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Alzheimer's Study Yields Early Clues

New imaging techniques can reveal subtle signs of disease many years before apparent symptoms, so that treatments--as they become available--can begin early.

November 02, 2000|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

The digital images framed on Dr. Gary Small's computer screen at UCLA are portraits of a mind in decline, lighted by the mental embers of dying memories.

In their abstract whorls of glowing gray matter, these pictures of the human brain reveal what even a clinical expert like Small normally cannot detect: the first subtle signs of Alzheimer's disease years before anything seems amiss.

Using an unusually sensitive medical imaging scanner at UCLA's Brain Mapping Center, Small and UCLA neuropsychologist Susan Bookheimer have demonstrated for the first time that the brains of people at genetic risk of Alzheimer's disease must work much harder than normal to marshal simple memories.

This heightened, unconscious mental effort occurs long before overt symptoms of the disease appear, at a point when no one would notice anything more out of the ordinary than the normal absent-mindedness of middle age.

Moreover, in retesting the same people two years later, the scientists discovered that those who had had to rack their brains hardest later developed the most severe memory loss.

"Now we have a way of combining genetic risk and brain imaging to track brain functional decline over time," said Small, a UCLA psychiatrist who is an expert on the neurobiology of aging and Alzheimer's disease.

Published recently in the New England Journal of Medicine, the new imaging research adds weight to a growing body of medical evidence strongly suggesting that Alzheimer's disease begins with subtle neural changes decades before any observable symptoms of mental decline. Indeed, the neural changes at work in Alzheimer's may begin so early in life that they may affect how well someone does in school.

The UCLA study "provides additional evidence that subtle changes in brain function can be observed early in the disease course," said Dr. Neil Buckholtz, chief of the Dementias of Aging Branch at the National Institute on Aging.

To better understand those at genetic risk of Alzheimer's disease, Small and his colleagues are using two computerized imaging techniques: positron emission tomography, or PET, which records changes in the brain's metabolism, and a more experimental technique called functional magnetic resonance imaging, or fMRI, which detects extremely rapid changes in neural blood flow. The techniques give researchers a way to monitor the speed, intensity and extent of neural activity.

By investigating how Alzheimer's disease changes the way the brain works, they hope to learn how someone can lose his place in time and memory as neurons die and synapses atrophy, stripping the mind of its links to the world it once knew.

So far, their findings suggest that these brain-imaging techniques may be able to predict who will develop the disease so far in advance that treatments--as they become available--can begin before the brain is severely affected.

Several experts have also suggested that the imaging techniques could one day serve as a reliable diagnostic tool for a condition easily confused with other causes of flagging memory and dementia.

Experimental PET scans, for example, reveal that Alzheimer's causes a distinctive pattern of declining brain metabolism. This is strikingly different from the patterns after stroke damage or degenerative disorders such as Huntington's disease and Pick's disease.

Today, however, Alzheimer's disease is almost impossible to diagnose clinically and all but intractable to treatment, despite a number of new experimental drugs.

Alzheimer's disease affects 4 million Americans, but that number is expected to approach 14 million by mid-century. So prevalent is the disease among those over 85 that some researchers suspect the disease is a normal consequence of aging and longevity. Yet, like so many other degenerative disorders of the human brain, it is hard to study directly because its effects are at first so subtle and so hard to distinguish from normal behavior.

No one knows what causes the disease and, so far, a definitive diagnosis can be made only after an autopsy, when researchers can detect the telltale amyloid plaques that build up around neurons in the hippocampus and parts of the cerebral cortex. Inside these affected brain cells are unusual twisted filaments of protein called tangles.

Researchers have linked the disease to risk factors ranging from traces of aluminum in drinking water to high-fat diets, lead exposure and a low tolerance for alcohol.

But the most telling link to the disease so far appears to be hereditary.

Signs of Genetic Risk

Alzheimer's does appear to show up more often in some families. Several genes have been implicated, most notably a gene on chromosome 19 that encodes a protein called apolipoprotein-E, which helps in the distribution of cholesterol.

A common variation of that gene, called APOE-4, increases the likelihood that someone will develop the disease. Although the gene is present in 15% of the population, its presence does not mean the onset of the disease is at all certain.

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