"It's kind of like finding high cholesterol" but not having drugs that can lower it, said Dr. Mark Sager, director of the Wisconsin Alzheimer's Institute at the University of Wisconsin-Madison. He was involved in a study of a different Alzheimer's-linked gene that will be reported this week.
Scientists also don't know if the plaque is a cause, an effect, or just a sign of Alzheimer's. Two experimental drugs seemed to clear plaque but did not lead to clinical improvement.
"We've still got a long way to go," Sager said.
Follow U.S. News Science on Twitter.