POLYDACTYL CATS (Part 1)
In the New Scientist of 12 May, 2001, it was asserted by Chris Hayes that "five is the magic number" of digits. This was based on the assumption that the genetic mutation that produces the extra toes is also responsible for deformities and that possession of more than five digits is a "counter-survival trait". His assertion was based on observation of mice with deformities caused by genetic mutations. However, what is true for mice is not necessarily true for other animals and there are many healthy cats with six or more digits. Fossil evidence shows that early amphibians also had 7 or 8 toes.
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The greatest number of toes EVER found on a cat is 32 (eight on each paw) reported in October 1974. This was male cat called "Mickey Mouse" owned by Mrs Renee Delgade of Westlake Village, California, USA. It is possible he had a condition known as double-paws where each paw is actually 2 fused mirror image paws; this is a different condition to polydactyly. The 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 had eight paws in a row. Double-paws is a developmental defect - 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.
A pure-bred Siamese named "Big Foot" owned by Miss Joan Conerly of Wauchula, Florida, USA in 1978, had 26 toes (seven on each front paw, six on each back paw). His mother had 22 toes, his sister had 22 toes and a brother had 24 toes.
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 had 2 complete lower leg extensions from the hock down, and one of those lower legs had 2 paws. This is probably a developmental 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.
In May 2002 Jennifer Beierle wrote to me 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. One was stillborn, 9 survived and seven were polydactyls. Two kittens had 26 toes (Peter and Paula,) two had 23 toes (Pollyanna and Penelope,) two with 22 (Phoebe and Peace,) one with 21 (Paprika,) and two with the normal 18 (Ace and Jean). Peter is double-pawed in front, with 7 toes on each front foot and six on the rear but no dewclaws at all. Paprika has a superclaw in front. Phoebe has the appearance of double-dewclaws on back, and Penelope has an under-developed toe with an ingrown nail.
In August 2002, the Canadian Press reported the case of a Manx cat that narrowly escaped death by euthanasia was a contender for the cat polydactyly Guinness world records. Bobbi has 28 toes, one more than the current record holder. Bobbi is owned by Kathy Williams of Stone Creek, near Prince George, British Columbia, Canada. She adopted Bobbi from the Prince George SPCA shelter where he was due to by put to sleep because of a heart condition (this turned out to be minor). His toe count must be authenticated by a vet before the record can be claimed.
Bobbi is not the first reported 28-toe cat, but he may be the first authenticated one. Saffy, owned by Joan Snoswell, was also reported to have 28 toes. Other cats with 28 toes are Patsy, a Maine Coon adopted from the Boston Animal Rescue League, and Bigfoot, owned by Tanya Welsch. Several others are reported on the internet including 28-toed Clyde from Albuquerque, New Mexico (below), whose details were emailed to me by his owner's sister who describes Clyde's oversized paws as resembling the feet of a snowshoe hare.
The current (i.e. verified) record holder (2002) is Tiger who has 27 toes. Tiger is owned by Gareth Ukrainetz of Leduc, Alberta, Canada and has seven toes on each front foot, and seven on her left hind foot, but only six toes on her right hind foot.
POLYDACTYLY AND NATURAL SELECTION
If polydactyls are common and not disadvantaged, why are there no polydactyl cat species or sub-species? There are, after all, localised polydactyl populations e.g. near Hemingway's home, some farm colonies.
Firstly there is the question of genetic isolation. For a distinct variety to be perpetuated, it must be genetically isolated from other cats. Farm colonies breed not only among themselves, but also mate with roaming feral tomcats and with other cats attracted into the colony. Unless the outsiders are polydactyls, this dilutes the genes. There are few cat populations isolated enough to give rise to a sub-species, let alone a species no longer able to interbreed with normal-toed cats. Recent artificial isolation of polydactyl cats (i.e. by establishing and controlling breeding lines) is giving rise to polydactyl breeds. An obvious case of an isolated population is the Manx cat from the Isle of Man. For genetic reasons (discussed later), though the tailless trait came to predominate (outnumber the fully tailed cats), it was never "fixed" i.e. it did not breed 100% true. Manx cats also produce non-Manx kittens.
