GDF2 and idiopathic pulmonary arterial hypertension: Considering the predominant role of rare variants of the Bone morphogenetic protein 9 (BMP9) gene in the occurrence of idiopathic pulmonary arterial hypertension (IPAH), here we conducted a case-control study, together with functional validation, to explore the relationships between variants of the BMP9 gene and development of IPAH.