Do you want to Google your genes or peer into your future risks of heart disease or cancer? Now you can, according to direct to consumer testing companies. Gone are the days when genetic testing was limited to doctors ordering tests for rare, but prognostically potent, single gene disorders such as Huntington’s disease, Duchenne’s muscular dystrophy, or cystic fibrosis. Thanks to an explosion of newly discovered single nucleotide polymorphisms, or SNPs (pronounced snips), companies are marketing genetic tests for traits ranging from the mundane—eye colour and wet ear wax—to serious conditions such as Crohn’s disease and Alzheimer’s disease.

While the global market for these tests is growing rapidly—estimated at $730m (£366m; €463m) last year and growing by 20% annually1—evidence that they can provide patients with clinically useful information is lagging far behind. There is little regulatory oversight of the tests, and even less in the way of clinical data to help doctors guide patients who go to them carrying printouts of their genetic details. Genetic tests and “personalised medicine” are supposed to enable doctors to customise each patient’s care, yet there is a paucity of studies on interventions for patients with genetic variants.

The promise being made to consumers is clear: forewarned is forearmed. The website for deCODE genetics, based in Reykjavik, says its tests will “help to empower individuals and their doctors.” The Californian company 23andMe, which has backing from Google and the biotech company Genentech, provides an “odds calculator” that the company says will allow customers to see which “health concerns are most likely to affect a person with your genetic profile.” Navigenics, also based …