By Natasha Persaud
Most of us are curious about our genes. Today you can find out exactly why your eyes are brown and why your hair is black. The explosion of genetic tests also has the potential to give you information about your risks for disease. While exciting and sometimes useful, the technology presents unique challenges for individuals and families. Here, James P. Evans, M.D., Ph.D., editor in chief of Genetics in Medicine and professor of genetics and medicine at the University of North Carolina at Chapel Hill, discusses the pros and cons of genetic testing.
What are genetic tests?
They are medical tests that inform you about your genetic makeup, including mutations in your genes. They’re useful for
- diagnosing many diseases
- identifying whether you’re at an increased risk for a particular disease
- You can find out whether a mutation you carry has been passed on to your child and possibly seek early medical treatment.
More than a thousand different genetic tests exist to test for a wide range of diseases and conditions. Typically, your doctor or a genetic specialist will order testing if he or she suspects you have a high risk for a specific disease such as breast cancer, cystic fibrosis or osteoarthritis. You might also seek genetic testing on your own to find out the likelihood you’ll develop or pass on a genetic condition.
While genetic testing is complex, the procedure itself is simple. Typically, only a blood sample or mouth swab or rinse is needed to gather a sample of your cells and DNA; there’s no special preparation. In the lab, a technician will closely examine the specific area of your genome—your genetic makeup—in question and look for errors that could contribute to your risk for a particular disease.
What can a genetic test tell me about my risk for disease?
At best, genetic tests give you probabilities about your risk for a particular disease; testing is by no means a perfect crystal ball. Some tests give you pretty clear results, while others describe only a modestly increased or decreased chance that you’ll develop the disease.
For example, if you’ve inherited a mutation for Huntington disease, a severe neurological condition, the odds are overwhelming that you will develop this disorder. Likewise, if you've inherited a mutation in your MEN2 gene (Multiple Endocrine Neoplasia Type 2), a cancer syndrome, the odds are extremely high that you will develop certain tumors.
A test for prostate cancer, on the other hand, may only tell a man that he has a slightly increased chance of developing the cancer. Those results are not sufficient to make a firm prediction that he will—or won’t—develop the cancer.
Many medical professionals question how useful widespread testing for conditions like prostate cancer is, given that the genetic test can’t predict whether a person will or won’t develop the disease.
For most diseases, there are multiple factors that contribute to their occurrence, including genetics, the environment and chance. Your genes rarely tell the whole story.
How valuable are genetic test results?
A genetic test is the most valuable when you can do something with the results. For example, a woman who finds out that she has a BRCA1 mutation that places her at a high risk of breast cancer may have preventive mastectomies, therapy or may choose to pursue more frequent screenings and testing in hopes of catching cancer at an earlier stage, when there are more options for successful treatment. If the woman informs her siblings and children, she gives them the opportunity to consult their doctors for testing and preventive care.
It makes sense to do certain types of genetic testing. For example, I saw a patient recently with a history of heart rhythm abnormalities that appeared to be caused by a mutation in a specific gene. In such cases, testing can fill a vital role and help guide treatment.
In my opinion, genetic testing for Alzheimer’s disease is less valuable, since no therapies currently exist to lower the risk for the disease. A person who finds out that she has an increased chance of developing Alzheimer’s disease by age 70 may simply end up feeling anxious and overwhelmed, with no good options for prevention.
For these reasons, I urge patients to see a genetic counselor or geneticist before having testing, to determine whether genetic testing is appropriate and what type would give useful information. A genetic counselor will not make decisions for you, but he or she can help you understand the benefits and risks of having and sharing that information.
What are some thorny issues that genetic testing raises?
Your genome is a funny thing: On one hand, it’s highly private, but, on the other hand, you share parts of your genome with your siblings and children.
If you do decide to have a genetic test, you may be deriving information that has an impact on others; but some of your family members may not want to know the results because of what it might mean for them. It’s a sensitive issue.
Other concerns center on the possibilities for genetic discrimination with employment and insurance. The Genetic Information Nondiscrimination Act, which was signed into U.S. law in April 2008, lessens some of those concerns by making it illegal to base decisions about employment and health insurance on genetic information. However, patients still have significant concerns when it comes to other types of insurance. An individual who finds out he is at increased risk for a variety of diseases may find it more difficult to get long-term care insurance, disability or life insurance. These are some of the issues to consider before launching into genetic testing.
What help can a genetic counselor provide?
Since genetic testing is filled with uncertainties, the genetic counselor is a critical hub in this whole process. He or she has a graduate degree in both medical genetics and counseling and is trained to educate and support patients with regard to decisions about genetic testing. The genetic counselor will ask extensive questions about your family medical history; review lab tests and reports from your doctors; educate you about inheritance, testing, prevention and resources; and help you think through your options in all their complexity.
The genetic counselor may be one part of a genetics team that also includes a geneticist, a medical doctor specializing in diagnosing and treating genetic conditions; and a Ph.D. geneticist, who has expertise in the laboratory study of genetic conditions.
In addition, oncologists, cardiologists and other physicians are increasingly requesting genetic testing to find out whether a patient has developed, say, cancer or a heart abnormality as a result of a genetic predisposition.
Genetic knowledge is not something many traditional medical practitioners feel comfortable with, so genetic counselors can also play a valuable role in educating physicians. It’s an exciting area of growth: Genetic counselors can help doctors and patients benefit from scientific advances in genetics.
If you need help locating a genetic counselor, visit the National Society of Genetic Counselors.
How accurate are at-home tests?
That depends entirely on the lab doing the test. The Centers for Medicare and Medicaid Services oversee laboratories and make sure they’re in compliance with the clinical laboratory improvement amendments.
It is important that testing be done in an accredited laboratory. However, even if the laboratory performing the testing is a state-of-the-art facility, I would generally recommend a person see a genetic counselor first, since the implication and the interpretation of genetic testing can be complex and nuanced.
What about tests that analyze your entire genome?
A few companies now offer to analyze your entire genome and inform you of your risk for a whole slew of diseases. I don’t think it’s very valuable at this point, since the results are at best probabilistic and it’s not at all clear what patients should do with that information. Finding out that your risk for Crohn’s disease, for example, is 1 in 650 instead of 1 in 1,000 is not very useful. Technology has allowed us to gather more information than we know what to do with. I believe in individuals getting information about themselves, but I think you need a knowledgeable guide, such as a genetic counselor, to help you understand all of it. Such testing is fun, but it can have its downsides.
Is genetic testing covered by insurance?
Yes, most genetic testing that is recommended by a physician or genetic counselor is covered by insurance.