Patent Application
20230140653
The invention is in the field of medicine.
The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Oct. 17, 2018, is named 103182-1107145_(000300PC)_SL.txt and is 159,304 bytes in size.
Understanding the timing and program of human development has been a topic of interest for thousands of years. In antiquity, the ancient Greeks had surprisingly detailed knowledge of various details of stages of fetal development, and they developed mathematical theories to try to account for the timing of important landmarks during development including delivery of the baby (Hanson 1995; Hanson 1987; Parker 1999). In the modern era, biologists have put together a detailed cellular and molecular portrait of both fetal and placental development. However, these results relate to pregnancy in general and have not led to molecular tests, which might enable monitoring of development and prediction of delivery for a given set of parents. The most widely used molecular metrics of development are determining the levels of human chorionic gonadotropin (HCG) and alpha-fetoprotein (AFP), which can be used to detect conception and fetal complications, respectively; however, neither molecule either individually or in conjunction has been found to precisely establish gestational age (Dugoff et al. 2005; Yefet et al. 2017).
Due to the lack of a useful molecular test, most clinicians use either ultrasound imaging or the patient's estimate of last menstruation period (LMP) in order to establish gestational age and a rough estimate for delivery date. However, these methods are neither particularly precise nor useful for predicting preterm delivery, which is a substantial source of mortality and cost in prenatal healthcare. Moreover, inaccurate dating can misguide the assessment of fetal development even for normal term pregnancies, which has been shown to ultimately lead to unnecessary induction of labor and cesarean sections, extended post-natal care, and increased expendable medical expenses (Bennett et al. 2004; Whitworth et al. 2015).
It would be useful both to develop a more precise approach to measure the gestational age of the fetus at various points in pregnancy, and more generally to monitor fetal and placental development for signs of abnormality or preterm delivery. Approximately 15 million neonates are born preterm every year worldwide (Blencowe et al. 2013). As the leading cause of neonatal death and the second cause of childhood death under the age of 5 years (Liu et al. 2012), premature delivery is estimated to annually cost the United States upward of $26.2 billion (Institute of Medicine (US) Committee on Understanding Premature Birth and Assuring Healthy Outcomes 2007). The complications continue later into life as preterm birth is a leading cause of life years lost to ill health, disability, or early death (Murray et al. 2012). Two-thirds of preterm delivery occur spontaneously, and the only predictors are a history of preterm birth, multiple gestations, and vaginal bleeding (Institute of Medicine (US) Committee on Understanding Premature Birth and Assuring Healthy Outcomes 2007). Efforts to find a genetic cause have had only limited success (Ward et al. 2005; York et al. 2009) and therefore most effort is focused on phenotypic and environmental causes (Muglia and Katz 2010).
Gestational age or time to delivery may be determined by (a) generating an expression profile using cfRNA or protein from a maternal sample, and (b) comparing the expression profile with one or more reference profiles that reflect an expression profile characteristic of a defined gestational age.
Risk of preterm delivery may be determined by (a) generating an expression profile using cfRNA (or protein) from a maternal sample, and (b) determining whether the expression profile is or is not characteristic of a population with a history of preterm delivery and/or whether the expression profile is or is not characteristic of a population with a history of full-term delivery.
In a first aspect, the disclosure provides a method of estimating gestational age of a fetus comprising, analyzing a maternal sample to determine an expression profile from a panel comprising one or more placental genes.
In some embodiments, the method includes an expression profile comprising three or more placental genes. In some embodiments, the method includes an expression profile from a panel comprising only of placental genes.
In some embodiments, the method further includes the expression level of each of the placental genes changing during the course of pregnancy. In some embodiments, the method includes the expression level of at least one placental gene is that is higher in the first trimester compared to the third trimester. In some versions, the expression level of all of the placental genes are lower in the first trimester compared to the third trimester. In some embodiments, the method includes the expression level of at least one placental gene that is lower in the first trimester compared to the third trimester.
In some embodiments, the method includes the placental genes selected from genes in TABLE 1. In some embodiments, the method includes the placental genes selected from CGA, CAPN6, CGB, ALPP, CSHL1, PLAC4, PSG7, PAPPA, and LGALS14.
In some embodiments, the method includes determining the expression profiles for three to nine placental genes. In some embodiments, the method includes determining the expression profile by measuring cell-free RNAs (cfRNAs) in the maternal sample. In some embodiments, the method includes determining the expression profile by measuring placental proteins in the maternal sample.
In some embodiments, the method includes a maternal sample from blood, blood plasma, blood serum, or urine. In some embodiments, the method includes a maternal sample obtained from the mother during the third trimester of pregnancy. In some embodiments, the method includes a maternal sample obtained from the mother during the second trimester of pregnancy.
In some embodiments, the method includes the steps: comparing the expression profile with a plurality of reference profiles, wherein each reference profile is characteristic of a defined gestational age, determining which of the plurality of reference profiles corresponds to the expression profile based on the comparing, and deducing the estimated gestational age of the fetus at the time the maternal sample was obtained based on the defined gestational age of the corresponding reference profile.
In a second aspect, the disclosure provides a method for estimating gestational age of a fetus including the steps: (a) obtaining a maternal expression profile for a sample, comprising expression levels for a panel of genes according to any of the embodiments of the first aspect, and (b) comparing expression levels to reference expression levels for the panel of genes, wherein the reference expression levels are obtained from a full-term delivery population, to determine whether the maternal expression profile is similar to, or is different from, the reference expression levels within a threshold.
In some embodiments, the method includes one or more reference expression levels for the full-term population are established using a machine learning technique. In some versions, the method further includes obtaining a plurality of training samples, each labeled as preterm or full-term, obtaining one or more measured expression levels for the panel of genes for each of the plurality of training samples, and iteratively adjusting the one or more reference expression levels using the machine learning technique to increase a number of the training samples that are classified correctly as a result of comparing the one or more measured expression levels to the one or more reference expression levels.
In some embodiments, the method further includes the steps: comparing the expression levels to other reference expression levels for the panel of genes, wherein the other reference expression levels are obtained from a preterm delivery population, to determine whether the maternal expression profile is similar to, or is different from, the other reference expression levels within a threshold.
In a third aspect, the disclosure provides a method for estimating gestational age of a fetus including the steps of: (i) determining a maternal expression profile of a panel comprising at least one placental RNA, and (ii) comparing the maternal expression profile to a reference profile, wherein the comparison of the maternal expression profile to the reference profile allows for the for estimation of gestational age. In some embodiments, the gestational age is known for the reference profile. In some embodiments, the comparison of the maternal expression profile to the reference profile is performed by comparing the maternal expression profile to a gestational function that provides a gestational age based on an input of one or more expression levels, wherein the gestational function is determined by fitting a model to a plurality of calibration samples having measured expression levels and of which a gestational age is known. In some versions, the method uses a regression model.
In some embodiments, the method includes a profile panel described in any of the embodiments of the first aspect. In some embodiments, the method is carried out by a computer.
In some embodiments, the method includes determining a first gestational age according to the method of the first or second aspect using a first maternal sample and determining a second gestational age according to the method of the first or second aspect using a second maternal sample obtained later in pregnancy.
The method of the first aspect, wherein the expression levels of individual placental genes are determined by qPCR or massively parallel sequencing.
The method of the first aspect, wherein the expression levels of individual placental genes are determined by mass spectrometry or using an antibody array.
The method of the first, second, or third aspect, wherein the expression of at least one additional gene is determined, and the additional gene is not a placental gene.
In a fourth aspect, the disclosure provides a composition comprising, primers for multiplex amplification of at least three and no more than fifty placental genes selected TABLE 1.
In a fifth aspect, the disclosure provides a kit comprising, primers suitable for multiplex amplification of at least three, and no more than fifty, placental genes selected from TABLE 1.
In a sixth aspect, the disclosure provides an antibody array for detecting at least three and no more than one hundred placental proteins isolated from maternal blood or urine.
In a seventh aspect, the disclosure provides a method for assessing risk of preterm delivery by a pregnant woman comprising, analyzing a maternal sample to determine an expression profile from a panel comprising one or more genes selected from TABLE 2.
In some embodiments, the method includes a panel comprising three or more genes from TABLE 2. In some embodiments, the method includes genes having higher expression levels in a preterm population than in a term population. In some embodiments, the method includes genes selected from: CLCN3, DAPP1, POLE2, PPBP, LYPLAL1, MAP3K7CL, MOB1B, RAB27B, RGS18, and TBC1D15, or from: CLCN3, DAPP1, PPBP, MAP3K7CL, MOB1B, RAB27B, and RGS18. In some embodiments, the method includes a panel comprising three genes selected from any combination of three from: CLCN3, DAPP1, POLE2, PPBP, LYPLAL1, MAP3K7CL, MOB1B, RAB27B, RGS18, and TBC1D15 (ten transcript panel), or from: CLCN3, DAPP1, PPBP, MAP3K7CL, MOB1B, RAB27B, and RGS18 (seven transcript panel).
In some embodiments, the method includes the expression profiles in which a panel of three to ten genes are determined. In some embodiments, the method includes the expression profile in which a panel comprising exactly three genes are determined.
In some versions the method includes, determining the expression profile by measuring cell-free RNAs (cfRNAs) in the maternal sample. In some embodiments, the method includes determining the expression profile by measuring proteins in the maternal sample.
In some embodiments, the method includes a maternal sample from blood, blood plasma, blood serum, or urine. In some embodiments, the method includes a maternal sample obtained more than 28 days prior to preterm delivery. In some embodiments, the method includes a maternal sample obtained more than 45 days prior to preterm delivery. In some embodiments, the method includes a maternal sample obtained after the second month and prior to the eighth month of pregnancy. In some embodiments, the method includes a maternal sample obtained during the second trimester of pregnancy.
In some versions, a maternal sample is obtained during the third trimester of pregnancy.
In some embodiments, the method of the seventh aspect includes, a maternal sample obtained at a specified week of pregnancy, comprising the steps: comparing the expression profile to a time matched reference profile, wherein the time matched reference profile is characteristic of a normal term pregnancy at the specified week of pregnancy, and identifying the pregnant woman as an elevated risk for preterm delivery if the expression profile differs significantly from the time matched reference profile within a threshold.
In some embodiments, the method of the seventh aspect includes a maternal sample obtained at a specified week of pregnancy, comprising the steps: comparing the expression profile to a time matched reference profile, wherein the time matched reference profile is characteristic of a preterm pregnancy, and identifying the pregnant woman as an elevated risk for preterm delivery if the expression profile is significantly similar to the time matched reference profile within a threshold.
In an eighth aspect, the disclosure provides a method for assessing risk of preterm delivery of a pregnant woman comprising the steps: (a) obtaining a maternal expression profile for a sample, comprising expression levels for a panel of genes according to the seventh aspect of the disclosure, and (b) comparing the expression levels to reference expression levels for the panel of genes, wherein the reference expression levels are obtained from a preterm delivery population, a full-term delivery population, or both populations, to determine whether the maternal expression profile is similar to, or is different from, the reference expression levels within a threshold.
In some embodiments, the method one or more reference levels are established using a machine learning technique.
In some embodiments, the methods of the seventh or eighth aspect are carried out by a computer.
In a ninth aspect, the disclosure provides a method including carrying out the steps of the claims provided in the seventh or eighth aspect with two or more maternal samples obtained at different times during the course of a pregnancy.
The method of the seventh aspect, wherein the expression levels of individual genes are determined by qPCR or massively parallel sequencing.
The method of the seventh aspect, wherein the expression levels of individual genes are determined by mass spectrometry or an antibody array.
In a tenth aspect, the disclosure provides a composition comprising primers for multiplex amplification of at least three genes selected from TABLE 2 and no more than one hundred different genes.
In an eleventh aspect, the disclosure provides a kit comprising primers for multiplex amplification of at least three genes selected from TABLE 2 and no more than one hundred different genes.
