SMAD9 and pulmonary arterial hypertension: The 6th WSPH listed BMPR2, EIF2AK4, TBX4, ATP13A3, GDF2, SOX17, AQP1, ACVRL1, SMAD9, ENG, KCNK3 and CAV1 mutations as higher level of evidence and SMAD4, SMAD1, KLF2, BMPR1B and KCNA5 with lower level of evidence of association with primary PAH (2).