BMPR2 and pulmonary arterial hypertension: Germ-line mutations in ALK1 underlie hereditary hemorrhagic telangiectasia type 2 (Johnson et al., 1996) and BMPR2 mutations underlie pulmonary arterial hypertension (PAH) (Lane et al., 2000; Deng et al., 2000; Machado et al., 2006).