EPISODIC ATAXIA type 2 (EA2) is a rare, usually dominantly inherited neurologic disorder characterized by episodes of vertigo and imbalance with interictal eye movement abnormalities; it can be dramatically responsive to acetazolamide.1 The disease loci in several large families with EA2 were mapped to the short arm of chromosome 19,2 where familial hemiplegic migraine (FHM), another unusual episodic neurologic disorder, had been mapped.3 Indeed, EA2 and FHM turned out to be allelic disorders, resulting from different mutations in the same gene, CACNA1A, a calcium channel subunit–encoding gene located on 19p.4
Jen J, Geschwind DH. Ataxia and Calcium Channels: What a Headache! Arch Neurol. 2001;58(2):179–180. doi:10.1001/archneur.58.2.179
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