Science has advanced the development of quick and inexpensive genetic tests, making these more accessible to consumers wanting detailed information about their ancestry and curious about their risk for certain diseases. As a board-certified genetic counselor who provides cancer risk assessment and genetic counseling for patients and their families,
Lisa Madlensky, PhD, says wanting to engage with one’s own genetic data to benefit personal health is important.
However, as director of the Family Cancer Genetics Program at Moores Cancer Center at UC San Diego Health, she has heard from people who clamor for help interpreting their disease risk after being alarmed by the resulting data from direct-to-consumer DNA tests. Madlensky cautions that these consumer tests are not intended to diagnose or predict disease. Still, there are pieces of health information that can be revealed from consumer genetic tests, but only about 3 percent of people will find “actionable” information in the results — in other words few results will lead to a change in a person’s medical care.
Should individuals take a genetic test?
Ancestry testing has driven direct-to-consumer genetic testing into a place where I think people are excited about genetics. I would ask, what was the reason you sought out a DNA test product? If you’re trying to verify old family stories about ancestry you might consider one of these tests. It falls into personal preference. But, you should consider what information you are really trying to uncover from the results. For people who are concerned about a specific disease that is running through their family or they’re worried about a specific medical issue then ancestry testing (including looking at your raw data) is not the best way to get the answer. I suggest you consider speaking to your physician or genetic counselor to help guide you in what tests, if any, you really need. To me, the level of severity and how you would use the information is what dictates whether it is right for you to consider a test. Regardless of the choice you make, you should research who is doing the genetic testing, whether it is medical-grade quality, what information you’ll receive and what you can do with that information.
What health information can I get from direct-to-consumer DNA tests?
Direct-to-consumer genetic tests do not diagnose disease. Although one consumer genetic testing company has been granted FDA authorization for three mutations related to hereditary breast and ovarian cancer, this testing is not adequate in most cases, and often leaves people thinking that they have had complete genetic testing of the BRCA genes — they haven’t.
There are many people who come in because their direct to consumer report (or their raw data) says they have a BRCA mutation or similar type of mutation related to cancer. Genetic counselors and physicians have to tell them that this information could be right or it could be an error. There are no quality control measures for most of these tests and sometimes it turns out to be correct, but often the data contains an error causing a “false positive” result. The way I think about this is that, if people chose to undergo a direct-to-consumer test and take a deeper look at their raw data manually or using an app, it is an opportunity for people to find something important about their health or about the risks of disease in future children. But most adults have a fairly “boring” genome and rarely have a major genetic finding. Everyone carries a lot of very “mild” genetic changes that might increase or decrease disease risk a small amount, but for most people it isn’t enough to warrant any changes in medical care.
Think of it this way, nearly everyone has a relative with cancer, heart disease or diabetes — the most common diseases in adults. You’ll go through your data from these tests and find that you have some mild risk factors for one or all of these things, because everyone does. That’s where I think this gets very confusing, and actually undermines a lot of trust in what are useful medical-grade genetic tests. The challenge is that when people are reading through the results they may only see the name of the disease and think they’re in trouble. Genetic counselors try to undo those perceptions of disease risk, and try to help people understand a lot of very technical information about how disease risk is determined that is not often well explained by the companies providing genetic data.
If a genetic test reveals a mutation or a gene that increases risk, does that mean I’ll get the disease?
To me, the most important message is that these tests are not predictive. Not everyone with a mutation will develop a disease. Most genetic tests for things like Alzheimer’s and breast cancer are tests that alter your risk of developing a disease in the future, they do not predict or diagnose it. It’s also important to think about context: Most people with common adult diseases do not carry a major gene that causes that disease.
If a genetic test reveals that you do have a mutation that increases your risk of a disease we may suggest that you do a confirmatory genetic test (in a lab that can issue medical-grade results) to confirm or dispel the findings. But, the bigger discussion is what can one do with this information if it is confirmed? Some people may be screened for a disease at a younger age or more often, others may discuss medication changes with their physicians, and still others might think differently about their long-term care planning.
For those rare cases where we can offer medical intervention they may choose to take preventive steps. The BRCA gene mutation is an example of when medical intervention might be recommended. Because of the high risk of ovarian cancer, and because we have no early detection test for ovarian cancer, we might recommend to a woman who tests positive for BRCA that she consider having her ovaries removed as she approaches age 40 or 50. This approach eliminates ovarian cancer in all of those women, and this recommendation is based on multiple research studies and is backed by evidence-based guidelines for women with BRCA mutations.
What is the difference between direct-to-consumer genetic tests like 23andMe and Ancestry and tests geneticists like you order?
In every one of your cells is a little library with 20,000 to 30,000 pairs of genes — think of these like instruction manuals that comes in pairs (one from mom and one from dad). Each manual has a particular function in a cell. For example, one pair of genes determines your blood type. Whole exome sequencing is basically spell-checking every single one of those books for a spelling mistake (called a mutation) that results in the book becoming unreadable — the manual doesn’t work. When we order medical genetic tests, each letter in that gene — or book — is being sequenced. When we find a mutation it’s like you’re reading the book and halfway through the pages become blank. Direct-to-consumer genetic tests do not typically spell-check the entire book, instead they may only sequence a handful of selected letters out of the entire book. So it’s not comparable to fully sequencing a gene. However, sometimes the direct-to-consumer tests do spell-check a specific letter that is known to be associated with disease risk; in that case the result would need to be confirmed in a medical lab, since there are many errors that have been reported in these tests. No medical decisions should be made until the results are confirmed.
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