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). This evidence concerns the gene ENG and pulmonary arterial hypertension.