2008-2015, Sarah Hartwell

The following categories of defect are frequently used to describe feline genetic anomalies. As with all things, there will be different opinions as to which category a particular defect is assigned to. The availability of medical or surgical care may be a factor in many regions; country-specific legislation also plays a part. The definitions used here are those in current usage by cat breeders and veterinarians. Researchers working independently of each other may use different terms for what is later found to be the same syndrome or anomaly and have slightly different descriptions. The list of genetic anomalies continues to grow with better reporting and better genetic screening.




Classical Lethal: kittens die in utero or are reabsorbed
Teratological lethal: kittens are stillborn or die shortly after birth (major birth defects; "teratological" means "monster-like")
Deferred lethal (sub-lethal, semi-lethal): lethal if the kitten inherits 2 copies of the mutated gene, impairing or not evident if only 1 copy is inherited (e.g. Manx mutation, polycystic kidney disease [PKD])


Non-lethal, non-cosmetic, but difficult or impossible to control with medicine or surgery at the current state of knowledge.
Non-lethal, non-cosmetic, but requires surgery to give cat good quality of life (e.g. mild cleft palate)
Non-lethal, non-cosmetic, but requires long-term or lifelong medical treatment


Cosmetic with medical or physical repercussions
Cosmetic, but cat can live healthy life without surgery or medical treatment, but with some limitations e.g. indoor only
Cosmetic with no known medical or physical repercussions

In genetics-speak, mutations are often referred to as "defects" as they are different from normal. Since one person's defect is another person's breed trait, the term "anomaly" is preferred by breeders. Genetic anomalies are most often noted in purebreds for several reasons:

When cats are bred for appearance, disease-causing genes risk being overlooked until the gene becomes sufficiently widespread that numerous cases of the genetic ailment appear in that breed. There are a number of factors involved:

Some breeds don’t have a high number of genetic conditions noted, but they show inbreeding depression (in the form of small litters, poor fertility, poor immune systems). The Singapura is so inbred (developed from less than 10 foundation cats) that it risks becoming extinct without outcrossing to unrelated cats.


Medical advances means currently lethal defects might become treatable in the future e.g. PKD might be mitigated through kidney transplant. Other defects (e.g. Manx spinal mutation and conditions caused by multiple genes) are variably expressed and can be mitigated by careful selective breeding so severely affected kittens are not born. To accommodate this, the convention lethal/impairing or cosmetic/impairing is used to indicate the variable severity. It is also used where the classification of some anomalies is debated. Deafness is considered cosmetic because medical treatment is not required. It is impairing in that affected cats are vulnerable to danger and may require restricted lifestyles or greater supervision (deaf females may have poorer maternal skills as they cannot hear crying kittens). Some apparently identical anomalies may be due to different mutations with different side-effects.

The March 1995 draft of the "European Convention for the Protection of Pet Animals" potentially bans abnormal or defective breeds and sets down, in legal terms, definitions of abnormal and defective. Defective (potentially legally banned breeds) include Manx, Scottish Fold (and derivative breeds), dominant white (due to deafness), albino (eye defects, skin cancer), Rex breeds, hairless breeds, Munchkin (and derivative breeds), Twisty Cats, polydactyly (described in legislation as semi-lethal, but possibly confused with radial hypoplasia), short-faced breeds (cleft palate, craniofacial defects). Other affected breeds are colourpointed cats (eye defects) and bobtailed breeds. These considerations have also been accommodated in this article hence some traits considered ourely cosmetic in the USA are considered impairing in Europe.

To oversimplify matters somewhat, chromosomes occur in pairs (one copy from each parent) therefore genes are inherited in pairs. The two copies can be identical (homozygous) or non-identical (heterozygous). Usually one gene out of each pair is dominant (expressed) while the other is recessive (suppressed). Genes on the X and Y sex-chromosomes are the exception and are not inherited in pairs. Terms such as partial dominant, incomplete dominant and incomplete penetrance mean a dominant gene that is not fully expressed.

Autosomal: the gene is not on the X or Y chromosome
Co-Dominant: the 2 forms of the gene are equally dominant
Dominant: the trait manifests (fully or partially) if only one copy of the gene is inherited
Epigenetic: results from gene expression, not gene mutation (some epigenetic effects are heritable)
Familial Incidence: observed within a single family or breed line, mode of inheritance not identified
Homozygous: 2 identical copies of the gene have been inherited, one from each parent
Heterozygous: 1 copy of the gene has been inherited.
Monogenic: trait is caused by variation of a single gene
Polygenic: trait is caused by interaction/additive effect of multiple genes (polygenes)
Recessive: the trait only manifests if 2 copies of the gene are inherited, if one copy is inherted the cat is a carrier
Predisposition: an inherited predisposition OR predisposition as a side-effect of other mutations in the breed (e.g. conformation)
Sex-limited: the gene is carreid by both sexes, but only shows up in one or other
Sex-linked: the gene is on one of the sex chromosomes (usually the X)
Syndrome: group of symptoms characteristic of a condition, but there may be several different genes involved

The following list of genetic anomalies appear to be heritable (genetic or epigenetic) rather than developmental. These include inherited susceptibility to diseases/conditions and syndromes. Several of these are depicted at Feline Medical Anomalies

Graphs and Additional Notes based on this list and affected breeds


Type: Autosomal dominant, semi-lethal, considered cosmetic.
Breeds: Munchkin and derivative breeds.
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals

Achondroplastic dwarfism results in short legs and enlarged head. Pseudoachondroplasia results in short limbs, but normal head proportions. The Munchkin mutation is often termed achondroplasia, but the head size is normal indicating pseudachondroplasia. Problems associated with the Munchkin mutation are lordosis (spine dips downwards around the shoulder blades) and pectus (flattened ribcage). Some short-legged dwarf cats may exhibit joint problems/pain. Care should be taken to select breeding stock free from health issues.Small litter sizes when short-legged cats are bred together suggests the gene is lethal when 2 copies are inherited.


Type: predisposition
Breeds: Siamese

Siamese cats are 3-8 times more likely to suffer from these growths compared to domestic shorthairs.


Type: impairing, autosomal recessive

Part of the colourpoint series of genes, pink-eyed albino is the most recessive of the albino alleles. Until compartively recently there was doubt whether it truly exists in cats due to the structure of the cat’s eye (blue-eyed albino also exists in cats). Associated with photosensitivity and poor immune system.



