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A full article on the various types and causes of polydactyly in cats can be found at Polydactyl Cats. Only a summary appears here.

The normal cat's front paw has 4 toes and one dewclaw (rudimentary toe or thumb not reaching the ground) making 5 toes in total. The back paw has 4 toes, giving a total of 18 toes. A polydactyl has one, two or more extra toes on one or more feet. There are different forms of polydactyly caused by a variety of genes that affect the foot in different ways. Some result in extra toes, others give extra dew-claws or turn the dew-claw from a rudimentary toe into a proper toe. The most common form is pre-axial polydactyl (mitten foot) where the extra toe(s) is on the thumb side of the foot. This is a simple autosomal dominant gene (not linked to gender, the cat only needs one copy of the gene for the effect to show) with no adverse side-effects. Usually only the front feet are affected, but sometimes the cat’s hind feet have extra toes as well. In Victorian times (mid-to-late 19th century), polydactyl cats were considered very lucky, especially by sailors, which explains the high incidence of such cats on the east coast of the United States. As well as being said to give better grip on board ships, polydactyly is claimed to help the cat in walking across snow - natural snowshoes.

A more damaging form affects the leg as well as the foot and is called "triphalangeal pollex-radial hypoplasia" (Twisty Cat mutation). This gives the thumb (pollex) an extra joint and 3 bones (tri-phalangeal) instead of 2, making it resemble a human finger rather than a rudimentary dew-claw. The triphalangeal thumb may be duplicated giving two thumbs. The toe next to it may also be duplicated. In its mild form, only the paw is affected and the only way to tell it apart from regular polydactylism is through X-ray to see whether the dew-claw has become a toe with extra bones (radial hypoplasia trait) or whether it is still a dew-claw (regular polydactyly). Its severe form produces radial hypoplasia (underdevelopment of the main forearm bone) or radial aplasia (complete absence of the main forearm bone) also known as radial agenesis ("main forearm bone not created") or simply as the Twisty Cat mutation.

Cats with radial hypoplasia (RH) have greatly shortened forelegs but normal length hind legs. They often sit upright on their haunches looking like a rabbit or squirrel. Their shortened forelimbs may be too short to use for walking so the cat must hop like a rabbit or kangaroo. The habit of sitting upright results in reports of "squittens" (squirrel-kitten hybrids).

The record number of toes found on a cat is 32 (8 on each paw) reported in October 1974. This was a male cat called "Mickey Mouse" owned by Mrs Renee Delgade of Westlake Village, California, USA. This cat may have had double-paws where each paw is actually 2 fused mirror image paws. This condition is seen in humans where there is a central thumb with four fingers either side of it (making a natural baseball catcher's glove!). There have been reports of a cat where all 4 paws are doubled. When the cat "sat to attention" it appeared to have 8 paws in a row. There are other reports of double-paws where the paw splits into two lobes; each lobe having 3 or 4 toes. During early development, the tip of the limb-buds fork to produce 2 mirror-image paws which may be set at right angles to each other (the photo is an artist impression only).

A female cat named "Triple" owned by Mr and Mrs Bertram Bobnock of Iron River, Michigan, USA in 1976, had 30 toes, but these are arranged on 5 legs and 6 paws! The back left leg has 2 complete lower leg extensions from the hock down, and one of those lower legs had 2 paws.  This is either due to the conjoined twin condition or possibly a birth defect which caused the growing tip of the limb bud to split into two and each part of the fork continued to develop into a limb. It would have forked twice, once as it got to the hock and one side would have forked again when it began to grow the paw. A pure-bred Siamese named "Big Foot" (see photo) and owned by Miss Joan Conerly of Wauchula, Florida, USA in 1978, had 26 toes (7 on each front paw, 6 on each back paw). His mother had 22 toes, his sister had 22 toes and a brother had 24 toes showing it to be an inherited trait.

In May 2002 Jennifer Beierle wrote about a litter of kittens whose total of toes exceeds that of Big Foot and his litter-mates. Her non-polydactyl cat got pregnant by an unknown tomcat and produced 10 kittens. Seven were polydactyls. Two kittens had 26 toes, two had 23 toes, two had 22, one had 21, and two kittens had the normal 18 toes. This includes one kitten with 7-toed double-paws in front and 6 toes on hind paws and one kitten with double dewclaws on the hind paws (which do not normally have dewclaws at all). Photos of some of these kittens' paws can be seen at Polydactyl Cats along with photos of other polydactyls and other paw oddities.

