Some scientists think Alzheimer's is not really a disease at all but the inevitable result of normal brain aging.
The world's oldest woman called that hypothesis into question by dying at the age of 115 with absolutely no evidence of Alzheimer's in her brain. That amazed scientists who studied her.
"Our observations suggest that, in contrast to general belief, the limits of human cognitive function may extend far beyond the range that is currently enjoyed by most individuals," they wrote in the journal Neurobiology of Aging.
At the age of 82, Henrikje van Andel-Schipper, who lived in the Netherlands, agreed to donate her body to the University of Groningen, nearby. At the age of 111, she contacted university leaders to ask if her body would be of any use to them now that she was so old.
The scientists informed her that her body would be more useful than ever because it might hold secrets to successful aging, and they made an appointment to meet with her.
What they encountered was "an alert and assertive lady, full of interest in the world around her, including national and international politics and sports," they reported.
She was living in an assisted living facility only because her eyesight had deteriorated. When they asked her about her life, the researchers wrote that she launched into a vivid and detailed account.
Ironically, when she was born in 1890, her mother did not expect her to live because she weighed only 3 1/2 pounds.
Shortly after starting school at the age of 5, she had to drop out because she became ill, and her father, a schoolteacher, taught her at home. She became a teacher herself, lived at home until the age of 47 and married at 49. She became a widow at 69 and lived independently until the age of 105.
Tests when she was 112 and 113 showed that she possessed the mental agility of a healthy adult half her age.
When she died at the age of 115, in 2005, an autopsy showed virtually no sign of clogged arteries. Even more striking, her brain appeared to be free of the changes that often appear years before people start showing signs of Alzheimer's. She also showed none of the brain shrinkage characteristic of the very old.
She died of stomach cancer that had spread to her liver and one kidney. Scientists found another tumor in her armpit that appeared to have spread from a breast tumor removed in 1990, when she was 100.
The woman's robust good health has caused a stir among scientists who study aging.
"This is way out of the realm of the normal," said Dr. Bruce Yanker, a professor at the Harvard Medical School and the lead author of an influential paper titled The Aging Brain.
"Almost every person over 85 has some degree of Alzheimer's-type pathology. She clearly had some genetic features that protected her from this, and if we could understand what they were, we might be able to develop useful therapies."
Freelancer Tom Valeo writes about medical and health issues. Write to him in care of Pulse, St. Petersburg Times, P.O. Box 1121, St. Petersburg, FL 33731, or e-mail email@example.com.