Type: lethal, autosomal recessive, but the phenotype may be impenetrant in some homozygotes (other sources suggest autosomal dominant with incomplete penetrance)
Breeds: American Burmese (European Burmese are unaffected).

Signs are meningoencephalocele and craniofacial abnormalities (incomplete duplication of features) associated with the round-headed "contemporary" American Burmese conformation. The lower jaw and tongue are normal, but the upper jaw, upper part of the muzzle and roof of mouth are duplicated; the area above the muzzle is incomplete; ears and eyes are malformed and the skull doesn't close completely, leaving part of the brain covered with skin only. Kittens may be born alive but cannot survive and should be euthanized. The "contemporary" conformation is due to incomplete penetrance of this defect (does always not show up when present). Gene symbol mc proposed


Type: impairing/lethal, autosomal incomplete dominant
Breed: American Shorthair (confirmed), American Wirehair (suspected)

Some lines of American Shorthair are genetically prone to head abnormalities related to breeding cats for domed heads in the 1970s/80s. Minor "cosmetic" defects were overlooked due to the cats generally having superior conformation, leading to the further spread of the defect. About 90% of cats with 1 copy of the mutant gene have a "dot" (longitudinal depression) on the nose evident from birth. Others have dermoids (abnormally located patches of whisker pad on nose, below eye or on the eye itself). Some have serious defects such as harelip, severe cleft palate, duplicated canine teeth, duplication of tongue tissue, crooked jaw, skewed nose, coloboma (fissure of the eye socket due to eyelid plate not developing properly) through to lethal athymia (missing or non-functional thymus gland) or seizures (indicating brain abnormalities). When a cat with a "dot" on the nose was bred to unaffected cats, about 50% of the offspring inherited the "dot" and one of more other defects e.g. dermoids, harelip and about 5% of the offspring inherited lethal defects. When 2 cats with "dots" were bred together, the homozygous offspring had gross and lethal head deformities e.g. skullcap missing and brain covered with skin only; hydrocephaly; grossly abnormal brain ranging from holoprosencephaly (malformed forebrain) to anencephaly (no forebrain) and abnormal of facial features ranging from wide spaced eyes, harelips and cleft palate to cyclopia (single deformed central eye). Other affected kittens had small rudimentary eyes located on the sides of the head rather than on the face. Some had severe cleft palate, extreme harelip on both sides of the mouth, brachygnathia (short or receding jaw, flat face) and protruding tongue.


Type: Lethal, predisposition (Abyssinian) or familial incidence (Siamese)
Breeds: Abyssinian, Siamese/Oriental

In affected Abyssinians, an amlyoid protein is deposited in organs, especially the kidneys. The liver and intestines may be affected. Undectable unless disease is moderate/severe. Post mortem studies of some older Abyssinians that had no sign of kidney disease found amyloid deposits on the kidneys. Symptoms are listlessness, poor coat condition, weight loss, excessive thirst, excessive urination. In affected Siamese, an amyloid is deposited and affects the liver resulting in liver dysfunction, haemorrhage, rupture and sudden death. Affected Siamese were 8 months – 7 years old and were related. In both breeds the degree of genetic predisposition/mode of inheritance is unknown.


Type: Impairing, familial inheritance suspected
Breeds: Siamese

Four Siamese littermates were found to have a fixed fibrous ring below the aortic valve and a familial inheritance is possible. Occasionally seen in other cats, but genetic link not established.


Type: Impairing
Breeds: Burmese (anecdotal), Manx

Degenerative changes occur in most elderly domestic cats. Some breeds are pre-disposed to osteo-arthritis due to other conditions e.g. luxating patella, hip dysplasia. Anecdotally, Burmese are prone to elbow arthritis at a relatively early age and those aged over 8 may show elbow abnormalities. They rest or move with the elbows held outwards (colloquially known as "clockwork kitty syndrome" due to posture and stiffness). Anecdotally stumpy-tailed Manxes are prone to arthritic changes in the tail therefore American breeders dock the tail as a preventive measure. Those who leave the stumpy tail intact claim arthritis is not inevitable.


Type: possible predipsosition, impairing
Breeds: Siamese/Oriental

The syndrome known as Feline Asthma is typified by wheezing and coughing attacks. It is not known whether it is tru easthma or is bronchitis (inflammation). Seems more common in Siamese/Oriental and a genetic link is possible. May be associated with the "tubular" body conformation and narrower chest of these breeds.


Ataxia (unco-ordinated gait) may be due to a range of conditions, some inherited, some developmental and some acquired after birth. An early onset ataxia (7-9 weeks) with similar progression to Cerebellar Abiotrophy (severe ataxia, wide-legged posture, high-stepping gait and spasticity progressing to blindness) but due to different changes in the brain was due to a recessive gene in inbred siblings.


Type genetic link possible

Inherited predisposition to become hypersensitive to environmental allergens; symptoms develop on areas that have not had physical contact with the allergen. Symptoms include miliary dermatitis ("scabby cat disease" resembling flea-bite eczema), fur loss and eosinophilic granulomas (rodent ulcers, plaques or linear granuloma such as swollen lip/chip). Diagnosis requires other causes of allergic reaction to be ruled out, plus skin tests to identify the allergen. Moriello (2001) noted atopy in 3 littermates, suggestive of genetic links


Type: possible genetic cause?
Breeds: any

Rectovaginal fistula with absent anus was diagnosed in 3 kittens by Suess et al (1992). The kittens had no anal opening, distended bellies and bulging perineums. Surgery was required to create an anal opening, but complications included scar tissue, faeces incontinence and constipation. A case documented in a cat magazine by a cat rescue worker (1990s) was apparently successfully treated.


Breeds: Siamese

Persistent atrial standstill described in a number of Siamese, found to have signs consistent with dilated cardiomyopathy (DCM) and atrial atrophy.


Type: autosomal recessive
Breeds: Birman

Affected cats have fine eosinophilic granules within the cytoplasm of neutrophils Neutrophil function is unaffected and cats with this anomaly are healthy.


