Maine Coon HCM testing explained: DNA test vs echo

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, and Maine Coons are a predisposed breed. It’s also the single most misunderstood item on a breeder’s health-testing sheet — because there are two different tests, they answer two different questions, and a breeder relying on only one of them is telling you far less than they think. Here’s how to read the results like someone who knows.

Two tests, two questions

The HCM-DNA test looks for a specific inherited mutation. In Maine Coons that’s the A31P mutation in the MYBPC3 gene — a gene coding for a heart-muscle protein. UC Davis’s Veterinary Genetics Laboratory describes it as autosomal recessive: cats with two copies are at significantly increased risk, while a single copy has not been shown to raise risk. It’s a cheek-swab test done once — the DNA never changes.

The echocardiogram (echo) is an ultrasound of the actual heart, performed and read by a veterinary cardiologist. Cornell’s Feline Health Center treats echocardiography as the gold standard for diagnosing HCM, and recommends at-risk cats be examined at least yearly, ideally by a cardiologist. It looks at the heart the cat has right now.

The difference matters: the DNA test asks “does this cat carry the known mutation?” The echo asks “is this cat’s heart actually thickening?” Those are not the same question.

Why DNA-clear is not a clear heart

Here’s the fact that changes how you shop: the DNA test only detects one known mutation, and a cat that tests negative can still develop it. Reviewing the published studies, UC Davis puts HCM incidence at 5.4% in Maine Coons negative for A31P and 5.4% in cats carrying it — and concludes plainly that “the MYBPC3-A31P mutation is not the sole cause of HCM in Maine Coons.” A longitudinal genotype–phenotype study of the A31P mutation found affected cats across genotypes — including cats that developed HCM while testing mutation-negative.

So a “DNA-clear” kitten can still develop HCM from a cause the DNA test can’t see. That’s not a reason to skip the DNA test — it’s a reason not to stop there. A DNA-clear result rules out one known cause; only the echo can look at the heart itself.

The reverse is also true: a cat carrying the mutation does not certainly develop the disease. Penetrance is incomplete. Which is exactly why breeders need the echo to see what’s actually happening, rather than reading a genotype like a verdict.

What a responsible breeder actually does

• Both tests, on the breeding cats — DNA to avoid knowingly doubling up on the mutation, and a cardiologist echo to confirm the hearts are currently clear.
• Echoes on a schedule, because they expire. A heart that echoed clear at two years can change. A responsible program re-echoes its breeding cats periodically; a single old echo is not a lifetime guarantee.
• Dated documents you can see — the DNA report from the lab, and the echo report with the cardiologist’s name and date.

“Vet checked” is not HCM testing. A routine wellness exam and a stethoscope do not detect early HCM — only an echo does. If a breeder says their lines are “heart healthy” but can’t show you a recent cardiologist echo, they’ve done the easy test and skipped the hard one.

Exactly what to ask

1. “Are both parents HCM-DNA tested? Can I see the reports?”
2. “Have both parents had a cardiologist echocardiogram — and how recent is it?”
3. “How often do you re-echo your breeding cats?”
4. “Which other screening do you run — SMA, PKD, hips?”

A breeder who welcomes those questions and hands over dated documents is showing you the two tests actually done. On TrueKitten, when a health document carries our verification badge, it means we authenticated that document and matched it to that cat by microchip — it is never a guarantee of the cat’s future health, which no test can promise. Understanding the two tests is what lets you read those documents yourself.

Sources: UC Davis VGL — Maine Coon HCM · Cornell Feline Health Center · Longitudinal genotype–phenotype study of A31P in Maine Coons