Saturday 27 September 2008

Genetic Diseases in Purebred Cats

Siamese cat
Siamese cat - photo copyright Stockxpert

Purebred cats and mixed-breed cats have a fairly equal propensity to get ill but it is generally considered to be the case that mixed-breed non-purebred non-pedigree cats have a lesser chance of suffering from an inherited disorder or genetic disease (or is this the case actually). This, it is argued, is because of the breeding practices of purebred cat breeders who are obliged (and no criticism is intended) to breed in a way which allows recessive, defective, genes that would otherwise stay dormant to become effective and visible. What I mean is that breeding purebred cats has to be to type (appearance) which requires a degree of inbreeding and a narrowing of the gene pool resulting in an "increased expression"2 of unhealthy recessive traits and, therefore a corresponding increase in the incidence of occurrence of these disorders. That said random bred cats also suffer from these diseases.

Clearly two "players" in the process of breeding cats, the cat breeders themselves and the cat associations (in respect of setting breed standards and good practice) require a good understanding of basic genetics, inheritance "patterns" and the practice of breeding for there to be successful breeding that does not negatively impact on the cat.

Note: The source is primarily a rather scarce book called: Medical, Genetic, & Behavioral Aspects of Purebred Cats; Ross D.Clark, DVM, Forum Publications, Fairway Kansas, 1992 (referred to as book 1)

Another respected source is The Cat, Its Behavior, Nutrition, Health by Linda P Case. Published by Blackwell Publishing ISBN 978-0-8138-0331-9 (referred to as book 2) 

Please also note that this page is not "breeder bashing". I am fine about cat breeders. But I just like writing about what really happens. I like a bit of reality.

Cats, like any other species can suffer from inherited diseases from defective and sometimes fatal genes. Polygenetic inheritance appears to be the cause of many genetic defects, which makes it difficult to see established patterns. As diseases transmitted by dominant genes often have "extreme effects"2 causing the offspring to die in the womb or soon after birth, most inherited genetic defects are due to recessive genes. Some breeds suffer from inherited diseases with greater frequency than other breeds.

Apparently, there are a total of 150 genetic disorders that can affect cats. I am not sure if that is all cats (meaning including wildcats) or only domestic cats. There are 400 genetic disorders that can affect dogs. The breeding programs of some dog breeds has been criticized causing the break up of long term business relationships at the Kennel Club in the UK (see purebred pedigree cat breeding ). Apparently humans can suffer from thousands of possible inherited disorders (src: - I don't know how reliable this source is).

However a Wikipedia
® article on human genetic diseases lists over 750. This is interesting. If the figures for cats is accurate it is only a fraction of the number of genetic disorders that occur in people. This is a strong counter argument to one which says that purebred cat breeding can promote ill health because of greater incidences of genetic diseases in purebred cats. However, one factor that is not discussed here is the number of occurrences of the genetic diseases set out below and those set out on the Wikipedia® website. Also there will have been much more funding into genetic diseases in humans so it could reasonably be expected that there are more Genetic Diseases in Purebred Cats or cats generally than as stated above especially as there is a lot of similarity between cat anatomy and human anatomy at a fundamental level.

Although, on the face of it the number of genetic diseases in purebred cats is much lower than the number affecting humans, it might be the case that the occurrences of the
genetic diseases in purebred cats is much higher. This might modify the counter argument.This is where the research comes to a stop as research into genetic disease in cats is work in progress. There is some funding but it might be fair to say that it is somewhat limited. I wonder how much funding goes into research on genetic illnesses compared to the disposal and/or recycling of euthanized feral and homeless cats? This is an upsetting area and comparison but one which informs us about ourselves and our deep rooted attitudes in a general sense towards other animals.

