Linkage analysis tests for co-segregation of a chromosomal region (or a marker) with a particular trait or phenotype. Such traits or phenotypes may include diseases caused by or associated with a particular genetic defect or defects or which create a predisposition or susceptibility to disease. Determining the association (e.g., cosegregation) of such markers and disease traits and characterization of those markers can ultimately result in the identification of therapeutic targets which through various interventions can result in a cure or the ameliorization of the disease trait.
The current state of the art includes mathematical tools for associating markers with genetic traits in single studies and does not include a method for mathematically associating markers to genetic traits with the use of gene scores from multiple studies and thus does not take advantage of abundance of data which may be brought to bear in attempting to identify and characterize specific genetic markers that play a role in disease or predisposition to disease. Thus, there remains a need for new methods which allow researchers to combine information from multiple studies to better determine which markers are most likely to be good targets for therapeutic intervention.
The present invention provides a method which utilizes genomic markers from whole-genome scans or gene association studies from one or more related disease/genetics publications, and a mathematical algorithm which allows the determination of the possible single or average contribution of any gene to the marker scores. The ability to use multiple data sets such as those found in more than one publication allows the method to both consider a broader pool of genes as well as more accurately determine which of the genes are linked to a particular trait. The method can be used for any genetic scan of any disease or trait and can be used to score any gene or genomic locus. Further the method can be implemented on multiple studies on multiple diseases with similar backgrounds.
The method produces several novel scores to rank the markers according to their linkage to a trait. Further, the method is able to use both a non-probabilistic and a probabilistic method to rank the markers. The method also combines non-probabilistic and probabilistic rankings. The scores the method provides are Average Contribution Scores for data in both a log-odds and an association p-value format. Further the method provides probability-weighted Average Contribution Score for data in both a log-odds and an association p-value format. Additionally, the method provides Evidentiary Scores that provide a researcher an indication of the validity of the contribution scores. The scores provide rankings that help a researcher determine those genes that are the most promising to send through a more rigorous, time-consuming and expensive in vitro and/or in vivo trial program.
The method is also directed to a computation system useful in the execution of the methods of the present invention. The computation system includes an input module to receive inputs of various genomic data and an output module to output the results of its calculations. A computation module performs the calculations. The results include scores for markers associated with genetic diseases or traits. A researcher also interactively uses the system in various manners including inputting data and changing parameters.
a and 8b are graphs of secreted proteins ACS scores for autoimmune diseases (RA, MS, PS, SLE).
System
The system 101 includes the following interconnected modules: a computation module 102, an input module 103, output module 104, data store module 105, and a display module 106. The computation module receives data inputs from the input module 103. The computation module then obtains the method to execute from the data store module 105. Once the computation module 102 receives both the data inputs and method, it executes the method on the data inputs and outputs the results to the output module 104. The output module 104 then provides and reports the results to other modules such as keyboard/display module 106 so that the user of the system may review the results. The system also receives commands, such as algorithm initiation and parameter setting, from the user through keyboard/display module 106. The parameters affect the execution of the methods including files that store genomic mapping data.
The system also allows for correction, augmenting or enhancement of the methods performed. The user merely updates the methods stored in data store module 105 in order to change the method executed by the system 101. The update, for instance, includes the revising of software in data store module 105 to reflect the updated method.
Methods
There are three algorithms described below. The algorithms can be implemented with any genome version, public or private. These genomic data include the public genome versions available from public sources like the National Institute of Health or private genome versions provided by companies such as Celera. One algorithm is for calculating average contribution scores and another is for calculating probability weighted average contribution scores. The last algorithm combines the scores generated by the first two algorithms into a third score.
Algorithm for Calculating Average Contribution Score for Sequence Features from Genome-Wide Scans and the Resulting-LOD (Log-Odds) Scores
The algorithm begins with genomic association data obtained from a study or studies of genome-wide scans that score markers according to probabilistic studies of genomic linkage to traits, such as a disease 201. The algorithm utilizes a collection of studies on a single disease, or a collection of studies on multiple different but related diseases, such as a set of autoimmune diseases. The data from the studies represent markers of genomic locations (markers) and a probability score attached to each marker. The type of score depends on the type of study done. However, these probability-based scores all represent, directly or indirectly, the probability of any marker (genomic locus) being associated with the manifestation of a disease within a studied population. Generally, the scores will be included in the studies themselves. However, a researcher using the system and method may also calculate the scores from information in a published study, from other laboratory generated data, from other sources of genomic data, or any combination thereof.
