DEPDC5: Modeling of the Two-Hit Wonder in Cortical Organoids
Mosaic Human Cortical Organoids Model 1 mTOR-Related Focal Cortical Dysplasia 2 Through DEPDC5 Deletion Maletic M, Bizzotto S, Ribierre T, Guerdoud K, Raoux C, Doladilhe M, Dalle C, Picard F, Baulac S. Brain 2026:awag086. doi: 10.1093/brain/awag086. Online ahead of print. PMID: 41789478 Focal cortical dysplasia type II (FCDII), a major cause of pediatric drug-resistant focal epilepsy, results from brain somatic variants in the mechanistic target of rapamycin (mTOR) pathway genes, including germline and somatic second-hit loss-of-function variants in the mTOR repressor DEPDC5. Here, we present a proof-of-concept model of DEPDC5 two-hit inactivation mosaicism using patient-derived human cortical organoids (hCOs). Mosaic hCOs displayed increased mTOR activity that was rescued by the mTOR inhibitor rapamycin. Mosaic hCOs also exhibited dysmorphic-like neurons and enhanced neuronal excitability, recapitulating key FCDII pathology hallmarks. Single-cell transcriptomics across 3 developmental stages revealed aberrant differentiation trajectories leading to premature upper-layer neuron generation, upregulated Notch and Wnt signaling pathways in neural progenitors, and altered expression of synaptic- and epilepsy-associated genes in excitatory neurons. In addition, we identified cell-autonomous alterations in metabolism and translation in mosaic DEPDC5 two-hit hCOs. This study provides novel insights into how DEPDC5 deficiency perturbs human corticogenesis, highlighting that mosaic bi-allelic inactivation of the gene is necessary for FCDII pathogenesis.