Kim HJ, Lee HS, Kazmi SZ, et al. - Researchers conducted a population-based nationwide cohort study with the aim to determine familial risk of endometriosis among full siblings. In addition, they examined interactions between family history and smoking, age at menarche or body mass index (BMI). The Korean National Health Insurance and Screening Program databases on kinship, healthcare utilization, lifestyle and anthropometrics yielded data of 2,109,288 females with full siblings and their environmental risk factors from 2002-2018. Among these, 19,195 females had affected siblings, from whom 1,126 cases had development of endometriosis with an incidence 35.45/10,000 person-years. Observations revealed the primary contribution of genetic factors to the familial aggregation of endometriosis. They indicated existence of significant gene-environment interaction between family history and smoking or early menarche.