ARI SHAPIRO, HOST:
Here's a glimmer of hope for people in the early stages of Alzheimer's disease. A new study shows that an experimental drug can scrub away plaques in the brain that are a hallmark of the disease. But as NPR's Jon Hamilton reports, it is still not clear whether the drug can improve memory and thinking.
JON HAMILTON, BYLINE: Pharmaceutical companies have come up with a lot of drugs meant to fight Alzheimer's. So far they've all failed. But last summer, scientists began hearing about a drug called aducanumab. Early reports suggested it had a remarkable ability to remove the toxic amyloid plaques that build up in the brains of people with Alzheimer's. Dr. Eric Reiman is executive director of the Banner Alzheimer's Institute in Phoenix.
ERIC REIMAN: It was surprising, encouraging and thought-provoking to see such a striking reduction of existing plaques.
HAMILTON: Now those findings have been published in the journal Nature. A study of 165 people in the early stages of Alzheimer's confirms that aducanumab is a potent plaque buster, and Reiman, who wrote an editorial accompanying the study, says that's not all.
REIMAN: There was a hint that the reduction in amyloid plaques may be associated with a slowing in memory and thinking problems.
HAMILTON: Reiman says people who took the highest dose of the drug had very little cognitive decline.
REIMAN: If that hint of a clinical benefit is confirmed, it would be a game changer in the fight against Alzheimer's disease.
HAMILTON: Even Biogen, the company that's developing aducanumab, is being cautious. Al Sandrock is the company's chief medical officer and an author of the new study.
ALFRED SANDROCK: We think we have something important here. We hope we're right because if it's true, it would benefit millions of patients. But we don't know where right yet. We're going to have to do a couple of large trials to confirm what we think we see.
HAMILTON: Those trials will include a total of 2,700 patients. Researchers began enrolling those patients last year, but results are still several years off. Sandrock says there are several reasons to think aducanumab will succeed where other drugs have failed.
SANDROCK: First of all, it seems to be more specific for the toxic forms of amyloid.
HAMILTON: The drug appears to target the amyloid cluster suspected of damaging brain cells while ignoring benign forms of the protein. Also, the drug appears to ramp up immune cells in the brain that devour toxins, including amyloid.
But there's a downside. The process of removing plaque sometimes causes fluid to build up in the brain. In rare cases it can also cause bleeding. Sandrock says these side effects are known as ARIA.
SANDROCK: We were actually anticipating that we would see it. We actually did frequent MRI scans to actually look for the ARIA. We did see it.
HAMILTON: But the problems were usually mild, and most patients were able to continue taking the drug. If aducanumab works in larger studies, it could help settle a long-running debate about whether amyloid is really the root cause of Alzheimer's. This idea is known as the amyloid hypothesis, and Sandrock says he's a believer.
SANDROCK: We're very hopeful that we'll actually see a cognitive benefit. And if we do, I believe it goes a long way toward validating the amyloid hypothesis.
HAMILTON: And it could lead to the first drug that would treat the underlying cause of Alzheimer's rather than just the symptoms. Jon Hamilton, NPR News.
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