The genetic basis of pulmonary arterial hypertension
Pulmonary arterial hypertension (PAH) is a rare disease characterized by distinctive changes in pulmonary arterioles that lead to progressive elevation of pulmonary artery pressure, pulmonary vascular resistance, right ventricular failure, and a high mortality rate. The etiology of PAH is heterogeneous and incompletely understood. Based on clinical classification, WHO Group 1 PAH includes sporadic disease (idiopathic PAH), inherited PAH (heritable PAH), and association with certain medical conditions (associated PAH). Genes play an important role in idiopathic and heritable PAH. Mutations in bone morphogenetic protein receptor 2 (BMPR2), a member of the transforming growth factor β (TGFβ) superfamily of receptors, have been identified in 70 % of cases of familial PAH, as well as in 10–40 % of cases of idiopathic PAH. Mutations in ALK-1, ENG, SMAD4 and SMAD8, other TGFβ family members, are additional rare causes of PAH. CAV1 regulates SMAD2/3 phosphorylation, and mutations in CAV1 are a rare cause of PAH. KCNK3 is a member of the two-pore domain potassium channels expressed in pulmonary artery smooth muscle cells, and mutations in KCNK3 are a rare cause of both familial and IPAH. The genetics of PAH are complex due to incomplete penetrance and genetic heterogeneity. In addition to rare mutations as a monogenic cause of HPAH, common variants in cerebellin 2 (CBLN2) increase the risk of PAH by approximately twofold. PAH in children is much more heterogeneous than in adults and can be associated with several genetic syndromes, specifically syndromes with congenital heart disease, vascular disease, and hepatic disease. Clinical genetic testing is available for PAH and should be considered in families to allow for more definitive risk stratification and allow for reproductive planning.