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.