Healthy people who have an abnormal build-up of a protein in the brain linked with Alzheimer's have a higher risk of developing the disease, two new studies have found.
Scientists have long assumed that amyloid brain plaques found in autopsies of Alzheimer's patients are harmful and cause the disease.
However, autopsies of people with no signs of mental impairment have also revealed brain plaques, challenging this theory.
For the first time, researchers at Washington University in St. Louis have shown that brain plaques in apparently healthy individuals are associated with increased risk of diagnosis with Alzheimer's disease years later.
In the study, volunteers with brain plaques were more likely to have declining scores on annual cognitive tests, to show signs of shrinkage in a key brain area affected by Alzheimer's and to eventually be diagnosed with the disease.
"We don't have enough data yet to definitively say that people who scan positive for these brain plaques have presymptomatic Alzheimer's disease, but something is clearly going on that does not bode well for the health of their aging brains," said John C. Morris, the Harvey A. and Dorismae Hacker Friedman Distinguished Professor of Neurology and director of Washington University's Alzheimer's Disease Research Center (ADRC) and the Friedman Center for Aging.
The studies have been published in Archives of Neurology.