Association of VDR BsmI polymorphism and vitamin D status with osteoarthritis susceptibility

BACKGROUND: Osteoarthritis (OA) is a chronic degenerative joint disease influenced by genetic, environmental, and immunological factors. Vitamin D exerts immunomodulatory and anti-inflammatory effects through the vitamin D receptor (VDR), and genetic variation in the VDR gene may influence susceptibility to OA. However, data from Middle Eastern and Kurdish populations remain limited. OBJECTIVE: This study aimed to evaluate the association between serum vitamin D status and four common VDR gene polymorphisms (FokI, ApaI, TaqI, and BsmI) in Kurdish adults with knee osteoarthritis. METHODS: A hospital-based case-control study was conducted, including 100 OA patients and 100 healthy controls recruited in Erbil, Iraq. Serum vitamin D levels were measured biochemically, and VDR polymorphisms were genotyped using PCR-RFLP and sequencing. Association analyses were performed for polymorphic loci using univariate logistic regression. RESULTS: No allelic or genotypic variation was detected at the FokI (rs2228570), ApaI (rs7975232), or TaqI (rs731236) loci, indicating allele fixation in this population. In contrast, the BsmI (rs1544410) polymorphism exhibited significant variability. The AA genotype was significantly more frequent among OA patients than controls and was associated with increased odds of OA (OR = 2.26, 95% CI = 1.21-4.23; p = 0.006). CONCLUSIONS: The findings indicate that the VDR BsmI polymorphism is associated with knee osteoarthritis in the Kurdish population, whereas FokI, ApaI, and TaqI loci were non-polymorphic. These results highlight population-specific genetic variation within the VDR gene and underscore the need for larger studies incorporating functional validation to clarify the biological relevance of BsmI variation in osteoarthritis.