One suchsyndrome in humans, hereditary hemorrhagic telangiectasia type-2, is caused by amutation in the gene encoding activin receptor like kinase 1 (ALK1or ACVRL1), a type I TGF-beta receptor in the BMP signalingpathway.11 This known mutation provides an opportunity to study thepathogenic mechanisms of AVMs in vertebrate models. Here, ACVRL1 is linked to hereditary hemorrhagic telangiectasia.