Project Summary Epilepsy affects up to 1% of the population worldwide, and 3 million in the United States alone. A growing proportion of pediatric epilepsies are tied to causative variants in ion channel genes, including the voltage-gated sodium channel gene SCN2A. The 2020 Epilepsy Research Benchmarks of NINDS prioritize identifying how genetic variants cause epilepsy and related neurodevelopmental disorders. SCN2A variants that manifest with loss-of-function are associated with severe neurodevelopmental disorders and late-onset epilepsy. On the other hand, gain-of-function SCN2A variants predominantly have a phenotype of early-onset epilepsy. The encoded sodium channel (NaV1.2) is highly expressed in excitatory glutamatergic neurons early in development, presenting a unique opportunity to examine how excitatory neuron dysfunction leads to early-onset epilepsy. Animal and human tissue-derived neuron models have brought mechanistic insight to how Dravet syndrome results in interneuron dysfunction and epilepsy. Among SCN2A-related diseases, animal models illuminate how loss-of-function leads to autism spectrum disorder with late-onset epilepsy. Due to lack of readily available disease models, there is sparse mechanistic understanding of how excitatory neuron dysfunction early in development leads to early-onset epilepsy. This proposal will exploit two early-onset epilepsy variants of SCN2A that have a convergent clinical phenotype yet divergent biophysical mechanisms. Patient-derived neuron models and mouse models provide the opportunity to define the point of mechanistic convergence at multiple scales: from single neurons to neural circuits influencing epilepsy phenotype. Aim 1 will determine how two gain- of-function SCN2A variants, encoding missense mutations M1879T and E430A, confer increased excitability by distinct mechanisms. Functional analysis of iPSC-derived neurons in isolation and in elementary circuits will define how the different variants impact excitability and thus converge toward an epileptic phenotype. Aim 2 will define hippocampal higher-level circuit perturbations in epileptic mice designed with genome editing to recapitulate the SCN2A-E430A human epileptic encephalopathy. Ex vivo analysis of changes in excitability, synaptic signaling, and network output in the hippocampus will lead to new understanding of how gain-of-function SCN2A variants affect neuronal networks. EEG and depth electrodes will provide spatiotemporal correlate to the in vivo epilepsy phenotype. This proposal will propel the awardee to independence as a physician-scientist by incorporating new expertise in multi-scale modeling of genetic epilepsy, focused relevant didactics, and a diverse career development team specializing in neurodevelopmental and genetic disorders, all in a highly collaborative environment fostering junior faculty development. This award will provide a platform to 1) define variant-specific contributions to epilepsy phenotype in self-limited and intractable epilepsies and 2) investigate how targeted epileptic circuit dysfunction influences circuit output and epilepsy phenotype in future R01-funded independent research.

Narrative Epilepsy affects up to 1% of the population, causing disruptions in quality of life and even mortality due to sudden death. In pediatric epilepsy especially, changes in a single gene of an ion channel are recognized as a major contributor to infantile-onset seizures that can be very difficult to control with medications. This proposal will provide new insight into the way single gene changes lead to recurrent seizures by examining single neurons and animal models, allowing for new approaches to therapy.