Accuracy of At-Home DNA Tests

Lisette Peres for Health Empowerment Coalition

The significant developments of DNA testing these past two decades have led the way for accessible at-home DNA tests. Their affordable price point and ease of use have unsurprisingly resulted in nearly 40 million tests being sold so far.¹ For just around $100, you can spit in a tube and figure out your family history. The prospect of finding out about certain health risks and ancestry are significant factors in why people are purchasing at-home DNA tests. A simple test can open doors to discovering parts of one's life that were previously unknown. However, not all of these results are always consistent.² For those who may have used these findings to rediscover a part of themself, having these results change or even disappear could be devastating and detrimental to their identity. This begs the question: how accurate are these DNA tests?

In order to answer that question, it is important to know how these DNA tests work. After a person spits into a tube and sends it to one of these companies, the DNA is isolated. Anything that is not DNA, such as debris, cells, or proteins must be removed before proceeding any further. Once this is completed, the DNA is amplified, meaning copied many times, and then broken down.³ Since 99.9% of our genetic make-up is similar to each other scientists look at certain parts of our genome where there are known variations called single-nucleotide morphisms or SNPs.³'⁴ From there, the variations are compared with reference samples in order to come up with percentages for a person’s ethnic background based on how similar the SNPs are between them and the reference sample. Here is where the possibility for inaccuracy arises. The reference samples vary between different companies and typically use self-reported data regarding an individual’s ancestry to add to their database. Humans have a long history of migration and intermixing with local populations; therefore, the self-reported data used for the reference samples may not accurately reflect the genetic makeup.⁵

The more reference samples available, the more accurate the results will be. However, certain populations tend to have more reference data than others. The groups that have the largest amount of samples are from Europe.⁶ Those who have ancestry in other regions of the world may experience a result that might not be entirely accurate. For example, my family is from Ecuador, a country, like many in Latin America, that has experienced a large amount of intermixing and migration, or as it is known in Spanish, mestizaje. If I were to take a DNA test, it could probably tell me about possible ties to the Iberian peninsula. However, any connections to Indigenous groups in Ecuador or the surrounding areas may not be accurate due to the low reference samples. Obtaining reference samples for Indigenous people is complicated due to mestizaje or intermixing of Indigenous and European people however, currently, the term means mixing of two or more races. Many people’s genes are a mix and can’t provide accurate samples. Another issue is that indigenous people tend to not want to provide their samples.⁶ AncestryDNA is one of the only companies that disclose the number of reference samples, and in 2018, they reported that they only had 146 samples for Native Americans from North, South, and Central America.⁶ On the other hand, they have 917 reference samples for Spain and 893 reference samples for Portugal.⁷ Fortunately, since this report, Ancestry.com has been able to increase its reference sample size, with nearly 10,000 reference samples from Indigenous peoples from Latin America. For the reference sample, “Indigenous Americas - Ecuador” there were 691 samples.⁷ Part of this switch is possibly due to the increased nature of participation and popularity within those who have mixed Native American ancestry.

Another example of a minority group that is underrepresented within these companies is those of African ancestry. Within Africa, there are over 3,000 ethnic groups, many spread between current national borders.⁸ Large companies such as 23andMe and AncestryDNA tend to use current national borders for their results. For example, in 2018, 23andMe could only match people to 3 broad regions in Sub-Saharan Africa.⁹ AncestryDNA’s reference panels show significantly fewer reference samples for groups in Africa in comparison to those in Europe. An example of this is how there are only 41 samples for Somalia.⁷ While large companies such as 23andMe, and AncestryDNA among others, have struggled with having sufficient samples for their reference panel, due to partially the mistrust present within the African American population and the medical community, there have been other black-owned businesses that have been able to accumulate a database for those who are interested in figuring out their connections to African Ancestry, is a black-owned company that focuses solely on African lineage and examines ethnic groups and ancestry. Their website states that they have 33,000+ lineages from over 35 African countries.¹⁰

It is important to understand how DNA is inherited from one's parents: a person only receives half of each of their parent's genes. This is why if someone takes the same DNA test as their sibling, they may not receive the same percentage breakdown. For example, they may receive a part of their parent’s gene that originates from Britain, while their sibling does not. Does that mean that person has no connection to that part of their ancestry? Not at all. It’s important to distinguish between ancestry and heritage. While a DNA test may be able to tell someone about where their ancestors lived, the culture that they share with their relatives is something that is still important to who they are.

