Associations between CAG repeat size, brain and spinal cord volume loss, and motor symptoms in spinocerebellar ataxia type 3: a cohort study

Spinocerebellar ataxia type 3 (SCA3) is a hereditary disease caused by abnormally expanded CAG repeats in the ATXN3 gene. The study aimed to identify potential biomarkers for assessing therapeutic efficacy by investigating the associations between expanded CAG repeat size, brain and spinal cord volume loss, and motor functions in patients with SCA3. In this prospective, cross-observational study, we analyzed 3D T1-weighted MRIs from 92 patients with SCA3 and 42 healthy controls using voxel-based morphometry and region of interest approaches. Associations between expanded CAG repeat size, brain and spinal cord volume loss, and International Cooperative Ataxia Rating Scale (ICARS) scores were investigated using partial correlation and mediation analyses. Sample sizes of potential biomarkers were calculated. Compared with healthy controls, SCA3 patients had lower cerebellar volume and cervical spinal cord area. SCA3 patients evolved along a stage-independent decline that began in the cerebellum, progressed to spinal cord, brainstem, thalami, and basal ganglia, and extensive subcortex. Expanded CAG repeat size was associated with right cerebellar lobule IV volume (r = - 0.423, P