Juvenile Polyposis – Hereditary Haemorrhagic Telangiectasia overlap syndrome (JP-HHT OMIM175050) was first observed in 1980 [1], although its genetic cause – heterozygous pathogenic SMAD4 loss of function variants [2] – was only identified in 2004 [2]. Here, SMAD4 is linked to hereditary hemorrhagic telangiectasia.