Abstracts

Rationale: Dravet syndrome is an epileptic encephalopathies that usually appears in the first year of life and is characterized by normal development before seizure onset. The first episode is often associated with fever and as seizures continue, development can be compromised. Although over 80% of children with Dravet have a disruption in the SCN1A gene, environmental factors also contribute to disease onset and progression. Here, we tested the interplay of gene x environment factors and sex in the Dravet disease.

Methods: Genetically, we used male and female mice that harbour a mutation in Scn1a and environmentally, we used heat since a warm bath or fever can trigger seizures in Dravet children. Breeding Scn1a^+/− mice on a 129S1/SvlmJ background with wild‐type C57BL/6J, led to three experimental groups for both sexes: control animals without the genetic disruption and without heat exposure (Scn1a+/+; “control”); animals with the Scn1a genetic mutation but no heat exposure (“Scn1a+/-”); animals with the genetic disruption and exposed to heat (“Scn1a+/- + heat”). At postnatal day (P) 18-20, animals underwent surgery to attach prefabricated EEG head mounts. Four electrodes (stainless steel screws affixed to the head mount) were placed on the brain surface and secured with dental cement. Animals were allowed to recover for 48 hours (h) and from P20-22 to P25-27, were continuously monitored 24 h per day by EEG and video. The electrical activity in the brain was analyzed for the frequency and amplitude of seizures with the corresponding video reviewed for the scoring of seizure behaviour using an adapted Racine scale. The environmental factor (heat) was introduced conducting a hyperthermia-induced experiment whereby a rectal probe was used to record body temperature increases while the core body temperature was raised 0.5°C every 2 min until the onset of the first clonic convulsion with loss of posture or until 42.5°C is reached and held for 3 minutes. If no seizure was observed during this holding period, the mouse was considered seizure‐free. Animal protocols used were approved by the University of Calgary Animal Care Committee and followed the Guidelines for the Canadian Council of Animal Care.

Results: We observed sex differences in the number of spontaneous seizures between groups, with males showing an interplay between genetic and environmental factors to initiate disease onset [t(12) = 3.188, P< 0.01], while in females the genetic component alone was sufficient to display seizures [t(16)= 2.073, P=0.05].

Conclusions: This work demonstrates that environmental factors, heat in this case, can sex-specifically influence the induction of seizures in a genetic model of Dravet. Our data suggest extra care perhaps should be taken to avoid over-heating specifically in boys who harbour a SCN1A mutation. Over the long-term it is important to gain a better understanding of the gene x environment x sex interactions in Dravet to help identify measures that can prevent disease onset and/or progression in these children.

Funding: Please list any funding that was received in support of this abstract.: Alberta Innovates, Alberta Children’s Hospital Research Institute, Hotchkiss Brain Institute, Brain Canada, Dravet Canada.