The true polydactyly - commonly called mitten foot, mitten cat or thumb cat condition - is a congenital abnormality, genetically inherited as an autosomal dominant trait of the Pd gene with incomplete penetrance. This type of polydactyly is not life-threatening and usually not even debilitating to a cat. Some polydactyl kittens initially have more difficulty in learning to walk and climb than normal animals. However in some cases it appears to improve the dexterity of the animal. For example, a common variation of polydactyly with six toes on the front paws, with two opposing digits on each, (comparable in use to human thumbs) enables the cat to learn and perform feats of manual dexterity generally not observed in non-polydactyl cats, such as opening latches or catching objects with a single paw.
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 a 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 that will have to be euthanized. 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.
Although there is some controversy over whether the commonest variant of the trait originated as a mutation in New England or was brought there from England, there does seem to be agreement that it spread widely as a result of cats carried on ships originating in Boston, and the prevalence of polydactylism 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 especially value polydactyl cats 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.
Other nicknames include "boxers" or "boxing cats", "mitten cats", "thumb cats", "six-finger cats", "Boston Thumb Cats", "Cardi-cats" and "double-pawed cats" (a misnomer since there is a specific double paw condition).
American Polydactyl Cats are also being bred as a specific cat breed, with specific physical and behavioral characteristics in addition to extra digits. A particular strain native to Ithaca, New York, is known as the "Ithacats". The American Polydactyl is not to be confused with the pedigree Maine Coon polydactyl. The polydactyl form of the Maine Coon is being reinstated by some breeders. Thanatos Cattery, Inc. , a primary breeder of Ithacats, is a prolific and renowned breeder in the area. John Thanatos himself typically breeds the cats.
Polydactyly has also been observed in big cats.
A little bit extra: polydactyl cats have extra toes, often on all four feet. Here's what you should know about this charming characteristic.(Physiology)
Feb 01, 2006; Larry Houck, a cat owner from Harrisburg, Pennsylvania, has a neutered male cat with more than the normal five toes on his front...