· 2 min read
What does an HCM 'negative' result actually mean?
Negative, carrier and affected are three different things, and two of them get confused constantly. How to read an A31P result without over- or under-reacting.
Anna Bronsky
Co-Founder of TrueKitten, a verified Maine Coon marketplace
Short answer: “negative” means the cat has no copies of the A31P mutation — written N/N. It does not mean the cat is guaranteed free of heart disease, and it says nothing about any other cause. UC Davis describes N/N cats as “not predicted to be at increased risk” — a careful phrase that is doing real work.
The three results, in plain terms
An A31P report comes back as one of three genotypes:
| Result | Written | What it means |
|---|---|---|
| Negative / clear | N/N | No copies. Cannot pass the mutation on. |
| Carrier / heterozygous | N/HCMmc | One copy. 1.8× the risk, and passes it to half its offspring. |
| Homozygous | HCMmc/HCMmc | Two copies. 18× the risk, highest risk of sudden cardiac death. |
The word that trips people up
In many genetic conditions, “carrier” means healthy-but-passes-it-on. Here it does not. A31P is autosomal dominant with incomplete penetrance — so a single copy raises the cat’s own risk, and UC Davis notes such cats “may still develop HCM.”
That is why a carrier result is a breeding decision, not a shrug. And it is why “our lines are clear” is a claim worth seeing paperwork for.
What negative does not cover
A negative result speaks only to A31P. UC Davis’s own review of the literature puts HCM incidence at 5.4% both with and without the mutation and states the mutation “is not the sole cause.” An N/N cat still needs its heart looked at — see why a DNA-clear cat still needs an echo.
Reading a real result
Check three things on the document: the cat’s name and microchip, the lab, and the genotype in the lab’s own notation. A screenshot of the word “clear” in a message is not a result. A registry- or lab-issued document naming the cat is.
If the paperwork does not name the individual cat, it is not evidence about that cat — which is the same principle behind what a verified breeder badge actually means.
Keep reading
Yes. UC Davis puts HCM incidence at 5.4% in Maine Coons without the A31P mutation and 5.4% in cats with it — the DNA test cannot see the heart.
An echocardiogram is a snapshot, not a certificate. Why breeding cats are rescreened on a schedule, and how to tell whether a result is still meaningful.
Spinal muscular atrophy sounds alarming and is easy to screen out. What the SMA test detects, what an affected cat's life looks like, and why carriers are fine.
