ACVRL1 and pulmonary arterial hypertension: Based on the World Health Organization (WHO) classification, PAH comprises different forms (WHO Group 1): idiopathic, heritable PAH (due to bone morphogenetic protein receptor type 2, activin receptor-like kinase-1, endoglin, decapentaplegic 9, caveolin-1, or KCNK3 gene mutations), anorexigen-induced PAH, and medical conditions associated with PAH (including portal hypertension, connective tissue disease [most commonly systemic sclerosis], human immunodeficiency virus, schistosomiasis, chronic hemolytic anemia, and congenital heart disease) [6].