromosome determines the presence of a fetal aneuploidy.
C48. The method of embodiment C47, wherein counts of sequence reads of about 3 to about 15 loci on the target chromosome and the reference chromosome is determined.
C49. The method of embodiment C47, wherein counts of sequence reads of about 16 or more loci on the target chromosome and the reference chromosome is determined.
C50. The method of any one of embodiments C37 to C49, wherein determining the amount of the minority nucleic acid species comprises use of a mass spectrometry method.
C51. The method of any one of embodiments C37 to C49, wherein determining the amount of the minority nucleic acid species comprises use of a sequencing method.
D1. A method for analyzing nucleic acid in a sample, comprising:
(a) enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, thereby generating enriched hypomethylated nucleic acid; and
(b) analyzing the enriched hypomethylated nucleic acid, which analyzing comprises determining the presence, absence or amount of a polynucleotide in one or more loci chosen from loci of Table 4.
D2. The method of embodiment D1, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; chr1: 209819233-209819714; chr15: 99270658-99271954; chr9: 110581951-110582676; chr11: 76039765-76040736; chr21: 37607430-37607980; chr2: 100226464-100227140; chr21: 40278885-40279778; chr20: 40125800-40126325; chr14: 96964341-96965236; chr1: 94566367-94567508; chr6: 32120324-32121235; chr6: 2158961-2159107; chr2: 85833089-85833413; chr4: 147936346-147936831; chr2: 33107594-33108530; chr22: 43407118-43407581; chr21: 39492468-39494149; chr9: 124359818-124360534; chr6: 164167085-164167560; chr4: 4674762-4675733; chr1: 23890894-23891476; chr15: 57844015-57844457; chr16: 68766035-68766853; chr1: 234961714-234962041; chr10: 32703471-32704423; chr13: 31100912-31101535; chr2: 216808192-216808391; chr12: 18476876-18477436; chr12: 120818881-120819190; chr19: 38673641-38674608; chr17: 36605585-36606403; chr7: 65736314-65736453; chr13: 51058670-51059041; chr11: 113766137-113766643; chr12: 26265265-26266147; chr5: 109673723-109674226; chr8: 10618285-10618795; chr19: 53244844-53245458; chr11: 105386196-105387277; chr21: 16248092-16248889; chr18: 55795530-55795975; chr3: 64598707-64599348; chr1: 196659363-196660153; chr4: 165952537-165954234; chr12: 124773668-124774705; chr6: 41666010-41666469; chr6: 159237124-159238595; chr9: 108544124-108545341; chr6: 13014688-13016135; chr16: 11443167-11443469; and chr9: 101265123-101265817.
D3. The method of embodiment D1, wherein the one or more loci are chosen from loci having genomic coordinates from human reference genome hg19 of: chr17: 8512152-8512589; chr12: 13267398-13267724; chr3: 161138353-161138975; chr3: 151869156-151870687; chr9: 131317330-131317804; chr6: 18022909-18023559; chr4: 106476287-106477106; chr3: 134045674-134046244; chr6: 35115863-35116124; chr1: 143963833-143964046; chr12: 77024511-77024859; chr18: 46293373-46293973; chr8: 90912968-90913639; chr9: 127573329-127573696; chr3: 6108611-6109391; chr22: 33017833-33018590; chr3: 150064304-150065444; chr15: 32856228-32856444; chr14: 99941483-99941851; chr11: 117043564-117043818; chr12: 105837821-105838093; chr6: 44145412-44146058; chr20: 56555622-56556195; chr15: 67470797-67471606; chr4: 172550817-172551369; chr3: 72077846-72078294; chr10: 70478675-70479033; chr10: 27600544-27601168; chr7: 30971230-30971923; chr2: 27220151-27220511; chr1: 198668454-198668878; chr11: 10372877-10373954; chr8: 42912750-42913015; chr4: 74511731-74512313; chr12: 11760705-11760985; chr15: 67054128-67054469; chr3: 126292144-126292819; chr3: 132325316-132325885; chr12: 104999139-104999560; chr7: 680256-681378; chr1: 110419703-110420528; chr1: 144994257-144995559; chr3: 105678334-105678651; chr17: 54776398-54777625; chr7: 33761864-33762747; chr17: 840170-840475; chr12: 64215983-64216721; chr9: 16867882-16868157; chr12: 47358208-47358689; and chr1: 209819233-209819714.
D4. The method of embodiment D1, wherein the one or more loci are chosen from Table 4 having a median t-statistic between −18.0 and −7.0.
D5. The method of embodiment D1, wherein the one or more loci are chosen from Table 4 having a median t-statistic between −18.0 and −9.0.
D6. The method of embodiment D1, wherein the one or more loci are chosen from Table 4 having a median t-statistic between −18.0 and −10.0.
D6.1. The method of any one of embodiments D4 to D6, wherein the median t-statistic is determined by a t-test.
D7. The method of any one of embodiments D1 to D6.1, wherein the one or more loci are chosen from loci in chromosome 21, 18 or 13.
D8. The method of embodiment D7, wherein the one or more loci are chosen from chromosome 13 in Table 4.
D9. The method of embodiment D7, wherein the one or more loci are chosen from chromosome 18 in Table 4.
D10. The method of embodiment D7, wherein the one or more loci are chosen from chromosome 21 in Table 4.
D11. The method of any one of embodiments D1 to D10, wherein the one or more loci are relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species.
D11.1. The method of embodiments D11, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species comprise a CpG density of about 800 CpG methylation sites per 50,000 base pairs, or less.
D11.2. The method of embodiment D11.1, wherein the CpG density is about 600 CpG methylation sites per 50,000 base pairs, or less.
D11.3. The method of embodiment D11.2, wherein the CpG density is about 400 CpG methylation sites per 50,000 base pairs, or less.
D11.4. The method of embodiment D11.3, wherein the CpG density is about 200 CpG methylation sites per 50,000 base pairs, or less.
D11.5. The method of any one of embodiments D11 to D11.4, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species comprise a CpG density of about 16 CpG methylation sites per 1,000 base pairs, or less.
D11.6. The method of embodiment D11.5, wherein the CpG density is about 12 CpG methylation sites per 1,000 base pairs, or less.
D11.7. The method of embodiment D11.6, wherein the CpG density is about 8 CpG methylation sites per 1,000 base pairs, or less.
D11.8. The method of embodiment D11.7, wherein the CpG density is about 4 CpG methylation sites per 1,000 base pairs, or less.
D11.9. The method of any one of embodiments D11 to D11.8, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species comprise a CpG density of about 0.016 CpG methylation sites per base pair, or less.
D11.10. The method of embodiment D11.9, wherein the CpG density is about 0.012 CpG methylation sites per base pair, or less.
D11.11. The method of embodiment D11.10, wherein the CpG density is about 0.008 CpG methylation sites per base pair, or less.
D11.12. The method of embodiment D11.11, wherein the CpG density is about 0.004 CpG methylation sites per base pair, or less.
D11.13. The method of any one of embodiments D11 to D11.12, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 5 CpG methylation sites.
D11.14. The method of embodiment 11.13, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 9 CpG methylation sites.
D11.15. The method of embodiment 11.14, wherein the one or more loci relatively less methylated in the minority nucleic acid species contain at least 12 CpG methylation sites.
D11.16. The method of any one of embodiments D11 to D11.15, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 5,000 base pairs or less.
D11.17. The method of embodiment D11.16, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 2,000 base pairs or less.
D11.18. The method of embodiment D11.17, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 1,000 base pairs or less.
D11.19. The method of embodiment D11.18, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 750 base pairs or less.
D11.20. The method of embodiment D11.19, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 500 base pairs or less.
D11.21. The method of embodiment D11.20, wherein the one or more loci relatively less methylated in the minority nucleic acid species are about 250 base pairs or less.
D11.22. The method of any one of embodiments D11 to D11.21, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.1 genes per 1000 base pair, or less.
D11.23. The method of embodiment D11.22, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.08 genes per 1000 base pair, or less.
D11.24. The method of embodiment D11.23, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.06 genes per 1000 base pair, or less.
D11.25. The method of embodiment D11.24, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.04 genes per 1000 base pair, or less.
D11.26. The method of embodiment D11.25, wherein the one or more loci relatively less methylated in the minority nucleic acid species comprise 0.02 genes per 1000 base pair, or less.
D11.27. The method of any one of embodiments D11 to D11.26, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 1 restriction endonuclease recognition sites per 1000 bp, wherein each of the at least one restriction endonuclease recognition sites can be specifically digested by at least one of the one or more methylation sensitive cleavage agents when the restriction endonuclease recognition site is non-methylated.
D11.28. The method of embodiment D11.27, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 10 restriction endonuclease recognition sites per 1000 bp.
D11.29. The method of embodiment D11.28, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 20 restriction endonuclease recognition sites per 1000 bp.
D11.30. The method of embodiment D11.29, wherein each of the one or more loci relatively less methylated in the minority nucleic acid species comprise at least 30 restriction endonuclease recognition sites per 1000 bp.
D12. The method of any one of embodiments D11 to D11.30, wherein the analyzing comprises determining the presence or absence of one or more polynucleotides in the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species.
D13. The method of any one of embodiments D11 to D11.30, wherein the analyzing comprises determining the amount of one or more polynucleotides in the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species.
D14. The method of any one of embodiments D11 to D13, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species is 5% or more.
D14.1. The method of embodiment D14, wherein a difference in methylation status is 10% or more.
D14.2. The method of embodiment D14.1, wherein a difference in methylation status is 20% or more.
D14.3. The method of embodiment D14.2, wherein a difference in methylation status is 40% or more.
D14.4. The method of embodiment D14.3, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species is determined by a statistical method chosen from a t-test, Z-test, Chi-square, Wilcox, ANOVA, MANOVA, MANCOVA and logistic regression.
D14.5. The method of embodiment D14.4, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species is determined by a t-test.
D14.6. The method of embodiment D14.5, wherein the difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species comprises a median t-statistic between −18.0 and −7.0 or comprise a statistical difference comparable to a t-statistic between −18.0 and −7.0.
