The dominantly-inherited ataxias characterised by expanded polyglutamine tractsspinocere bellar ataxias (SCAs) 1, 2, 3, 6, 7, 17, dentatorubral pallidoluysian atrophy (DRPLA) and, in part, SCA 8have all been shown to result in various degrees of cognitive impairment. We survey the literature on the cognitive consequences of each disorder, attempting correlation with their published neuropathological, magnetic resonance imaging (MRI) and clinical features. We suggest several psychometric instruments for assessment of executive function, whose results are unlikely to be confounded by visual, articulatory or upper limb motor difficulties. Finally, and with acknowledgement of the inadequacies of the literature to date, we advance a tentative classification of these disorders into three groups, based on the reported severity of their cognitive impairments, and correlated with their neuropathological topography and MRI findings: group 1SCAs 6 and 8mild dysexecutive syndrome based on disruption of cerebello-cortical circuitry; group 2SCAs 1, 2, 3, and 7more extensive deficits based largely on disruption of striatocortical in addition to cerebello-cerebral circuitry; and group 3SCA 17 and DRPLAin which cognitive impairment severe enough to cause a dementia syndrome is a frequent feature.