There are several reports of cats with 28 toes (the current record), but currently none that exceed this number. A 2003 report of a cat with 32 toes at an American rescue shelter has not been verified, photos suggest it is more likely to be 22 toes.

Syndactyly (hypodactyly) or split-foot is the opposite of polydactyly. Instead of having additional toes, the cat's forefeet (rarely the hind feet) have two toes giving it the appearance of a crab or lobster claw. In humans, the condition is sometimes known as "lobster-hand". The other digits have either been suppressed altogether or each of the cat's toes is made up of two or more fused digits. A paper by A G Searle (in "Annals of Eugenics" Vol. 17, Part 4, pp. 279-283, 1953) discussed the lobster-claw condition in cats; Searle noted that the anomaly was usually inherited as a dominant, and had suggested that the right side was often more severely affected than the left.

Syndactyly is rarer than polydactyly so I was interested to receive details of a cat with 4 affected paws. Each paw resembles a crab's pincer (hence the common name of "Lobster Claw Syndrome"), having only 2 toes which are semi-opposable. The cat even uses them as pincers to hold toys and small objects. The toes are apparently oriented one facing upwards and one facing downwards (i.e. a degree of twisting). Syndactyly varies from webbed toes to fused digits. The fused digits can be simple with the digits connected only by skin, or it can be complicated with the bones, tissues and claws fused. It occurs when the cells between each toe do not die during embryo development and the toes do not separate (these cells are normally programmed to die during digit formation).

Like polydactyly, the condition rarely causes problems so long as the claws are kept clipped. The cat can still run and climb. The only time I have seen a lobster-clawed cat was with a feral cat in a trap-neuter-release program. This may not have caused problems to the cat in the wild (on a farm), but it caused problems in temporary captivity as the claws kept getting caught on the wire mesh. The actual claws were slightly overgrown due to problems with stropping them. In pet cats this can easily be rectified by frequent claw clipping.

Where the two toes are made of fused digits, the claws may form superclaws in the same way as described earlier. There is also the possibility that the cleft between the toes extends further than is normal into the paw itself. Small objects, thorns etc may become trapped between the toes. If the toes splay apart e.g. when the cat has jumped down from a high platform, there is the small chance that the claws will spread apart under its weight and the skin between them may tear. These problems are not common and cats with split foot rarely suffer any real disability.

In May 2005, Stephanie Rubeck of Newark, Ohio, sent this picture of her 4 week old kitten "Faith" who has syndactyly of the left front paw. The vet refused to see the kitten until she reached 6 weeks old on the grounds that a defective kitten would be rejected by the mother and not survive that long. Syndactyly is a minor (cosmetic) defect that does not affect suckling or threaten long-term survival. Faith is one of a litter of two and her brother is solid black with no abnormalities. At 4 weeks, Faith had a few problems walking, mainly when trying to turn around or turn to the left, but should soon learn to compensate. Her climbing abilities are not impaired and the photo shows Faith playing on the couch with her brother.

Theo was taken to the vets after Carly got him when he was a few months old. Carly wondered if the claw hanging away from the paw could be cut off so it didn't hinder him. The vet explained that in order to have done that, Theo should have had the surgery as a very young kitten. Theo had already adapted to his deformity and the vet explained that he'd have little trouble using that paw (but would operate if Theo did experience problems). Theo walked and jumped without any problems, but sometimes sprints using only 3 legs and holding the other paw off the ground so it doesn't slow him!

Oddly, he likes to sit with his left paw up as though it is in a sling and sometimes likes to wave it as though batting at something. Carly says he also has a strange obsession where he digs at things with the deformed paw, especially the corners of sheets of paper or plastic bags. Possibly he feels the need to stimulate the paw, or possibly it is related to unusual nerve signals related to the deformity.

Nikki Raver provided this photo of her syndactyl kitten, Eugene. On Monday April 16, 2007 a stray tortie cat that had "adopted" her family gave birth to 3 kittens. The final and smallest kitten to be born had deformed front paws. The other 2 kittens have normal paws. The photo was tekn when Eugene was less than a day old. His right paw is more severely deformed than the left paw. The left paw (harder to see in the photo) has the correct number of toes, but 2 are fused at the bottom, one is misshappen, and the toes point in opposite directions as though they are divided with 2 going one way and 2 the other (lobster foot). Eugene has no problems nursing. As an adult, he will need his claws clipped as they may snag on soft furnishings and will be harder for him to strop on a cratching post.