HUMAN INDUCED PLURIPOTENT STEM CELL-DERIVED NEURONAL MODELS OF GABA<SUB >A</SUB> RECEPTOR-RELATED DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHIES REVEALED ACCELERATED NEURODEVELOPMENT

Developmental and epileptic encephalopathies (DEE) is a severe neurodevelopmental disorder characterised by childhood-onset seizures and other comorbidities, including but not limited to, intellectual disabilities, motor deficits and developmental regression. The main causes of DEE are genetic with mutations in GABA_A receptors representing a large subset of patients. GABA_A receptor-related DEEs have a diverse range of clinical phenotypes though trends have started to emerge based on the electrophysiological characteristics of the mutant receptor, namely gain- vs loss-of-function (GoF vs LoF). While GABA_A receptor-related DEEs have been studied in genetically engineered mice, these models do not provide the developmental insights or human context. Here, we developed the first human induced pluripotent stem cell (hiPSC)-derived neuronal model of GABA_A receptor-related DEE by engineering patient-relevant mutations into control cell lines. Cortical glutamatergic neurons were differentiated from control and mutant hiPSC lines using a small molecule protocol onto high density multi-electrode array (MEA) plates. In a GoF GABA_A receptor a1 subunit cell line, hiPSC-derived neurons displayed elevated spontaneous spiking with burst-like firing patterns compared to the control. Interestingly, the mutant neurons also showed an increase in neurite outgrowth. Therefore, both functional and morphological assessments suggest that the a1 GABA_A receptor GoF variant leads to accelerated neurodevelopment, consistent with the role of GABA in promoting neuronal maturation during embryogenesis. Our study revealed how GABA_A receptor-related DEEs may manifest during early neurodevelopment, establishing a platform to investigate detailed disease mechanisms and potential interventions in a human context.