Null Genotypes of <i>GSTM1</i> and <i>GSTT1</i> and Endometriosis Risk: A Meta-Analysis of 25 Case-Control Studies

<div><p>Endometriosis is one of the most frequent benign gynecological disorders. Numerous studies have shown an association between <i>GSTM1</i> and/or <i>GSTT1</i> polymorphisms and endometriosis susceptibility. However, these associations remain inconclusive. To derive a more precise estimation, we conducted a comprehensive search to identify all existing studies and then performed a meta-analysis. Electronic literature searches of the PubMed, Chinese Biomedical, and China National Knowledge Infrastructure databases were performed up to December 2013. <i>GSTM1-</i>, <i>GSTT1-</i>, and dual-null genotypes were analyzed independently, and pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated by comparing the null genotype with other genotypes using the random-effects or fixed-effects model. Twenty-five and 16 independent studies on <i>GSTM1</i> and <i>GSTT1</i> polymorphisms, respectively, and five <i>GSTM1-GSTT1</i> interaction analyses were identified and included in this meta-analysis. Both <i>GSTM1-</i> and <i>GSTT1-</i>null genotypes increased risk of endometriosis (OR = 1.54, 95% CI: 1.30–1.83, <i>P</i><0.001; OR = 1.41, 95% CI: 1.10–1.82, <i>P</i> = 0.007; respectively). Moreover, we found a significant positive association between the dual null genotype <i>GSTM1-GSTT1</i> and endometriosis susceptibility (OR = 1.33, 95% CI: 1.03–1.72, <i>P</i> = 0.027). This meta-analysis provides evidence that null genotypes of <i>GSTM1</i> and/or <i>GSTT1</i> contribute to risk of endometriosis. Further investigations are required to confirm these findings.</p>