ACVRL1 and pulmonary arterial hypertension: Interestingly, imbalanced TGFβ signaling is a characteristic feature in all PAH subtypes that includes loss-of-function genetic mutations in components of the bone morphogenetic protein (BMP) signaling pathway (i.e., ACVRL1, BMPR1B, BMPR2) and reduced expression of the BMP type-II receptor (BMPR2) in mutation-positive and -negative cases of PAH [9].