In these cases, PAH likely results from a dysfunctional relationship between ACVRL1, ENG and the bone morphogenic protein receptor type II, BMPR2, another member of the TGF-β superfamily of receptors, whose mutations are often the cause of inherited as well as sporadic cases of PAH (Atkinson et al., 2002). The gene discussed is ACVRL1; the disease is pulmonary arterial hypertension.