Polydactyl cats are cats that have extra toes on either their front and/or hind feet. The condition has been seen in many breeds of pedigree cat as well as non-pedigree cats.
Polydactyly is inherited as an autosomal dominant gene defect, sometimes with variable gene penetration. Recent work has shown that the defect is generally the same in cats as in humans. However, more than one gene may be involved and affected genes may vary between breeds.
The extra digits vary in number and also in structure from being small pieces of soft tissue, through to being complete functioning digits. In some cases the additional toes may not be fully functional and may not be connected properly to other bones – this can make them more susceptible to accidental injury.
In some situations, breeders have deliberately tried to perpetuate polydactyl cats (eg, in some lines of the the Maine Coon breed, and sometimes by developing a breed defined by the presence of polydactylism – eg, the American Polydactyl), but International Cat Care believe such deliberate breeding of a genetic mutation should be discouraged. While minimally harmful in most cases, there is no reason to deliberately breed cats with this defect for human gratification.