Heterozygosity for IL23R p.Arg381Gln confers a protective effect not only against Crohn's disease but also ulcerative colitis

Background A recent study reported that a non-synonymous single nucleotide polymorphism (rs1 1209026, p.Arg381Gln) located in the IL23R gene is a protective marker for inflammatory bowel disease. Aim To analyse the frequency of p.Arg381Gln in three independent European inflammatory bowel disease cohorts and to evaluate how this variant influences disease behaviour. Methods We assessed a European cohort of 919 inflammatory bowel disease patients and compared the IL23R p.Arg381Gln genotype frequency with 845 healthy controls. Inflammatory bowel disease patients originated from Germany [Crohn's disease (CD): n = 318; ulcerative colitis (UC): n = 178], Hungary (CD: n = 148; UC: n = 118) and the Netherlands (CD: n = 157). Ethnically matched controls were included. We performed subtyping analysis in respect to CARD15 alterations and clinical characteristics. Results The frequency of the glutamine allele of p.Arg381Gln was significantly lower in inflammatory bowel disease patients compared with controls in a pooled analysis of all three cohorts (P < 0.000001) as well as in the individual cohorts (Germany: P = 0.001, Hungary: P = 0.02 and the Netherlands: P = 0.0002). The p.Arg381Gln genotype distribution was similar between CD and UC. We did not observe either statistical interactions between p.Arg381Gln and CARD15 variants or any significant associations between p.Arg381Gln genotype and subphenotypes. Conclusions The p.Arg381Gln IL23R variant confers a protective effect against both CD and UC, but does not determine disease phenotype.