[Spinocerebellar ataxia type 8 in Russian patients]

To assess the incidence of spinocerebellar ataxia type 8 (SCA8) in patients with progressive cerebellar ataxia and describe the clinical features of the SCA8 phenotype in Russian patients.

Genotyping of CTA/CTG repeats in ATXN8OS gene was carried out in 411 patients with degenerative ataxias using fragment analysis. SCA types 1, 2, 3 and 6 as well as Friedreich's ataxia were preliminarily excluded. All patients underwent brain MRI study. Scale for the Assessment and Rating of Ataxia (SARA), and the Montreal Cognitive Assessment Scale (MoCA) to screen for cognitive impairment were used.

Six patients with SCA8 (1.5%) were identified as carriers of the expansion in the ATXN8OS gene (91-152 CTA/CTG repeats). All cases were sporadic. Age of onset ranged from 14 to 42 years. All patients had slowly progressive cerebellar ataxia, oculomotor disturbances, dysarthria, pyramidal signs, and two patients had cognitive impairment. In one patient the clinical presentation corresponded to multiple system atrophy cerebellar type (ataxia, orthostatic hypotension, cerebellum and brainstem atrophy). Brain MRI study in all patients revealed cerebellar atrophy.

SCA8 is a rare form of autosomal dominant ataxia with a predominance of the classical phenotype. All identified cases of SCA8 were sporadic, which should be taken into account when planning genetic testing in patients with spinocerebellar ataxia.