Two large and important studies have found more evidence that deposits, called plaques, of a substance called amyloid can help predict who will develop Alzheimer's disease and, someday, diagnose the condition.
The two studies which were done by overlapping groups of researchers were published in the Journal of the American Medical Association. The researchers looked at data from more than 9,000 people around the world and found that amyloid plaques appear in the brain 20 to 30 years before symptoms of dementia appear. They also found that the vast majority of patients with Alzheimer's have such plaques and that a gene known to increase the risk of Alzheimer's speeds up the formation of amyloid plaques.
Screening for amyloid plaques, using positron emission (PET) scans of the brain or testing for the presence of amyloid in cerebrospinal fluid can help research into the disease. Finding a drug that prevents amyloid build-up requires finding patients whose brains are not already damaged by amyloid and avoiding patients who have dementia from other causes.
Amyloid scanning could help physicians diagnose Alzheimer's, but currently such testing is expensive. Screening people for amyloid plaques who don't have dementia would not be helpful at the moment because there is no drug that prevents Alzheimer's.
The two studies involved analysis of data from many other studies. One looked at studies of people who did not have dementia or who had mild cognitive impairment, which is considered a precursor to Alzheimer's. About 30% of those with mild cognitive impairment had no amyloid plaques, which may mean they had a type of dementia that is not Alzheimer's. It was also found that those with more education were more likely to have plaques than those with less education, a finding that could mean that well-educated people have more brain pathways that compensate as dementia begins.
The second study evaluated people with Alzheimer's and several other types of dementia. It found that 88% of Alzheimer's patients had amyloid present. Amyloid was present in other dementia, but less commonly and it was more likely to be present in older individuals.
