Please note that you're reading the old version of this article. You can find the updated article here.
Polydactylism is one of the traits both humans and cats have. Actually, mice, dogs and even horses also have extra toes (or small supernumerary digits terminating in hooves either side of the main hoof). Alexander the Great and Caesar both rode polydactyl horses.
Cats usually have four toes and one dewclaw (thumb) on each front paw and four toes on each hind paw. Polydactyl cats may have up to seven digits on front and/or hind paws, and various combinations of anywhere from four to seven are common. The hind feet are rarely affected and are only ever affected if the front feet are also affected. The current world record is set by Jake from Ontario, Canada, who has 28 toes – seven on each paw, each having its own claw, pad and bone structure.
There are two particular breeds that can claim historical reference to polydactylism: the Pixie-bob and the Maine Coon. While Pixie-bob is the only breed that accepts polydactyls in the breeding program, the Maine Coon Polydactyl is different from the Maine Coon and is recognized as an official breed by many cat fanciers, as well as by the TICA.
There are a lot of articles out there that can tell you about the history of this trait, but we want to talk about genes. Surprisingly, the polydactyl gene can be dominant in one breed and recessive in others. For those who are new to these terms please read our Genetics 101 post
There are two forms of polydactyly described by embryologists. Post-axial polydactyly refers to extra digits on the outer side (little finger side) of the paw and is uncommon. Pre-axial polydactyly refers to extra digits on the inside edge (thumb-side) of the paw.
The thumb-cat form is dominant with incomplete penetrance. That means that other genes can prevent the poly trait from manifesting. This is the safe form of poly. There is a different form ("patty foot") linked to the twisty cat syndrome. Unlike the "safe" polys, the "patty foot" gene is lethal. With this trait the thumb has an extra joint, making it look more like a human finger than the usual rudimentary feline dewclaw. A cat with such thumb may produce kittens with hypoplasia (under development) or aplasia (absence) of the radius, one of the two bones that make up the forearm. Because the usual form of polydactyly is so variable in expression, X-rays are needed in order to distinguish between the harmless usual form of polydactyly and the form associated with RH. When the polydactyl Maine Coon started being selectively bred, there was lots of x-ray screening to remove any parent that showed traits indicating radial hypoplasia from breeding.
During the 1990s, other researchers reported forms of polydactyly which they believed to be recessive. One researcher suggested two different dominant forms and one recessive form all of which had subtly different effects on the structure of the paw. This was based on the sudden appearance of polydactyl cats in a population of normal-toed cats. This could only have occurred through a gene mutation or through recessive genes. Apparently, the evidence among a number of random-breeding cats suggested a recessive gene for polydactyly.
To put it in other words, there are different genes involved and they produce different configurations, some with issues and some perfectly safe. Remember we spoke about the white spotting gene when in the same heterozygous form can vary between a white hair on one extreme and quite a lot of white on the other extreme: between 1 and thousands of white hairs? Same story here, theoretically, the expression of polydactylism can vary between 0 and 8-10 extra toes. Even with the well-documented Maine Coon Polydactyl, there exists a very big variation in expression of the poly trait. Although polydactyl means having extra toes/fingers/digits, people responsible for the Polytrak (litter tracking program) noted that the responsible gene the known point mutation) could make the changes to the paw, making it very small or very big (extra digits), the dewclaw can be enlarged or developed into a thumb, meaning the cat’s front paw would have no extra digits. And in some rare cases, the change would even be smaller.
Since polydactyly is seen more commonly in cats compared to other mammalian species, what is it about the cat genome (or kitten developmental processes) that makes polydactyly this common? It could simply be the location of certain gene(or genes?) on the chromosome(s). Because of the way chromosomes are duplicated and shared out in cell division when eggs and sperm are made, some areas of chromosomes are more prone to mutation than others. These are known as mutational hot-spots. During cell division, chromosomes duplicate and the chromosome pairs are physically joined together; these are pulled apart and during separation, genes can cross over from one copy to the other. Genes adjacent to the join might be affected by the separation process, resulting in small changes. This hot-spot effect could account for the spontaneous appearance of unrelated polydactyl cats in widely separated areas.
