The majority of HHT cases involve loss-of-function mutations in two genes originally implicated in transforming growth factor-beta (TGFB) signaling pathways: (1) ENG, encoding an accessory protein of TGFB receptor complexes; and (2) ACVRL1, encoding a transmembrane kinase [6]. The gene discussed is ENG; the disease is hereditary hemorrhagic telangiectasia.