Type: possibly sex-linked

A progressive degenerative neuropathy, signs are hypermetria (high-stepping walk), plantigrade stance (‘dropped hocks’) and hindlimb ataxia (uncoordinated movement). The age of onset is 8-10 weeks of age. Reported in a group of inbred kittens, possibly sex-linked as all the affected cats were female.


Breeds: Birman

In a survey, around 80% of Birman cats under 6 months old had increased urea and/or creatinine concentrations in their blood, indicating possible kidney dysfunction. A minority suffer renal failure at less than 2 years old with symptoms following routine neuter/spay surgery. This anomaly of renal function is important when medicating Birman cats.


Type: Unknown
Breeds: Abyssinian

A very large study in the USA in 2001 indicated Abyssinian cats have an increased risk of bacterial urinary tract infections. The reason was not established.


Type: possible predisposition
Breeds: Siamese/Oriental (unconfirmed)

A basal cell tumour is a benign skin tumour, usually a solid mass or fluid-filled cyst, sometimes pigmented and may become ulcerated (can be removed surgically if causing a problem). Common on older cats both pedigree and randombred. Sweat gland tumours may be benign or malignant and either single tumour or diffuse plaque and may occur anywhere on body. Unconfirmed predisposition to both types of tumour in Siamese and Oriental cats.


Type: Codominant

In cats, blood grouping conflicts are similar to rhesus factor conflicts in humans due to the maternal antibodies in the milk attacking the conflicting blood group of the kittens. Kittens of blood type A that are born to queens of blood type B that are allowed to suckle maternal colostrum in their first 18-24 hours may absorb enough maternal anti-A antibodies to destroy the kitten's red cells.


Type: polygenes, impairing
Breeds: Persian/Himalayan, Exotic

Syndrome due to the abnormal facial conformation/anatomy of short-faced breeds: narrowed nostrils and nasal passages, elongated soft palate, possibly narrowed windpipe. Cats must exert more effort to nose-breathe through the narrowed passages, causing chronic suction around the pharynx which can cause inflammation resulting in further constriction of airways. Cats are usually unwilling to mouth-breathe, but a number of Persians do become mouth breathers.


Type: cosmetic, autosomal dominant with incomplete penetrance
Breeds: Japanese Bobtail, Pixie Bob, non-Manx bobtailed breeds, some Siamese strains

Note: Considered potentially impairing under the 1995 European Convention for the Protection of Pet Animals

In affected Siamese, the shortened tail appears to be a recessive trait.
In Japanese Bobtails and other bobtailed breeds, a short, bent tail is the distinguishing breed trait. Heterozygous cats have abnormal tails. Homozygous cats have the preferred full bobtailed trait therefore breeders treat the gene as though it were recessive.
it has also been seen in the Scottish Fold, often with thickening of the tail, as an effect of the Fold gene which causes problems with hindlimbs and the tail.


Type: impairing, probably autosomal recessive
Breeds: Colourpoint Persian (Himalayan)

Inherited cataracts (opacity) has been seen to occur in both eyes. The cataracts are extensive by as early as 12 weeks old.


Outdated term covering the constriction of any of orifices into/out of the heart, including orifices leading from one heart chamber to another. Additionally the lower part of the oesophagus does not relax, causing problems with food reaching, or being retained in, the stomach. Kittens may have problems holding down food after weaning and may vomit/retch. Before the cardiac stenosis develops, the oesophagus may be dilated. Growth is retarded and kittens may become emaciated. Death may be due to a number of causes (starvation, choking, organ failure etc). This term encompasses many different conditions now individually identified in this list and is included because it appears in older literature.


Type: possible genetic predisposition
Breeds: Burmese, Siamese, Abyssinian

More often related to taurine deficiency or Panleukopaenia infection than to hereditary causes. Burmese, Siamese and Abyssinian are reported to be predisposed to DCM, but a genetic link has not been confirmed. The increased risk of DCM in these breeds was reported before diets contained sufficient taurine. Possibly these breeds have a higher taurine requirement/were fed insufficient taurine and/or are predisposed to DCM. Dilated Cardiomyopathy (DCM)


Type: various depending on breed
Breeds: Maine Coon, Persian/Exotic, British Shorthair, American Domestic Shorthair, Ragdoll

Kittleson et al (1999) identified autosomal dominant (with 100% penetrance) HCM in a family of Maine Coon cats.
Martin et al (1994) identified left ventricular hypertrophy in a closed colony of Persian cats.
Baty et al (2001) found a hereditary predisposition to HCM and aortic thromboembolism (AT) in a family of American domestic shorthairs.
Meurs et al (1997) found a hereditary predisposition to HCM and abnormal mitral valve in a family of American domestic shorthairs.
Saunders et al (2001) found a hereditary predisposition to severe HCM in the Ragdoll.
Some Maine Coon/Maine Coon crosses with HCM have a mutated Myosin Binding Protein C; some Ragdolls have a different mutation of the same protein. A colony of maine Coons had the Myosin Binding Protein C mutation and all had HCM. However, other Maine Coons with HCM lack this mutation and have as yet unidentified mutations. The same mutation has been found in the Siberian, but no reports of HCM. Increased incidence of HCM reported in the Ragdoll due to mutation of Myosin Binding Protein C (different from that in Maine Coon) causing sever HCM with earlier onset of congestive failure and poor prognosis.
A familial incidence of HCM reported in both British Shorthairs, but an inherited gene defect has not yet identified. HCM is also reported in Bengals, but no gene marker identified. An instance of HCM has been reported in the Australian Mist. Anecdotal reports of familial incidence of HCM in Cornish Rex and Devon Rex. Sudden death from HCM (diagnosed post mortem or through x-rays/scans) have been reported in cat magazines by owners of Persians, Exotics (and crosses of either of these breeds) and British Shorthairs (mainly British Blues). These breeds are related. Lethal, autosomal dominant with 100% penetrance in Persians - characterized by progressive enlargement of heart and thickening of heart muscle. Heterozygotes develop the heart disease, homozygotes are stillborn. Sudden death has been noted in cats only a few years old although 10-11 years seems more usual (by which time the cats may already have been bred). Increased incidence of HCM reported in the Norwegian Forest Cat, Persian, Scottish Fold, suspected genetic defect, but no specific mutations/mode of inheritance identified. Anecdotal reports of familial incidence of HCM in Sphynx and Turkish Van. Many cats adapt their lifestyle as the disease progresses and may die of other causes before heart failure occurs.


