ACVRL1 and pulmonary arterial hypertension: Mutations in the ACVRL1 gene (reviewed in Abdalla and Letarte 2006), which encodes ALK1, causehereditary hemorrhagic telangiectasia type II [OMIM #600376]—a disease characterized byarteriovenous malformations (Roman and Hinck2017)—and are associated with pulmonary arterial hypertension (Trembath et al.