Plasma Ab peptides and apolipoprotein E in sporadic Alzheimer's disease and mild cognitive impairment

Summary Introduction: Plasma Ab levels have been examined in sporadic Alzheimer's disease (AD) patients yield- ing conflicting results. Some studies showed no difference between plasma concentrations of Ab 1-42 and Ab 1-40 in sporadic cases of AD as compared to controls, others found increased levels of Ab 1-42 in at least some AD patients. The results of several recent studies suggest that elevated plasma Ab 1-42 levels may be detected several years before the onset of symptoms, though the value of that effect in predicting progres- sion to dementia in mildly cognitively impaired (MCI) subjects is not known. Finally, it's been proposed that plasma Ab levels increase merely with age and are neither sensitive nor specific for AD or MCI. Material and method: Levels of Ab 1-40 and Ab 1-42 were measured in plasma from 54 patients with AD, 39 subjects with MCI and 35 controls using a commercially available ELISA. Results: Mean plasma Ab 1-42 levels were significantly higher in MCI as compared to both AD (p<0.001) and control subjects (p<0.001) while levels of Ab 1-40 did not differ between the groups. In contrast to some earlier reports no correlations were observed between Ab species levels and age or MMSE scores. However, Ab 1-42 were significantly lower in subjects carrying at least one apoliprotein e4 allele. Employing ROC curve analysis we found that the maximum accuracy in discriminating MCI versus both controls and AD subjects has been achieved using a cut-off value of 3.8. Conclusions: Mean plasma levels of Ab peptides differ between AD, MCI and control subjects though their usefulness in the differential diagnosis of AD is doubtful. Further studies are needed to establish the value of Ab peptides levels in identifying patients with MCI and (possibly) in prediction of their progres- sion to clinically overt AD.