In a twelfth aspect, the disclosure provides a method of estimating time to delivery comprising analyzing a maternal sample to determine an expression profile from a panel comprising one or more placental genes.
In some embodiments, the method includes an expression profile from a panel comprising three or more placental genes.
In some embodiments, the method includes an expression profile from a panel comprised only of placental genes.
In some embodiments, the method includes the expression level of each of the placental genes changes during the course of pregnancy. In some embodiments, the method includes the expression level of at least one placental gene that is higher in the first trimester compared to the third trimester. In some embodiments, the method includes the expression level of at least one placental gene that is lower in the first trimester compared to the third trimester. In some versions, the expression levels of all of the placental genes are lower in the first trimester compared to the third trimester.
In some embodiments, the method includes determining the expression profile by measuring cell-free RNAs (cfRNAs) in the maternal sample. In some embodiments, the method includes determining the expression profile by measuring placental proteins in the maternal sample.
In some embodiments, the method includes a maternal sample from blood, blood plasma, blood serum, or urine.
In some embodiments, the method includes a maternal sample obtained from the mother during the third trimester of pregnancy.
In some embodiments, the method includes a maternal sample obtained from the mother during the second trimester of pregnancy.
In some embodiments, the method includes the steps: comparing the expression profile with a plurality of reference profiles, wherein each reference profile is characteristic of a time to delivery, determining which of the plurality of reference profiles corresponds to the expression profile, and deducing the estimated time to delivery at the time the maternal sample was obtained based on the time to delivery of the corresponding reference profile.
In a thirteenth aspect, the disclosure provides a method for estimating time to delivery including the steps: (a) obtaining a maternal expression profile for a sample, comprising expression levels for a panel of genes according to any one of the embodiments of the ninth and seventh aspect, and (b) comparing the expression levels to reference expression levels for the panel of genes, wherein the reference expression levels are obtained from a full-term delivery population to determine whether the maternal expression profile is similar to, or is different from, the reference expressions levels within a threshold.
In some embodiments, the method includes one or more reference levels for the full-term population are established using a machine learning technique. In some embodiments, the method is carried out by a computer.
In some embodiments, the method includes determining a first time to delivery according to the method of the twelfth or thirteenth aspect using a first maternal sample and determining a second time to delivery according to the method of the twelfth or thirteenth aspect using a second maternal sample obtained later in pregnancy.
The method of the twelfth aspect, wherein the expression levels of individual placental genes are determined by qPCR or massively parallel sequencing.
The method of the twelfth aspect, wherein the expression levels of individual placental genes are determined by mass spectrometry or an antibody array.
The method of the twelfth or thirteenth aspect, wherein expression of at least one additional gene is determined, and the additional gene is not a placental gene.
In a fourteenth aspect, the disclosure provides a composition comprising, primers for multiplex amplification of at least three placental genes selected from TABLE 1 and no more than one hundred different genes.
In a fifteenth aspect, the disclosure provides a kit comprising, primers for the multiplex amplification of at least three genes selected from TABLE 1 and no more than one hundred placental genes.
In a sixteenth aspect, the disclosure provides an antibody array for detecting at least three and no more than one hundred placental proteins isolated from maternal blood or urine.
We have discovered a panel of genetic biomarkers for non-invasively predicting gestational age or time to delivery of a fetus in a pregnant woman. We have also discovered an orthogonal set of genetic biomarkers for non-invasively predicting whether a woman is at risk for preterm delivery of a fetus. The discovery that a set of genetic markers for predicting gestational age or time to delivery of a fetus is significant, in part, because of the potential advantages of replacing ultrasounds as the gold standard for predicting gestational age and thus avoiding substantial health care expenses associated with ultrasounds and sonographers. Additionally, the discovery that a set of genetic markers for predicting whether a woman is at risk for preterm delivery is also significant, in part, because of the potential advantages of prophylactically treating women at risk from preterm delivery and thus negating substantial health care expenses associated with neonatal intensive care units (NICU's).
We performed a high time-resolution study of normal human development by measuring cfRNA in blood from pregnant women longitudinally during each week of pregnancy. Analysis of tissue-specific transcripts in these samples enabled us to follow fetal and placental development with high resolution and sensitivity, and also to detect gene-specific response of the maternal immune system to pregnancy. The data from this study establish a “clock” for normal human development and enable a direct molecular approach to establish expected delivery date with comparable accuracy to ultrasound at a fraction of the cost. We also identified an orthogonal gene set that accurately discriminates women at risk of preterm delivery up to two months in advance of labor, forming the basis of a screening or diagnostic test for risk of prematurity.
As used herein, the terms “cell free RNA” or “cfRNA” refer to RNA, especially mRNA, expressed by cells of the mother, fetus and/or placenta and recoverable from the non-cellular fraction of maternal blood, and includes fragments of full-length RNA transcripts. In some embodiments “cfRNA” does not include rRNA. In some embodiments “cfRNA” does not include miRNA. In some embodiments “cfRNA” refers to mRNA. Cf RNA can also be recovered from maternal urine.
As used herein, the terms “placental gene,” “placental gene product,” “placental cfRNA,” or “placental protein” refer to a gene or corresponding gene product that is expressed in the placenta but not expressed (or expressed at significantly lower levels) by maternal or fetal tissues. Publicly available resources exist to identify placental genes including databases such as Tissue-Specific Gene Expression and Regulation (TiGER) which identifies 377 RefSeq (NCBI Reference Sequence Database) genes as being preferentially expressed in the placenta (http://bioinfo.wilmer.jhu.edu/tiger). Other databases such as Expression Atlas (https://www.ebi.ac.uk/gxa/home) can also be used to identify placental genes. Placental gene products include mRNA and protein.
As used herein, the term “expression profile,” refers to the level of expression of one or a plurality of gene products obtained from a maternal sample. The gene products may be cfRNAs or proteins. For gene products recovered from maternal plasma, expression levels may be expressed as the number of transcripts of a specified RNA per mL maternal plasma, mass of a specified polypeptide per mL maternal plasma, transcript count calculated from RNA-Seq, or any other suitable units. Analogous units may be used for gene products obtained from other maternal samples, such as urine. Expression of gene products may be determined using any suitable method (e.g., as described below). Measured values are typically normalized to account for variations in the quantity and quality of the sample, reverse-transcription efficiency, and the like. When an expression profile reflects expression from multiple different gene products (e.g., different cfRNA transcripts) the gene products may be given different weights when generating or comparing expression profiles or reference profiles. For example, when comparing an expression profile comprising cfRNA 1 and cfRNA 2 in a sample from a pregnant woman with a reference profile (discussed below), a 2-fold difference in values for cfRNA 1 may be given more weight than a 2-fold difference in values for cfRNA 2 in determining a degree of similarity or difference between the expression profile and the reference profile. An expression profile from a maternal (e.g., patient) sample is sometimes referred to as a “maternal expression profile” and a maternal expression profile from a sample collected at a specified time may be referred to as a “[time] maternal expression profile,” e.g., a “24 week maternal expression profile.”
As used herein, a “reference profile” is an expression profile derived from a reference population. For illustration, examples of reference populations are pregnant women, pregnant women who delivered at term, or pregnant women who delivered prematurely. In some embodiments the reference population is a subpopulation of pregnant women characterized by maternal age (e.g., women 20-25 years old who delivered at term), race or ethnicity (e.g., African-American women who delivered at term), and the like. A reference profile is generated by combining expression profiles of a statistically significant number of women in the population and, for a specified gene product, may reflect the mean transcript level in the population, the median transcript level in the population, or may be determined using any of a number of methods known in the fields of epidemiology and medicine. A reference population will typically comprise at least 10 subjects (e.g., 10-200 subjects), sometimes 50 or more subjects, and sometimes 1000 or more subjects.
As used herein, the term “profile panel” refers to the set of gene products measured in a particular assay. For example, in an assay for six (6) different cfRNAs (“RNAs A-F”), those six cfRNAs would be the profile panel. Likewise, in an assay for six (6) different proteins from maternal plasma or urine, those six proteins would be the profile panel. As another illustration, in an assay in which expression data are collected for transcripts of a large number of genes (e.g., the entire transcriptome, or a large number of placental gene transcripts) the subset used for estimating gestational age or time to delivery, or assessing risk of preterm delivery may be referred to as the profile panel. It will be recognized that measurements of RNAs or proteins not included in the panel may be used as controls, to normalize measurements within or across samples, or for similar uses. In some embodiments a profile panel may include a set of gene products that includes both cfRNAs and proteins. A profile panel is sometimes referred to as a “panel.”
As used herein, the terms “preterm pregnancy,” “preterm delivery,” “full-term pregnancy,” “full-term delivery,” and “normal term pregnancy” have their normal meanings. Full-term refers to delivery after the fetus reached a gestational age of 37 weeks and preterm refers to delivery prior to the fetus reaching a gestational age of 37 weeks. In some contexts preterm refers to delivery in the period from 16 weeks to 35 weeks gestational age or 24 weeks to 30 weeks gestational age. Preterm populations used in the studies discussed below (see Examples) delivered a fetus prior to 29 weeks gestational age in one case (Pennsylvania cohort) and 33 weeks gestational age in another (Alabama cohort). See
As used herein, “maternal sample” refers sample of a body fluid obtained from a pregnant woman. The body fluid is typically serum, plasma, or urine, and is usually serum. In some embodiments a sample of a different body fluid may be used, such as saliva, cerebrospinal fluid, pleural effusions, and the like. Maternal samples may be obtained at multiple different time points during pregnancy and stored (e.g., frozen) until assayed. It will be appreciated that the date of collection of a maternal sample is an integral property of the sample.
As used herein, “time to delivery” refers to the number of weeks from a specified time (present time, date of maternal sample collection) to the delivery date or predicted delivery date. Time to delivery is calculated as (gestational age at delivery) minus (gestational age at sample collection).
As used herein, the terms “protein” and “polypeptide” are used interchangeably. Reference to a protein obtained from a maternal sample does not necessarily imply that the protein is a full-length gene expression product. Portions, fragments, and cleavage products may be detected and identifed according to the invention.
The invention relates to discovery of a high resolution molecular clock for fetal development and the invention of methods to establish time to delivery, fetal gestational age, and risk of preterm delivery. In one aspect, methods and materials for estimating gestational age or time to delivery of a fetus using expression profiles of placental gene(s) are described. In another aspect, methods and materials for assessing risk of preterm delivery are described.
For illustration and not limitation, gestational age or time to delivery may be determined by (a) generating an expression profile using cfRNA (or protein) from a maternal sample and (b) comparing the expression profile with one or more reference profiles that reflect an expression profile characteristic of a defined gestational age. For illustration, the maternal expression profile is compared to 37 reference profiles (characteristic of 1 through 37 weeks of gestational age) and gestational age or time to delivery is estimated based on the relatedness of the maternal expression profile to one of the 37 reference profiles. For illustration and not limitation, risk of preterm delivery may be determined by (a) generating an expression profile using cfRNA (or protein) from a maternal sample and (b) determining whether the expression profile is or is not characteristic of a population with a history of preterm delivery and/or whether the expression profile is or is not characteristic of a population with a history of full-term delivery. In another approach, machine learning (e.g., random forest regression, support vector machines, elastic net, lasso) is used to predict gestational age, time to delivery, and risk of prematurity based on the maternal expression profile generated from a maternal sample.
A maternal sample (e.g., plasma or urine) may be collected and cfRNA may be isolated from the sample immediately or after storage. See Example 1 below. Art-known methods may be employed to guard the RNA fraction against degradation including, for example, use of special collection tubes (e.g. PAXgene RNA tubes from Preanalytix, Tempus Blood RNA tubes from Applied Biosystems) or additives (e.g. RNAlater from Ambion, RNAsin from Promega) that stabilize the RNA fraction.