Another point that comes to mind is this. The list below refers to 20 cat breeds. There are over 70 listed on the home page of this website. Does that mean the other breeds do not suffer from
genetic diseases in purebred cats? I think not. In fact I know not. The conclusion is that this list is not complete but it is still a lot fuller than is commonly available, I believe. In fact I have added to the list. The added diseases are in italics. These are added to the list from the source referred to at the base of the post.

The list of Genetic Diseases in Purebred Cats is interesting in another way. The cat breed with the highest number of genetically linked diseases is the Siamese cat (Modern Siamese). Also see Siamese Cat Health Problems (a full discussion). There are a wide range of types (conformations) of this cat breed, from the more standard looking cat, the traditional to the Classic looking cat, which I say is like the new breed called the Thai to the extreme Modern Siamese, a very slender cat. I don't know to which conformation the list refers. Perhaps it simply refers to the Siamese cat generally not making a distinction. Paradoxically the Siamese cat is one of the most popular cat on the basis of a long running poll on the website. Also a good 60% of people say that the health of a cat breed is very important to them (based on another poll on the website - see cat health problems). Is there a particular reason why this breed should have the longest list of genetic diseases? Another cat breed has a long list, the Persian (see Persian cat health problems) Both are very long standing cat breeds. The Persian is also a very popular cat. I have put the date of origin against the breed to see if there is some correlation.

Perhaps the answer is in their popularity. The more popular a breed the more breeding there will be. The more breeding, the more inbreeding as there is more competition amongst the breeders. The more inbreeding, the more disease...? Not sure.

Update July 2010: A discussion on the prevalence of Feline Infectious Peritonitis (FIP) in cat breeds.
Update August 2010: A discussion on Hip Dysplasia in Cats - this is based on a well researched scientific study

Update Jan 2011: "Elimination of anomalies" is how the authors of Robinson's Genetics for Cat Breeders & Veterinarians (4th ed) call the section on how to eliminate genetic diseases in cat breeds. This is the foremost book on cat genetics in the world.

They say that the anomalies persist despite a desire to remove them. They cite two reasons why this is the case:
  1. Complex problem
  2. The remedy demands drastic action and the breeders find this unacceptable  - where have we heard that before! Think national debt as one example.
The procedure for eliminating these genetic illnesses depends on the "mode of inheritance" - whether the anomaly displays dominant, recessive mongenic or polygenic heredity.

Sometimes the illness may not be an inherited one. And simply avoiding the breeding of two carriers of a genetic disease does not mean that the disease will be wiped out according to an Abyssinian cat breeder, Gene Rankin, who is quoted in the book at page 92.

However, in theory every genetic disease transmitted by a single dominant gene can be eliminated if "every descendant of every afflicted cat was prevented from breeding" (Robinson's Genetics).

The late onset of some genetic disease present a barrier to this process. One such genetic disease that is late onset is Progressive Retinal Atrophy causing feline blindness. Abyssinians and Bengals can inherit this disease and see list above.

Recessive monogenic heredity presents another problem: detecting the heterozygote or carrier. Test matings can detect the carrier. If the kittens are normal the cat can judged to not be a carrier. Test matings are now considered irresponsible due to advances in testing.

"A major factor in the spread of an anomaly is the relaxation of culling (culling in this context means a cat being removed from the breeding process). Commercial demands on cattery owners are a resistance to culling breeding cats.

There is the constant clash, too, of preserving the breed through inbreeding and outcrossing to eliminate the disease.

The occurence of an anomaly can occur several generations from the "ancestral origin". In the meantime a first class breeding cat that is a carrier has spread the disease far and wide. There is resistance to removing genetic diseases in purebred cats. The major reason in my view is shortsightedness of the cat associations and breeders. They would rather take the easy route and sweep the problems under the carpet.

In the purebred dog world the Kennel Club in the UK have changes the rules, under pressure from the press and sponsors, such that show dogs are to be cleared for good health by veterinarians at the shows before being allowed to win awards. 


