The double-edged helix: advances in genetic testing reveal yet another reason we need national health insurance.

A 20-year Veteran of the postal service loses his vision because of a genetic disorder known as Leber's Optic Atrophy. No longer able to work, he applies for and receives disability benefits. But upon a routine review, the supervising government agency cuts off his benefits: Though he had no symptoms when he started as a mailman and, in fact, did not even know of his condition until its onset, the agency says his genetic predisposition for the disease represents a pre-existing condition.

A health insurer denies coverage to a five-year-old boy with a genetic predisposition to heart disease but no symptoms whatsoever. Deducing his condition from the medicine his doctor prescribes to prevent the onset of disease, the insurer says his genetic code disqualifies him for insurance.

A three-year-old boy is diagnosed with MPS syndrome, a genetic disease that causes severe damage to bones, joints, and tissue. The family's private health insurer promptly informs the boy's parents that it is canceling the boy's policy. Diagnosed or not, it says, any genetic disease is pre-existing because the genetic cause has been with the boy since conception.

Welcome to the dark side of the genetic revolution. As with the other great advances in knowledge and technology--the invention of dynamite and the discovery of the atom, for instance--genetic research's enormous potential for good is shadowed by an equally immense potential for harm.

Genetic research is marching forward, uncovering the roots of more and more diseases, and inspiring hope that they may one day be curable. But at the same time, the extraordinary medical benefits are clouded by the fact that gene research now offers insurance companies new ways to trim their expenses by denying coverage to those most in need of insurance.

The promise and peril of the genetic revolution were never in sharper relief than this past summer, when scientists announced they had traced the root of colon cancer to a gene mutation found primarily in Jews of Eastern European descent. The medical implications, of course, are breathtaking Those who carry the gene mutation can get regular colonoscopies to detect the disease in its early, treatable stages. But the same information that may save lives may be used by insurance companies to raise premiums, deny applicants, or cancel coverage for those who carry the colon cancer gene.

The fact that the gene mutation for colon cancer occurs almost exclusively in Jews begs a haunting question: Could being Jewish soon be a handicap to finding good health insurance?

In many ways this is just a new revision of an old problem. Insurance companies have always looked for better ways to weed out those who may one day fall ill and, consequently, need expensive treatment. In the '70s, insurance companies raised rates on African-Americans because of the risk of sickle-cell anemia. At the outset of the AIDS epidemic, some health insurers refused coverage to people who lived in what were known to be gay neighborhoods.

Though the opportunities for genetic discrimination are now limited to those diseases known to be inherited, the chances for abuse will multiply along with our understanding of the science. Before long, scientists will uncover the genetic roots to more and more diseases, and it will be more possible than ever--for ourselves, our doctors, and our insurance companies--to predict who will come down with what illness.

This poses an extremely thorny public policy question: How do we pursue genetic information and the benefits for individual health while preventing its misuse? That is, how can we ensure that patients enjoy the full benefits of genetic research without fear that their DNA code may be used to deny them insurance?

We need an answer soon. Our understanding of DNA accelerates with every new discovery. But there is something darkly reassuring about its direction. Before long, we will all be uninsurable. Somewhere in our genetic makeup there will likely be some defect, some risk to turn an actuary's knees to jelly.

Therein lies reason to be optimistic. Because every American faces the same challenge--genetic diseases are not subject to geographical or economic distinctions--every American has an equal stake in finding a solution.

The country took a giant step toward meeting this challenge when President Clinton proposed legislation that would make it illegal for employers and health and life insurers to discriminate in any way on the grounds of genetic information. If the bill passes, insurers will not be able to raise rates or deny coverage to anyone on the basis of their genetic code, whether that information is determined from a DNA test or a family-history questionnaire. Nor would employers be able to fire or not hire a qualified employee because they fear picking up the tab for a genetic illness down the road. The legislation would eliminate the most blatant form of discrimination.

But it is not a final answer to the challenge posed by the genetic dawn, as the president himself has said. An insurance company does not need a DNA test to keep applicants with questionable genes off their rolls. If an insurer wanted to keep those with genetic predispositions for, say, hemophilia off their rolls, they might merely eliminate coverage for clinics that specialize in treating the disease. They could also place a $500-per-year cap on blood transfusion services. Someone who suspects that they or their children may develop hemophilia would naturally want to shop elsewhere.

Furthermore, insurers can treat people with genetic flaws differently without giving reasons why. A medical director of a large insurance company in Canada described how this might work for the Human Genome Project's Ethical, Legal, and Scientific Implications Task Force on Genetic Information and Insurance. As quoted in an article by Brandeis Professor Deborah A. Stone, the medical director said: "If a woman has a family history of breast cancer, I'll ignore the breast cancer. I won't rate her for the breast cancer, but I'll scrutinize her record extra carefully. I'll rate her for hypertension. I'll hope there is something else I can find in the record to rate her on. I'll tell her I rated her on hypertension. I won't tell her I rated her higher than someone else with the same hypertension."

As despicable as this sounds, it isn't difficult to understand where insurers are coming from. Health insurers, we must remember, are businesses. They exist to make money, not to care for us when we get sick. If they determine with more accuracy who is going to get sick and who will not, they make more money. To them, the genetic revolution is a dream come true, and one way or another, they will make it work for them.

The real difficulty, therefore, doesn't lie in the genetic information and who has access to it, but in the practice of underwriting itself--that is, in the right of insurance companies to deny someone coverage or set different rates for health reasons. After all, why is it unfair to deny health insurance because someone carries the breast cancer gene, but okay to deny coverage to someone who has chronic back problems because a drunk driver once crashed into her car? In either case, we penalize people--often with the gravest of consequences--for circumstances beyond their control.

So long as matters of life and death are left to the blind and often cruel logic of the marketplace, injustices will occur. Gene research only presents more opportunities, thus making it more common. As the research progresses, it becomes ever clearer that the country must ensure that every American has access to affordable health care coverage.

Right now, it is time for the nation and its political leaders to take a second look at national, universal health insurance so that no American will have to fear that his or her genes will be used against them.

Most politicians consider this suggestion the equivalent of asking Napoleon to take a second crack at Russia. Who can blame them? But they may want to consider a 1995 Harris poll that showed that 85 percent of Americans fear that they may one day be the victim of genetic discrimination. Last time I checked, that was enough to win any election.

Kathleen Kennedy Townsend is lieutenant governor of Maryland and sits on the advisory board of the University of Maryland's Institute of Human Virology.