A polydactyl cat is a cat with a congenital physical anomaly called polydactyly (or polydactylism, also known as hyperdactyly), a type of cat body-type genetic mutation that causes the cat to be born with more than the usual number of toes on one or more of its paws. Cats with this genetically inherited trait are most commonly found along the East Coast of North America (in the United States and Canada) and in South West England and Wales.
Normal cats have a total of 18 toes, with five toes on each front paw and four toes on each hind paw; polydactyl cats may have as many as eight digits on their front and/or hind paws. Tiger, a Canadian polydactyl cat with 27 toes, was recognised by Guinness World Records as having the highest number of toes on a cat. Various combinations of anywhere from four to seven toes per paw are common, and the number of toes on either the front or rear paws is typically the same. Polydactyly is most commonly found on the front paws only, it is rare for a cat to have polydactyl hind paws only, and polydactyly of all four paws is even less common.
The nickname "double-pawed cat" is a misnomer since there is a specific double paw condition, although this condition may be interrelated with polydactyly.
Feline radial hypoplasia (see squitten) is a mimic of polydactyly and is considered a severe condition. Radial hypoplasia may cause the formation of extra jointed toes, but it is not a result of the Pd gene normally associated with polydactyls. It thus does not cause the "mitten cat" or "thumb cat" condition where the extra toes occur separated from the normal ones just like a dewclaw, usually associated with an additional pad which makes them look like an underdeveloped foot sticking out near the base of the normal toes. Rather, radial hypoplasia-related extra toes are immediately adjacent to the normal ones, giving the cat overly large, flat feet — colloquially known as "patty feet" or "hamburger feet". Though this looks less serious than true polydactyly (as the feet appear "normal" apart from having one or two extra toes), breeding such cats will eventually result in severely crippled offspring. Cats used in polydactyl breeding programs can be screened by x-ray for indicators of radial hypoplasia, and cats suspected to have radial hypoplasia should not be used for breeding.
The condition seems to be most commonly found in cats along the East Coast of North America (in the United States and Canada) and in South West England, Wales and Kingston-upon-Hull. Polydactyl cats have been extremely popular as ship's cats. Although there is some controversy over whether the most common variant of the trait originated as a mutation in New England or was brought there from Britain, there seems to be agreement that it spread widely as a result of cats carried on ships originating in Boston, Massachusetts, and the prevalence of polydactyly among the cat population of various ports correlates with the dates when they first established trade with Boston. Contributing to the spread of polydactyl cats by this means, sailors were long known to value polydactyl cats especially for their extraordinary climbing and hunting abilities as an aid in controlling shipboard rodents. Some sailors also considered them to be extremely good luck when at sea.
Genetic work studying the DNA basis of the condition however indicates that many different mutations can all lead to polydactyly and since samples from the UK and USA were shown to possess different mutations it seems likely that these cats have originated multiple times independently, rather than spreading from a single origin.
Nobel Prize-winning author Ernest Hemingway was a famous aficionado of polydactyl cats, after being first given a six-toed cat by a ship's captain. Upon Hemingway's death in 1961, his former home in Key West, Florida, became a museum and a home for his cats, and it currently houses approximately fifty descendants of his cats (about half of which are polydactyl). Because of his love for these animals, polydactyl cats are sometimes referred to as "Hemingway Cats".
Nicknames for polydactyl cats include "conch cats", "boxing cats", "mitten cats", "mitten-foot cats", "snowshoe cats", "thumb cats", "six-fingered cats", "Cardi-cats", and "Hemingway cats". Two specific breeds recognized by some but not all cat fancier clubs are the American Polydactyl and Maine Coon Polydactyl, and named regional populations include the Boston thumb cat, Cardi-cat, Ithacat, and Vermont snowshoe cat.
American Polydactyl cats are bred as a specific cat breed, with specific physical and behavioral characteristics in addition to extra digits.
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