SMAD9 and pulmonary arterial hypertension: Other genes which have been reported to be involved in the PAH pathogenesis so far are: partners in the transforming growth factor (TGF)-β signaling pathway including activin receptor-like kinase type 1 gene (ACVRL1) [8], endoglin gene (ENG) [9], SMAD9 gene (SMAD9) [10], and genes coded for caveolin-1 (CAV1) [11], potassium channel subfamily K, member 3 (KCNK3) [12], cerebellin 2 (CBLN2) [13].