– Donald Jackson, 81, and his partner of more than 40 years, Myrna Roach, 74, are the kind of older people many of us would like to be one day.

Both still work and are energetic enough to travel extensively. They take medicine for high blood pressure and he has diabetes, but they feel healthy. They like to join clinical trials and know from one that their mental abilities have been stable for years.

Still, Roach has a strong family history of Alzheimer’s disease. Jackson doesn’t, but Alzheimer’s is the disease he dreads above all others.

So, it was with a mixture of curiosity, anxiety and altruism that the couple entered an unusual clinical trial at the University of Pennsylvania. Using a PET scan, their brains were examined for deposits of amyloid, one of the hallmark proteins found in dementia.

Then — even though there are currently no treatments that change the course of the disease and even though no one knows for sure how much amyloid deposits raise the risk of getting dementia — they were told the results so that researchers could measure how the news affected them.

Jason Karlawish, a Penn physician who is leading the psychological study, said people often join trials like this because they have seen what Alzheimer’s does up close and want to help.

On many levels, this is the stuff of science fiction: If you could know the future, would you want to? If you did, how would you change? Would other people treat you differently?

His study is part of a larger clinical trial known as A4 (short for Anti-Amyloid Treatment in Asymptomatic Alzheimer’s) that is testing the anti-amyloid drug solanezumab in people who are at risk for Alzheimer’s but don’t have symptoms yet. Frustrated that drugs like solanezumab haven’t worked in patients who already are sick, doctors want to test in people with less damaged brains.

The trial is both an attempt to prevent Alzheimer’s and to further define what it is.

Scientists now believe that the processes that lead to memory and thinking deficits in Alzheimer’s start many years before symptoms are noticeable. Just as doctors try to prevent heart attacks by encouraging patients to exercise, lose weight and take drugs, they hope to prevent Alzheimer’s someday.

Robert Green, a medical geneticist at Boston’s Brigham and Women’s Hospital who studied how people responded to learning they had a mutation that raises the risk for Alzheimer’s, said we are entering an era when we could learn about all kinds of genetic time bombs that might — even will — make us sick in the future. He is now studying how people react to whole-genome results from direct-to-consumer companies.

“We are very close to a point where anyone who wants to learn genetic risk information will have the opportunity to do that,” Green said.

Or, as Karlawish puts it, our ability to study risk factors for disease is transforming the “natural experience of aging” into the “monitored life at risk.”

Karlawish thinks disclosure has no place in a regular doctor’s office until there’s treatment. But, he thinks it should be studied in clinical trials because someday people will have to know before they get medicines. That knowledge could affect how they respond to treatment.

As for Roach, she wasn’t all that relieved to learn her brain is clear. “I’m probably going to get it anyway,” she said.

Jackson received bad news, but was calm it. He credits his equanimity to a tough childhood and years spent working on Air Force planes during missions. “So it’s there,” he said. “What can you do about it? Nothing. That’s the way I look at it.”