While ancestry DNA tests are merely a tool to get an educated estimate of one’s lineage, another common use for these DNA tests is for health reasons. These are much more accurate and can provide meaningful results for an affordable price. The reason these tests are much more accurate is that scientists look at the DNA and compare it with genes that make up certain markers for diseases or traits. It is pretty straightforward, a person either has it or they don't. With these types of DNA tests, there may be a concern that the results of such tests may be used against an individual when applying for jobs or health insurance. However, in 2008, the Genetic Information Nondiscrimination Act (GINA) was passed, which made it illegal for health insurance companies or workplaces to require your DNA or make decisions regarding those results.¹¹

Ultimately, a person is more than their DNA. DNA tests can’t tell people anything about their culture or the migration patterns of their ancestors. Rather, it simply provides a geographical location of origin. These DNA tests may not always be 100% accurate, but perhaps they are a good way to get started for those interested in learning more about their ancestry. Being aware of the potential inaccuracies when using these tests and not being fully dependent on the test results is important when buying an at-home DNA test.

References:

1. Copeland, L. (2021, June 18). Perspective | genetic testing is changing our understanding of who fathers are. The Washington Post. Retrieved December 22, 2021, from https://www.washingtonpost.com/outlook/dna-testing-fathers/2021/06/17/7f607c54-ce20-11eb-8cd2-4e95230cfac2_story.html

2. Rajewski, G. (2018, April 30). Pulling back the curtain on DNA ancestry tests. Tufts Now. Retrieved December 22, 2021, from https://now.tufts.edu/articles/pulling-back-curtain-dna-ancestry-tests

3. U.S. National Library of Medicine. (2020, September 21). What is genetic ancestry testing?: Medlineplus Genetics. MedlinePlus. Retrieved December 22, 2021, from https://medlineplus.gov/genetics/understanding/dtcgenetictesting/ancestrytesting/

4. National Human Genome Research Institute. (2018, September 7). Genetics vs. genomics fact sheet. Genome.gov. Retrieved December 22, 2021, from https://www.genome.gov/about-genomics/fact-sheets/Genetics-vs-Genomics

5. Wahome, C. (n.d.). What to know about the accuracy of DNA ancestry tests. WebMD. Retrieved December 31, 2021, from https://www.webmd.com/a-to-z-guides/features/accurate-dna-ancestry-tests

6. Weise, E. (2018, December 3). Looking for your roots? for Asians, blacks and Latinos, DNA tests don't tell whole story. USA Today. Retrieved December 22, 2021, from https://www.usatoday.com/story/news/2018/12/02/asians-blacks-latinos-genealogical-tests-dont-tell-full-story/2132681002/

7. AncestryDNA® Reference Panel. Ancestrysupport. (n.d.). Retrieved December 22, 2021, from https://support.ancestry.com/s/article/AncestryDNA-Reference-Panel?language=en_US

8. Moulton, S. (2021, December 6). Ethnic Groups in Africa. Study.com . Retrieved December 22, 2021, from https://study.com/academy/lesson/ethnic-groups-in-africa.html

9. Resnick, B. (2019, January 28). The limits of ancestry DNA tests, explained. Vox. Retrieved December 22, 2021, from https://www.vox.com/science-and-health/2019/1/28/18194560/ancestry-dna-23-me-myheritage-science-explainer

10. The science. African Ancestry. (n.d.). Retrieved December 22, 2021, from https://africanancestry.com/pages/the-science

11. Spiggle, T. (2020, August 11). The legality of DNA testing in the workplace. Forbes. Retrieved December 22, 2021, from https://www.forbes.com/sites/tomspiggle/2020/08/11/the-legality-of-dna-testing-in-the-workplace/?sh=569ab176fb5b

Author: Lisette Peres

Edited by: Mateya Rettig, Joy Jarnagin, and Michelle Pan

The Health Empowerment Coalition is a student-led organization that aims to empower individuals across the United States to improve their health literacy and take charge of their health. The views expressed in this article are the authors’ own and do not reflect the official opinions of the institutions at which they work and study. Additionally, the content in this article is not intended to provide medical advice.