 Genetic Diseases in Purebred Cats the list:-

Abyssinians (date of origin 1860)

American Shorthair



British Shorthair (late 1800s) - read about these on this page: British Shorthair Health.

Burmese (early 1900s) - read about Burmese Cat Health covering some of the diseases mentioned below.

  • Keratoconjunctivitis sicca
  • Erosion of cartilage of third eyelid
  • Lethal midfacial malformation
  • Ocular dermoids
  • Feline Orofacial Pain Syndrome 
  • Primary endocaridal fibroelastosis
  • Meningoencephalocele
  • Hypokalemic myopathy
  • Diabetes Mellitus (Sugar Diabetes) may have a genetic propensity (Cat Owner's Home Veterinary Handbook updated edition 2011).

Chartreux (14th century)

Cornish Rex (1950)

  • Hypothyroidism
  • Hypotrichosis2|1

Devon Rex (1960) - see Devon Rex cat breeding for more on this

Don Sphynx (1987) - also called Donsky
  • Reported that the gene that causes hairlessness in this Russian hairless cat (and the Peterbald) can cause ectodermal dysplasia in homozygous form.

Dwarf Cats (first Muchkin 1953) - see dwarf cat health issues

Himalayan (1930-1950)

Korat (14th century)

  • Gangliosidosis.

Maine Coon (1860s)

Manx (1730)

Norwegian Forest Cat
Ocicat (1964)
  • Pectus Excavatum
Oriental Shorthair

Persian (1530s) - note the Exotic Shorthair is a shorthaired Persian (American Shorthair and the Persian). These diseases may affect the Exotic Shorthair as well. Certainly PKD does. Visit Persian Cat Health Problems for more on these diseases.
  • Mannosidosis 1 | 2
  • Seborrhea
  • Polycystic kidney disease (PKD)
  • Chediak-Higashi syndrome 1 | 2
  • Congenital ankyloblepharon
  • Entropion (scroll down) 1 | 2
  • Congenital epiphora
  • Primary glaucoma
  • Peripheral pseudocysts
  • Patellar luxation
  • Hip dysplasia 
  • Report Daily Mail (UK)16-3--09: male Persians prone to a condition in that causes one or both testicles to remain inside the body, which can result in cancer. I am not sure if this is genetically linked.

    Ragdoll (1960s)

    Scottish Fold (1961) - click on this link: Scottish Fold genetic diseases and more.

    • Incapacitating joint disease with Scottish Fold to Scottish Fold breeding
    • Polycystic kidney disease
    • Severe vertebral abnormalities
    • Prognathis
    • Crippling epiphyseal dysplasia2

    Siamese (14th century - traditional and 1960s - Modern). See a full discussion on Siamese Cat Health Problems.

    Somali (1950s)

    Sphynx (1966)

    • Spasticity 1 | 2
    • Alopecia universalis.

    Tonkinese (1950s)

    Genetic Diseases in Purebred Cats - Source: Medical, Genetic, & Behavioral Aspects of Purebred Cats; Ross D.Clark, DVM.

    This is something I produced before building this page. There is an overlap with the above list, but I have reproduced it verbatim:

    Genetically linked diseases

    Genetic disorders are Important cat health problems. I have divided this section into two. The first part deals with cat breeds that are breeds due to a genetic mutation and the mutation has accompanying cat health problems. In the second part I deal with "normal" cat breeds that to the best of my knowledge have a propensity to a genetically linked disorder. Breeders always strive to minimize and eventually eliminate these disorders. Both are in summary form with links.

