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Everything you need to know about genetic testing and personalized medicine

In 2015, the Obama White House committed $215 million to support efforts to develop personalized medicine.

What is genetic testing?

Your cells contain chromosomes made up of chemical strands called DNA, which carry genetic information. Those genes are recipes for proteins that give you the wide variety of traits that make you who you are: from the curl of your hair to the texture of your earwax to the color of your eyes.

Genetic tests look for changes or mutations in your DNA. They can tell you whether you have a genetic condition or are at risk of developing a disease.

Tests for specific genetic conditions have long been available from health care professionals. For example, a doctor might test for mutations in genes called BRCA-1 and BRCA-2, which are linked to breast and ovarian cancers, to understand if a patient is at a higher-than normal risk for these diseases.

But in recent years, a new generation of genetic testing products has removed the middleman and given patients direct access to a different kind of DNA test. With "direct-to-consumer" genetic testing, you can now pay a private company to sequence part of your genome and provide you with a wealth of information about your ancestry and your predisposition to various illnesses.

These tests haven't yet cleared regulatory approval by the Food and Drug Administration, but they have proven popular with consumers who argue that they empower patients with more information about their health. Critics (including the regulators) don't quite see it the same way for two main reasons: they think direct-to-consumer tests aren't as accurate as the ones ordered by your doctor, and they worry that patients get incomplete and uncontextualized information from them, leading to unnecessary worry and fear or ill-informed medical decisions.

What is personalized medicine?

Personalized medicine uses genetic testing to tailor medical treatments to the specific biology of individual patients.

Advocates say that this targeted approach to treatment is a safer and more effective way to practice medicine than the conventional "one size fits all" approach. However, critics argue that we don't yet understand enough about the human genome (and how it interacts with the environment and other factors) to routinely use genes as the basis for medical decisions.

Despite it being singled out as the future of medicine, Hank Greely at Stanford put it this way: "It's been the hot thing coming for almost 20 years." Writing in the New York Times, Mayo Clinic physician-researcher Michael Joyner called it a "moonshot" medical research project, summing up: "Unfortunately, precision medicine is unlikely to make most of us healthier."

Still, there are already several popular applications of personalized medicine.

One is for predictive testing of disease in someone who is at a high risk. For example, there are mutations of the BRCA-1 and BRCA-2 genes that can heighten a woman's risk of developing breast and/or ovarian cancers. If you have a history of these cancers in your family or you're from an ethnic group that's predisposed, your doctor might order a genetic test that would look for mutations of those specific genes.

Angelina Jolie

Angelina Jolie, who famously got a double mastectomy after discovery she carried genetic mutations that put her at a higher risk for breast cancer. (Getty Images)

If you test positive, you would then work with a physician and/or genetic counselor to decide how to proceed: you may opt for a preventive mastectomy (as Angelina Jolie famously did), or make lifestyle changes that mitigate your risk of cancer and get mammograms more frequently than other women who don't carry the mutation.

Also consider Lynch syndrome — an inherited illness linked to colorectal cancer. There are several genes associated with Lynch syndrome, and if you test positive, you might begin getting colonoscopies in your 20s rather than your 60s — a screening regime that is tailored to your particular genetic risk instead of the general population. Again, health care tailored to your genes.

The promise of pharmacogenomics

Another form of personalized medicine is pharmacogenomics, which uses genetics to predict an individual's response to a drug. Proponents say this is the future of pharmaceuticals — since a person's genetic make-up can impact how and whether they respond to medications. They argue that using genes to guide treatments would lead to more effective therapies.

With cystic fibrosis, for example, a drug a drug called ivacaftor (brand name Kalydeco) was recently approved by the Food and Drug Administration for about 4 percent of patients who have a particular genetic mutation that causes the deadly and chronic lung disease in them. It's the first drug to treat the genetic cause of CF — but only in people with the mutation.

Another promising area of pharmacogenomics has been cancer therapeutics. Cancer has its own DNA and genetic mutations, and there are some drugs that target those — as opposed to just giving a patient radiation that would not be as precise. In these cases, patients are tested for genetic variations and then prescribed therapies for their tumors. One example is Herceptin for the treatment of breast cancer in women with a gene known as HER2/neu. A doctor will test a breast-cancer patient to see if she is HER2/neu positive, and if she is, consider prescribing Herceptin as a treatment.

Still, there are big barriers here between the dream of pharmacogenomics and the reality. For the most part, the science of genetics just isn't refined enough to help most patients, and developing targeted therapies is hugely expensive and time-consuming.
For example, Bill Gardner at the Incidental Economist ran some numbers on the promising cystic fibrosis therapy: "It took 24 years and tens of millions of dollars to get from the discovery of the CFTR [the particular genetic mutation that causes CF in some people] to the FDA approval of a drug. Moreover, this drug was designed for a mutation found in only a small fraction of the population of an already rare disease."

Gardner noted that the drug costs about $300,000 per year, not only because of the manpower and years of research behind it, but because the market for the drug is small.

Even if they weren't so expensive and challenging, the Mayo's Joyner writes in the Times, "for widespread diseases like diabetes, heart disease and most cancers, no clear genetic story has emerged for a vast majority of cases." Easy to gather characteristics — like age, sex, and body weight — are still better predictors of Type 2 diabetes than any genetic test. For the risk of lung cancer, we may not have a genetic test or targeted therapy in mainstream medicine yet — but we do know smoking puts most people at a higher risk for early death and disease.

