Elevation of βAmyloid 1-42 Autoantibodies in the Blood of Amnestic Patients With Mild Cognitive Impairment.

OBJECTIVE: To develop a blood-based test for screening populations at risk for Alzheimer disease. DESIGN: Case-control study. Subjects A total of 180 patients with mild cognitive impairment (MCI) and 105 age-matched, cognitively normal controls. INTERVENTIONS: The titer of beta-amyloid 1-42 autoantibodies in the plasma was obtained at the time of diagnosis and evaluated by enzyme-linked immunosorbent assay before and after dissociation of the antigen-antibody complexes. A total of 107 patients with MCI were followed up for 36 months; 70 of the 107 cases progressed to Alzheimer disease. RESULTS: The average level of beta-amyloid 1-42 plasma autoantibodies in patients with MCI that progressed to Alzheimer disease, but not that of the stable cases, was significantly higher than in cognitively normal controls (P < .001). CONCLUSIONS: The results suggest that the plasma beta-amyloid 1-42 autoantibodies parallel beta-amyloid 42 deposition in the brain, which is known to precede by several years the clinical onset of Alzheimer disease. The evaluation of beta-amyloid 1-42 autoantibodies after dissociation of the complexes is a simple and inexpensive method that can be used to predict the occurrence of Alzheimer disease.