Vitamin D receptor (VDR) is a member of the nuclear receptor family of transcription factors that plays an immunomodulatory role in the gastrointestinal tract through binding Vitamin D. Single-nucleotide polymorphisms (SNPs) in the VDR gene have been related to inflammatory bowel disease. Indeed, Crohn′s disease (CD) patients carrying the Taq I polymorphism in VDR gene run a higher risk of developing a penetrating behaviour. We analyse here the association between the VDR SNPs Taq I, Bsm I, Apa I and Fok I and the clinical characteristics of CD.
DNA was extracted from blood samples from 80 patients diagnosed with CD from the Hospital of Manises (Valencia). Four polymorphisms identified in the VDR gene (Bsm I, Fok I, Apa I and Taq I) were genotyped using PCR-RFLP. Clinical data for each patient, including the Montreal classification was collected. Statistical significance was done using contingency tables and measured by Chi-squared or Fisher test.
Results reveal a strong linkage disequilibrium between Apa I, Bsm I and Taq I polymorphisms. Apa I appears next to Bsm I and it is negatively associated with Taq I. The presence of at least a risk allele for Apa I is significantly associated with a stricturing behaviour in CD patients (P=0.014, Table 1), while the ancestral genotype (WT) of Apa I was significantly associated with a penetrating behaviour (P=0.062, Table 2). Finally, the presence of the risk genotype of Apa I is associated with a non-colonic location of the disease (P=0.059, Table 3). Fok I was not significantly associated with any of the parameters analysed.
Our results in CD patients reveal that the presence of the risk allele of Apa I in the VDR genotype is associated with a stricturing behaviour and tends towards a non-colonic location of the disease. This suggests that the analysis of this polymorphism may be useful for clinicians as a prognostic factor.