Bossler et al. reported the c.1-10 C > T mutation in the ENG 5'-UTR of a patient with HHT [31], which is the only known 5'-UTR mutation among reported ACVRL1 and ENG mutations, except large deletion mutations that include the 5'-UTRs [14]. Here, ACVRL1 is linked to hereditary hemorrhagic telangiectasia.