It has been established that genetic variation in the transforming growth factor β (TGF-β) signaling pathway plays an important role in the pathogenesis of idiopathic and heritable PAH, such as BMPR2, activin receptor-like kinase 1 (ACVRL1), and endoglin (ENG) [6,17,18,19]. The gene discussed is ACVRL1; the disease is pulmonary arterial hypertension.