Forecasting Alzheimer's Disease: Brain Scans and Writing Samples May Predict Dementia
Fackelmann, Kathleen, Science News
First, there was a subtle, almost imperceptible, switch to simpler language.
As time went on, the woman started using short phrases. Then, she could utter only a word. In the end, even that stopped.
That progression describes one of the most destructive aspects of Alzheimer's disease: the patient's loss of language.
The most common form of senility in people age 65 and older, Alzheimer's is a degenerative brain disease that often starts with mild forgetfulness. Indeed, it's difficult to distinguish early stages of Alzheimer's from normal memory lapses. Neurologists diagnose Alzheimer's dementia only after observing a pattern of ever-worsening cognitive problems, eventually including an inability to reason.
Two scientific reports now suggest that doctors may one day be able to identify healthy people who will develop Alzheimer's disease. In one study, researchers discovered that characteristics of a person's writing early in life appear to predict the disease. In the other, scientists demonstrate that a brain scan highlights changes that may precede dementia.
Do such procedures offer a practical test for Alzheimer's disease? Not now, says Steven T. DeKosky, director of the Alzheimer's disease research center at the University of Pittsburgh Medical Center. He also questions the value of such a test.
"We have no treatment for the disease," he notes. "What good does it do for someone to find out at age 45 that they have a chance of developing the disease?" Yet he believes the recent findings will help researchers searching for ways to prevent Alzheimer's disease.
One team turned to a surprising set of subjects for its study-the Roman Catholic School Sisters of Notre Dame. In many ways, though, the sisters make ideal research subjects. Because they all have a similar lifestyle, environmental factors that might otherwise confuse the results of an Alzheimer's study are minimized or eliminated.
More important, this religious group keeps detailed, decades-long records on its members. These archives proved invaluable to David A. Snowdon of the University of Kentucky in Lexington and his colleagues in their study of aging and dementia.
The researchers knew that Alzheimer's disease leads to progressive impairment of language, and they wondered if subtle signs of difficulty would appear early in life. To find out, they studied 93 nuns whose handwritten autobiographies were on file in the convent archives. The autobiographies had been written as part of their religious training at an average age of 22. At the time of the study, these nuns were age 75 and older.
Team members looked at the number of ideas expressed in a passage of text, a concept called idea density. In addition, they studied the grammatical complexity of each autobiography. They then gave the elderly sisters a battery of tests that measure memory, concentration, language ability, and other cognitive skills.
Nuns whose autobiographies received the lowest scores in the idea density category were more likely than high-scoring nuns to perform poorly on cognitive tests. Low-scoring nuns were 30 times as likely as the high scorers to flub the Mini-Mental State Exam, a standard test of cognitive function.
When the investigators looked for links between grammatical complexity and Alzheimer's disease, they found only a weak association.
Snowdon's team knew that studies by other groups had indicated that education protects against Alzheimer's dementia, perhaps by building up a cognitive reserve early in life that offsets the disease process. To rule out education as a confounding factor, Snowdon's team repeated its analysis with a subgroup of highly educated sisters. In that group, low idea density also predicted dementia and Alzheimer's disease.
Finally, Snowdon's group took a close look at the brains of 14 sisters who had died since the study began in 1991. On the basis of autopsy results and earlier cognitive testing, the team confirmed a diagnosis of Alzheimer's in 5 of the 14. …