Modeling Dravet syndrome using induced pluripotent stem cells (iPSCs) and directly converted neurons

Severe myoclonic epilepsy of infancy (SMEI, also known as Dravet syndrome) and genetic epilepsy with febrile seizures plus (mild febrile seizures) can both arise due to mutations of SCN1A, the gene encoding alpha 1 pore-forming subunit of the Nav1.1 voltage-gated sodium channel. Owing to the inaccessibility of patient brain neurons, the precise mechanism of mild febrile seizures and SMEI remains elusive, and there is no effective pharmacotherapy. Induced pluripotent stem cells (iPSCs) and induced neurons (iNs) have been successfully generated from patients and applied for modeling various neuronal diseases. In this study, we established iPSC lines from one SMEI patient and one mild febrile seizures patient, respectively. Functional glutamatergic neurons were subsequently differentiated from these iPSCs. Electrophysiological analysis of patient iPSC-derived glutamatergic neurons revealed a hyperexcitable state of enlarged and persistent sodium channel activation, more intensive evoked action potentials and typical epileptic spontaneous action potentials. In consistent with the severity of the symptoms, the hyperexcitability of the neurons derived from SMEI patient was more serious than that of mild febrile seizures patient. Furthermore, the hyperexcitability of the neurons can be alleviated by treatment with phenytoin, a conventional antiepileptic drug. In parallel, iNs were directly converted from patient fibroblasts which also showed a delayed inactivation of sodium channels. Our results demonstrate that both iPSC-derived neurons and iNs from mild febrile seizures and SMEI patients exhibited a hyperexcitable state. More importantly, patient iPSC-derived neurons can recapitulate the neuronal pathophysiology and respond to drug treatment, indicating that these neurons can be potentially used for screening appropriate drugs for personalized therapies.