Tumor necrosis factor gene polymorphisms and endometriosis in Asians: A systematic review and meta-analysis

Background: Numerous studies have described the association between polymorphisms in the tumor necrosis factor (TNF) gene and risk of endometriosis. However, the results remain controversial. Here we reviewed studies reporting the association between TNF gene polymorphisms and endometriosis risk in Asians. Methods: PubMed and Embase were searched. Twelve case-control studies assessing the role of multiple TNF gene polymorphisms in endometriosis were included. If no less than two articles evaluated one variant, meta-analysis was conducted; otherwise, narrative analysis was chosen. A fixed- or random-effects model was employed according to the heterogeneity among studies. The strength of the association between TNF gene polymorphisms and endometriosis risk was assessed by odds ratios and 95% confidence intervals. Results: For TNF-α -238G>A, -308G>A, -857C>T, and -863C>A, no significant associations were identified from all genetic models. For TNF-α -850T>C, results from one study showed that patients harboring the heterozygote TC were less susceptible to endometriosis than patients harboring the homozygote TT. For TNF-α -1031T>C, a mild increase in endometriosis risk was found in the Asian population. Meta-analysis from two studies found that the TNF-β +252>G polymorphism had a protective effect in Chinese individuals. Due to the limitations of the included studies, it is necessitated to perform more studies to elucidate the possible roles of TNF gene polymorphisms in the pathogenesis of endometriosis. Conclusions: TNF-α -1031T>C and TNF-β +252A>G were significantly associated with the risk of endometriosis in Asian and Chinese populations, respectively. To further evaluate these associations, more large-scale, rigorously designed studies are needed.