At-home genetics tests are accurate for determining ancestral origins, but not for predicting diseases

Some genetic tests for sale to the public claim that they can reveal the origins of our ancestors and the diseases to which we are susceptible. These genetic ancestry tests have been a booming trend for years already and, due to their popularity, a number of videos of people sharing their results have popped up on social media. But how reliable are these tests? We’ll tell you!

How the tests work

Companies sell the tests on their websites. They send their customers, i.e. users, the instructions for collecting the sample, which is usually taken from saliva or the oral epithelium, plus the vial and swab for doing it. The users return the sample and wait about three weeks for the results.

The labs then extract the genetic material of the sample, which is present in the nucleus of the cells, and analyse a series of variables present in the person’s DNA. “They do not sequence the full genome”, Gemma Marfany, professor of Genetics at the University of Barcelona (UB), explains to Verificat. “They only look at some of the variable positions of the genome, a technique called sampling, […] thus determining the polymorphic variability”, which is to say, the combination of shared genetic variants contained in each individual.

The procedure then involves comparing the combination of variants in the person who ordered the test with the variants in the databases, in order to compare it with other people and draw conclusions about their origins.

The tests’ reliability

“A person does not have all the DNA of his or her ancestors, but some of the pieces”, explains Marfany. These tests compare the users’ genetic material with the global genome database belonging to each company and, as a result, “results can be somewhat varied, but they are quite reliable. Different companies may produce slightly different percentage values. The rarer the combinations of variants and more specific a population, the more accurate the test […], whereas if the population of a geographic region is genetically diverse, the accuracy of the results declines”, Marfany points out.

They are not suitable tools for clinical diagnosis

Some of these tests also claim to be able to detect the user’s genetic predisposition to various diseases such as Alzheimer’s, diabetes or osteoporosis. “Since they do not sequence the entire genome, they cannot make a precise clinical diagnosis […] They cannot identify the high-impact rare or unique variants”, Marfany explains. Furthermore, it must always be taken into account that the environment plays a very important role in the development of diseases, as we explained on a previous occasion, because genetics are not the only determinant.

Privacy

The information that the users of at-home genetic tests provide to these companies for free is sensitive and personal information: thanks to all the people who do the test, these companies can figure out in which parts of the world certain genetic variants are most frequently found.

This information can be very valuable for organisations in the health sector or public agencies, as was shown in 2018 when a pharmaceutical company bought the data from one of these companies or in 2018 when another one of these companies allowed the FBI to access its data. In fact, in 2018, the US Federal Trade Commission (FTC) investigated several of these companies. That is why it is always necessary to carefully read and compare the different privacy policies of each company when doing these tests.