It is suggested that the lack of a polydactyl sub-species means there is some sort of natural selection against the trait e.g. there may be hidden ill-effects or polydactyls are somehow at a disadvantage compared to normal-toed cats. This is the case in Manx cats where the gene can cause spinal abnormalities and pre-natal death. However, polydactyly is a "neutral" mutation - it is neither advantageous nor disadvantageous to the cat (tales of natural snowshoes notwithstanding). So why has it not become fixed in isolated populations?
The answer is in the mode of inheritance. Polydactyly in cats is due to a dominant gene mutation. This means that many polydactyls also carry the gene for normal toes. Polydactyl cats can produce normal-toed kittens so the trait is never "fixed" (true-breeding). In an isolated population, the trait could become common through inbreeding, but there will still be normal-toed cats because of the hidden recessive gene.
Even if there was some form of natural selection in favour of polydactyly and all normal-toed cats died before breeding age, the mode of inheritance means that the hidden recessive gene for normal toes is still present in the population. Non-poly kittens will still occur i.e. the cats do not breed true for polydactyly. Recessive genes are practically impossible to eradicate in a random-breeding population. In a breeding programme, a polydactyl would have to be test-mated to normal toed cats to see if the polydactyl carried the hidden recessive.
If, however, a recessive gene for polydactyly arose and for some reason the polydactyl cats had an advantage over normal-toed cat, this could give rise to a true-breeding polydactyl population, but only so long as they were isolated from other cats. In this case, polydactyly would not merely predominate, it would become fixed as the cats would be true-breeding.
Because recessive genes breed true, two normal-toed cats almost always produced only normal-toed kittens. "Almost always" because there is a very small chance of a fresh mutation or of one of the cats being genetically polydactyl but not showing the trait.
Since polydactyl cats sometimes use their "thumbs" to manipulate or grasp objects, why is the trait not actually advantageous? In spite of the potential usefulness of the opposable thumb, nature does not seem to select in favour of thumbed cats. The best explanation is that although cats have intelligence, it is not the sort of intelligence that makes an opposable thumb an evolutionary advantage over other cats, nor do they walk upright in order to keep their "hands" free for manipulating objects.
Polydactyly is an ancient trait and but for a quirk of evolution, all modern animals would have 7 or 8 digits instead of just 5. The oldest known four-legged animals, Ichthyostega and Acanthostega, had 7 or 8 digits per limb. The "extra" digits were next to the thumb. The extra digits disappeared 350 million years ago, leaving modern animals with just 5 per limb. 100 million years after evolution opted for five digits, throwbacks to ancestral polydactyly occurred, as a fossil of a seven-toed reptile demonstrates. The fossil, an aquatic marine reptile called Nanchangosaurus, was an mutant or evolutionary throwback which lived 100 million years after other seven-toed amphibians had died out.
Nanchangosaurus lived about 242 million years ago in China. The fossil reveals that it had seven complete digits on its forelimbs and six on its hind limbs. Other fossils didn't have well-preserved digits, so we can't be sure whether polydactyly was a trait of the whole species or if was restricted to a single mutant animals.
SYNDACTYLY (OLIGODACTYLY) & ECTRODACTYLY
Syndactyly (hypodactyly) or split-foot is the opposite of polydactyly. Instead of having additional toes, the cat's forefeet (rarely the hind feet) have one or more toes fused. In the most familiar form, called Ectrodactyly, there is a central split and two toes giving 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 and Ectrodactyly are visually similar. Ectrodactyly is the "lobster claw" defect where the paw is split longitudinally, most commonly between the first and second toes. In different mammals there are both dominant and recessive forms of this defect. It often occurs on one side only and there may be other abnormalities: deformed or under-developed toes and partly fused toes. Syndactyly involves the union of bony and/or soft tissue of two or more toes and can be hereditary or congenital (non inherited). Hereditary syndactyly usually occurs on both sides while congenital syndactyly often affects only one side. As the conditions are similar and rarely distinguished from each other in cats, I have used the term syndactyly from hereon.
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.
Jazmin Powell's cat Forest (born August 24th 2007) is another ectrodactyl. He also suffered from horny growths on his “lobster claw” since birth. The claws of the affected paw have had to be removed as they started to grow into his paw pads causing great discomfort to Forest.
