ACVRL1 and hereditary hemorrhagic telangiectasia: HHT, also named Rendu–Osler–Weber disease, is an autosomal-dominant familial disease with an estimated prevalence of 1 in 5,000, and it is most commonly caused by mutations in ENG, endoglin (HHT1), ACVLI/ALK1 (HHT2), or Smad4 (HTJP) (1).