ATXN3 and multiple system atrophy: So far, four longitudinal MRI studies have used T1-weighted imaging in conjunction with global volumetry or voxel-based morphometry (VBM) to investigate the progression of brain atrophy in autosomal dominant inherited ataxias (including SCA1, SCA3, SCA6 [17], [18] and SCA17 [19]) as well as in multi system atrophy (MSA) [20].