Biochemical assay of Alzheimer's disease--associated protein(s) in human brain tissue. A clinical study.

The concentration of Alzheimer's disease-associated protein (ADAP) was measured in postmortem brain tissue samples of temporal or frontal cortex from 111 human brains using a sandwich immunoassay. Alzheimer's disease-associated protein has three major ALZ-50-reactive subunits, including A-68. This assay utilizes ALZ-50 and a rabbit antibody raised against a highly ADAP-enriched brain protein fraction. The frequently observed cross-reactivity of ALZ-50 with normal brain components in direct immunoassays is minimized by this configuration. There were 27 normal controls, 28 neurologic disease controls, and 56 Alzheimer's disease cases. The normal control and neurologic disease control cases had essentially no detectable level of ADAP, while ADAP was clearly detected in 85.7% of the Alzheimer's disease cases. Clinical dementia, neuritic plaques, and old age per se are not correlated with increased ADAP levels. This biochemical assay of ADAP may prove to be helpful as an adjunct in the clinicopathologic diagnosis of Alzheimer's disease.