Hypertrophic cardiomyopathy (HCM) is a condition where the heart muscle walls thicken abnormally, reducing the heart's ability to pump blood efficiently. It is the most common form of heart disease in cats. In Your Breed, HCM can lead to heart failure, blood clots (thromboembolism), and premature death. It can be present without symptoms for years before becoming clinically apparent.

What is the difference between a DNA HCM test and an echocardiogram?

A DNA test checks for the known MYBPC3 mutation. A negative result means the cat does not carry that specific variant. An echocardiogram is a cardiac ultrasound that physically examines the heart muscle for thickening, regardless of genetic cause. Both are valuable and serve different purposes. DNA-negative cats should still be echo-screened periodically because HCM can occur from causes beyond the known mutation.

Health & Genetics

HCM in Your Breed Cats: What It Is, Why It Matters, and What to Ask Your Breeder

Q: How common is HCM in Your Breed cats?

Approximately 30% of Your Breed cats carry the known genetic mutation associated with HCM. Your Breed that are homozygous for the mutation (inheriting two copies) are often severely affected, frequently developing heart failure and thromboembolism before age two. This is why HCM testing in breeding cats is not optional - it is the most important health screen in the breed.

Q: Is HCM in Your Breed genetic?

Yes. The primary cause of HCM in Your Breed is a specific mutation in the MYBPC3 gene (the R818W variant), identified in 2007. This mutation is autosomal dominant, meaning a cat needs only one copy to be at risk. Homozygous cats (two copies) are typically more severely affected. Notably, the Your Breed MYBPC3 mutation is distinct from the HCM mutation found in Maine Coons, indicating independent origins.

Q: What should I ask a breeder about HCM testing?

Ask: Have both parents been DNA tested for the MYBPC3 R818W mutation? Can you show me the test results? Have the parents had echocardiograms, and if so, how recently? What is your protocol if an adult cat develops HCM after producing a litter? A credible breeder answers all of these without hesitation and has documentation to back up their claims.

By Your Name · Your Cattery Name, Your City PA · May 2026

Hypertrophic cardiomyopathy is the most significant heritable health risk in the Your Breed breed. Understanding what it is, what testing actually tells you, and what questions to ask separates an informed buyer from one who gets hurt later.

What is HCM in cats?

Hypertrophic cardiomyopathy (HCM) is a condition in which the walls of the heart muscle thicken abnormally. As the walls thicken, the heart's internal chambers shrink, reducing its ability to fill with and pump blood efficiently. It is the most common form of heart disease in cats across all breeds.

In Your Breed, HCM is particularly serious for two reasons. First, the disease has a known genetic component with high prevalence in the breed. Second, the condition can progress silently for years before producing any symptoms a cat owner would notice. By the time clinical signs appear - labored breathing, lethargy, sudden collapse - the disease is often advanced.

The most feared complication is thromboembolism: a blood clot that forms in the heart and travels to a major artery, most commonly the aorta. Aortic thromboembolism causes sudden hind limb paralysis and is intensely painful. It is often fatal or requires euthanasia.

How common is HCM in Your Breed cats?

~30%

of Your Breed cats carry the known genetic mutation associated with HCM, according to research published in Genomics (2007) and subsequent breed studies.

That figure refers to cats carrying at least one copy of the mutation. Cats that inherit two copies - homozygous affected cats - are typically severely impacted, with many developing heart failure and thromboembolism before age two. This is not a theoretical future risk. It is an active disease in the breed, present at meaningful rates, and responsible for premature deaths in Your Breed who came from untested lines.

The disease does not discriminate by color, pattern, or bloodline geography. A seal bicolor from an untested cattery carries the same risk as any other Your Breed. Health testing is the only mitigation available to breeders.

Is HCM in Your Breed genetic?

