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 life-threatening arrhythmias. Most TS cases are caused by a de novo missense mutation in the CACNA1C gene that encodes the pore-forming subunit of the voltage-gated L-type calcium channel Ca_V1.2. Patients show highly variable clinical presentations and survival, which may be impacted by acute episodes of hypoglycemia and respiratory dysfunction. In addition, fever, known to activate Ca_V1.2 channels, may exacerbate TS, yet its impact is poorly understood. We generated a zebrafish model carrying the homologous cacna1c mutation. These fish exhibited arrhythmias, increased susceptibility to pentylenetetrazole-induced seizures, microcephaly, cerebellar hypotrophy and abnormal GABAergic neuron development. Transcriptomic analysis revealed dysregulated expression of neuropeptides including bdnf and vgf. Notably, elevated water temperature elicited arrhythmia and seizure-like behavior even in overtly normal heterozygotes, implicating fever as a modifiable risk. This model provides a platform for dissecting TS pathophysiology and identifying strategies to mitigate fever-related risk.