Anastopoulos Thanos of Sparti, Greece provided images and details of a different form of fused toes: "A few months ago I adopted a pair of stray kittens found on the street outside my house. 1female and 1male. They have developed a liking to the indoors. The reason for this email is an anomaly on the hind paws of the female cat ("Zooka", see photos). If I’m right its called syndactyl, a union of the ‘toes’. It does not appear on the front legs of the cat. The number of nails is correct but the cushion is united. The bone structure feels to the touch normal. The affected nails seem to have problem retracting. It does not hinder the cat’s movement other than a "clicking" sound due to the nails hitting the floor tiles. I am not thinking of seeking medical or surgical treatment because the cat shows no distress over it."
Fused centre hind toes
Brachydactyly is not to do with the number of toes, but the length of the toes. Brachydactyly means "short toes". I have only seen one brachydactylous cat - a ginger and white male rescue cat whose toe-pads attached directly to the palm of the paw i.e. he lacked the "finger sections". It was necessary to trim the claws regularly and they grew at irregular angles. The lack of jointed toes resulted in minor mobility problems e.g. in running and on landing when jumping, but he was otherwise not inconvenienced by the condition. Also, he could not knead properly.
This case was believed to be due to a birth defect (developmental abnormality). In humans, brachydactyly is associated with some forms of dwarfism.
Arachnodactyly (spider-digits), a condition causing longer than normal toes, has not been reported in cats to my knowledge. The condition of extra joints/extra bones in one or more of the digits (causing them to be extra-long or extra-flexible) is hyperphalangy.
Uneven Length Toes #1. As well as heritable traits, some individual cats simply have curious toes e.g. uneven length of toes or a twisted toe. These are one-offs caused by early injury or the way the limb has developed in the womb (i.e. not inherited trait). "Bryn" writes "One of our cats has a curious toe on one back foot. It is much smaller than the other four, and is pushed up, so that when the foot is viewed from the bottom, she appears to have three toes. The small toe has a claw. All of her other feet seem to be normal" (photos provided, see below).
Uneven Length Toes #2. Courtney Kahler (2003) provided the following photos and information about her cat Kolohe whose condition is similar to syndactyly, but probably congenital (birth defect) not hereditary. "I have a cat (Kolohe) who either was born with syndactyly in one front paw or she has a congenital defect very similar. She is essentially missing one toe, has a thumb for a dew claw with a non-retractable claw, and the other 3 toes are semi-fused but do have retractable claws. The smallest toe on the outside of the paw is not as fused as the 2 next to it. The paw pads in 2 places on her paw seem to grow and she tends to chew on one of them, but it never bleeds. So that part of her paw pads looks a bit rough. The other paw pad grows out from her foot almost in the shape of a claw, but it’s tough paw pad and nothing else. You will be able to see that in the picture. She must occasionally chew that off too ‘cause it’s not always that long.
Her breeder believed this was a congenital defect not genetic since she has never seen it before in any other kittens. But both parents are spayed/neutered so if it is genetic it won’t appear again. Kolohe is also spayed. It has no effect on her whatsoever, she is as active as any other Tonkinese and can play and climb with no problem. I do have to keep the one claw clipped because it can snag on the carpet. When she sits up she sits with that paw out to the side. She’s an adorable cat regardless of anything and we often call that foot her lobster claw. "
Another reader reports that her male polydactyl Lynx-point Siamese mix, Tommy, had horny growth similar to those of Kolohe. Tommy's growths grow right up to his claws if left unclipped. In addition, some of his claws are mis-shapen: one is almost flat, and grows square, but twists like a DNA strand while a double dewclaw on the back looks like 2 claws side by side, fused halfway up and barely fits in the claw clippers.
Off-Centre Claws. Bernice adopted a kitten called Ashley in November 2005. She has long toes (she is a very long cat) and some claws are off-centre as shown by the photo of her back foot (below).
For cats with "horned paws" or "horned paw pads" see Horned Paws
POLYDACTYLY IN HUMANS AND OTHER SPECIES: See Polydactyly in Humans and Other Species
Twisty Cats and the Ethics of Breeding for Deformity - more information on Twisty cats
Feline Medical Curiosisites - other anomalies in cats
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