Pathogenic variants in endoglin (ENG, chromosome 9q34), activin A receptor type II-like 1 (ACVRL1/ALK1, chromosome 12q13), and SMAD4 (chromosome 18q21) cause HHT1 (OMIM 187300), HHT2 (OMIM 600376), and combined Juvenile Polyposis/HHT (JP/HHT) syndrome (OMIM 175050), respectively [7,8,9]. The gene discussed is ACVRL1; the disease is hereditary hemorrhagic telangiectasia.