How secure is the information revealed in our DNA tests?

At the time, it looked like a bargain. Over the past couple of decades, the price has dropped about $1000 to less than $100 today. No wonder, then, that consumer DNA testing has skyrocketed and is now an $8 billion industry. It’s promoted as an easy and fun way to find relatives or uncover ethnic origins. Discovering you are, for example, 20% Italian is a fun fact to share with friends on Facebook or over drinks.

But this is only scraping the surface of the technology. DNA therapies open the door for personalised medical measures to both prevent and cure disease. DNA analysis has the potential to give us real insight into our traits and behaviours. The pious entreaties of philosophers down the ages “to know thyself” takes on new meaning. But we’re not there yet. And where we are now can sometimes be scary and threatening.

Most people would be reluctant to shed their clothes in public, but nudity is nothing compared to how they expose themselves by handing over their DNA. Personal privacy is ripped to shreds and family secrets laid bare. Sperm donor conceptions, infidelities, adoptions and even crimes can no longer be covered up. DNA testing means it’s no longer possible to bury the past. That drunken one-night stand, workplace romance or holiday fling decades ago could turn out to be unfinished business that involves a back demand for child support. It takes only one relative to upload DNA to a genealogy site to make it possible to trace an individual.

Even taking family secrets to the grave is no longer a certainty. Canadian firm Lazarus DNA, for example, works with undertakers to collect DNA samples for families. Australian company totheletter DNA offers “commercially available testing of envelopes, postcards with stamp/s, aerogrammes and other artefacts from deceased relatives”. Presumably, it could also be used to find out who your grandmother’s lover was from her stash of love letters or track down the sender of a poison pen letter.

Although consumer DNA tests are great for tracing relatives, they can be less accurate about determining ethnicity, especially if you are non-European. Genealogy sites provide a pie chart showing percentages of your ethnicity estimates. But an estimate is all it is: it all depends on the size and composition of the company’s database and the algorithms it uses. Ancestry, for example, has correctly pegged me as 100% unadulterated bog Irish, while another site insists I am 6% East ­European. If your DNA ethnicity test shows that you are, say, 11% Greek, that percentage can change or even disappear as the company’s database grows or it refines its algorithms.

When the thrill of discovering they have a third cousin twice removed in Patagonia wears off, many people want to know what else they can get for their 100 bucks. If they haven’t taken the 23andMe DNA test, which combines ancestry and health reports, there are plenty of sites where they can upload their DNA profile to find out about possible health risks and traits. It can be a hypochondriac’s fantasy. For example, when I tested on the reputable Promethease website, I found I was a carrier of a potentially deadly genetic disorder, had increased risk of coronary heart disease and type 2 diabetes, among other things. None of which caused me concern. The genetic disorder is only a problem when both partners are carriers and higher risks of heart disease and diabetes are common for my age group and can be mitigated by a healthy lifestyle. But I guess I would say that, because my DNA suggests I am optimistic by nature and less prone to be neurotic.

23andMe says its health reports are 99% accurate and have the seal of approval of the US Food and Drug Administration. The company offers a range of health predisposition reports for kidney disease, dementia, lung and liver disease, coeliac and Parkinson’s disease. It is probably best known for detecting BRCA1/BRCA2 variants, which predispose women to breast, ovarian and other cancers. The results are accurate – as far as they go. Which is not far enough. Consumer DNA tests focus on only 700,000 letters of the 3 billion that make up a complete genome, an exercise that has been likened to spellchecking just one paragraph of a book. In 2019, the New York Times reported on a study of 100,000 people which found nearly 90% of participants who carried a BRCA mutation would have been missed by 23andMe’s test.

However, the company is upfront on test limitations, stating on its site: “Having a risk variant does not mean you will definitely develop a health condition. Similarly, you could still develop the condition even if you don’t have a variant detected. It is possible to have other genetic risk variants not included in these reports.”

In any case, DNA is not destiny. Most identical twins do not die or even suffer from the same diseases.