Neonatal but not Juvenile Gene Therapy Reduces Seizures and Prolongs Lifespan in SCN1B-Dravet Syndrome Mice

Dravet syndrome (DS) is a developmental and epileptic encephalopathy (DEE) that begins in the first year of life. While most cases of DS are caused by variants in SCN1A, variants in SCN1B, encoding voltage-gated sodium channel β1 subunits, are also linked to DS or to the more severe early infantile DEE. Both disorders fall under the OMIM term DEE52. Scn1b null mice model DEE52, with spontaneous generalized seizures and death in 100% of animals in the third postnatal week. Scn1b null cortical parvalbumin-positive interneurons and pyramidal neurons are hypoexcitable. The goal of this study was to develop a proof-of-principle gene replacement strategy for DEE52. We tested an adeno-associated viral vector encoding β1 subunit cDNA (AAV-Navβ1) in Scn1b null mice. We demonstrated that AAV-Navβ1 drives β1 protein expression in excitatory and inhibitory neurons in mouse brain. Bilateral intracerebroventricular administration of AAV-Navβ1 in Scn1b null mice at postnatal day (P) 2, but not at P10, reduced spontaneous seizure severity and duration, prolonged life span, prevented hyperthermia-induced seizures, and restored cortical neuron excitability. AAV-Navβ1 administration to WT mice resulted in β1 overexpression in brain but no obvious adverse effects. This work lays the foundation for future development of a gene therapeutic strategy for SCN1B-linked DEE patients. .