Transgenic A6 mice developed hallmarks of LS and NARP including premature death (mortality ~ 80%), paralysis (see video), seizures and vision loss. Neuropathology showed spongiform encephalopathy and loss of retinal neurons. Intravenous mito-targeted AAV9 with wild-type ATP6 was injected into two groups of A6 mice, (I) without disease onset at three months of age and (II) the other group with LS at eighteen months. After 1.5 years, treated A6 mice of group I had 100% survival, while untreated A6 mice mortality was 70% suggesting mito-targeted AAV9 prevented A6 mice disease onset. The second group of A6 mice with paraplegia typically seen prior to spontaneous death was reversed 3 days after intravenous mito-targeted AAV9 containing wild-type ATP6 (see video).