Elevated body temperature exacerbates arrhythmia and seizure-like activity in a zebrafish model of Timothy syndrome

Timothy syndrome (TS) is a multisystem disorder with autistic-like features, seizures and arrhythmia as the main symptoms. Most TS cases are caused by a de novo single amino acid substitution G406R in the CACNA1C gene that encodes the pore-forming subunit of the voltage-gated L-type calcium channel Ca_V1.2. We generated a zebrafish model of TS with a homologous amino acid substitution in the cacna1c-encoded protein. Unlike patients, heterozygous mutants showed only mild impairments with no changes in mortality. However, homozygous mutants showed increased mortality, arrhythmias, neural activity and sensitivity to pentylenetetrazole-induced seizure-like behavior. Mutants also exhibited microcephaly, cerebellar hypotrophy and abnormal development of GABAergic neuron populations, and transcriptomic analysis revealed dysregulated expression of neuropeptide genes (including bdnf and vgf). Consistent with the idea that Ca_V1.2 channels activate during fever, we found that heterozygous larvae manifested arrhythmia and seizure-like behavior when exposed to elevated environmental temperature, and homozygous larvae switched from bradycardia to tachycardia. These data provide a basis for using zebrafish to study the etiology of TS abnormalities and suggest that fever may be a particular risk for TS patients.