SMAD9 and pulmonary arterial hypertension: A recent study carried out by our Clinical Genome Resource (ClinGen) pulmonary hypertension gene curation expert panel (PH GCEP) thoroughly characterized 27 genes and classified 12 of them to have a definitive gene–disease relationship with IPAH/HPAH (ACVRL1, ATP13A3, BMPR2, CAV1, EIF2AK4, ENG, GDF2, KCNK3, KDR, SMAD9, SOX17, and TBX4), three to have moderate evidence (ABCC8, GGCX, and TET2), six with limited evidence (AQP1, BMP10, FBLN2, KLF2, KLK1, and PDGFD), and one to have no evidence for the relationship with PAH (TOPBP1) [12].