The platelet amyloid precursor protein ratio as a diagnostic marker for Alzheimer's disease in Thai patients.

The platelet amyloid precursor protein (APP) ratio has recently been shown to be a promising diagnostic marker for Alzheimer's disease (AD). To evaluate its usefulness in Thai patients, platelet APP was analyzed by immunoblotting. The APP ratio was calculated as the ratio of the combined band density of the 120-kD and 130-kD isoforms compared to that of the 110-kD isoform. The mean ages (and ranges) of 27 normal and 13 AD-affected subjects were 68.3 (60-84) and 79.3 (70-97) years, respectively. The Thai Mental State Examination (TMSE) scores demonstrated that the AD patients had significantly poorer cognitive functions than the normal subjects, with mean TMSE scores of 20.3 and 27.6 (maximum score of 30 points), respectively (p<0.05). The platelet APP ratios of the AD patients were significantly lower than those of normal subjects: values (mean ± standard deviation) were 7.32 ± 1.29 and 9.13 ± 3.00, respectively (p<0.05) for AD patients and normal subjects. However, the ranges of the APP ratios from both groups markedly overlapped, which precluded the establishment of a cutoff level to differentiate between the AD and normal subjects. In addition, no significant correlations were observed between the platelet APP ratio and the TMSE score or between the APP ratio and the serum cholesterol in this study, in contrast to previous reports.