Stem cell-derived human glutamatergic neurons with pathogenic KCNQ2 variants display hyperactive bursting phenotypes

Pathogenic variants in the KCNQ2 gene, which encodes a potassium channel subunit, are associated with neonatal seizures, epileptic encephalopathy, intellectual disability, and autism. Although the consequences of disrupted KCNQ2 channel function have been studied in the past, the detailed molecular mechanisms underlying the development of neurological phenotypes remain unclear, and neuronal models of specific patient variants are lacking. We generated patient-specific induced pluripotent stem cells (iPSCs) from fibroblasts from three individuals with distinct KCNQ2 pathogenic variants. We corrected the KCNQ2 variants using CRISPR-Cas9 editing to create isogenic controls and differentiated these iPSCs into glutamatergic neurons to study the effects of each variant on neuronal function. The three KCNQ2 variants were: 1) KCNQ2 c.875_877delTCCinsCCT, L292_L293delinsPF, 2) KCNQ2 c.766G>T, G256W, and 3) KCNQ2 c.821C>T, T274M. Our data revealed longer neurite outgrowth in two patient lines (T274M and G256W). Transcriptional profiling showed that all three KCNQ2 lines had increased expression of genes involved in synaptic transmission/signaling, cell adhesion, and GTPase signal transduction. Functional analyses of neuronal networks revealed increased burst duration in all three KCNQ2 lines compared with their isogenic controls. Furthermore, neurons from the L292_L293delinsPF and T274M lines displayed increased network connectivity associated with increased density of synaptic markers. Finally, we detected hyperexcitable neuronal networks in the G256W line with electrical stimulation of the neural networks on a high-density microelectrode array, and this phenotype was rescued with retigabine. These disease-related phenotypes for each of the KCNQ2 pathogenic variants can be used for drug screening to identify treatment options for the patients.