June 09, 2023

What Exactly Is Genetic Testing… And Could It Change the Future of Medicine?

This piece originally appeared on katiecouric.com

In a new series, “The Exact Science Of,” we explore how genetic testing could impact your health.

You’ve probably heard of genetic testing. It’s used during pregnancy and to find long-lost relatives, though one of its most crucial uses when it comes to health might be determining whether you’re a carrier of a BRCA gene variant, which can increase your chances of developing certain cancers. But that’s just the tip of the iceberg when it comes to this technology’s capabilities.

How can we use genetic testing to help us learn even more about our own bodies, or to diagnose rare conditions that might otherwise remain a mystery? We called up an expert, Dr. Robert Steiner, a practicing physician specializing in Genetics and the Chief Medical Officer at PreventionGenetics, part of Exact Sciences, to explain. The PreventionGenetics lab tests for thousands of rare conditions, including Marfan Syndrome, hereditary cataracts, and even Alzheimer’s Disease. He told us what genetic panel tests can tell you about your health, how accurate they are, who’s eligible for one, and how these tests can change lives.

What is genetic testing?

This question is pretty complicated, but Dr. Steiner breaks it down this way: “Genetic testing is the sequencing of our DNA, which is the blueprint for who we are. It can tell us if we have a genetic issue that can potentially be treated, or whether we might develop an illness in the future. To do this, a sample is taken from a patient and then sent off to a lab where the DNA is extracted and then sequenced.”

How is a test done by a company like PreventionGenetics different from a profile you could get from a site like 23AndMe?

23andme and similar companies offer what’s called “direct to consumer” genetic testing. That means you can go online and order a genetic test without going through a healthcare provider. Since anyone can order one of these tests, they’re heavily regulated, and your results will only reveal a small sample of genetic information. This option may make sense for individuals who don’t suspect they have a genetic disease, but are curious to learn about their overall health.

On the other hand, a lab like PreventionGenetics can test for rare genetic diseases, but not just anyone can order these tests. As Dr. Steiner explains, “PreventionGenetics requires that a healthcare provider orders the test, so they’re generally ordering it for a patient who’s suspected of having a genetic disease. Our test offerings are broad and comprehensive: Essentially any known genetic condition that someone is suspected of having, we’re able to test for it.”

What should patients keep in mind before having a DNA test done?

There can be a personal and moral implication to some genetic tests, where results can impact a patient’s mental health. A good example of this is Alzheimer’s disease, which has no known cure. “With Alzheimer’s, you might be tested for a potentially devastating and untreatable condition before you have any symptoms,” explains Dr. Steiner. “Generally, you’d be required to go through genetic counseling to learn all the pros and cons about going through that sort of testing. But at the end of the day, if you and your provider agree a test like this is the right thing to do, we could conduct the test and share the results with your doctor.”

How accurate is genetic testing?

If the lab gives you a result that says you have a disease-causing variant in gene X, you can be 99.9 percent sure that result is accurate.

The challenge, says Dr. Steiner, is when you’re testing for a genetic disease and the result comes back as inconclusive. “For example,” he says, “if someone is exhibiting symptoms of cystic fibrosis (CF), we would assume that genetics are the cause of the disease. Since this is a recessive condition, you have to have two variants, and some of the variants are what we call ‘uncertain significance,’ meaning we can’t be sure those gene variants are causing the symptoms. So that’s not terribly satisfying, but it’s the nature of science these days.” While this result is technically accurate, it doesn’t always give the answer that a patient is hoping for.

On the other hand, symptoms that look like one thing might be genetically determined to be something else entirely. Dr. Steiner shares an example: “We had a sample come into the lab recently for a patient that had a few symptoms associated with CF, but the provider thought it was more likely that the patient had a very rare genetic lung disease. So we did the testing and sure enough, the chronic cough and respiratory infections were not caused by this rare lung disease — testing revealed this patient likely had CF. So we may find relatively common diseases that were not suspected by the doctors.”

How can genetic testing help determine your likelihood of developing certain cancers?

