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There has been a lot of debate in recent years about heart health in endurance athletes. Current evidence, in my opinion, suggests that it’s very, very unlikely that years of training for marathons will end up damaging your heart. But there is another angle to this problem that is often overlooked: apparently healthy young athletes who drop dead during marathon Where basketball games Where football matches.
For these young athletes, their passing has 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 likely to trigger fatal arrhythmias. Researchers now have a pretty good idea of ​​how and why this happens (for more information, see David Epstein’s 2007 classic piece for Illustrated sports), but several mysteries remain.
A new article in the journal Cardiology offers a new hypothesis to explain two of these mysteries: why such a deadly genetic disease has remained so prevalent in the population, and why athletes in particular seem to be so susceptible. The article comes from a team at the University of Amsterdam, led by Sjoerd Verwijs, and it is billed as a “speculative scoping review” – another way of saying it is a wacky idea they championed, and they decided to comb through the existing literature to see if the evidence could back it up.
The crazy idea is this: maybe the genes that cause cardiomyopathies (a group of related heart diseases, of which HCM is the most common) have positive as well as negative effects. Specifically, maybe the resulting changes in your heart initially give you a performance advantage before, in some people, they reach a point where they become potentially fatal.
Estimates of the prevalence of cardiomyopathy genes range from about one in 500 to one in 200 people. For a disease that kills people, this is surprisingly common. But if this condition makes you stronger or faster, it is easier to see how it could have continued to be passed down from generation to generation among our ancestors. A comparison offered by Verwijs and colleagues: Sickle cell anemia is a serious health problem of genetic origin, but having one version of the gene confers protection against malaria, thus ensuring its continued prevalence.
It is not entirely clear whether athletes are more likely to have HCM than non-athletes. Researchers note that there is an unusually high frequency of sudden cardiac death in young athletes, with particular clustering in basketball, soccer, and soccer. It may simply be that non-athletes with mild HCM are more likely to go through life without triggering symptoms, as intense exercise and competitive stress are believed to increase the risk of arrhythmia. But another possibility is that people with HCM have heart 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 falls a long way from proving anything about their theory, but it is intriguing. Some mouse studies explore the effects of genetic variants associated with various cardiomyopathies on athletic performance: one variant produces mice with a faster running speed, and another produces mice that can run longer distances and generate increased speed. greater strength with their heart muscles. In humans, cardiomyopathy genes were linked to higher VO2 max, greater improvement in VO2 max with training, and faster marathon times (by the relatively subtle margin of 2:26: 28 at 2:28:53 out of a total of 140 highly trained runners).
You can find plausible explanations why genes linked to cardiomyopathy might (at first, at least) improve performance. For example, the gene related to VO2 max and marathon times is called TTN, which encodes a protein called titin which acts as a “molecular spring” giving elasticity to the heart muscle. It’s possible that a genetic variant will give you a more elastic, compliant heart that pumps blood more efficiently, but also increases your risk for dangerous cardiomyopathy.
When I called Martin Maron, a cardiologist who runs Tufts University Hypertrophic Cardiomyopathy Center and Research Institute, to get his point of view on paper, he had three main points. First of all, it’s an interesting and new idea. Second, the science to back it up at this point is somewhere between weak and non-existent. And third, it’s not even close to being the most interesting debate on HCM these days. That honor, Maron said, goes to the debate about what should happen to promising young athletes diagnosed with HCM – and who needs to decide.
Maron brought up the case of basketball player Jared Butler, who was would have first diagnosed with HCM three years ago before taking a scholarship in Alabama. He was then transferred to Baylor, likely 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 himself for the NBA Draft, he was declared ineligible to practice or play in the NBA until cleared by a Fitness-to-Play panel of three doctors. He got clearance to play in July and was drafted by the Utah Jazz, in stark contrast to a 1996 affair in which the United States Court of Appeals for the Seventh Circuit sided with Northwestern University to prevent a rookie diagnosed with suspected HCM from playing.
These are delicate questions and the risks involved are, at least for now, unquantifiable. But one thing everyone can agree on is that greater awareness of the disease can help people be diagnosed before disaster strikes. Butler is collaborating with pharmaceutical company Bristol Myers Squibb on an advertising campaign, as the Salt Lake Tribune reports, with two key elements: if you are related to someone with HCM, get tested; and if you experience unusual shortness of breath, dizziness, chest pain, or fainting during or after exercise, get tested. Whether or not Verwijs’ hypothesis comes true, it is clear that being a competitive athlete, no matter how young and fit you are, does not protect you from cardiomyopathies.
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