Objective: To quantify the oculomotor features of the common spinocere
bellar ataxia (SCA) syndromes. Setting: University ataxia clinic. Pati
ents: Twenty probands with documented SCA mutations. Methods: Electro-
oculographic recordings of saccadic, smooth pursuit, optokinetic, vest
ibular, and visual-vestibular eye movements. Results: Distinct phenoty
pe and genotype patterns were identified with modest overlap between p
atterns. Slowing of saccade peak velocities occurred only in SCA1 and
SCA2, being present in 100% of patients with SGA2, Impaired vestibule-
ocular reflex gain occurred with SCA3 only. Patients with SCA6 had pro
minent deficits in smooth tracking but normal saccade velocities and v
estibuloocular reflex gain. Conclusions: The oculomotor findings are c
onsistent with pure cerebellar involvement in SCA6, pontine involvemen
t in SCA1 and SCA2, and vestibular nerve or nuclei involvement in SCA3
. These phenotypes can be useful for clinical diagnosis and for invest
igating the mechanism of system Specificity with the SCA syndromes.