Episodic ataxia type 1 is a rare autosomal dominant paroxysmal ataxia syndrome caused by a point mutation in KCNA1, the gene for the voltage-gated potassium channel. It is characterized by episodes of ataxia (poor coordination and balance), dysarthria, nystagmus, tremor, and/or facial twitching. Some individuals also experience vertigo, diplopia, nausea, shortness of breath, diaphoresis, carpal spasm, or headache.

Attacks may be triggered by sudden movement, exercise, excitement, illness, or fatigue, and may be preceded by sensory auras. Episodes typically last seconds to minutes and may occur fewer than once daily to several times daily. Patients are largely normal between attacks, although myokymia may be present between attacks. Age of onset is typically in childhood or adolescence. In some cases, attacks lessen in adulthood. About 20% of individuals with this disorder will develop progressive cerebellar symptoms. Some individuals will also have cognitive dysfunction, muscle hypertrophy, shortened Achilles tendons, seizures, or scoliosis.