Oculomotor phenotypes in autosomal dominant ataxias

Objective: To quantify the oculomotor features of the common spinocerebellar ataxia (SCA) syndromes. Setting: University ataxia clinic. Patients: Twenty probands with documented SCA mutations: Methods: Electro- oculographic recordings of saccadic, smooth pursuit, optokinetic, vestibular, and visual-vestibular eye movements. Results: Distinct phenotype and genotype patterns were identified with modest overlap between patterns. Slowing of saccade peak velocities occurred only in SCA1 and SCA2, being present in 100% of patients with SCA2. Impaired vestibulo-ocular reflex gain occurred with SCA3 only. Patients with SCA6 had prominent deficits in smooth tracking but normal saccade velocities and vestibulo-ocular reflex gain. Conclusions: The oculomotor findings are consistent with pure cerebellar involvement in SCA6, pontine involvement in SCA1 and SCA2, and vestibular nerve or nuclei involvement in SCA3. These phenotypes can be useful for clinical diagnosis and for investigating the mechanism of system specificity with the SCA syndromes.