Heat-induced seizures, premature mortality, and hyperactivity in a novel Scn1a nonsense model for Dravet syndrome

Vagus nerve stimulation for the therapy of Dravet syndrome: a systematic review and meta-analysis

Objective

Dravet syndrome (DS) is a refractory developmental and epileptic encephalopathy characterized by seizures, developmental delay and cognitive impairment with a variety of comorbidities, including autism-like behavior, speech dysfunction, and ataxia. Vagus nerve stimulation (VNS) is one of the common therapies for DS. Here, we aim to perform a meta-analysis and systematic review of the efficacy of VNS in DS patients.

Methods

We systematically searched four databases (PubMed, Embase, Cochrane and CNKI) to identify potentially eligible studies from their inception to January 2024. These studies provided the effective rate of VNS in treating patients with DS. The proportions of DS patients achieving ≥50% reduction of seizure frequency were extracted from these studies. Meta-analyses were performed to respectively evaluate the efficacy of VNS for DS after 3, 6, 12, 18, 24 and 36 months.

Results

Sixteen trials with a total of 173 patients were included. Meta-analyses showed that the pooled efficiency was 0.54 (95% CI 0.43-0.65) in the DS patients treated with VNS (p < 0.05). Meanwhile, the pooled efficiency respectively was 0.42 (95% CI 0.25-0.61), 0.54 (95% CI 0.39-0.69), 0.51 (95% CI 0.39-0.66), and 0.49 (95% CI 0.36-0.63) in the DS patients treated with VNS after 3, 6, 12 and 24 months (p < 0.05).

Conclusion

This study suggests that VNS is effective in the treatment of DS. However, few studies have focused on VNS for DS, and there is a lack of high-quality evidence. Thus, high-quality randomized controlled trials are needed to confirm the efficacy of VNS in DS.

Are we there yet? A critical evaluation of sudden and unexpected death in epilepsy models

Although animal models have helped to elaborate meaningful hypotheses about the pathophysiology of sudden and unexpected death in epilepsy (SUDEP), specific prevention strategies are still lacking, potentially reflecting the limitations of these models and the intrinsic difficulties of investigating SUDEP. The interpretation of preclinical data and their translation to diagnostic and therapeutic developments in patients thus require a high level of confidence in their relevance to model the human situation. Preclinical models of SUDEP are heterogeneous and include rodent and nonrodent species. A critical aspect is whether the animals have isolated seizures exclusively induced by a specific trigger, such as models where seizures are elicited by electrical stimulation, pharmacological intervention, or DBA mouse strains, or whether they suffer from epilepsy with spontaneous seizures, with or without spontaneous SUDEP, either of nongenetic epilepsy etiology or from genetically based developmental and epileptic encephalopathies. All these models have advantages and potential disadvantages, but it is important to be aware of these limitations to interpret data appropriately in a translational perspective. The majority of models with spontaneous seizures are of a genetic basis, whereas SUDEP cases with a genetic basis represent only a small proportion of the total number. In almost all models, cardiorespiratory arrest occurs during the course of the seizure, contrary to that in patients observed at the time of death, potentially raising the issue of whether we are studying models of SUDEP or models of periseizure death. However, some of these limitations are impossible to avoid and can in part be dependent on specific features of SUDEP, which may be difficult to model. Several preclinical tools are available to address certain gaps in SUDEP pathophysiology, which can be used to further validate current preclinical models.

AAV-mediated interneuron-specific gene replacement for Dravet syndrome

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 SCN1A , which has been associated with inhibitory neuron dysfunction. Here we developed an interneuron-targeting AAV human SCN1A gene replacement therapy using cell class-specific enhancers. We generated a split-intein fusion form of SCN1A to circumvent AAV packaging limitations and deliver SCN1A 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 in vivo . 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 Scn1a, 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 SCN1A , or the dual vector system targeting interneurons. In contrast, nonselective neuronal targeting of SCN1A conferred less rescue against mortality and presented substantial preweaning lethality. These findings demonstrate proof-of-concept that interneuron-specific AAV-mediated SCN1A gene replacement is sufficient for significant rescue in DS mouse models and suggest it could be an effective therapeutic approach for patients with DS.