Multiple maternal samples may be collected. For example, maternal samples can be collected each trimester, or monthly for a period during the course of pregnancy (e.g., months 3-8). When indicated, maternal samples may be collected more frequently. For example, gestational age or time to delivery may be monitored frequently (e.g., biweekly) as a method for monitoring fetal health.
As another example, a woman identified at 24 weeks as at risk of preterm delivery may elect biweekly assays to monitor risk. In cases in which intervention to avoid preterm delivery (e.g., progesterone supplementation) has been used, a maternal sample may be obtained after the initiation of the intervention to assess whether the intervention has changed the maternal expression profile. Remarkably, methods of the invention may be used to accurately discriminate women at risk of preterm delivery up to two months in advance of labor. See Example 6. In some embodiments of the invention a maternal sample is obtained more than 28 days prior to the preterm delivery. In some embodiments of the invention a maternal sample is obtained more than 45 days prior to the preterm delivery. In some embodiments a maternal sample is obtained after the second month and prior to the eighth month of pregnancy. In some embodiments a maternal sample is obtained during the second trimester of pregnancy In some embodiments a maternal sample is obtained during the third trimester of pregnancy. As discussed above, in many cases a maternal sample may be obtained and assayed more than once during the course of a pregnancy.
Cell-free RNA can be isolated from a maternal sample using techniques well known in the art. See Example 1 below. Isolation of cfRNA from blood or blood fractions is described in Qin et al., BMC Res. Notes., 26; 6:380 (2013) and Mersy et al., Clin. Chem., 61(12)1515-23 (2015), both of which are incorporated herein by reference. Kits for isolating cfRNA from blood are known and are commercially available (e.g., PaxGene Blood RNA kit (Qiagen, Catalog No. 762164). Kits for isolating cfRNA from plasma/serum are known and are commercially available (e.g., Plasma/Serum RNA Purification Kit from Norgen Biotek Corporation, Canada, Catalog No.: 56900 and Quick-cfRNA™ Serum & Plasma from Zymo Research, Catalog No.: R1059; NextPrep Magnazol cfRNA Isolation Kit (Bioo Scientific); Quick-cfRNA™ Serum & Plasma Kit (Zymo Research), and the QIAamp® Circulating Nucleic Acid Kit (Qiagen).
Isolation of cfRNA from urine has been described (see, e.g., Zhao et al., 2015, Int J. Cancer, 1; 136(11):2610-5, incorporated herein by reference, describing use of cfRNA for identification of biomarkers and monitoring disease status). Kits for isolating cfRNA from urine are known and are commercially available (e.g., Urine Cell Free Circulating RNA Purification Kit from Norgen Biotek Corporation, Canada, Catalog No.: 56900).
Quantification of specific transcripts from a cell free RNA sample can be accomplished in a variety of ways including, but not limited to, array-based methods, amplification-based methods (e.g., RT-qPCR), and high-throughput sequencing (RNA-Seq). The methods of the invention are not limited to a particular method of quantitation.
3.3.1 RT-qPCR Assays
RT-qPCR assays are described in Example 1, below. Briefly, RNA is transcribed into complementary DNA (cDNA) by reverse transcriptase from total RNA or messenger RNA (mRNA). Alternatively, cDNA is generated using template-specific primers specific for selected RNA transcripts (e.g., one of more of SEQ ID NOS:1-19). The cDNA is then used as the template for the qPCR reaction.
RT-qPCR can be performed in a one-step or a two-step assay. One-step assays combine reverse transcription and PCR in a single tube and buffer, using a reverse transcriptase along with a DNA polymerase. One-step RT-qPCR only utilizes sequence-specific primers. In two-step assays, the reverse transcription and PCR steps are performed in separate tubes, with different optimized buffers, reaction conditions, and priming strategies (such as random primers, oligo-(dT) or sequence specific primers in the reverse transcription followed by sequence specific primers in the qPCR step. As described above, it will be apparent that reference to RT-qPCR herein includes either a one or two step RT-qPCR assay.
RT-qPCR can be performed using various buffers and optimizations. See Example 1 below. Isolation of cfRNA from blood and subsequent analysis by RT-qPCR is known in the art (for example, see US Patent Publication No.: 20140199681, incorporated herein by reference). Kits for performing one step RT-qPCR are known and are commercially available (e.g., TaqPath™ 1-step RT-qPCR Master Mix, CG (Thermo Fisher Scientific, Catalog No. A15299). Kits for performing two step RT-qPCR are known and are commercially available (e.g., Maxima First Strand cDNA Synthesis Kit for RT-qPCR (Thermo Fisher Scientific, Catalog No. K1641).
3.3.2 RNA-Seq Assays
RNA-Seq (RNA-sequencing) assays also known as whole transcriptome shotgun sequencing uses next-generation sequencing (NGS) to reveal the presence and quantity of RNA in a sample at a given point in time (see, Zhong et al. Nat. Rev. Gen. 10 (1): 57-63 (2009), incorporated herein by reference). RNA-Seq assays are described in Example 1, below. RNA-Seq facilitates the ability to look at changes in gene expression over time or differences in gene expression in different groups or treatments (see, Maher et al. Nature. 458 (7234): 97-101 (2009), incorporated herein by reference).
The following sets forth an exemplary method to analyze cfRNAs isolated from a maternal body fluid sample. Briefly, cfRNAs are isolated from a maternal sample, for example using sequence specific primers, oligo(dT) or random primers to generate cDNA molecules. In one approach cDNA is generated using template-specific primers specific for selected RNA transcripts (e.g., corresponding to genes listed in TABLES 1 and 2; one of more of SEQ ID NOS:1-19). The cDNA molecules can be fragmented and optimized such that sequencing linkers are added to the 3′ and 5′ ends of the cDNA molecules to produce a sequencing library. Fragmentation is typically not needed for cfRNA. The optimized cDNAs are then sequenced using an NGS sequencing platform. Suitable kits for amplifying cDNA and analyzing sequencing products in accordance with the methods of the invention include, for example, the Ovation™ RNA-Seq System (NuGen). Other methods for preparing RNA-Seq libraries for use with a sequencing platform are known such as Podnar et al., 2014, “Next-Generation Sequencing RNA-Seq Library Construction” Curr Protoc Mol Biol. 2014 Apr. 14; 106:4.21.1-19. doi: 10.1002/0471142727.mb0421s106; Schuierer et al., 2017, “A comprehensive assessment of RNA-Seq protocols for degraded and low-quantity samples. BMC Genomics. 2017 Jun 5; 18(1):442. doi: 10.1186/s12864-017-3827-y; Hrdlickova R, 2017, RNA-Seq methods for transcriptome analysis, Wiley Interdiscip Rev RNA. 2017 January; 8(1). doi: 10.1002/wrna.1364), all of which are incorporated herein by reference.
Sequencing libraries suitable for use with RNA-Seq assays can include cDNAs derived from cfRNAs isolated from a maternal sample. It will also be apparent that the sequencing libraries can include cDNAs derived from other RNA species (e.g., miRNAs) that may have been collected during total RNA isolation rather than a cfRNA isolation procedure. Accordingly, either a partial or complete transcriptome analysis can be performed on the RNA content obtained from the maternal sample. In one embodiment, it is preferred that only cfRNAs obtained from the maternal sample are used as the input material for preparing cDNAs suitable for RNA-Seq.
The inventors have discovered that certain combinations of gene products are of particular use in practicing the invention. That is, certain combinations of gene products have been identified as sufficient or preferred for providing accurate estimates of gestational age, time to delivery or predicting likelihood of preterm delivery. For example, as described in Example 4, a subset of 9 placental genes provided more predictive power for estimating gestational age or time to delivery than a larger gene panel.
It will be appreciated that, although certain features of panels are discussed in this section, the invention is not limited to these particular described embodiments. It also will be understood that although this section describes panels by reference to cfRNA transcript expression, panels based on expression levels of circulating proteins encoded by the those gene subsets may also be used to determine gestational age or time to delivery and identify women at risk of preterm delivery. See Section 4, below.
In some approaches, multiple different profile panels are used during the course of a woman's pregnancy. For example, a first profile panel may be used in the second trimester and a different profile panel may be used in the third trimester.
3.4.1 Profile Panels for Determining Gestational Age or Time to Delivery
In one aspect, the invention provides a method for estimating gestational age or time to delivery of a fetus by analyzing a maternal sample to determine an expression profile of placental genes (e.g., cfRNA or protein encoded by a placental gene). Suitable panels may be selected based on the information provided in this disclosure. In one embodiment the panel includes one, at least 2, or at least 3 placental genes. In some embodiments, the profile panel can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 placental genes. In some embodiments, the profile panel can include exactly 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 placental genes. In some embodiments the profile panel includes fewer than 100 genes, e.g., fewer than 100 placental genes, sometimes fewer than 50 placental genes, sometimes fewer than 20 placental genes, sometimes fewer than 15 placental genes, sometimes fewer than 10 placental genes, and sometimes fewer than 5 placental genes.
In some embodiments the expression level of each of the placental genes in the profile panel changes during the course of pregnancy. See Examples below. Thus, in one embodiment, the expression level of at least one placental gene in the panel is higher in the first trimester compared to the third trimester. In some embodiments the expression levels of most or all placental genes in the panel are higher in the first trimester compared to the third trimester. In some embodiments, the expression level of at least one placental gene is lower in the first trimester compared to the third trimester. In some embodiments the expression levels of most or all placental genes in the panel are lower in the first trimester compared to the third trimester
In some embodiments at least one placental gene is selected from genes in TABLE 1. In some embodiments all of the placental genes in a profile panel are genes listed TABLE 1.
In some embodiments the expression profile includes at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9]. In some embodiments the expression profile includes 1, 2, 3, 4, 5, 6, 7, 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9]. In one approach the set of placental genes includes at least one gene other than CGA and CGB. In one approach, the profile panel comprises from three (3) to nine (9) cfRNAs selected from SEQ ID NOS:1-9.
In one embodiment gestational age is determined using a profile panel profile of 9 genes: CGA, CAPN6, CGB, ALPP, CSHL1, PLAC4, PSG7, PAPPA, and LGALS14. We trained several distinct models on subpopulations of women (i.e., nulliparous or multiparous women, women carrying male or female fetuses) to determine the importance of the 9 genes that compose the transcriptomic signature identified. Training 4 distinct models for women carrying male or female fetuses and nulliparous or multiparous women revealed that 2 of the 9 genes identified in the main text were sufficient to (CGA, CSHL1) or female (CGA, CAPN6) fetuses and multiparous (CGA, CSHL1) women. However, all 9 genes were necessary to optimally predict time until delivery for nulliparous women, highlighting the importance of the transcriptomic signature identified. In some embodiments of the invention the panel comprises CGA and CSHL1 or CGA and CAPN6.
The nine transcripts used to predict gestational age were weighted by the model in the following order of importance (from most to least): CGA, CAPN6, CGB, ALPP, CSHL1, PLAC4, PSG7, PAPPA, and LGALS14. Thus, in some embodiments the determined level of expression for individual genes are given different weights (or coefficients) when compared to expression in a reference profile. For example, when all 9, or a subset comprising fewer than 9 genes in this group (e.g., 2, 3, 4, 5, 6, 7 or 8) expression values for each gene are ranked CGA>CAPN6>CGB>ALPP>CSHL1>PLAC4>PSG7>PAPPA>LGALS14.
In one embodiment the panel includes one, at least 2, or at least 3 genes from TABLE 1. In some embodiments, the profile panel can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 genes from TABLE 1. In some embodiments, the profile panel can include exactly 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 genes from TABLE 1. In some embodiments the profile panel includes fewer than 100 genes, sometimes fewer than 50 genes, sometimes fewer than 20 genes, sometimes fewer than 15 genes, sometimes fewer than 10 genes, and sometimes fewer than 5 genes. In certain approaches the profile panel comprises a number of genes in the range 1-100 genes, 1-50 genes, 1-25 genes, 3-100 genes, 3-50 genes, 3-25 genes, or 3-10 genes.
