BMPR2 and idiopathic pulmonary arterial hypertension: Taking the most predominant causal gene, bone morphogenetic protein receptor type 2 (BMPR2 [OMIM 600799]), as an example, its variants only account for 17% of patients with IPAH.8 For other known predisposing genes, such as CAV1 and KCNK3, the genetic variants are rare in patients with IPAH.9,10