Playing sports is an excellent way for young people to stay active, strong and focused. But in rare cases, a young athlete collapses in the middle of a game and dies suddenly from cardiac arrest.

What causes this harrowing scenario, and how can you find out if you or your young athlete is predisposed to the condition that causes it?

A disease called hypertrophic cardiomyopathy is the most common cause of heart-related sudden death in people younger than 30. It’s also the most common cause of sudden death in all athletes. About 1 in 500 people have the disease, according to the Hypertrophic Cardiomyopathy Association. Around half those people have symptoms such as shortness of breath, chest pain and lightheadedness. Sometimes people have no symptoms at all and learn they have the condition only when they collapse.

“Often it’s underdiagnosed,” says Dr. Chintan Desai, a cardiovascular disease specialist at Northwestern Medicine Regional Medical Group in Illinois.

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On average, about 66 young athletes die from sudden cardiac causes each year in the United States, according to a 2009 issue of the journal Circulation. While the number of incidents is low, the deaths often draw public attention because athletes tend to be young and seemingly healthy, and they’re generally well-known in their communities.

The issue first became a public topic of discussion in 1976 when Owen Brown, star of the University of Maryland’s championship basketball team, died during a pickup basketball game and was later found to have hypertrophic cardiomyopathy. “It was a sentinel event that caused people to start to look at sudden cardiomyopathy deaths in young athletes,” says Dr. Edward Kasper, clinical director for cardiology at Johns Hopkins Hospital.

Hypertrophic cardiomyopathy causes the heart muscle to become abnormally thick and stiff so it cannot properly pump blood. As the disease progresses, it narrows the heart’s chambers, hindering blood flow. Sudden death during exercise happens because temporary stress causes the heart to race uncontrollably and beat erratically, stopping blood circulation.

Males are almost seven times as likely to develop the condition as females, according to a study published in The American Journal of Medicine in November 2016. It’s a genetic disease, usually passed down from parents to children. “You’re born with this mutation,” Kasper says. “Most people don’t develop it until around puberty or after 12 to 20 years old, generally.”

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If a parent or sibling has the disease, doctors recommend getting genetic tests to see if you have it, as well. But genetic testing doesn’t show the whole picture, because many people who have the mutations associated with the condition never develop signs of it, Kasper says. In those cases, tests such as an EKG or echocardiogram show the patients have normal hearts. “Just because I know this person has a gene mutation doesn’t mean I know what their course will be,” Kasper says.

In patients who have a mutation but no signs of the disease, doctors will assess on a case-by-case basis, but generally allow them to play sports with the recommendation of regular heart screenings to see if the condition develops. Patients should also keep an eye out for symptoms such as shortness of breath, chest pain and fainting.

Some doctors recommend EKG and other pre-approval diagnostic tests for all high school and college athletes, but the practice is controversial because of reasons including cost, access to the tests and false positive results. In the November 2016 issue of the Journal of the American College of Cardiology, the American College of Cardiology and the American Heart Association recommend that during a yearly physical, doctors perform a 14-point screening checklist for young athletes to evaluate their fitness for playing sports. Questions include whether the athlete has high blood pressure, chest pain or a relative under 50 with a heart condition.

If an athlete is found to have an enlarged heart, doctors will recommend the athlete stop competing altogether as a safety measure. “With a clear-cut case, they will be told they should not participate in intense competitive athletics,” Kasper says. “Everything with [the] exception of bowling and golf.”

Both Kasper and Desai say it’s difficult to deliver news about cardiomyopathy to a family. “It’s a tough conversation to have; some athletes think their livelihood depends on their sport,” Desai says. “We’ve had college athletes we had to stop from playing.”

Desai recalled several cases in which a young athlete’s heart was slightly enlarged, and it was unclear if it was due to extreme exercise — a condition called athlete’s heart that’s not considered dangerous — or if it was cardiomyopathy. In those instances, he performs several diagnostic tests, including a cardiac MRI. If it’s still unclear, he recommends a break from athletics. “Sometimes we say an athlete should abstain from competitive sports, and if it regresses in four to six months, they can go back to training,” Desai says. If not, they have to stop competing.

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In some cases, doctors implant a small defibrillator to help regulate the patient’s heartbeat. This works well for some people, but it’s controversial, Kasper says, because the defibrillator can break during contact sports, causing it to malfunction when needed. For patients with chest pain or shortness of breath from hypertrophic cardiomyopathy, doctors prescribe medications such as beta blockers and calcium channel blockers to help regulate heart beat and blood flow. Other treatments are surgery to thin out the thick walls of the heart or, ultimately, a heart transplant. “There are a lot of things we can do,” Kasper says.

He stresses that while some with the condition will die suddenly, the vast majority will not. “Most patients with hypertrophic cardiomyopathy will have normal life expectancy,” Kasper says.

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What to Know About Hypertrophic Cardiomyopathy originally appeared on usnews.com