Abstracts

Rationale: Dravet syndrome (DS), a severe congenital epilepsy, is caused in 25% of the cases by nonsense variants in SCN1A, a gene encoding the alpha subunit of the voltage-gated sodium channel Nav1.1. Characterized by frequent and drug-resistant seizures, DS also leads to cognitive deficits, motor dysfunction, behavioural problems, language impairment and a 15% premature mortality rate. Preclinical development of new targeted therapies requires the use of animal models that recapitulate the disease at the genetic and clinical levels. We present a novel open-access mouse model of DS, carrying a pathogenic R613X nonsense mutation found in Dravet patients.

Methods: A CRISPR/Cas9-generated A >T point mutation at nucleotide 1837 (converting Arg613 into a STOP codon) and a silent C >T mutation at position 1833 were introduced to exon 12 of the mouse Scn1a gene using 129S1/SvImJ embryos. We analysed Scn1a expression and characterized the epileptic phenotypes of the Scn1a^R613X/WT mice on the pure 129S1/SvImJ and on the mixed background (50:50, 129S1/SvImJ: C57BL/6J).

Results: The premature stop codon induced by the R613X nonsense mutation reduced the Scn1a mRNA and Nav1.1 protein levels on all genetic backgrounds. Moreover, at postnatal day 21, Scn1a^R613X/WT on either background were susceptible to thermally induced seizures. However, the threshold temperature was lower in mice of mixed background.

Conclusions: The novel SCN1AR613X mice (JAX stock 034129) are a valid DS animal model that can be used to examine the safety and effectiveness of readthrough therapeutic drugs and advanced gene therapies on DS-induced seizures and comorbidities, such as cognitive impairment, hyperactivity or motor abnormalities, similar to those associated with a SCN1A knock-out allele.

Funding: Please list any funding that was received in support of this abstract.: Dravet Syndrome Foundation Spain.