BMPR2 and idiopathic pulmonary arterial hypertension: A breakthrough in our understanding of the pathobiology underlying PAH was the discovery of heterozygous germline mutations in the gene encoding the bone morphogenetic protein receptor type 2 (BMPR2),3 responsible for over 70% of familial PAH cases and 15% to 20% of idiopathic PAH (IPAH) cases.