AAV9/SLC6A1 gene therapy rescues abnormal EEG patterns and cognitive behavioral deficiencies in Slc6a1^–/– mice

The solute carrier family 6 member 1 (SLC6A1) gene encodes the γ-aminobutyric acid (GABA) transporter GAT-1, the deficiency of which is associated with infantile encephalopathy with intellectual disability. We designed 2 AAV9 vectors, with either the JeT or MeP promoter, and conducted preclinical gene therapy studies using heterozygous and homozygous Slc6a1-KO mice at different developmental ages and various routes of administration. Neonatal intracerebroventricular administration of either vector resulted in significantly normalized EEG patterns in Slc6a1^–/– or Slc6a1^+/– mice as well as improvement in several behavioral phenotypes of Slc6a1^–/– mice. However, some mortality and adverse effects were observed in neonatal-treated mice. Intrathecal administration of either vector at P5 normalized EEG patterns in Slc6a1^+/– mice, but in Slc6a1^–/– mice, the treatment only rescued nest building without impact on EEG. Both vectors were well tolerated in all mice treated at P5 or later (including WT mice), up to 1 year after injection. Overall, our data demonstrate compelling efficacy when mice are treated at an early development age. We also identified that outside of the neonatal treatment window, the severe homozygous KO model is more refractory to treatment, whereas our treatments in the heterozygous mice, which genotypically match human patients, have resulted in stronger benefits.