[Episodic ataxias].

BACKGROUND: Episodic ataxias (EAs) exist in sporadic and familial forms. They have considerable genetic and clinical heterogeneity. Better understanding of the disorders will hopefully improve management.

MATERIAL AND METHODS: This review is based on personal experience and recent literature.

RESULTS: EAs are rare autosomal dominant paroxysmic disorders. At present, five forms have been identified. EA 1 is caused by mutations in the potassium channel gene KCNA1 on chromosome 12p13, EA 2 by mutations in the calcium channel gene CACNA1A gene on chromosome 19p13, and EA 5 by mutations in the calcium channel gene CACNB4&beta on chromosome 2q22-q23. Neither gene nor linkage has been identified for EA 3 and 4. As the name indicates, EAs are characterized by paroxystic ataxia. Patients with EA 1 also have interictal myokymia. EAs are characterized by both locus and allelic heterogeneity, since different genes can cause an almost similar phenotype and different mutations in a gene can cause different disorders. Beside EA, mutations in the KCNA1 gene can cause partial epilepsy and myokymia alone, mutations in the CACNA1A gene can cause familial hemiplegic migraine 1 and spinocerebellar ataxia 6, while mutations in the CACNB4&beta4 gene can cause generalized epilepsy and juvenile myoclonic epilepsy. EA can often be efficiently treated with acetazolamide.

INTERPRETATION: EAs are rare autosomal dominant disorders caused by mutations in ion-channel genes. The disorders are not life threatening but disabling without treatment or when medical treatment is ineffective or not tolerated.