Abstract

Gene-set analysis has been proposed as a powerful tool to deal with the highly polygenic architecture of complex traits, as well as with the small effect sizes typically found in GWAS studies for complex traits. We developed a tool, Joint Association of Genetic variants (JAG), which can be applied to Genome Wide Association (GWA) data and tests for the joint effect of all single nucleotide polymorphisms (SNPs) located in a user-specified set of genes or biological pathway. JAG assigns SNPs to genes and incorporates self-contained and/or competitive tests for gene-set analysis. JAG uses permutation to evaluate gene-set significance, which implicitly controls for linkage disequilibrium, sample size, gene size, the number of SNPs per gene and the number of genes in the gene-set. We conducted a power analysis using the Wellcome Trust Case Control Consortium (WTCCC) Crohn’s disease data set and show that JAG correctly identifies validated gene-sets for Crohn’s disease and has more power than currently available tools for gene-set analysis. JAG is a powerful, novel tool for gene-set analysis, and can be freely downloaded from the CTG Lab website.

Highlights

  • The advent of genome-wide association (GWA) analysis has resulted in the identification of a large number of human disease genes and disease-related genetic variants for several traits such as type-2 diabetes, macular degeneration and Crohn’s disease [1,2,3,4]

  • We removed the single nucleotide polymorphisms (SNPs) with a minor allele frequency (MAF) 5% and 3321 SNPs that were assigned to chromosome 0 by Wellcome Trust Case Control Consortium (WTCCC)

  • We showed that using a standard dataset Joint Association of Genetic variants (JAG) correctly identifies validated gene-sets and has more power than currently available tools for gene-set analysis

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Summary

Introduction

The advent of genome-wide association (GWA) analysis has resulted in the identification of a large number of human disease genes and disease-related genetic variants for several traits such as type-2 diabetes, macular degeneration and Crohn’s disease [1,2,3,4]. Several software tools for gene-set analysis have been proposed, such as GATES [16], ALIGATOR [12], the set-based test in PLINK [17], GENGEN [18] and GRASS [19], and see the review by Wang et al [20] These tools differ on several aspects such as the type of input data required (raw data versus summary statistics), using a self-contained or competitive test and the actual alternative hypothesis being tested [20]. Available tools for gene-set analysis do not necessarily include both self-contained and/or competitive tests, do not always accommodate the use of custom gene-sets and some of them do not optimally make use of the multivariate evidence of association of all genetic variants in a gene-set. We show that JAG correctly identifies previously validated gene-sets for Crohn’s disease and is more powerful than any of the other tools tested

Implementation
SNP to Gene Annotation
Competitive Test
Application and Performance of JAG
Genes and Canonical Pathways for Gene-Set Analysis
Comparison of JAG Performance with other Tools
Type I Error Analysis
Relative Power Indication Analysis
Type I Error Analysis—Gene-Set Based Test
Power Analysis—Gene-Set Based Test
Type I Error Analysis—Gene-Based Test
Power Analysis—Gene-Based Test
Conclusions

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