Abstracts

Rationale: Dravet syndrome (DS) is a severe and intractable form of pediatric epileptic encephalopathy. Approximately 15% of DS patients undergo Sudden Unexpected Death in Epilepsy (SUDEP). A growing body of evidence suggests that cardiac arrhythmia may precede SUDEP in DS. We demonstrated previously that DS mouse cardiac myocytes (CMs) have increased transient and persistent sodium current (I_Na) density that resulted from increased activity of a tetrodotoxin-resistant I_Na, likely Na_v1.5. DS mouse myocytes also exhibited increased excitability, action potential prolongation, and triggered activity. Continuous radiotelemetric ECG recordings in DS mice showed QT prolongation, ventricular ectopic foci, idioventricular rhythms, beat-to-beat variability, ventricular fibrillation, and focal bradycardia. Methods: To test whether cardiac excitability is altered in DS patients, we generated induced pluripotent stem cells (iPSCs) from one control and two DS patients with distinct mutations in SCN1A. We previously found that iPSC neurons from one patient in this study were hyperexcitable, with increased I_Na density. For the present work, we differentiated the iPSCs into CMs. Results: Immunofluorescence staining showed that iPSC-CMs were positive for the cardiac markers, MLC2a or MLC2v, with some cells positive for both. Functionally, confluent iPSC-CMs from both DS patients had an increased intrinsic beating rate when compared to control (80±6 and 104±2 vs. 46±2 for DS4, DS2 and Cont 2 respectively; P<0.05, N≥8 per group). Multielectrode array data confirmed that both the beat period (the time between beats) and field potential duration (a correlate of action potential duration) were decreased in DS iPSC-CMs vs control. Consistent with our previous studies in DS mice, we observed an increase in peak I_Na density in iPSC-CMs from both DS patients (-302 ± 65 and -404 ± 38 vs. -230 ± 15 for DS4, DS2 and Cont 2 respectively; P<0.05 for DS2 vs Cont2 and P=0.07 for DS4 vs. Contr2, N=3, 10, and 10 respectively). Recordings from additional DS patient and control iPSC CMs are ongoing. Conclusions: Taken together our data suggest that alterations in cardiac excitability may contribute to the mechanism of SUDEP in DS via increased I_Na density, which may underlie arrhythmia in DS patients. Furthermore, DS patient-derived iPSC-CMs may provide a valuable model for advancing our knowledge of how cardiac abnormalities play a role in the mechanism of SUDEP.