Abstracts

Rationale: Mutations in the synaptic machinery gene syntaxin-binding protein 1, STXBP1, also known as MUNC18-1, have been linked to childhood epilepsy and other neurodevelopmental problems. We identified a family with a mutation in STXBP1 that was associated with autism and epilepsy. Zebrafish (Danio rerio) have emerged as a powerful model system for studying the electrophysiological, anatomical, and behavioral effects of epilepsy. Mutant zebrafish lines, which can be rapidly generated, now provide the opportunity to characterize the electrophysiological (EEG), behavioral, and pharmacological outcomes of epilepsy candidate gene knockout.Methods: To study loss-of-function mutations in syntaxin-binding protein, we used CRISPR/Cas9 gene editing to disrupt zebrafish stxbp1a. Zebrafish have two copies of stxbp1, stxbp1a and stxbp1b, and stxbp1a is highly similar to human STXBP1. We cloned and sequenced a novel loss-of-function mutant allele of stxbp1a. Using a behavioral videotracking system, we recorded velocity, movement duration, and distance traveled for 5-day-old larval zebrafish. To assay epilepsy and possible epilepsy comorbidity phenotypes, we used video data to measure diurnal rhythms, startle responses, and heart rate.Results: Homozygous stxbp1a mutant zebrafish exhibited profound developmental problems including reduced movement at baseline and in response to light/dark transitions, developmental delay, excess pigmentation, and early death. Heterozygous stxbp1a mutant zebrafish had more subtle defects, including decreased light-induced startle responses compared to wildtype siblings.Conclusions: Loss of stxbp1a function in zebrafish larvae causes severe locomotor impairment. By studying the small and tractable zebrafish with high-throughput behavioral analyses, we are able to test causal roles for candidate genes and may identify precision therapies for specific genetically defined epilepsies.