DIY DNA testing.
Credit: Illustration by Brian Stauffer

DIY DNA testing.

Jonathan Zittrain, a 43-year-old Harvard law professor, went to the hospital suffering from a mysterious fever when his doctors found a mass in his liver that they couldn't explain. To find out just what was wrong, Zittrain turned to a test he had ordered online previously from 23andMe, the largest company in an expanding field of "personal genomics," which teases out your genetic info from a saliva sample as if you were a perp on CSI and estimates your risk for more than 100 diseases and conditions. A very ill Zittrain found that he was at high risk for blood clots – "venous thromboembolism" – a clue that helped his doctors figure out his liver had enlarged due to a clot, which they removed. He soon recovered completely. "I'm a data-driven guy," says Zittrain, "and I saw the test as more than just a curiosity."

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Ten years ago, the Human Genome Project deciphered the entire human DNA code at a cost of about $3 billion. What no one dreamed at the time was that the technology would quickly become so accessible and so cheap. 23andMe, for one, recently slashed the price of its product to $99 and aims to serve a million people by the end of this year. The genomic panels offered by 23andMe and its competitors can arm us with data about disease risk that we can use to help make lifestyle decisions or, as in Zittrain's case, pull out of our pocket in an emergency. And while doctors are not yet routinely sending off samples to personal genomic companies, this simple online test is one of the most all-encompassing – and high-tech – ways to take health care into your own hands.

What Our Genes Tell Us

Unlike blood work or an MRI, a genetic test is neither invasive nor time-consuming. The drill goes something like this: You order a test off the website of 23andMe or Massachusetts-based Inherent Health, and when it arrives in the mail, you produce the DNA sample – a vial of saliva for 23andMe and a cheek swab for Inherent – and mail it back. In about a month, the genetic analysis will be sent to you via email. Or, in the case of San Diego-based Pathway Genomics, a doctor orders the test, receives the results electronically, and interprets them for the patient, usually with the help of a script provided by Pathway.

When you get your results from a genetic test, don't expect to find out if you've got cancer or how your cholesterol is responding to medication. That kind of information requires interacting with a doctor and getting biopsies or blood tests – the old-school routine. What you will get, with 23andMe, for instance, is an estimated lifetime risk for 120 diseases including asthma, gallstones, rheumatoid arthritis, and scoliosis. If you so choose, you will also receive information on more lethal diseases like Alzheimer's or Parkinson's, which Google co-founder Sergey Brin discovered he had a 50 percent chance of developing by the age of 70. (He donated money to 23andMe, which was co-founded by his wife, Anne Wojcicki, to subsidize its Parkinson's research.) The panel also tests for 50 diseases that are caused by much less common gene mutations, like cystic fibrosis or sickle-cell anemia, and sensitivities to dozens of drugs.

"These tests give people a better idea of where they are and where they need to be," says San Diego-based cardiologist Samir Damani. "It's a probabilistic look at your health that is a critical component of an integrated approach to wellness."

Arguably, the genomic data that can make the biggest impact in your life concerns diseases that may have missed the older generations of your family or that you were unaware afflicted them. Take the venous thromboembolism that contributed to Zittrain's illness. This is the third most common cardiovascular disease, and a particular gene variant puts you at double the risk for it. This information can guide doctors in scenarios such as Zittrain's blood clot, but it can also encourage you to take more mundane precautionary measures, like trying to get an aisle seat on a plane to take regular walking breaks, and wearing compression socks to reduce the chances of developing a blood clot in your leg, which often requires heavy-duty blood-thinning drugs and can kill you.

Atrial fibrillation, the most common kind of irregular heartbeat, is another life-threatening, often hidden condition that can be reliably predicted. If the genomic panel reveals that you're at higher risk, there are no wonder drugs at your disposal yet, but you do have extra motivation to carefully manage your stress and blood-pressure levels.

Another aspect of these tests is in predicting how you'll react to everyday prescription drugs. A dirty little secret of modern medicine is that some drugs vary hugely in their effectiveness and toxicity, depending on an individual's genetic makeup. 23andMe provides a preliminary report on statin side effects, which can suggest that you may be at higher risk for painful and sometimes debilitating muscle damage experienced among some statin users. Both 23andMe and Pathway test genetic sensitivity for two commonly prescribed blood thinners, Coumadin and Plavix, both notoriously hard for doctors to get the dosages right. (Mistakes can be serious, sometimes lethally so.)

