If you could easily find out whether your genes put you at risk of developing a progressive, fatal disease, would you want to know?

How about if that disease can't be prevented or cured? What if the test's prediction would almost certainly be inconclusive and possibly misleading — potentially giving you a false sense of security or plunging you into despair over a false positive?

That's essentially the situation with genetic testing for Alzheimer's disease. Thanks to scientific advances in the past decade, genetic tests for heritable diseases have become available and inexpensive. Until about a year ago, for about $100 consumers could send in a saliva sample and receive an evaluation of their chances for developing hundreds of diseases, including Alzheimer's.

But last fall the Food and Drug Administration ordered the manufacturers of such tests to stop providing medical information while the agency considers regulating them (although people who bought kits before the FDA's order last November can still receive results and access the information online).

Many experts, including those at the Alzheimer's Association, are leery of genetic testing for Alzheimer's, especially without a doctor's supervision.

The tests "risk making hundreds of thousands of people paranoid that they're going to develop dementia," said Dr. Richard Caselli, a neurologist at the Mayo Clinic's Phoenix branch "Every time something goes bump in the night, they're going to be calling their doctor and wanting a PET scan."

Alzheimer's is the most common form of dementia. It is currently untreatable and always fatal. It affects more than 5 million people in the United States; barring a medical breakthrough, that number is expected to nearly triple by 2050 as the boomer generation ages.

So it's not surprising that many people, even those with no symptoms, are curious about whether they'll eventually get it. Proponents argue that people are entitled to the information, and that if the news is bad people can take steps to improve their odds, such as adopting healthier habits.

"We believe everyone has the right to access, understand and benefit from their DNA and that access to this genetic information can help people make more informed decisions about their health, and help accelerate research discoveries," said Emily Drabant Conley, a research scientist with 23andMe, the most well-known of the companies offering testing, in an e-mailed statement. "Over the last eight years, we have heard hundreds of stories from customers about how genetic information has enabled them to make better decisions about their lives."

Aside from a rare form of early onset Alzheimer's that involves a genetic mutation (estimated at less than one percent of cases) susceptibility to the disease can't be predicted with certainty by examining genes. One form of one particular gene — the E4 form of the APOE gene — is linked to an increased chance of Alzheimer's. Between 40 and 65 percent of people with Alzheimer's carry one or two copies of E4; someone with two copies of it is 12 times more likely to get Alzheimer's than someone with none, said Dr. Michael Rosenbloom, clinical director of the Health Partners Center for Memory and Aging.

But some people have E4 and don't develop Alzheimer's. And some people with Alzheimer's don't have E4. So a genetic test can only predict the elevated risk.

"It's like saying, 'If you smoke, you're at an increased risk for a heart attack.' It doesn't mean you'll necessarily have a heart attack," Rosenbloom said.

Besides, while you can quit smoking, there's little you can do to avoid Alzheimer's. Unlike conditions such as heart disease, Alzheimer's is not strongly linked to lifestyle habits. Preliminary research suggests exercise might help reduce or postpone dementia. And a history of head injuries is linked to Alzheimer's — so you might avoid contact sports when planning your exercise regimen (or wear a helmet). Healthy habits have other benefits, of course. But so far, there's little evidence they keep minds sharp.

Caselli recently conducted a survey and found that this is widely misunderstood. More than 90 percent of the 4,000-plus respondents said that learning they were genetically predisposed to Alzheimer's would lead them to "pursue a healthier lifestyle." In addition to the strategy's limitations, Caselli pointed out that even patients at risk for diseases that clearly are tied to healthy habits don't necessarily adopt them.

"Talk is cheap," he said. "Our experience in the cardiovascular world is pretty poor."

More worrisome still, 11 percent of respondents in Caselli's survey said that getting bad news would lead them to consider suicide. Caselli suggests that anyone considering genetic testing should do it under a doctor's supervision, so if the news is bad they can find help dealing with the emotional impact.

"There are a lot of depressed people out there, a lot of anxious people, and if you don't have any type of regulation of who's getting tested, what they're being told, how they're being followed, I really do fear that we're opening the door to more harm than good," he said.

But Conley pointed out that a study reported five years ago in the New England Journal of Medicine found that adults who received the results of genetic testing for Alzheimer's, including some who carried the E4 form of APOE, were not significantly more anxious or depressed six weeks to a year later than people who did not receive the information.