Primary hereditary episodic ataxia (EA) syndromes are characterized by attacks of imbalance and incoordination or ataxia. Seven subtypes of EA have been described (EA1 to EA7) that vary by phenotype and/or genotype, and all are inherited in an autosomal dominant pattern. EA1 and EA2 are the best characterized of the EA subtypes and have a combined incidence of 1:100,000. The clinical characteristics of EA1 and EA2 are similar, although the duration of ataxia episodes is typically longer for EA2 (minutes to hours) than for EA1 (seconds to minutes). For both EA1 and EA2, the episodes of ataxia are usually triggered by physical exertion or emotional stress. Onset of symptoms of EA1 and EA2 is usually before 20 years of age. EA1 is caused by sequence variants in the KCNA1 gene that encodes the Kv1.1 subunit of a voltage-gated potassium channel. The cause of EA2 is sequence variants in the CACNA1A gene, which encodes the alpha-1a subunit of a calcium channel called CaV2.1. Treatment of EA1 and EA2 with acetazolamide may be effective.