The Manx Syndrome Myth: The Myths & The Truth

Last reviewed October 2026

A note on this article

This piece was written for the American Manx Club and has been on this site since the 1990s. It is reproduced exactly as written, because its central argument has held up: “Manx syndrome” is loosely defined, freely over-applied, and a great many tailless cats are perfectly sound. Work published since bears that out — roughly four in five short-tailed Manx have no additional abnormality at all.

On two specific points, however, the genetics has moved and the article has not:

“Homozygous rumpy is a meaningless term.” It is not. Taillessness traces to the T (brachyury) gene, and a 2013 study found no cat carrying two mutant copies — consistent with two copies being lethal in early development. That is also the practical reason two tailless cats are not usually bred together.
“Spina bifida is not related to the Manx gene.” The Merck Veterinary Manual records sacrocaudal dysgenesis in Manx cats as an autosomal dominant trait, and notes that spina bifida can occur alongside it.

The sources for both are listed on Manx Breed Facts & Health. We have left this article alone rather than editing the authors’ words, and would rather show you both than quietly pick one.

by Richard Cullen & Sherman Ross, BS Eng.Phy., MS Ed, President, American Manx Club.

Technical Consultant: Karen Commings for Manx Cats: Complete Pet Owners Manual, (Barons, 1999) & Joanne Mattern for The Manx Cat, (Capstone Press, 2002)

Manx Syndrome is a subject of great concern to all lovers of the Manx breed. It is fraught with emotion, steeped in misinformation, and perpetuated by the ignorant. Perhaps some light can be shed on this subject by comparing some of the myths of Manx Syndrome to the actual truth.

Myth

Truth

Manx Syndrome is any of several birth defects related to the Manx gene and afflicting the Manx breed.

There is no common definition of what Manx Syndrome is. All of the conditions commonly called Manx Syndrome occur in other breeds of cat and other species of animals. Therefore these conditions cannot be linked to the Manx gene.

Manx have shorter backs than other cats because they have fewer vertebrae. This leads to severe neurological problems.

The Manx gene does not impact the spine above the pelvis. The gene causes the cat to have fewer caudal vertebrae causing a shorter tail. Manx have the same number of vertebrae in the upper spine as any other cat.

Spina Bifida is a Manx condition.

Spina Bifida is a condition found in all animal species that have spines. It is caused by the neural tube that forms the spine not closing completely in the fetus. It is not related to the Manx gene. It has been shown to be a combination of genetic and environmental factors. In humans the environmental trigger is insufficient folic acid during pregnancy. The environmental factor in cats is not known. Some Veterinarians have bred Manx with Spina Bifida in their genes and related it as a Manx Syndrome. This is really bad science. But unfortunately, since it was published in a Veterinary Journal, many vets believe this.

Urinary and fecal incontinence is a part of Manx Syndrome. It is due to insufficient nerve endings.

Incontinence occurs in all breeds of cats; it is not related to the Manx gene. There is no diagnostic for missing nerves except extremely careful and complete autopsy. Incontinence is related to spina bifida.

Not all spina bifidas are visible externally. In all probability, most cases of incontinence in the Manx are related to spina bifida.

The homozygous rumpy is an automatic lethal, and is never born.

The Manx gene for taillessness is a variable-expression gene. This type of gene is also called an incomplete dominant. The gene is always present, but always variable. It acts very much like the white spotting or bicolor gene. Homozygous rumpy is in fact a meaningless term.

It is necessary to use tailed Manx in the breeding to prevent Manx Syndrome.

This is demonstrably untrue. A good MANX breeder can point to sound healthy Manx without tails in the pedigree for six generations. A much more important consideration is the length of the upper spine. Breeding excessively for shorter bodies causes the individual vertebrae in the upper spine to be shorter. Bred to the extreme, this causes problems in any breed.