A total of 13 patients (52%) had a mutation in the ENG gene, 11 (44%) patients had a mutation in the ACVLRL1 gene and in 1 patient (4%) with clinical HHT, no disease-causing mutation was found in the ENG, ACVLR1 or SMAD4 genes. This evidence concerns the gene SMAD4 and hereditary hemorrhagic telangiectasia.