Hereditary episodic ataxia

**Definition:** Autosomal dominant disorders associated with intermittent episodes of cerebellar dysfunction, with normal functioning or minimal ataxia and nystagmus between episodes. The two major subtypes include EA1 and EA2. EA1 is caused by a mutation of the KCNA1 gene coding and characterized by episodes triggered by exercise and muscle myokymia. EA2 is caused by a mutation in CACNA1A gene and involves more prolonged attacks of ataxia (lasting hours to days), and interictal residual ataxia with nystagmus.