For instance, the probability scores include: (1) the log-odds (LOD) likelihood of a genomic region associated with a disease, and (2) the association p-value (ASN) from regional scans. These scores result from calculations of genome-wide scan data in the case of LOD scores, or association scans in the case of association scores. An example of a genome-wide scan is given in Kong A, Cox N J (1997) Allele-sharing models: LOD scores and accurate linkage tests. Am J Hum Genet 61:1179-88. Other methods that express the probability of a genomic location being associated with a disease also can be used with the algorithm by replacing the LOD or ASN scores with the other method's corresponding score. The rest of the steps of the algorithm would remain relatively unchanged.
The LOD scores determined from the studies are represented as SLOD 202. The ASN scores determined from the studies are represented as SASN. The SASN are derived from associated p-values pASN with the equation SASN=(1−pASN) 203. The pASN is determined by reviewing the studies. The p-value of association as reported in the literature from association studies can also be converted into a probability score S when normalized to one. In the cases where association scores are not presented as p-values, the association scores are converted into p-values and then calculate for S. The probability scores SLOD and SASN, as they are associated with specific genetic/genome location markers, are then tabulated with the associated marker and its genomic position and recorded 204.
Features are then selected 205. The features include any sequence element of interest, including genes, transcriptional regulatory regions, untranslated regions and intergenic regions. A feature locus is the genomic location that corresponds to a feature.
The features are located on the same chromosome as the markers that are selected 206. Further refinement on selecting features includes selection of features in the vicinity of each marker or markers, or the selection of a certain class of feature in the vicinity of the marker or markers. If selection is based on vicinity to a marker(s), the selected vicinity may be within 10 Mb\10 cM of a marker, or broadly based on a feature locus sharing the same chromosome as a marker. As the range of the selection is enlarged, asymptotic effects of the algorithms cause the features far from the markers to have a limited effect.
The distance between the feature loci and the scored marker is calculated 207. The distance calculation may be performed using any relevant metric to calculate distance between genetic loci including: radiation hybrid, genetic and physical distances.
As a first example, when using physical (nucleotide) distance, the method divides the marker's score S by the selected distance of the feature locus to that of the marker locus 208. The result is the contribution score (CS) of that feature's position versus one particular marker position. The algorithm then samples from all markers in the feature's vicinity or chromosome. The average score for that feature against all markers is the ACS, average contribution score for nucleotide distance.
In equation (1), d1 is the feature distance to the scored markeri in nucleotides and Si is the probability score.
As a second example, the algorithm can use the average reported recombination rates between the marker and the feature from public-domain sources to transform the nucleotide distance into genetic distance in centiMorgans (cM). This allows for normalization of marker-feature recombination rates and provides a genetic distance between the two 210. This ACS represents the average genetic distance in cM and is described in equation (2).
In equation (2) the average recombination rate (Ri) is calculated between a feature and LOD marker i. Further, the average recombination rate in cM/Mb and di is the feature distance to markeri as reported in Mb. The ACS score can be used like the nucleotide ACS score to determine the relative rankings for possible contribution of sequence feature elements and markers 211.
The relative ACSLOD and ACSASN can differ for the same genes, as both scores reflect different approaches to studying populations and probability-scoring mechanisms, and as such may not be directly comparable. Therefore, both scores should be calculated separately from the different data sources.
The above algorithm can be used stand-alone, or as part of a pipeline or other process to score genes according to additional criteria such as literature or expression data.
Algorithm for Calculating Probability-Weighted Average Contribution Score (PACS) for Sequence Features from Genome-Wide Scans and the Resulting Scores
The algorithm begins with the collection of a series of results on genetic studies of disease where the results relate genomic locations to genetic scores associated with a trait (i.e. genomic association data), such as a disease, within a population 401. There are two main types of scores for genetic markers, log-odds likelihood and association scores.
