Context-dependent hyperactivity in and zebrafish models of SYNGAP1-related disorder.

Background And Aims: SYNGAP1-related disorder (SYNGAP1-RD) is a prevalent genetic form of Autism Spectrum Disorder and Intellectual Disability (ASD/ID) and is caused by or inherited mutations in one copy of the gene. In addition to ASD/ID, SYNGAP1 disorder is associated with comorbid symptoms including treatment-resistant-epilepsy, sleep disturbances, and gastrointestinal distress. Mechanistic links between these diverse symptoms and variants remain obscure, therefore, our goal was to generate a zebrafish model in which this range of symptoms can be studied.

Methods: We used CRISPR/Cas9 to introduce frameshift mutations in the and zebrafish duplicates () and validated these stable models for Syngap1 loss-of-function. Because is extensively spliced, we mapped splice variants to the two zebrafish and genes and identified mammalian-like isoforms. We then quantified locomotory behaviors in zebrafish larvae under three conditions that normally evoke different arousal states in wild-type larvae: aversive, high-arousal acoustic, medium-arousal dark, and low-arousal light stimuli.

Results: We show that CRISPR/Cas9 indels in zebrafish and produced loss-of-function alleles at RNA and protein levels. Our analyses of zebrafish Syngap1 isoforms showed that, as in mammals, zebrafish Syngap1 N- and C-termini are extensively spliced. We identified a zebrafish α1-like variant that maps exclusively to the gene. Quantifying locomotor behaviors showed that mutant larvae are hyperactive compared to wild-type but to differing degrees depending on the stimulus. Hyperactivity was most pronounced in low arousal settings, and hyperactivity was proportional to the number of mutant alleles.

Limitations: loss-of-function mutations produce relatively subtle phenotypes in zebrafish compared to mammals. For example, while mouse homozygotes die at birth, zebrafish survive to adulthood and are fertile, thus some aspects of symptoms in people with Related Disorder are not likely to be reflected in zebrafish.

Conclusion: Our data support mutations in zebrafish as causal for hyperactivity associated with elevated arousal that is especially pronounced in low-arousal environments.