D15. The method of any one of embodiments D1 to D14.6, wherein the nucleic acid enriched for hypomethylated nucleic acid comprise one or more polynucleotides in one or more loci that are 60% or less methylated in the minority nucleic acid species than in the majority nucleic acid species.
D15.1. The method of any one of embodiments D11 to D15, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species are 60% or more methylated in the majority nucleic acid species.
D15.2. The method of embodiment D15.1, wherein the loci are 70% or more methylated in the majority nucleic acid species.
D15.3. The method of embodiment D15.2, wherein the loci are 75% or more methylated in the majority nucleic acid species.
D15.4. The method of embodiment D15.3, wherein the loci are 80% or more methylated in the majority nucleic acid species.
D16. The method of any one of embodiments D11 to D15.4, wherein the one or more loci relatively less methylated in the minority nucleic acid species than in the majority nucleic acid species are 40% or less methylated in the minority nucleic acid species.
D16.1. The method of embodiment D16, wherein the loci are 30% or less methylated in the minority nucleic acid species.
D16.2. The method of embodiment D16.1, wherein the loci are 20% or less methylated in the minority nucleic acid species.
D16.3. The method of embodiment D16.2, wherein the loci are 10% or less methylated in the minority nucleic acid species.
D17. A method for analyzing nucleic acid in a sample, comprising:
(a) enriching for hypomethylated nucleic acid present in a nucleic acid sample from a pregnant female, which nucleic acid comprises a minority nucleic acid species and a majority nucleic acid species, thereby generating enriched hypomethylated nucleic acid; and
(b) analyzing the enriched hypomethylated nucleic acid, which analyzing comprises non-targeted analysis of substantially all of the hypomethylated nucleic acid.
D18. The method of any one of embodiments D1 to D17, wherein the enriching comprises exposing the nucleic acid sample to conditions that selectively separate the hypomethylated nucleic acid from methylated nucleic acid.
D19. The method of embodiment D18, wherein the enriching comprises contacting the nucleic acid in the nucleic acid sample with a binding agent that specifically associates with methylated nucleic acid, thereby generating separated and enriched hypomethylated nucleic acid.
D19.1. The method of embodiment D19, wherein the contacting the fragments with the binding agent provides bound nucleic acid fragments and unbound nucleic acid fragments.
D19.2. The method of embodiment D19.1, wherein the bound nucleic acid fragments are selectively separated from the unbound nucleic acid fragments.
D19.3. The method of embodiments D19.1, comprising exposing the bound nucleic acid fragments, or a portion thereof, to conditions that dissociate the bound nucleic acids from the binding agent thereby providing one or more elution products.
D20. The method of any one of embodiments D19 to D19.3, comprising amplifying the separated and enriched hypomethylated nucleic acid.
D21. The method of embodiment D20, wherein the amplification comprises ligating one or more adaptors to the enriched hypomethylated nucleic acid.
D22. The method of embodiment D20 or D21, wherein the amplifying comprises a targeted amplification.
D23. The method of embodiment D21 or D22, wherein the one or more adaptors comprise a capture agent.
D24. The method of any one of embodiments D20 to D23, wherein the enriched nucleic acid is amplified by a process comprising a bridge amplification.
D25. The method of any one of embodiments D18 to D24, wherein the conditions that separate hypomethylated nucleic acid from methylated nucleic acid comprise binding substantially all of the nucleic acid in the nucleic acid sample and selectively eluting the hypomethylated nucleic acid.
D26. The method of any one of embodiments D19.1 to D24, wherein the conditions that separate hypomethylated nucleic acid from methylated nucleic acid comprise binding substantially all of the methylated nucleic acid in the nucleic acid sample, wherein the unbound nucleic acid fragments comprises enriched hypomethylated nucleic acid.
D27. The method of any one of embodiments D19 to D26, wherein the binding agent, or a portion thereof, comprises a methyl-specific binding agent.
D28. The method of embodiment D27, wherein the methyl-specific binding agent comprises an antibody or a portion thereof.
D29. The method of embodiment D28, wherein the antibody, or portion thereof, specifically binds an unmethylated portion of one or more nucleic acid in the sample.
D30. The method of embodiment D28, wherein the antibody, or portion thereof, specifically binds a methylated portion of one or more nucleic acids in the sample.
D31. The method of embodiment D27, wherein the methyl-specific binding agent comprises a methyl-CpG binding domain protein or a portion thereof.
D32. The method of embodiments D27 or D31, wherein the methyl-CpG binding domain protein is chosen from MeCP2, MBD1, MBD2, MBD3 and MBD4.
D33. The method of any one of embodiments D1 to D32, wherein the enriching comprises digesting the nucleic acid sample with one or more methylation sensitive cleavage agents that specifically digest the nucleic acids at a recognition site comprising a methylation site.
D34. The method of D32 or D33, wherein the digesting produces digested nucleic acid fragment and non-digested nucleic acid fragments.
D35. The method of embodiment D34, wherein the enriching comprises selectively separating the digested nucleic acid fragments from non-digested nucleic acid.
D36. The method of any one of embodiments D33 to D35, wherein the one or more methylation sensitive cleavage agents comprise one or more restriction endonucleases.
D36.1. The method of embodiment D36, wherein the one or more restriction endonucleases digest the nucleic acids at an unmethylated methylation site.
D36.2. The method of embodiment D36, wherein the one or more restriction endonucleases digest the nucleic acids at a methylated methylation site.
D37. The method of any one of embodiments D36 to D36.2, wherein the one or more restriction endonucleases are selected from a Type I, Type II, Type III, Type IV or Type V restriction endonuclease.
D38. The method of any one of embodiments D36 to D37, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 6 base pairs or less.
D39. The method of any one of embodiments D36 to D38, wherein the one or more restriction endonucleases recognize or bind to a recognition sequence comprising 4 base pairs or less.
D40. The method of any one of embodiments D36 to D39, wherein the one or more restriction endonucleases produce overhangs.
D41. The method of embodiment D40, wherein each of the digested nucleic acid fragments comprises one or more unpaired nucleotides at the 5′ or 3′ end of the fragment.
D42. The method of any one of embodiments D36 to D41, wherein one or more of the restriction endonucleases are selected from HHAI, HinP1I and HPAII.
D43. The method of any one of embodiments D36 to D39, wherein the one or more restriction endonucleases produce blunt ends.
D44. The method of any one of embodiments D36 to D43, wherein the average, mean, median or nominal length of the digested nucleic acid fragments is about 40 bases to about 100 bases.
D45. The method of any one of embodiments D34 to D44, wherein the enriching comprises amplifying the digested nucleic acid fragments relative to the non-digested nucleic acid.
D46. The method of embodiment D45, wherein the digested nucleic acid fragments are amplified by a process comprising ligating one or more adaptors to one or both ends of each of the digested nucleic acid fragments.
D47. The method of embodiment D46, wherein the ligating comprises a blunt end ligation.
D48. The method of embodiment D46 or D47, comprising ligating the one or more adaptors to one or more unpaired nucleotides at the 5′ or 3′ end of the digested nucleic acid fragments.
D49. The method of any one of embodiments D46 to D48, wherein the one or more adaptors comprise one or more capture agents.
D50. The method of embodiment D49, wherein the one or more capture agents are selected from an antibody, an antigen and a member of a binding pair.
D51. The method of embodiment D49 or D50, wherein the one or more capture agents comprise biotin.
D52. The method of any one of embodiments D45 to D51, wherein the digested nucleic acid fragments are amplified by a process comprising a bridge amplification.
D53. The method of any one of embodiments D1 to D52, wherein the nucleic acid from the pregnant female comprises cell-free circulating nucleic acid.
D54. The method of embodiment D53, wherein the nucleic acid is from blood serum, blood plasma or urine.
D55. The method of any one of embodiments D1 to D54, wherein the analyzing comprises determining an amount of feta nucleic acid in the nucleic acid sample.
D56. The method of embodiment D55, wherein determining the amount of feta nucleic acid comprises determining a ratio of feta nucleic acid to a total amount of nucleic acid in the sample.
D57. The method of embodiment D56, wherein the ratio is a percent representation.
D58. The method of any one of embodiments D1 to D57, wherein the analyzing comprises determining the presence of absence of a fetal aneuploidy.
D59. The method of embodiment D58, wherein the fetal aneuploidy is a trisomy.
D60. The method of embodiment D59, wherein the trisomy is a trisomy of chromosome 13, 18 or 21.
D61. The method of any one of embodiments D1 to D60, wherein the analyzing comprises a target-based approach.
D62. The method of any one of embodiments D1 to D60, wherein the analyzing comprises a non-target-based approach.
D63. The method of any one of embodiments D1 to D62, wherein the analyzing comprises sequencing the enriched hypomethylated nucleic acid, or a portion thereof or sequencing the enriched hypermethylated nucleic acid, or a portion thereof.
D64. The method of embodiment D63, where the sequencing comprises non-targeted sequencing.
D65. The method of embodiment D63, where the sequencing comprises targeted sequencing.
D66. The method of any one of embodiments D1 to D65, which comprises contacting the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid with an agent that modifies a methylated nucleotide to another moiety.
D67. The method of any one of embodiments D58 to D66, wherein determining the presence or absence of a fetal aneuploidy comprises obtaining counts of sequence reads mapped to portions of a reference genome, which sequence reads are normalized and which sequence reads are from the enriched hypomethylated nucleic acid or the enriched hypermethylated nucleic acid.
D68. The method of embodiment D67, wherein determining the presence or absence of a fetal aneuploidy comprises comparing the normalized counts of sequence reads for a target chromosome to the normalized counts of sequence reads for the reference chromosome, whereby a statistically significant difference between the counts for the target chromosome and the counts for the reference chromosome determines the presence of a fetal aneuploidy.
D69. The method of embodiment D68, wherein counts of sequence reads of about 3 to about 15 loci on the target chromosome and the reference chromosome is determined.
D70. The method of embodiment D68, wherein counts of sequence reads of about 16 or more loci on the target chromosome and the reference chromosome is determined.