In some versions the placental genes are selected from genes in TABLE 1. In some embodiments, the placental genes are selected from CGA, CAPN6, CGB, ALPP, CSHL1, PLAC4, PSG7, PAPPA, and LGALS14. In some embodiments, the genes include at least one gene other than CGA. In some embodiments, the genes include at least two, three, four, five, six, seven or eight genes other than CGA. In some embodiments, the genes include at least one gene other than CGB. In some embodiments, the genes include at least two, three, four, five, six, seven or eight genes other than CGB. In some embodiments, the genes include at least one gene other than CGA and CGB. In some embodiments, the method includes determining the expression profile for three (3) to nine placental genes.
3.4.2 Profile Panels for Determining Risk of Preterm Delivery
In one aspect, the invention provides a method for estimating risk of preterm delivery by analyzing a maternal sample to determine an expression profile. In one embodiment, the profile panel used for such a determination comprises one or more cfRNA transcripts with higher expression levels in a preterm population than in a term population. In one embodiment, a preterm population refers to a set of women who delivered a fetus prior to 37 weeks gestational age. In another embodiment, a preterm population refers to women who delivered a fetus prior to 33 weeks gestational age. In another embodiment, a preterm population refers to women who delivered a fetus prior to 29 weeks gestational age. In yet another embodiment, a preterm population refers to women who delivered a fetus between 12 and 33 weeks gestational age. In another embodiment, a preterm population refers to a set of women who delivered a fetus between 16 and 29 weeks gestational age. In an embodiment, a preterm population refers to a set of women who delivered a fetus between 16 and 33 weeks gestational age. As noted above, one preterm population used in the Examples consisted of women who delivered a fetus prior to 29 weeks gestational age and this population (or subpopulations thereof) is preferred for making reference profiles characteristic of high risk of prematurity. The Examples also show that biomarkers discovered in a population of women who delivered a fetus prior to 29 weeks are applicable in a population of women who delivered a fetus prior to 33 weeks gestational age.
In one approach the profile panel includes 1 or more, preferably 3 or more, genes listed in TABLE 2.
In one approach the profile panel includes three (3) or more genes are selected from the ten transcript panel CLCN3 [SEQ ID NO:10], DAPP1 [SEQ ID NO:11], POLE2 [SEQ ID NO:12], PPBP [SEQ ID NO:13], LYPLAL1 [SEQ ID NO:14], MAP3K7CL [SEQ ID NO:15], MOB1B [SEQ ID NO:16], RAB27B [SEQ ID NO:17], RGS18 [SEQ ID NO:18], and TBC1D15 [SEQ ID NO:19]. In one approach the profile panel comprises three (3) or more genes. In one approach the profile panel comprises three (3) or more genes selected from SEQ ID NOS:10-19. In one approach the profile panel comprises exactly three (3) genes selected from SEQ ID NOS:10-19. In some embodiments the panel comprises only genes selected from SEQ ID NOS:10-19. For example, in various embodiments, the profile panel will comprise the following combinations: (i) CLCN3, DAPP1, POLE2; (ii) DAPP1, POLE2, PPBP; (iii) POLE2, PPBP, LYPLAL1; (iv) PPBP, LYPLAL1, MAP3K7CL; (v) LYPLAL1, MAP3K7CL, MOB1B; (vi) MAP3K7CL, MOB1B, RAB27B; (vii) MOB1B, RAB27B, RGS18; and (viii) RAB27B, RGS18, TBC1D15. It will be appreciated that the full list of combinations of 3 genes selected from SEQ ID NOS:10-19 is easily generated, and this paragraph is intended to convey possession of each said combination of 3 genes.
In one approach the profile panel includes three (3) or more genes are selected from the seven transcript panel CLCN3 [SEQ ID NO:10], DAPP1 [SEQ ID NO:11], PPBP [SEQ ID NO:13], MAP3K7CL [SEQ ID NO:15], MOB1B [SEQ ID NO:16], RAB27B [SEQ ID NO:17], and RGS18 [SEQ ID NO:18]. In one approach the profile panel comprises three (3) or more genes. In one approach the profile panel comprises three (3) or more genes selected from SEQ ID NOS:10, 11, 13, and 15-18. In one approach the profile panel comprises exactly three (3) genes selected from SEQ ID NOS: 10, 11, 13, and 15-18. In some embodiments the panel comprises only genes selected from SEQ ID NOS: 10, 11, 13, 15, and 16-18.
In one approach the profile panel comprises exactly three genes selected from TABLE 2. In one approach the profile panel comprises exactly three genes selected from SEQ ID NO:10-19. In one approach the profile panel comprises exactly three genes selected from SEQ ID NOS: 10, 11, 13, 15, and 16-18.
The seven transcripts used to identify women at elevated risk or preterm delivery were weighted by the model in the following order of importance (from highest to lowest): RAB27B>PPBP>DAPP1>RGS18>(MOB1B, MAP3K7CL, and CLCN3), where MOB1B, MAP3K7CL, and CLCN3 are equally ranked. Thus, in some embodiments the determined level of expression for individual genes are given different weights (or coefficients) when compared to expression in a reference profile. For example, when all 7, or a subset comprising fewer than 7 genes in this group (e.g., 2, 3, 4, 5, 6) expression values for each gene are ranked): RAB27B>PPBP>DAPP1>RGS18>(MOB1B, MAP3K7CL, and CLCN3).
In one aspect, the invention provides a method for determining risk of preterm delivery by analyzing a maternal sample to determine an expression profile of a set of genes (e.g., cfRNA or protein) listed in TABLE 2, such as SEQ ID NOS: 10, 11, 13, 15, and 16-18. In one embodiment the panel includes one, at least 2, or at least 3 genes from TABLE 2. In some embodiments, the profile panel can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 genes from TABLE 2. In some embodiments, the profile panel can include exactly 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 genes from TABLE 2. In some embodiments the profile panel includes fewer than 100 genes, sometimes fewer than 50 genes, sometimes fewer than 20 genes, sometimes fewer than 15 genes, sometimes fewer than 10 genes, and sometimes fewer than 5 genes. In certain approaches the profile panel comprises a number of genes in the range 1-100 genes, 1-50 genes, 1-25 genes, 3-100 genes, 3-50 genes, 3-25 genes, or 3-10 genes. In one approach at least one of the genes in the profile panel does not listed in FIG. 3A and/or FIG. 3B and/or FIG. 4 of US Patent Publication No. 2013/0252835.
In one approach a maternal sample is obtained at a specified week of pregnancy and the maternal expression profile is compared to a time matched reference profile, wherein the time matched reference profile is characteristic of a full-term pregnancy profile at the specified week of pregnancy. In one approach a maternal sample is obtained at a specified trimester (e.g, first, second or third trimester) of pregnancy and the maternal expression profile is compared to a time matched reference profile, wherein the time matched reference profile is characteristic of a full-term pregnancy profile at the specified trimester of pregnancy. Significant deviations of the maternal profile from the reference profile is indicative that the woman as at elevated risk of preterm delivery. It will be immediately apparent that, in an alternative approach, a maternal sample is obtained at a specified week of pregnancy and the maternal expression profile is compared to a time matched reference profile, wherein the time matched reference profile is characteristic of a preterm pregnancy profile at the specified week of pregnancy. Significant similarities between the maternal profile and the reference profile is indicative that the woman as at elevated risk of preterm delivery. In one approach a machine learning model is used to compare the maternal profile and the reference profile.
Proteins can be isolated from a maternal sample using methods well known in the art. In one appropach total protein is from a maternal blood fraction or urine and assayed for the presence and/or quantity of particular proteins. In one approach an assay is carried out using a protein fraction (e.g., a fraction enriched for protein(s) of interest. In one approach an assay is carried out using one or more purified proteins. Isolation and fractionation of proteins can be performed using fractionation by molecular weight, protein charge, solubility/hydrophobicity, protein isoelectric point (pI), affinity purification (e.g., using a an antiligand, such as an antibody or aptamer, specific from a protein among other methods. Kits for isolating proteins from blood are known and are commercially available (e.g., Total Protein Assay Kit from ITSIBiosciences, Catalog No.: K-0014-20). Kits for isolating proteins from plasma/serum are known and are commercially available (e.g., Antibody Serum Purification Kit (Protein A) from Abcam, Catalog No.: ab109209). Kits for isolating protein and RNA from the sample are also known (e.g., Protein and RNA Isolation System (PARIS) from Thermo Fisher Scientific, Catalog No. AM1921).
Specific proteins from a maternal sample can be identifed and/or quantified using well know methods, including enzyme-linked immunoadsorbent assay (ELISA); radioimmunoassay (RA) (see, e.g., Anthony et al., Ann. Clin. Biochem., 34:276-280 (1997) describing detection of low levels of protein undetectable using comparable ELISA conditions, incorporated herein by reference); proximity ligation and proximity extension assays (see, e.g., US Pat. Pub. Nos. 20170211133; 20160376642; 20160369321; 20160289750: 20140194311; 20140170654; 20130323729; and 20020064779, incorporated herein by reference), protein binding arrays (e.g., antibody or aptamer arrays), mass spectroscopy (see, e.g., Han, X. et al.(2008), incorporated herein by reference. Mass Spectrometry for Proteomics. Current Opinion in Chemical Biology, 12(5), 483-490. http://doi.org/10.1016/j.cbpa.2008.07.024; Serang, O et al (2012). A review of statistical methods for protein identification using tandem mass spectrometry. Statistics and Its Interface, 5(1), 3-20, incorporated herein by reference). Any suitable method may be used.
Protein binding arrays may be used to detect and quantitate proteins, including but not limited to antibody based arrays and aptamer based arrays (see, e.g., Gold L, et al. (2010) Aptamer-Based Multiplexed Proteomic Technology for Biomarker Discovery. PLoS ONES(12): e15004. https://doi.org/10.1371/journal.pone.0015004, incorporated herein by reference). An antibody array (also known as antibody microarray) is a specific form of protein array. In this technology, a collection of capture antibodies are fixed on a solid surface such as glass, plastic, membrane, or silicon chip, and the interaction between the antibody and its target antigen is detected (see, e.g., U.S. Pat. Nos. 4,591,570; 4,829,010; and 5,100,777, all of which are incorporated herein by reference). Antibody arrays can be used to detect protein expression from various biological fluids including serum, plasma, urine and cell or tissue lysates (see, Knickerbocker T., MacBeath G. Detecting and Quantifying Multiple Proteins in Clinical Samples in High-Throughput Using Antibody Microarrays. In: Wu C. (eds) Protein Microarray for Disease Analysis. Methods in Molecular Biology (Methods and Protocols), vol 723. Humana Press (2011), incorporated herein by reference).
Kits for performing antibody arrays are known and are commercially available (e.g., custom designed antibody arrays or predetermined antibody arrays from RayBiotech, Norcross, Ga.).
A maternal expression profile may be compared with a reference profile(s) in a variety of ways. In one approach, a comparison between two data sets is performed to determine whether one data set differs or is similar to another data set, e.g., to within statistical significance. In one embodiment, a first data set can comprise a maternal expression profile, and a second data set comprises a reference profile, where the first and second data sets include one or more data points (for example, median values) for gene expression data for one or more genes, collected over one or more time points during pregnancy (e.g., once a week or once a trimester during the course of the pregnancy). In some embodiments, the second data set comprises a plurality of data points from a preterm maternal sample or a maternal sample having a known gestational age.
