ACVRL1 and hereditary hemorrhagic telangiectasia: The fact that overexpression of Alk1 rescued the phenotypes in Eng mutant mice suggests that overexpression Alk1 in ECs may be effective for both HHT2 (caused by ALK1 mutation) and HHT1 (caused by ENG mutation) patients, which together make up more than 80% of the HHT patient population.