We describe four families with late onset episodic vertical oscillopsia and progressive gait ataxia. Probands presented between the ages of 40 and 64 with initial symptoms of episodic vertical oscillopsia and interictal downbeat nystagmus. A mild gait ataxia developed over several years. Triggers included physical exertion, alcohol and caffeine. Patients did not respond to acetazolamide. Genetic screening for episodic ataxia types 1 and 2, SCA 1, 2, 3 and 6 were negative. Using ancestral IBD analysis and dense SNP genotyping throughout the genome, an interval of 28.6cM (~14.2Mb) on chromosome 13q12.11-q13.3 composed of 1259 SNPs, was shared between affected individuals in two of the four families and highlighted a region of suggestive linkage (LOD > 2.7).
- downbeat nystagmus
- episodic ataxia
- identity by descent
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