PERSONALIZED MEDICINE

What Is Genetic Testing?

By Stephanie Watson @WatsonWriter
 | 
July 27, 2016

What can a look inside your genome tell you about your disease risks?

What if you could look into a crystal ball and see your medical future? And what if that mystical ball revealed that you were at risk for heart disease, Alzheimer’s disease, or breast cancer? What would you do? Would you even want to know?

A glimpse inside your medical future is possible today, thanks to the scientists of the Human Genome Project. In April 2003, they finalized sequencing of the 3 billion base pairs and roughly 25,000 genes that make up the entire human genome — all the instructions that make us who we are. Through this blueprint, scientists have been able to identify thousands of genetic variations that cause disease, and develop genetic tests to determine our susceptibility to those diseases. Today, more than 1,000 tests are available to help us both learn our risk for medical conditions and treat them once they start.

 

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How your doctor uses genetic tests

Genes are a series of code — stretches of DNA that carry the instructions for producing all the proteins your body needs to function. Your genes determine whether you have blond hair and blue eyes, and if you’re tall or short. Aberrations in the genetic code, known as mutations, influence your risk for diseases.

With a tiny sample of your blood, hair, or skin, your doctor or other healthcare provider can look for specific changes to individual genes or stretches of DNA. These tests can diagnose a genetic disease you already have, predict whether you might develop a particular disease in the future, or find out if you carry a disease gene that you could pass on to your children. For example, you might learn whether you carry one of the two BRCA gene mutations, which dramatically increase the risk for breast and ovarian cancers. Or, if you’re planning to have children, you could get tested for cystic fibrosis or Tay Sachs disease, conditions that are passed down through families. Gene tests can also help guide treatment for cancers and other diseases by predicting how well your body will respond to certain medications.

Direct-to-consumer tests

Once gene analysis technology became available, it wasn’t long before a number of companies recognized the moneymaking potential of such tests and started marketing them directly to consumers through TV commercials and over the internet. Many of these companies claim the information they provide can help consumers make smarter, more informed choices about their health.

With direct-to-consumer tests, you typically swab the inside of your cheek to collect a tissue sample, which you then send in to the company for analysis. For a price that ranges from a few hundred to a few thousand dollars (which insurance will generally not cover), the company then sends you a snapshot of your genetic disease risk. Future Genetics’ test assesses your risk for 28 common health conditions, including Alzheimer’s disease, obesity, breast cancer, and age-related macular degeneration. Some companies, including Sure Genomics, will sequence your entire genome. Others, like 23andMe and Family Tree DNA, let you explore your genetic ancestry, seeing who in the world shares your DNA, and which genetic variations you have in common with people of a similar heritage.

 

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Benefits and risks of direct-to-consumer genetic tests

Knowing that you’re at higher risk for a health condition such as heart disease or cancer could make you more proactive about your health. In theory, this knowledge might encourage you to improve your diet or start an exercise program, for example. Yet in reality, consumers don’t seem to take action based on their test results. When researchers at the University of Cambridge analyzed 18 studies on consumers who were informed of their genetic risks, they discovered the knowledge had virtually no influence on people’s health behaviors. “Expectations have been high that giving people information about their genetic risk will empower them to change their behavior – to eat more healthily or to stop smoking, for example – but we have found no evidence that this is the case,” said study author Theresa Marteau, PhD.

Another issue with commercial gene tests is that many haven’t been proven or validated by scientific studies. Without research, there is no way to confirm these tests accurately detect gene variants, or that the gene variants they analyze accurately predict disease. In 2013, the Food and Drug Administration (FDA) ordered 23andMe to stop marketing its Personal Genome Service to consumers because it hadn’t been proven safe and effective. The agency pointed out the risks of consumers acting on the results of an improperly validated test. “For instance, if the BRCA-related risk assessment for breast or ovarian cancer reports a false positive, it could lead a patient to undergo prophylactic surgery, chemoprevention, intensive screening, or other morbidity-inducing actions, while a false negative could result in a failure to recognize an actual risk that may exist,” the FDA wrote. (In 2015, the FDA allowed 23andMe to begin marketing a more rigorously validated gene carrier test for the inherited disorder Bloom syndrome.)

Acting on gene test results without medical guidance adds another layer of concern. Genetic tests require complex analysis and more information than a DNA sample alone can provide – such as your personal and family medical history. Without an experienced doctor or genetic counselor to interpret and help you understand the implications of your test results, you might make assumptions that aren’t necessarily true, and take steps that could prove risky.

Even when tests have been properly validated, they can yield unclear results. While certain conditions, like Huntington’s disease, stem from a mutation in a single gene, most – like heart disease, cancer, and diabetes – are caused by a complex interaction of multiple genes plus environmental factors. So a genetic test generally can’t tell you definitively that you’ll get a disease – only that you’re at increased risk. Misunderstanding your real risk can lead to worry and further testing that may be unnecessary or even harmful.

Privacy is another concern with genetic tests. What if your results were to get out to your insurance company, or your employer? The American College of Medical Genetics and Genomics Board of Directors recommends approaching direct-to-consumer tests with caution. “Prior to testing, the consumer should be informed as to who will have access to test results, what processes are in place to protect these results, what will happen to the DNA sample once testing is complete, and whether the test results may have any personal or family-related implications for life, long-term care, or disability insurance,” they wrote in a 2016 position statement.

 

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Updated:

July 27, 2016

Reviewed By:

Christopher Nystuen, MD, MBA

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