Prime editing of a pathogenic <i>Scn1a</i> allele ameliorates seizure phenotypes in a GEFS ⁺ mouse model

Generalized epilepsy with febrile seizures plus (GEFS + ) is an inherited epileptic disorder predominantly linked to autosomal-dominant, loss-of-function mutations in the sodium voltage-gated channel α subunit 1 ( SCN1A ) gene, which encodes the α subunit of the neuronal voltage-gated sodium ion channel type 1 (Na V 1.1). Reduced Na V 1.1 function in γ-aminobutyric acid (GABA)–ergic interneurons impairs inhibitory signaling and leads to neuronal hyperexcitability. Clinically, GEFS + is characterized by a spectrum of seizure types, often beginning with febrile seizures in early childhood and progressing to generalized tonic-clonic seizures later in life. Here, we used prime editing to correct the pathogenic SCN1A -K1270T mutation in the Scn1a KT/ + mouse model of GEFS + . Adeno-associated viral (AAV) vectors were used to deliver an intein-split prime editor under the control of a neuron-specific promoter into the cerebral ventricles of neonatal mice. This enabled efficient in vivo editing, achieving 34.7 ± 14.5% correction of the mutant allele in cortical bulk DNA, 81.2 ± 5.9% correction of mRNA, and improved multiple disease-relevant phenotypes. Survival increased from 80% in control-treated animals to 100% in treated mice, cortical inhibitory neuron transmission was improved (frequencies of inhibitory postsynaptic currents were increased from 0.32 to 1.32 hertz), and the frequency of induced febrile seizures decreased from 78.6% to 13.3%, approaching the frequency seen in wild-type mice (8%). These findings suggest the therapeutic potential of prime editing for the treatment of patients with SCN1A -associated GEFS + .