By Kate Hughes
When it comes to dogs, there is a lot of genetic variation. They come in all shapes, sizes, and colors, and it is kind of mind boggling to consider that Chihuahuas and Great Danes are both members of the same species. When it comes to cats, however, there is much less variation—house cats are all unmistakably genetically related. This means that when a cat exhibits a genetic anomaly, it stands out all the more. Throughout the years, veterinarians and cat owners alike have noticed weird and interesting genetic variations in their patients and pets. Here are just a few of the more common anomalies seen in cats.
Perhaps the most common genetic anomaly in cats is polydactyly, a condition that results in extra toes. It’s more common to find these toes on the front paws, and a polydactyl cat may have more than just one extra toe, she could have an entire set.
Dr. Margret Casal, associate professor of medical genetics at the University of Pennsylvania’s School of Veterinary Medicine in Philadelphia, has seen many forms of polydactyly in her feline patients. “I’ve seen cats with as many as five extra toes,” she describes. “And I’ve seen cats with paws that look like mittens. There are all kinds of variations.”
Polydactyly can be a dominant genetic trait, so if a cat has it, it’s quite likely that at least some of that cat’s offspring will as well. It’s also unrelated to a cat’s health, so if your cat has extra toes, they’re typically just a fun, quirky feature.
Pet owners with a polydactyl cat should just keep an eye on those extra toes when clipping nails to ensure there aren’t any hidden claws that may become overgrown. They should also be aware that sometimes the extra toes are not attached to any bones. When that is the case, your veterinarian may recommend that they be amputated. “Because they’re not attached, the cat can’t retract his claw and may become stuck or even accidentally tear off the extra appendage,” says Dr. Krista M. Vernaleken, medical director at Bulger Veterinary Hospital in North Andover, Massachusetts.
To understand why male tortoiseshell cats (cats with black and orange fur) are a genetic anomaly, let’s start with a quick genetics lesson. Like male humans, male cats have an X chromosome and a Y chromosome. Female cats have two X chromosomes. When it comes to fur color, both orange and black are only carried on the X chromosome and each X chromosome can only carry one color. As a result, male cats, which only have one X chromosome, can be black or orange, but not both at the same time.
“This means that male cats that carry tortoiseshell coloring have a chromosomal abnormality,” explains Casal, who estimates that male tortoiseshell cats occur at a rate of about 1 in 50,000 animals. According to Casal, there are two genetic variants that result in a male tortoiseshell. The first is the cat has an extra X chromosome, so instead of XY, the cat is XXY. There are also “mosaic” cats, which have XX constitutions in some cells and XY in others.
While they don’t typically have health problems, male tortoiseshell cats are almost always sterile and cannot reproduce.
Like humans, cats can have vitiligo, a condition that causes the loss of skin pigmentation. In cats, it looks like white spots start appearing in the cat’s fur. “You’ll just see that your cat’s fur starts turning white,” Casal says. “It doesn’t hurt the cat at all, it just looks interesting.”
Casal also notes that some cats might not be what they initially appear, when it comes to fur color. “For example, if you have a white cat with green or dark gold eyes and black eyelids, that’s not a white cat. That’s actually, genetically speaking, a black cat with a huge white spot. Or, if you have a white cat with really light blue eyes, that’s not a white cat, but actually an albino.”
Manx cats are cats born with short, stubby tails, or even no tails at all. This anomaly can be a little tricky to identify if you don’t know your cat’s entire medical history, as cats without tails may not have been born that way. Typically, cats who have lost their tails will have some scar tissue to indicate that their tails were previously not quite so short.
While some Manx cats are healthy, Dr. Ann Hohenhaus, a staff doctor at NYC’s Animal Medical Center who specializes in small animal internal medicine and oncology, says that the anomaly may cause issues with a cat’s spine and back legs. “The mutation causing the loss or shortening of the tail affects the spine and spinal cord, resulting in a form of spina bifida,” she explains. Spina bifida is a birth defect where the spinal cord does not develop properly. “In turn, this could cause back leg abnormalities, and they may also have issues with controlling urination and defecation.”
Scottish Fold cats, a breed with ears that bend forward, have gained popularity over the past few years, perhaps in part due to the fact that Taylor Swift’s two kitties are of this breed. However, while these cats are cute, pet owners should be wary of if and how they breed Scottish Fold cats. The ears of Scottish Fold cats fold because of a cartilage defect. The defect is a dominant genetic trait, and Casal warns that breeding two cats with this same defect together will lead to a quarter of the kittens receiving a “double dose” of that fold ear gene. “This leads to joint issues and scoliosis, among other problems,” she describes. As such, you should always breed a fold ear cat, with a non-fold ear cat.
Another ear-related anomaly found in cats is much rarer: Cats with four ears. “Well, it’s not really four ears, it just looks like they have four,” Casal says. “They really have two, but then they have a little appendage that looks like an ear near the real one.” She says there are no health issues associated with this anomaly, it’s just a cute, purely aesthetic, genetic mutation.
Undoubtedly, Munchkin cats are adorable. They have short little legs, kind of like a cat version of a Corgi. However, owners should note that these cats are, for all intents and purposes, cats with dwarfism. Munchkins are bred to exhibit these short legs, and, according to Hohenhaus, there is a lot of controversy regarding this mutation’s impact on health. “There is some disagreement between Munchkin breeders and other feline experts regarding the overall healthiness of these animals,” she says. Due to the length of their legs, Munchkins can’t run, jump, or climb as well as their long-legged counterparts and are prone to arthritis and other health problems.
One fairly uncommon genetic anomaly is when a cat is born with two faces. Known as “Janus Cats” (for the Roman god Janus, who is often depicted with two faces), these cats may look frightening, but, depending on the severity of their defect, can live a long life. The Janus cat that currently holds the record, Frank and Louie (sometimes known as Frankenlouie), lived to be 15 years old.
There are several anomalies that, like Munchkin cats, are associated with specific breeds. While some are breed hallmarks, like curly fur in Rex cats, others are subtler and require a practiced eye to identify. For example, many Siamese cats often exhibit pendular nystagmus, which causes their eyes to look like they’re quivering. “I’ve had clients not recognize when their cats have this issue,” Hohenhaus says. “But it’s fairly common in Siamese cats. Owners have to be observant if they want to catch some of these anomalies."