ACVRL1 and pulmonary arterial hypertension: The most common phenotypes of PH in HHT include WHO group 1 heritable pulmonary arterial hypertension (PAH), which is typically associated with an ALK1 genetic mutation; WHO group 2 PH due to high output heart failure from hepatic AVMs and/or anemia; and WHO group 2 PH due to high pulmonary artery wedge pressure (PAWP) [4,8].