Polymorphic Variants in the Vitamin D Receptor and Clinical Parameters of Rheumatoid Arthritis Patients Undergoing Anti-TNF Treatment

Vitamin D levels have been related to the severity and progression of various autoimmune disorders. In this study, we aimed to investigate the impact of genetic variability in the vitamin D receptor (VDR) gene on disease susceptibility and progression in patients with rheumatoid arthritis (RA) treated with tumor necrosis factor (TNF) inhibitors. The study comprises 121 RA patients subjected to anti-TNF therapy genotyped for four VDR polymorphic variants: rs1544410 (BsmI), rs2228570 (FokI), rs731236 (TaqI), and rs7975232 (ApaI). There was no significant association between RA susceptibility and VDR genetic variants. The study results revealed that patients with the rs2228570 CC genotype were characterized by lower vitamin D3 levels (p = 0.028) than those with the T allele. Also, the vitamin D3 levels (p = 0.029) and age at diagnosis (p = 0.017) were significantly lower in rs7975232 A allele carriers compared to CC homozygotes. However, after 6 months of therapy, the A allele seemed to be related to lower disease activity score 28 (DAS28) values (p = 0.030) and more common in patients who achieved remission (p = 0.004) compared to the CC genotype. Concerning other investigated polymorphisms, patients carrying rs1544410 AA and rs731236 CC homozygosity had lower C-reactive protein (CRP) levels before therapy (p = 0.009). In conclusion, VDR rs2228570 and rs7975232 polymorphic variants were found to be related to vitamin D3 levels. Moreover, the genotyping of rs7975232 was also useful in evaluating disease onset and disease activity after 6 months of therapy with TNF inhibitors in RA patients.