It's possible that Alzheimer's disease shortens life, so people who are susceptible to it simply don't make it into the older age group, reasoned Ince, a professor of neuropathology and head of the Academic Unit of Pathology at Sheffield University Medical School in the U.K.
Also, he added, the study suggests that people who become senile at a very old age may be affected by another factor -- shrinking of the brain.
As for future research, "we need to take account of the ability of some people's brains to withstand Alzheimer's better than others," he said. "If we knew why, it might help us with strategies to delay the onset of dementia."
For now, doctors are very limited in how they can treat Alzheimer's, Kennedy said. Medications can treat symptoms, much as painkillers help some people tolerate arthritis, but they don't cure the disease, he said.
And in many cases, the drugs simply don't work, he said.
To learn more, try the Alzheimer's Association.
SOURCES: Gary Kennedy, M.D., director, division of geriatric psychiatry, Montefiore Medical Center, New York City; Paul Ince, M.D., professor, neuropathology, and head, Academic Unit of Pathology, Sheffield University Medical School, U.K.; May 28, 2009, New England Journal of Medicine
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