Altered cardiac excitability and arrhythmia in models of SCN1B-linked developmental and epileptic encephalopathy.

Biallelic variants in SCN1B, which encodes the voltage-gated sodium channel β1/β1B subunits, are linked to DEE52, a developmental and epileptic encephalopathy with a high risk of sudden unexpected death in epilepsy (SUDEP). DEE52 patients present clinically with Dravet syndrome or the more severe early infantile DEE. SCN1B is expressed in brain and heart in humans and in mice. Thus, we have proposed that, in addition to generalized seizures, cardiac arrhythmia may play a role in SUDEP. Mice with homozygous expression of the DEE52 variant Scn1b-c.265C>T, predicting p.R89C, have spontaneous and hyperthermia-induced generalized seizures and SUDEP. Here we conducted cardiac characterization of Scn1b-c.265C>T mice and studied induced pluripotent stem cell cardiomyocytes (iPSC-CMs) derived from 2 SCN1B-c.265C>T DEE52 patients. Scn1bC89/C89 mouse CMs showed increased transient outward potassium current (Ito) density and heart sections revealed ventricular fibrosis. Scn1bC89/C89 mice were susceptible to pacing-induced cardiac arrhythmias. Patient-derived iPSC-CMs with biallelic SCN1B-c.265C>T variant expression showed increased sodium current (INa), late INa, and Ito current densities. We conclude that, while mouse and human cardiac AP waveforms have critical differences, increased Ito is common to both models of DEE52. Overall, our data suggest that electrical and structural substrates may lead to arrhythmias and contribute to SUDEP in DEE52.