Your health is determined by a lot of factors, and your DNA is a big one. But the information you can learn from your DNA—such as your risk for certain diseases— isn’t available unless you undergo genetic testing, a type of medical test that identifies mutations in genes, chromosomes or proteins.
While genetic testing can be a beneficial tool in decoding your health, the results you get from commercial genetic testing labs such as Helix and 23andMe aren’t likely to be accurate, says James Evans, MD, PhD, who recently retired from his role as Bryson Distinguished Professor of Genetics and Medicine and director of adult and cancer clinical genetics services at UNC Medical Center.
We asked him some common questions about genetic testing.
What can genetic testing tell us about our health?
In the proper context—which means it’s the right situation for testing, it’s done properly, and it’s interpreted correctly—genetic testing can be valuable in identifying your risk for various conditions. For example, if you’re from a family with a strong history of breast cancer, it can be very helpful in evaluating your risk and figuring out what you can do to spare you from problems in the future.
When should someone get genetic testing?
The kind of patients I saw who needed genetic testing were people who either had a condition that was enigmatic, where it hadn’t been able to be diagnosed, or people for whom it was clear that something genetic was going on because of family history. For example, if there is a family history of colon cancer, people might want to consider genetic testing to see if their risk of getting the disease is substantially elevated. Those are the kinds of situations where we routinely pursue genetic testing.
But what I would emphasize is that, like any medical test, it’s a mistake to have testing you don’t need. No test is 100 percent accurate, and the chance of being misled, getting false results or results that shouldn’t be acted upon is much higher when you have a test that doesn’t make sense in your situation. That’s the reason no one in medicine recommends, say, whole-body CT scans or MRIs for the general population: There’s a better chance you’ll find something false that will lead to down-the-stream testing (which can be risky, harmful and costly) versus getting helpful information. The same thing goes with genetic tests. First you should figure out if the test makes sense to perform; if so, it can be a valuable adjunct to the rest of your medical care.
Do commercial genetic testing services such as 23andMe and Helix work?
The tests done by those direct-to-consumer labs are usually not the right tests. Most of the testing done by these groups is what’s called genotyping, where you’re only looking at a small subset of variation in selected genes. Therefore, the testing is likely to be horribly incomplete. For example, one company, 23andMe, was recently approved by the FDA to look at three specific mutations in the BRCA1 and BRCA2 genes that can increase a woman’s risk of breast and ovarian cancer. The problem is, anybody who needs that test shouldn’t have just those three mutations looked at. Moreover, while the BRCA genes are the ones most commonly associated with a high genetic risk of breast cancer, a host of other, more rare mutations in other genes can confer such elevated risk, too. So, these commercial testing options are unbelievably incomplete and will leave people thinking that they are off the hook if they test negative, but in reality, they didn’t even have the right test and may actually be at high risk.
Additionally, these companies typically test what are called SNPs [pronounced like “snips”], or single-nucleotide polymorphisms, which are variations at specific sites of the genome. What they try to tell you is that those SNPs put you at higher risk for common diseases, like heart disease, cancer or diabetes. The truth is, they’re just not meaningfully relevant to your health. In studies of large numbers of people you may be able to show a statistical correlation between a SNP and a disease, but it essentially means nothing for your health. Your risk of common disease is relatively high anyway—that’s why it’s called a common disease—so parsing whether you’re at slightly more or less risk than the average person is meaningless.
More to the point, those tests often aren’t even accurate. You can take the same blood sample and send it to three different commercial labs, and they will come up with diametrically opposed results. One lab will say you’re at high risk, one at low risk and one at normal risk for the same sample. It’s not necessarily that one lab got it “right” and the others got it “wrong” but rather that we simply don’t know how to interpret these kinds of SNP-based genotyping tests. Nobody does. It’s really a truth-in-advertising issue. So, the results you’re getting are at worst incomplete, and at best incorrect information.
A medical test has to be interpreted in context of your medical history, your family history, your life. So, to do a medical test in the absence of that, one with conceivable medical implications, doesn’t make sense, isn’t useful and is potentially harmful.
What is the appropriate way to get genetic testing?
Again, a genetic test is a medical test and should be treated as such. That means you should go through a hospital or doctor to get the test done for accurate results and proper interpretation. If you go to a certified genetic counselor or a physician like me who specializes in genetics, we can say whether it makes sense to go through that process. From there, if such a test is indicated, we’ll take a sample of blood, saliva, amniotic fluid or other tissue and interpret the results based on the context of your life, which those commercial tests don’t do.
What kind of information can someone get from a genetic test that has been appropriately interpreted?
The results can show a variety of things. For example, it might show that you have a certain disease that might explain previously unexplained symptoms, and now that we have this diagnosis, you have to be aware of X, Y and Z. Or it might tell you that you are carrying a gene that puts you at high risk of breast or ovarian cancer, so you need to consider doing certain preventive things, and your daughters and sisters should also consider testing because they might be at risk, too.
Will there be increasing uses for genetic testing in the future?
As we learn more about genetics and disease, and as we can do more about those genetic risks, genetic testing will likely expand. I think that one realm that society is going to have to come to grips with is how far are we going to go in testing and potentially intervening in embryos by things such as “gene editing.” Such uses present serious considerations, because if you alter an embryo’s genes you’ve altered all of that individual’s descendants as well … and sometimes in medicine, as we all know, things go wrong. Thus we’re reaching the point where we could do both good and harm to untold generations. Those are the kinds of things that society will have to grapple with as technology continues to evolve.