A meta-analysis of the relationship between vitamin D receptor gene ApaI polymorphisms and polycystic ovary syndrome

Background. Emerging evidence from pre-clinical and clinical studies has shown that vitamin D (VD) plays an important role in the pathogenesis of polycystic ovary syndrome (PCOS). Potentially functional ApaI polymorphism of vitamin D receptor (VDR) gene has been implicated in PCOS risk, but individually published studies have yielded inconclusive results. Objectives. Studies on the associations of VDR gene polymorphisms with PCOS susceptibility reported conflicting results. The objective of this study was to perform a systematic meta-analysis to clarify this issue. Material and methods. We searched for all publications regarding the associations mentioned above in PubMed, Web of Science, Embase, and China National Knowledge Infrastructure (CNKI) databases updated up to April 2017. A meta-analysis of the overall odds ratios (ORs) with 95% confidence interval (CI) was calculated with the fixed or random effect model. Results. A total of 7 studies fulfilling the inclusion criteria were included in this meta-analysis (1,350 cases and 960 controls). Pooled ORs showed a significant association between ApaI polymorphism and PCOS risk in all 4 genetic models. Subgroup analysis by ethnicity showed that ApaI polymorphism was associated with the risk of PCOS in Asians (aa vs AA: OR = 1.54, 95% CI = 1.04-2.28, p = 0.03). However, ApaI polymorphism (a vs A: OR = 1.34, 95% CI = 1.00-1.79, p = 0.02; aa+Aa vs AA: OR = 1.36, 95% CI = 1.04-1.79, p = 0.03) was associated with the risk of PCOS in Caucasians. Conclusions. Our meta-analysis demonstrated that PCOS risk was significantly associated with VDR gene ApaI polymorphism. However, due to the relatively small sample size in this meta-analysis, further studies with a larger sample size should be conducted to confirm the findings.