New research suggest that doctors could diagnose people in the early stages of Alzheimer's, or even predict the onset of the disease, by looking for abnormal levels of the two substances, called beta-amyloid and tau. Some scientists also believe that draining cerebrospinal fluid may stall the advance of Alzheimer's by shunting away harmful proteins from the brain. That approach is still experimental and hasn't been proven to work.
However, Alzheimer's experts agree that early diagnosis of the disease is key because the few treatments now available can slow the progression of symptoms by six months or so. What's more, new drugs are being developed to inhibit toxic beta-amyloid. A test that detects Alzheimer's before it surfaces could maximize the effectiveness of these therapies if and when they arrive, says Dr. Trey Sunderland, an Alzheimer's expert at the National Institute of Mental Health and lead author of the study.
"We think that's very important," Sunderland says. "Once you identify people at risk, then you can target them with the new medications aimed at slowing down the development" of the disease. A report on the findings appears in the April 23/30 issue of the Journal of the American Medical Association.
Alzheimer's disease, which is thought to be caused by a buildup of toxic beta-amyloid in the brain, affects an estimated 4 million Americans. The number of patients is expected to quadruple over the next 50 years as the population ages.
In the latest work, Sunderland and his colleagues compared tau and beta-amyloid levels in spinal fluid samples from 131 men and women with suspected Alzheimer's disease -- 31 had a confirmatory diagnosis upon autopsy -- and 72 without the condition.
As expected, levels of tau were about 2.5 times higher in the people with brain disease than in healthy subjects, while levels of beta-amyloid were about half as high in the sick group.
Tau is released by dying brain cells, so higher concentrations of the molecule in cerebrospinal fluid reflect increased damage to neurons. The reason beta-amyloid levels fall in the spinal fluid of Alzheimer's patients, experts say, is because more of the protein stays in the brain to cause harm.
Sunderland and his colleagues also reviewed 51 previous studies of the link between tau and beta-amyloid in spinal fluid and Alzheimer's. Taken together, these studies included more than 3,100 people with the brain disorder, and the overall results echoed his group's own findings.
Sunderland says testing for the two proteins is a better gauge of Alzheimer's disease than a doctor's examination, sorting diseased brains from normal ones roughly 90 percent of the time. Alzheimer's is commonly diagnosed through symptoms and by ruling out other diseases.
Researchers must now learn if the protein changes occur as a result of brain damage caused by Alzheimer's, or whether they somehow precede it. Sunderland's group also would like to study how levels of the two substances fluctuate over time, in both people with Alzheimer's and in those with a healthy brain.