Hereditary cancers are relatively common, and geneticists can test for a link to these diseases. There are tests which can predict the likelihood that a patient will develop genetic breast, ovarian, or colon cancer at some point.

One of the tests PreventionGenetics offers is Riskguard, a specific panel that provides lots of useful information for patients with a strong family history of hereditary cancers. “The great thing about this test,” says Dr. Steiner, “is that the results are actionable. In other words, if you get a positive Riskguard result, there’s typically going to be something that can be done in advance. That might mean early screening, or surgery to prevent a disease from forming, like a prophylactic mastectomy to avoid breast cancer.”

Are there any other genetic tests I can get as an adult that could help diagnose a pre-existing issue?

Yes — in fact, there are a bunch. But some are more straightforward than others. For example, you can do genetic tests for the likelihood you’ll develop common issues like obesity and hereditary forms of cataracts, each of which will give you accurate results. Other conditions are a bit more complicated. Dr Steiner explains: “For a condition like chronic pancreatitis, we can test for it, but this becomes complicated since only some cases are due to a single gene disorder.”

There are also neurogenetic and hereditary heart diseases that can be accurately detected through genetic testing. One that you’ve probably never even heard of is Charcot-Marie-Tooth disease, which affects the motor and sensory nerves and causes abnormalities in the nerves that supply your feet, legs, hands, and arms. Others include Huntington’s disease, myotonic dystrophy (which causes progressive muscle weakness), spinocerebellar ataxia (a brain disorder which causes progressive problems with coordination usually impacting the eyes and hands), Long QT syndrome (a heart signaling disorder that can cause arrhythmias), and cardiomyopathy (a disease that makes it harder for the heart to pump blood to the rest of the body, and can result in heart failure). Knowing you have one of these conditions may help you take preventative measures to control future symptoms.

What’s a rare disease that genetic testing helped to diagnose and treat?

Dr. Steiner shares one of his favorite success stories: “We once dealt with a newborn who was deathly ill with seizures and the inability to feed. Nobody knew what was wrong, and the chemistry was showing up as seriously abnormal. So the doctor sent a sample to PreventionGenetics for testing using our Neonatal (NICU) crisis panel.”

The results came back in about a week, and they showed that the baby had a very rare genetic condition caused by a defect in vitamin metabolism. “At that point,” says Dr. Steiner, “the baby was comatose. The genetic test result led the treating doctor to conclude that the treatment simply required administering a vitamin. The symptoms were not at all classic for this disorder, so it had never occurred to doctors that this might be the cause. When the doctor got the result, she immediately administered a form of vitamin B. The seizures stopped, and the baby woke up and went home from the hospital in a few days. The baby’s condition dramatically improved, and I believe that diagnosis helped to save the baby’s life.”

What’s next in genetic testing?

Knowing what genetic testing is capable of, it’s a bit freaky to think about a future where, as sci-fi authors have suggested, you might be able to choose what color eyes your kid will have, or how tall they’ll be. Luckily, Dr. Steiner says that’s something he believes will never happen. “The genetics of something seemingly simple like eye color are actually quite complex and difficult to predict, and there are probably a thousand different genes that contribute to height. Characteristics that aren’t disease-causing are very difficult to determine,” he says. “Even if that’s something we could do, there’s a strong agreed-upon ethical prohibition against selecting for certain traits in infants and children. Geneticists really are focused on preventing and treating diseases, and we abide by strict guidelines outlined by genetic ethicists for where to draw the line on genetic testing.”

But Dr. Steiner is excited about the future of genetic testing. “I think in the not-too-distant future, everybody will have comprehensive genetic testing done in order to prepare healthcare providers for any future issues a patient might develop,” he explains. “So if that patient gets sick and it looks like there could be a genetic contribution, doctors can go right to an electronic health record, look at the DNA sequence, and determine if there might be a genetic cause for that condition.”

In other words, genetic testing helps us imagine a world where people can be saved from the grief and heartache of unexpected diagnoses. And that’s something for all of us to look forward to.