Accordingly, a maternal data set can be a measured value of an expression level of one or more genes, where the expression level can be determined from individual expression values for each of the genes, e.g., as an average, weighted average, or median of the individual expression levels. In other embodiments, the individual expression levels can be treated as different dimensions of a multi-dimensional data point, e.g., for use in clustering. For determining a gestational age or time to delivery, the comparison can be between a measured expression level(s) of a maternal sample and the reference expression level(s) of each of a plurality of reference having different known gestational ages, thereby identifying a group or representative data point that is closest (e.g., least difference in a distance between the measured expression level(s) and the reference expression level(s)). The known gestational age of the closest reference sample (or representative data point of a group of reference samples all having a same gestational age) can be used as the gestational age or time to delivery of the maternal sample. Such a comparison can be performed by comprising the measured expression level(s) to a gestational function that is determined from the reference samples, e.g., a linear function that defines a functional relationship between the expression level(s) (e.g., in a multi-dimensional space when individual expression levels correspond to different dimensions or in a 2D-plot when individual expression levels are combined to provide a single metric).
In embodiments where a discrimination is made between term and preterm samples, the comparison can involve determining whether the measured expression level(s) are more similar to preterm reference level(s) or term reference level(s). Such a comparison can involve determining which cluster of reference levels is closest to the measured expression level(s). One or more values may be used for determining whether the measured expression level(s) are sufficiently close (e.g., as measured by a distance or a weight distance where differences along one dimension are weighted differently) for the measured level(s) to be considered part of either cluster of term or preterm samples. An indeterminate classification may result if the expression level(s) are not sufficiently close. A threshold can be used to determine whether the measured expression levels are sufficiently close to reference expression levels of a term or preterm population. A threshold can be selected based on a desired sensitivity and specificity, as will be apparent to one skilled in the art.
To determine the reference level(s), a set of training samples can be labeled with different classifications, e.g., term or preterm. Then, the reference levels can be chosen as being representative of a classification or as values that separate the different classifications, e.g., as cutoffs for assigning different classifications to a new sample. A machine learning technique can analyze different expression levels of different genes to determine which set of expression levels (features) provide the best discrimination for an optimized set of reference levels. A tradeoff between specificity and sensitivity can be optimized, e.g., by a ROC (receiver operating characteristic) curve. In some embodiments, a plurality of training samples, each labeled as preterm or full-term, can be obtained. In some embodiments, training samples are labeled as nulliparous, multiparous women, carrying male fetus, carrying female fetus, or the like. One or more measured expression levels for the panel of genes can be obtained for each of the plurality of training samples. Using the machine learning technique (e.g., by optimizing a cost function as defined by the model), the one or more reference expression levels can be iteratively adjusted to increase a number of the training samples that are classified correctly as a result of comparing the one or more measured expression levels to the one or more reference expression levels.
In some aspects, the first and second data sets can be analyzed to establish relative differences or similarities (e.g., fold increase or fold decrease) between the data sets (e.g., the expression level(s) of the data sets). Such a procedure can be performed when a single expression level is determine for a panel of genes. In another aspect, a pairwise comparison of expression level(s) at each time point for each gene across the duration of pregnancy can be used to identify which reference level(s) are most similar, where each set of reference level(s) can correspond to a different gestational age. In some embodiments, the pairwise comparison (e.g., pairwise between expression levels of different genes and/or between reference level(s) at different times) can include statistical analysis via a range of statistical methodologies, including but not limited to Fisher's exact test, Wilcox rank test, permutation test, linear regression, generalized linear models and quasi-likelihood tests coupled with the appropriate multiple hypothesis correction (e.g., Benjamini Hochberg).
In one embodiment, differentiating gene activity (e.g., between preterm and term maternal samples, see Example 1 and
In another aspect, a sample data set can be analyzed using a random forest model (see, e.g., Chen and Ishwaran, Genomics, 99:323-329 (2012), incorporated herein by reference) that was generated using the second data set. See Examples. Random forest is a form of machine learning that selects training sets randomly for building multiple models (e.g., decision trees or regression models) and uses the outputs of this ensemble of models to determine a final output (e.g., via majority voting for a term/preterm classification or an average when determining gestational age or time to delivery). Each model can have the same or different features (e.g., expression levels of genes), but have different reference levels as determined from the different training sets that are randomly selected. It will be recognized that other techniques of machine learning can be used to compare two data sets, including but not limited to, support vector machines, elastic net, lasso or neural networks. It will also be apparent that machine learning models (e.g., supervised machine learning; see, for example Mohri et al. (2012) Foundations of Machine Learning, The MIT Press, incorporated herein by reference) can be developed to account for particular attributes of a population such as ethnicity and that multiple models can be prepared based on different needs (e.g., an Eastern European model versus a North African model).
In one aspect, a machine learning model (e.g., to predict gestational age or time to delivery) can be prepared as follows:
(1) Curate a labeled training set (e.g., where gestational age of each sample is known);
(2) Iterate through selecting features of interest (e.g., recursive feature selection);
(3) Build a regression model (e.g., random forest) based on the selected features; and
(4) Select a regression model and feature subset using cross validation data (e.g., by withholding part of the training set and determining how accurately the regression model evaluated the withheld data).
In one embodiment, once the regression model is prepared, it can be saved and used for future data interpretations. In other embodiments, a single regression model can be determined, e.g., by fitting a line or a curve to a set of measured expression level(s) that are measured at known gestational ages. The regression model can be considered a gestational function, e.g., when a model (e.g., a linear or non-linear function) is fit to expression levels of a plurality of calibration samples having measured expression levels and of which a gestational age is known. Accordingly, the comparison of the maternal expression profile to the reference profile can be performed by comparing the maternal expression profile to a gestational function that provides a gestational age based on an input of one or more expression levels.
In another aspect, the first and second data sets can be analyzed using SAMS (Scoring Algorithm of Molecular Subphenotypes) available at http://statweb.stanford.edu/˜tibs/SAM/ (see, Tusher et al., PNAS, 98:5116-5121 (2001), incorporated herein by reference). SAMS is a classification algorithm of gene expression data generated from the calculation of two scores (e.g., an up score and a down score). In one embodiment, a maternal expression profile data set of the instant invention (e.g., cfRNAs) can be compared to a reference expression profile data set and a maternal sample having an up score above the median value (as compared to the reference expression profile) and a down score above the median value (as compared to the reference expression profile) can be classified as statistically significant (see., e.g., Herazo-Maya, Lancet Respir Med, September 20, (2017) doi:org/10.1016/52213-2600(17)30349-1 and Dinu et al., BMC Bioinformatics, 8:242 (2007), both incorporated herein by reference). Other evaluations of a first data set and a second data set using SAMS can be performed according to the SAMS user manual (available at http://www-stat.stanford.edu/˜tibs/SAM/sam.pdf).
Various additional statistical analyses exist for the comparison of a first and second data set directed to gene expression data (e.g., preterm data set versus a maternal sample) including for example, methods set forth by Efron and Tibshirani (On Testing the Significance of Sets of Genes. Ann Appl. Stat., 1. 107-129 (2007) and Zhao et al. (Gene expression profiling predicts survival in conventional renal cell carcinoma, PLOS Medicine, 3. E13. 13. 10.1371/journal.pmed.0030013. (2006), both incorporated herein by reference).
As discussed above, maternal expression profiles may be compared to reference profiles and a measure of similarity or difference may be made. In one approach, comparing a maternal expression profile to a reference profile includes compiling gene expression data (e.g., the number or relative number of transcripts of a specified cfRNA sequence on a computer-readable medium) and processing said data on said computer to identify degrees of similarity and difference between said profiles.
Women identified as at risk for preterm delivery may elect medical interventions (e.g., progesterone supplementation, cervical cerclage), behavioral changes (smoking cessation), or ultrasound imaging to monitor and reduce the likelihood of preterm delivery or to extend the pregnancy for as long as possible. See Newnham et al. “Strategies to Prevent Preterm Birth.” Frontiers in Immunology 5 (2014):584, incorporated herein by reference. Progesterone may be used to treat and/or prevent the onset of preterm labor in women identified as at risk for preterm delivery. In some embodiments, a pregnant woman may be administered an amount of progesterone, e.g., as a vaginal gel, that is sufficient to prolong gestation by delaying the shortening or effacing of cervix. The administration can be as infrequent as weekly, or as often as 4 times daily. Antibiotic treatment (amoxicillin, ampicillin, erythromycin, azithromycin, and cephalosporin) is indicated in some women with premature rupture of the membranes (PROM), a precursor of premature delivery, and may be administered to women identified as at risk for preterm delivery. When a woman is identified as at risk of preterm delivery the medical provider may recommend an ultrasound examination at least once per four week period, biweekely, or weekly.
In some embodiments, the methods described herein are used for theranosis. In one approach a first maternal expression profile is obtained from a woman at risk of preterm delivery at a first point in time, medically appropriate steps (e.g., medical interventions) are initiated or carried out, and then a second maternal expression profile is obtained from the woman at a second point in time. Each maternal expression profile is compared to an appropriate reference profile (e.g., time matched, population matched, etc.). If the difference between the second maternal expression profile and the appropriate corresponding reference profile is less than the difference between the first maternal expression profile and its appropriate corresponding reference profile this is an indication that the steps carried out have a beneficial therapeutic effect. In some cases, the first and second maternal expression profiles are compared to the same reference profile. In one approach the process is carried out without any medical intervention, in which case a spontaneous improvement may be observed.
In some embodiments, the methods described herein are used for prognosis. It is believed that certain maternal expression profiles are indicative of particular prognoses. For example, certain maternal expression profiles may be used to estimate time until preterm delivery (absent intervention). Reference profiles for this purpose can be generated from sub-populations grouped by specific pregnancy outcomes (dates of prematurity), by genetic risk, or by phenotypic factors such as age and previous pregnancy history. The methods disclosed herein may also be used for identifying and monitoring fetuses having congenital defects; in some cases the methods may be used to inform decisions about in utero treatment. Maternal expression profiles can be used to estimate time to delivery and gestational age for the fetus, and the results used for providing advice or treatment for either the mother or the fetus. Similarly, with appropriately chosen genes such profiles can be used to estimate the risk of adverse events such as preterm delivery.
Methods of the invention may be implemented using a computer-based system. As used herein, “a computer-based system” refers to the hardware means, software means, and data storage means used to analyze the information of the present invention. The minimum hardware of the computer-based systems of the present invention comprises a central processing unit (CPU), input means, output means, and data storage means. A skilled artisan can readily appreciate that any one of the currently available computer-based system are suitable for use in the present invention. The data storage means may comprise any manufacture comprising a recording of the present information as described above, or a memory access means that can access such a manufacture.
In some embodiments, a database comprising reference profiles is used in methods of the invention. In some embodiments, a database comprising expression data from a plurality of women, and optionally different subpopulations of women, is provided. Accordingly, aspects of the invention provide systems and methods for the use and development of a database. In some approaches the database is used in combination with an algorithm that enables generation of new reference profiles selected based on characteristics of an individual woman.
Any of the computer systems mentioned herein may utilize any suitable number of subsystems. In some embodiments, a computer system includes a single computer apparatus, where the subsystems can be the components of the computer apparatus. In other embodiments, a computer system can include multiple computer apparatuses, each being a subsystem, with internal components. A computer system can include desktop and laptop computers, tablets, mobile phones and other mobile devices.
A computer system can include a plurality of the same components or subsystems, e.g., connected together by external interface, by an internal interface, or via removable storage devices that can be connected and removed from one component to another component. In some embodiments, computer systems, subsystem, or apparatuses can communicate over a network. In such instances, one computer can be considered a client and another computer a server, where each can be part of a same computer system. A client and a server can each include multiple systems, subsystems, or components.
Aspects of embodiments can be implemented in the form of control logic using hardware circuitry (e.g. an application specific integrated circuit or field programmable gate array) and/or using computer software with a generally programmable processor in a modular or integrated manner. As used herein, a processor can include a single-core processor, multi-core processor on a same integrated chip, or multiple processing units on a single circuit board or networked, as well as dedicated hardware. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will know and appreciate other ways and/or methods to implement embodiments of the present invention using hardware and a combination of hardware and software.
