The exact frequency of polydactylism in cats may depend on the breed, with some domestic cat breeds, such as the Maine coon, boasting a greater occurrence of extra-toed cats than other breeds; overall, however, this is a relatively common condition, and it is totally harmless for the cat who is born with extra toes. The word 'polydactyl' means 'many toes,' and the term refers to the fact that polydactyl cats are born with more than the standard 18 toes. This is technically a genetic mutation, but it is not an issue or a burden in and of itself.
Though polydactylism is usually a benign condition, it can be caused or accompanied by some other genetic mutations that pose problems for cats. For example, some polydactyl cats also have a condition known as feline radial hypoplasia, which can also cause problems with the cat's forelegs. For most cats, though, polydactylism simply means that they have some extra digits on their paws. There have been some famous polydactyl cats in history, including President Theodore Roosevelt's pet cat Slippers, which was one of the first pet cats ever to live in the White House. The American author Ernest Hemingway was particularly fond of these cats, which is why some people refer to polydactyls as Hemingway cats.