Autism-related phenotypes in a heterozygous Scn2aR854Q mouse model and their partial rescue via a potassium channel opener

The voltage-gated sodium channel Na V 1.2, encoded by the SCN2A gene, is frequently implicated in neurodevelopmental and neurological disorders, including developmental and epileptic encephalopathy (DEE) and autism spectrum disorder (ASD). Genotype-phenotype studies show that Na V 1.2 mutations with mixed gain- (GoF) and loss-of-function (LoF) effects are associated with the most severe clinical outcomes. The R853Q mutation in the second gating charge of Domain II reduces current density by 50-60% and was initially classified as a LoF mutation, suggesting reduced neuronal firing. However, this does not fully explain its recurrent association with DEE and severe ASD. Our recent findings indicate that R853Q induces a gating pore current (I gp ) in the resting state, introducing a GoF component that may increase cortical neuronal excitability. This mixed GoF/LoF effect may underlie the strong clinical phenotypes observed in patients carrying this mutation. To explore this, we generated a mouse model carrying the orthologous R854Q mutation. Behavioral analyses revealed that heterozygous Na V 1.2(R854Q) mice exhibit ASD-like phenotypes, including impaired social interaction and social novelty, repetitive rearing, and increased risk-taking behaviors. In silico modeling suggests that, in cortical neurons, the net effect of the R854Q mutation is a reduction in neuronal excitability due to decreased sodium conductance, although I gp alone increases excitability and partially offsets this reduction. Notably, acute administration of retigabine, a potassium channel opener, rescues specific ASD-related phenotypes, possibly by restoring decreased firing through reduction of slow sodium inactivation. Comparative analysis with Scn2a knockout models, which show similar current reduction, highlights the unique severity of R854Q, suggesting a role of I gp in modulating neurobehavioral outcomes and informing potential therapeutic strategies. • The Na V 1.2 R853Q mutation exhibits mixed gain- and loss-of-function effects, combining reduced sodium current density with a pathogenic gating pore current (I gp ). • Heterozygous Na V 1.2(R854Q) mice display ASD-like behavioral phenotypes, including impaired social behaviors, repetitive rearing, and increased risk-taking. • In silico modeling shows that I gp partially counteracts reduced sodium conductance, yet the net effect is decreased cortical neuronal excitability. • Acute retigabine administration rescues select ASD-related behaviors, revealing a potential therapeutic strategy for GoF/LoF Na V 1.2 mutations.