What can a health DNA test really tell you?

Home genetic testing kits claim to reveal the secret blueprint of your future health. But how accurate are they, and what are the downsides?

DNA HEALTH SCREENING TESTS are booming: in the US around 25% of the population is believed to have taken a commercial genetic test. Now the saliva tests that are sent off to a laboratory for DNA analysis are taking off in the UK, too. You may even have had one for Christmas. 

Who wouldn’t be intrigued to know more about their DNA? Rory Larkin, chef and HFG nutritionist, certainly was – enough to pay £149 to the website 23andme.com last year to have the test. He was a bit skeptical about what it could tell him, however. 

‘Coming from 100% Irish stock, I wondered if I had some DNA from any other ethnic groups that I didn’t know about,’ says Rory. ‘But I’d also come across science podcasts about how genetic variants can affect your nutritional status and I was curious about that, too.’ The makers of these tests have obviously tapped into our curiosity about our genetic predispositions, but was Rory gaining useful insights into his future health, or wasting his money on a gimmicky but medically meaningless test?

What they can test

DNA is an instruction manual ‘blueprint’ for making a life form – be it human, animal or plant. Humans share 99% of the same DNA code but it’s the 1% that varies between us that is responsible for our individuality. The booming health test market claims to give you a detailed breakdown of your individual genetic make-up – highlighting which diseases you might be genetically predisposed to.

The tests vary widely, from an analysis of your genetic heritage to whether you’re susceptible to heart disease and weight problems or a carrier for cystic fibrosis. Some of the more obscure claims cover whether you flush when you drink alcohol, what type of ear wax you have or whether mosquitoes find you irresistible or not. This means, of course, tests vary in price from around £79 (from ancestry. com, which looks at your genetic ancestry) to upwards of £1,000 for an extensive health test. As a general rule of thumb, pricing reflects the number of results you get for different conditions and traits.

So what are the concerns?

Just how useful these health DNA tests remain to be seen, as the science is evolving rapidly. They’ve been criticized by some as being an ethical can of worms as well as unreliable and – at the moment, at least – unregulated. There are also fears about the security of personal data, as well as concerns that people may discover potentially devastating news without having any counseling or support. 

Dr. Helen Wallace, executive director of the not for profit group GeneWatch UK, which monitors developments in all genetic technologies, confirms that health DNA tests aren’t currently regulated, although the EU is planning to bring in regulations in 2022. ‘Obviously, with Brexit coming we are uncertain about whether this will cover the UK or not,’ says Helen.

 ‘At the moment, if you buy one of these tests you have absolutely no idea whether the information they give you is accurate or not. You could order two different tests from two different companies and be told something completely different by each one,’ she adds. 

Another problem is that you may not be aware of the context for your results. ‘You may be falsely reassured by news such as testing negative for the BRAC-1 or BRAC-2 breast cancer gene,’ says Helen, ‘but not realize that these account for only 5% of breast cancer cases, for instance. Or you could be unnecessarily worried by a test that tells you you’re likely to get a certain disease.’

Why it’s not all about genes

Experts have estimated in the past that between 15% and 30% of the variability in human lifespan is due to genetics. A new study, however, published in the journal Genetics in November 2018 and based on data from the website ancestry.com, found these differences could be explained by people simply choosing partners with traits that resemble their own.

‘This study shows that in longevity, for instance, very little is determined by genes and much more by the environment,’ says Helen. ‘In other words, well-off healthy people marry other well-off healthy people and produce well-off healthy children.’

Do you know what’s happening to your data?

There are also concerns about the security and confidentiality of test results. ‘You have to be really careful and read the small print as some companies will use your data and sell it on to pharmaceutical companies,’ says Helen.

‘Another issue that has come up in the US is that the police have been applying to courts to access DNA test results in an attempt to solve crimes where they have a DNA sample,’ she adds. ‘This has proved to be controversial because of the police look for possible matches with relatives. ‘There are reports that everyone could eventually be tracked like this, which is a potentially quite scary surveillance society scenario.

‘At the moment, there’s a voluntary agreement in the UK between the insurance industry and the a government that they won’t ask about the results of any genetic test – but of course, this may change in the future.’

What DNA tests can’t tell you

The big flaw with most DNA tests is that although they can give you your genetic code, they don’t take into account environmental factors such as your diet, how much exercise you take, whether you smoke, and how much stress and sleep you get. After all, your health is modifiable to a certain extent.

HFG nutrition editor Amanda Ursell confirms that diet and lifestyle are incredibly important factors in determining your health, including the likelihood of developing cancer, heart disease, and type 2 diabetes. ‘You can’t just rely on having good genes to protect you against ill health,’ she says.

‘Maybe these types of tests are useful for highlighting genetic predispositions so that people can change their lifestyle, but at the moment it’s clear that genes are not the whole story.’