**3.1 Episodic ataxias**

Episodic ataxias (EAs) are a clinically and genetically heterogeneous group of autosomal dominant inherited channelopathies characterised by recurrent episodes of cerebellar ataxia [36]. EAs usually start during childhood or adolescence. Ataxia episodes can vary from seconds to hours or days and are often triggered by different specific stimuli [37]. Eight different forms of autosomal dominant or familial AD are currently identified [38]. EA1 and EA2, represent the most prevalent group of EAs patients and have recognisable ictal and interictal phenotypes [37].

EA1 is associated with mutations in a voltage-gated K channel gene (KCNA1) [36]. EA1 begins usually in childhood and ataxic episodes are associated with vertigo [38]. In EA1 the episodes are frequent, brief (seconds to minutes) and are triggered by abrupt exercise, stress, startle, fever, caffeine or alcohol [38, 39]. Dysarthria, tremors, diplopia, blurred vision, vertigo, nausea, migraine, or diaphoresis may also be present during the ataxia episodes. Between attacks, EA 1 is associated with myokymia [38]. Approximately 20% of EA1 individuals evolve with persistent cerebellar symptoms [37]. Different medications have been reported to be effective in EA1, including acetazolamide (AZT), carbamazepine and valproic acid [37, 38].

EA2 is caused by heterozygous variants in the calcium channel, voltage-dependent, P/Q type, and α1A subunit (CACNA1A) gene [38]. EA 2 usually presents with recurrent episodes of ataxia that last up to several hours or days and the frequency of the attacks ranges from four times per week to once per year [37]. During the attack, patients can


### **Table 2.** *Causes of intermittent ataxia.*

### *Childhood-Onset Ataxia DOI: http://dx.doi.org/10.5772/intechopen.112968*

also manifest Vertigo and dizziness, dysarthria, migraine, nausea and vomiting, diplopia, tinnitus, and generalised muscle weakness. Ataxic episodes are triggered by emotional stress, exercise, phenytoin, and caffeine but not by startle [36]. Clinical onset is usually in the first two decades of life, although late-onset cases have been reported [38]. In EA2 often an interictal downbeat nystagmus with other cerebellar dysfunctions is present [38]. Acetazolamide is the first line treatment for EA2, patients unresponsive to or unable to tolerate acetazolamide may respond to 4-aminopyridine [39].
