Recognition
While a few cat registries have recognized the breed, others have not, including the Fédération Internationale Féline, which refuses to recognise what they consider a breed based on a "genetic disease", achondroplasia. The Governing Council of the Cat Fancy likewise refuses to recognise the breed, considering this breed and others like it to be "unacceptable" because they are based on an "abnormal structure or development". The breed is also not recognized by the Cat Fanciers' Association.
Among the cat fancies that recognise the breed are The International Cat Association, the Southern Africa Cat Council, and the Waratah National Cat Alliance in Australia.
Advocates and critics
There is controversy among breeders of pedigree cats as to what genetic mutations are abnormal and potentially disadvantageous to the cat. While several dog breeds such as Dachshunds have short legs, some critics note the higher dependence cats put on their legs for climbing ability and overall agility. Some governments consider the munchkin breed to be "malformed animals" and the deliberate breeding of them "unacceptable" because of the "genetic health problems associated with such breeding". But keepers and breeders of munchkins declare them to be "a sound breed" that is "ideal" for small homes and not particularly susceptible to health problems.
Biology
Although the genetic mutation causing the short-legged trait in munchkin cats is often referred to as achondroplasia, it has not yet been proven that the trait is due to a gene at the same locus as causing achondroplasia in humans. Furthermore, while achondroplasia is typically associated with an enlarged head as well as short legs, a combination of features not seen in munchkin cats, the condition has sometimes been referred to as hypochondroplasia instead.
As well as shorter limbs, munchkin cats are prone to lordosis and pectus excavatum, suggesting that Munchkin cats may have a particular predisposition to these conditions. Small litter sizes when two munchkin cats are crossed indicate that embryos that are homozygous for the munchkin gene are non-viable.
Genetics
The munchkin gene is an autosomal dominant one. Homozygous embryos for the munchkin gene are not viable due to gene lethality. Only kittens that are heterozygous for the munchkin gene develop into viable munchkin kittens. Because only heterozygous munchkin cats are able to pass on the gene, all litters with at least one munchkin parent have the possibility of containing all munchkin kittens, all normal kittens, or a combination of munchkins and normal kittens. A litter with two munchkin parents may be all munchkin kittens, all normal kittens, all non-viable kittens with two copies of the munchkin gene, or any combination of the three.
