Plasma Amyloid-β as a Function of Age, Level of Intellectual Disability, and Presence of Dementia in Down Syndrome

Adults with Down syndrome (DS) are at risk for developing Alzheimer's disease (AD). While plasma amyloid-beta (A beta) is known to be elevated in DS, its relationship to cognitive functioning is unknown. To assess this relationship, samples from two groups of subjects were used. In the first group, nondemented adults with DS were compared to: 1) a group of young and old individuals without DS and 2) to a group of patients with AD. Compared to these controls, there were significantly higher levels of plasma A beta in nondemented adults with DS while AD patients showed lower levels of plasma A beta. A larger second group included demented and nondemented adults with DS, in order to test the hypothesis that plasma A beta may vary as a function of dementia and Apolipoprotein E (ApoE) genotype. Plasma A beta levels alone did not dissociate DS adults with and without dementia. However, in demented adults with DS, ApoE4 was associated with higher A beta(40) but not A beta(42). After controlling for level of intellectual disability (mild, moderate, severe) and the presence or absence of dementia, there was an improved prediction of neuropsychological scores by plasma A beta. In summary, plasma A beta can help predict cognitive function in adults with DS independently of the presence or absence of dementia.