Alzheimer’s signs found before decline
Alzheimer’s begins years before mental deterioration is detected, according to a new study that could result in the doubling of the estimated number of people with the neurodegenerative disease.
Cognitively normal individuals who had elevated levels of a toxic brain protein called amyloid experienced more rapid declines in thinking than those with normal levels. The 445 subjects were followed for up to 10 years after their assessment to detect changes. The median time was 3.1 years, and the subjects’ average age was 74.
The study, published in the Journal of the American Medical Association, adds to evidence that Alzheimer’s begins years before symptoms appear, said Dr. Paul Aisen, senior author of the study, who directs the University of Southern California’s Alzheimer’s Therapeutic Research Institute in San Diego.
The finding has vast implications for health care, according to an accompanying JAMA editorial. It poses unsettling questions about how to tell people they may be on the path to Alzheimer’s well before any impairment occurs.
The definition of the disease should be changed to reflect that people can live with Alzheimer’s for a long time without cognitive impairment, the editorial says.
The study points a way to beginning treatment far earlier — early enough to stop the disease before irreversible brain damage occurs, Aisen said. Alzheimer’s is diagnosed with cognitive tests, aided in recent years by detection of amyloid, long implicated in Alzheimer’s, in living patients.
Previously, Alzheimer’s could only be definitively diagnosed by autopsy, when the pathological changes characteristic of Alzheimer’s could be detected. Amyloid and another abnormal protein, tau, are believed to start the process, causing neurons to become diseased and die. That has changed with the development of imaging technology to non-invasively detect amyloid and tau in the brains of living people.
The JAMA study, and its use of the amyloid biomarker, significantly expands knowledge about how Alzheimer’s begins, said Dr. James Brewer, a neuroscientist at University of California San Diego.