Two genes that have been linked to the development of HHT are the ENG gene, which is correlated with HHT1 as well as a higher prevalence of AVMs, and the ACVRL1 or ALK1 gene, which is associated with the HHT2 phenotype and a lower brain AVM incidence [11,12]. The gene discussed is ACVRL1; the disease is hereditary hemorrhagic telangiectasia.