Polydactyl cat

A polydactyl cat is a cat with a congenital physical anomaly called polydactyly (or polydactylism, also known as hyperdactyly), 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.

The true polydactyly is a congenital abnormality, genetically inherited as an autosomal dominant trait of the ZRS cis element of the Pd gene with incomplete penetrance.

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. Jake, a Canadian polydactyl cat with 28 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. 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 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 disabled 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.

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Wikipedia