Scientists have developed a blood test that may reveal changes in the brain caused by Alzheimer's disease. The technique, tested so far only in mice, predicts the amount of amyloid plaque (formed from clumps of proteins that kill surrounding cells) in an animal's brain. The research, detailed in a report in the current issue of the journal Science, holds promise for the development of predictive methods to diagnose the disease years ahead of the onset of clinical symptoms.

David Holtzman of the Washington University School of Medicine and colleagues worked with mice that had been genetically engineered to develop an Alzheimer's-like disease. They measured the amount of amyloid-b (Ab) protein in the animals' blood and found that it did not correlate to the extent of plaque formation in the brain, which is also the case for humans. But when they treated 49 animals with an artificial antibody known as m266, they found that their levels of Ab increased dramatically within as little as five minutes. Moreover, the increased blood levels correlated with the amount of amyloid in two regions of the brain affected by Alzheimer's, the hippocampus and the cingulate cortex. According to study co-author Ronald B. DeMattos of Washington University School of Medicine, "a simple injection of m266 altered the metabolism of Ab and unmasked important correlations with brain pathology."

Whether the results will apply to humans suffering from Alzheimer's disease remains unclear. Even if the test does work, it can only diagnose patients who have already started to accumulate amyloid. But as Holtzman notes, "such a test also could distinguish individuals suffering from dementia caused by Alzheimer's from those with other types of dementia, and may help us evaluate an individual's response to particular medical therapies."