Dravet syndrome is an early-onset epileptic encephalopathy characterized by seizures, developmental delay, and cognitive impairment. The disorder results from haploinsufficiency of SCN1A, a neuronal voltage-gated sodium channel gene. The encoded channel, Nav1.1, is an abundant sodium channel in the mammalian nervous system. We propose to investigate the reversibility of prenatal and early postnatal effects of Scn1a haploinsufficiency using a mouse model that recapitulates seizures, behavioral abnormalities, and cognitive impairment. We will use a floxed-stop cassette and an inducible CRE transgene to achieve regulated activation of the transcriptionally inactive targeted Scn1a locus. We will generate the inactive allele, Scn1aFS, by inserting the floxed-stop cassette into intron 1 of Scn1a using CRISPR-Cas9 targeting. The Scn1aFS allele will be activated by tamoxifen-induced expression of an ER-CRE transgene. We will administer tamoxifen to heterozygous Scn1aFS/+ mice at 3 weeks or 6 weeks of age, and assess the effects on seizure onset, seizure susceptibility, and survival. These experiments will provide proof of principle regarding the effectiveness of restoring Scn1a activity for treatment of Dravet syndrome. We will also assess the time window for effective therapy. This work will provide a novel mouse model for future investigations of reversibility of behavioral and cognitive comorbidities, and unique information regarding reversibility of the features of Dravet syndrome as a guide for future therapeutic interventions.
A major uncertainty in the development of treatments for Dravet syndrome is the reversibility of the major clinical features, which include developmental delay and cognitive impairment in addition to seizures. Ion channel mutations, such as haploinsufficiency of SCN1A in Dravet syndrome, may irreversibly alter brain development prior to the onset of seizure activity in the first year of life. We will generate a reversible Dravet mouse model to provide 'proof of principle' regarding the extent to which the seizures and comorbidities of Dravet Syndrome may be reversed by effective treatment.
