Abstracts

Rationale: Heterozygous mutations in the SCN1B voltage-gated sodium channel subunit result in genetic epilepsy with febrile seizures plus (GEFS+), and homozygous SCN1B mutations cause the more severe epilepsy known as Dravet syndrome. To better understand the underlying pathogenesis and develop a tool to screen anti-seizure medications, we used patient-derived induced pluripotent stem cells (iPSCs) to model mutant SCN1B-related epilepsy syndromes. Methods: We obtained fibroblasts from patients with: 1) GEFS+ caused by a mutation involving a cysteine to tryptophan substitution at position 121 (C121W) in SCN1B; and 2) Dravet syndrome due to a homozygous R89C mutation in SCN1B. Using episomal reprogramming of patient fibroblasts, we generated multiple iPSC lines per patient. In addition, we used CRISPR gene editing to introduce frameshift mutations into the first exon of SCN1B in control human iPSCs, generating compound heterozygous SCN1B knock-out lines with an isogenic control for comparison. The iPSCs were differentiated into excitatory cortical-like neurons (2-D cultures) and cerebral organoids (3-D cultures). Results: We successfully differentiated patient-derived iPSCs into excitatory cortical-like neurons, with expression of various cortical layer markers, such as CTIP2 and TBR1. We performed whole-cell patch-clamp recordings as well as multi-electrode array recordings on these neurons, and demonstrated mature functional electro-physiological characteristics. We also generated cerebral organoids from patient and control iPSCs, and these displayed markers for mature neurons and various cell layer markers, and also generated astrocytes. Ongoing studies are comparing the electrophysiological properties of mutant SCN1B and control lines, and assaying for morphological abnormalities in the 2-D and 3-D cultures. Conclusions: Using iPSCs to model genetic epilepsies is a viable strategy to study SCN1B-related epilepsy syndromes. This platform will help us understand the underlying mechanisms of childhood genetic epilepsies, test new therapies, and develop approaches for precision medicine. Funding: 1). NS076752 2). NIH 5 K12 HD 028820