So as you can see, personalized medicine is the future, but getting targeted therapies and treatments into the hands of most Americans is pretty far afield.

What are the limitations of genetic testing?

There was a time when the scientific community believed that one gene caused one trait in humans. While there are associations between certain genetic variations and particular diseases, we now know that whether a person actually develops a disease is more often than not influenced by a lot more than just genes.

Your risk of developing a particular disease can be determined by environmental and lifestyle factors as much as it can by your genetics. (The study of the interplay between genes and these other factors is called epigenetics.) There is also usually more than just one gene that brings about a certain trait or disease; often times multiple genes work in concert to do so. Science is only just in its infancy when it comes to understanding how all these factors come together and influence human health.

That means that the results of many genetic tests about disease risks need to be properly interpreted. While your genome might reveal a predisposition to a particular medical condition, there's almost always a lot of uncertainty about your medical future and how much your DNA will drive your health.

How do conventional genetic tests differ from direct-to-consumer testing products?

A genetic test ordered up by your doctor is usually used for a specific purpose: to find out whether a person is a carrier of a genetic disease based on his or her family history, for example, or to test whether a newborn infant has particular mutations in their proteins that are likely to lead to disease. (See here for the CDC's take on the evidence for these.)

Direct-to-consumer tests, on the other hand, are less specific. They usually look at a large sample of your genome for a number of health conditions instead of testing specific genes to answer one question. Before a Food and Drug Administration crackdown, 23andMe would give consumers a risk assessment for their chances of developing more than 250 diseases based on the sample of DNA that they examined. They also marketed these tests as a way to improve their customers' health.
One example of how the two kinds of genetics tests differ is in testing for the BRCA1/2 genes and their relationship to breast and ovarian cancers. A test ordered by your doctor would be prompted by family history of the disease or the fact that your ethnicity puts you at a higher risk. The test would screen for many mutations of the genes to see if you have any that might lead to cancer. Direct-to-consumer services, such as 23andMe, only screened for a few of the most common mutations of the gene. So they'd give their customers a read-out of risk based on that incomplete information, potentially resulting in a false negative.

Tim Caulfield, a health law professor who examined many of those promises about personal genetics testing in his book The Cure for Everything, notes that there's little evidence that getting a personal genome test improves users' health.

"There are a few studies that suggest 23andMe might lead to better drug compliance but the data are weak," he explains. "Why would 23andMe lead to any behavior change? People don't change their behavior based on what they see on the scale, and that's way more predictive of their future health than almost anything else."

What's more, personal genetic test results sometimes aren't quite accurate and different companies turn up contradictory results for the same person. The Centers for Disease Control and Prevention warns consumers that the risk assessments for the most common diseases are usually incomplete since actual risk is driven by multiple genes and their interaction with the environment, which these tests can't reflect.

Still, advocates of 23andMe and personal testing say any information about the genome is better than nothing at all. They point out that direct-to-consumer genetic tests don't pose direct safety risks to patients, making the argument for regulating them weaker than for many conventional medical devices. And they argue that the FDA's burdensome approval process will slow the pace of innovation in this nascent industry, potentially hurting patients in the long run.

Finally, they contend that the vast datasets being accumulated by companies like 23andMe could help researchers learn about the correlation between genetic characteristics and health outcomes, improving the effectiveness of genetic testing in the future.

23andMe also says consumers can be empowered by this data and that it gives patients more health information to act upon.

Why did 23andMe get into trouble with the FDA?

After four years of negotiations between the Food and Drug Administration and 23andMe, the FDA sent a warning letter to 23andMe in November 2013 asking the company to immediately discontinue marketing their health-related genetic tests.

The FDA said 23andMe failed to provide evidence that their tests were "analytically or clinically validated." The warning letter was also prompted by 23andMe's alleged failure to communicate with the FDA for several months during regulatory negotiations and 23andMe's marketing of its health services, in spite of the FDA's requests that they shouldn't do so.

23andMe is currently making regulatory submissions to the FDA. While awaiting a decision, the company won't be offering its health interpretations, however users can download raw data from their genetic tests and ancestry and genealogy services are still available.

Can the results of genetic tests impact my insurance?

In 2008, the Genetic Information Nondiscrimination Act became law. The law protects consumers from the potentially damaging impact of genetic test results on their insurance policy or employment.

But the legislation has limits. As this article points out, loopholes include the fact that the law doesn't cover life insurance, long-term care insurance or disability insurance. What's more, health insurers aren't necessarily barred from using genetic test results to determine insurance payments. The law also doesn't apply in companies with fewer than 15 workers, nor does it cover people who get benefits from the Veterans Health Administration or Indian Health Service.

How much do genetics tests cost?

The cost of genetic testing can range from less than $100 into the thousands. There are several websites from which you can order a genetic test. 23andMe is probably the most well known, and the test costs $99. Other services include Family Tree DNA (between $99-$199), AncestryDNA ($79), and National Geographic's Genographic Project ($159).

As for tests ordered through your physician, there are services such as Pathway Genomics or Navigenics. Because they don't deal directly with the consumer, costs aren't disclosed but they reportedly run into the thousands.

If your doctor has a particular concern about a health issue (ie. a genetic predisposition to breast cancer) and wants to order a specific test, that may be covered by your health insurance.

You didn't answer my question!

This is very much a work in progress. It will continue to be updated as events unfold, new research gets published, and fresh questions emerge.

So if you have additional questions or comments or quibbles or complaints, send a note to Julia Belluz at


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