Abstracts

Rationale: Individuals who suffer from epilepsy have an increased risk of dying suddenly for unknown reasons due to sudden unexpected death in epilepsy (SUDEP), the leading cause of epilepsy-related mortality. One of the risk factors for SUDEP is being male but the reasons for this association are not well understood. To explore differences in SUDEP risk due to sex, male and female mice with epilepsy due to Kcna1 gene deletion (Kcna1^–/–) were investigated for differences in SUDEP susceptibility. Kcna1, which encodes voltage-gated Kv1.1 potassium channel alpha subunits, is a human epilepsy gene that has been linked to SUDEP in at least one reported case. In addition, Kcna1^–/– mice are an extensively utilized genetic model of human epilepsy and SUDEP because of their genotypic and phenotypic similarity to the human condition, including severe early-onset seizures, brain-driven cardiac arrhythmias, seizure-related cardiorespiratory dysfunction, and premature death. Methods: SUDEP incidence was measured using Kaplan-Meier survival curves. Seizure thresholds were measured as the latency to flurothyl-induced or pentylenetetrazol (PTZ)-induced seizures (n=3-5/sex per genotype). Simultaneous video electroencephalography (EEG) – electrocardiography (ECG) recordings (n=2 mice/sex) were performed to measure spontaneous seizures and cardiac dysfunction. Hippocampal gene expression analyses (n=3/sex per genotype; 30-d old animals) were performed using mRNA microarrays and significant differences identified as genes with an ANOVA P-value of =0.05 and a fold change of =2. Results: Male Kcna1^–/– mice (n=290) exhibited significantly higher SUDEP incidence (PKcna1^–/– mice (n=2) may exhibit higher seizure frequencies (P=0.10) and longer seizure durations (P=0.067) than Kcna1^–/– females (n=2). In addition, male Kcna1^–/– mice exhibited a 3-fold increase in the frequency of interictal skipped heart beats compared to females (P=0.006). In mRNA microarray experiments, male Kcna1^–/– hippocampi exhibited significantly higher expression of synaptic plasticity and neuronal excitability genes (Nptx2, Adgrf4 and Egr3). Male Kcna1^–/– hippocampi also exhibited significant decreases in expression of circadian rhythm genes (Per3, Dbp and Npas2) and mitochondrial genes (mt-TK, Acss1, and GatC). Conclusions: The higher mortality rate in Kcna1^–/– males seems to be related to longer seizure durations and higher seizure frequencies, which leads to greater seizure burdens. The higher frequency of skipped heart beats in Kcna1^–/– males may indicate increased risk of deleterious cardiac dysfunction, especially due to parasympathetic mechanisms. Sex-specific differences in hippocampal gene expression may contribute to the higher risk of SUDEP in Kcna1^–/– males by augmenting neuronal excitability in epileptogenic brain regions, destabilizing sleep-wake patterns, and disturbing energy metabolism. Funding: This work was supported by grants from the National Institutes of Health (R01NS100954 and R01NS099188).