D71. The method of any one of embodiments D55 to D70, wherein determining the amount of feta nucleic acid comprises use of a mass spectrometry method.
D72. The method of any one of embodiments D55 to D70, wherein determining the amount of feta nucleic acid comprises use of a sequencing method.
D73. The method of embodiment D72, wherein the sequencing method comprises sequencing by synthesis.
D74. The method of any one of embodiments D1 to D73, wherein the analyzing comprises mass spectrometry.
D75. The method of embodiment D74, wherein the mass spectrometry analysis comprises a targeted-mass spectrometry.
E1. A method for preparing a collection of amplification primers, comprising:
(a) selecting one or more genomic loci, wherein each locus comprises three or more features selected from:
(b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared.
E1.1. The method of embodiment E1, wherein each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a).
E1.2. The method of embodiment E1.1, wherein each of the primer pairs in configured for amplifying the target polynucleotide located in one or more of the loci selected in (a) for which the primer pair is specific.
E1.3. The method of embodiment E1.1 or E1.2, wherein each of the primers of the primer pair can hybridize to a portion of the target polynucleotide for which the primer is specific.
E1.4. The method of any one of embodiments E1.1 to E1.3, wherein each of the loci selected in
(a) comprise one or more target polynucleotides.
E1.5. The method of any one of embodiments E1.1 to E1.4, wherein each of the one or more target nucleic polynucleotides comprises at least one of the restriction endonuclease recognition sites in (a)(vi), wherein each of the primer pairs flank at least one of the restriction endonuclease recognition sites in (a)(vi).
E2. The method of any one of embodiments E1.4 or E1.5, wherein each locus comprises at least two target polynucleotides.
E3. The method of any one of embodiments E1 to E2, wherein the feature of (a)(i) is 2000 contiguous nucleotides, or less.
E4. The method of embodiment E3, wherein the feature of (a)(i) is 1000 contiguous nucleotides, or less.
E4.1. The method of embodiment E3, wherein the feature of (a)(i) is 750 contiguous nucleotides, or less.
E4.2. The method of embodiment E3, wherein the feature of (a)(i) is 500 contiguous nucleotides, or less.
E4.3. The method of embodiment E3, wherein the feature of (a)(i) is 250 contiguous nucleotides, or less.
E5. The method of any one of embodiments E1 to E4.3, wherein the CpG density of (a)(ii) is 12 CpG methylation sites per 1000 base pairs, or less.
E6. The method of embodiment E5, wherein the CpG density of (a)(ii) is 8 CpG methylation sites per 1000 base pairs, or less.
E7. The method of embodiment E6, wherein the CpG density of (a)(ii) is 4 CpG methylation sites per 1000 base pairs, or less.
E8. The method of any one of embodiments E1 to E7, wherein the CpG density of (a)(ii) is about 0.016 CpG methylation sites per base pair, or less.
E9. The method of embodiment E8, wherein the CpG density of (a)(ii) is about 0.012 CpG methylation sites per base pair, or less.
E10. The method of embodiment E9, wherein the CpG density of (a)(ii) is about 0.008 CpG methylation sites per base pair, or less.
E11. The method of embodiment E10, wherein the CpG density of (a)(ii) is about 0.004 CpG methylation sites per base pair, or less.
E12. The method of any one of embodiments E1 to E11, wherein the at least 5 CpG methylation sites of (a)(iv) are at least 9 CpG methylation sites.
E13. The method of embodiment E12, wherein the at least 5 CpG methylation sites of (a)(iv) are at least 12 CpG methylation sites.
E14. The method of any one of embodiments E1 to E13, wherein the gene density of (a)(iii) is 0.08 genes per 1000 base pair, or less.
E15. The method of embodiment E14, wherein the gene density of (a)(iii) is 0.06 genes per 1000 base pair, or less.
E16. The method of embodiment E15, wherein the gene density of (a)(iii) is 0.04 genes per 1000 base pair, or less.
E17. The method of embodiment E16, wherein the gene density of (a)(iii) is 0.02 genes per 1000 base pair, or less.
E18. The method of any one of embodiments E1 to E17, wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site of (v) about 40 to about 100 base pairs.
E19. The method of any one of embodiments E1 to E18, the feature of (a)(vi) is at least 10 restriction endonuclease recognition site per 1000 base pairs
E20. The method of embodiment E19, wherein the feature of (a)(vi) is at least 20 restriction endonuclease recognition sites per 1000 bp.
E21. The method of embodiment E20, wherein the feature of (a)(vi) is at least 30 restriction endonuclease recognition sites per 1000 bp.
E21.1. The method of any one of embodiments E1 to E21, wherein genomic loci having features (vii), (viii) and (ix) are selected in (a).
E21.2. The method of any one of embodiments E1 to E21, wherein genomic loci having features (ii), (iv) and (ix) are selected in (a).
E21.3. The method of any one of embodiments E1 to E21, wherein genomic loci having features (ii), (vii) and (ix) are selected in (a).
E21.4. The method of any one of embodiments E1 to E21, wherein genomic loci having features (iii), (iv) and (ix) are selected in (a).
E21.5. The method of any one of embodiments E21.1 to E21.4, wherein genomic loci having feature (i) is selected in (a).
E21.6. The method of any one of embodiments E21.1 to E21.5, wherein genomic loci having feature (v) is selected in (a).
E21.7. The method of any one of embodiments E21.1 to E21.6, wherein genomic loci having feature (vi) is selected in (a).
E22. The method of any one of embodiments E1 to E21.7, wherein at least one of the oligonucleotide primers of each of the primer pairs comprises a non-native element.
E23. The method of any one of embodiments E1 to E21, wherein each of the oligonucleotide primers comprises a non-native element.
E24. The method of embodiment E22 or E23, wherein the non-native element comprises a heterologous nucleotide sequence.
E25. The method of embodiment E22 or E23, wherein the non-native element comprises an identifier.
E26. The method of embodiment E25, wherein the identifier comprises a label
E27. The method of any one of embodiments E22 to E26, wherein the non-native element comprises a binding agent.
E28. The method of embodiment E27, wherein the binding agent comprises a member of a binding pair.
E29. The method of any one of embodiments E22 to E28, wherein the non-native element comprises a non-native nucleotide.
E30. The method of embodiment E29, wherein the non-native nucleotide comprises a chemical modification.
E31. The method of any one of embodiments E1 to E30, wherein both of the oligonucleotide primers of each of the primer pairs comprises a hybridization sequence that is complimentary to a portion of the locus that the primer pair is configured to amplify.
E32. The method of embodiment E31, wherein the locus, which the primer pair is configured to amplify, is longer than the combined length of the hybridization sequences of the target specific primer pair.
E33. The method of embodiment E31 or E32, wherein each of the oligonucleotide primers of each of the primer pairs comprises a sequence tag.
E34. The method of embodiment E31 or E32, wherein each of the oligonucleotide primers of each of the primer pairs comprises an different hybridization sequence.
E35. The method of any one of embodiments E1 to E34, wherein each of the target polynucleotides comprises a length of about 500 nucleotides to about 30 nucleotides. (nucleosomes are 146 or 166)
E36. The method of embodiment E35, wherein each of the target polynucleotides comprise a length of about 1000 nucleotides to about 40 nucleotides.
E37. The method of embodiment E36, wherein the target polynucleotide is about 180 nucleotides to about 40 nucleotides.
E38. The method of any one of embodiments E1 to E37, wherein the target polynucleotide is single stranded.
E39. The method of any one of embodiments E1 to E37, wherein the target polynucleotide is double stranded.
E40. The method of any one of embodiments E1 to E37, wherein the target polynucleotide is circulating cell free DNA.
E41. The method of embodiment E40, wherein the circulating cell free DNA comprises a length of 360 nucleotides to about 40 nucleotides.
E41.1. The method of any one of embodiments E1 to E41, comprising contacting target polynucleotides with the collection of amplification primers under amplification conditions, thereby generating amplicons.
E42. The method of any one of embodiments E1 to E41, comprising:
(a) digesting the target polynucleotides of a first sample and a second sample with the one or more methylation sensitive restriction endonucleases that specifically digest the target polynucleotides at the at least one restriction endonuclease recognition site when the at least one restriction endonuclease site is unmethylated, wherein each of the samples comprise one or more of the selected loci;
(b) contacting each sample with the collection of oligonucleotide primers under amplification conditions, thereby providing target specific amplicons of undigested target polynucleotides; and
(c) analyzing the target specific amplicons from each sample, wherein a differentially methylated locus is identified according to the analyzing.
E43. The method of embodiment E42, wherein the analyzing comprises determining an amount of the target specific amplicons from each sample.
E44. The method of embodiment E43, wherein the amount of target specific amplicons of the first sample is significantly different from the amount of target specific amplicons of the second sample.
E45. The method of any one of embodiments E42 to E44, wherein the first sample and the second sample are from different sources.
E46. The method of any one of embodiments E42 to E45, wherein the first sample and/or the second sample comprise circulating cell free nucleic acid.
E47. The method of any one of embodiments E42 to E46, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the first sample.
E48. The method of any one of embodiment E42 to E47, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the second sample.
E49. The method of any one of embodiments E42 to E48, wherein the first sample comprises a minority nucleic acid species.
E50. The method of any one of embodiments E42 to E49, wherein the second sample comprises a majority nucleic acid species.
E51. The method of any one of embodiments E42 to E50, wherein the first sample comprises fetal nucleic acid.
E52. The method of any one of embodiments E42 to E51, wherein the first sample comprises enriched fetal nucleic acid.
E53. The method of any one of embodiments E42 to E52, wherein the second sample comprises maternal nucleic acid.
