AAV-mediated interneuron-specific gene replacement for Dravet syndrome

Abstract

Dravet syndrome (DS) is a devastating developmental epileptic encephalopathy marked by treatment-resistant seizures, developmental delay, intellectual disability, motor deficits, and a 10-20% rate of premature death. Most DS patients harbor loss-of-function mutations in one copy of <i>SCN1A</i> , which has been associated with inhibitory neuron dysfunction. Here we developed an interneuron-targeting AAV human <i>SCN1A</i> gene replacement therapy using cell class-specific enhancers. We generated a split-intein fusion form of <i>SCN1A</i> to circumvent AAV packaging limitations and deliver <i>SCN1A</i> via a dual vector approach using cell class-specific enhancers. These constructs produced full-length Na _V 1.1 protein and functional sodium channels in HEK293 cells and in brain cells <i>in vivo</i> . After packaging these vectors into enhancer-AAVs and administering to mice, immunohistochemical analyses showed telencephalic GABAergic interneuron-specific and dose-dependent transgene biodistribution. These vectors conferred strong dose-dependent protection against postnatal mortality and seizures in two DS mouse models carrying independent loss-of-function alleles of <i>Scn1a,</i> at two independent research sites, supporting the robustness of this approach. No mortality or toxicity was observed in wild-type mice injected with single vectors expressing either the N-terminal or C-terminal halves of <i>SCN1A</i> , or the dual vector system targeting interneurons. In contrast, nonselective neuronal targeting of <i>SCN1A</i> conferred less rescue against mortality and presented substantial preweaning lethality. These findings demonstrate proof-of-concept that interneuron-specific AAV-mediated <i>SCN1A</i> gene replacement is sufficient for significant rescue in DS mouse models and suggest it could be an effective therapeutic approach for patients with DS.