A log-odds (LOD) score is the likelihood of a marker being associated with selected physiological manifestations such as traits, diseases or other biological condition. These data represent LOD scores per genomic sequence markers used in the study or studies. These scores result from genome-wide scans (yielding linkage, LOD (log-odds) scores) as given for instance in the Kong et al. paper referenced below. The LOD scores are reported as numerical values.
Association scores result from genetic association studies such as those obtained from high-resolution scans of genomic regions. The association scores are reported as p-values with decreasing numbers indicating increasing probability.
Numerical LOD 402 or association 403 scores for these markers are obtained from the study or studies. The studies can be focused on one disease type, or several disease types that are believed to be associated in some way, such as a collection of results on different autoimmunity diseases, or several studies on metabolic diseases. LOD and association scores are separate types of scores and processed separately by the algorithm. The algorithm tabulates these marker scores along with the marker name, the score type (LOD or association), and the marker's obtained genomic position, using a mapping program such as BLAT or BLAST. These steps 402, 403 yield j LOD scores and k association scores.
As described above, genomic features include any sequence element of interest, including genes, transcriptional regulatory regions, untranslated regions and intergenic regions. The algorithm scores those features to determine the likelihood that they contribute to the LOD or association scores as determined from the genetic studies. The algorithm also maps all features to the genome using a mapping program such as BLAT or BLAST 404.
The algorithm then iterates over the mapped features the following calculations:
For instance, if a genetic distance between a feature and a disease marker is calculated as 2.7 centiMorgans using the Decode map of the Kang reference as a metric, the recombination likelihood value used in the calculation is: 2.7/100=0.027. The conversion to recombination likelihood is performed in a single or multiple steps. For example recombination rates can be utilized to convert between nucleotide distance and genetic distance. The genetic distance can then be converted to the recombination likelihood or other metric.
Genetic distances between the feature and the marker that are greater than 100 centiMorgans may be omitted due to asymptotic effects and in one embodiment are left from the calculation 409. The LOD score, as a log-odds score, is left intact for the calculation so that SLOD=LOD score, as determined from the studies. On the other hand, the association score, as a p-value (pasn), is defined as Sasn=(1−pasn).
For the feature-marker pair, the algorithm calculates the probability that this feature locus and the marker will NOT recombine relative to one another 410. This probability, the Plink, is given by equation (4).
Plink=(1−rl) (4)
In equation (4), rl is the recombination likelihood (rl) between the disease marker and the feature locus. In the case where rl is very small, Plink will be close to one, and when rl is large, Plink will decrease towards zero. Therefore, Plink represents a probabilistic adjustment to the LOD score based on genetic distance.
The algorithm in turn now multiplies Plink with that marker's LOD or association score (S) as described in equation (5). This value is defined as the probability-weighted contribution score (PCS), which represents a probability-adjusted score (LOD or association score) for the feature versus disease marker i of j total markers.
PCS=PlinkSi (5)
The algorithm further identifies PCSLOD for the probability-weighted contribution LOD score, and PCSASN for the probability-weighted contribution association score 311. The CSLOD and CSASN are considered separate types of scores and are kept independent of one another during the derivation.
The algorithm continues to sample from the N LOD-scored disease markers, and the M association-scored disease markers in the feature's selected vicinity. The algorithm keeps the LOD and association score calculations distinct and separate. At the end of the calculation, the algorithm provides two independent groups of data for each feature. It creates N probability-weighted LOD contribution scores (PCSLOD) for this single feature. It also creates M probability-weighted association contribution scores (PCSASN) for this single feature.
From the LOD and association scores, the algorithm produces five score values, the probability-weighted average contribution score (PACS) and the evidentiary score (ES) which is the non-normalized PACS score 412:
The PACS (probability-weighted average contribution score) is an averaged PCS score, and represents the feature's score in terms of LOD or association, as a contribution from each disease marker. The PACS score represents the average adjusted LOD or association score. The algorithm provides the relative rankings of PACS scores. The relative ranking of the PACS scores allows a user to determine those features that may best contribute to the LOD or association scores in the arrangement of markers from the genetic studies. Specifically, the algorithm reports the PACSLOD and PACSASN scores. The PACSLOD and PACSASN scores represent different types of data that can be difficult to combine. However, both can simultaneously be used in a selection process to score or rank features of interest as both provide information on the likelihood a given gene will be a good candidate for further study.
