PAH can be either idiopathic (iPAH, where the cause is unknown) or heritable (hPAH) due to mutations in predisposing genes (mainly in BMPR2), induced by drugs or toxins, or associated with overt features of venous/capillaries (pulmonary veno-occlusive disease, PVOD). This evidence concerns the gene BMPR2 and pulmonary arterial hypertension.