ASSESSMENT OF AMYLOID-BETA PROTEIN IN CEREBROSPINAL-FLUID AS AN AID IN THE DIAGNOSIS OF ALZHEIMERS-DISEASE

The principal constituent of amyloid plaques found in the brains of in dividuals with Alzheimer's disease (AD) is a 39-42-amino-acid protein, amyloid beta protein (A beta). This study examined whether the measur ement of A beta levels in CSF has diagnostic value, There were 108 sub jects enrolled in this prospective study: AD (n = 39), non-AD controls (dementing diseases/syndromes; n = 20), and other (n = 49), CSF was o btained by lumbar puncture, and A beta concentrations were determined using a dual monoclonal antibody immunoradiometric sandwich assay. The mean A beta Value for the AD group (15.9 +/- 6.8 ng/ml) was not signi ficantly different from that for the non-AD control group (13.0 +/- 7. 1 ng/ml; p = 0.07), and substantial overlap in results were observed. A beta values did not correlate with age (r = -0.05, p = 0.59), severi ty of cognitive impairment (r = 0.22, p = 0.21), or duration of AD sym ptoms (r = 0.14, p = 0.45). These findings are in conflict with other reports in the literature; discrepant results could be due to the inst ability of A beta in CSF. A beta immunoreactivity decays rapidly under certain conditions, particularly multiple freeze/thaw cycles. Use of a stabilizing sample treatment buffer at the time of lumbar puncture a llows storage of CSF without loss of A beta reactivity, In conclusion, the total CSF A beta level is not a useful marker for current diagnos is of AD.