Mutations in endoglin (ENG) and activin receptor-like kinase 1 (ACVRL1) (encoding ALK1) have been linked to a human vascular disorder hereditary hemorrhagic telangiectasia (HHT1 and HHT2, respectively), often resulting in arteriovenous malformations (AVM) [75,76]. Here, ACVRL1 is linked to arteriovenous hemangioma/malformation.