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

SCN2Aencodes NaV1.2, an excitatory neuron voltage-gated sodium channel and major monogenic cause of neurodevelopmental disorders, including developmental and epileptic encephalopathies (DEE) and autism. Clinical presentation and pharmocosensitivity vary with nature ofSCN2Avariant dysfunction with gain-of-function (GoF) cases presenting with pre- or peri-natal seizures and loss-of-function (LoF) patients typically having infantile spasms after 6 months of age. Here, 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.Patient-derived iPSC lines were differentiated using a Neurogenin-2 overexpression yielding populations of cortical-like glutamatergic neurons. Electrophysiological and transcriptomic profiles were assessed after 2-4 weeks in culture. Increased neuronal activity at both cellular and network level was observed for R1882Q iPSC-derived neurons at three weeks of differentiation. In contrast, R853Q neurons showed only subtle changes in excitability after four weeksin vitro. In alignment with the reported efficacy in some GoFSCN2Apatients, phenytoin (sodium channel blocker) reduced excitability of neurons to the control levels in R1882Q neuronal cultures. Transcriptomic alterations in neurons were detected for each variant and convergent pathways pointed at the shared mechanisms underlyingSCN2ADEE.