SMAD4 and hereditary hemorrhagic telangiectasia: HHT gene testing pathways are now in place in multiple countries worldwide [7,8,18,19,20,21,22,23,24,25] and facilitate the diagnosis of HHT, targeted AVM screening programmes, and direction of SMAD4 families to SMAD4-specific preventative measures [26,27,28,29,30,31].