    Cat breeds due to genetic mutation

    1. Scottish Fold - The genetic mutation that causes the ear pinna (flaps) to fold over also results in an arthritic condition at the joints, tail flexibility and thickness, lack of mobility or hardening of the cartilage. Click here to read about this breed.
    2. Dwarf cats - The dwarfism gene that produces short legs can also bring health issues such inward curvature of the spine - the spine drops down around the shoulder blades) and pectus excavatum (funnel chest - flattened ribcage). Flat chest kitten may be present.
    3. Devon Rex - The mutated gene that produces the soft curly coat may bring abnormal blood clotting and muscle weakness. Read more. The "Rex" gene also produces a curly coat in the other Rex cats (Selkirk and Cornish) and the LaPerm. I don't know if the same problem affects these breeds.
    4. Manx - constipation and fecal incontinence due to the deformities of the spine.

    "Normal" cat breeds

    1. Persian - This breed has a number of health problems some of which are genetically based, such as (a) Polycystic Kidney Disease (PKD). Click here for all the problems and PKD information (b) Progressive retinal atrophy (PRA) affects Persians (click this link to read about PRA and Bengal cats). It is an early onset type for Persians (c) Eyelid rolled inwards (d) Chronic Degenerative Keratitis, causes a clouded eye and black or brown spot on the cornea (sequestrum).
    2. Himalayans and Exotic Shorthair cats are bred from the Persian so these two breeds will have the same health issues at least potentialy.
    3. Himalayans may suffer from cataracts due to a single genetic defect.
    4. All breeds, Maine Coon and Bengal - Heart disease hypertrophic cardiomyopathy (HCM). Read about this in reference to the Maine Coon and Bengal.
    5. Maine Coon - Polycystic Kidney Disease (PKD) and Hip Dysplasia and other disease (see Maine Coon cat health for details).
    6. Bengal - Progressive retinal atrophy (PRA) - mid-onset (more).
    7. Abyssinian - Progressive retinal atrophy (PRA) - late-onset
    8. Somali - Progressive retinal atrophy (PRA)
    9. Siamese - Chronic Degenerative Keratitis, causes a clouded eye and black or brown spot on the cornea (sequestrum). See Siamese cat health problems for a full discussion on health including genetically linked diseases.


    1. This comment has been removed by a blog administrator.

    2. A one sided, poorly written, and poorly researched article. Not scientific and poorly documented to be making so many inaccurate assumptions and conclusions. DMV

    3. Response to last comment. The list comes almost totally from a well respected book, which I refer to at the top of the article. Other sources are also sound.

      You do not say what is wrong. You just say it is poorly researched.

      What assumptions are innaccurate?

      I think also you should provide your name. No good hiding behind "anonymous". This shows a lack of courage.

      And why is it one sided? It is highly objective.

      Are you a USA vet? (if you are really a vet at all).

    4. I read the articule and now i'm even more concern, my siames is being very ill lately, it seems like hip dysplatia and after a visit to the vet, anti inflamatory medication helped for about two weeks but now my cat is even worse, how does one deal with all the genetic diseases? is it some thing that could be controled with medication or is my cat eventually going to get worse and die? please some one tell me.

      Gladys Ramos

    5. I'm a new cat breeder and enjoyed the article very much! I'm constantly reading and learning everything I can about cats. I'm also doing everything possible to ensure that my cats are healthy without genetic defects. I have had all the genetic testing available for my breed. I wish there was more genetic testing for other diseases. I also have had echocardiograms done on many of my breeding cats to ensure that they don't have (HCM). It's a very time consuming and expensive endeavor to breed healthy, beautiful cats. My expenses are much higher than the income I take in from the sale of my kittens.

      I love my cats and I try to make sure they will live long lives and that my kittens that I sell will live long lives.

    6. I wonder if new breeds like the 'Snowshoes' will suffer less inherited conditions or more, since they're bred from other pedigre cats.

    7. The wider the gene pool the better. Inbreeding brings defective recessive genes to the fore. So crossing various breeds and introducing new breeding lines helps keep cats healthy.

      The moggie is the healthiest and Dr. Morris, a respected biologist who is the author of "Cat Watching", says that not just me, in case a breeder comes on and insults me!

