updated 6/22/2008 3:15:53 PM ET 2008-06-22T19:15:53

Researchers have uncovered a new clue to the cause of Alzheimer’s disease.

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Researchers says they have caused symptoms of the memory-robbing form of dementia in rats by injecting them with a particular form of sticky protein called beta-amyloid. The protein forms a kind of plaque that is found in the brains of people with Alzheimer’s.

There long has been a question whether the protein is a cause of the disease or a side effect. Some people have beta-amyloid plaque in their brains but do not show disease symptoms.

The researchers say they were surprised to find that injections of two forms of the protein did not cause illness, while the third type did. Now, they say the question is why?

The findings are reported in the online edition of the journal Nature Medicine.

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