MD/PhD Student University of Iowa, The NINDS Center for SUDEP Research Coralville, Iowa
This abstract is a recipient of the Young Investigator Award This abstract has been invited to present during the Better Patient Outcomes through Diversity Platform poster session This abstract is recognized by Partners Against Mortality in Epilepsy for its contribution to improving the understanding of epilepsy-related mortality
Rationale: Sudden Unexpected Death in Epilepsy (SUDEP) is a major cause of mortality in people with refractory epilepsy. We recently showed that patients with Dravet syndrome (DS) commonly have peri-ictal breathing dysfunction and that postictal death in Scn1aR1407X/+ (DS) mice is due to seizure-induced respiratory arrest (S-IRA). De novo mutations of the SCN8A gene have recently been recognized as a cause of epileptic encephalopathy. Mice that harbor a gain-of-function mutation (N1768D) identified in patients with epileptic encephalopathy have spontaneous convulsive seizures and SUDEP. Here, we use Scn8aN1768D/+ (D/+) mice to monitor cardiorespiratory function during spontaneous seizures and seizure-induced death. Methods: Unanesthetized D/+ and WT (Scn8a+/+) mice of ages P25-P30 were placed in a whole-body plethysmograph. Mice were exposed to hyperoxic (50% O2; balance N2) air to measure baseline breathing, and then to increasing levels of CO2 (3, 5, and 7%; 50% O2; balance N2) to measure the hypercapnic ventilatory response (HCVR). After a brief washout period with room air (21% O2; balance N2), mice were exposed to 10% O2 to measure the hypoxic ventilatory response (HVR). Data were normalized to body weight and statistical analysis was performed with a 2-way ANOVA with Bonferroni’s multiple comparison test as appropriate (p< 0.05). Additional D/+ mice were instrumented with headmounts customized with electroencephalography (EEG), electrocardiography (EKG) and electromyography (EMG) leads and housed individually in custom mouse epilepsy-monitoring unit/plethysmography chambers for continuous 24-hour surveillance. Only seizures that qualified as R5 on a modified Racine scale were analyzed. Results: The baseline (inter-ictal) slope of the HCVR and HVR were significantly lower in D/+ mice (n=8) compared to WT littermates (n=6) by 47% (p = 0.0096) and 31% (p = 0.002), respectively. A total of 28 spontaneous nonfatal seizures were recorded from 5 D/+ mice, all of which presented with apnea. Spontaneous seizure-induced deaths were recorded in 6 D/+ mice (See Figure). In each case S-IRA occurred first, followed by cardiac activity persisting for several minutes until terminal asystole. Conclusions: There is increasing evidence that respiratory dysfunction and defects in CO2 homeostasis play a major role in SUDEP. Our findings demonstrate that S-IRA and subsequent failure to resume breathing, rather than cardiac dysfunction, are the determining events that cause seizure-induced death in D/+ mice. Future directions include implanting a depth electrode into the amygdala, a brain region implicated in seizure propagation and breathing control, in D/+ mice to determine whether seizure spread to the amygdala correlates with the onset of respiratory dysfunction. Our results suggest that inter-ictal and post-ictal ventilatory abnormalities play a major role in SUDEP in patients with epileptic encephalopathy and may be a biomarker for those at highest risk. Funding: Please list any funding that was received in support of this abstract.: NIH NINDS (U01 NS090414 & U01 NS090407) to GR & F31 NS110333 to FT Click here to view image/table