E54. The method of any one of embodiments E50 to E53, wherein the analyzing comprises identifying one or more of the selected loci 60% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
E55. The method of embodiment E54, wherein the analyzing comprises identifying one or more of the selected loci 70% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
E56. The method of embodiment E55, wherein the analyzing comprises identifying one or more of the selected loci 75% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
E57. The method of embodiment E56, wherein the analyzing comprises identifying one or more of the selected loci 80% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
E58. The method of any one of embodiments E50 to E57, wherein the analyzing comprises identifying one or more of the selected loci 40% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
E59. The method of embodiment E58, wherein the analyzing comprises identifying one or more of the selected loci 30% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
E60. The method of embodiment E59, wherein the analyzing comprises identifying one or more of the selected loci 20% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
E61. The method of embodiment E60, wherein the analyzing comprises identifying one or more of the selected loci 10% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
E62. The method of any one of embodiments E50 to E61, wherein the analyzing comprises identifying one or more of the selected loci, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more selected loci is 5% or more.
E63. The method of embodiment E62, wherein the difference in methylation status is 10% or more.
E64. The method of embodiment E63, wherein the difference in methylation status is 20% or more.
E65. The method of embodiment E64, wherein the difference in methylation status is 40% or more.
E66. The method of any one of embodiments E42 to E65, wherein the methylation status of the one or more selected loci in the first sample is 15% or less methylated and the methylation status of the one or more loci in the second sample is 60% or greater.
E67. The method of any one of embodiments E42 to E66, wherein the one or more methylation sensitive restriction endonuclease comprises two or more methylation sensitive restriction endonucleases.
E68. The method of any one of embodiments E42 to E67, wherein the one or more methylation sensitive restriction endonuclease does not digest nucleic acid when the at least one restriction endonuclease recognition site is methylated.
E69. The method of any one of embodiments E42 to E68, wherein the differentially methylated locus identified in E42(d) is hypomethylated in the first sample.
E70. The method of any one of embodiments E42 to E69, wherein the differentially methylated locus identified in E42(d) is hypermethylated in the second sample.
E71. The collection of oligonucleotide primer pairs of any one of embodiments E42 to E70, wherein the analyzing comprises analyzing target polynucleotides that a cleaved by the one or more methylation sensitive restriction endonucleases.
E72. The collection of oligonucleotide primer pairs of any one of embodiments E42 to E70, wherein the analyzing comprises analyzing target polynucleotides that a not cleaved by the one or more methylation sensitive restriction endonucleases.
F1. A collection of oligonucleotide primer pairs for identifying the presence or absence of a hypomethylated locus prepared by a process comprising:
(a) selecting one or more genomic loci wherein each locus comprises three or more features selected from;
(b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared.
F1.1. The collection of oligonucleotide primer pairs of embodiment F1, wherein each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a).
F1.2. The collection of oligonucleotide primer pairs of embodiment F1.1, wherein each of the primer pairs in configured for amplifying the target polynucleotide located in one or more of the loci selected in (a) for which the primer pair is specific.
F1.3. The collection of oligonucleotide primer pairs of embodiment F1.1 or F1.2, wherein each of the primers of the primer pair can hybridize to a portion of the target polynucleotide for which the primer is specific.
F1.4. The collection of oligonucleotide primer pairs of any one of embodiments F1.1 to F1.3, wherein each of the loci selected in (a) comprise one or more target polynucleotides.
F1.5. The collection of oligonucleotide primer pairs of any one of embodiments F1.1 to F1.4, wherein each of the one or more target nucleic polynucleotides comprises at least one of the restriction endonuclease recognition sites in (a)(vi), wherein each of the primer pairs flank at least one of the restriction endonuclease recognition sites in (a)(vi).
F2. The collection of oligonucleotide primer pairs of any one of embodiments F1.4 or F1.5, wherein each locus comprises at least two target polynucleotides.
F3. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F2, wherein the feature of (a)(i) is 2000 contiguous nucleotides, or less.
F4. The collection of oligonucleotide primer pairs of embodiment F3, wherein the feature of (a)(i) is 1000 contiguous nucleotides, or less.
F4.1. The collection of oligonucleotide primer pairs of embodiment F3, wherein the feature of (a)(i) is 750 contiguous nucleotides, or less.
F4.2. The collection of oligonucleotide primer pairs of embodiment F3, wherein the feature of (a)(i) is 500 contiguous nucleotides, or less.
F4.3. The collection of oligonucleotide primer pairs of embodiment F3, wherein the feature of (a)(i) is 250 contiguous nucleotides, or less.
F5. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F4.3, wherein the CpG density of (a)(ii) is 12 CpG methylation sites per 1000 base pairs, or less.
F6. The collection of oligonucleotide primer pairs of embodiment F5, wherein the CpG density of (a)(ii) is 8 CpG methylation sites per 1000 base pairs, or less.
F7. The collection of oligonucleotide primer pairs of embodiment F6, wherein the CpG density of (a)(ii) is 4 CpG methylation sites per 1000 base pairs, or less.
F8. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F7, wherein the CpG density of (a)(ii) is about 0.016 CpG methylation sites per base pair, or less.
F9. The collection of oligonucleotide primer pairs of embodiment F8, wherein the CpG density of (a)(ii) is about 0.012 CpG methylation sites per base pair, or less.
F10. The collection of oligonucleotide primer pairs of embodiment F9, wherein the CpG density of (a)(ii) is about 0.008 CpG methylation sites per base pair, or less.
F11. The collection of oligonucleotide primer pairs of embodiment F10, wherein the CpG density of (a)(ii) is about 0.004 CpG methylation sites per base pair, or less.
F12. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F11, wherein the at least 5 CpG methylation sites of (a)(iv) are at least 9 CpG methylation sites.
F13. The collection of oligonucleotide primer pairs of embodiment F12, wherein the at least 5 CpG methylation sites of (a)(iv) are at least 12 CpG methylation sites.
F14. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F13, wherein the gene density of (a)(iii) is 0.08 genes per 1000 base pair, or less.
F15. The collection of oligonucleotide primer pairs of embodiment F14, wherein the gene density of (a)(iii) is 0.06 genes per 1000 base pair, or less.
F16. The collection of oligonucleotide primer pairs of embodiment F15, wherein the gene density of (a)(iii) is 0.04 genes per 1000 base pair, or less.
F17. The collection of oligonucleotide primer pairs of embodiment F16, wherein the gene density of (a)(iii) is 0.02 genes per 1000 base pair, or less.
F18. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F17, wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site of (v) about 40 to about 100 base pairs.
F19. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F18, the feature of (a)(vi) is at least 10 restriction endonuclease recognition site per 1000 base pairs
F20. The collection of oligonucleotide primer pairs of embodiment F19, wherein the feature of (a)(vi) is at least 20 restriction endonuclease recognition sites per 1000 bp.
F21. The collection of oligonucleotide primer pairs of embodiment F20, wherein the feature of (a)(vi) is at least 30 restriction endonuclease recognition sites per 1000 bp.
F21.1. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21, wherein genomic loci having features (vii), (viii) and (ix) are selected in (a).
F21.2. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21.1, wherein genomic loci having features (ii), (iv) and (ix) are selected in (a).
F21.3. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21, wherein genomic loci having features (ii), (vii) and (ix) are selected in (a).
F21.4. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21, wherein genomic loci having features (iii), (iv) and (ix) are selected in (a).
F21.5. The collection of oligonucleotide primer pairs of any one of embodiments F21.1 to F21.4, wherein genomic loci having feature (i) is selected in (a).
F21.6. The collection of oligonucleotide primer pairs of any one of embodiments F21.1 to F21.5, wherein genomic loci having feature (v) is selected in (a).
F21.7. The collection of oligonucleotide primer pairs of any one of embodiments F21.1 to F21.6, wherein genomic loci having feature (vi) is selected in (a).
F22. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21.7, wherein at least one of the oligonucleotide primers of each of the primer pairs comprises a non-native element.
F23. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F21, wherein each of the oligonucleotide primers comprises a non-native element.
F24. The collection of oligonucleotide primer pairs of embodiment F22 or F23, wherein the non-native element comprises a heterologous nucleotide sequence.
F25. The collection of oligonucleotide primer pairs of embodiment F22 or F23, wherein the non-native element comprises an identifier.
F26. The collection of oligonucleotide primer pairs of embodiment F25, wherein the identifier comprises a label
F27. The collection of oligonucleotide primer pairs of any one of embodiments F22 to F26, wherein the non-native element comprises a binding agent.
F28. The collection of oligonucleotide primer pairs of embodiment F27, wherein the binding agent comprises a member of a binding pair.
F29. The collection of oligonucleotide primer pairs of any one of embodiments F22 to F28, wherein the non-native element comprises a non-native nucleotide.
F30. The collection of oligonucleotide primer pairs of embodiment F29, wherein the non-native nucleotide comprises a chemical modification.
F31. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F30, wherein both of the oligonucleotide primers of each of the primer pairs comprises a hybridization sequence that is complimentary to a portion of the target sequence which the primer pair is configured to amplify.
F32. The collection of oligonucleotide primer pairs of embodiment F31, wherein the target sequence, which the primer pair is configured to amplify, is longer than the combined length of the hybridization sequences of the target specific primer pair.
F33. The collection of oligonucleotide primer pairs of embodiment F31 or F32, wherein each of the oligonucleotide primers of each of the primer pairs comprises aa sequence tag.
F34. The collection of oligonucleotide primer pairs of embodiment F31 or F32, wherein each of the oligonucleotide primers of each of the primer pairs comprises an different hybridization sequence.
F35. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F34, wherein the target polynucleotide comprises a length of about 500 nucleotides to about 30 nucleotides. (nucleosomes are 146 or 166)
F36. The collection of oligonucleotide primer pairs of embodiment F35, wherein the target polynucleotide comprises a length of about 360 nucleotides to about 40 nucleotides.
F37. The collection of oligonucleotide primer pairs of embodiment F36, wherein the target polynucleotide comprises a length of about 180 nucleotides to about 40 nucleotides.
F38. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F37, wherein the target polynucleotide is single stranded.
F39. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F37, wherein the target polynucleotide is double stranded.
F40. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F37, wherein the target polynucleotide is circulating cell free DNA.
F41. The collection of oligonucleotide primer pairs of F40, wherein the circulating cell free DNA comprises a length of 360 nucleotides to about 40 nucleotides.
