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Building a family portrait: how accurate are DNA ancestry testing kits?


With the rise of popular online genetic testing services, more and more people are spending money to see if there’s any truth in old family tales of a royal ancestor. But just how accurate are these tests? And what implications can they have for customers who use the service?

Ever since the groundbreaking 2003 Human Genome Project mapped the human DNA sequence in its entirety, rapid advances in technology have enabled us to read a person’s genetic code more quickly and cost-effectively than ever before.

In response, a slew of DNA testing companies have exploded onto the market, each claiming to provide the most accurate genetic results to date.

With a simple cash transaction and a vial of saliva sent in the post, genomics companies are able to sequence the DNA of hundreds of thousands of customers. By building an ever-growing database of genetic information, companies can collect valuable insights into human evolution, inheritance and disease. But just how accurate are they, and what are the ethical implications?

Revisiting the past with consumer genomics

From 23andMe to AncestryDNA, genomics websites are making the most of the public fascination with heritage that stems from cultural phenomena like the hit BBC show Who Do You Think You Are?. In 2019, an estimated 4.7 million in the UK have already used a DNA testing service.

By 2022, the ancestry testing market is predicted to be worth £261 million almost five times the £53 million it was worth in 2015.

Consumer genomics is big business, and a flurry of startups are flooding the marketplace to compete with the big hitters. There’s even a service to test your pet’s DNA.

57% of Brits believe that connection to family is a key factor in driving wellbeing, so there’s certainly an element of hearth-and-home nostalgia in the online ancestry boom. But are consumers being swindled into believing a fiction?

The science and ethics behind such ventures have been called into question by many geneticists, public figures and consumers. Not only do many claim the results are not accurate, but some are concerned that DNA testing companies are collecting private data for undisclosed means.

In this article, we look at the main problems that persist around DNA testing in a bid to help consumers make more informed decisions about giving up their genetic data and, if so, how they interpret their results.

DNA is an inherently complex business

The key cause of confusion when it comes to ancestry testing is that it can only reveal part of a person’s DNA and not the entirety of their genome.

For the uninitiated, the human genome is the complete set of nucleic acid sequences in a person’s body. This is encoded by three billion individual letters of DNA, organised (roughly speaking) into 23 pairs of chromosomes.

To further complicate matters, there are three kinds of DNA test that can help a user ascertain their family history. The first of these is an autosomal DNA test, which reveals our ethnicity and connects us to our living cousins.

Half of autosomal DNA comes from the mother and the other half from the father, giving valuable insights into a person’s paternal and maternal lineage at the same time. However, the complicated way autosomal DNA is inherited means researchers can only go back around six generations.

What’s more, if test results state that a person is 5% Native American, for example, the customer won’t know which side of the family it comes from unless both of their parents get tested, too.

The second type is the Y chromosome (Y-DNA) test. Y-DNA is passed through the generations from father to son and can be used to trace a person’s paternal line back by around ten generations.

However, as women do not have Y chromosomes, a female researcher who wishes to find out her paternal ancestry will need to get someone with the same Y-DNA as her biological father (such as a brother or paternal uncle) to take the test.

The third major type of DNA test is mitochondrial DNA (mtDNA), which is used to trace maternal lineage. Unlike Y-DNA, this is passed through the generations from mother to daughter.

mtDNA is frequently used by genealogists to explore ancient ancestry and then pick out people who are not related through their maternal lines. If two people’s mtDNA don’t match exactly, it’s likely that they’re not closely related.

These different kinds of DNA and therefore different types of DNA test present a picture of genetic complexity. For consumers, deciding on which test to get depends on their own line of inquiry, and some may find themselves opting to get all three.

Genomics companies use a statistical approach to analyse ancestry

This infinite variation in human genomes makes it nigh on impossible for geneticists to map a person’s ancestry with 100% certainty.

Companies like 23andMe and LivingDNA use their own proprietary databases. These are full of DNA samples known as ancestry information markers (AIMs), which draw genetic information from current populations in Africa, Asia, Europe, and the Americas.

Once a company receives a sample, they compare it to other samples in their database to spot similarities or differences in the genetic markers. As such, the science employed by genomics and biotech companies is one of probability rather than one of certainty.

When customers receive their ancestry report, most testing companies also provide a list of DNA “cousins”. Like much of the DNA extraction process, cousin matching isn’t an exact science.

While it can determine close family members with extreme accuracy (parents, siblings, half-siblings, aunts, and uncles), beyond that any possible familial connections are based on probability. Y-DNA and mtDNA can reveal some form of relation to another person, but it’s hard to know whether the two people are first cousins or seventh cousins.

What’s more, if a DNA test estimates that someone is third cousins with another person who also uses the service, it cannot tell them which pair of great-great-grandparents they share. To ascertain the exact shared lineage, old-fashioned genealogical research has to supplement autosomal DNA, y-DNA or mtDNA tests.

DNA tests do not only just apply to ancestry. For services like 23andMe which also provide health reports, a DNA sample does not act as a diagnosis. Instead, it indicates that a person has a greater likelihood of developing a certain genetic condition.

Breaking down a person’s ethnicity can be tricky

As we have seen, people have sent their DNA to different companies and received suspiciously different results. Of course, a person’s genetic makeup can’t just change overnight, so it’s clear that these differences partly stem from the methods employed by each test provider.

Ethnic ancestry is measured by by evaluating common genetic variations (single nucleotide polymorphisms or SNPs) across a person’s entire genome. Far from being definitive, SNPs are compared with the results of other people who have taken a test to estimate the probability that a person’s ancestry is, say, 60% British/Irish, 20% Ashkenazi Jewish, 10% Eastern European, etc. Again, this is not an exact science.

