Other genes with mutations contributing to some cases of HHT include MADH4, which encodes SMAD4 (leading to the juvenile polyposis-HHT phenotype), and GDF2, which encodes BMP9, a ligand of ALK1 (HHT5 phenotype) [2,8,9]. The gene discussed is ACVRL1; the disease is hereditary hemorrhagic telangiectasia.