F41.1. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F41, comprising contacting target polynucleotides with the collection of amplification primers under amplification conditions, thereby generating amplicons.
F42. The collection of oligonucleotide primer pairs of any one of embodiments F1 to F41.1, wherein the process comprises:
(a) digesting the target polynucleotide of a first sample and a second sample with the one or more methylation sensitive restriction endonucleases that specifically digest the target polynucleotide at the at least one restriction endonuclease recognition site when the at least one restriction endonuclease site is unmethylated, wherein each of the samples comprise one or more of the selected loci;
(b) contacting each sample with the collection of oligonucleotide primers under amplification conditions, thereby providing target specific amplicons of undigested target polynucleotides; and
(c) analyzing the target specific amplicons from each sample, wherein a differentially methylated locus is identified according to the analyzing.
F43. The collection of oligonucleotide primer pairs of embodiment F42, wherein the analyzing comprises determining an amount of the target specific amplicons from each sample.
F44. The collection of oligonucleotide primer pairs of embodiment F43, wherein the amount of target specific amplicons of the first sample is significantly different from the amount of target specific amplicons of the second sample.
F45. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F44, wherein the first sample and the second sample are from different sources.
F46. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F45, wherein the first sample and/or the second sample comprise circulating cell free nucleic acid.
F47. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F46, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the first sample.
F48. The collection of oligonucleotide primer pairs of any one of embodiment F42 to F47, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the second sample.
F49. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F48, wherein the first sample comprises a minority nucleic acid species.
F50. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F49, wherein the second sample comprises a majority nucleic acid species.
F51. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F50, wherein the first sample comprises fetal nucleic acid.
F52. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F51, wherein the first sample comprises enriched fetal nucleic acid.
F53. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F52, wherein the second sample comprises maternal nucleic acid.
F54. The collection of oligonucleotide primer pairs of any one of embodiments F50 to F53, wherein the analyzing comprises identifying one or more of the selected loci 60% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
F55. The collection of oligonucleotide primer pairs of embodiment F54, wherein the analyzing comprises identifying one or more of the selected loci 70% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
F56. The collection of oligonucleotide primer pairs of embodiment F55, wherein the analyzing comprises identifying one or more of the selected loci 75% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
F57. The collection of oligonucleotide primer pairs of embodiment F56, wherein the analyzing comprises identifying one or more of the selected loci 80% or more methylated in the majority nucleic acid species relative to the minority nucleic acid species.
F58. The collection of oligonucleotide primer pairs of any one of embodiments F50 to F57, wherein the analyzing comprises identifying one or more of the selected loci 40% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
F59. The collection of oligonucleotide primer pairs of embodiment F58, wherein the analyzing comprises identifying one or more of the selected loci 30% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
F60. The collection of oligonucleotide primer pairs of embodiment F59, wherein the analyzing comprises identifying one or more of the selected loci 20% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
F61. The collection of oligonucleotide primer pairs of embodiment F60, wherein the analyzing comprises identifying one or more of the selected loci 10% or less methylated in the minority nucleic acid species relative to the majority nucleic acid species.
F62. The collection of oligonucleotide primer pairs of any one of embodiments F50 to F61, wherein the analyzing comprises identifying one or more of the selected loci, wherein a difference in methylation status between the minority nucleic acid species and the majority nucleic acid species for the one or more selected loci is 5% or more.
F63. The collection of oligonucleotide primer pairs of embodiment F62, wherein the difference in methylation status is 10% or more.
F64. The collection of oligonucleotide primer pairs of embodiment F63, wherein the difference in methylation status is 20% or more.
F65. The collection of oligonucleotide primer pairs of embodiment F64, wherein the difference in methylation status is 40% or more.
F66. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F65, wherein the methylation status of the one or more selected loci in the first sample is 15% or less methylated and the methylation status of the one or more loci in the second sample is 60% or greater.
F67. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F66, wherein the one or more methylation sensitive restriction endonuclease comprises two or more methylation sensitive restriction endonucleases.
F68. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F67, wherein the one or more methylation sensitive restriction endonuclease does not digest nucleic acid when the at least one restriction endonuclease recognition site is methylated.
F69. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F68, wherein the differentially methylated locus identified in F42(d) is hypomethylated in the first sample.
F70. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F69, wherein the differentially methylated locus identified in F42(d) is hypermethylated in the second sample.
F71. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F70, wherein the analyzing comprises analyzing target polynucleotides that a cleaved by the one or more methylation sensitive restriction endonucleases.
F72. The collection of oligonucleotide primer pairs of any one of embodiments F42 to F70, wherein the analyzing comprises analyzing target polynucleotides that a not cleaved by the one or more methylation sensitive restriction endonucleases.
G1. A collection of amplification primer pairs for identifying the presence or absence of a hypermethylated locus prepared by a process comprising:
(a) selecting one or more genomic loci wherein each locus comprises three or more features selected from:
(b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared.
G1.1. The collection of amplification primer pairs of embodiment G1, wherein each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a).
G1.2. The collection of amplification primer pairs of embodiment G1.1, wherein each of the primer pairs in configured for amplifying the target polynucleotide located in one or more of the loci selected in (a) for which the primer pair is specific.
G1.3. The collection of amplification primer pairs of embodiment G1.1 or G1.2, wherein each of the primers of the primer pair can hybridize to a portion of the target polynucleotide for which the primer is specific.
G1.4. The collection of amplification primer pairs of any one of embodiments G1.1 to G1.3, wherein each of the loci selected in (a) comprise one or more target polynucleotides.
G2. The collection of amplification primer pairs of any one of embodiments G1.1 to G1.4, wherein each of the one or more target nucleic polynucleotides comprises at least one of the restriction endonuclease recognition sites in (a)(iv), wherein each of the primer pairs flank at least one of the restriction endonuclease recognition sites in (a)(iv).
G3. The collection of amplification primer pairs of any one of embodiments G1.4 or G2, wherein each locus comprises at least two target polynucleotides.
G4. The collection of amplification primer pairs of any one or embodiments G1 to G3, wherein the feature of (a)(i) is 2000 contiguous nucleotides, or less.
G5. The collection of amplification primer pairs of embodiment G4, wherein the feature of (a)(i) is 1000 contiguous nucleotides, or less.
G6. The collection of amplification primer pairs of embodiment G4, wherein the feature of (a)(i) is 750 contiguous nucleotides, or less.
G7. The collection of amplification primer pairs of embodiment G4, wherein the feature of (a)(i) is 500 contiguous nucleotides, or less.
G8. The collection of amplification primer pairs of embodiment G4, wherein the feature of (a)(i) is 250 contiguous nucleotides, or less.
G9. The collection of amplification primer pairs of any one of embodiments G1 to G8, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 9 CpG methylation sites.
G10. The collection of amplification primer pairs of embodiment G9, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 12 CpG methylation sites.
G11. The collection of amplification primer pairs of any one of embodiments G1 to G10, wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site of (iii) is about 40 to about 100 base pairs.
G12. The collection of amplification primer pairs of any one of embodiments G1 to G11, wherein the feature of (a)(iv) is at least 10 restriction endonuclease recognition site per 1000 base pairs
G13. The collection of amplification primer pairs of embodiment G12, wherein the feature of (a)(iv) is at least 20 restriction endonuclease recognition sites per 1000 bp.
G14. The collection of amplification primer pairs of embodiment G12, wherein the feature of (a)(iv) is at least 30 restriction endonuclease recognition sites per 1000 bp.
G14.1. The collection of amplification primer pairs of any one of embodiments G1 to G14, wherein genomic loci having features (ii), (iii) and (iv) are selected in (a).
G14.2. The collection of amplification primer pairs of any one of embodiments G1 to G14, wherein genomic loci having features (ii), (iii) and (vii) are selected in (a).
G14.3. The collection of amplification primer pairs of any one of embodiments G1 to G14, wherein genomic loci having features (ii), (iv) and (vii) are selected in (a).
G14.4. The collection of amplification primer pairs of any one of embodiments G1 to G14, wherein genomic loci having features (iii), (iv) and (vii) are selected in (a).
G14.5. The collection of amplification primer pairs of any one of embodiments G14.1 to G14.4, wherein genomic loci having feature (i) is selected in (a).
G14.6. The collection of amplification primer pairs of any one of embodiments G14.1 to G14.5, wherein genomic loci having feature (v) is selected in (a).
G14.7. The collection of amplification primer pairs of any one of embodiments G14.1 to G14.6, wherein genomic loci having feature (vi) is selected in (a).
G15. The collection of amplification primer pairs of any one of embodiments G1 to G14, wherein at least one of the amplification primers of each of the primer pairs comprises a non-native element.
G16. The collection of amplification primer pairs of any one of embodiments G1 to G15, wherein each of the amplification primers comprises a non-native element.
G17. The collection of amplification primer pairs of embodiment G15 or G16, wherein the non-native element comprises a heterologous nucleotide sequence.
G18. The collection of amplification primer pairs of embodiment G15 or G16, wherein the non-native element comprises an identifier.
G19. The collection of amplification primer pairs of embodiment G18, wherein the identifier comprises a label
G20. The collection of amplification primer pairs of any one of embodiments G16 to G19, wherein the non-native element comprises a binding agent.
G21. The collection of amplification primer pairs of embodiment G20, wherein the binding agent comprises a member of a binding pair.
G22. The collection of amplification primer pairs of any one of embodiments G15 to G21, wherein the non-native element comprises a non-native nucleotide.
G23. The collection of amplification primer pairs of embodiment G22, wherein the non-native nucleotide comprises a chemical modification.
G24. The collection of amplification primer pairs of any one of embodiments G1 to G23, wherein both of the amplification primers of each of the primer pairs comprises a hybridization sequence that is complimentary to a portion of the target sequence which the primer pair is configured to amplify.
G25. The collection of amplification primer pairs of embodiment G24, wherein the target sequence, which the primer pair is configured to amplify, is longer than the combined length of the hybridization sequences of the target specific primer pair.
G26. The collection of amplification primer pairs of embodiment G24 or G25, wherein each of the amplification primers of each of the primer pairs comprises a sequence tag.
