The ENG gene encodes endoglin, with loss-of-function mutations causing hereditary hemorrhagic telangiectasia type 1 (HHT1), whereas ACVRL1 encodes ALK1, whose pathogenic variants underlie HHT type 2 (HHT2). The gene discussed is ACVRL1; the disease is telangiectasia, hereditary hemorrhagic, type 1.