SMAD9 and pulmonary arterial hypertension: Targeted next-generation sequencing was performed on PAH-associated genes (ABCC8, ACVRL1, AQP1, ATP13A3, BMPR2, CAV1, GDF2, GGCX, EIF2AK4, ENG, KCNK3, KDR, KLK1, SMAD1, SMAD4, SMAD9, SOX17, TBX4, TET2).