ACVRL1 and juvenile polyposis syndrome: HHT is transmitted as an autosomal dominant condition due to a single mutation in Endoglin (ENG; HHT1)[7], Activin Receptor-Like Kinase 1 (ACVRL1/ALK1; HHT2)[8], or MADH4/SMAD4 (JHPT, a combined syndrome of juvenile polyposis and HHT)[9].