The likelihood of receiving granular results from a particular geographic region very much depends on how many individuals with similar ancestry are on a company’s reference dataset. In simple terms, the more people who use a service, the more refined that company’s results become.

Given that SNP testing requires a comparative approach, the fact that ethnicity estimates are more detailed for people of European descent is hardly surprising.

As a response, 23andMe have used data gathered from initiatives such as The African Genetics Project and Global Genetics Project to add more regional subgroups to ancestry reports and improve accuracy for people of colour.

With this additional data, test providers can produce more accurate reports that better reflect the true diversity of the global population.

Can ancestry test results be too close to the bone?

At present, genomics companies do not share their data with the public, nor are their methods validated by an independent group of scientists. This poses a quandary for consumers seeking precise readings of their DNA and ethnic ancestry. Namely, how trustworthy are these DNA testing kits?

Privacy concerns

A key reason for the growing scepticism around genomics companies is the way they make their money. Revenue does not come from the tests but from selling the genetic information to other companies who see a competitive advantage in having a large genetic database.

The privacy policies of companies offering testing services often state that they bear no responsibility for a customer’s data if their business (and therefore database) is sold.

Once the data is sold to another company, the records can become de-anonymised. For customers to have control over where their data appears or is used, they need to contact the company and keep up-to-date on its policies. However, this would take a degree of vigilance that should not be expected of paying customers.

Most DNA testing services also keep the samples of their customers, with only about 10% of such services destroying them. So aside from mining data, these companies are holding onto actual saliva.

Unearthing family secrets

Since the genomics industry became widespread, there have been various cases of people finding long-lost aunts, cousins and even siblings after doing an ancestry test.

By looking for DNA matches within their database, genomics testing companies can provide a list of people who appear to be part of a customer’s larger family ancestry based on the SNPs shared between them.

For people with gaps in their family history, this can often cause some fairly seismic revelations and not always welcome ones.

For example, a user may find out that the person they have always believed to be their mother is actually their aunt or grandmother. The risk of opening up an unwanted pandora’s box of family secrets can therefore come as a surprise to some customers, and genomics companies do not always give users enough of a warning for such a possibility.

Last year, the Human Fertility and Embryology Authority (HFEA), expressed concern about the ease at which companies that buy data can uncover the names of sperm and egg donors who donated anonymously. For both the donors and their offspring, this can cause unwelcome consequences that they didn’t explicitly consent to.

The majority of DNA testing websites do not currently have sufficient safeguarding guidelines or signposting in place for such an outcome, again raising concerns about the ethics of such a service.

Health reports

Website such as 23andMe and Thriva also provide customers with a DNA-based health report that informs them of their genetic predisposition to certain conditions, ailments, physical traits, and behaviours.

23andMe, for example, gives users feedback on the likelihood of them developing illnesses such as Type 2 diabetes and Parkinson’s disease. Meanwhile, another report gives information on how the user’s DNA makes them prone to things as diverse as lactose intolerance to misophonia.

However, the accuracy of such reporting has been called into question with one study claiming that 40% of results from "direct-to-consumer" DTC tests may be false positives. Perhaps the most profound implication, however, is the level of stress and anxiety that such results can bring to users especially when it comes to something like carrier status.

As one GP, Margaret McCartney, told the Guardian:

“Often people are told [by genomics companies] to go to see their GP and that then places a direct stress on the NHS, at no cost to the company. The companies make their profits and walk away, letting the NHS sort out all the fallout, the push-back, from the test results, in a way I find absurd. Why should the NHS have to prop up the problems that these companies create?”

If controversy about the accuracy of DNA ancestry reporting is one thing, genomics-based health reporting could open up a whole new can of worms.

Yes, customers can receive useful information about their genetic proclivity to a certain illness, but not having the benefit of a genetic counsellor to properly interpret the results in an empirical manner can precipitate hypochondria.

Worse still, it can put unnecessary pressure on the UK’s already beleaguered health system.

Conclusion: a healthy dose of scepticism

Direct-to-consumer testing may be an inexact science, but genetic sequencing continues to improve in accuracy. As scientists begin to understand more about the complexities of our DNA and gather more varied data, the efficacy of such tests will also improve.

For the curious researcher, the results of DNA tests can prove extremely useful in their quest to uncover their own biogeographical background. Given the drawbacks that we have discussed, however, such a line of inquiry is best undertaken in combination with traditional genealogical research.

With many different kinds of DNA test on offer (and the different methods employed by different companies), customers looking for a more accurate reading of their heritage or health may have to take a number of different tests.

Minor variations in samples can lead to different results for even the same person. This probably explains why a pair of identical twins from Canada who have virtually identical DNA did not receive matching results from any of the five companies they tested with.

However, none of the commercial DNA test providers claim to give customers a complete information about their genetics and health. It’s worth reminding ourselves that direct-to-consumer testing is a commercial endeavour. While the results are grounded in scientific inquiry, they should certainly be taken with a pinch of salt.

That said, the onus is on genomics companies to ensure better protection for the personal data of those who use the services. By making a commitment to safeguarding customer data and making it easier for customers to opt to have their sample destroyed after testing, genomics companies can help give their burgeoning industry some much-needed legitimacy.

To get a fuller picture of a their DNA, amateur researchers may need to take more than one test.

For consumers, it’s best to keep an open mind. That means trying out different tests, staying abreast of the latest developments in genomics, and being fully aware of a company’s terms and conditions.

It seems consumer genomics is here to stay, and that’s not necessarily a bad thing. As science improves, the human family tree will start to reveal itself in ever more fascinating ways.

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