Genome-wide epistasis screening for Crohns’ disease

Genome-wide association (GWA) studies of Crohn's disease have identified numerous genes. However, a substantial portion of the heritability of this disease remains unexplained. Some gene variants, not detectable via main effects GWA study, may manifest themselves only in interaction with other variants. To search for interacting genes involved in the regulation of Crohn's disease, we performed GWA epistasis screening in a large human cohort (1851 cases/2938 controls) belonging to the Wellcome Trust Case Control Consortium (WTCCC). All subjects were genotyped with the GeneChip 500K Mapping Array Set (Affymetrix chip). SNPs that passed our quality control (359,479 SNPs) were processed in Biofilter (a software package that looks for candidate epistatic genes contributing to disease risk) giving rise to 14,185 SNPs. Subsequent MB-MDR epistasis screening discovered four pairs of interacting SNPs on chromosome 4q35.1 and eight pairs on chromosome 11q23.2. The identified pairs of SNPs were confirmed with synergy-based measures. Notably, despite their mapping to the same genomic regions, the interacting SNPs were not in LD (r^2 < 0.5). Our findings support the idea of close chromosomal localization of two pairs of interacting genes that are involved in development of Crohn's disease.