Where genomic tests fall short is in figuring out your risk for the most common life-threatening diseases, like coronary artery disease and type 2 diabetes, something that conventional medicine already does fairly well with simple blood pressure, blood sugar, and cholesterol tests. Because these conditions arise from a complex combination of genetic and lifestyle factors, the "bad" genes that might turn up on the genomics panel might increase your lifetime risk for one of these killers by only, say, 1.3 times the national average, a risk that your doctor might tell you is easily offset by a healthy diet and regular exercise. "If you're worried about type 2 diabetes and you're 50 pounds overweight," says Lawrence Brody, a top genetics researcher at the National Institutes of Health, "it would be crazy to fixate on that 1.3 figure. You've got to look at the whole picture."

Genes for the Gym

With the Fit Panel, Pathway has gone the farthest in creatively interpreting genomic data to make it practical, accessible, and even gym-ready. Starting with a pilot program planned for this fall at six Equinox gyms in the San Francisco Bay Area, Los Angeles, and Dallas, you can bring the results from the Pathway Fit Panel to a specially prepped Equinox trainer who will help you figure out the healthiest ways to eat and work out. It's a lively grab bag that looks into your genes for things like food cravings, the risk of having lower levels of various vitamins (A, B2, B6, B12, C, D, and E), and some common food sensitivities. Then there are the questions about the most effective fitness regimen: Are you likely, genetically speaking, to be the sort of person who readily puts on muscle from weight training, or, conversely, will aerobic endurance work efficiently tune up your metabolism? Odds are experience has already given you answers here, but some of the other tests may prove useful, like one that looks at your propensity for Achilles tendinopathy (which will make you want to start stretching your calves daily) or your body-mass response to exercise (which could give you a hint about the best strategy to shed those last 10 pounds).

The part of the Fit Panel that has attracted the most attention draws on genetics to personalize nutrition advice. The panel will, in theory, put to rest the controversy that has launched a host of diet books: Should you be on a low-fat, low-carb, or Mediterranean diet to stay healthy and lose weight?

For its part, Pathway cherry-picks 79 genetic markers that it matches against data from population studies. People with one genotype are more likely to have higher than average "good" HDL cholesterol when they eat less animal fat. If you share that genetic profile, it may be evidence that you would do best with a low-fat diet. Your genetic variations might instead match those in a population who eat a lot of the monounsaturated fats found in avocados and olive oil and tend to be thinner. In this case, your results will push you toward a Mediterranean diet.

How well does it work? There's no lab-tested research tracking how people actually do on their genetic diets. Pathway's rival in the diet market, Inherent Health, did persuade one Stanford researcher to analyze DNA from a large study that took a long-term look at the effectiveness of four common diets. The company reports that the subjects who were eating diets that matched their Inherent genetic type (Carb Reducer, Fat Trimmer, or Better Balance) did better than average. It's a start, and even skeptics in academia allow that these tests can be a great motivational tool for sticking to a diet.

Promises of Personal Genomics

Today, the full utility of personal genomics is rapidly growing as researchers build a menu of genetic tests that clue you in to ways to improve your everyday life that wouldn't occur to you if you didn't have your genetic data at your fingertips. For instance, both 23andMe and the Pathway Fit Panel include a genetic test for caffeine sensitivity that seems innocuous enough until you discover that your risk of heart attack increases by about 50 percent if you drink four cups of coffee a day (the average American drinks about three). A new set of tests from a small start-up offers a guide for fish consumption based on how your system handles mercury toxicity. And research on Alzheimer's, the sine qua non of bad-news genomics, is likely reaching the point where we can make self-preservational decisions about whether to play contact sports – if you have a particular genotype and lower your risk of head trauma, you may reduce the odds of Alzheimer's. "We've learned how to read the genome," says NIH's Lawrence Brody. "Now we're moving into the heavy lifting of learning how to use it to create action." With the genomic revolution at hand, your genes will tell you to do the right thing.