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New research shows that Alzheimer’s disease hits people in their 60s and 70s harder than people who are 80 years and older.
Researchers at the University of California, San Diego School of Medicine note that the greatest risk factor for Alzheimer’s is age. In fact, by the age of 85, the likelihood of developing the dreaded neurological disorder is roughly 50 percent, they say.
But in their study, they found that the “younger elderly” — those in their 60s and 70s — showed higher rates of cognitive decline and faster rates of tissue loss in brain regions that are vulnerable during the early stages of Alzheimer’s, according to Dominic Holland, Ph.D., a researcher in the Department of Neurosciences at UC San Diego and the study’s first author.
“Additionally cerebrospinal fluid biomarker levels indicate a greater disease burden in younger than in older individuals,” he said.
Holland and his colleagues, using imaging and biomarker data from participants in the Alzheimer’s Disease Neuroimaging Initiative, examined 723 people, ages 65 to 90 years, who were categorized as either cognitively normal, with mild cognitive impairment (an intermediate stage between normal, age-related cognitive decline and dementia) or suffering from full-blown Alzheimer’s disease (AD).
The findings have implications for diagnosing the disease — which currently afflicts an estimated 5.6 million Americans, a number expected to triple by 2050 — and efforts to find new treatments, the researchers said.
At present, there is no cure for Alzheimer’s and existing therapies do not slow or stop the disease’s progression.
A key feature in the diagnosis of Alzheimer’s is its “relentless progressive course,” Holland said.
“Patients typically show marked deterioration year after year. If older patients are not showing the same deterioration from one year to the next, doctors may be hesitant to diagnose AD, and thus these patients may not receive appropriate care, which can be very important for their quality of life.”
Holland said it’s not clear why the disease is more aggressive among the younger elderly.
“It may be that patients who show onset of dementia at an older age, and are declining slowly, have been declining at that rate for a long time,” added co-author Linda McEvoy, Ph.D., associate professor of radiology. “But because of cognitive reserve or other still-unknown factors that provide ‘resistance’ against brain damage, clinical symptoms do not manifest till later age.”
Another possibility is that older patients may be suffering from mixed dementia — a combination of Alzheimer’s and other neurological conditions, Holland said. These patients might withstand the effects of Alzheimer’s until other adverse factors, such as brain lesions caused by cerebrovascular disease, take hold. At that time, Alzheimer’s can only be definitively diagnosed by an autopsy, he said.
Clinical trials to find new treatments for the disease may be affected by the differing rates of progression, researchers said.
“Our results show that if clinical trials of candidate therapies predominately enroll older elderly, who show slower rates of change over time, the ability of a therapy to successfully slow disease progression may not be recognized, leading to failure of the clinical trial,” said Holland. “It’s critical to take into account age as a factor when enrolling subjects for AD clinical trials.”
While the obvious downside of the findings is that younger patients with Alzheimer’s lose more of their productive years, “the good news in all of this is that our results indicate those who survive into the later years before showing symptoms of AD will experience a less aggressive form of the disease,” Holland concluded.
The research appears online in the journal PLOS One.