There are no documented ill effects of the polydactyl gene in the Maine Coon. It is a totally benign and harmless gene with the single effect of producing extra toes on the paws. In my experience, sometimes this is confined to the front paws and sometimes the cats have all four feet with extra toes. There has not, to my knowledge, been any polydactyl Maine Coons that are unsymmetric. Both front feet are affected, not one and both back feet are affected. Maine Coons with the mitten paw configuration can produce kittens with the hamburger paw configuration and vice versa.

As discussed by Wright and Walters (1980) polydactylism “does not seem to do the animal any harm...the same cannot be said for a number of other feline abnormalities caused genetically”. This is backed up by Dr Montgomery (Bone and Joint Specialist, Auburn College of Veterinary Medicine) who states “Polydactylism is a fairly common anomaly in cats that is not detrimental to their orthopaedic soundness”. It is not sex-linked and it has complete penetrance.

In their 2007 paper "Point mutations in a distant sonic-hedgehog cis-regulator generate a variable regulatory output responsible for pre-axial polydactyly", Lettice, Hill et al write: "Since these mutations produce a limb-specific phenotype in human with no other discernible physiological defects, we submit that this type of polydactyly has no further detrimental affect on the cat’s health." (Ref 3)

Well known NZ Feline Veterinarian and columnist, Dr Mary Austin says she has never come across any increased risk of infection in a polydactyl paw. 

“In the Maine Coon polydactyls  I have seen (those bred by the author from a single line) they appear to have widespread toes with very good flexibility between the digits, which leads to good air flow and therefore with normal feline care there should be no problems”.

In addition to those pedigreed Maine Coon polydactyls, Dr Austin has a number of domestic polydactyls in her practice that she has treated for many years. She estimates the number of these domestic polydactyls to be 30-40 individuals. She has not seen any problems in these cats over the time they have been clients at her clinic.

In the population of Maine Coons that the author has experience with, the extra “thumb” or pre-axial digit is structured as a normal toe with a retractible claw and is fully jointed. This is stropped on a scratching post in the same manner as the usual toes. Occasionally the polydactyl can also have a normal dew claw, and, as for the normal toed cat, this dew claw must be kept regularly clipped to ensure it does not grow inwards.

Owners of polydactyls, as with owners of ordinary footed cats, should be instructed to check their cats claws and clip if necessary.

Mitten paw configuration - Digitally Enhanced.

S Hartwell states;
“Many cat registries happily recognise breeds defined by mutations which can have lethal or crippling effects such as spina bifida in the Manx, but refuse to permit polydactyl cats as either breeds or breed variants.

The blunt statement is that polydactyly is a fault and cats with such defects are not allowed to be shown. This is a totally inconsistent approach since tailessness is also a fault, yet the Manx breed is perpetuated and shown. There are far fewer detrimental side-effects associated with polydactyly than there are with the Manx. The usual argument in these cases is that the Manx is a historical breed even though the polydactyly trait is equally historical. …. It has to be noted that cat fancies are consistently inconsistent in their approach in such matters!”