Every year, headlines surface about a young, seemingly healthy athlete — sometimes a teenager, sometimes a college or professional player — who collapses on the field and doesn't get back up. In a striking number of these cases, the underlying cause turns out to be the same condition: hypertrophic cardiomyopathy, an inherited thickening of the heart muscle that can exist for years without a single warning sign.
What's Actually Happening in the Heart Muscle
Hypertrophic cardiomyopathy (HCM) causes the heart's muscle wall — usually the left ventricle — to thicken abnormally, without an external cause like high blood pressure or valve disease. That thickened muscle can obstruct blood flow out of the heart, disrupt the heart's electrical system, and create the conditions for a sudden, dangerous arrhythmia. It's a structural problem with an electrical consequence, which is part of why it's so dangerous: the heart can look and feel functional right up until an arrhythmia strikes.
The condition is caused by mutations in genes that encode proteins in the sarcomere — the basic contracting unit of muscle tissue. Two genes account for the majority of identified genetic cases:
- MYBPC3 (myosin binding protein C) — the single most frequently implicated gene in most populations studied, encoding a protein that regulates how heart muscle fibers contract and relax.
- MYH7 (beta-myosin heavy chain) — one of the core motor proteins of the sarcomere itself, and historically the first HCM gene identified.
Together with several other sarcomere genes, MYBPC3 and MYH7 account for up to roughly 60% of cases where a genetic cause is identified — though a meaningful share of HCM cases still have no identifiable genetic cause using current testing.
The Autosomal Dominant Pattern — And Why That Matters for Families
HCM is typically inherited in an autosomal dominant pattern, meaning a single copy of a pathogenic variant from one parent is enough to cause the condition — each child of an affected parent has roughly a 50% chance of inheriting it. But HCM also shows "incomplete penetrance," meaning not everyone who carries a pathogenic variant develops the same degree of disease, or develops it at the same age. Some carriers remain asymptomatic their whole lives; others develop severe disease in their teens or twenties.
| Without genetic testing | With genetic testing |
|---|---|
| Diagnosis usually relies on symptoms or an abnormal echocardiogram — often only ordered after a cardiac event | A pathogenic variant can be identified before any structural changes appear on imaging |
| Family members are only screened if someone is already diagnosed, and often only with periodic imaging | Relatives can be tested directly for the specific familial variant, resolving their risk with one test |
| Athletic screening relies on physical exam and ECG, which can miss early or mild cases | A genetic result adds a layer of information physical screening alone cannot provide |
| Risk stratification for sudden death is based on imaging and symptoms alone | Specific variants can inform more individualized risk assessment alongside clinical findings |
What Happens After a Positive Result
A pathogenic MYBPC3 or MYH7 finding doesn't mean a hard stop on physical activity for everyone — management is individualized, developed with a cardiologist, and can include:
- Regular cardiac imaging (echocardiogram, sometimes cardiac MRI) to monitor for structural changes over time, even before symptoms appear.
- Activity guidance tailored to the individual's specific risk profile, since not every carrier needs to avoid competitive sports — but some genuinely do, and that distinction matters enormously.
- Cascade testing for first-degree relatives, since a confirmed familial variant means each parent, sibling, and child has a coin-flip chance of carrying the same risk.
- Medication or, in higher-risk cases, an implantable defibrillator to manage arrhythmia risk directly.
See What Your Heart Genes Say Before They Have to Speak Up
Dante Labs' whole genome sequencing reads MYBPC3, MYH7, and the broader panel of sarcomere genes linked to hypertrophic cardiomyopathy.
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