Human brain organoids reveal MGE interneuron defects independent of mTOR-hyperactivation in genetic focal epilepsy

The pathogenic mechanisms of non-acquired focal epilepsy (NAFE) are underexplored. As the most common monogenic cause of NAFE, the epileptogenic mechanism of mutations in the GTPase-Activating Protein Activity Toward Rags 1 (GATOR1) genes remains unclear. Here, using patient-derived neuron-type-specific organoids, we show that focal epilepsy-associated transcriptional dysregulation is highly pronounced in ventral GABAergic organoids (VGOs). Patient VGOs exhibit significant impairments in GABAergic interneuron differentiation, migration, and functional GABA release. Mechanistically, these interneuron defects are independent of the canonical mTOR-hyperactivation and are instead driven by the deficiency of MAFB. MAFB expression is significantly decreased in both patient-derived VGOs and brain tissues. MAFB knockdown leads to similar interneuron defects in VGOs. Importantly, MAFB overexpression rescues the abnormal phenotypes in patient VGOs. Collectively, our study reveals a non-canonical cellular and molecular mechanism underlying GATOR1-related focal epilepsy, providing a mechanistic basis for precise therapy. Using human brain organoids, here authors report that GATOR1 loss impairs GABAergic interneurons via MAFB downregulation, independently of mTOR hyperactivation, offering new mechanistic insights into genetic focal epilepsy.