    8. Really i am very impressed from this post.. just awesome...i haven’t any word to appreciate this post.

      Good Health

    9. Out of date and low on current data. The books you reference are old by the fast moving scienticfic research standards.

      The number of cats with the most widely spread genetic disorders are the ones that have a genetic tests to identify the carriers. Look at any of the labs offering feline genetic testing and there are NO tests for the Siamese breed.

      There is no money in researching something they cant sell to the masses so researchers go for the largest effected groups.

      Current research projects

      Inbreeding doesn't just happen in purebreds. It happens naturally in all cat colonies too.

    10. Response to last comment. Thanks for the comment. You say the page is "low on current data" yet the links that you provide point to very little current data. There appears to be little in the way of current data and I know of only one page (or site) on the internet that comes close to matching this page for comprehensiveness.

      You say that there are "fast moving scientific research standards." Yes, in general but in the world of purebred cat genetic research I don't see it because there is not enough money in the market and in any case breeders don't want to find out how badly they are doing! They tend to brush the genetic problems under the carpet.

      You seem to be a modern Siamese cat breeder. The fact that there are no tests carried out on Siamese cats genetic disorders does not mean that they don't exist. It just means that Siamese breeders aren't funding the tests.

      The modern Siamese is overbred and in my opinion this has compromised the cat's immune system.

      Breeders should pay greater attention to a breed's health and less to extreme breeding for appearance. Anyone with common sense would agree that.

    11. What an amazing article…coooooollll…could not believe it…something as fabulous as this never crossed my mind…..Thumbs up to your supreme imagination!!! Well done, I hope to see more such good things in futur

    12. This really is common sense. If you breed cats with homozygous genes they will have disease that are homozygous as well. In other words, incurable. You got to get some fresh genes in their somewhere and stop using the worn out ones!

    13. ROFLOL Despite their claims this author is clearly biased against purebred breeding and of the modern Siamese in particular. The use of the term "extreme" demonstrates this.

      Siamese cats are the basis of many newer breeds and yet the genetic diseases listed for the Siamese have not been included for those breeds? Is the author implying that the genes have not been passed on?

      I agree with previous comments that this information is out of date and no longer accurate. Many doctors make assumptions about illnesses and give them a genetic connection that may not exist. Kidney disease (non poly cystic)in all cats is on the rise at an epidemic rate. Is this genetics as many vets claim, with nothing scientific to back it up, or is it because we went through a chemical revolution in the 1960's? We now have so many chemicals in our homes that cats consume by normal feeding, grooming and licking of surfaces and we inject our cats on a regular basis with chemicals in the form of vaccinations. I believe all cat kidneys are under assault like they have never been in the past.

      Another example of chemical induced disease that was thought to be genetic not to many years ago is feline hyperthyroidism. It was recently discovered the cause of the recent epidemic of hyperthyroidism in cats is the chemicals that are used in the pull top cans of wet food.

      Here are a couple articles that have more information.

      Until genetic testing is available for the diseases listed about this list is inaccurate, anti breeder, and inflammatory at best.

      Just because someone who is respected at a point in time publishes something doesn't make it so. It was widely believed and published that the world was flat and you could sail off the edge.

      Anyone can make a fake named account to post comments, having a name doesn't make a comment any more valid. Some of us just value our privacy. A real discussion should be about the subject facts and not the posters fake name.

      1. Hi, I am not anti-breeder or anything like that. I am for healthy cats that are normal looking.

        The word "extreme" is commonly used for breeding cats that are highly selectively bred. You must realise that.

        This page is not out of date. Breeders tend to ignore health issues and go on breeding to extreme with respect to some breeds such as the Persian. That breed is as ill as it ever was.

        Before the early-mid 1900s the Persian was pretty normal and not a ill cat.

        This is a comprehensive page and has ranked v.well for years in Google search listings. It was carefully prepared.

        Sorry, but all I am doing is presenting facts. You are defending breeders. Fine. But I believe you are a breeder.


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