Any of the software components or functions described in this application may be implemented as software code to be executed by a processor using any suitable computer language such as, for example, Java, C, C++, C#, Objective-C, Swift, or scripting language such as Perl or Python using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions or commands on a computer readable medium for storage and/or transmission. A suitable non-transitory computer readable medium can include random access memory (RAM), a read only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a compact disk (CD) or DVD (digital versatile disk), flash memory, and the like. The computer readable medium may be any combination of such storage or transmission devices.
The databases may be provided in a variety of forms or media to facilitate their use. “Media” refers to a manufacture that contains the expression information of the present invention. The databases of the present invention can be recorded on computer readable media, e.g. any medium that can be read and accessed directly by a computer (e.g., an internet database). Such media include, but are not limited to: magnetic storage media, such as floppy discs, hard disc storage medium, and magnetic tape; optical storage media such as CD-ROM; electrical storage media such as RAM and ROM; and hybrids of these categories such as magnetic/optical storage media. One of skill in the art can readily appreciate how any of the presently known computer readable media can be used to create a manufacture comprising a recording of the present database information. “Recorded” refers to a process for storing information on computer readable medium, using any such methods as known in the art. Any convenient data storage structure may be chosen, based on the means used to access the stored information. A variety of data processor programs and formats can be used for storage, e.g. word processing text file, database format, etc.
Such programs may also be encoded and transmitted using carrier signals adapted for transmission via wired, optical, and/or wireless networks conforming to a variety of protocols, including the Internet. As such, a computer readable medium may be created using a data signal encoded with such programs. Computer readable media encoded with the program code may be packaged with a compatible device or provided separately from other devices (e.g., via Internet download). Any such computer readable medium may reside on or within a single computer product (e.g. a hard drive, a CD, or an entire computer system), and may be present on or within different computer products within a system or network. A computer system may include a monitor, printer, or other suitable display for providing any of the results mentioned herein to a user.
Any of the methods described herein may be totally or partially performed with a computer system including one or more processors, which can be configured to perform the steps. Thus, embodiments can be directed to computer systems configured to perform the steps of any of the methods described herein, potentially with different components performing a respective step or a respective group of steps. Although presented as numbered steps, steps of methods herein can be performed at a same time or at different times or in a different order. Additionally, portions of these steps may be used with portions of other steps from other methods. Also, all or portions of a step may be optional. Additionally, any of the steps of any of the methods can be performed with modules, units, circuits, or other means of a system for performing these steps.
Primers and probes that specifically hybridize to or amplify cfRNA from placental genes (including genes in TABLE 1) and other informative genes (including genes in TABLE 1 and TABLE 2) may be used in the practice of aspects of the invention. In particular, useful primers and probes include those that specifically hybridize to or amplify SEQ ID NOS: 1-19. These primers and probes are used for amplification (including multiplex PCR, multiplex RT-qPCR, or other amplification methods), for reverse transcription, for construction of sequencing libraries (e.g., RNA-seq libraries), for addition of adaptor sequences, for hybrid capture of RNAs of interest, for construction nucleic acid arrays, for primer extension and for other uses known to the practitioner with knowledge of the art. It is well within the ability of persons of ordinary skill in the art to design probes and primers for their intended uses, taking into account methods of amplification (e.g., addition of adaptors or universal primers), target sequence composition, base composition, avoiding artifacts such as primer dimer formation, as well as the fragmented nature of cfRNA.
For example, it is within the ability of persons of ordinary skill in the art to use SEQ ID NOS:1-19 to design primers, primers pairs, and probes that are specific for each gene and work for their intended purposes (e.g., use in a multiplex reaction). It will be appreciated that for each RNA transcript there are many different primers and combinations of primers that can amplify at least a portion of the transcript. A person of skill in the art can therefore design primer combinations to amplify informative sequences of any of SEQ ID NOS:1-19 or any combination thereof, as well as other gene sequences identified in TABLES 1 and 2. Exemplary primers and probes are described in TABLES 3-5. Probes may be nucleic acid probes, such as RNA or DNA probes. Primers or probes may be immobilized (e.g., for capture based enrichment) or detectably labeled (e.g., with fluorescent, enzymatic, or chemiluminescent moieties or the like).
In one aspect, the invention provides primers for multiplex amplification of at least 3 and not more than 50, optionally no more than 25, optionally no more than 10 genes, selected from genes in TABLE 1. In some embodiments, the invention provides primers for multiplex amplification of at least 3 mRNA transcripts provided in TABLE 1. In another embodiment, the invention provides primers for multiplex amplification of any combination of at least 3 mRNA transcripts selected from SEQ ID NOS:1-9. In one embodiment, the primers are for multiplex amplification, wherein the primers comprise at least one pair, and optionally three or more primer pairs. Exemplary primer pairs are provided in TABLE 3. In another embodiment, the primers for multiplex amplification comprise at least three and no more than 100 primer pairs, optionally no more than 50, optionally no more than 25, optionally no more than 10 primer pairs selected from any of the primer pairs provided in TABLE 3.
In a related aspect, the invention provides compositions comprising primer(s) or primer pair(s) as described above. The composition may be an admixture. The composition may be a solution. The composition may additionally contain one or more of (a) maternal cfRNA, (b) buffer, (c) enzymes (e.g., one or a combination of reverse transcriptase, DNA polymerase, RNA or DNA ligase), (d) dNTPs.
In one aspect a composition is provided, comprising (1) cfRNAs with cfRNA sequences corresponding to at least 2 genes in TABLE 1, or amplicons of, or cDNAs from, said cfRNA sequences and (2) primers for amplifying said cfRNA sequences or amplicons or cDNAs, or probes for detecting said cfRNA sequences or amplicons or cDNAs, with the proviso that the composition does not comprise primers for amplifying more than a threshold number of different genes, amplicons or cDNAs; and does not comprise probes for detecting more than the threshold number of different cfRNA sequences or amplicons or cDNAs. In one embodiment the composition does not comprise cfRNAs with cfRNA sequences corresponding to more than the a threshold number of different genes from the human genome, or amplicons of, or cDNAs from more than the threshold number of different genes. In some embodiments the threshold number is 200. In some embodiments the threshold number is 150. In some embodiments the threshold number is 100. In some embodiments the threshold number is 50. In some embodiments the threshold number is 25.
In a related aspect, the invention provides nucleic acid arrays comprising primer(s), primer pair(s), or probes as described above.
In one aspect, the invention provides primers for multiplex amplification of at least 3 and no more than 100 genes, optionally no more than 50, optionally no more than 25, optionally no more than 10 genes, selected from genes in TABLE 2. In some embodiments, the invention provides primers for multiplex amplification of at least 3 mRNA transcripts provided in TABLE 2 (i.e., RefSeq identifiers). In another embodiment, the invention provides primers for multiplex amplification of any combination of at least 3 mRNA transcripts selected from SEQ ID NOS:10-19, or, alternatively at least 3 mRNA transcripts selected from SEQ ID NOS: 10, 11, 13, and 15-18. In one embodiment, the primers are for multiplex amplification, wherein the primers comprise at least one pair, and optionally three or more primer pairs. Exemplary primer pairs are provided in TABLE 3. In another embodiment, the primers for multiplex amplification comprise at least three and no more than 100 primer pairs, optionally no more than 50, optionally no more than 25, optionally no more than 10 pairs selected from any of the primer pairs provided in TABLE 3.
In a related aspect, the invention provides compositions comprising primer(s) or primer pair(s) as described above. The composition may be an admixture. The composition may be a solution. The composition may additionally contain one or more of (a) maternal cfRNA, (b) buffer, (c) enzymes (e.g., reverse transcriptase, DNA polymerase, RNA or DNA ligase), (d) dNTPs.
In a related aspect, the invention provides kits comprising primer(s) or primer pair(s) as described above packaged together. In one approach, a mixture of different primers are combined in a single mixture. In another approach, primers specific for individual cfRNAs are packaged together in separate vials. The kit may additionally contain one or more of (a) maternal cfRNA, (b) buffer, (c) enzymes (e.g., reverse transcriptase, DNA polymerase, RNA or DNA ligase), (d) dNTPs.
In one aspect a composition is provided, comprising (1) cfRNAs with cfRNA sequences corresponding to at least 2 genes in TABLE 2, or amplicons of, or cDNAs from, said cfRNA sequences and (2) primers for amplifying said cfRNA sequences or amplicons or cDNAs, or probes for detecting said cfRNA sequences or amplicons or cDNAs, with the proviso that the composition does not comprise primers for amplifying more than a threshold number of different genes, amplicons or cDNAs; and does not comprise probes for detecting more than the threshold number of different cfRNA sequences or amplicons or cDNAs. In one embodiment the composition does not comprise cfRNAs with cfRNA sequences corresponding to more than the a threshold number of different genes from the human genome, or amplicons of, or cDNAs from more than the threshold number of different genes. In some embodiments the threshold number is 200. In some embodiments the threshold number is 150. In some embodiments the threshold number is 100. In some embodiments the threshold number is 50. In some embodiments the threshold number is 25.
In a related aspect, the invention provides nucleic acid arrays comprising primer(s) or primer pair(s) as described above.
This section describes implementation of the methods for determination of gestational age and risk of preterm delivery. Examples in this section are intended as illustrations and are in no sense limiting.
In one approach a maternal sample(s) is collected, frozen, and shipped to a centralized laboratory for analysis. In one approach methods of the invention are carried out in a local medical facility (e.g., hospital lab) optionally using a kit for isolation of cfRNA, production of cDNA, qPCR and/or sequencing. In one approach the kit includes reagent for cfRNA isolation. The use of a standardized kit is advantageous in ensuring uniformity of sample collection, cfRNA isolation, and analysis by qPCR or transcriptome sequencing. The kit may contain reagents for cfRNA, production of cDNA, qPCR and/or sequencing as well as primers or probes described herein for determining expression levels of cfRNA transcripts or combinations of transcripts described herein. In one approach cfRNA, cDNA, or a library is produced and shipped to a centralized laboratory for analysis.
In one approach a maternal sample(s) is collected and an expression profile is determined using a distributed system including client systems and server systems communicating over a computer network server-client, frozen, and shipped to a centralized laboratory for analysis. The server system may comprise databases of reference profiles and may receive data (e.g., expression profile information) from a client system. The expression profile information from the patient is compared to the reference profile using a computer product, e.g., comprising a computer readable medium storing a plurality of instructions for controlling a computer system to perform a method of the invention. the method of any one of the preceding claims. The databases of reference profiles may be produced using the machine learning approaches described herein. Advantageously, as expression profiles from individual patients is collected that information may be used as training data. This may be particularly useful when training and validation data are collected from demographically distinct patient populations (e.g., populations identified by age, race or ethnicity, geographical location, or other criteria).
Patient expression profiles will be most useful when they are tied to particular outcomes (e.g., term delivery or preterm delivery) or gestational age at birth. Thus, in one aspect the invention involves (1) collecting cfRNA from a pregnant woman one or multiple times during pregnancy, determining an expression profile using the cfRNA (i.e., an expression profile corresponding to a set of genes identified herein, e.g., genes from TABLE 1, TABLE 2, or TABLE 6 or combinations or subsets described herein); and recording the expression profile, e.g., on a suitable non-transitory computer readable medium; and then (2) determining the delivery date for the woman, categorizing the delivery as term or preterm (and if preterm, by how many days) or otherwise characterizing the outcome of the pregnancy, and (3) associating the information in (2) with the expression profiles in (1), e.g., by linking the information and expression profile(s) in the computer readable medium.
