AAV-mediated neuronal expression of FOXG1 restores oligodendrocyte maturation, myelination, and hippocampal structure in mouse models of FOXG1 Syndrome

FOXG1 syndrome is a devastating neurodevelopmental disorder caused by haploinsufficiency of the transcription factor FOXG1, leading to intellectual disability, epilepsy, and white-matter deficits. Although FOXG1 is well known for its neuronal functions, its role in glial pathology remains poorly understood. Here, we show that reducing FOXG1 selectively in neurons impairs oligodendrocyte lineage progression and myelination, establishing a critical non-cell-autonomous role for neuronal FOXG1 in glial maturation. To restore FOXG1 in neurons, we developed AAV vectors expressing human FOXG1 under neuron-specific promoters. Neonatal administration of these vectors normalized oligodendrocyte precursor cell (OPC) accumulation, enhanced myelination, and corrected hippocampal structural abnormalities in Foxg1 conditional heterozygous mice. To test therapeutic robustness under stringent conditions, we used the patient-specific W300X heterozygous model, which combines FOXG1 loss-of-function with a toxic truncated protein and represents one of the most severe FOXG1 syndrome genotypes. Remarkably, neuron-restricted AAV-FOXG1 delivery produced substantial rescue even in this high-bar model, suppressing OPC overaccumulation, restoring myelination, and progressively improving dentate gyrus morphology, with benefits persisting into adulthood. Moreover, adolescent administration remained highly effective, rescuing myelination, axonal bundle thickness, and microglial activation. These findings identify neuronal FOXG1 as a master regulator of neuron-glia interactions and establish neuron-targeted AAV-FOXG1 as a potent and clinically translatable therapeutic strategy across diverse severities of FOXG1 syndrome.