ApaI, BsmI, FokI, and TaqI Polymorphisms in the Vitamin D Receptor Gene and Parkinson's Disease

BACKGROUND The vitamin D receptor (VDR) gene has been identified as a candidate gene for susceptibility to Parkinson's disease (PD), but results from genetic association studies to date are inconsistent. Here, we conducted a meta-analysis of published case-control studies to evaluate the association of the extensively studied VDR ApaI (G/T), BsmI (G/A), FokI (C/T), and TaqI (T/C) gene polymorphisms with risk of PD. METHODS Electronic search at PubMed, EMBASE, EBSCO, China National Knowledge Infrastructure, Weipu database, and Wanfang database was conducted to identify all relevant studies. Odds ratio (OR) with 95% confidence interval (CI) values was applied to evaluate the strength of the association. RESULTS A total of seven studies with 2034 PD cases and 2432 controls were included in the meta-analysis following the inclusion and exclusion criteria. Overall, no significant association between ApaI, BsmI, and TaqI gene polymorphisms and PD susceptibility in all four genetic models was found (T vs. G: OR = 1.00, 95% CI: 0.89-1.12, P = 0.97; A vs. G: OR = 0.94, 95% CI: 0.77-1.15, P = 0.53; C vs. T: OR = 1.03, 95% CI: 0.85-1.25, P = 0.77) while a significant association between FokI (C/T) and PD risk was observed (C vs. T: OR = 1.41, 95% CI: 1.14-1.75, P = 0.001; CC vs. TT: OR = 2.45, 95% CI: 1.52-3.93, P = 0.0002; CT vs. TT: OR = 2.21, 95% CI: 1.38-3.52, P = 0.0009, CC vs. CT+TT: OR = 2.32, 95% CI: 1.49-3.61, P = 0.0002). CONCLUSIONS Polymorphisms of ApaI, BsmI, and TaqI may not be associated with the susceptibility to PD while the FokI (C/T) polymorphism is possibly associated with increased PD risk. However, conclusions should be cautiously interpreted due to the relatively small number of studies included.