Meanwhile, researchers have identified mutations in over 16 genes in patient with hereditary PAH (HPAH) that may predispose to PAH, including BMPR2 of course, but also receptors that are part of or are interacting with the BMPR2 pathway such as activin A receptor type II-like 1 (ACVRL1), endoglin (ENG), caveolin-1 (CAV1), SMAD1, SMAD4, SMAD9, bone morphogenetic protein receptor type 1B (BMPR1B), eukaryotic translation initiation factor 2 α kinase 4 (EIF2AK4), and growth differentiation factor 2 (GDF2) [17]. The gene discussed is SMAD1; the disease is pulmonary arterial hypertension.