Man running up outdoor stairs
There’s been plenty of debate in recent years about heart health in endurance athletes. (Photo: Solskin/Getty)
Sweat Science

A New Theory on Sudden Cardiac Deaths in Young Athletes

The genes that make some people vulnerable to a fatal heart stoppage may be the same ones that give them an athletic edge, researchers suggest

Man running up outdoor stairs

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

There’s been plenty of debate in recent years about heart health in endurance athletes. The current evidence, as I see it, suggests that it’s very, very unlikely that years of training for marathons will eventually damage your heart. But there’s another angle to this issue that’s often ignored: young, seemingly healthy athletes who drop dead during marathons or basketball games or soccer matches.

For these young athletes, their deaths have nothing to do with years of accumulated wear and tear. Instead, the most common cause of death is hypertrophic cardiomyopathy, or HCM, a genetic condition leading to thickened and abnormal heart walls that are more susceptible to triggering fatal arrhythmias. Researchers now have a pretty good handle on how and why this happens (for more background, check out David Epstein’s classic 2007 piece for Sports Illustrated), but several mysteries remain.

A new paper in the journal Cardiology offers a novel hypothesis to explain two of these mysteries: why such a lethal genetic condition has remained so prevalent in the population, and why athletes in particular seem to be so susceptible. The paper is from a team at the University of Amsterdam, led by Sjoerd Verwijs, and it’s presented as a “hypothesis-generating scoping review”—another way of saying that this is a wacky idea they’ve been batting around, and they decided to comb through the existing literature to see if the evidence might back it up.

The wacky idea is this: Maybe the genes that cause cardiomyopathies (a group of related heart conditions, of which HCM is the most common) have positive effects as well as negative ones. Specifically, maybe the resulting changes to your heart initially give you a performance advantage before, in some people, reaching a point where they become potentially fatal.

Estimates of the prevalence of cardiomyopathy genes range from about one in every 500 people to one in 200. For a condition that causes people to drop dead, that’s surprisingly common. But if that condition makes you stronger or faster, it’s easier to see how it might have kept getting passed down from generation to generation among our ancestors. One comparison offered by Verwijs and his colleagues: sickle-cell anemia is a serious genetically driven health condition, but having one version of the gene confers protection against malaria, thus ensuring its continuing prevalence.

It’s not entirely clear whether athletes are more likely to have HCM than non-athletes. The researchers note that there’s an unusually high frequency of sudden cardiac deaths among young athletes, with particular clustering in basketball, soccer, and football. It may just be that non-athletes with mild HCM are more likely to get through life without triggering symptoms, since intense exercise and the stress of competition are thought to raise the risk of arrhythmia. But another possibility is that people with HCM have cardiac characteristics that make them slightly more likely to be good at sports and thus end up training and competing at a high level.

The evidence the researchers found is a long, long way short of proving anything about their theory, but it’s intriguing. There are some mouse studies that explore the effects of gene variants associated with various cardiomyopathies on athletic performance: one variant produces mice with faster running speed, and another produces mice who can run for longer distances and generate greater force with their heart muscles. In humans, cardiomyopathy genes were linked with higher VO2 max, greater VO2 max improvement with training, and faster marathon times (by the relatively subtle margin of 2:26:28 to 2:28:53 in a total of 140 highly trained runners).

You can come up with plausible explanations for why cardiomyopathy-linked genes might (initially, at least) be performance-enhancing. For example, the gene linked with VO2 max and marathon times is called TTN, which encodes a protein called titin that acts as a “molecular spring” giving elasticity to heart muscle. It’s possible that a genetic variant might give you a springier, more compliant heart that pumps blood more effectively, but also raises your risk of a dangerous cardiomyopathy.

When I called Martin Maron, a cardiologist who heads Tufts University’s Hypertrophic Cardiomyopathy Center and Research Institute, to get his take on the paper, he had three main points. First, it’s an interesting and novel idea. Second, the science to back it up at this point is somewhere between weak and nonexistent. And third, it’s not even close to being the most interesting debate about HCM these days. That honor, Maron said, goes to the debate about what should happen to promising young athletes diagnosed with HCM—and who gets to decide.

Maron pointed to the case of basketball player Jared Butler, who was reportedly first diagnosed with HCM three years ago before taking up a scholarship at Alabama. He then transferred to Baylor, presumably because Alabama wouldn’t let him play, where he was cleared to compete and led the team to a national title earlier this year. After declaring for the NBA draft, he was ruled ineligible to practice or play in the NBA until cleared by a three-physician Fitness-to-Play panel. He got approval to play in July, and was drafted by the Utah Jazz—in sharp contrast to a 1996 case in which the U.S. Court of Appeals for the Seventh Circuit sided with Northwestern University in preventing a recruit diagnosed with suspected HCM from playing.

These are tricky issues, and the risks involved are, at least for now, unquantifiable. But one thing everyone can agree on is that greater awareness of the condition can help people get diagnosed before catastrophe strikes. Butler is collaborating with the pharmaceutical company Bristol Myers Squibb on a publicity campaign, as the Salt Lake Tribune reports, with two key planks: If you’re related to someone with HCM, get tested; and if you feel unusual shortness of breath, dizziness, chest pains, or fainting spells during or after exercise, get tested. Whether or not Verwijs’s hypothesis pans out, it’s clear that being a competitive athlete, no matter young and fit you are, doesn’t protect you from cardiomyopathies.

For more Sweat Science, join me on Twitter and Facebook, sign up for the email newsletter, and check out my book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.

Lead Photo: Solskin/Getty