Pulmonary arterial hypertension (PAH) is a rare blood vessel disorder that can be fatal. The development of PAH in early childhood, often accompanied by other medical issues, is likely caused by genetic factors but few of the underlying genes have been identified. By connecting doctors and researchers around the world, we identified MECOM, a master regulator of embryonic development and blood cell formation, as a candidate gene for PAH associated with other medical features. Genetic variants in MECOM cause a pediatric-onset condition associated with bone marrow failure and skeletal, heart, and other abnormalities at birth or early in life. Protein modeling suggested that patient mutations may cause PAH and congenital heart disease by dysregulation of blood vessel development, growth, and maintenance. The novel association of PAH with MECOM syndrome could have significant implications for clinical monitoring and management of all individuals with rare MECOM variants. (By Carrie L Welch, https://jmg.bmj.com/content/early/2026/01/29/jmg-2025-111027 )