Type: possible genetic predisposition
Breeds:Burmese, Siamese

Increased numbers of fibrous stands across the heart chambers. Anecdotal evidence that Burmese and Siamese cats may be predisposed to increased or enlarge moderator bands across left ventricle.


Breeds: Burmese, Siamese and derivative breeds

Affects the myocardium or endomyocardium and restricts the diastolic ventricular function (relaxation). Hypothetically related to endomyocardial fibroelastosis (EMF) which has been reported in Burmese and possibly Siamese (and their derivatives).


Type: autosomal dominant
Breeds: any. Rare in cats originating from Asian region

50% - 60% of cats originating from areas where catnip is indigenous have the gene enabling them to detect nepetalactone, the active ingredient in catnip. Breeds whose ancestors originated from areas where catnip is not indigenous typically lack the required gene and won't react to catnip. The latter group includes most randombred cats in Australia. The catnip response includes face-rubbing, drooling and temporary euphoria due to stimulating pheromone receptors. The effect lasts around 10 minutes and it is normally about 2 hours before the cat becomes receptive to nepetalactone again.



Due to premature death of brain cells. Causes severe ataxia, wide-legged posture, high-stepping gait and spasticity progressing to degeneration of eye responses/reflexes. Ataxia manifests around 18 months and blindness by about 36 months.


Type: autosomal recessive

A cause of ataxia (in-coordination) noted in 2 generations of cats.


Type: both genetic and infection causes suspected, impairing

CH was seen in 3 litter mates and hereditary factors suspected. This condition can occur when the mother has a viral infection during pregnancy. Known colloquially in the UK as spasticity (old name for cerebral palsy in humans). In general the ataxia does not worsen and life expectancy is unaffected. It is managed by arranging the environment to accommodate the unco-ordinated cat. Owners of CH cats also report a "sunny personality".


Type: autosomal recessive suspected
Breeds: Siamese

Possibly a lysosomal storage disease resulting seizures, altered behaviour and hindlimb weakness at 2 years old.


Type: impairing, autosomal recessive
Breeds: various, notably Blue smoke Persian

Chediak-Higashi syndrome is associated with a light bluish coloured coat and pale yellow-green iris (reflects red in photo flash) due to reduced/absent pigmentation of the tapetum (reflective layer) of the eye. Photo-sensitivity is common and there may be early development of cataracts. The optic nerves mis-routed, causing squint or cross-eyes. White blood cells and melanocytes contain enlarged granules. Bleeding time, even after minor surgery or injury, is increased and haematomas (blood-blisters) can form in the tissues. It has been seen in some blue-smoke, yellow-eyed Persian cats.


Type: unknown
Breeds: Siamese, Abyssinian, Persian, Himalayan, Burmese (pre-disposition to condition)

Genetic links are suspected in chronic mouth and gum inflammations where other causes have been ruled out. Certain breeds show a predisposition to chronic mouth inflammation and may have the usual symptoms associated with inflamed and painful mouths. Some cases in randombred cats have been resolved by extraction of all teeth and the cause described as "auto-immune".


Type: impairing, presumed autosomal recessive
Breeds: any (observed in a domestic cat colony)

Affected cats have reduced body mass, slow growth rate and increased numbers of stillborn kittens in cats homozygous for the mutation.


Type: lethal/impairing
Breeds: Various, but more common in round-headed cats such as ultra-type Persians

These two defects are linked though they may occur independently. Though some are random developmental defects, there is also evidence for a hereditary link so it is advisable not to breed from affected cats. In the lethal form of cleft palate, the entire soft and hard palates may be absent or nearly so. In the mild form, there are small holes in the palates that can be surgically repaired. There are many stages intermediate between these extremes. Complications include ear infections. Tube feeding is necessary if kittens with repairable clefts are to survive.


Type: impairing (not confirmed if hereditary in all affected breeds)
Breeds: Birman, Persian

Hereditary cataracts have been reported in Persian and Himalayan.


Type: possible predisposition in some breeds
Breeds: Persian, British Shorthair, Siamese

Possible genetic component to some congenital heart defects though toxins, environment, nutrition are also causes. In descending order of frequency are atrioventricular defects (various types of hole in the heart), atrioventricular valve defects, endocardial fibroelastosis (see Restrictive Cardiomyopathy), patent ductus arteriosis, aortic stenosis (predisposition reported in the Siamese) and tetralogy of fallot (combination of pulmonic stenosis, right ventricular hypertrophy, ventricular septal defect and dextrorotation of the aorta). Pulmonic stenosis reported occasionally.


Type: impairing
Breeds: Birman, Burmese Asian

Dermoids are cystic patch of skin, complete with fur; in this case they are found on the cornea.


Type: impairing, probably autosomal recessive
Breeds: Colourpoint

A type of corneal mummification found in adult Colourpoint cats from extensively inbred lines may have a genetic component.


Type: impairing
Breeds: Manx

Bilateral corneal oedema (cloudiness) develops from around 4 months of age and is progressive.


Type: impairing, possibly monogenic, inheritance mode not determined
Breeds: various

An apparently inherited form of corneal oedema has been reported. Fluid accumulates in the layers of the cornea causing cloudy eayes at about 4 months old. The condition is progressive; corneal tissues break down and bacterial infection follows.


Type: predisposition, impairing
Breeds: Persian Himalayan

Corneal degeneration with brown to black discolouration, often linked to feline herpesvirus-1. Persian appears predisposed either as an inherited predisposition or a side-effect of their facial conformation.


Type: probably polygenes, cosmetic/impairing (retained testicle may be prone to cancer)
Breeds: any, though more common in some lines of Persian, Himalayan/Colourpoint Persian

Bilateral cryptorchids have both testes retained in the body and are sterile. Unilateral cryptorchids (monorchids) have one descended testicle and may be fertile. Affected males should not be bred from, but the recurrence of the trait suggests a genetic component carried and transmitted by the female. Believed to be polygenic with a threshold (where sufficient polygenes must be present to cause the trait). Some cats are late developers where one or both testicles descend at anything up to 12 months old; if used for breeding this perpetuates the trait.


