Breakthroughs in genetic testing offer insight into whether individuals will suffer from a growing number of diseases. These tests can tell us whether a fetus in the womb carries disease-causing genetic defects, such as cystic fibrosis. Should parents use such a test to decide on abortion? Tests can be used to confirm a suspected diagnosis of genetically-related disease such as Alzheimer's. Should it be used to predict whether relatives of a person with the disease is also predisposed to it? Tests can also predict whether an individual will develop a disease later in life, such as Huntington's.Should it be available to young people, even children, when the onset of the disease will only occur much later in life? And because of the complex relationship among genes and with the environment, even when a test predicts a genetic disease there is no way to predict how serious its effects will be.

What's your opinion?

"Through the Looking Glass: Making Sense of Genetic Tests" is the fourth and final part of a series on genetics issues. Part 3: Nature's Genes, but Whose Profits, Whose Labor? Part 2:Genetic Testing and Insurance Part 1:Genetic Testing: The Future is Here

One answer is that good decisions start with good information. A pitfall of the uncertainty of genetic information is that it could lead patients to make decisions they will come to regret. A blurred vision of the future can sometimes be worse than being blind to the possibilities of what our health will hold, since it can lead to wrong conclusions. Should a woman who tests positive for BRCA-1/2--the so-called breast cancer gene--have both her breasts removed to prevent the possibility of developing breast cancer, even though her "true" risk of cancer may range from a 20 percent increase over that of a "normal" woman to near certainty? One answer is that medical geneticists and genetic counselors must be available both to advise patients and to educate other health professionals about the value and interpretation of genetic tests.

A very troubling development is the commercial availability of newly-developed genetic tests, which -- without any requirement for expert counseling -- can be ordered by sending a blood sample to a lab. There is even an expectation that labs may market their services directly to the public. Access to health information can be positive, but given the complexity and seriousness of genetic test results, it is far too easy to make bad decisions based on incomplete, inaccurate or misunderstood information when results are not interpreted by professionals.

With all the high-technology precision being poured into the discovery of genetic links to disease, it is ironic that even the best genetic information is far from perfect. But to expect more from genetic testing is to hold genetics to a higher standard than other areas of medicine. Certainty is not the currency by which medicine can or should be measured, but in the late 20th century we have come to expect unattainable and unreasonable levels of certainty in our medical care.

One of the benefits of genetic testing is that it will cause us to reevaluate the meaning of medical information for our lives. Rather than relying on the false objectivity of an isolated medical test, genetic testing will force us to realize the complex relationship between our bodies, our environment, our behavior, and our health.

We have the opportunity -- and more important, the responsibility -- to create an environment that will assure the appropriate and effective use of genetic testing. But it is an opportunity whose window is open for a limited time. Controlling access to some genetic testing and enforcing a requirement for expert counseling will go some way towards encouraging its responsible use.