ACVRL1 and pulmonary arterial hypertension: Moreover, several signs of pulmonary arterial hypertension (PAH), including elevated right ventricular systolic pressure leading to hypertrophy, reduced vascular density, and increased thickness and outward remodeling of pulmonary arterioles, were observed in adult but not newborn Eng+/– and Acvrl1+/– mice relative to wild-type littermate controls.