It’s in the Genes: Genetic Testing Tutorial
by Mia James, Medically reviewed by Dr. C.H. Weaver M.D. 11/2018
Advances in genetic testing are offering women more information than ever before about their genetic makeup and are providing opportunities for empowered decision making related to a wide range of health issues. In this recurring column, experts provide vital information about how genetic testing suits one’s individual needs, potential risks and benefits, and the role of genetic testing in advancing treatment approaches that target cancer and other diseases.
Genetic Testing Tutorial
If you are considering genetic testing, it’s important to understand the purpose and scope of available genetic tests.
In a survey conducted by Anna Middleton, PhD, MSc, RGC, of the Sanger Institute, 7,000 people were asked whether they would want to know what’s in their DNA. Interestingly, 98 percent of those surveyed said yes, even if the findings revealed a gene linked to a serious health condition.1
The results revealed a general sense of excitement about the idea of preserving one’s health through the use of genetic information. Also indicative of this trend: when actress Angelina Jolie announced her decision to have prophylactic surgery to reduce her inherited risks of breast and ovarian cancer, genetic testing rates increased significantly.2
As the science of genetics advances, the possibility of disease prevention is intriguing. But navigating the maze of genetic-testing options can be tricky. If you are considering learning more about what’s in your DNA, it is important to understand some of the nuances. We have bucketed DNA tests into five distinct categories to help simplify the information available to you.
Recreational DNA Tests
A recreational DNA test is one that gives you some fun tidbits about you and your family, such as ancestry, bitter taste perception, or the propensity for freckles. Recreational DNA tests do not require the involvement of a healthcare professional and are not used to make medical decisions. Some recreational DNA tests market their kits as “wellness” or “health” tests, but the fact is that the genetic components of your overall health are complex and cannot be attributed to any one particular DNA finding. If you want to learn about some interesting physical or ancestral traits, a recreational DNA test can be a cool family activity. These tests should not be confused with medical advice.
Predictive DNA tests
A predictive DNA test is one that is ordered and interpreted by a physician, genetic counselor, or qualified health professional. There are thousands of predictive DNA tests, and they are used to determine whether you may have inherited (or can pass to children) a particular disease, such as colon cancer, Huntington’s disease, or cystic fibrosis. Some predictive DNA tests are actionable, while others are not. An actionable result means that you can use the information to reduce your risks or plan ahead, as Angelina Jolie did with her DNA test for breast and ovarian cancer. Testing for Huntington’s, a degenerative neurological disease with no available treatment, is not actionable. Despite the fact that there is no medical action to take, some people feel that simply knowing their risk allows for preparation, estate planning, and relief from the burden of the unknown. Predictive DNA tests are used for medical decision-making during adulthood or pregnancy, and the choice to pursue the information is very personal.
Diagnostic DNA Tests
A diagnostic DNA test is also ordered by a physician, and it is used to help figure out the underlying cause of symptoms in a patient experiencing health issues. For example, a child who has delayed walking or difficulty balancing may undergo neurological DNA tests to look for certain types of inherited muscular dystrophy.
An exciting new area within the field of diagnostic testing is whole-exome sequencing. Rather than focus on targeted genes, whole-exome sequencing looks at all of a patient’s DNA to determine the potential cause of a disease.
Therapeutic DNA Testing
Certain therapeutic DNA tests can guide decisions regarding which therapies or medications are best for a particular diagnosis. One example involves the biomarker called HER2 (human epidermal growth factor receptor 2), which provides therapeutic insight in about 20 percent of breast cancer cases. The HER2 gene, when mutated (called HER2-positive), codes for a protein that advances cancer cell growth. A HER2-positive breast cancer tends to be less likely to respond to hormonal therapy; however, hormonal treatments that specifically target HER2 are very successful. These treatments are in fact so effective that the prognosis for HER2-positive breast cancer is quite good.
Research Genetic Testing
Some genetic tests are available as part of research, often as part of clinical drug trials. The scope of results may be limited, however, because the research is often designed to accelerate drug development rather than provide health information. The results from such testing are usually not available to patients or to the referral source, and enrolled family members may not get results from this type of testing. If you are considering research genetic testing, talk with your doctor, genetic counselor, or other healthcare professional about the benefits and limitations.
As you can see, most of the time the information you will receive from DNA testing is really useful. But there are times when results are difficult to interpret or may bring up unknown variables (nonpaternity as a classic example). Understanding the benefits and limitations of testing options is important so that whatever path you choose, you are comfortable with the decision.
- Middleton A, Morley KI, Bragin E, et al. Attitudes of nearly 7,000 health professionals, genomic researchers and publics toward the return of incidental results from sequencing research. European Journal of Human Genetics. 2016;24(1):21-29. doi: 10.1038/ejhg.2015.58.
- Evans DG, Barwell J, Eccles DM, et al. The Angelina Jolie effect: How high celebrity profile can have a major impact on provision of cancer related services. Breast Cancer Research. 2014;16(5):442. doi: 10.1186/s13058- 014-0442-6.