An Op-Ed from a staff member at the Center for Individualized Medicine, Noralane Lindor, M.D.
“I’d like to know what diseases I have high risk for. Why can the direct-to-consumer companies give risk for diseases like coronary artery disease and Alzheimer’s, but my family doctor can’t?”
A recent report in the New York Times featured a woman who submitted her DNA to three direct-to-consumer companies: 23andMe, Genetic Testing Laboratories (GTL), and Pathway Genomics. Comparing her resulting health risk reports from the three, she found multiple, major differences. For example, 23andMe said her most elevated risks were for psoriasis and rheumatoid arthritis, but GTL said risks for these diseases were in the lowest range.
This type of report is not surprising. The truth is that our understanding of DNA changes detected by direct-to-consumer tests cannot yet be used to give a risk prediction for common diseases. That is why your family doctor is not offering this testing to you—and why the FDA recently sent a warning to 23andMe to stop sending out unsubstantiated health risk figures.
Why? All genetic testing is not all equal.
First, let’s not throw the baby out with the bath water. Many disorders are caused by a single gene mutation. There are several thousand uncommon diseases for which genetic testing can be both predictive and diagnostic with excellent science to back it up. Genetic testing for these disorders typically involves analyzing the entire sequence of the causative gene. Examples are the BRCA1 mutation causing hereditary breast/ovarian cancer syndrome or FBN1 mutations causing Marfan syndrome. This type of genetic testing is of high value.
However, when you are talking about more common diseases (like obesity, hypertension, and osteoporosis), these conditions are not generally caused by a mutation in one single gene—they are complex multifactorial conditions. They are due to complex interactions between a person’s environmental factors (diet, exercise, etc.) and multiple types of genetic input. Figuring out the exact interactions that cause these common diseases in any one individual has remained elusive so far!
Contrary to popular belief, the direct-to-consumer tests are not reading your entire genetic code. They do an extremely limited reading of a few genes (which have been linked to the disease in various studies) from each page of your genetic code, yet they claim to be able to predict disease risk. There is much missing information!
Further, even if they were sequencing all the genes already associated with a common disease that still may not account for most of what causes it —we still don’t know enough about how the complex interactions impact us. Solving this will require many more large studies to figure out how to legitimately combine these results into a meaningful risk number.
Genetic risk profiling for common complex diseases like coronary artery disease, Alzheimer’s and breast cancer is simply not useful...for now.