Long-term downregulation of SCN8A in mouse models of developmental and epileptic encephalopathy

De novo mutations of the voltage-gated sodium channel SCN8A cause severe developmental and epileptic encephalopathy (DEE). Since pathogenic variants have gain-of-function effects on SCN8A activity, reduction of SCN8A expression is an effective therapeutic strategy. We previously described an antisense oligonucleotide (ASO) that delays seizure onset in a mouse model of SCN8A-DEE when administered at postnatal day 2. To investigate the potential effectiveness of post-onset ASO treatment, we first examined the extent of differential gene expression in hippocampus during the pre-onset period. Hippocampal single-nucleus RNA-sequencing detected only minor expression changes after the two month pre-seizure period. ASO treatments that were initiated after seizure onset were protective in the Scn8a mutant mice during the 12 month observation period. As an alternative treatment for down-regulation of Scn8a, we administered a single dose of an AAV10 virus expressing Scn8a shRNA. The viral shRNA was protective against seizures and lethality during the 12 month observation period. These data indicate that reduction of SCN8A expression, either by repeated administration of ASO or a single dose of shRNA virus, may be effective for longterm control of SCN8A-DEE.