Abstracts

Rationale: SUDEP is the most devastating consequence of epilepsy, yet little is understood about its causes and no biomarkers exist to identify at risk patients. To gain insight into these critical issues, we are focusing on epilepsy syndromes with a high SUDEP incidence. Homozygous variants in SCN1B, encoding voltage-gated sodium channel (VGSC) β1 subunits, are linked to Dravet syndrome (DS), a severe developmental and epileptic encephalopathy. SCN1B variants are also linked to cardiac arrhythmias that are associated with sudden death. We have proposed that the high incidence of SUDEP in DS results from cardiac arrhythmia in addition to central nervous system hyperexcitability, reflecting the expression of mutant VGSC subunits in heart and brain. Previous work in Scn1b null mice showed prolonged QT intervals on the ECG, as well as increased Scn3a and Scn5a expression, aberrant calcium handling that was sensitive to tetrodotoxin, and increased transient and persistent sodium current (INa) in isolated ventricular cardiomyocytes (CMs). Here, we asked whether the SCN1B-linked DS variant, p.R89C, alters VGSC expression, INa density, or INa kinetics in human iPSC-derived CMs. Investigating the patho-physiological changes resulting from SCN1B-linked DS in a human model system is crucial to the development of novel therapeutics and predictive SUDEP biomarkers. Methods: We obtained fibroblasts from two DS patients with different homozygous variants in SCN1B. Using episomal reprogramming of patient fibroblasts, we generated iPSC-CM lines. In addition, we used CRISPR gene editing to generate SCN1B knock-out lines along with isogenic controls. The iPSCs are cultured and ventricular CMs will be selected for experiments. Ventricular iPSC-CMs are purified and gene expression analysis are measured by qPCR. Using the whole-cell configuration of the patch-clamp, I measured transient and persistent INa, voltage dependence of INa activation and inactivation, and INa kinetics to characterize VGSC function in CMs from SCN1B-linked DS patients, CRISPR-derived SCN1B null, healthy controls. Results: SCN1B-p.R89C iPSC-CMs have increased transient INa density compared to healthy control iPSC-CMs. Preliminary results suggest altered expression of a subset of VGSC genes in the SCN1B-p.R89C iPSC-CMs compared to controls. Conclusions: The Scn1b null mice mouse model of DS, which die suddenly by post-natal day 19, exhibited increased INa. Thus far, the SCN1B-p.R89C iPSC-CMs similarly have increased INa, thereby suggesting that INa in CMs as a potential identifier of SUDEP risk. We will continue to investigate other SCN1B patient derived iPSC-CMs, and by elucidating changes in CMs excitability, we can provide insights into the cardiovascular pathophysiology of SUDEP. Funding: NIH R37-NS076752, NIH R01-NS088571, The Pharmacological Sciences Training Program (PSTP) (T32), Rackham Merit Fellowship