G27. The collection of amplification primer pairs of embodiment G24 or G25, wherein each of the amplification primers of each of the primer pairs comprises a different hybridization sequence.
G28. The collection of amplification primer pairs of any one of embodiments G1 to G27, wherein the target polynucleotide comprises a length of about 500 nucleotides to about 30 nucleotides.
G29. The collection of amplification primer pairs of embodiment G28, wherein the target polynucleotide comprises a length of about 360 nucleotides to about 40 nucleotides.
G30. The collection of amplification primer pairs of embodiment G28, wherein the target polynucleotide comprises a length of about 180 nucleotides to about 40 nucleotides.
G31. The collection of amplification primer pairs of any one of embodiments G1 to G30, wherein the target polynucleotide is single stranded.
G32. The collection of amplification primer pairs of any one of embodiments G1 to G31, wherein the target polynucleotide is double stranded.
G33. The collection of amplification primer pairs of any one of embodiments G1 to G32, wherein the target polynucleotide is a circulating cell free nucleic acid.
G34. The collection of amplification primer pairs of G33, wherein the circulating cell free nucleic acid comprises a length of about 500 nucleotides to about 30 nucleotides.
G35. The collection of amplification primer pairs of any one of embodiments G1 to G34, wherein the minority nucleic acid species and the majority nucleic acid species comprise one or more target polynucleotides.
G36. The collection of amplification primer pairs of any one of embodiments G1 to G35, wherein the process comprises:
(a) digesting the target polynucleotides of a first sample and a second sample with the one or more methylation sensitive restriction endonucleases that specifically digest the target polynucleotides at the at least one restriction endonuclease recognition site when the at least one restriction endonuclease recognition site is unmethylated, wherein each of the samples comprise one or more of the selected loci;
(b) contacting each of the samples with the collection of amplification primers under amplification conditions, thereby providing target specific amplicons of undigested target polynucleotides; and
(c) analyzing the target specific amplicons from each sample, wherein one or more differentially methylated loci are identified according to the analyzing.
G37. The collection of amplification primer pairs of embodiment G36, wherein the analyzing comprises determining an amount of the target specific amplicons from each sample.
G38. The collection of amplification primer pairs of embodiment G37, wherein the amount of target specific amplicons of the first sample is significantly different from the amount of target specific amplicons of the second sample.
G39. The collection of amplification primer pairs of any one of embodiments G37 to G38, wherein the first sample and the second sample are from different sources.
G40. The collection of amplification primer pairs of any one of embodiments G36 to G39, wherein the first sample and/or the second sample comprise circulating cell free nucleic acid.
G41. The collection of amplification primer pairs of any one of embodiments G36 to G40, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the first sample.
G42. The collection of amplification primer pairs of any one of embodiment G36 to G41, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the second sample.
G43. The collection of amplification primer pairs of any one of embodiments G36 to G42, wherein the first sample comprises the minority nucleic acid species.
G44. The collection of amplification primer pairs of any one of embodiments G36 to G43, wherein the second sample comprises the majority nucleic acid species.
G45. The collection of amplification primer pairs of any one of embodiments G36 to G44, wherein the second sample does not include the minority nucleic acid species.
G46. The collection of amplification primer pairs of any one of embodiments G36 to G45, wherein the minority nucleic acid species is partially or entirely removed from the second sample.
G47. The collection of amplification primer pairs of any one of embodiments G1 to G46, wherein the minority nucleic acid species is fetal nucleic acid.
G48. The collection of amplification primer pairs of any one of embodiments G36 to G47, wherein the first sample is enriched for the minority nucleic acid species.
G49. The collection of amplification primer pairs of any one of embodiments G1 to G48, wherein the majority nucleic acid species is maternal nucleic acid.
G50. The collection of amplification primer pairs of any one of embodiments G1 to G49, wherein the feature of (a)(vi) is 65% or more in the minority species.
G51. The collection of amplification primer pairs of any one of embodiments G1 to G50, wherein the feature of (a)(vi) is 70% or more in the minority species.
G52. The collection of amplification primer pairs of any one of embodiments G1 to G51, wherein the feature of (a)(vi) is 75% or more in the minority species.
G53. The collection of amplification primer pairs of any one of embodiments G1 to G52, wherein the feature of (a)(vi) is 80% or more in the minority species.
G54. The collection of amplification primer pairs of any one of embodiments G1 to G53, wherein the feature of (a)(vii) is 40% or less in the majority nucleic acid species.
G55. The collection of amplification primer pairs of any one of embodiments G1 to G54, wherein the feature of (a)(vii) is 30% or less in the majority nucleic acid species.
G56. The collection of amplification primer pairs of any one of embodiments G1 to G55, wherein the feature of (a)(vii) is 20% or less in the majority nucleic acid species.
G57. The collection of amplification primer pairs of any one of embodiments G1 to G56, wherein the feature of (a)(vii) is 10% or less in the majority nucleic acid species.
G58. The collection of amplification primer pairs of any one of embodiments G1 to G57, wherein the feature of (a)(viii) is a difference in methylation status of 7.5% or more.
G59. The collection of amplification primer pairs of any one of embodiments G1 to G58, wherein the feature of (a)(viii) is a difference in methylation status of 10% or more.
G60. The collection of amplification primer pairs of any one of embodiments G1 to G59, wherein the feature of (a)(viii) is a difference in methylation status of 20% or more.
G61. The collection of amplification primer pairs of any one of embodiments G1 to G60, wherein the feature of (a)(viii) is a difference in methylation status of 40% or more.
G62. The collection of amplification primer pairs of any one of embodiments G36 to G61, wherein the methylation status of the one or more selected loci in the first sample is 60% or more and the methylation status of the one or more loci in the second sample is 40% or less.
G63. The collection of amplification primer pairs of any one of embodiments G36 to G62, wherein the one or more methylation sensitive restriction endonuclease comprises two or more methylation sensitive restriction endonucleases.
G64. The collection of amplification primer pairs of any one of embodiments G36 to G63, wherein the one or more methylation sensitive restriction endonucleases do not digest nucleic acid when the at least one restriction endonuclease recognition site is methylated.
G65. The collection of amplification primer pairs of any one of embodiments G36 to G64, wherein the differentially methylated locus identified in G36(c) is hypermethylated in the first sample.
G66. The collection of amplification primer pairs of any one of embodiments G36 to G65, wherein the differentially methylated locus identified in G36(c) is hypomethylated in the second sample.
G67. The collection of amplification primer pairs of any one of embodiments G36 to G66, wherein the analyzing comprises analyzing target polynucleotides that a not cleaved by the one or more methylation sensitive restriction endonucleases.
H1. A method of amplifying one or more target polynucleotides in a hypermethylated locus comprising: contacting a sample with one or more of the primer pairs of embodiments G1 to G67 under amplification conditions, thereby generating target specific amplicons.
H2. The method of embodiment H1, wherein the sample comprises circulating cell free nucleic acid obtained from a human subject.
H3. The method of embodiment H2, wherein the circulating cell free nucleic acid of the sample comprises one or more of the target polynucleotides.
H3.1. The method of any one of embodiments H1 to H3, wherein each of the primer pairs is configured for amplifying the target polynucleotide for which the primer pair is specific, wherein each of the primers of the primer pair hybridize to a portion of the target polynucleotide for which the primer pair is specific.
H3.2. The method of any one of embodiments H1 to H3, wherein each of the target polynucleotides comprise at least one of the restriction endonuclease restriction recognition sites in (a)(iv), wherein each of the primer pairs flank at least one of the restriction endonuclease sites in (a)(iv).
H4. The method of any one of embodiments H3 to H3.2, wherein the human subject is a pregnant female subject.
H5. The method of any one of embodiments H1 to H4, comprising, prior to contacting with the primer pairs, digesting sample nucleic acid with a methylation sensitive restriction endonuclease that specifically digests the target polynucleotide at the at least one restriction endonuclease recognition site when the at least one restriction endonuclease site is unmethylated.
H6. The method of embodiment H5, wherein the amplification conditions comprise amplifying target polynucleotides that were not cleaved by the one or more methylation sensitive restriction endonucleases.
H7. The method of any one of embodiments H1 to H6, wherein the amplification conditions comprise a known amount of one or more competitor nucleic acids.
H7.1. The method of embodiment H5 or H6, wherein the amplification conditions comprise amplifying the competitor nucleic acids, thereby providing competitor specific amplicons.
H8. The method of embodiment H7 or H7.1, wherein each of the one or more competitor nucleic acids comprise a nucleic acid sequence that is substantially identical to a target polynucleotide.
H9. The method of embodiment H8, wherein each of the one or more competitor nucleic acids comprises a feature that distinguishes the competitor nucleic acid from the target polynucleotide to which it is substantially identical to.
H10. The method of any one of embodiments H7 to H9, wherein each of which primer pairs is configured to specifically amplify one of the target polynucleotides and its competitor nucleic acid.
H11. The method of embodiment H10, comprising analyzing the target specific amplicons and the competitor specific amplicons.
H12. The method of embodiment H11, wherein the analyzing comprises determining the presence or absence of a genetic variation.
H13. The method of embodiment H12, wherein the genetic variation is a chromosome aneuploidy.
H14. The method of embodiment H13, wherein the chromosome aneuploidy is chosen from an aneuploidy of chromosome 13, 18 and 21.
H15. The method of embodiment H11, wherein the analyzing comprises determining the presence or absence of a cancer.
H16. The method of any one of embodiments of H11 to H15, wherein the analyzing comprises determining a ratio of target specific amplicons to competitor specific amplicons for each of the target polynucleotides in the sample.
H17. The method of any one of embodiments H11 to H16, wherein the analyzing comprises determining an amount of fetal nucleic acid in the sample.
H18. The method of embodiment H17, wherein the analyzing comprises normalizing each of which ratios to the amount of fetal nucleic acid in the sample.
H19. The method of any one of embodiments H16 to H18, wherein the amplification conditions comprise a portion of the fetal nucleic acid from the sample and each of which ratios is normalized according to the portion of fetal nucleic acid.
