Two novel CACNA1A gene mutations associated with episodic ataxia type 2 and interictal dystonia.

BACKGROUND: Episodic ataxia type 2 (EA2) is an autosomal dominant condition that results from mutations in the CACNA1A gene. It is characterized by episodes of ataxia and nystagmus that typically last hours.

OBJECTIVE: To describe the clinical and genetic features of 2 unrelated patients who developed EA2 in childhood and late-onset dystonia.

DESIGN: Pedigree study.

SETTING: University academic teaching hospital.

PATIENTS: Two unrelated patients with childhood-onset EA2 and adult-onset dystonia were identified through a neurogenetics clinic. The CACNA1A gene was screened by heteroduplex analysis and sequencing for mutations.

MAIN OUTCOME MEASURE: Mutations in the CACNA1A gene.

RESULTS: Novel mutations in the pore-forming subunit of the P/Q-type calcium channels were found in both pedigrees. None of the family members carried an expansion of the CAG sequence that is found in the carboxy terminus of the CACNA1A gene.

CONCLUSIONS: Truncating mutations are the most common mutations to cause EA2. We have identified 2 novel truncating mutations that are associated with interictal dystonia. The dystonia is a late feature in this disease and may be a manifestation of a degenerative cerebellar process.