By Dr. Lynn Webster, PNN Columnist

Three years ago, I gave my family members DNA kits as Christmas gifts. I thought the genetic health aspects of the test would be an entertaining exercise -- a bit like visiting a psychic who would read tarot cards to predict the future. I didn’t think of it as a serious medical test, and I made sure my family understood that.

These kits have become very popular. More than 26 million people have taken an at-home genetics test, hoping to learn more about their ancestral background, along with their risks of developing certain diseases. But the tests may not live up to either of those expectations.

The U.S. Government Accountability Office (GAO) sent a report to Congress in 2010 alleging that some DNA testing companies used deceptive marketing and other questionable practices. 

The GAO stated that results from DNA tests were “misleading and of little or no practical use.” Their investigation also uncovered the fact that different DNA testing companies provided different results from the same sample. 

Not only were the test results dubious, but the companies made some deceptive claims. One company alleged the results from their testing could help cure diseases. Another claimed the data could predict at which sports a child would excel.

Admittedly, the accuracy of the tests has improved since 2010, but the tests still are, at best, imperfect.

Our genome (the whole of our hereditary information, encoded in our DNA) contains about three billion genes. Of those, only about 20,000 are responsible for disease. But we are more than our genes. Whether or not we will get most diseases depends on a combination of our genes and environment. This interaction of environment and genes is what we call a phenotype.

Of course, there are genetic mutations that are responsible for specific diseases. Single-gene mutations are responsible for about 10,000 diseases, the majority of which are considered rare. Some of the more common single-gene disorders include sickle cell anemia, cystic fibrosis, phenylketonuria, and Huntington's disease.

However, there is no guarantee that direct-to-consumer DNA kits are capable of detecting all common single genetic mutations. Moreover, the absence of a reported mutation from these kits does not mean the mutation does not exist.

Testing may uncover some benign and interesting traits, though. For example, some genetic kits (but not all) can tell you if you have a gene associated with how your earlobes are shaped, whether your urine has an offensive odor after you eat asparagus, or if you are inclined to dislike cilantro.

The accuracy of the health-related portion of the tests is improving. It is now possible to test for genes that predict a person's risk for certain types of breast and prostate cancers. However, placing too much weight on the results of those tests can be dangerous. For example, the tests do not screen for all types of breast cancer, which can lead consumers to falsely conclude their risk of all breast cancers is low if their test results do not indicate a gene mutation associated with breast cancer.

At best, the types of DNA tests that provide information on single-mutation diseases should be accompanied by appropriate genetic counseling. Since most diseases are based on multiple genes and environment, a genetics counselor can help put the test results into perspective.

Deciding how to use the information may be more important than knowing the results of the test. In medicine, we never order a test unless it will help us provide better care for our patient. This may be an important principle to apply here as well.

Privacy Is a Big Concern

We should also be very concerned about how our DNA data will be stored and used. The testing companies' DNA databases can be hacked by people with nefarious motives, or shared with insurance companies or law enforcement. Laws protecting consumers are evolving, but clearly, at-home DNA tests expose consumers to unknown and, perhaps, unintended consequences.

DNA tests were first pitched to consumers as a way in which they could learn about their ancestry. However, the reference data sets were largely European and less accurate in showing lineages in other areas of the world. If your roots were Asian or African, the reports were less likely to accurately reflect where your ancestors lived.

Over time, the data sets have improved and expanded, so consumers with non-European ancestry may get more accurate information about their heritages now than they would have previously. That trend will likely continue.

Whether DNA kits are mostly a gimmick, I cannot say. But it is important to recognize their limitations in providing trustworthy information about our health or ancestry. Certainly, we should not base health decisions on their results, and I would think twice about paying for the privilege of delivering my DNA profile to a for-profit company.

Maybe this year I’ll just give everyone tarot decks.

Lynn R. Webster, MD, is a vice president of scientific affairs for PRA Health Sciences and consults with the pharmaceutical industry. He is the author of the award-winning book, “The Painful Truth,” and co-producer of the documentary, “It Hurts Until You Die.”

You can find Lynn on Twitter: @LynnRWebsterMD.

Opinions expressed here are those of the author alone and do not reflect the views or policy of PRA Health Sciences or Pain News Network.