Type: cosmetic, autosomal dominant
Breeds: American Curl and derivative breeds

No defects have been associated with this anomaly in either the heterozygous or homozygous state.


Type: impairing, autosomal dominant

The skin is excessively loose and fragile due to defects in the collagen. It forms folds and is prone to stretching and tearing. It presents a problem in surgery because it is hard to stitch.


Type: Cosmetic/impairing, autosomal dominant (epistatic white masking gene)
Breeds: any in which dominant white is permitted
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals, ban on breeding dominant white cats

Deafness is associated with blue-eyed white cats whose colouration is due to the epistatic (dominant) white gene. Not all blue-eyed whites are affected, but deafness is statistically higher than in orange-eyed whites. Deafness may be evident at birth or may be progressive. Odd-eyed cats (one blue eye, one orange eye) may be deaf it is on the blue-eyed side. The epistatic white gene adversely affects the inner ear and is also associated with light-sensitivity, poor night vision and reduced immune response. Deafness may also occur in association with congenital peripheral vestibular disease. Anecdotally fold-eared cats were considered at risk of deafness, but this does not seem to be the case.


Type: predisposition due to fur type
Breeds: Persian and other longhairs

Predisposition to developing disease due to dermatophytosis with Microsporum canis being most common type. Long fur appears more likely to harbour spores than short hair.


Type: impairing
Breeds: any, possibly more frequent in European Burmese

Diabetes mellitus is due to inadequate insulin production and may be controlled by insulin injection. Symptoms include increased hunger and thirst, increased urine production and sugar in the urine. In cats, Type 2 Diabetes is far more common than Type 1 Diabetes. The risk increases with age and obesity and is more common in male cats. Burmese in Britain, Australia and New Zealand showed a predisposition; the American Burmese is distinct from these and no predisposition has been reported.


Type: polygenes?
Breeds: various (anecdotally Persians and Siamese)

Some breeds are noted for food sensitivities resulting in bloating, discomfort, vomiting and/or diarrhoea. Anecdotally, Persians may be sensitive to the cereal content of dried foods. Anecdotally Siamese cats may have "dodgy tummies". In humans, ability/inability to digest certain foodstuffs is known to have a genetic basis i.e. whether a particular digestive enzyme is produced (milk and alcohol digestion have been studied). In cats it is likely that some breeds have similar mutations relating to mutation/absence of certain digestive enzymes.


Type: impairing
Breeds: Bengal, domestic shorthair

Bengal cats appear to be predisposed. In mixed breed cats, the average age when symptoms of weakness are noticed is 6 years (axonal degeneration with or without demyelination) and 4 years (demyelination or depletion of intramuscular nerve branches). An early onset form is found in Bengals with symptoms at 12 months. Other symptoms included high-pitched sound in the airways, suspected laryngeal paralysis, megacolon (with constipation) and chronic non-healing wounds. Around half the early onset cats improved or recovered fully by around 3 years.


Type: lethal, presumed autosomal recessive
Breeds: Birman Cats

A degenerative polyneuropathy was found in several litters of Birman cats bred from the same parents. Symptoms began at 8-10 weeks. Affected kittens fell frequently, tended to stand and walk plantigrade (on their hocks), had exaggerated limb action and progressive pelvic ataxia.


Type: impairing, autosomal recessive

If reports are correct, this elastic skin condition is a different mutation from the autosomal dominant form cutaneous asthenia also observed in cats. Skin is easily extendible (elastic), very fragile skin where slight scratches cause severe lacerations due to defective collagen.


Type: Familial incidence
Breeds: Burmese, Siamese

Familial pattern of inheritance of thickening of the left ventricle of the heart observed in Burmese. Also seen in Siamese. Clinical signs developed between 3 weeks and 4 months of age.


Type: predisposition, impairing
Breeds: Persian, Himalayan, Exotic

Brachycephalic (short faced) breeds such as the Persian may suffer from entropion (rolling in of the eyelids) due to their facial conformation. The abrasion of lashes against the cornea causes discomfort, infection and possible scarring. Surgically correctable.


Type: impairing
Breeds: Birman

Reported in a group of inbred Birmans. Epibular dermoids are hairy, pigmented skin-like growths that are attached to the conjunctiva at the corner of the eye. In all reported cases, only one eye was affected. The hairs of the dermoid caused irritation and inflammation, but removal of the growth resolved the problem. Mode of inheritance not known, but a genetic factor is indicated as affected cats were related.


Type: impairing, suspected autosomal recessive
Breeds: Siamese, Oriental, Balinese

Blistering in and around the mouth and on limbs. Where blisters occur on limbs, the nails separate from the skin and the cat becomes unable to stand. Blistering of skin occurred between birth and 6 weeks in an affected litter; the claws being shed at 5 weeks old. The sire, but not the dam was known to be affected.


Type: cosmetic/impairing, polygenes
Breeds: Persian, Colourpoint Persian/Himalayan, Exotic

Brachycephalic (short-faced) breeds may suffer from epiphora (continually weeping eyes) due to their facial conformation. It is due to a combination of hairs growing at the inner edge of the eyelid near the nose, abnormal eyelid conformation and blockage of the lower tear duct. In some cases, the tear duct appears absent. It is mainly a cosmetic problem, but can sometimes result in inflammation of the skin around the eyes. More prevalent in extreme/ultra-typed cats and less common in traditional-typed/old-style cats.


Type: impairing, autosomal recessive
Breeds: Burmese

Signs appear between 4 - 10 months of age (average 7.4 months). The cat appears normal until an episode is triggered by factors such as excitement or mild stress. During an episode, the head is held close to the chest when walking or resting; When walking, the head nods up and down and the forelegs are stiff, straight and high stepping while the hind legs flex normally, but are more widely splayed. The pupils are dilated and the claws extended. Afflicted eats can only walk a short distance and cannot land properly from a jump.


Type: familial incidence
Breeds: Abyssinian, Somali

Increased osmotic fragility of erythrocytes occurred in closely related Abyssinian and Somali cats, aged 0.5 - 5 years, causing mild to severe intermittent macrocytic haemolytic anaemia, often associated with enlarged spleen, hyperglobulinaemia, lymphocytosis, mildly elevated bilirubins and elevated liver enzymes.


