Passing the Test


One of my worst recurring nightmares is having to take a final exam for a class I never bothered to attend. You can’t avoid a real final exam, but other tests are completely voluntary. One of my happiest tests was the little “plus” sign telling Jay and me that we were going to have a baby. You’ve probably seen giant billboards enticing suspicious men to take paternity tests. One step up from that is the online site, 23andMe, which offers the “DNA test that’s right for you.” You can have your DNA evaluated for dozens of diseases, ranging from asthma to ulcerative colitis. 23andMe also offers to perform an ancestry analysis, finding your nearest relatives, as well as your ancestral lineages and your global origins.

Before you take this kind of test, there is some important information for you to consider.

First, what can a DNA test reveal? Many human diseases have a genetic link, and the test can show these genetic abnormalities. It can reveal whether a person is a carrier of the disease, such as cystic fibrosis, but will not get it herself. She can also learn if she is at risk for getting a disease, not just passing it on.

However, there are a number of things that a genetic test cannot tell us.

One limitation is linked to penetrance. Penetrance is the probability that a particular gene will lead to a particular disease, such as colon cancer or breast cancer. Is it 80%? Or just 15%? Even if the penetrance is 100%, there is no way to predict how serious the disease will be. Did you know that some people who have the cystic fibrosis gene have such a mild case, they don’t even realize they have it.? Someone else with an identical DNA profile can have a debilitating experience.

Even if there is a high probability, there is still the unknown question about age of onset: just when might the disease manifest? If it’s not likely to show up until you’re 70 or 80, is that risk any different than any of the other ordeals of an average lifespan?

Another consideration is treatability. A serious genetic disease such as pancreatic cancer might have a low survival rate. But in twenty years, there may be cures or more effective treatments. Survival rates could go up dramatically.

Even if you have a genetic disposition for a disease, you might not get it at all. And other diseases, such as breast cancer, can wound women who do not have the breast cancer gene. Lifestyle decisions and environmental factors, such as sunlight and chemicals, also affect whether we’ll get a disease.

So, now that you have a small picture of the what, let me ask you why would anyone want this test? It could be idle curiosity. Or, we might want to protect ourselves from a serious illness. Is this the kind of knowledge that is not for our good? Could it genuinely harm us? Will it cause unnecessary anxiety, or create false assurance? As Christians, we know that it isn’t good for us to desire every kind of knowledge. We are called to discern both the content and our motivation. Our better wisdom may tell us, “no, thanks.”

Before taking this kind of test, let’s make sure we “go to class” and “do our homework.” Think about it.


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