ACVRL1 and pulmonary arterial hypertension: Genetic studies have indicated that mutations of some genes involved in the transforming growth factor-β (TGF-β) pathway, including bone morphogenetic protein receptor 2 (BMPR2), activin receptor-like 1 (ACVRL1), and endoglin (ENG), are associated with childhood-onset PAH (Barst et al., 2011; Rosenzweig et al., 2019).