The map of mutations (Fig. 3) suggests that mutations specific for PAH (continuous line) are widely distributed in a few genes: ACVRL1, BMPR2, EIF2AK4, ENG, KCNA5, and SMAD4. Nevertheless, there are many other mutations not yet found in PAH patients that have been found in other diseases. The gene discussed is BMPR2; the disease is pulmonary arterial hypertension.