P1200 Study of correlation between polymorphisms of vitamin D metabolism genes and perianal disease in Crohn's disease

Background Vitamin D (VD) is a fat-soluble vitamin essential for calcium homeostasis and that acts at the extraskeletal level. UVB skin exposure allows the synthesis of provitamin D. This undergoes a first hydroxylation in the leaver by the CYP2R1 enzyme and a second hydroxylation in the kidney by the CYP27B1 enzyme: active VD is obtained. VD is transported into the circulation by VDBP and exerts its activity in the target cells binding its VDR receptor. Finally, VD is inactivated by the renal enzyme CYP24A1. Perianal disease (pCD) is a severe phenotypic manifestation of CD that may present as perianal fistula, abscess, recto-vaginal fistula, or stenosis. Among the mechanisms involved in its pathogenesis we recognise local inflammation and intestinal microbiota alteration. Vitamin D (VD) seems to act on these elements. As there are currently no studies on this subject in the literature, the aim of this study is to evaluate the presence of an association between SNPs of genes coding for enzymes, transporters and receptors involved in the VD pathway and the occurrence of pCD in CD patients. Methods The study was carried out on the biological samples of 206 patients with CD, including 34 with pCD, who were followed up at the inflammatory bowel disease clinic in Turin, Italy. Through the use of Real-Time PCR, the genotype distribution of the following genes were assessed: VDR, CYP27B1, CYP24A1, and GC. For the association study, chi-square test was performed with calculation of p value and, when significant, logistic regression and calculation of OR with 95% CI was performed. Results Studying the association between SNPs and the presence of pCD, the following results were obtained: BsmI p=0.0470 and Apal p=0.0251. For BsmI heterozygous genotype there was an OR=2.5 (95% CI 1.2-5.3) of developing perianal disease and p value=0.02, while for ApaI heterozygous there was OR=2.91 (95% CI 1.3-6.6) of presenting pCD, with p value=0.01. Conclusion In the literature, there are several studies examining the association between the heterozygous Aa genotypes of ApaI and Bb genotypes of BsmI and increased inflammatory markers. In addition, some studies suggest that these two genotypes represent a risk factor for some diseases, including multiple myeloma, systemic lupus erythematosus, and mild cognitive disorder. This study demonstrates for the first time an impact of polymorphisms of genes associated with the VD pathway in predicting the onset of pCD. Specifically, the presence of the heterozygous genotype of BsmI and ApaI significantly increases the risk. Future studies need to be performed in different and larger cohorts of patients in order to confirm these data.