Long-awaited federal funding has been approved for a first-of-its-kind, Boston-led study to test whether drugs can hold off Alzheimer’s disease in people who have no symptoms of the illness, but who have an abnormal protein in their brains believed to be a marker of the disease.
The National Institutes of Health announced Monday that the clinical trial, to be led by Dr. Reisa Sperling, an Alzheimer’s specialist at Brigham and Women’s Hospital, is one of four that will be funded this year to find treatments for the disease.
Sperling’s three-year study will receive the lion’s share of the money, roughly $36 million. The federal biomedical research agency said it will give the four trials a total of $11 million this year and as much as $55 million over five years.
“I am very excited after all this time to really get started,” said Sperling, who has been planning the study for nearly two years.
Sperling’s trial will enroll 1,000 adults, ages 70 to 85, who have abnormal proteins, known as amyloid plaques and revealed by brain scans, and who are exhibiting subtle cognitive problems that are typically reported in people years before they are diagnosed with Alzheimer’s.
The study will give half of the participants a drug designed to clear amyloid plaques and the others a placebo, and researchers will track the rate of cognitive decline in both groups. Sperling said that if the researchers’ hypothesis is right, the group that receives the amyloid-clearing medications will have a 25 to 35 percent slower rate of decline than those receiving a placebo.
Other drug trials aimed at clearing the amyloid proteins in the brains of Alzheimer’s patients have produced disappointing or very modest results, with little or no apparent easing of symptoms, and researchers think that is because the drugs were used too late.
Scientists believe that more than half of certain critical brain cells are lost by the time a patient displays even mild cognitive impairment. There is no known cure for Alzheimer’s disease.
“As a clinician, I am always upset when I talk about going earlier and earlier in the disease because it could seem to people that we are leaving a generation of people with dementia behind as we move earlier, and that’s not true,” Sperling said.
“I am not giving up on finding a successful treatment for people with dementia already,” she said. “I just think we will have success if we move earlier.”
Sperling said her study will recruit volunteers from 50 sites across the country, including two in Boston, at the Brigham and probably at Boston University School of Medicine.
The researchers will seek volunteers from a wide range of ethnic, racial, and socioeconomic backgrounds.
“It’s important,” Sperling said, “that we get a broad sampling of older individuals who represent the population in this country.”
Advocates, who have been frustrated by the pace of funding for Alzheimer’s studies, hailed Monday’s announcement.
“This is a message that the government is really serious about coming up with meaningful treatments for this very tough disease that is overwhelming our society,” said James Wessler, chief executive of the Alzheimer’s Association Massachusetts and New Hampshire chapter.
“We know there are no guarantees. But we’ve got to keep trying, and this is a significant study,’’ Wessler said.
Sperling said the researchers are still finalizing which medication they will study. The NIH money is just a piece of the needed funding, but she expects to hear soon on funding from industry and charitable foundations to finalize the support for the $140 million study.
The first participants are expected to be enrolled by the fall, but the Food and Drug Administration still must approve the research.
“We believe we will need to screen 10,000 people,” Sperling said. “It’s a very hierarchal process, starting with phone screening, then questionnaires, then an in-clinic visit.”
Ultimately, Sperling estimates the researchers will perform brain scans on 3,000 of those 10,000 to select the final 1,000 in the study.
The three other NIH-funded studies include one that will test whether exercise — often widely recommended to maintain physical function and reduce age-related declines — is effective in slowing further cognitive losses and brain atrophy in people with mild cognitive impairment, a condition that often leads to Alzheimer’s disease.
Exercise has not been shown in a longer-term clinical trial to improve cognition or alter the course of Alzheimer’s disease.
The yearlong trial, led by researchers in North Carolina and California, will compare brain scans, cognitive testing, and spinal fluid from two groups of sedentary older volunteers, who already have some mild cognitive impairment. One group will do high-intensity aerobic exercise, and the other will do stretching.Kay Lazar can be reached at email@example.com. Follow her on Twitter @GlobeKayLazar.