Meet some REAL "mitten" cats from the Basepaws community:
Mumpsy, 2 yo, Bend, OR
"Mumpsy is the sweetest soul. He has a very soft nature but watch out if you're a fly, He is a wizard of the leap and catch! He loves to play and wrestle with his brothers, his signature move is to wait until they are laying down then he sits on them"
- Amber Plunk
Simon, 1 yo, Lewiston, ID
"He is not only special because of his extra and adorable toes, but because he and his litter mates were rescued when they were only two-weeks-old because their mother died of distemper. The kittens also had to overcome some of the sickness, but the volunteers with Helping Hands Rescue in the Lewis-Clark Valley (Lewiston, Idaho/Clarkston, Washington) did an amazing job of hand raising these babies. Simon is an amazingly loving kitten, cuddling around my head several times each night. One of our nightly routines is to watch videos of mice, birds, squirrels, and other cats on my cell phone. His patience and interest are very unusual for a young cat - often lasting 25 or 30 minutes. Rather than pack Simon around like a normal cat, he "demands" that my husband and I pack him around on his back like a baby."
- Mia Carlson
Oreo, 10 yo, Toronto, Ontario
"Oreo 'Big Paws' Livingstone, born on a small farm in Hudson, Quebec in 2007, now lives in Toronto Ontario. He was the first of his litter to start eating dry food and eating is still his favourite activity. He is always using his extra thumbs to get into trouble, including toppling over garbage cans, pulling kleenex out of the kleenex box and opening cupboards in the search of food."
- Julie Livingstone
Panther, 1 yo, NE, Arkansas
"Our Cats' name is Panther, we live in NE Arkansas. He is a year old. Panther is a very loving Cat. He likes to be held and petted.Panther has 24 Toes."
- Donna Emmons
Zoe Lynn, 11 yo, Fort Wayne, IN
"Zoe is quite a unique cat. Not only does she have "mitten paws" but she actually uses her "thumbs" to help her grab onto things. Although she is mostly a grouch, she loves sitting by or on me, but does not like being held. She is queen of head bumps to show her affection."
- Lori Tiffner
Odin, 8 yo, Seekonk, MA
"Odin is an albino polydactyl, he has 7 toes on both front feet and 6 toes on both back which sure help him with his patented dance moves! He loves laying in sunbeams, playing with his two brothers and sister, going for fun walks on his leash, catnip and all the turkey he can get his big paws on. He lives a perfectly normal happy go lucky life, except for all the work he does to keep those toes clean!"
- Meaghan Paliotta
Pippin (affectionately called Pipperoni), 2 yo, South Texas
"He took really quickly to the comforts of a proper home and now you're hard pressed to get him out of bed. He comes when called, is incredibly vocal and will follow me around waiting for a chance to cuddle all day it takes him less than a minute to get into my lap. All cat lovers love toe beans, I just got lucky enough to have about 7 extras."
- Samantha La Gesse
Levi, 4 years old. He is originally from Sydney, Nova Scotia. Currently living in Ingonish, Nova Scotia
"Levi doesn't like catnip, but people food on the other hand is a whole other story. The second you open a bag of chips he is there to help eat them. He is a big ball of love all 15lbs (not fat just a big cat!), his favourite is belly rubs... unless you are lazy and use your foot or just get lazy then you need to prepare to get bit! His favorite place to sleep is in crates, unless it includes a car ride. He also has an obsession with licking plastic bags (but we love him anyways). He is simply spectacular."
- Michaela duChêne
Clawdius Maximus Toesus (Clawd for short) is approx 8 years old and lives in Victoria, British Columbia
"Clawd was adopted as one of a 'bonded pair' from the local SPCA last fall along with his partner in crime, Bonnie Wee Lass (non-poly). Bonnie and Clawd are the outlaws that stole my heart. When Clawd needs attention he sits next to my knee and puts one giant paw on my knee and stretches the other up towards my face with a look that says 'You are the best thing that ever happened to me and I need you to pet me NOW!" He also likes to wake me up with a few bops to the nose - but he tends to lean into those bops and squish my nose with his big feet. His wide back feet and powerful legs give him great traction for leaping very high when chasing the kitty toys - it's an amazing thing to watch".
- Tahna Neilson