In particular, mutations in the 5'UTR may explain the pathogenesis of the disorder in some cases, since most of the transcription and/or translation protein complexes bind and regulate expression from the 5'UTR of the gene [21,22] Based on this information, combined with supportive linkage data to the ENG, we decided to investigate the role of the 5'UTR region of ENG. We sequenced this region in 154 unrelated HHT patients who do not carry a disease causing mutation in the coding region of the ACVRL1 and ENG genes by sequencing and deletion/duplication analyses. The gene discussed is ACVRL1; the disease is hereditary hemorrhagic telangiectasia.