Platelet amyloid precursor protein abnormalities in mild cognitive impairment predict conversion to dementia of Alzheimer type: a 2-year follow-up study.

BACKGROUND: Alteration of the amyloid precursor protein (APP) forms ratio has been described in the platelets of patients with dementia of Alzheimer type (DAT) and in a subset of subjects with mild cognitive impairment (MCI). OBJECTIVE: To evaluate the potential role of the platelet APP forms ratio in predicting progression from MCI to DAT. DESIGN: Thirty subjects with MCI underwent a clinical and neuropsychological examination and a determination of the platelet APP forms ratio. Subjects were followed up periodically for 2 years, and the progression to dementia was evaluated. SETTING: Community population-based sample of patients admitted for memory complaints. RESULTS: Patients who progressed to DAT at the 2-year follow-up (n = 12) showed a significant decrease of baseline platelet APP forms ratio values (mean +/- SD, 0.36 +/- 0.28) compared with stable MCI subjects (mean +/- SD, 0.73 +/- 0.32) (P<.01) and patients who developed other types of dementia (mean +/- SD, 0.83 +/- 0.27) (P =.03). By fixing a cutoff score of 0.6, 10 (83%) of the 12 DAT patients showed baseline values below the cutoff, whereas 10 (71%) of 14 subjects who either developed non-Alzheimer-type dementia or maintained cognitive functions had values in the normal range. CONCLUSION: Mild cognitive impairment is a major risk factor for DAT, and Alzheimer disease-related pathological changes can be identified in patients converting to DAT within a 2-year follow-up.