Slow saccades and other eye movement disorders in spinocerebellar atrophy type 1.

In order to study the relation between genotype and phenotype, a detailed study of the course of oculomotor deficits was performed in three patients with autosomal-dominant cerebellar ataxia, subtype spinocerebellar atrophy type 1 (SCA 1) using clinical testing and electrooculography. DNA analysis revealed a CAG repeat expansion of 65 in the SCA 1 gene on chromosome 6p in all patients. A progressive disorder of the saccadic system became obvious, leading to a marked slowing of saccadic eye movements and loss of pathological and physiological nystagmus. An upward gaze palsy developed early, followed by horizontal and downward gaze palsy at a later state of the disease. Smooth pursuit eye movements were disturbed to a lesser extent; the vestibulo-ocular reflex was reduced. As an additional feature, severe loss of visual acuity developed due to progressive optic nerve atrophy. The oculomotor deficits can be explained by progressive damage to the brain stem rather than to the cerebellum. Each combination of oculomotor deficits with or without optic atrophy may occur irrespective of the gene locus of the disease, making a correlation between clinical signs and genetic findings difficult.