[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.


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.


CONCLUSIONS
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.
Herrmann
Antje
A
Nevrologisk avdeling, Akershus universitetssykehus, 1478 Lørenskog. antje.herrmann@ahus.no
Braathen
Geir J
GJ
Russell
Michael Bjørn
MB
D000293:Adolescent; D000328:Adult; D015220:Calcium Channels / Q000235:genetics*; D002524:Cerebellar Ataxia / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics*; D002675:Child, Preschool; D006801:Humans; D051662:Kv1.1 Potassium Channel; D009154:Mutation; D015221:Potassium Channels / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D020864:Calcium Channels, N-Type
D015220:Calcium Channels; D051662:Kv1.1 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C105656:CACNA1A protein, human; D020864:Calcium Channels, N-Type; C496946:KCNA1 protein, human