Determination of Gestational Age
In one approach a method performed using a computer for estimating gestational age of a fetus is provided comprising: (a) obtaining one or more expression profiles from a maternal sample of a pregnant woman carrying a fetus, wherein the expression profile(s) corresponds to the expression of cfRNA transcripts from a first panel of genes; (b) comparing, using a computer system, the expression profile(s) to one or more reference profile(s) characteristic of a defined gestational age(s) to estimate the gestational age of the fetus, wherein the reference profile(s) characteristic of the defined gestational age(s) are determined using a machine learning model that analyzes first training samples that are cfRNA expression profiles labeled with a defined gestational age; (c) updating, using the computer system, the reference profile(s) by: (1) receiving second training samples, wherein the second training samples are cfRNA expression profiles labeled with a defined gestational age, and (2) iteratively adjusting the reference profile(s) via a machine learning model to increase the number of the first and second training samples that are classified correctly. The reference profiles can form a line or curve or be discrete values. In some embodiments the first panel of genes comprises any combination of genes disclosed herein as predictive of gestational age, including placental genes, placental genes listed in Table 1, and at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9].
Also provided is a computer system comprising: (a) a database comprising reference profile(s), each including a level of expression in a population of pregnant women of cfRNA transcripts corresponding to a first panel of genes and corresponding to a defined gestational age; (b) a user interface configured to interact with a client computer over a network and to receive expression profile(s) including the level of expression in a pregnant woman carrying a fetus of cfRNA transcripts corresponding to the first panel of genes; and (c) one or more processors configured to analyze the reference profile and expression profile, including comparing the reference profile(s) and expression profile(s) to determine gestational age of the fetus; and (d) a network interface that transmits the gestational age of the fetus to the client computer. In one embodiment the the reference profile(s) and expression profile(s) comprise expression levels of a panel of cfRNAs in any combination disclosed herein, including transcripts from placental genes; placental genes listed in Table 1; and at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9].
Risk of Preterm Delivery
In one approach a method performed using a computer for assessing risk of preterm delivery by a pregnant woman is provided comprising: (a) obtaining one or more expression profiles from a maternal sample of a pregnant woman, wherein the expression profile(s) corresponds to the expression of a plurality of cfRNA transcripts from a first panel of genes; (b) comparing, using a computer system, the expression profile(s) to one or more reference profile(s) characteristic of a woman with (a) a high risk of preterm delivery or (b) a low risk of preterm delivery, or characteristic of a woman with a defined length of pregnancy, wherein the reference profiles are determined using a machine learning model that analyzes first training samples that are cfRNA expression profiles preterm or full-term, or labeled with a length of pregnancy (c) updating, using the computer system, the reference profile(s) by: (1) receiving second training samples, wherein the second training samples are cfRNA expression profiles labeled as preterm or full-term or labeled with a length of pregnancy, and (2) iteratively adjusting the reference profile(s) via a machine learning model to increase the number of the first and second training samples that are classified correctly. The reference profiles can form a line or curve or be discrete values. In some embodiments the first panel of genes comprises any combination of any combination of genes disclosed herein as predictive of risk of premature delivery, including genes listed in Table 1, and at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9] or at least least 2, at least 3, at least 4, at least 5, at least 6, or 7 genes selected from CLCN3 [SEQ ID NO:10], DAPP1 [SEQ ID NO:11], PPBP [SEQ ID NO:13], MAP3K7CL [SEQ ID NO:15], MOB1B [SEQ ID NO:16], RAB27B [SEQ ID NO:17], and RGS18 [SEQ ID NO:18]. In some embodiments the first panel of genes comprises at least one combination selected from (1) RGS18; DAPP1; PPBP; (2) RGS18; RAB27B; PPBP; (3) RGS18; MOB1B; PPBP; (4) RGS18; PPBP; MAP3K7CL; (5) RGS18; PPBP; CLCN3; (6) DAPP1; RAB27B; PPBP; (7) DAPP1; MOB1B; PPBP; (8) DAPP1; PPBP; CLCN3; (9) RAB27B; MOB1B; PPBP; (10) RAB27B; PPBP; MAP3K7CL; (11) RAB27B; PPBP; CLCN3; (12) MOB1B; PPBP; MAP3K7CL; and (13) MOB1B; PPBP; CLCN3.
For determining risk of preterm delivery maternal samples can be labeled “preterm” and “term”; or with the gestational age of the child at birth; or with the length of the pregnancy (e.g., week of delivery), combinations of these, or labels suitable for quantitatively or qualitatively distinguishing a full-term delivery from a preterm delivery.
Also provided is a computer system comprising: (a) a database comprising reference profile(s), each including a level of expression in a population of pregnant women of cfRNA transcripts corresponding to a first panel of genes and risk of preterm delivery; (b) a user interface interface configured to interact with a client computer over a network and to receive expression profile(s) including the level of expression in a pregnant woman of cfRNA transcripts corresponding to the first panel of genes; and (c) one or more processors configured to analyze the reference profile and expression profile, including comparing the reference profile(s) and expression profile(s) to determine the risk of preterm delivery; and (d) a network interface that transmits the risk of preterm delivery to the client computer. In some embodiments the reference profile(s) and expression profile(s) comprise expression levels of a panel of cfRNAs in any combination disclosed herein, including genes listed in Table 1 and at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, or 9 genes selected from CGA [SEQ ID NO:1], CAPN6 [SEQ ID NO:2], CGB [SEQ ID NO:3], ALPP [SEQ ID NO:4], CSHL1 [SEQ ID NO:5], PLAC4 [SEQ ID NO:6], PSG7 [SEQ ID NO:7], PAPPA [SEQ ID NO:8], and LGALS14 [SEQ ID NO:9] or at least least 2, at least 3, at least 4, at least 5, at least 6, or 7 genes selected from CLCN3 [SEQ ID NO:10], DAPP1 [SEQ ID NO:11], PPBP [SEQ ID NO:13], MAP3K7CL [SEQ ID NO:15], MOB1B [SEQ ID NO:16], RAB27B [SEQ ID NO:17], and RGS18 [SEQ ID NO:18].
11. EXAMPLES
Sample Collection
Blood samples from pregnant Danish women were collected weekly (high-resolution cohort) and at one time point during the second or third trimester from the University of Pennsylvania (preterm discovery cohort) and the University of Alabama at Birmingham (preterm validation cohort) under an Institutional Review Board-approved protocol. Women who participated in the study in Pennsylvania and Alabama were at elevated risk for spontaneous premature delivery. All women who delivered preterm except one patient from Pennsylvania (preeclampsia) experienced spontaneous preterm birth. As per the standard of care, all women with a history of preterm delivery received weekly progesterone injections. The blood samples were collected into EDTA-coated Vacutainer tubes (Becton Dickinson, NJ). Plasma was separated from blood using standard clinical blood centrifugation protocol.
Cell-Free RNA (cfRNA) Isolation
Cell-free RNA was extracted from 0.75-2 mL of plasma using Plasma/Serum Circulating RNA and Exosomal Purification kit (Norgen Biotek Corp, Canada, Catalog No. 42800). The residue of DNA was digested using Baseline-ZERO DNase (Epicentre, WI) and then cleaned by RNA Clean and Concentrator™-5 kit (Zymo Research, CA). The resulting RNA was eluted to 12 μl in elution buffer.
RT-qPCR Assay
RT-qPCR assays consist of two main reactions: reverse transcription/preamplification of extracted cfRNA and qPCR of pre-amplified cDNA. The primers for our gene panels were designed and synthesized by Fluidigm Corporation, CA (TABLE 3). Either 1-2 μl or 10 μl out of the 12 μl of total purified RNA was used for reverse transcription/preamplification reaction using the CellsDirect™ One-Step RT-qPCR Kit (Invitrogen, CA, Catalog No. 11753-100) and a pool of 96 primer pairs from TABLE 3. Preamplification was performed for 20 cycles and residual primers of the reaction were digested using exonuclease I treatment. Multiplex qPCR reactions of 96 samples for the 96 primer pairs were performed using 96×96 Dynamic Array Chip on BioMark System (Fluidigm Corp., CA). The BioMark Dynamic Array Chip loads individual samples (cDNA) and individual reagents (primer pairs) separately into wells on the Dynamic Array chip. The integrated fluidics circuit controllers push samples and reagents through channels until full; then coordinated releasing and closing of fluidic values allows mixing of samples and reagents into individual compartments within the chip. The 96×96 Dynamic Array Chip can simultaneously analyze up to 9,216 reactions. Threshold cycles (Ct values) of qPCR reactions were extracted using Fluidigm real-time PCR analysis software.
cfRNA-Seq Library Preparation
A cell-free RNA sequencing library was prepared by SMARTer Stranded Total RNAseq—Pico Input Mammalian kit (Clontech, CA, Catalog No. 634413) from 6 μl of eluted cfRNA according to the manufacturer's manual. Short read sequencing was performed on Illumina NextSeq™ (2×75 bp) platform (Illumina, CA) to the depth of more than 10 million reads per samples.
cfRNA-Seq Differential Expression Analysis
28 samples (14 term and 14 preterm) cfRNA samples of the preterm discovery cohort were sequenced. The sequencing reads were mapped to human reference genome (hg38) using STAR aligner. Duplicates were removed by Picard and then unique reads were quantified using htseq-count. After preprocessing, 16 samples containing sequencing reads that mapped to more than 3000 genes were used for subsequent statistical analyses. Differentiating genes between term and preterm samples were identified using a quantile-adjusted conditional maximum likelihood method, a generalized linear model (GLM) likelihood ratio test, and a quasi-likelihood F-test implemented in R using the edgeR package.
RT-qPCR Sample Analysis
Raw Ct values were quantified in absolute terms. Absolute quantification estimated the transcript counts contained in each sample based on cycle thresholds for known quantities of ERCC (
Multivariate Random Forest Modeling
Recursive feature selection and model construction were performed in R using the caret package. Longitudinal data was smoothed using a 3-week centered moving average and divided into a 21 patient training set and a 10 patient validation set. Model selection was performed using 10-fold cross validation repeated 10 times.
Expected Delivery Date Estimation
Expected delivery dates were derived from random forest model predictions. Longitudinal data for this application were not smoothed using a centered moving average. For any given sampling period (second trimester (T2), third trimester (T3), or both (T2&T3), time to delivery estimates were shifted to a specified reference time point and then averaged using the median to establish an expected delivery date.
Preterm Biomarker Candidate Selection and Validation
Absolute RT-qPCR values were normalized using a modified multiple of the median approach as applied in Rose and Mennuti (Fetal Medicine, West J Med., 1993; 159:312-317, incorporated herein by reference) that is both time and epidemiologically invariant, allowing for consistent comparisons across cohorts of different ethnicities. At-term patient medians were quantified by trimester on a cohort level for each gene. Biomarker discovery was performed using the combined criterion of an effect size and significance value threshold calculated using Hedges' g and the Fisher exact test, respectively, as described in Sweeney et al. (J. Pediatric Infect. Dis. Soc., 2017, doi: 10.1093/jpids/pix021, incorporated herein by reference). Genes were considered significantly different between cohorts using an effect size threshold of 0.8 and a false discovery rate (FDR) of 5%. Candidate gene biomarkers were then tested in unique combinations of 3 to estimate their ability to detect both true and false positives. Combinations with a true positive rate of greater than 0.75 and a false positive rate less than 0.05 were selected for further validation using an independent cohort. The ROC curve was based on the fraction of biomarker combinations where all genes showed a fold increase of at least 2.5 over median expression.
