Such discrimination appears to be rare; even proponents of federal legislation that would outlaw it can cite few examples of it. But thousands of people accustomed to a health insurance system in which known risks carry financial penalties are drawing their own conclusions about how a genetic predisposition to disease is likely to be regarded.

As a result, the ability to more effectively prevent and treat genetic disease is faltering even as the means to identify risks people are born with are improving.

“It’s pretty clear that the public is afraid of taking advantage of genetic testing,” said Dr. Francis S. Collins, director of the National Human Genome Research Institute at the National Institutes of Health. “If that continues, the future of medicine that we would all like to see happen stands the chance of being dead on arrival.”

Caught in a Bind

For Ms. Grove, 59, keeping her genetic condition secret finally became impossible. When her symptoms worsened she was told to come back to the clinic before antibiotics would be prescribed. But there had been a snowstorm that day, and she could not summon the strength to drive.

“I have alpha-1,” she remembers sobbing into the phone. “I need this antibiotic!”

The clinic called in the prescription.

Ms. Grove, who does freelance accounting from home and has health insurance through her husband’s employer, allowed herself to be identified here because she said she felt an obligation to others  including some in her own family  to draw attention to the bind she sees herself in.

“Something needs to be done so that you cannot be discriminated against when you know about these things,” she said. “Otherwise you are sicker, your life is shorter and you’re not doing what you need to protect yourself.”