Cortical versus hippocampal network dysfunction in a human brain assembloid model of epilepsy and intellectual disability

Neurodevelopmental disorders often impair multiple cognitive domains. For instance, a genetic epilepsy syndrome might cause seizures due to cortical hyperexcitability and present with memory impairments arising from hippocampal dysfunction. This study examines how a single disorder differentially affects distinct brain regions by using human patient iPSC-derived cortical- and hippocampal-ganglionic eminence assembloids to model Developmental and Epileptic Encephalopathy 13 (DEE-13), a condition arising from gain-of-function mutations in the SCN8A gene. While cortical assembloids showed network hyperexcitability akin to epileptogenic tissue, hippocampal assembloids did not, and instead displayed network dysregulation patterns similar to in vivo hippocampal recordings from epilepsy patients. Predictive computational modeling, immunohistochemistry, and single-nucleus RNA sequencing revealed changes in excitatory and inhibitory neuron organization that were specific to hippocampal assembloids. These findings highlight the unique impacts of a single pathogenic variant across brain regions and establish hippocampal assembloids as a platform for studying neurodevelopmental disorders. Overall design: We generated iPSC-derived organoids from a DEE-13 patient, with a gain-of-function variant (p.R1872>L) in the SCN8A gene, associated with refractory seizures and intellectual disability. Organoids from this patient line (Mut) as well as matched CRISPR-corrected control line (iCtrl) were directed toward cortical, hippocampal, or ganglionic eminence (GE) fates. On Day 59, GE organoids were fused with cortical (Cx) or hippocampal (Hc) organoids.