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AUDIE CORNISH, HOST:

From NPR News, I'm Audie Cornish.

ROBERT SIEGEL, HOST:

And I'm Robert Siegel.

Today on ALL THINGS CONSIDERED, we have reports on the $1.2 billion fine against Toyota for mishandling safety problems; also, the crisis in Crimea; and the FBI's new task in the search for Malaysia Airlines Flight 370.

CORNISH: Right now, the challenge of identifying people with Alzheimer's. Figures released today by the Alzheimer's Association show that more than 5 million Americans have the disease. But those numbers only include people who have symptoms, such as memory loss.

NPR's Jon Hamilton reports on efforts to identify and treat millions more Americans. These are people who have brain changes associated with Alzheimer's but who don't yet have symptoms.

JON HAMIILTON, BYLINE: For 30 years, doctors have relied on tests of memory and thinking to diagnose Alzheimer's. But Maria Carrillo, of the Alzheimer's Association, says that approach is becoming outdated.

MARIA CARRILLO: Today, we know that the diagnosis of Alzheimer's disease made in that way - by the symptoms of the disease - is really a representation of a disease process that's been happening in the body for potentially 10 to 20 years.

HAMIILTON: So for several years now, the NIH and Alzheimer's Association have been pushing for a new diagnostic category, something called preclinical Alzheimer's. People with this diagnosis wouldn't have problems with memory or thinking. But their brains would have the amyloid plaques and tangles associated with Alzheimer's. Carrillo says it's becoming possible to detect those signs of trouble using brain scans, tests of spinal fluid, and other so-called biomarkers.

CARRILLO: Biological markers that can tell us that underlying biology is really changing in the body before memory starts to change.

HAMIILTON: Carrillo says these biomarkers aren't ready for widespread use yet. But when they are, they should make it possible to identify people at high risk for Alzheimer's, much the way cholesterol tests identify people at high risk for heart disease. Carrillo says that should make it easier to do something about Alzheimer's.

CARRILLO: We haven't completely obliterated heart disease. But we've reduced risk by about 30 percent, which is huge and has saved millions of lives. We can do the same for Alzheimer's disease. We just need to apply the research and the resources.

HAMIILTON: At the moment, there aren't any treatments that slow down the disease. But Reisa Sperling, a researcher at Harvard, says that may change because of something known as the A4 study.

REISA SPERLING: The study will test whether or not we can slow the earliest cognitive changes, the earliest problems with memory that people experience years before they get to the stage of dementia.

HAMIILTON: Sperling, the study's principal investigator, says 60 centers around the country have just started enrolling the first of about a thousand people who don't have symptoms of Alzheimer's but do have brain scans showing a build-up of amyloid plaque. She says some of them will be given an experimental drug.

SPERLING: We're going to test what's called a monoclonal antibody. This is a protein that helps clear amyloid out of the brain - in a three-and-a-half-year trial.

HAMIILTON: This drug, like several others, failed to help people in the later stages of Alzheimer's. But Sperling says the drug appeared to slow cognitive decline in people who started taking it early on, when they had only mild symptoms.

SPERLING: And that was exciting to us because we thought if we could go 10 years earlier and have the same rate of slowing of cognitive decline, we'd make a huge dent in preventing dementia.

HAMIILTON: Sperling says it will be five years before it's clear whether the drug works. In the meantime, she says, it's important to begin identifying people with preclinical Alzheimer's.

SPERLING: When I look around at every other field of medicine where we've really made progress, I think it is in detecting people before they have symptoms.

HAMIILTON: Sperling says that approach paid off in diseases like diabetes and HIV, where screening tests came along well before good treatments were available. She says with Alzheimer's, better tests and effective treatments may arrive at nearly the same time.

SPERLING: It's a race. So we need to develop these screening tests and the biomarkers simultaneously with working on these clinical trials so that if, in fact, we succeed, we're prepared for how we would go about screening individuals to receive those treatments.

HAMIILTON: Sperling says millions of people in the U.S. could benefit from a drug that prevents or delays Alzheimer's. She says about 30 percent of people older than 65 have amyloid plaque building up in their brains.

Jon Hamilton, NPR News.

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