Background: Recent genomic surveys have identified IL23R and IL12B as susceptibility loci for inflammatory bowel disease (IBD). Our aim in the present study was to ascertain whether the IL23R and IL12B associations with IBD are also observed in our population, and to analyze possible genetic interactions between polymorphisms at IL12B and IL23R, ligand and receptor, respectively.
Methods: In all, 707 IBD patients (344 with Crohn's disease and 363 with ulcerative colitis) and 547 healthy controls from the same ethnic origin (Caucasian Spaniards) were included in the present study. Two single nucleotide polymorphisms (SNPs) in IL23R (rs7517847 and rs11209026) and 2 in IL12B (rs3212227 and rs6887695) genes were analyzed by TaqMan technology. Genetic frequencies were compared with a chi-square test. Interaction between genes was analyzed by case-only comparisons.
Results: The data show an association of both IL23R SNPs with overall IBD (statistically stronger, rs7517847; odds ratio [OR] = 0.79, 95% confidence interval [CI]: 0.67-0.94, minor allele frequencies: 0.355 in IBD patients versus 0.410 in controls; P = 0.005), somewhat stronger in Crohn's disease (OR = 0.74, 95% CI: 0.61-0.91) than in ulcerative colitis (OR = 0.84, 95% CI: 0.69-1.03). IL12B rs6887695 showed a weak association with IBD (OR = 1.24, 95% CI: 1.04-1.47, minor allele frequencies: 0.375 in IBD patients versus 0.326 in controls, P = 0.012), stronger in UC (OR = 1.31, 95% CI: 1.07-1.60, P = 0.007). No statistically significant differences were apparent when patients were stratified according to clinical characteristics. No interaction was observed between any of the polymorphisms studied at IL12B and IL23R.
Conclusions: Our study confirms the association of IL23R and IL12B with IBD in the Spanish population, but no interaction between either loci could be detected.