The brains of Alzheimer's patients accumulate beta-amyloid plaque. For a long time, there's been a controversy over whether the plaque is a cause or a side effect. This is tremendously important, because it will direct treatment research for a horrendous disease.

Well, now it looks like we may have resolved the chicken and egg problem:

Now, researchers have caused Alzheimer's symptoms in rats by injecting them with one particular form of beta-amyloid. Injections with other forms of beta-amyloid did not cause illness, which may explain why some people have beta-amyloid plaque in their brains but do not show disease symptoms.

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