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Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy caused by loss-of-function variants in SCN1A, with seizures typically emerging during the first year of life. Although DS pathophysiology has largely been attributed to inhibitory network dysfunction underlying seizures, early developmental alterations in inhibitory interneurons remain poorly understood.

We generated inhibitory interneuron-enriched subpallial organoids from patient-derived induced pluripotent stem cells carrying an SCN1A loss-of-function variant and the corresponding isogenic control. Using complementary molecular and functional approaches, including quantitative polymerase chain reaction, bulk RNA sequencing, whole-cell patch-clamp electrophysiology, and two-photon calcium imaging, we investigated early inhibitory interneuron development and functional maturation in a human cellular context.

Transcriptomic profiling revealed early dysregulation of ventral forebrain interneuron developmental programs, including altered expression of medial ganglionic eminence-associated transcriptional regulators, preceding inhibitory network dysfunction. Patient-derived organoids exhibited marked reductions in intrinsic neuronal excitability and synaptic activity. Acute application of fenfluramine, a clinically approved antiseizure medication for DS, partially restored neuronal activity, demonstrating the translational relevance of this model.

These findings demonstrate that SCN1A loss of function disrupts early inhibitory interneuron development and functional maturation, defining a developmental vulnerability that likely precedes the emergence of epilepsy in DS. This work establishes patient-derived inhibitory organoids as a human-relevant platform for dissecting disease mechanisms and evaluating therapeutic responses in SCN1A-related epileptic encephalopathies.