Vitamin D Receptor Gene Polymorphism in Type 1 Diabetes in South Indian Population

Pancreatic beta cell destruction in Type 1 diabetes (T1D) is a possible consequence of an intricate autoimmune crosstalk between environmental factors and genetic elements. The vitamin D receptor (VDR) gene apart from regulating insulin secretion from the pancreas, also functions as a mediator of immune response through vitamin D. These interplay mechanisms vary across studies and population groups. Therefore, the aim of this study is to explore the association between VDR gene polymorphisms and T1D among South Indian subjects. This was a single-centre, prospective, case-control study that included 150 T1D and 155 non-diabetic control participants. All the participants' blood samples were analysed for vitamin D levels. TaqMan real-time assays were used to analyse the FokI (rs2228570), BsmI (rs1544410) and TaqI (rs731236) polymorphisms. The levels of vitamin D were significantly lower in the T1D group than in the control group. A statistically significant variation in the genotype of VDR polymorphism BsmI was noted between T1D and controls, with the homozygous variant (AA) of BsmI rs 1544410 present more frequently in the T1D group (44%) compared to the control group (23.2%) (odds ratio [OR] = 2.265, 95% confidence interval [CI]: 1.380-3.719, p < 0.001). The frequency of the A allele of the BsmI polymorphism was also significantly higher in the T1D (p < 0.002). Analysis of haplotype showed that combinations T-A-T and C-A-T were statistically linked with susceptibility to T1D (p < 0.008 and p < 0.005, respectively). High linkage disequilibrium (LD) was found between TaqI and BsmI (D' = 0.71). Statistically significant differences were not encountered in genotype and allelic frequencies of VDR polymorphism of either FokI or TaqI. This study findings revealed that BsmI polymorphism in the VDR gene and particular haplotypes are possibly associated with susceptibility to T1D in the South Indian population.