Abstracts

Rationale: Dravet Syndrome is a childhood epileptic disorder that begins in the first year of life and leads to febrile seizures, frequent episodes of status epilepticus, cognitive dysfunction, ataxia, and increased mortality. This syndrome is usually caused by de novo mutations in the SCN1A gene leading to insufficient production of the Nav1.1 sodium channel. Current treatment options are limited to anti-seizure drugs that address the symptoms, albeit poorly, but not the underlying genetic defect. Readthrough drugs, which are able to read through the premature termination (stop) codons produced by nonsense mutations, have the potential to be a viable treatment for the 15-20% of subjects with Dravet Syndrome caused by these mutations. These drugs have shown potential efficacy in treating other diseases with nonsense mutations such as cystic fibrosis. We sought to test the hypothesis that readthrough drug therapy of a mouse knock-in nonsense mutation model of Dravet Syndrome would partially correct the insufficient production of sodium channels and ameliorate seizures.Methods: We tested this hypothesis using mice carrying the human SCN1A nonsense mutation R1407X (Ogiwara et al, J. Neurosci. 2007). Two litters of heterozygous knock-in mice were treated for 14 days with 50 mg/kg or 100 mg/kg gentamicin, or with vehicle, given subcutaneously once daily. The mice were then tested for seizure susceptibility using a temperature elevation-induced seizure paradigm. Results: We found that the average temperatures to first seizure for the first treatment group (50mg/kg) and untreated mice were 40.6 C and 40.2 C respectively (p=0.65, student s t-test). The average temperatures to most severe seizure for the first treatment group (50mg/kg) and untreated mice were 42.5 C and 41.8 C respectively (p=0.47). Additionally we found the average temperatures to first seizure for the second treatment group (100mg/kg) and untreated mice were 40.78 C and 40.25 C respectively (p=0.45, student s t-test). The average temperatures to most severe seizure for the second treatment group (100mg/kg) and untreated mice were 42.3 C and 42.8 C respectively (p=0.02, student s t-test). Thus there was no significant difference in seizure susceptibility between transgenic Scn1a+/-mice treated with either dose of gentamicin compared with vehicle treatment.Conclusions: Systemic gentamicin readthrough therapy did not alter seizure susceptibility in a Dravet Syndrome knock-in mouse model. One possible explanation for the lack of effect is that gentamicin may not sufficiently cross the blood-brain barrier. Ongoing studies are testing the effects of intracerebroventricular gentamicin infusion, as well as newer generation readthrough drugs that are more likely to be blood-brain barrier permeable.