Episodic ataxia type 5

Episodic ataxia type 5 (EA5) is an extremely rare neurological disorder characterized by recurrent episodes of ataxia — a lack of voluntary coordination of muscle movements — that can last from hours to days. It is caused by mutations in the CACNB4 gene, which encodes the beta-4 subunit of voltage-gated calcium channels. These calcium channels play a critical role in neuronal signaling, particularly in the cerebellum, the brain region responsible for coordinating movement and balance. During episodes, affected individuals may experience unsteady gait, limb incoordination, slurred speech (dysarthria), and vertigo. Episodes can be triggered by physical or emotional stress, fatigue, or sudden movements. Between episodes, neurological examination may be normal or may show subtle signs of cerebellar dysfunction such as mild nystagmus (involuntary eye movements). Some patients may also experience seizures, as CACNB4 mutations have been associated with epileptic phenotypes in some families. Episodic ataxia type 5 is inherited in an autosomal dominant pattern, meaning a single copy of the altered gene is sufficient to cause the condition. Due to its extreme rarity, the natural history and full clinical spectrum of EA5 remain incompletely characterized. Treatment is largely symptomatic and supportive. Acetazolamide, a carbonic anhydrase inhibitor that has shown benefit in other forms of episodic ataxia (particularly types 1 and 2), may be trialed in EA5, though evidence for its efficacy in this specific subtype is limited. Avoidance of known triggers and supportive physical therapy may also help manage symptoms.

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