SCN1B and cardiac arrhythmia: We proposed previously using multiple models, including Scn1a-haploinsufficient mice that model DS (13), Scn1b-null mice that model DS or DEE52 (14, 15), Scn8a mice that model DEE13 (16), and SCN1A-linked DS patient–derived induced pluripotent stem cell cardiomyocytes (iPSC-CMs) (17), that increased sodium current (INa) density may be a biomarker for SUDEP risk by providing a substrate for cardiac arrhythmia.