Polydactyly in Cats
Dr. Dawn Ruben
Kittens are usually born with five toes on each forepaw and four toes on each back paw. Occasionally, though, a "special" kitten is born – one with more digits than normal. This condition is referred to as polydactyly (paw-lee-dak-till-lee), which means "many fingers." Cats with this condition are commonly called mitten foot, mitten cat or thumb cat.
What are Polydactyl Cats?
Polydactyly is an inherited trait that is not uncommon and may have arisen from a genetic mutation. Polydactyly occurs in various forms, and it is thought that several genes and several methods of inheritance may be involved. In some cases the gene is dominant, which means that at least half of all offspring from a polydactyl cat will be polydactyl. Offspring receive one half of their genes from their mother and one half from their father. If one parent has only one polydactyl gene, that gene will be passed on to only half the offspring. If a parent carries both polydactyl genes, all offspring will be polydactyl, whether the other parent is polydactyl or not.
Some forms of polydactyly are thought to be recessive, meaning that the kitten must have both polydactyl genes from the mother and father in order to be polydactyl. In other forms, polydactyly is thought to be incompletely dominant, meaning that the gene is expressed at different levels. Some cats may have just one or two extra toes, while others may have multiple toes on every paw.
A polydactyl cat is easy to recognize. Polydactyly always affects the forepaws, so most cats just have extra toes on their front feet. But a few may have extra toes on the back feet, too. Rear paw polydactyly does not occur without forepaw polydactyly. The number of toes can vary on each foot or can be the same. Most often, a polydactyl cat have one or two extra toes on each front paw, usually arising from the thumb area. Some cats have opposable toes and can use them as thumbs, doing some amazing things like opening doors and picking up objects.
An Uncommon Form
Most common forms of polydactyly affect only the paws and do not harm the cat in any way. Unfortunately, a devastating deformity, known as radial hypoplasia, has recently been associated with a form of polydactyly. This has caused an increased interest in determining the exact mode of inheritance of the polydactyl gene in order to prevent this specific deformity.
In radial hypoplasia, a genetic mutation results in a lack of development of the radius, one of the long bones in the forearm, along with extra toes. These cats have significant abnormalities in their fore legs and unfortunately are being bred intentionally. They are known as twisty cats and pixie-bobs. These cats do not move like normal cats; instead, they hop around on their hind legs much like a kangaroo. If they do use all fours, they use their front elbows as a means of movement or balance. In order to differentiate between cats with radial hypoplasia or the harmless form of polydactyly, X-rays are needed to tell if the radius is normal or deformed.
History of Polydactyly
The exact history of the polydactyl trait is unknown, but it has likely been around for centuries. It was first scientifically described in 1868, and it has been found in cats all over the world including the United States, Great Britain, Nova Scotia, Prince Edward Island and Asia. This mutation has even been reported in leopards.
In the Unites States, the largest population of polydactyl cats is found in Boston, Mass. Some believe that cats brought to the United States by English Puritans may have been the first to develop the mutation in the 17th century. The offspring of these cats may have then traveled to other parts of the world on ships, as sailors believed that polydactyl cats were lucky and were superior mousers, and they carried the cats with them during their travels. This is the likely reason why some ports in the United States and Great Britain have a higher incidence of polydactyl cats that other regions of the same area.
To date, the greatest number of toes found on a cat is 32. This cat, born in 1974, had eight toes on each paw. However, there is some dispute whether this cat was actually polydactyl or had a different condition known as double-paw, in which the cat has two paws on each leg. Unlike polydactyly, this is a developmental defect and not inherited.
Polydactyl cats have been known by many different names. Some of these include mitten cats, boxers, boxing cats, thumb cats, six-finger cats and Hemingway cats. The Hemingway name comes from the colony of polydactyl cats previously owned by the writer Ernest Hemingway. It is said that Hemingway adored cats and had about 50 of them at his home in Key West, Florida. A ship captain had given him a six-toed cat that bred with other cats on the island and resulted in his polydactyl colony, which still thrives today.
Special Care and Concerns
Polydactyl cats require some extra care. Their claws need to be kept trimmed since they are prone to overgrowth and can potentially curl around and grow into the toe pad.
An additional concern is that sometimes the nail beds of two toes can be fused together at birth. This results in a claw that can also be fused, leading to the superclaw syndrome. These claws are thicker than normal claws and may grow in an abnormal position. The thick twisted claws can catch easily on things and can even inflict serious damage if not kept trimmed. Surgical removal is often the best solution.
Intentionally breeding cats to produce polydactyly kittens is strongly discouraged. This is not an uncommon trait and there are plenty of polydactyly cats sitting in shelters waiting for homes. Although these kittens appear cute with their excessive toes, there can be complications and the drive to produce kittens with more and more toes will only result in additional mutations and cats that may eventually have difficulty walking.
For the most part, polydactyl cats make excellent pets and the abnormality doesn't harm them in any way. It just makes them a little more special than they already are.