The neuropsychological assessment of age related cognitive deficits in adults with Down's syndrome

There is substantial evidence that older adults who have Down's syndrome are at risk for developing Alzheimer's disease. However, whilst the neuropathological signs of Alzheimer's disease are almost always apparent in those over the age of 30, the clinical signs may not be evident. This may be because the neuropathological changes are not sufficiently advanced to impair performance or because detecting neuropsychological deficits is more difficult in the presence of substantial, global cognitive impairment. In this study, 70 adults with Down's syndrome were assessed using a battery of neuropsychological tests, some of which had been used to assess dementia arising from Alzheimer's disease in the general population. Participants were screened to rule out advanced dementia or a pre-existing degree of cognitive impairment which would preclude participation in the tests. Analysis of test results for those under the age of 40, showed significant negative correlations between the Vineland Adaptive Behavior Scales and performance on all neuropsychological tests, thus demonstrating the effect of pre-existing global cognitive impairment on these particular tests. The results of a cross-sectional age group comparison, showed no difference between age groups on neuropsychological deficits which may indicate advanced dementia. This was almost certainly due to the screening procedure. However, the older age groups showed significantly impaired performance on memory tests in comparison to the younger age group. It is concluded that the more subtle cognitive impairments which associate to Alzheimer's disease can be identified in the presence of a global cognitive impairment with sufficiently sensitive tests.