ENG and endothelial dysfunction: Several genes encoding proteins involved in the BMP signal transduction and highly expressed in vascular endothelial cells are mutated in PAH, including BMPR2, ALK1, and endoglin (ENG) [23], leading to endothelial dysfunction, i.e., cell apoptosis, compromised barrier function, altered vasoactive mediator release, and permeability in lung vasculature [23].