Background. Studies investigating plasma Aß levels in patients with sporadic Alzheimer's disease (AD) yielded discrepant results. Some authors reported no difference between plasma concentrations of Aß1-42 and Aß1-40 in sporadic cases of AD as compared to controls, while others found increased levels of Aß1-42 in at least some AD patients. The results of several recent studies suggest that elevated plasma Aß1-42 levels may be detected several years before the onset of symptoms, though the value of that effect in predicting progression to dementia in subjects with mild cognitive impairment (MCI) is unknown. Finally, it has been proposed that plasma Aß levels increase merely with age and are neither sensitive to nor specific for AD or MCI.
Method. Plasma levels of Aß1-40 and Aß1-42 were measured in 54 AD patients, 39 MCI subjects and 35 controls using a commercially available ELISA.
Results. Mean plasma Aß1-42 levels were significantly higher in the MCI group as compared to both AD patients (p<0.001) and controls (p<0.001). Levels of Aß1-40 did not differ between the groups. In contradistinction to some earlier reports no correlations were noted between Aß species levels and either age or MMSE scores. Employing the ROC curve analysis we found that the maximum accuracy in discriminating MCI subjects from both controls and AD subjects was achieved using the cut-off value of 3.8.
Conclusions. Although mean plasma levels of Aß peptides differentiate between AD, MCI and control subjects, their usefulness in differential diagnosis of AD is doubtful. Further studies are needed to establish the value of Aß levels in identifying patients with mild cognitive impairment and (possibly) in predicting their progression to clinically overt AD.