Type: unconfirmed

In addition to conditions separately listed, there is anecdotal evidence of hereditary factors for the following:
- Eyelid agenesis (lack of eyelids)
- Nictitans gland protrusion (protrusion of third eyelid)
- Persistent pupillary membrane remnants (tags of tissue in the eye attached to the lens)
- Glaucoma
- Lens luxation (slipping lens)
Because environmental factors (including exposure to toxins/illness during pregnancy) can also be the cause, the link may be shared environment rather than genetic.


Type: Predisposition
Breeds: Persian, American Shorthair

As a result of facial conformation, Persians may have predisposition to eyelid coloboma - focal absence of eyelid, usually bilateral. Affects outside aspect of the upper eyelid. Also found in American Shorthair as part of the American Shorthair Craniofacial Defect.


Type: Undetermined, probably sex-linked

A blood coagulation deficit.



Type: lethal, autosomal recessive

A degeneration of neurons of the brain stem. Associated with a pale coat colour similar to non-agouti lilac. Affected kittens show head-nodding at 5 weeks old; more pronounced head-shaking at 6 weeks and incoordinated gait at 8 weeks. These symptoms worsen as the disease progresses. Sight and hearing may deteriorate and growth is stunted.


Type: possible genetic predisposition, impairing
Breeds: Himalayan/Colourpoint Persian, Persian, British Shorthair, Exotic Shorthair, Burmese, Foreign/Oriental Shorthair, Havana Brown, Ragdoll, Scottish Fold, Chartreux.

Cystitis causes frequent, difficult or painful urination, often with bloodstained urine and is less common in older cats. In younger cats the cause is often idiopathic (unknown) while older cats are more likely to get cystitis as a result of infection, bladder stones or bladder cancer. Age, sex, diet and stress levels are factors. Some breeds seem predisposed to cystitis. There is an increased risk for bladder stones in Russian Blue, Himalayan/Colourpoint Persian and Persian cats; increased risk of bacterial urinary tract infections in Abyssinian; increased risk of congenital urinary tract defects in Persian and Manx and urinary incontinence in Manx cats. Idiopathic cystitis is generally more common in pedigree cats, especially Persian cats. Various studies have found Himalayan/Colourpoint Persian, Persian, British Shorthair, Exotic Shorthair, Burmese, Foreign Shorthair, Havana Brown, Ragdoll and Scottish Fold are at increased risk of developing calcium oxalate bladder stones. Chartreux, Foreign Shorthair, Himalayan, Oriental Shorthair and Ragdoll are at increased risk of struvite (magnesium ammonium phosphate) bladder stones.


Type: Predisposition
Breeds: Burmese, Domestic Sorthair, Burmilla, Siamese

Has been observed in closely related Burmese, affecting males more often. Cats show signs of anxiety followed by oral discomfort. In the episodic form, signs appear after eating, lasting up to 2 hours and may resemble seizures. In the continuous form, discomfort intensifies when the cat is excited or stressed and the cats are unable to eat and may self-mutilate through pawing the mouth/muzzle. Often associated with oral disease/pain (e.g. teething, gingivitis, dental extraction). Spontaneous remission and recurrence is common. Similar to trigeminal neuralgia in humans and may result from neurological disorder.


Type: Possible predisposition
Breeds: British Shorthair (UK), Siamese

Separation of the head of the femur from the shaft observed in several males under age of 2 years. The affected cats were also overweight. Signs were severe hind limb lameness.


Type: unknown if genetic or developmental, impairing
Breeds: random

While Radial (front limb) Hypoplasia is more common and has a known genetic cause, Femoral Hypoplasia (under-development of the femur) and Tibial/Femoral Hypoplasia (under-development of both femur and tibia) has only been reported 3 times; 2 cases by Isola, Baron & Zotti (2005) and one case by Alvarez (2006). Associated with hip dysplasia, cardiovascular problems, broad nose and small or narrow jaw.


Type: polygenes (immune system response?)
Breeds: various (pedigree cats more at risk than randombred cats)

FIP is due to the immune response to Feline Coronavirus (FCoV). In studies, purebred cats showed a greater tendency to develop FIP compared to random-bred cats. The immune systems of some breeds is significantly different in how it responds to FCoV, this may result from inbreeding. Australian studies found higher FCoV antibody levels in British Shorthair, Cornish Rex, Burmese, Birman, Russian Blue and Ragdoll compared to Siamese, Persian, Bengal, Devon Rex and randombred shorthairs. British Shorthairs, Cornish Rex and Burmese were more likely to develop FIP. American studies showed an increased risk of FIP in Abyssinian, Bengal, Himalayan/Colourpoint Persian, Rex, Birman and Ragdoll cats compared to Burmese, Exotic Shorthair, Manx, Persian, Russian Blue and Siamese. Some of this variation was found to be due to genetic factors. Inbreeding is known to reduce genetic diversity and reduce immune response.


Type: lethal/impairing, probably autosomal recessive influenced by environmental factors
Breeds: any, more common in Burmese, also seen in Bengal, Oriental

The kitten's chest appears concave, compressed or flattened instead of convex. Spine may be depressed towards the ground. Reduced chest volume causes problems breathing and fast breathing rate. In mild cases, the flat-chested appearance is slight or intermittent and kittens are bright and active. In more severe cases kittens have breathing difficulties, are distressed, have stunted growth and may die. Internal organs are dislocated (severity depends of degree of flat chest). Mildly affected kittens can recover and the chest appears to become less obvious as they grow suggesting the ribcage muscles are involved rather than a skeletal defect.
See also: PECTUS


Type: cosmetic/impairing, autosomal incomplete dominant
Breeds: Scottish Fold and derivative breeds
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals

Ears are folded forwards and downwards like those of many dogs. Kittens are born with normal ears and the folding occurs from 4 weeks of age, being complete by 3 months. Heterozygous cats are generally healthy. Homozygous cats, and a few heterozygous cats, are afflicted by a crippling condition that causes a short, thickened tail, swollen feet and reluctance to be active. Selective breeding reduces the number of cats affected by skeletal problems.


Type: Cosmetic/impairing, autosomal recessive
Breeds: random bred

The affected cat has a small extra pair of ears (pinnae/flaps without ear canals or with dead-ended ear canals). In one group of affected cats, the eyes were small, the jaw slightly undershot, the head was peculiarly shaped and the cats were notably lethargic. The brain was presumed affected. In more recently reported cases, the extra ear flaps were not accompanied by any other deformities or ill-effects. The configuration of the additional ears is highly variable indicating multiple causes (not all genetic), not all of which affect the brain.


