Cabrera-Pérez et al. [43] further demonstrated that a human alpha-1-antitrypsin (hα1-AT) promoter improves the efficacy of an AAV vector for the gene therapy of MNGIE by regulating exogenous thymidine phosphorylase (TP) expression not only in the liver but also in the brain and small intestinal tissues. Here, TYMP is linked to mitochondrial neurogastrointestinal encephalomyopathy.