ApaI Polymorphism in the Vitamin D Receptor Gene Decreases the Risk of Perianal Fistulas in Crohn’s Disease

Background: Vitamin D, through the activation of its receptor (VDR), plays an immunomodulatory role in the gastrointestinal tract. Single-nucleotide polymorphisms (SNPs) in the VDR gene have been associated with Crohn’s disease (CD) risk, and patients carrying the TaqI polymorphism in this gene run a higher risk of developing a penetrating behavior. Aims: We analyzed the association of BsmI, ApaI, TaqI, and FokI SNPs in the VDR gene with the clinical characteristics of CD. Methods: Four polymorphisms identified in the VDR gene (BsmI, FokI, ApaI, and TaqI) were genotyped in blood samples from CD patients (n = 115) by using PCR-RFLP. The disease’s location and behavior and the presence of perianal fistulas were collected from each patient. Intestinal fibroblasts from ileal resections of CD patients (n = 10) were genotyped, and the expression of fibrotic and inflammatory markers was analyzed by RT-PCR. Results: The data reveal no association between any of the polymorphisms and CD risk. A strong linkage disequilibrium was detected between TaqI and both ApaI and BsmI, which in turn were strongly associated. Homozygosis or heterozygosis for the a allele of the ApaI SNP or b allele of the BsmI SNP was significantly associated with a lower risk of a penetrating behavior, while the aa genotype was associated with a lower risk of perianal fistulas. Fibroblasts carrying the aa genotype expressed lower levels of fibrotic and inflammatory markers. Conclusion: The aa genotype of the ApaI SNP in the VDR gene is associated with a lower risk of perianal fistulas in CD and a reduced expression of fibrotic and inflammatory markers in intestinal fibroblasts.