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Protein Levels Signal Alzheimer's
April 22, 2003 -- Levels of two proteins found in the body may one day serve as markers of Alzheimer's disease and help doctors diagnose and treat the disease earlier than with currently available methods. A new study shows significant differences in the levels of two proteins found in spinal fluid in a large group of Alzheimer's disease patients when compared with a group of healthy older adults.
The exact cause of Alzheimer's disease is unknown. Since there is no test for the disease, doctors usually diagnose the disease on the basis of a person's medical history, dementia-related symptoms, and elimination of other possible illnesses.
Many potential biological indicators of Alzheimer's disease have been identified, but researchers say these two proteins, called CSF beta-amyloid and tau proteins, are among the most obvious candidates for use in diagnostic testing because the proteins are closely related to the plaques and other deposits found in the brains of Alzheimer's disease patients.
In this study, published in April 23/30 issue of The Journal of the American Medical Association, researchers measured levels of these proteins in 131 people with Alzheimer's disease and 72 healthy adults.
They found levels of CSF beta-amyloid protein were significantly lower, on average, in people with Alzheimer's disease than the comparison group (183 pg/mL vs. 491 pg/mL). In addition, levels of CSF tau protein were significantly higher in Alzheimer's disease patients than in the others (587 pg/mL vs. 244 pg/mL).
"To our knowledge, our study is the largest to confirm the decrease of CSF beta-amyloid and an increase in tau levels in AD participants," write researcher Trey Sunderland, MD, of the National Institute of Mental Health, and colleagues. "In addition, these differences appear to be found in patients with mild AD as well in patients with moderate to severe AD."
Researchers also looked at a group of 51 previous studies of these proteins and found similar differences between people with Alzheimer's disease and other adults.
Although this study shows the proteins may be useful in identifying Alzheimer's disease, researchers say it's still too soon to for them to be used for testing individuals.
Researchers say current testing methods for these proteins are not standardized, nor are they sensitive or specific enough.
For example, this study compared the proteins only between a group of people with Alzheimer's disease and healthy individuals. For a diagnostic test based on these proteins to be truly accurate, it would also have to be able to differentiate among other types of dementia.
They say future studies should address these issues as well as determine if the proteins might serve as useful predictors of a person's risk of developing Alzheimer's disease or in evaluating the effectiveness of Alzheimer's disease treatment.
SOURCE: The Journal of the American Medical Association, April 23/30, 2003.
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