Last week, the US Senate passed a bill that would bar employers and insurance providers from considering the results of a person's genetic tests when making hiring or coverage decisions. The House has passed a similar bill and the Bush administration has indicated it would sign legislation of this sort. In the wake of the bill's passage, however, a number of people have questioned why it shouldn't be an employer's or insurer's right to make decisions based on genetics. As a matter of policy, these questions were answered a decade ago, and the intervening progress in human genetics has only reinforced some of the reasoning of the initial decision.

A history of favoring genetic agnosticism

Health policy issues were considered well in advance of the completion of the human genome, as the project's funding included money for an Ethical, Legal and Social Implications Working Group. That group made its first recommendations in 1993, and has continued to advance a similar set of arguments.

Even in 1993, the Working Group recognized a "health care coverage crisis," and it suggested that genetic testing could make this situation worse. As genetic studies have focused on identifying disease loci, biologists would create an ever-expanding set of negative risk factors that would allow insurers to deny coverage to an ever-larger population.

The rational consumer response to a situation where most tests would have negative implications for coverage would simply be to forgo the tests and remain insured, although ignorant of potential risks. The working group felt this situation would not benefit the US public and would squander the promise of the Human Genome Project. As such, its policy has been to favor legislation such as the bill just passed.

Progress in genetics reveals limits of genetic tests

The staggering progress up to and beyond the completion of the human genome might suggest that the sophisticated tests now available will allow employers and insurers to make rational and fine-grained assessments of genetic risks. A careful examination of the actual record, however, reveals that any genetic tests are subject to enough caveats that their value in making rational decisions is extremely limited.

To begin with, it's worth considering what it would take to have a complete picture of a person's genetic risks. The human genome contains over three billion individual DNA bases. About 5 percent of these bases are conserved in the genomes of our fellow mammals, suggesting that they are functionally significant. That means there are over 150 million locations in the genome where genetic differences may have significance to human health. In addition, as much as 17 percent of the human genome may have copy number variations, being duplicated in some individuals and reduced in others. It's clear that health care will be fundamentally different by the time we have anything approaching a complete grip on human genetic risk.

But there are genetic variants that cause well-defined risks, such as the ones that increase the probability of developing Type-II diabetes. It's easy to believe that a test for a variation of this sort would allow rational decision making. But no gene ever operates in a vacuum; the probability that Type-II diabetes will develop is also influenced by the remainder of a person's genetic legacy which, as discussed above, we won't have a clear picture of any time soon.

Environmental factors also play a key role; it's likely that a careful diet could suppress the risk—these tests would ideally identify those who need to change their diets—but neither employers or insurers are able to track diet in the same way they can track genetics.

It's worth commenting on the science behind the tests as well. For most scientific research, the standard of evidence is 95 percent confidence, meaning that there is still a five percent chance that the appearance of genetic associations are the product of random events. Given the number of papers published on human genetics each year, this suggests that at least some of the results are the product of honest error; the potential for dishonest error in the competitive field of human genetics may also be significant. Environment may play into the studies themselves, as they are often performed in a population from a single country, such as Iceland or Japan, which has a very different set of habits from the US. The net result is that a genetic risk factor may not actually create any risk in the US population.

The final factor to consider is the nature of the tests themselves. Most genetic association studies and many current genetic testing protocols rely on DNA chips that examine tens of thousands of individual sequence differences simultaneously. Carefully optimized conditions mean that the chances of error at any single sequence is low. But, when multiplied by the number of sequences examined, the probabilities that an error occurs are significant. This affects both the initial identification of a risk factor and any subsequent genetic testing. Expand the testing to a broad population, and the chances are good that something will inevitably go wrong.

Depersonalized medicine

Combined, the complexities and potential for error limit the informational value of most genetic tests. Any proper use of this information will require both care in interpreting cutting edge scientific information and care in performing the genetic tests, including retesting for confirmation. Are employers or insurance companies up for the expense involved in the level of care necessary to make personalized genetic decisions? This seems improbable. Even if they do, the picture generated by our current level of genetic knowledge would be, at best, incomplete.

Worse yet, the very concept threatens to undermine another of the greatest potential benefits of the genome: personalized medicine. The goal of personalized medicine is to tailor treatments to a the unique genetic defects that have helped foster a disease, be it diabetes or cancer. But, if insurers can deny coverage based on those same genetic traits, the patient may never see the treatment.

There are a whole host of other reasons to be leery of decisions based on genetic factors, including the fact that some factors are more prevalent within some ethnic groups, raising the specter that genetics may serve as a rationale for some forms of racism. But the most powerful argument is that any genetic policies will be extremely difficult to do well and, even if done properly, could still get things wrong. Combine that with the potential for genetic-based decision making to inhibit the use of our new-found knowledge, and there is a potential for harm that could arise from policies such as the ones that may soon be outlawed.