Moyamoya angiopathy is a rare cerebrovascular disorder. Its main clinical manifestations include ischemic and hemorrhagic stroke. A few genes and cytogenetic anomalies have been reported in a limited number of patients. However, the molecular causative anomaly is so far unknown in most moyamoya patients. In this study, we identified a novel association between an Xq28 copy number gain and moyamoya angiopathy in both typical moyamoya disease and moyamoya syndrome associated with venous anomalies and pulmonary hypertension. These data are important for clinical care and genetic counseling and also open clues to better understand the mechanisms of this very rare but emblematic large vessel, non-atherosclerotic disease. (By Chaker Aloui, https://jmg.bmj.com/content/early/2020/01/10/jmedgenet-2019-106525 )