SLOW SACCADES AND OTHER EYE-MOVEMENT DISORDERS IN SPINOCEREBELLAR ATROPHY TYPE-1

In order to study the relation between genotype and phenotype, a detai led study of the course of oculomotor deficits was performed in three patients with autosomal-dominant cerebellar ataxia, subtype spinocereb ellar atrophy type 1 (SCA 1) using clinical testing and electrooculogr aphy. DNA analysis revealed a CAG repeat expansion of 65 in the SCA 1 gene on chrome some 6p in all patients. A progressive disorder of the saccadic system became obvious, leading to a marked slowing of saccadi c eye movements and loss of pathological and physiological nystagmus. An upward gaze palsy developed early, followed by horizontal and downw ard gaze palsy at a later state of the disease. Smooth pursuit eye mov ements were disturbed to a lesser extent; the vestibulo-ocular reflex was reduced. As an additional feature, severe loss of visual acuity de veloped due to progressive optic nerve atrophy. The oculomotor deficit s can be explained by progressive damage to the brain stem rather than to the cerebellum. Each combination of oculomotor deficits with or wi thout optic atrophy may occur irrespective of the gene locus of the di sease, making a correlation between clinical signs and genetic finding s difficult.