Distinctivein vitrophenotypes in iPSC-derived neurons from patients with gain- and loss-of-functionSCN2Adevelopmental and epileptic encephalopathy

Abstract

SCN2Aencodes NaV1.2, an excitatory neuron voltage-gated sodium channel and a major monogenic cause of neurodevelopmental disorders, including developmental and epileptic encephalopathies (DEE) and autism. Clinical presentation and pharmocosensitivity vary with the nature ofSCN2Avariant dysfunction and can be divided into gain-of-function (GoF) cases with pre- or peri-natal seizures and loss-of-function (LoF) patients typically having infantile spasms after 6 months of age.We established and assessed patient induced pluripotent stem cell (iPSC) - derived neuronal models for two recurrentSCN2ADEE variants with GoF R1882Q and LoF R853Q associated with early- and late-onset DEE, respectively. Two male patient-derived iPSC isogenic pairs were differentiated using Neurogenin-2 overexpression yielding populations of cortical-like glutamatergic neurons. Functional properties were assessed using patch clamp and multielectrode array recordings and transcriptomic profiles obtained with total mRNA sequencing after 2-4 weeks in culture.At 3 weeks of differentiation, increased neuronal activity at cellular and network levels was observed for R1882Q iPSC-derived neurons. In contrast, R853Q neurons showed only subtle changes in excitability after 4 weeks and an overall reduced network activity after 7 weeksin vitro. Consistent with the reported efficacy in some GoFSCN2Apatients, phenytoin (sodium channel blocker) reduced the excitability of neurons to the control levels in R1882Q neuronal cultures. Transcriptomic alterations in neurons were detected for each variant and convergent pathways suggested potential shared mechanisms underlyingSCN2ADEE.In summary, patient iPSC-derived neuronal models of SCN2A GoF and LoF pathogenic variants causing DEE show specific functional and transcriptomic in vitro phenotypes.Significance statementSCN2Aencodes one of the major brain voltage-gated sodium channels, NaV1.2, and is a major monogenic cause of neurodevelopmental disorders, including severe infantile epilepsy and autism. SCN2A pathogenic variants cause either gain or loss of channel function, which correlates well with the clinical phenotype. Gain of function variants are associated with early-onset seizures with or without developmental delay, whereas loss of function results in late-onset severe epilepsy and/or autism. We used patient-derived induced pluripotent stem cells to generate neuronal cultures for two recurring SCN2A variants causing early and late seizure onset epilepsy. Identified electrophysiological and transcriptome changes compared to the isogenic control lines can be correlated with the distinguishable clinical phenotype.