While calculating “probability-weighted average contribution score” (PACS) for a single feature of equation (6) Si is the marker i's LOD or association score, rli is the recombination likelihood between the feature and the marker i in Morgans, and n is the number of markers used to calculate the PACS.
The ES is the evidentiary score. It is used as a relative score, to rank those features that show the “best evidence” for association with disease(s). Also one can combine ESLOD and ESASN into ESCMB as combined evidentiary scores, which represent the sum total of evidence that a feature may contribute to the genetic scores of disease markers. The ES score provides the researcher with an indication as to the reliability of the associated ACS and PACS scores.
While calculating the “evidentiary score (ES)” for a single feature, the Si is the marker i's LOD or association score, and rli is the recombination likelihood between the feature and the marker i in Morgans.
The PACS or ES can be used alone or together to calculate the relative ranking of features to select them for further study, exploration, and discovery. The above algorithm can be used stand-alone, or as part of a pipeline or other process to score genes with additional criteria such as literature or expression data.
Algorithm for Calculating a Combined Contribution Score
After calculating the ACS and PACS scores for association scores and p-values, the method allows for these scores to be combined in a number of different methods. One method to combine the scores is to first determine the rankings generated for the markers by the ACSLOD, ACSASN, PACSLOD and PACSASN scores. Then, ACSCMB (ACS Combined) and PACSCMB (PACS Combined) scores are generated by re-ranking the markers based on the average ranking of the two ACS and two PACS scores, respectively. Another method of combining the scores would be to generate new ranking based on weighted ranking of the two ACS and two PACS scores. The weighting could be based on the generated ES scores.
As an example, a subset of the genomic compliment called the GPCRs, the G-Protein Coupled Receptors, were examined using the algorithm describe above. The scores used by the algorithm were generated from the literature. An example of a portion of the scores used by the algorithm is shown in
After ranking the ACSLOD scores of the GPCRs, the top five non-olfactory receptor hits found in order of relative score were:
1. Proteinase activated receptor 2 precursor (PAR-2)
2. Human seven transmembrane signal transducer PGR1
3. Probable G protein-coupled receptor GPR35
4. Proteinase activated receptor 1 precursor (PAR-1) (Thrombin receptor)
5. Putative G-protein coupled receptor, EDG6 precursor
In the example, the literature was mined for studies related to autoimmune diseases (with both LOD and p-values). Then a list of genomic regions on Celera R27 associated with four autoimmune diseases (MS, PS, SLE and RA) was assembled.
Further, only markers were selected that possessed a whole-genome scan LOD score of greater than 1.0 (with some exceptions made for values below but very close to 1.0), or actual genetic association P-values less than 0.005. However, all regions even with sub-optimal scores were retained, and all LOD or association scores are paired with the marker information to allow for scoring choices and future meta-analyses.
The example used the following papers to determine the original scores.
As mentioned above, Par-2 was found to have the highest ACSLOD scoring receptor. PAR-2, is a receptor implicated in nociception and inflammatory processes. This receptor has recently (Ferrell, infra., January 2003) been validated in the literature as a key inflammation target. The algorithm scored PAR-2 as possibly contributing to MS and RA genetic marker LOD scores. Thus, our algorithm appropriately scored this receptor as being linked to RA.
G-Protein Coupled Receptors Data Output
The data from the G-Protein Coupled Receptor study are provided and reported to a researcher in several useful formats. The first type of statistical data output is a table such as Table 1.
Table 1 is a partial exemplary chart of scores calculated and reported by the system and method of the invention for G-Protein Coupled Receptor ACS scores for autoimmune diseases (RA, MS, PS, SLE). This exemplary chart provides the information for the proteins (features) in the study with the twelve highest ACSLOD scores. The chart includes for each protein: mRNA_ID, gene location, associated diseases with markers cited for the gene location, the name of the markers in the literature, chromosome, ACSLOD score, the number of LOD-scores used in the method's calculations, ACSASN score, and the number of association scores used in the method's calculation. Further, separate columns can be provided for the other scores and statistics, such as the PACS and ES scores, produced by the methods.
Secreted Proteins Data Output
In the case of performing a study on secreted proteins,
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US05/45286 | 12/14/2005 | WO | 6/20/2007 |
Number | Date | Country | |
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60637914 | Dec 2004 | US |