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New marker may aid Alzheimer's diagnosis.

New marker may aid Alzheimer's diagnosis

Discovery of an association between an important brain enzyme and Alzheimer's disease may help researchers understand the biological basis for this dementia and help physicians diagnose the illness sooner.

Most Alzheimer's victims -- and some individuals suffering other forms of dementia--appear to carry a variant form of the enzyme acetylcholinesterase (AChE), a study in the Feb. 23 LANCET indicates. Normal forms of AChE break down acetylcholine, which acts as a messenger between individual nerve cells. The variant's function in the brain remains undetermined, says neuropharmacologist A. David Smith of Oxford University in England, an author of the new study.

Smith and his colleagues sampled cerebrospinal fluid from 61 people who died from various causes. Assays from 19 of the 23 individuals diagnosed with only Alzheimer's during an autopsy contained a form of AChE not found in the 19 people without dementia. The same variant AChE turned up in four of eight people who had suffered from other forms of dementia.

Though healthy neurons produce as many as eight discrete forms of AChE, scientists do not yet understand why, Smith says. The new variant might result from a genetic defect, or some later alteration of a normal enzyme.

Some form of AChE occurs in many of the neural pathways affected by Alzheimer's. As a result, Smith says, researchers have suspected that an AChE abnormality might play a role in the disease. Though previous research showed that AChE levels in brain tissues affected by the disease are lower than normal, researchers remain unsure of the enzyme's role in Alzheimer's, he notes.

The new AChE finding may eventually help researchers answer this question. But for now Smith plans to develop its potential as a marker to help physicians more accurately diagnose Alzheimer's in living patients, thereby offering the prospect of earlier treatment. Though other potential markers are being explored, physicians still confirm this disease only through postmortem exams.

A good Alzheimer's marker would be very important, agrees Israel Hanin, a neuropharmacologist at Loyola University of Chicago's Stritch School of Medicine in Maywood, Ill. However, he stresses the new findings must be confirmed elsewhere, because "different populations may [develop Alzheimer's] for different reasons." In the United States, Alzheimer's disease afflicts an estimated 4 million individuals, primarily aged 65 and older.

Smith's team has already begun follow-up work to determine the newly discovered AChE's frequency among people with various dementias and to study its potential as a marker for Alzheimer's.
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Title Annotation:acetylcholinesterase, an enzyme
Author:Gibbons, Wendy
Publication:Science News
Date:Mar 2, 1991
Words:410
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