H20. The method of any one of embodiments H11 to H19, wherein the analysis comprises matrix assisted laser desorption ionization (MALDI) mass spectrometry.
H21. The method of any one of embodiments H11 to H20, wherein the analysis comprises sequencing the target specific amplicons.
H22. The method of any one of embodiments H11 to H21, wherein the analysis comprises sequencing the competitor polynucleotide specific amplicons.
H23. The method of any one of embodiments H11 to H22, wherein the amount of one or more target polynucleotides in the sample is determined according to the analysis.
H24. The method of any one of embodiments H11 to H23, wherein the analysis comprises comparing the ratios from two or more samples.
H25. The method of embodiment H24, wherein the two or more samples comprise one or more control samples.
H26. The method of embodiment H25, wherein the ratios from one or more of the samples are normalized to the one or more control samples.
H27. The method of any one of embodiments H1 to H26, wherein the methylation sensitive restriction endonuclease is selected from AatII, AccII, ACiI, AcII, AfeI, AgeI, AgeI-HF, Aor13HI, Aor51HI, AscI, AseI, BceAI, BmgBI, BsaAI, BsaHI, BsiEI, BspDI, BsrFI, BspT1041, BssHII, BstBI, BstUI, Cfr10I, ClaI, CooI, EagI, Eco52I, FauI, FseI, FspI, DpnI, DpnII, HaeII, HaelII, HapII, HfaI, HgaI, HhaI, HinP1I, HPAII, Hpy99I, HpyCH4IV, KasI, MaeII, McrBC, MluI, MspI, NaeI, NgoMIV, NotI, NotI-HF, NruI, NsbI, NtBsmAI, NtCviPII, PaeR7I, PIuTI, PmII, PmaCI, Psp1406I, PvuI, RsrII, SadII, SaII, SaII-HF, ScrFI, SfoI, SfrAI, SmaI, SnaBI, TspMI, ZraI and isoschizomers thereof.
H27.1. The method of any one of embodiments H1 to H27, wherein the methylation sensitive restriction endonuclease is selected from HpaII, HinP1I, HhaI, MaeII, BstUI and AciI.
H27.2. The method of any one of embodiments H1 to H27.1, wherein the methylation sensitive restriction endonuclease is selected from HHAI, HinP1I and HPAII.
H28. The method of any one of embodiments H1 to H27, wherein each locus comprises at least two target polynucleotides.
H29. The method of any one of embodiments H1 to H27, wherein the feature of (a)(i) is 2000 contiguous nucleotides, or less.
H30. The method of embodiment H29, wherein the feature of (a)(i) is 1000 contiguous nucleotides, or less.
H31. The method of embodiment H30, wherein the feature of (a)(i) is 750 contiguous nucleotides, or less.
H32. The method of embodiment H31, wherein the feature of (a)(i) is 500 contiguous nucleotides, or less.
H33. The method of embodiment H30, wherein the feature of (a)(i) is 250 contiguous nucleotides, or less.
H34. The method of any one of embodiments H1 to H33, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 9 CpG methylation sites.
H35. The method of any one of embodiments H1 to H34, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 12 CpG methylation sites.
H36. The method of any one of embodiments H1 to H35, wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site of (iii) is about 40 to about 100 base pairs.
H37. The method of any one of embodiments H1 to H36, wherein the feature of (a)(iv) is at least 10 restriction endonuclease recognition site per 1000 base pairs
H38. The method of any one of embodiments H1 to H37, wherein the feature of (a)(iv) is at least 20 restriction endonuclease recognition sites per 1000 bp.
H39. The method of any one of embodiments H1 to H38, wherein the feature of (a)(iv) is at least 30 restriction endonuclease recognition sites per 1000 bp.
H40. The method of any one of embodiments H1 to H39, wherein the target polynucleotide comprises a length of about 500 nucleotides to about 30 nucleotides.
H41. The method of any one of embodiments H1 to H40, wherein the target polynucleotide comprises a length of about 360 nucleotides to about 40 nucleotides.
H42. The method of any one of embodiments H1 to H41, wherein the target polynucleotide comprises a length of about 180 nucleotides to about 40 nucleotides.
H43. The method of any one of embodiments H1 to H42, wherein the target polynucleotide is single stranded.
H44. The method of any one of embodiments H1 to H42, wherein the target polynucleotide is double stranded.
H45. The method of any one of embodiments H1 to H44, wherein the target polynucleotide is a circulating cell free nucleic acid.
H46. The method of any one of embodiments H1 to H45, wherein the circulating cell free nucleic acid comprises a length of about 500 nucleotides to about 30 nucleotides.
H47. The method of any one of embodiments H1 to H46, wherein the feature of (a)(v) is 65% or more in the minority species.
H48. The method of any one of embodiments H1 to H47, wherein the feature of (a)(v) is 70% or more in the minority species.
H49. The method of any one of embodiments H1 to H48, wherein the feature of (a)(v) is 75% or more in the minority species.
H50. The method of any one of embodiments H1 to H49, wherein the feature of (a)(v) is 80% or more in the minority species.
H51. The method of any one of embodiments H1 to H50, wherein the feature of (a)(vi) is 35% or less in the majority nucleic acid species.
H52. The method of any one of embodiments H1 to H51, wherein the feature of (a)(vi) is 30% or less in the majority nucleic acid species.
H53. The method of any one of embodiments H1 to H52, wherein the feature of (a)(vi) is 20% or less in the majority nucleic acid species.
H54. The method of any one of embodiments H1 to H53, wherein the feature of (a)(vi) is 10% or less in the majority nucleic acid species.
H55. The method of any one of embodiments H1 to H54, wherein the feature of (a)(vii) is a difference in methylation status of 7.5% or more.
H56. The method of any one of embodiments H1 to H55, wherein the feature of (a)(vii) is a difference in methylation status of 10% or more.
H57. The method of any one of embodiments H1 to H56, wherein the feature of (a)(vii) is a difference in methylation status of 20% or more.
H58. The method of any one of embodiments H1 to H57, wherein the feature of (a)(vii) is a difference in methylation status of 40% or more.
H59. The method of any one of embodiments H5 to H58, wherein the target polynucleotides of the sample are digested, prior to (b), with two or more methylation sensitive restriction endonucleases, wherein each of the two or more methylation sensitive restriction endonucleases recognize a different restriction endonuclease recognition sequence.
H60. The method of any one of embodiments H1 to H59, wherein the minority nucleic acid species is fetal nucleic acid.
H61. The method of any one of embodiments H1 to H60, wherein the majority nucleic acid species is maternal nucleic acid.
I1. A method for preparing a collection of amplification primers, comprising:
(a) selecting one or more genomic loci wherein each locus comprises three or more features selected from:
(b) preparing a plurality of oligonucleotide primer pairs, wherein each primer of each primer pair hybridizes to a portion of a strand of the locus selected in (a) for which the primer pair is specific, whereby a collection of amplification primers is prepared.
I1.1. The method of embodiment I1, wherein each of the primers of each of the primer pairs is specific for a target polynucleotide located in one or more of the loci selected in (a).
I1.2. The method of embodiment I1.1, wherein each of the primer pairs in configured for amplifying the target polynucleotide located in one or more of the loci selected in (a) for which the primer pair is specific.
I1.3. The method of embodiment I1.1 or I1.2, wherein each of the primers of the primer pair can hybridize to a portion of the target polynucleotide for which the primer is specific.
I1.4. The method of any one of embodiments I1.1 to I1.3, wherein each of the loci selected in (a) comprise one or more target polynucleotides.
I2. The method of any one of embodiments I1.1 to I1.4, wherein each of the one or more target nucleic polynucleotides comprises at least one of the restriction endonuclease recognition sites in (a)(iv), wherein each of the primer pairs flank at least one of the restriction endonuclease recognition sites in (a)(iv).
I3. The method of any one of embodiments I1.4 or I2, wherein each locus comprises at least two target polynucleotides.
I4. The method of any one or embodiments I1 to I3, wherein the feature of (a)(i) is 2000 contiguous nucleotides, or less.
I5. The method of embodiment I4, wherein the feature of (a)(i) is 1000 contiguous nucleotides, or less.
I6. The method of embodiment I4, wherein the feature of (a)(i) is 750 contiguous nucleotides, or less.
I7. The method of embodiment I4, wherein the feature of (a)(i) is 500 contiguous nucleotides, or less.
I8. The method of embodiment I4, wherein the feature of (a)(i) is 250 contiguous nucleotides, or less.
I9. The method of any one of embodiments I1 to I8, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 9 CpG methylation sites.
I10. The method of embodiment I9, wherein the at least 5 CpG methylation sites of (a)(ii) are at least 12 CpG methylation sites.
I11. The method of any one of embodiments I1 to I10, wherein the average, mean, median or absolute distance between each restriction endonuclease recognition site of (iii) is about 40 to about 100 base pairs.
I12. The method of any one of embodiments I1 to I11, wherein the feature of (a)(iv) is at least 10 restriction endonuclease recognition sites per 1000 base pairs
I13. The method of embodiment I12, wherein the feature of (a)(iv) is at least 20 restriction endonuclease recognition sites per 1000 bp.
I14. The method of embodiment I12, wherein the feature of (a)(iv) is at least 30 restriction endonuclease recognition sites per 1000 bp.
I14.1. The method of any one of embodiments I1 to I14, wherein genomic loci having features (ii), (iii) and (iv) are selected in (a).
I14.2. The method of any one of embodiments I1 to I14, wherein genomic loci having features (ii), (iii) and (vii) are selected in (a).
I14.3. The method of any one of embodiments I1 to I14, wherein genomic loci having features (ii), (iv) and (vii) are selected in (a).
I14.4. The method of any one of embodiments I1 to I14, wherein genomic loci having features (iii), (iv) and (vii) are selected in (a).
I14.5. The method of any one of embodiments I14.1 to I14.4, wherein genomic loci having feature (i) is selected in (a).
