Over-the-counter DNA tests: Do they have a place in clinical practice?

Many consumers are attracted to the promises of over-the-counter DNA health tests. Many purport to offer insights on ancestry, inherited traits, and even genetic propensity for certain diseases and conditions.

As these tests proliferate, patients may bring test results into clinical encounters. However, how clinically relevant are these test findings?

Clinical vs consumer DNA health testing

There’s a critical distinction between clinical-grade DNA health testing, and consumer-grade testing, research indicates.

Consumer DNA tests serve different purposes, including genealogy, and predicting traits, such as eye color. They can also screen for a limited number of inherited diseases. Consumers provide a mouth swab or saliva sample, which they mail to a lab for analysis.

The FDA breaks consumer tests into four categories.

• Carrier screening tests determine if a person has a genetic variant they might pass to future children. CarrierCheck is an example.

• Genetic health risk (GHR) testing identifies genetic risk for certain diseases. GHR tests include 23andMe, AncestryDNA, and Living DNA.

• Pharmacogenetics tests can explain how genetics affect a person's reaction to certain drugs. GENETWORx is an example.

• Cancer predisposition tests can provide information about individual risk for certain cancers. For example, Circle touts its ability to detect many types of cancer. 23andMe advertises that it can detect genetic risk for breast cancer, looking for three genetic variants of BRCA1 and BRCA2, according to a 2020 Scientific Reports article. However, more than a thousand known variants can increase breast and ovarian cancer risk, making the test limited.

Unlike consumer-grade testing, healthcare professionals oversee clinical-grade genetic testing. The clinician collects a blood or saliva sample and sends it to a laboratory to be processed and evaluated. The test considers the patient's medical and family history, covering myriad genetic conditions.

According to the CDC, common clinical-grade genetic testing options include:

• Single gene testing, which looks for changes in one gene. A physician might recommend single gene testing if someone has symptoms of an inherited condition. Single gene testing is helpful when there is a family history of a medical condition.

• Panel gene testing, which looks at several genes in one test. These tests determine risk for different cancers, or conditions such as epilepsy or poor muscle tone.

• Large-scale genetic testing, including exome and genome sequences, screens people with complex medical histories or who are unsure of their family history.

What clinicians need to know about consumer tests

Direct-to-consumer tests are limited in their findings. According to a 2019 Genomics & Informatics report, consumer tests cannot provide conclusive results on whether someone will develop a medical condition. Moreover, most of these tests are limited to analyzing a few significant variants, which leads to inconclusive results.

Consumers can sometimes experience stress when they receive DNA test results related to the risk for serious diseases, such as cancer. This underscores the need for consultation with a qualified clinician to evaluate the results. Without clinical consultation, a consumer may make decisions independently and act without physician advice, leading to dangerous consequences.

The Genomics & Informatics report also notes a deficiency of scientific evidence for genetic testing conducted by direct-to-consumer companies. Additionally, these tests raise patient privacy concerns. Patient information can be stolen, or used for other purposes without a patient’s permission. 

Are consumer tests clinically relevant?

Consumer DNA health testing can help patients understand their genetic risks, however, clinical relevance is largely limited by inaccuracy, the narrow scope of the tests, and a lack of appropriate clinical context. According to a 2018 European Journal of Human Genetics review, the lack of scientific evidence on genetic testing is a significant challenge, making many clinicians reluctant to incorporate these tests in their practices.

The review authors note that gathering clinical evidence on genetic testing is complicated by the complexity of available testing, rapid development, marketing efforts, the impact on society, and the lack of universal standards for interpreting results. Additionally, there is little evidence that genetic testing leads to improved quality of life or increased survival. And without proven benefits, researchers cannot evaluate whether DNA health testing methods are cost-effective.

Sources

1. Oh B. Direct-to-consumer genetic testing: advantages and pitfalls. Genomics Inform. 2019;17(3):e33.doi:10.5808/GI.2019.17.3.e33

2. Direct-to-consumer tests. US Food and Drug Administration.

3. Genetic testing. Centers for Disease Control and Prevention.

4. Tennen RI, Laskey SB, Koelsch BL, McIntyre MH, Tung JY. Identifying Ashkenazi Jewish BRCA1/2 founder variants in individuals who do not self-report Jewish ancestry. Sci Rep. 2020;10(1):7669. Published 2020 May 6. doi:10.1038/s41598-020-63466-x

5. Pitini E, De Vito C, Marzuillo C, et al. How is genetic testing evaluated? A systematic review of the literature. Eur J Hum Genet. 2018;26(5):605-615. doi:10.1038/s41431-018-0095-5