Given that IL-23, a cytokine involved in Th17 cell differentiation, activates not only STAT3 but also to a lesser degree STAT4, we next investigated potential epistasis with the IBD susceptibility gene IL23R. Analysis for 10 SNPs in the IL23R region which have previously shown to significantly influence CD susceptibility [14] found weak interactions between the STAT4 SNPs rs8179673, rs7582694 and rs10174238 with the coding IL23R SNP rs11209026 = p.Arg181Gln in CD (Supplemental Table S6) but significance was lost after correction for multiple comparisons. Here, IL23R is linked to inflammatory bowel disease.