SMAD9 and pulmonary arterial hypertension: A recent large study of >1000 PAH patients confirmed the prevalence of causal mutations in BMPR2, as well as in five other established genes (TBX4, ACVRL1, ENG, SMAD9 and KCNK3), and identified PAH-associated mutations in four new genes (ATP13A3, SOX17, AQP1 and GDF2), altogether accounting for 23.5% of the cases studied [4].