Causal effects of glycemic traits and endometriosis: a bidirectional and multivariate mendelian randomization study

Observational studies have suggested an association between endometriosis and glycemic traits, but causality remains unclear. We used bidirectional and multivariate Mendelian randomization (MR) to examine the causal effect of glycemic traits on endometriosis and vice versa.

We obtained genome-wide association studies summary data of endometriosis and glycemic traits in our study. Inverse variance weighted (IVW), Weighted median, MR-Egger and Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) were applied in bidirectional two-sample MR analyses. MVMR was implemented to estimate the causal effect for fasting insulin (FI), fasting glucose (FG), and glycosylated hemoglobin A1c (HbA1c) on endometriosis. To test the validity of our findings, a number of sensitivity analyses were conducted.

The risk of endometriosis was significantly increased by genetically predicted T1DM (OR = 1.02, 95% CI 1.00-1.04, p = 0.0171, q = 0.0556) and GDM (OR = 1.01, 95% CI 1.01-1.02, p = 1.34 × 10^- 8, q = 1.74 × 10^- 7). Endometriosis had a suggestive association with HbA1c (Beta = 0.04, 95% CI 0.00-0.08, p = 0.0481, q = 0.1251). Using multivariate Mendelian randomization (MVMR), a significant causal effect of FI on genetically predicted endometriosis was found (OR = 2.18, 95% CI 1.16-4.09, p = 0.0154, q = 0.0547). Moreover, no causal associations between endometriosis and other glycemic traits were detected.

Our findings supported the significant causal associations of T1DM, GDM and FI with endometriosis, respectively. Additionally, a suggestive association was found of endometriosis on HbA1c. Importantly, our study may shed light on etiology studies and clinical management of endometriosis.