ACVRL1 and hereditary hemorrhagic telangiectasia: In humans, heterozygous mutations of either ACVRL1 (encoding ALK1) or ENG (encoding Endoglin, an endothelial co-receptor for MP9/10) genes cause hereditary hemorrhagic telangiectasia (HHT), a genetic disease with multisystemic vascular defects ranging from small cutaneous and mucosal telangiectasias, to severe arteriovenous malformations (AVMs) in the lung, liver, and the brain, which drive severe cardiac complications [18,19].