Type: predisposition/polygenes (immune system response?)
Breeds: Siamese, Abyssinian, Persian, Devon Rex

Fungal infections rarely cause illness in healthy cats, but cause secondary infections in cats with poor immune response (FIV/FAIDS, FeLV, FIP) or on certain drugs. Siamese, Abyssinian and Persians were found to be predisposed to some fungal infections. Symptoms were nasal discharge, respiratory symptoms, gastrointestinal symptoms, fever, swollen lymph nodes and neurological signs. Devon Rex were found to be more susceptible to yeast infections of the nail bed.


Type: Sex-linked (X chromosome), recessive

Neonatal jaundice and haemolytic anaemia. Found in inbred feral colonies in the Southern USA. Also found in Safari cats in laboratory studies, but was initially induced for epigenetic studies and does not represent a mutation in that breed.


Type: lethal, behaves as autosomal recessive
Breeds: Siamese, Korat and other breeds

A lysosomal storage disease caused by mutated GLB1 gene. Degenerative disease of the brain and spinal cord due to an inherited deficiency of the enzyme beta-galactosidase. Early signs are head tremor and hind limb tremor at 2-3 months old; high-stepping gair, ataxia and flickering eye movements. By 8 months, the cat usually cannot stand up. By 12 months there are seizures and loss of vision. GM1 shows up later and progresses more slowly than GM2. Kittens are stunted with poor appetite and a flat broad head with small ears. This progresses to hind-limb weakness, depression, dementia, seizures, aggression and death at a young age. More common in the US and found in some parts of Europe, but not in the UK (this may change as breeding stock more easily crosses national borders). It has been reported in one Siamese.

Although this defect behaves like a recessively inherited condition, the enzyme deficiency can also be detected in heterozygous cats so that carriers are not bred from.


Type: lethal, autosomal recessive
Breeds: Korat, Burmese

Lysosomal storage disease. A degenerative disease of the nervous system caused an inherited deficiency of the enzyme beta-hexosaminidase . This shows up earlier and progresses faster than GM1. Begins with head tremor at 6-10 weeks, unco-ordinated movement (ataxia) and falling and finally seizures. The head is unusually rounded and the cornea of the eye is slightly opaque. Though the condition is inherited recessively, the enzyme deficiency may be detected in heterozygous carriers of the gene so that carriers are not bred from. In Korats Gangliosidosis GM2 is due to lack of hexosaminidase A and B, resembling Sandhoff’s disease, due to mutated HEXB gene. A different HEX B mutation causes GM2 in domestic longhairs.


Type: lethal, possibly autosomal recessive

Kittens with globoid leukodystrophy develop a tremor, weakness and lack of coordination of the back legs at around 5-6 weeks. The poor coordination progresses to the forelegs due to degenerative changes in the brain. By about 12 weeks the hindlimbs become rigid and straight and the cat cannot empty its bladder. By around 15 weeks there is hindlimb paralysis and by 21 weeks respiratory problems lead to death. The condition is known to be hereditary and believed to be recessive.


Type: deferred lethal, undetermined mode of inheritance

Poor growth, incoordination, muscle weakness and eventual recumbency.


Type: lethal, autosomal recessive
Breeds: Norwegian Forest Cat

Glycogen storage disease type IV is an inherited deficiency of a glycogen branching enzyme. Most commonof the 2 forms causes stillbirth or death within a few hours of birth due to kittens having insufficient glucose to produce energy during birth and the first hours of independent life. If (rarely) an affected kitten survives, it appears normal until 5 months old. Abnormal glycogen accumulates; the nervous system, muscle and heart degenerate. Symptoms were fever, general muscle tremors, bunny-hopping gait, muscle weakness and difficulty swallowing by 5 months of age. Severe muscle weakness, atrophy and contractures occurred by 8 months. Fever disappeared at 8 months. If the cat has not already been euthanised it progresses to tetraplegia. Ventricular hypertrophy occurs by 13 months. If not already euthanized, sudden death occurs from heart failure.


Type: impairing, sex-linked

Breeds: Persian

Characterised by prolonged bleeding after injury or surgery, poor blood clotting and haematomas (blood blisters) under the skin. The gene is sex-linked; carried on the X chromosome and therefore shows up in males, but may be carried undetected by females. Females are only affected if 2 copies of the gene are inherited. Affected cats can survive if care is take to prevent injury.


Type: impairing, sex-linked
Breeds: Birman, Siamese, British Shorthair

Similar symptoms to Haemophilia A, but usually results in milder bleeding. Mode of inheritance is the same as Haemophilia A. Has been noted in inbred strain of British Shorthair


Breeds: Maine Coon


Type: impairing, autosomal incomplete dominant (autosomal recessive has also been reported)

A deficiency of a blood clotting factor that results in a bleeding disease, but usually no prolonged bleeding.


See: cleft palate


Type: XY chromosomal abnormality (occasionally chimerism)

Characterised by ambiguous genitalia. Internal reproductive organs may be under-developed with ovo-testes (not differentiated into either male or female function) located in the abdomen. The causes may be chromosomal or developmental.


Type: impairing
Breeds: Maine Coon, Persian, Himalayan/Colourpoint Persian, Bengal, Devon Rex, Abyssinian; more common in larger breeds

Abnormal development of hip tissue results in fibrous tissue replacing bone. Shallow hip socket and sometimes misshapen head of femur. Severe cases result in lameness. The cats may also suffer slipping kneecaps (luxating patella) and osteoarthritis. Maine Coons may be x-rayed and hip-scored to sheck for hip dysplasia prior to breeding. May also occur in other breeds and randombred cats and is possibly linked to large cobby conformation. In affected cats can be surgically corrected and further managed by keeping the cat from becoming overweight.


Type: lethal, autosomal recessive
Breeds: Siamese
Notes: Hydrocephalus also occurs at random due to developmental mishaps.

