Zhao Y, Xu Y, Wang X, et al. - Given the observational studies indicating a correlation between elevated BMI and the risk of polycystic ovary syndrome (PCOS) and Mendelian randomization (MR) studies in Europeans suggesting a causal role of increased BMI in PCOS, researchers sought to determine if the same role is suggested in Asians. Using summary statistics from genome-wide association studies of BMI (with up to 173,430 individuals) and PCOS (4,386 cases and 8,017 controls) in East Asian populations, a 2-sample bidirectional MR analysis was performed. Using the inverse-variance weighted method, the causal effect of BMI on PCOS was estimated employing 78 single nucleotide polymorphisms correlated with BMI as genetic instrumental variables. The results established that BMI increase causes PCOS, while PCOS does not cause an increased BMI. Further genetic support was gained for a correlation between BMI and PCOS.