Hypertrophic Cardiomyopathy (HCM): The Silent Killer Explained#

If you own a Maine Coon, these three letters should terrify you: HCM.

Hypertrophic Cardiomyopathy is the most common heart disease in cats, and unfortunately, it loves our breed. It is a genetic condition that causes the walls of the heart (specifically the left ventricle) to thicken. As the walls get thicker, the heart chamber gets smaller. The heart has to work harder to pump blood, eventually leading to heart failure or sudden blood clots (Saddle Thrombus).

The scariest part? It is often silent. A cat can look perfectly healthy, play fetch, and eat well, right up until the moment they collapse.

Here is what you need to know about the gene, the scan, and the reality of the disease.

The Genetics: The A31P Mutation#

In 2005, researchers identified a specific genetic mutation in Maine Coons linked to HCM, known as MYBPC3-A31P.

This discovery changed breeding forever. We can now test for this specific gene.

Negative (N/N): The cat does not carry the known mutation.
Heterozygous (N/A): The cat has one copy. They might develop the disease and can pass it on.
Homozygous (A/A): The cat has two copies. They are at very high risk of developing severe HCM early in life.

The Catch: This test is not a guarantee. There are likely other mutations we haven’t discovered yet. A cat can test “Negative” for the gene and still get HCM. That is why Echocardiograms are essential.

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The Gold Standard: The Echocardiogram#

A genetic test tells you the risk. An echocardiogram (ultrasound of the heart) tells you the reality.

Responsible breeders have their breeding cats scanned by a Board Certified Veterinary Cardiologist every 12-18 months.

What they look for: They measure the thickness of the heart wall.
The Diagnosis: If the wall is thicker than 6mm, it is usually diagnosed as HCM.

As an owner, you should ask your breeder for proof of the parents’ most recent scans, not just their DNA results.

Symptoms: What to Watch For#

Because cats hide illness, symptoms often only appear when the heart is already failing (CHF).

Rapid Breathing: More than 30 breaths per minute while sleeping.
Lethargy: Not playing as long as usual.
Panting: Cats should never pant like dogs unless extremely stressed or overheated. Open-mouth breathing after mild play is a red flag.
Paralysis: If your cat suddenly screams and cannot move their back legs, this is a Saddle Thrombus (blood clot). Rush to the ER immediately.

Living with HCM#

If your cat is diagnosed, it is not an immediate death sentence. Many cats live for years with medication.

Beta Blockers (Atenolol): Slow the heart rate to reduce strain.
Blood Thinners (Plavix): Prevent clots.
Diuretics (Lasix): Clear fluid from the lungs if heart failure begins.

Conclusion#

HCM is the dragon that stalks the Maine Coon breed. We cannot kill it yet, but with DNA testing and regular heart scans, we can see it coming. Knowledge is your only shield.

Resources & Further Reading#

NC State Veterinary Hospital. (n.d.). Genetics of Feline HCM.
EveryCat Health Foundation. (2022). Update on Feline Cardiomyopathy.