美国国家公共电台 NPR Scientists Push Plan To Change How Researchers Define Alzheimer's（在线收听）

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A large coalition of brain researchers has unveiled a plan to redefine Alzheimer's disease. The goal here is to study Alzheimer's by focusing on biological changes in the brain rather than symptoms like memory loss. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: The plan offers a new and different way of looking at Alzheimer's. Clifford Jack of the Mayo Clinic says the old way worked like this.

CLIFFORD JACK: A person displayed a certain set of signs and symptoms, and it was expected that they had Alzheimer's pathology.

HAMILTON: Jack says researchers began to see the flaws in that approach when they took a close look at the brains of people receiving experimental drugs for the disease.

JACK: About 30 percent of people who met all the appropriate clinical criteria did not have Alzheimer's disease.

HAMILTON: Their memory or thinking problems were being caused by something else. So Jack says researchers began looking for more reliable ways of determining who really has Alzheimer's.

JACK: What we're saying now is that Alzheimer's disease is defined by the presence of plaques and tangles in your brain.

HAMILTON: Sticky plaques and threadlike tangles of proteins that build up over time. Jack says in this new view, researchers treat these abnormal proteins along with evidence of brain damage as hallmarks of Alzheimer's.

JACK: And symptoms become a result of the disease, not the definition of the disease.

HAMILTON: Eliezer Masliah of the National Institute on Aging says defining Alzheimer's by plaques and tangles also solves another big problem for researchers.

ELIEZER MASLIAH: There is a stage of the disease where there are no symptoms, and we need to have some sort of a marker.

HAMILTON: What scientists call a biomarker. And now there are a range of biomarkers for plaques and tangles. They are detected through special brain scans and tests of spinal fluid. Masliah says that means scientists can now do experiments that would have been impossible relying on symptoms alone.

MASLIAH: One could, let's say, start preventive treatment five years before the onset of the symptoms based on the presence of the biomarkers.

HAMILTON: Scientists outlined the new approach in several papers in the journal Alzheimer's And Dementia. But proponents say the new definition is intended for researchers, not doctors and their patients. That's because current biomarker tests are expensive, often difficult to perform. And, even if they find something, there's still no way to stop the underlying disease. Maria Carrillo is the Alzheimer's Association's chief scientific officer.

MARIA CARILLO: It's a research framework meant to be tested, a tool for researchers, not for the doctor's office.

HAMILTON: But she says a few doctors who specialize in Alzheimer's are already beginning to use tests for plaques and tangles.

CARILLO: Some of those physicians actually are able to incorporate some biomarkers to actually make a more precise diagnosis.

HAMILTON: That can help in some special cases. And Carillo hopes that when drugs to prevent Alzheimer's finally arrive, biomarker tests can show who should get them. Jon Hamilton, NPR News.