I14.6. The method of any one of embodiments I14.1 to I14.5, wherein genomic loci having feature (v) is selected in (a).
I14.7. The method of any one of embodiments I14.1 to I14.6, wherein genomic loci having feature (vi) is selected in (a).
I15. The method of any one of embodiments I1 to I14.7, wherein at least one of the amplification primers of each of the primer pairs comprises a non-native element.
I16. The method of any one of embodiments I1 to I15, wherein each of the amplification primers comprises a non-native element.
I17. The method of embodiment I15 or I16, wherein the non-native element comprises a heterologous nucleotide sequence.
I18. The method of embodiment I15 or I16, wherein the non-native element comprises an identifier.
I19. The method of embodiment I18, wherein the identifier comprises a label
I20. The method of any one of embodiments I16 to I19, wherein the non-native element comprises a binding agent.
I21. The method of embodiment I20, wherein the binding agent comprises a member of a binding pair.
I22. The method of any one of embodiments I15 to I21, wherein the non-native element comprises a non-native nucleotide.
I23. The method of embodiment I22, wherein the non-native nucleotide comprises a chemical modification.
I24. The method of any one of embodiments I1 to I23, wherein both of the amplification primers of each of the primer pairs comprises a hybridization sequence that is complimentary to a portion of the target sequence which the primer pair is configured to amplify.
I25. The method of embodiment I24, wherein the target sequence, which the primer pair is configured to amplify, is longer than the combined length of the hybridization sequences of the target specific primer pair.
I26. The method of embodiment I24 or I25, wherein each of the amplification primers of each of the primer pairs comprises a sequence tag.
I27. The method of embodiment I24 or I25, wherein each of the amplification primers of each of the primer pairs comprises a different hybridization sequence.
I28. The method of any one of embodiments I1 to I27, wherein the target polynucleotide comprises a length of about 500 nucleotides to about 30 nucleotides.
I29. The method of embodiment I28, wherein the target polynucleotide comprises a length of about 360 nucleotides to about 40 nucleotides.
I30. The method of embodiment I28, wherein the target polynucleotide comprises a length of about 180 nucleotides to about 40 nucleotides.
I31. The method of any one of embodiments I1 to I30, wherein the target polynucleotide is single stranded.
I32. The method of any one of embodiments I1 to I31, wherein the target polynucleotide is double stranded.
I33. The method of any one of embodiments I1 to I32, wherein the target polynucleotide is a circulating cell free nucleic acid.
I34. The method of I33, wherein the circulating cell free nucleic acid comprises a length of about 500 nucleotides to about 30 nucleotides.
I35. The method of any one of embodiments I1 to I34, wherein the minority nucleic acid species and the majority nucleic acid species comprise one or more target polynucleotides.
I35.1. The method of any one of embodiments I1 to I35, comprising contacting target polynucleotides with the collection of amplification primers under amplification conditions, thereby generating amplicons.
I36. The method of any one of embodiments I1 to I35.1, wherein the process comprises:
(a) digesting the target polynucleotides of a first sample and a second sample with the one or more methylation sensitive restriction endonucleases that specifically digest the target polynucleotides at the at least one restriction endonuclease recognition site when the at least one restriction endonuclease recognition site is unmethylated, wherein each of the samples comprise one or more of the selected loci;
(b) contacting each of the samples with the collection of amplification primers under amplification conditions, thereby providing target specific amplicons of undigested target polynucleotides; and
(c) analyzing the target specific amplicons from each sample, wherein one or more differentially methylated loci are identified according to the analyzing.
I37. The method of embodiment I36, wherein the analyzing comprises determining an amount of the target specific amplicons from each sample.
I38. The method of embodiment I37, wherein the amount of target specific amplicons of the first sample is significantly different from the amount of target specific amplicons of the second sample.
I39. The method of any one of embodiments I37 to I38, wherein the first sample and the second sample are from different sources.
I40. The method of any one of embodiments I36 to I39, wherein the first sample and/or the second sample comprise circulating cell free nucleic acid.
I41. The method of any one of embodiments I36 to I40, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the first sample.
I42. The method of any one of embodiment I36 to I41, wherein the analyzing comprises determining a methylation status of the one or more selected loci in the second sample.
I43. The method of any one of embodiments I36 to I42, wherein the first sample comprises the minority nucleic acid species.
I44. The method of any one of embodiments I36 to I43, wherein the second sample comprises the majority nucleic acid species.
I45. The method of any one of embodiments I36 to I44, wherein the second sample does not include the minority nucleic acid species.
I46. The method of any one of embodiments I36 to I45, wherein the minority nucleic acid species is partially or entirely removed from the second sample.
I47. The method of any one of embodiments I1 to I46, wherein the minority nucleic acid species is fetal nucleic acid.
I48. The method of any one of embodiments I36 to I47, wherein the first sample is enriched for the minority nucleic acid species.
I49. The method of any one of embodiments I1 to I48, wherein the majority nucleic acid species is maternal nucleic acid.
I50. The method of any one of embodiments I1 to I49, wherein the feature of (a)(vi) is 65% or more in the minority species.
I51. The method of any one of embodiments I1 to I50, wherein the feature of (a)(vi) is 70% or more in the minority species.
I52. The method of any one of embodiments I1 to I51, wherein the feature of (a)(vi) is 75% or more in the minority species.
I53. The method of any one of embodiments I1 to I52, wherein the feature of (a)(vi) is 80% or more in the minority species.
I54. The method of any one of embodiments I1 to I53, wherein the feature of (a)(vii) is 40% or less in the majority nucleic acid species.
I55. The method of any one of embodiments I1 to I54, wherein the feature of (a)(vii) is 30% or less in the majority nucleic acid species.
I56. The method of any one of embodiments I1 to I55, wherein the feature of (a)(vii) is 20% or less in the majority nucleic acid species.
I57. The method of any one of embodiments I1 to I56, wherein the feature of (a)(vii) is 10% or less in the majority nucleic acid species.
I58. The method of any one of embodiments I1 to I57, wherein the feature of (a)(viii) is a difference in methylation status of 7.5% or more.
I59. The method of any one of embodiments I1 to I58, wherein the feature of (a)(viii) is a difference in methylation status of 10% or more.
I60. The method of any one of embodiments I1 to I59, wherein the feature of (a)(viii) is a difference in methylation status of 20% or more.
I61. The method of any one of embodiments I1 to I60, wherein the feature of (a)(viii) is a difference in methylation status of 40% or more.
I62. The method of any one of embodiments I36 to I61, wherein the methylation status of the one or more selected loci in the first sample is 60% or more and the methylation status of the one or more loci in the second sample is 40% or less.
I63. The method of any one of embodiments I36 to I62, wherein the one or more methylation sensitive restriction endonucleases comprises two or more methylation sensitive restriction endonucleases.
I64. The method of any one of embodiments I36 to I63, wherein the one or more methylation sensitive restriction endonucleases do not digest nucleic acid when the at least one restriction endonuclease recognition site is methylated.
I65. The method of any one of embodiments I36 to I64, wherein the differentially methylated locus identified in I36(c) is hypermethylated in the first sample.
I66. The method of any one of embodiments I36 to I65, wherein the differentially methylated locus identified in I36(c) is hypomethylated in the second sample.
I67. The method of any one of embodiments I36 to I66, wherein the analyzing comprises analyzing target polynucleotides that are not cleaved by the one or more methylation sensitive restriction endonucleases.
The entirety of each patent, patent application, publication and document referenced herein hereby is incorporated by reference. Citation of the above patents, patent applications, publications and documents is not an admission that any of the foregoing is pertinent prior art, nor does it constitute any admission as to the contents or date of these publications or documents.
Modifications may be made to the foregoing without departing from the basic aspects of the technology. Although the technology has been described in substantial detail with reference to one or more specific embodiments, those of ordinary skill in the art will recognize that changes may be made to the embodiments specifically disclosed in this application, yet these modifications and improvements are within the scope and spirit of the technology.
The technology illustratively described herein suitably may be practiced in the absence of any element(s) not specifically disclosed herein. Thus, for example, in each instance herein any of the terms “comprising,” “consisting essentially of,” and “consisting of” may be replaced with either of the other two terms. The terms and expressions which have been employed are used as terms of description and not of limitation, and use of such terms and expressions do not exclude any equivalents of the features shown and described or portions thereof, and various modifications are possible within the scope of the technology claimed. The term “a” or “an” can refer to one of or a plurality of the elements it modifies (e.g., “a reagent” can mean one or more reagents) unless it is contextually clear either one of the elements or more than one of the elements is described. The term “about” as used herein refers to a value within 10% of the underlying parameter (i.e., plus or minus 10%), and use of the term “about” at the beginning of a string of values modifies each of the values (i.e., “about 1, 2 and 3” refers to about 1, about 2 and about 3). For example, a weight of “about 100 grams” can include weights between 90 grams and 110 grams. Further, when a listing of values is described herein (e.g., about 50%, 60%, 70%, 80%, 85% or 86%) the listing includes all intermediate and fractional values thereof (e.g., 54%, 85.4%). Thus, it should be understood that although the present technology has been specifically disclosed by representative embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and such modifications and variations are considered within the scope of this technology. —Certain embodiments of the technology are set forth in the claim(s) that follow(s).
This patent application is a national stage of international patent application number PCT/US2014/025132, filed Mar. 13, 2014, entitled METHODS AND PROCESSES FOR NON-INVASIVE ASSESSMENT OF GENETIC VARIATIONS, naming Taylor Jensen and Mathias Ehrich as inventors, and designated by Attorney Docket No. SEQ-6063-PC, which claims the benefit of U.S. Provisional Patent Application No. 61/780,162 filed on Mar. 13, 2013, entitled METHODS AND PROCESSES FOR NON-INVASIVE ASSESSMENT OF GENETIC VARIATIONS, naming Taylor Jensen and Mathias Ehrich as inventors, and designated by Attorney Docket No. SEQ-6063-PV. The entire content of the foregoing applications are incorporated herein by reference, including all text, tables and drawings.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/025132 | 3/13/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61780162 | Mar 2013 | US |
