Doc’s Corner

The Truth About Mail-In DNA Tests


Lots of Info and Some Confusion

If you’re curious about where your ancestors came from or concerned about diseases you might be likely to get, mail-in DNA tests make it easy to get some answers. Dozens of companies offer them, and they can be done with a sample of your saliva or a swab of your cheek. The catch is, you may learn “facts” about yourself that aren’t quite factual.

Myth: Predict Chances of Disease

These tests look for information in your genes that shows you might be more likely to get a specific disease, such as Alzheimer’s or cancer. But they can’t tell if you’ll end up getting it. They can’t even really tell you your chances of it. Other things, like your lifestyle or habits, affect your risk of getting diseases, too. I like to think of the DNA risk as the “loaded gun” and life style as the “trigger”. Aside from a very small number of dominantly inherited diseases, our inherited genetics account for perhaps about 30% of adult health risks, while lifestyle influences about 70%. There are unknown “chance” factors that affect our epigenetic changes as well that are very difficult to quantify or predict.

Myth: Map Your Family Tree

Numerous companies now provide information relating to ancestral heritage, such as 23 and ME and  Each company has its own database of samples from people who live in different areas of the world, and they match yours against the others in their database. So your results won’t include everyone who’s been tested — they’ll only include people who’ve been tested by the company you choose. The testing may accurately reflect the DNA but the conclusions drawn from the data may result in flawed results based on limited data base information.

Myth: Same Info for Siblings

Everyone gets 50% of their DNA from each parent, but what’s in each half can be different. So it’s totally possible that you got more of your mom’s European DNA and your sister got more of her Asian DNA. Add your dad to the mix, and things get scrambled further. Just as siblings don’t always look alike, their DNA might not look alike, either. When the DNA result is applied to an incomplete database, the conclusions may be inaccurate.

Myth: Nutritional Needs

Some testing companies offer personalized advice on dietary supplements based on your test results. Some even try to sell them to you. But no studies show that genetic tests can give you useful information about those or dietary choices.  The FDA has not certified the accuracy of any DNA testing that provides reliable information related to specific beneficial dietary intake including supplements. One should have a high degree of suspicion when a company that promotes DNA testing also sells the products it recommends.

Myth: Effects of Toxins

Not everyone who smokes gets cancer, and some DNA testing companies suggest that the reason for that is in your genes. It may be, at least in part, but there’s no strong science that proves genetic tests can tell you how well your body handles certain things in the environment. Rather than trying to assign blame, the health promoting approach is to “control the controllables”.

Myth: Insurance Rates

Laws are in place to protect you from being denied health insurance or charged more for it. But those laws don’t apply to life insurance, disability insurance, or long-term care insurance. That means it’s possible your genetic test results could be used by the companies that sell these types of insurancepolicies.

Myth: Government Regulations

Most of these tests are made privately and can be sold to you without any proof that they work as advertised. That may soon change, though. The FDA is coming up with guidelines for genetic tests.

Myth: All Tests Are the Same

While no testing company can guarantee that the information it gives you is 100% accurate, some are better than others. If you decide to try at-home DNA testing, look for one that meets the U.S. standards called Clinical Laboratory Improvement Amendments (CLIA), and check to see if the tests have been approved by the FDA.

Myth: Personal Info

Read the fine print. Most companies make an effort to keep personal data “private,” but that can mean different things. Make sure you understand what data they’re collecting and who will see it.

Myth: Harmless Fun

At-home DNA tests can be entertaining, even if they’re not always accurate. But they can cause stress, too. Sometimes genetic tests reveal not-so-happy surprises, like a family member not being related to you or the possibility that you’ll get a certain condition. Results from genetic testing, both normal and abnormal, may have major implications for management. As an example, patients might make treatment decisions regarding prophylactic mastectomy, chemoprevention, or aggressive surveillance based on false-positive or false-negative BRCA1genotypes.You shouldconsider talking with a genetic counselor before deciding whether to get tested. And if you decide to test, a genetic counselor or experienced physician can help you understand the results and bring perspective before acting on the results.

Generalizability and Summary: In most cases, data about genetic risk has been obtained from testing individuals with a known personal or family history of disease. Data from testing a healthy population has not yet been obtained for most conditions, and it has not been demonstrated that risk is similar when a variant is identified in an individual with a negative personal and family history of disease. The accuracy of identifying mutations or disease-associated single nucleotide polymorphisms (SNPs) is one concern; the accuracy of using the resulting information to predict the risk of disease is a separate concern of equal or greater importance. At-home DNA testing is now widely available. Use caution prior to acting on the results.

Comments and questions are welcome at

Paul R. Block, MD, FACP, FCCP

Ref: WebMD,com, Up to Date,,

End of Illness, David Agus, MD

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