If you're thinking of spitting into a tube for one of the genetic testing companies, such as 23andMe or Ancestry, Heather Zierhut (M.S. ’06, Ph.D. ’12), assistant professor in the College of Biological Sciences, has advice for you. A genetic counselor, Zierhut helps people understand the implications of the tests and how to choose the right one; she also researches their ethical and public health implications.

How accurate are these tests?

When it comes to reading the DNA letters, they are up to 99.9 percent accurate. That means if a testing company is looking at a million different letters—or parts of the code—they are going to be wrong at least 1,000 times. If that wrong spot is an important letter, that impact can be substantial. It’s possible to compare one test to another and see some differences. Most people don’t care when they’re talking about ancestry. But when they are digging deep into increased risk of disease, those differences are more significant. Anytime anybody finds something they are concerned about, they should have it repeated in a clinical lab and speak to a medical professional such as a genetic counselor.

If a test says you are predisposed to heart disease, does that mean you’ll get it?

Not necessarily. The ability to predict disease accurately is different than the accuracy of the test. If you look at heart disease and cancer, there are lots of different factors, including environmental, family history, and lifestyle factors. The test has the potential to help people understand very specific genetic information, but it does not give you the full story. 

Will a genetic test tell me the cities in which my ancestors were born?

At-home tests are getting better at specifically nailing down where in Western or Eastern Europe you are from, but in general you will get a broad area or region. As they add more people to the databases, they are able to do a better job of predicting. But one may say you are 20 percent German and another might say 12 percent because there are differences in how they may interpret the data. Certain ethnic backgrounds have more information and are therefore more accurate than others. 

What should a person look for when deciding which test to take?

If you are looking for a relative in the U.S., find one with a large database of customers from the U.S. If you are looking for where your Swiss and German relatives are, look for one with an international database. Go to the websites and see what their portals look like. Knowing what you’re looking for and what the testing results will look like is an important first step.

Is privacy a concern?

As with any data that is stored electronically and is accessible, there is the ability for hacking and breaches. Even more concerning is when you take that data and share it with third parties. When you sign up with some of these companies, you agree to allow data to be accessible by others and even sometimes included in anonymous public databases. Some use it for research and other purposes outside the original reason for the test.

Should people brace themselves for the revelation of family secrets?

You may not think you’ll find a DNA surprise, but they are more common than people think. I have had individuals find cousins they didn’t know existed. I have had people discover they aren’t genetically related to their fathers. They say, “My father put a test in, I gave him the test for Fathers’ Day, but we didn’t connect. What does that mean?” Another situation that’s becoming more common is when children conceived by IVF and sperm donation discover biological relatives; there are reports of 20 siblings being connected via one donor. It helps to bring people together who didn’t know they were relatives.