Photo-Illustration: Photo: Mike Kemp/Getty Images

It starts with a twitch, maybe a stumble. There’s a forgotten word or name here and there. Really, it appears a little like drunkenness. But when symptoms of Huntington’s disease progress, they consume the person who has it. The neurodegenerative disease simultaneously disintegrates mental and physical functioning, leaving the patient completely dependent on a caretaker or medical devices, or both, for the smallest of tasks: eating, sitting up, swallowing. A person with Huntington’s will eventually lose control over their own body and mind. There is no treatment, and no cure.

The disease is rare, affecting only about 30,000 American adults. But if either of your parents has Huntington’s, your risk of having the disease yourself is 50-50, a terrifying coin flip. In 1993, a genetic test for Huntington’s was developed, and at the time up to 70 percent of those at risk for the disease indicated that they would be interested in finding out their medical future. In recent years, the taking of that test has been played out to dramatic effect on shows like This American Life or last summer’s HBO documentary The Lion’s Mouth Opens.

And yet the numbers show that the actual testing rate among those who know they are at risk for Huntington’s has turned out to be incredibly low, hovering around 7 to 10 percent. A recent study led by Brown University economist Emily Oster attempted to find out why this is, and the paper comes to a surprising conclusion: Maybe so few among this population get the genetic test because they are, and they believe themselves to be, better off not knowing.

Oster’s data, which she analyzed with Huntington’s researchers Ira Shoulson and E. Ray Dorsey, includes about 1,000 Americans who are at risk for Huntington’s, taken from a nationwide data set known as PHAROS. Their responses suggest that the lack of testing is not due to the test being too inconvenient or too expensive to acquire. “No one says costs are a problem,” Oster said in a presentation at the Society for Personality and Social Psychology’s annual meeting earlier this year. “What they say is ‘I don’t want to know.’”

So what happens to a person’s life who chooses to live in such dramatic uncertainty? This is the fascinating part of Oster’s research. Because, in a way, the not-knowing allowed these people to steal their lives back from the specter of Huntington’s. Compared to the major life decisions made by those who had both gotten tested and subsequently learned they had the disease, those who chose the unknown lived their lives as if they didn’t have it and never would.

They pursued more education and more job training than those who knew they had the disease, who, in contrast, were more likely to leave the workforce and retire early. In addition, those who choose not to take the test are more likely to get and stay married; they’re also more likely to have children. “People who are uncertain about their status behave exactly like people who do not have it,” Oster said. “Until you know for sure, you are acting like you do not have it.” By choosing not to know, they get to create a kind of alternate reality for themselves, at least for a little while.

In a lot of ways, Jennifer Leyton is a living, breathing example of Oster’s research. Her mom died of Huntington’s; so, for that matter, did her grandmother, her aunt, her cousin — and, just three years ago, her brother, Peter. Leyton is now in her 40s and decided in her 20s she would rather not know her genetic fate. “I decided that if I knew I had the gene, I would make certain decisions in my life,” she told Science of Us. “And not knowing I had the gene, I’m just going to go on with my life and do what I need to do.”

Unlike many of those in Oster’s study who knew they had the gene, Leyton earned both a bachelor’s and a master’s degree. She also got married and had children. Those children, by the way, know for sure that they do not have the gene for Huntington’s; they were born via in vitro fertilization, and Leyton’s doctor only implanted embryos that did not carry the gene. And this means, of course, that her doctor learned whether or not Leyton herself had the gene — even still, Leyton chose not to know. She’s hedging her bets by purchasing both life insurance and long-term care for herself, in case the worst happens; her husband is also well aware of her wishes, should the darker version of her future eventually play out. But so far, uncertainty has been a gift, allowing her the freedom to live her life the way she always wanted to live it.

And yet, for many people, uncertainty is a psychologically uncomfortable place to stay. Some are better at handling ambiguity than others, and this no doubt plays a role in the decision to learn your medical fate. Leyton’s brother, Peter, was always haunted by the idea of Huntington’s, to a greater degree than Leyton ever was.

“For me, the biggest difficulty about this uncertainty comes when I drop a bar of soap, or when I can’t think of somebody’s last name, or when I stumble over pavement. I think for a moment, Oh no, I have the gene,” Leyton said. “Other than that, I’m not losing sleep over it. I’m okay.

“But my brother, he was not okay,” she continued. “He thought about Huntington’s disease all the time.” Shortly after genetic testing became widely available in the 1990s, he took the test. He had the gene. “And when he found out, it was actually such a huge relief for him,” Leyton said. “Because he was like, ‘I don’t have to worry about it anymore. I know the answer, and I’m just going to give into it.’” Soon after the test, Leyton’s brother quit his job, bought a studio in Manhattan, and stopped dating. “He just started doing what he wanted to do,” she said.

Two siblings with equal chances of inheriting this disease, and yet they took two very different approaches to learning their individual medical futures. But their respective decisions allowed each of them to live the lives they wanted. Leyton believes that if she had taken the test and learned that she had Huntington’s, her life would’ve turned out much differently than it had. No husband, no now-teenage twins. It’s not something she thinks about often.

Oster and other academics, perhaps particularly economists, typically make the argument for more information, and that more is always better. If you know what’s coming, you can plan accordingly. But instead of taking a scolding, these-people-should-know-better tone, Oster’s conclusion from her data is compassionate. Maybe pretending everything is fine for most of their years on Earth is the best decision for some people who are at risk for Huntington’s. It’s a unique disease, and thus so is the question of testing for it. Unlike, for example, breast cancer, there is no treatment and currently no real hope for a cure. (Though even testing for BRCA, the genetic mutation that signifies an increased risk for developing breast cancer, has been lower than researchers initially expected.)

“It may be optimal to choose overly optimistic beliefs,” Oster said. “And it may not be optimal to force information on people.” It’s hard to place an economic value on those years of living as if you’re healthy, but for some people, that time may prove to be priceless, especially in comparison to a life lived in deference to a terrible future. (Though preparation for the worst, as Leyton has done with both her finances and her two children, is unquestionably the smartest, safest route.) After you learn your fate, after all, there is no unlearning it.