Still, a recent study by the Georgetown University Health Policy Institute found otherwise. In 7 of 92 underwriting decisions, insurance providers evaluating hypothetical applicants said they would deny coverage, charge more for premiums or exclude certain conditions from coverage based on genetic test results.

The medical cost

Regardless of whether discrimination actually occurs, many health care professionals say the pervasive anxiety over it demands legislative action. Geneticists complain that discrimination fears prevent them from recruiting research participants, delaying cures and treatments for disease. At Memorial Sloan-Kettering Cancer Center in New York, the same concern is a leading reason why people cancel appointments for tests that detect cancer risk.

"We are dealing with potential life-saving interventions," said Kenneth Offit, chief of the center's clinical genetics service. "It's a tragedy that people are being scared off by this."

The Genetic Information Nondiscrimination Act, which passed the House of Representatives by a wide margin last year, would prohibit insurers from using genetic information to deny benefits or raise premiums for both group and individual policies. (It is already illegal to exclude individuals from a group plan because of their genetic profile.) The bill would also bar employers from collecting genetic information or using it to make decisions about hiring, firing or compensation. But it has yet to reach the Senate floor.

Meanwhile, a $300 genetic test for prostate cancer risk announced last month immediately drew callers to a public radio station in Washington, that was discussing the test, voicing fears of insurance discrimination. Karim Kader, who made the test possible with his discovery that men who carry certain DNA variants are four to five times likelier to develop prostate cancer, assured one caller that the test would be "very private."

For some, that is not good enough.

Linda Vahdat, director of the breast cancer research program at New York-Presbyterian Hospital/Weill Cornell Medical Center, estimates that 20 percent of her patients choose to pay for the DNA test for inherited breast cancer risk with cash, to avoid submitting insurance claims.

And last year, hundreds of customers paid the startup company DNA Direct for tests that range in cost from $175 to $3,456 to ensure that no third party, not even a doctor, had access to their results. Mary, a freelance camera assistant in New York, for instance, sent a swab of her cheek cells to DNA Direct to find out if her extreme fatigue was caused by hemochromatosis, a genetic condition in which the body retains too much iron.