Alzheimer’s disease begins years before mental deterioration is detected, suggests a new study that could result in doubling 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 as long as 10 years after their assessment to detect any 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 actually begins years before symptoms appear, said Paul Aisen, M.D., senior author of the study. Aisen directs the University’s of Southern California’s Alzheimer’s Therapeutic Research Institute, located 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.
And the very 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 also points a way to beginning treatment far earlier than is done now, early enough to stop the disease before irreversible brain damage is done, Aisen said.
Alzheimer’s disease is today diagnosed with cognitive tests, aided in recent years by detection of amyloid, which has long been 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 eventually die.
That has changed with the development of imaging technology to noninvasively detect amyloid and tau in the brains of living people. This work has been coordinated by the Alzheimer’s Disease Neuroimaging Initiative at USC, which seeks to find biomarkers associated with Alzheimer’s.
The JAMA study, and its use of the amyloid biomarker, significantly expands knowledge about how Alzheimer’s begins, said James Brewer, M.D., a neuroscientist at University of California San Diego.