Common variation in the vitamin D receptor gene and risk of inflammatory bowel disease in an Irish case-control study

Vitamin D may protect against the development of inflammatory bowel disease (IBD). Several preliminary studies in separate geographical locations suggest that these effects may be partly mediated by genetic variants of the vitamin D receptor (VDR). The data, however, are yet to be confirmed in large European cohorts. This study aimed to determine if common VDR polymorphisms affected IBD risk in an Irish population.

The study was based on a cohort of 1359 Irish participants. Frequencies of the common VDR gene polymorphisms rs2228570 (FokI), rs1544410 (BsmI), rs7975232 (ApaI), and rs731236 (TaqI) were determined using allele-specific PCR in a case-control analysis of 660 patients with IBD and 699 controls. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between these variants and risk of IBD.

There was no statistically significant effect observed on IBD risk for any of the four VDR polymorphisms tested. Furthermore, no significant differences were observed in susceptibility when the population was stratified by sex or IBD subtype (Crohn's disease or ulcerative colitis). Notably, however, there was an increased risk observed for both IBD and ulcerative colitis associated with heterozygote carriage of the FokI allele that approached significance (OR=1.21, 95% CI=0.95-1.53, P=0.12 and OR=1.36, 95% CI=0.98-1.89, P=0.06, respectively), this merits further investigation.

This study indicates that there is no major effect for common variation in the VDR gene alone on predisposition to IBD in the Irish population.