Aeran and colleagues present research on targeted gene therapy vector engineering and pre-clinical testing of neuron-targeted AAV9-based constructs for STXBP1-related neurodevelopmental and epileptic encephalopathies. Candidate vectors designed to target specific neuronal types and detarget tissues associated with toxicity produced robust phenotypic reversal in Stxbp1 +/− mice and were well tolerated in monkeys.