Mitochondrial DNA-associated LS and NARP are progressive neurodegenerative disorders caused by mutated mitochondrial T8993G DNA that encodes for the ATP6 subunit of complex V.  Children develop a subacute necrotizing encephalomyelopathy characterized by hypotonia, spasticity, movement disorders, ataxia and neuropathy. Half die by 3-5 years of age, the rest by age 10. Adults develop NARP with vision loss and die in their 30s-40s.  There is no treatment.

To provide the FDA required preclinical data of our proposed gene therapy for Leigh syndrome (LS) and NARP (neurogenic muscle weakness, ataxia, and retinitis pigmentosa). 

We created a mutant T8993G ATP6  transgenic mouse (A6) by microinjection of mito-targeted AAV2 containing the mutant human ATP6 gene linked to fluorescent  mCherry  into mouse zygotes. Females with mCherry detected by CLSO were backcrossed with wild-type males for 6 generations.  A rescue AAV9 vector was assembled by appending the COX8 presequence to VP2 capsid of AAV2 containing  a wild-type ATP6 gene that was administered intravenously prior to or after disease onset.

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).

Mito-targeted AAV9  wild-type ATP6 gene therapy may be a novel approach for LS or NARP caused by the ATP6 mutation.