ACVRL1 and hereditary hemorrhagic telangiectasia: Mutations in Activin receptor-like kinase gene (ACVRL1) encoding the type I receptor ALK1, a major partner in the TGFβ signaling pathway, has been associated with hereditary hemorrhagic telangiectasia type 2 (HHT2, OMIM 600376) (Johnson et al., 1996).