ACVRL1 and pulmonary arterial hypertension: This suggests that the HHT phenotype is influenced by the tissue distribution and function of ENG and ACVRL1. Although pulmonary arterial hypertension (PAH) is a much rarer event than the occurrence of HHT, it has also been associated with ACVRL1 and ENG mutations (Govani and Shovlin, 2009).