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A fundamental but unanswered question in neuropsychiatry is whether the psychiatric symptoms of epilepsy are caused by the same or a separate pathophysiology as seizures. To address this question, we investigated a monogenic form of epilepsy (pyridoxine-dependent epilepsy) caused by aldehyde dehydrogenase 7 family member A1 (ALDH7A1) mutations. ALDH7A1 global knockout mice exhibited both seizure-associated and maladaptive affective behavioral phenotypes. However, seizure phenotypes were caused by ALDH7A1 deletion in hepatocytes whereas maladaptive affective behaviors were caused by ALDH7A1 deletion in astrocytes. Deletion in astrocytes disrupted astrocyte redox homeostasis, impairing regulation of extracellular ion concentrations and reducing neuronal activity in the prelimbic cortex. Sulforaphane, which activates the NRF2 antioxidant pathway, restored prelimbic neuronal activity and rescued maladaptive affective behaviors in ALDH7A1 knockout mice but did not prevent seizures. These studies implicate astrocyte redox homeostasis and prelimbic hypoactivity in maladaptive affective behavioral phenotypes in a congenital form of epilepsy, which are mechanistically and therapeutically dissociable from seizure pathophysiology.