These declines among younger patients paralleled the accelerated rate of brain tissue loss and the increase in a spinal-fluid indicator of Alzheimer's seen among the younger age group, compared with older patients, the study authors added.
The researchers aren't sure why Alzheimer's is more aggressive in younger patients. One explanation might be that the older patients have been declining at that slower rate over a longer time, with some unknown factor keeping symptoms at bay, they suggest.
Another possibility is that the older patients have dementia plus Alzheimer's, which might stall the full effect of Alzheimer's on the brain. But such a diagnosis must be made with an autopsy, which is the only way Alzheimer's is accurately diagnosed, Holland noted.
Alzheimer's disease currently affects an estimated 5.6 million Americans, and that number is expected to triple by 2050 as the baby boom generation ages.
The finding that the earlier one develops the disease, the more aggressive it is isn't good news for those younger elderly patients who will suffer the worsening loss of their mental abilities for a long time, Holland said.
Another expert said the findings may affect both health cost projections and clinical trials.
"This is an extremely important paper with implications for both the projections of cost of care for Alzheimer's disease and for planning clinical trials," said Dr. Sam Gandy, associate director of the Mount Sinai Alzheimer's Disease Research Center at the Mount Sinai School of Medicine in New York City.
If the clinical picture in the over-85 population is milder than what is typical in younger populations, those older patients would remain independent longer, and the projections for the economic burden to the health care system should be adjusted, he said.
"The annual cost now is $200 billion in the U.S.; the projection
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