Dear Editor, In patients with slowly progressing ataxia, molecular genetic investigation can be considered for the identification of underlying cause. Before considering genetic tests, comprehensive neurological and ophthalmological investigations should be done first. In this report, we present a rare case of a patient who was diagnosed with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) based on thickened retinal nerve fiber layers (RNFLs) and whole genome sequencing.

A 53-year-old male was referred from the department of neurology for diplopia of 6 months’ duration. His past medical history was significant for the gait disturbance since age of 10. The patient had experienced progressive gait difficulty with frequent falls and was unable to walk independently at the age of 17. At the age of 40 years, dysarthria and dysphagia developed, and brain magnetic resonance imaging (MRI) showed cerebellar atrophy. His younger sister had similar symptoms, which indicated an autosomal recessive trait. Best-corrected visual acuity was 20/25 in the right eye and 20/40 in the left eye. Slit lamp examination revealed pseudophakia in the right eye and cortical opacity in the left eye. The patient had a full range of eye movement, but defective pursuit movements were noted. Extraocular motility examination showed 25 prism diopters exotropia at near with Krimsky methods. Dilated fundus examination showed diffuse peripapillary retinal nerve fiber striations in both eyes. Optical coherence tomography (OCT) revealed thickening of RNFLs in both eyes (Fig. 1A-1D). Neurophysiologic studies were consistent with predominantly demyelinating sensori-motor