We performed a high time-resolution study of normal human development by measuring cfRNA in blood from pregnant women longitudinally during each week of pregnancy. cfRNA provides a window into the phenotypic state of the pregnancy by providing information about gene expression in fetal, placental and maternal tissues. Koh et al. described using tissue-specific genes for direct measurement of tissue health and physiology, and that these measurements are concordant with the known physiology of pregnancy and fetal development at low time resolution (Koh et al. PNAS, Vol. 111, 20:7361-7366, (2014), incorporated herein by reference). Analysis of tissue-specific transcripts in the instant samples enabled us to follow fetal and placental development with high resolution and sensitivity, and also to detect gene-specific response of the maternal immune system to pregnancy. The data from the present study establishes a “clock” for normal human development and enables a direct molecular approach to establish time to delivery and gestational age using nine placental genes. We demonstrate that cfRNA samples from both the second and third trimesters of pregnancy can predict expected delivery date with comparable accuracy to ultrasound, creating the basis for a portable, inexpensive dating method.
We recruited 31 pregnant Danish women from the Danish National Biobank, each of whom agreed to give blood on a weekly basis, resulting in 521 total plasma samples to analyze (
Cell-free RNA was isolated from each of the Denmark cohort individuals blood samples as set forth in Example 1. RT-qPCR assays were performed on the isolated cfRNA essentially as set forth in Example 1. A primer pair for each of the genes set forth in
Gene-specific inter-patient monthly averages±standard error of the mean (SEM) were plotted over the course of gestation (
The results of the gene expression assays motivated us to apply a machine learning approach in order to build a model, which would predict gestational age or time to delivery from cfRNA measurements. We used a random forest model and were able to show that a subset of nine placental genes provided more predictive power than using the full panel of measured genes (
We also built a separate model to predict gestational age (as estimated by ultrasound) and using the same nine placental genes, the model performed comparably well both on training (r=0.91, P<2.2×10−16) and validation data (r=0.90, P<2.2×10−16) (
The random forest model selects placental genes as most predictive of time from sample collection until delivery and gestational age. Although several of these genes show similar time trajectories, their detection rate early on pregnancy varies, suggesting that redundancy may improve accuracy at early time points, when both placental and fetal cfRNA are low and lead to drop-out effects. As cfRNA increases during gestation, the accuracy of the model improves. This is in contrast with the efficacy of ultrasound dating, which relies on a constant fetal growth rate, an assumption that deteriorates over time (Savitz et al. 2002; Papageorghiou et al. 2016).
Further investigating drivers of the model reveals markers with known roles during pregnancy. CGA and CGB, the two main model drivers together with CAPN6, behave differently from other genes in the model. CGA and CGB are the two subunits of HCG, known to play a major role in pregnancy initiation and progression and involved in trophoblast differentiation (Jaffe et al. 1969). The trend observed for these two genes is compatible with what is known from protein levels during pregnancy (Cocquebert et al. 2012). Free CGB and PAPPA are also used as biochemical markers for at risk of Down Syndrome in the first trimester (Wald and Hackshaw 1997), and other genes selected by the model are related to trophoblast development (e.g., LGALS14, PAPPA).
We then used our model to estimate expected delivery date from samples taken during the second, third, or both trimesters (
Prior studies report that under normal circumstances it is possible to determine the week in which a woman may deliver with 57.8% accuracy using ultrasound and 48.1% using LMP (Savitz et al. 2002). Our results are not only comparable to ultrasound measurements at a fraction of the cost but also use a method that is more easily ported to resource challenged settings.
For gestational age prediction, we trained several distinct models on subpopulations of women (i.e., nulliparous or multiparous women, women carrying male or female fetuses) to determine the importance of the 9 genes that compose the transcriptomic signature identified. Training 4 distinct models for women carrying male or female fetuses and nulliparous or multiparous women revealed that 2 of the 9 genes identified in the main text were sufficient to predict time to delivery for women carrying male (CGA, CSHL1) (Root mean squared error (RMSE) of 5.43 and 4.80 in the second and third trimesters respectively) or female (CGA, CAPN6) fetuses (RMSE of 5.58 and 4.60 in the second and third trimesters respectively) and multiparous (CGA, CSHL1) women (RMSE of 5.22 and 4.56 in the second and third trimesters respectively). However, all 9 genes were necessary to predict time until delivery for nulliparous women (RMSE of 5.09 and 4.50 in the second and third trimesters respectively), highlighting the importance of the transcriptomic signature identified. The nine transcripts used to predict gestational age were weighted by the model in the following order of importance (from most to least): CGA, CAPN6, CGB, ALPP, CSHL1, PLAC4, PSG7, PAPPA, and LGALS14. See TABLE 10.
In summary, we have discovered a molecular clock of fetal development which reflects the roadmap of developmental gene expression in the placenta and fetus, and enables prediction of time to delivery, gestational age, and expected delivery date with comparable accuracy to ultrasound. Our method has several advantages to ultrasound, namely cost and applicability later during pregnancy. At a fraction of the cost of ultrasound, cfRNA measurements can be easily ported to resource challenged settings. Even in countries that regularly use ultrasound, cfRNA presents an attractive, accurate alternative to ultrasound, especially during the second and third trimesters, when ultrasound predictions deteriorate to 15 (T2) or 27 (T3) day estimates of delivery (Altman and Chitty 1997). We expect that this clock will also be useful for discovering and monitoring fetuses having congenital defects that can be treated in utero, which represents a rapidly growing part of maternal-fetal medicine.
While the first generation “clock” model is able to predict gestational age and time of delivery for a normal pregnancy, we were also interested in testing its performance on preterm delivery. We therefore used two separately recruited cohorts from communities at high risk for premature delivery recruited at the University of Pennsylvania and the University of Alabama at Birmingham to test performance on preterm pregnancies (see,
To further investigate this question and develop a second generation “clock” model capable of predicting preterm delivery, we performed RNAseq, essentially as set forth in Example 1, on cfRNA obtained from plasma samples from term (n=7) and preterm (n=9) women collected from one of the preterm-enriched cohorts (Pennsylvania) (see,
Analysis of this RNAseq data suggested that nearly 40 genes could separate term from preterm with statistical significance (p<0.001) (see,
We then created a PCR panel with the highest scoring candidate preterm biomarkers and other immune and placental genes. We confirmed that the differential expression observed in RNAseq was also observed with this qPCR panel (
The top ten genes from this panel (CLCN3, DAPP1, POLE2, PPBP, LYPLAL1, MAP3K7CL, MOB1B, RAB27B, RGS18, TBC1D15) (FDR 5%, Hedge's g≥0.8) (
When used in combination, these ten genes also showed successful validation in an independent preterm-enriched cohort from Alabama, accurately classifying 4 out of 6 preterm samples (66%) and misclassifying 3 out of 18 at-term samples (17%) (see,
Moreover, this independent validation cohort shows that it is possible to discriminate preterm from term pregnancy up to 2 months in advance of labor with an AUC of 0.74 (
In subsequent refinements we determined that one woman in the cohort experienced induced preterm birth due to preeclampsia rather than spontaneous preterm birth We removed the data points associated with her plasma sample. Rerunning the analysis with this sample removed yielded 7 transcripts (CLCN3, DAPP1, PPBP, MAP3K7CL, MOB1B, RAB27B, RGS18) as opposed to 10, that when used in combinations of 3 produced a true positive rate of greater than 75% and misclassified less than 5%.
As described in Example 7, below, we identified several subcombinations of the 7 transcripts that may be used to determine a woman's likelihood or risk of preterm delivery. Thus, in some approaches one or more of the following panels is used to assess the likelihood of full-term, or preterm, delivery: (1) RGS18; DAPP1; PPBP; (2) RGS18; RAB27B; PPBP; (3) RGS18; MOB1B; PPBP; (4) RGS18; PPBP; MAP3K7CL; (5) RGS18; PPBP; CLCN3; (6) DAPP1; RAB27B; PPBP; (7) DAPP1; MOB1B; PPBP; (8) DAPP1; PPBP; CLCN3; (9) RAB27B; MOB1B; PPBP; (10) RAB27B; PPBP; MAP3K7CL; (11) RAB27B; PPBP; CLCN3; (12) MOB1B; PPBP; MAP3K7CL; and (13) MOB1B; PPBP; CLCN3.
We found that PPBP, DAPP1, and RAB27B were all individually elevated in women who delivered preterm in both the Pennsylvania and Alabama cohorts (FDR≤5%, Hedge's g≥0.8), demonstrating the robustness of their effect. The ranking the weight order (from highest to lowest) is RAB27B>PPBP>DAPP1>RGS18>(MOB1B, MAP3K7CL, and CLCN3).
In summary, we have discovered and validated a set of biomarkers which enables prediction of time to delivery for patients at risk of preterm delivery. Furthermore, our preterm delivery model suggests that the physiology of preterm delivery is distinct from normal development, forming the basis for the first screening or diagnostic test for risk of prematurity.
Seven transcripts of interest RAB27B, PPBP, DAPP1, RGS18, MOB1B, MAP3K7CL, CLCN37 can be grouped in 35 unique combinations of genes. We filtered those combinations using the criterion of 75% true positive rate and less than 5% false positive rate. This yielded 13 combinations shown in TABLE 11. We generated an ROC curve to determine the which combinations predict risk of delivering preterm.
Each of these 13 combinations of 3 genes may be used as a panel for assessing risk of preterm delivery. Thus, in some embodiments a panel comprising one or more of the following combination of genes is used to determine of the following panels Thus, in some approaches a panel comprising one or more of the following combinations of genes is used to assess the likelihood of full-term, or preterm, delivery: (1) RGS18; DAPP1; PPBP; (2) RGS18; RAB27B; PPBP; (3) RGS18; MOB1B; PPBP; (4) RGS18; PPBP; MAP3K7CL; (5) RGS18; PPBP; CLCN3; (6) DAPP1; RAB27B; PPBP; (7) DAPP1; MOB1B; PPBP; (8) DAPP1; PPBP; CLCN3; (9) RAB27B; MOB1B; PPBP; (10) RAB27B; PPBP; MAP3K7CL; (11) RAB27B; PPBP; CLCN3; (12) MOB1B; PPBP; MAP3K7CL; and (13) MOB1B; PPBP; CLCN3.
We have tested for the effect of BMI on circulating cfRNA levels using estimated transcript counts of GAPDH per milliliter of plasma and found no significant difference between underweight (BMI<18.5), normal weight (18.5≤BMI<25), overweight (25≤BMI<30), and obese (BMI≥30) individuals both before and after Bonferroni correction using a Wilcoxon rank sum test.
P-values for distinct tests of GAPDH levels before and after Bonferroni correction, respectively, were as follows: (1) underweight versus normal weight (P=0.58, 1), underweight versus overweight (P=0.12, 0.80), underweight versus obese (P=0.26, 1), normal weight versus overweight (P=0.06, 0.35), normal weight versus obese (P=0.16, 0.95), and overweight versus obese (P=0.72, 1). Similar results were obtained for placental-specific cfRNAs such as CAPN6, CGA, and CGB.
All comparisons were done within cohorts so that differences in BMI distribution between cohorts were not confounding.
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While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure, that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims. The invention is therefore not to be limited to the exact components or details of methodology or construction set forth above. Except to the extent necessary or inherent in the processes themselves, no particular order to steps or stages of methods or processes described in this disclosure, including the Figures, is intended or implied. In many cases the order of process steps may be varied without changing the purpose, effect, or import of the methods described.
All publications and patent documents cited herein are incorporated herein by reference as if each such publication or document was specifically and individually indicated to be incorporated herein by reference. Citation of publications and patent documents (patents, published patent applications, and unpublished patent applications) is not intended as an admission that any such document is pertinent prior art, nor does it constitute any admission as to the contents or date of the same.
This application is a national phase application of PCT Application No. PCT/US2018/057142, filed Oct. 23, 2018, which claims benefit of U.S. Provisional Application No. 62/576,033 (filed Oct. 23, 2017) and No. 62/578,360 (filed Oct. 27, 2017), each of which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/057142 | 10/23/2018 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62576033 | Oct 2017 | US | |
| 62578360 | Oct 2017 | US |
