As genetic testing edges its way into the mainstream, more and more consumers will get results — and be left to wonder what they mean and what to do with them. Americans need help navigating and understanding everything from so-called recreational genetic tests to potentially scary medical tests, so we’ve created this guide.
Medical Tests for Susceptibility to Disease
There are many different types of clinical genetic tests, so we’ll take them one by one, starting with one of the most common — susceptibility tests. These tests gauge your inherited likelihood to develop a particular disease or condition, and the BRCA1 and BRCA2 tests for breast cancer susceptibility are probably the best known. Such tests cannot tell if you have cancer; instead, they try to predict whether you’re at increased risk of one day getting it (or another disease). Susceptibility tests are really, really important. People who know they’re at higher risk can often adopt more rigorous screening regimens to enable early detection and improved outcomes for themselves. However, too many people struggle with the results, which are known as “probabilistic.” Let’s say there’s a disease for which average population risk is 5 percent. I take a test and find out that my risk is twice as high as average. That sounds terrifying, right? But it really just means that instead of a lifetime risk of 5 percent, I have a lifetime risk of 10 percent. That probably isn’t a cause for alarm.
The area where we see the biggest medical impact from susceptibility tests comes in cases where there are options for prophylactic treatment or surgery to reduce risk. There’s no better example than BRCA1-positive patients who choose to get a preventive mastectomy or hysterectomy before the onset of cancer. I applaud women who make these difficult decisions to avoid a possible prolonged battle with cancer. But if you’re someone who is considering undergoing one of these radical procedures, it’s critical that you start by getting a second genetic test. Technology is constantly evolving, and our ability to read DNA accurately isn’t as good as it should be. If a genetic variant is going to drive your decision to have surgery or any other medical treatment, take the extra time to make sure you really do have that variant.
Another form of susceptibility testing is carrier screening, which uses genetics to predict your chances of passing a disease-causing variant along to a child. When both biological parents get screening done, experts can establish with very high confidence the likelihood that a child will become a carrier of or even develop a specific disease. (For many diseases or disorders, a child must inherit specific mutations from its mother and father.) Like susceptibility testing, carrier screening does not guarantee that a disease will take root; it simply offers a good indication of the chances that something will happen. For people in populations where there is high risk of passing on a certain disease, such as Ashkenazi Jews, carrier screening can play an essential role in family planning.
Amniocentesis and other conventional prenatal tests have largely fallen by the wayside as genetic testing offers a simpler, safer, and less invasive means of determining the health of a fetus. Since these tests target very specific conditions — like situations in which there’s a whole extra chromosome present — their accuracy is quite good. Typically, doctors will follow up with a second type of test if genetic results come back positive, to confirm that the findings are correct. One oddball thing about prenatal testing that consumers should know: Because it begins with a maternal blood sample, it can also reveal health anomalies for the mother. A number of pregnant women have been diagnosed with cancer as a result of prenatal genetic testing.
Medical Tests for Active Disease
There are also genetic tests to diagnose patients or to learn more about an ongoing disease. Exome sequencing and whole genome sequencing are two frequently used methods. For example, clinicians have made tremendous strides in diagnosing people with rare diseases using genetic testing. This is also widely used for patients with cancer; testing can reveal mutations to guide treatment selection. These tests are carefully validated in clinical labs, but your healthcare team should always perform a follow-up test to ensure accuracy. If you’re not sure whether this was done, ask whether results were confirmed with “orthogonal technology” to verify that results have been double-checked.
Non-Medical Health Tests
Today, you can get health-related results without seeing a doctor. Services such as 23andMe provide direct-to-consumer testing; with FDA approval, they are able to return results that have medical implications. These tests should be considered interesting but not necessarily authoritative. 23andMe can screen for some breast cancer susceptibility genes, for instance, but not nearly as many as a typical clinical lab would use to determine your risk. These services can point you in a new direction, possibly helping to explain health-related questions you’ve had, but at this time it is not wise to make healthcare decisions based solely on these results.
Genome sequencing is another test available to consumers, but for most people the only reason to have this done outside of a medical setting is because you like to be an early adopter. Each person’s genome may return millions of variants, most of which are not yet understood or associated with any function or trait — and even those with some research attached to them do not have the level of evidence required to say anything with certainty. I had my genome sequenced and learned very little from it — that’s just a reflection of how early we are in the genomic era.
This type of genetic test has gained traction the fastest, with providers such as Ancestry and 23andMe offering users a peek into their roots with a simple saliva sample. These tests work by comparing your DNA to DNA that’s already been analyzed from a broad range of populations, and accuracy is highest for populations that have been very well sampled. If your ancestors came from a rarer population or a group that hasn’t been analyzed as much, you can expect your results to be less accurate. Overall, ancestry testing falls into the recreational bucket: it’s fun, it’s mostly harmless, and it shouldn’t affect any major life choices. Results are improving all the time, but you should always assume there’s a margin of error in the report you receive.
There are many genetic tests that claim to offer scientific insight into what type of diet is best for your body (with many users hoping they’ll be the lucky ones who are biologically hardwired to gorge on carbs). While some tests are better than others, scientists agree that there just hasn’t been enough research to precisely link your genetic data to an ideal type of diet. Save your money. And if you’ve already shelled out for one of these tests, you can safely assume that the information you received is not supported by enough research to be definitive.
Genetic tests purporting to reveal which type of exercise is best for you, or which type of sport you’ll succeed in, were among the first to launch when consumer genetics emerged as a nascent market. There are some research studies underlying these tests, but in general, scientists believe there are many factors that have an impact on sports and exercise aptitude; betting the ranch on genetics doesn’t make sense in this case.
Believe it or not, there are companies that claim to use genetic data to match you into a successful relationship. Let’s not mince words: Romance is not encoded in your DNA. This is snake oil in its purest form.