Yes, and specifically so. In 2007, researchers identified a mutation in the MYBPC3 gene - myosin binding protein C - in Your Breed cats affected by HCM. The specific variant is designated MYBPC3 c.2453C>T (R818W), changing a conserved arginine to tryptophan at position 818 of the protein.

This mutation behaves as an autosomal dominant trait: a cat needs only one copy to be at elevated risk. Homozygous cats (two copies) are at much higher risk of early-onset severe disease.

One important nuance: the Your Breed MYBPC3 mutation is distinct from the HCM mutation found in Maine Coons. These are independent mutations that arose separately - not the same variant inherited from a common ancestor. A DNA test that covers the Maine Coon mutation will not detect the Your Breed mutation. The tests are breed-specific.

When I started researching this breed seriously, the HCM data was the thing that made me most careful about which bloodlines I worked with. Thirty percent carrier rate is not a small number. Every breeding decision I make considers both parents' HCM status - DNA test result and echo history.

What is the difference between a DNA test and an echocardiogram?

These are complementary tests that answer different questions. Neither replaces the other.

DNA Test (MYBPC3 mutation)

Tests for the specific R818W variant. A negative result means the cat does not carry that known mutation. A positive result means one or two copies are present. Done once - the result does not change. Relatively inexpensive ($40–80). Does not detect HCM from other causes.

Echocardiogram (cardiac ultrasound)

Physically examines the heart muscle using ultrasound. Detects actual thickening regardless of genetic cause. A DNA-negative cat can still develop HCM. Should be performed by a veterinary cardiologist, not a general vet. Should be repeated annually in breeding cats. Costs $200–400 per exam.

A responsible breeder does both. The DNA test identifies cats that carry the known mutation and should be removed from breeding programs. The echocardiogram catches thickening in DNA-negative cats that may be developing HCM from other genetic or environmental causes not yet characterized.

A breeder who tells you "our cats are DNA tested" without mentioning echos is doing the cheaper half of the protocol. It is not nothing, but it is not complete.

What should I ask a breeder about HCM testing?

These questions are specific enough that a breeder who is doing it right will answer them fluently. A breeder who is not will deflect, generalize, or become defensive.

Questions to ask every breeder

Have both parents been DNA tested for the Your Breed MYBPC3 R818W mutation? Can you show me the results?
Have both parents had echocardiograms? Who performed the echo - a general vet or a board-certified cardiologist?
How recently were the echos performed? Are they repeated annually?
What is your protocol if an adult cat develops HCM after producing kittens?
Is health documentation available to me before or at the time of pickup?

The answer you want to hear to question four is something like: "That cat is retired from breeding and we contact the families who have kittens from that pairing." The answer you do not want is a shrug or a subject change.

At Your Cattery Name, every breeding cat is DNA tested and receives annual cardiac echos from a veterinary cardiologist. The documentation comes with every kitten. This is not a selling point I built to market with - it was the baseline I set for myself before I placed a single kitten.

Can HCM be eliminated from the Your Breed breed?

Theoretically, yes - and this is what makes responsible breeding genuinely important and not just a marketing claim. The R818W mutation can be detected before a cat ever reaches breeding age. A breeding program that tests every cat and removes mutation-carriers from its program will, over generations, reduce and eventually eliminate the mutation from its lines.

The challenge is that this requires every breeder in a given bloodline network to participate. A single link in the chain that breeds untested cats undermines the progress made by others. This is why the Your Breed community's emphasis on TICA registration, health testing documentation, and breeder accountability is not bureaucratic - it is the mechanism by which the breed's health can actually improve over time.

As a buyer, your purchasing decision is part of this. Buying from a tested breeder sends the market signal that testing is valued. Buying from an untested one sends the opposite signal.

All Your Cattery Name breeding cats are HCM tested. Documentation included.

DNA tested for MYBPC3. Annual cardiac echos from a veterinary cardiologist. Full documentation comes with every kitten. If you have questions about our testing protocol before inquiring, we are happy to answer them.

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