Blarney Manx

Manx cat knowledge since 1970

Manx Breed Facts & Health

The genetics, the tail types, and what the evidence says about Manx syndrome

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The Manx is the only cat breed most people can name from across a room, and the thing they are naming is an absence. That absence has attracted more folklore than any other feature in the cat fancy — some of it affectionate, some of it alarming, and a good deal of it wrong in both directions. What follows is what the evidence actually supports.

1. What Makes the Manx Unique?

The Manx comes from the Isle of Man, where an ordinary mutation in an island population had nowhere to disperse to and became the local norm. The cats are muscular and round-bodied, with the hind legs longer than the front, and they are known for attaching themselves firmly to one or two people.

The longhaired Manx is called the Cymric, and some registries judge it as a breed of its own.

2. Tail Types: More Than Just “Tailless”

Breeders and registries sort Manx into four groups by what the tail does:

  • Rumpy: completely tailless, often with a dimple where the tail would be.
  • Rumpy riser: a bump or slight rise of cartilage at the end of the spine.
  • Stumpy: a short, partial tail, often stiff or kinked.
  • Longy: a full or nearly full tail, on a cat with Manx body type.

These are descriptions, not separate conditions. A single litter can contain all four.

3. The Gene Behind the Tail

Taillessness in the Manx traces to the T gene, also called TBXT or brachyury, which directs how the body axis forms in the embryo. A 2013 study sequenced this gene across Manx lines in the United States and on the Isle of Man and found four different mutations in it — three single-base deletions and one duplication-deletion — each of which shortens the resulting protein. The mutations were largely specific to particular family lines, and 95% of the short-tailed cats studied carried exactly one copy.

One copy is the whole story. The working copy of the gene cannot quite do the job alone, and the tail comes out short — a mechanism called haploinsufficiency, which is why the same mutation produces anything from a rumpy to a longy.

Why two tailless cats are not usually bred together

No cat in that study carried two mutant copies, and none has been found since. The straightforward reading is that an embryo inheriting two copies does not develop far enough to be born. That is the practical reason most breeding programmes pair a tailless cat with a tailed one: not because a tailed parent cures anything, but because two tailless parents risk a quarter of each litter simply never arriving.

A DNA test for the Manx variants exists, through the feline genetics laboratory at the University of Missouri.

4. Manx Syndrome: What It Is, and What It Is Not

“Manx syndrome” is not a diagnosis a laboratory can return. It is an umbrella people throw over several different problems, which is exactly why it causes so much argument. The condition underneath it has a proper name: sacrocaudal dysgenesis, the incomplete formation of the sacral and tail vertebrae and the nerves that run with them. The Merck Veterinary Manual records that in Manx cats this is inherited as an autosomal dominant trait, and that spina bifida can occur alongside it.

Where it occurs, it can show as:

  • urinary or faecal incontinence, or chronic constipation
  • weakness or an odd gait in the hind legs
  • fused or malformed vertebrae at the base of the spine

The important number is this: in the 2013 study, about 20% of short-tailed Manx had at least one additional congenital abnormality, most often in rumpies. Four out of five did not.

So both of the usual stories are wrong. The Manx is not a breed of sick cats, and signs tend to appear early — by around four months — rather than lying in wait. But it is not a breed without a known, inherited risk either, and a breeder who tells you otherwise is not being straight with you.

Where this site disagrees with itself

Our own The Manx Syndrome Myth, written by Richard Cullen and Sherman Ross of the American Manx Club, argues that spina bifida is unrelated to the Manx gene and that “homozygous rumpy” is a meaningless term. Current veterinary genetics does not support either point. We have kept their article as they wrote it, because it is part of this site’s history and because its central argument — that the syndrome is loosely defined and freely over-applied — has held up well. That page carries a note explaining the difference.

5. How to Care for a Manx

  • Watch the kitten. Problems that are going to appear usually do so in the first few months. Litter-box trouble that never resolves is worth a vet’s opinion rather than patience.
  • Make the litter box easy to enter. A low side matters to any cat whose back end is not quite right.
  • Keep the weight down. Less load on a short spine and on the hocks.
  • Be careful at the base of the spine. Risers and stumpies in particular can be tender there; do not press or pull.

Most Manx need none of this beyond ordinary good sense. They are active, agile cats who will out-jump the expectations of anyone who assumes a tail is required for balance.

6. Sources

This page was written by a breeder, not a veterinarian, and checked against the sources above. It is not a substitute for your own vet, and a reviewer from the breed council or a veterinary geneticist would improve it further.

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