A Proposal for Classification of Retinal Degeneration in Spinocerebellar Ataxia Type 7

The aim of this study is to propose a classification system for the spinocerebellar ataxia type 7 retinal degeneration (SCA7-RD). Twenty patients with molecularly confirmed SCA7 underwent slit lamp examination, fundus photography, and optical coherence tomography (Spectralis®). Scale for the Assessment and Rating of Ataxia (SARA) and International Cooperative Ataxia Rating Scale (ICARS) were applied, and age, sex, age at symptom onset, and number of CAG expansions were recorded. After analyzing the ophthalmological findings in each participant, a panel of retinal disease experts created a qualitative classification system for SCA7-RD comprising four stages. We assessed the correlations of retinal degeneration severity with SARA and ICARS scores, number of CAG repeats in ATXN7 allele, and age at symptom onset. We graded retinal degeneration as stage 1 in nine participants, as stage 2 in five, and as stage 3 in six. No differences in age and visual symptoms duration were found between groups. SARA and ICARS scores correlated with the severity of SCA7-RD on the classification system (p = 0.024 and p = 0.014, respectively). After adjusting for disease duration, retinal disease stage association with SARA and ICARS scores remained significant (ANCOVA, p < 0.05). The classification system for SCA7-RD was able to characterize different disease stages representing the landmarks in the cone-rod dystrophy natural history. Neurodegeneration appears to occur in parallel in the cerebellum and in the visual pathway. We conclude that retinal degeneration in SCA7 is a potential biomarker of the neurological phenotype severity.