It’s in the Genes: Genetic Testing Tutorial

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.

By Shivani Nazareth and Caroline Lieber

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.

Conclusion

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.


References
1. 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.
2. 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.


Shivani Nazareth is director of wom­en’s health at Counsyl, a DNA-testing and genetic-counseling service. She worked as a clinical genetic counselor for more than 10 years in New York City, most recently at Weill Medical College of Cornell University. Shivani obtained her graduate degree from the Icahn School of Medicine at Mount Sinai and currently serves on the National Society of Genetic Counselors’ Public Policy Committee.

Caroline Lieber is director emeritus of Sarah Lawrence College’s Joan H. Marks Graduate Program in Human Genetics, the country’s first and largest master’s program in genetic counseling. She has 35 years of experience in human genetics, 18 years as a clinical genetic counselor/supervisor, and 15 years in her role as educator/administrator. She currently serves as a consultant for Counsyl, a fast-growing genomics company based in San Francisco.

Copyright © 2016 CancerConnect. All Rights Reserved.