Cases of hydrocephalus due to a recessive gene have been reported. The kitten is born large and bloated. The head is swollen, dome-shaped and fluid-filled causing pressure on the brain and progressive debility. There may be other cranial defects such as cleft palate, hare lip, squints or abnormal eye positions (in some cases lack eyes) and also deformed feet. Kittens may be mentally slow and lethargic and suffer seizures and/or dementia; this being progressive as fluid pressure increases. The condition should be considered lethal though there are reported cases of hydrocephalus that have responded to surgery. Adult survivors have unusually wide-set eyes and the upper part of the skull unusually broad or tall.


Type: predisposition
Breeds: Siamese, Oriental

Behavioural problem involving rippling skin, tail twitching, compulsive/frantic behaviour, over-grooming and self-injury e.g. biting the tail or rippling area of skin. Intermittent and can be induced by touching/stroking. Note: diagnosis is by ruling out all other causes of itching/pain and other neurological conditions (fits).
Case study, 2009: Bonnie and Chris Whitford's cat developed FHS following a vaccination at the age of 6.5. He had previously had no symptoms. The condition has responded well to the drug Amitriptyline (a tricyclic antidepressant). There have been no changes in personality, but he is less fixated on tail-chewing. It requires blood tests every 6 months to ensure his liver is unaffected. In addition to Amitriptyline, the 5 inches of the end of his tail are wrapped with Nexcare water resistant adhesive tape. This is tolerated well with only a little pulling when stressed (mostly at mealtimes). Keeping the tip immobile has kept his mind off the tail's tendency to twitch and snake about involuntarily. The tape is periodically changed (with difficulty) for sanitary reasons although the cat "turns into a demon when it’s uncovered".


Type: lethal, autosomal recessive
Breeds: any

Rare. Affected cats to develop fatty masses (xanthomata) due to fatty blood leaking out of damaged blood vessels. The fatty masses compress peripheral nerves causing nerve damage. Lipoprotein lipase (LPL) activity is absent or reduced and there may be associate anaemia. In some cases (not typical presentations and in retrospect probably Transient Hyperlipidaemia) kittens grew normally but had persistent lipaemia (excessive fatty substances in the blood resembling "cream of tomato" soup). Around 8-9 months they became unable to move their eyelids, chew properly or extend the toes and lost the knee reflex. Multiple haematomas affected peripheral nerves, causing loss of sensation. There was facial paralysis, limb paralysis/muscle atrophy and laryngeal paralysis causing breathing problems. Some symptoms were reduced after 2-3 months on a low fat diet, but prognosis was generally poor.


Type: lethal, autosomal recessive

Acute renal failure occurs between 5-9 months old. Cats become depressed, anorexic, dehydrated and weak. Death occurs soon after (euthanasia is necessary due to deteriorating condition). Other symptoms include a crouching, cow-hocked stance, reluctance to stand or walk, depressed patellar reflex. The kidneys are painful and kidney failure is caused by deposited oxalate crystals in the kidney tubules. The liver and spinal cord are also affected. Heterozygous cats may have intermediate liver levels of the enzyme D-glycerate dehydrogenase, allowing carriers to be removed from breeding programmes.


Type: impairing/lethal, inheritance mode not proven
Breeds: Burmese

Manifests in Burmese kittens aged 2-6 months as muscle weakness due to transient low blood potassium as more potassium enters cells. There is general muscle weakness and pain, extreme neck weakness, head tremor, a stiff stilted gait and affected kittens are reluctant to walk. When they walk, there is knuckling of the wrists and a tendency to sink onto the hocks and to sit with the knees out. These symptoms may be induced or worsened by exercise, stress or cold weather. Severely affected cats may collapse and die of respiratory paralysis, but in milder cases potassium supplements can give relief. See also Episodic Weakness (Hypokaleamic Myopathy))


Type: impairing, autosomal recessive
Breeds: any
Note:Siamese show a reduced risk of hyperthyroidism developing compared to other breeds or randombred cats.

A hereditary form of hypothyroidism has been observed in single research colony of Abyssinian cats, but not in the general Abyssinian breeding population. Homozygous kittens were normal-looking at birth, but had reduced growth rate, and were disproportionate dwarfs by 6-9 months old with short limbs, round body, enlarged broad head, kitten-like features, constipation and goiter, and were dull and lethargic (cretinism). Treatment with oral thyroxin gave variable results.


Type: cosmetic/impairing, autosomal dominant (Donskoy, Peterbald) and recessive (Sphynx) forms exist
Breeds: Siamese, Cornish/Devon Rexes, Sphynx, Donskoy, Peterbald, Hawaiian Hairless
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals

Sparse hairs, often poorly formed; the hair bulbs are poorly formed and hairs are easily dislodged. Skin may be abnormal and thickened. Affected newborn kittens may have light coat of fur and lose it within weeks; it may (or may not) regrow patchily. Cornish and Devon Rexes with hypotrichosis may not be bald, but have significantly less fur than normal-furred Cornish/Devon Rexes (the Devon Rex mutation affects the same gene involved in the Sphynx mutation). Hairless breeds generally have a fine down that may be lost as the animal ages. Cats in Canada (Sphynx), France and England all had different recessive mutations. The Hawaiian Hairless (Kohana) is genetically identical to the Canadia Sphynx, but also lacks hair follicles due to interaction of other genes, these cats breed poorly.Some Rex cats are prone to temporary hairlessness, termed "baldness" to differentiate it from true hairlessness, during moulting. Some advocate destroying random-born hairless kittens, but the condition can be managed provided the cats are not exposed to extremes of weather or to environments where skin damage is likely. The decision to perpetuate new hairless mutations as breeds should not be made lightly.


Type: Predisposition
Breeds: Persian, Exotic and other brachycephalic (short-muzzled) cats

Signs include facial itchiness, redness and ulceration where no causal agent can be identified. Chin dermatitis is often attributed to an allergy to plastic foodbowls.


Type: possible genetic predisposition, impairing
Breeds: Persian

Seen in cats aged 9+ years and Persians seem over-represented in reported cases. Respiratory distress, shortness of breath, lung sounds and coughing. The lungs become mildly inflamed, but no pathogens are found. Most cats died within days to months of symptom.


Type: autosomal, recessive, impairing
Breed: Toyger, other cats with the short, rounded ear mutation

A male Oriental with unusually short and rounded ears, was imported from Italy to the USA for use in Toyger breeding. The short and rounded ear trait was found to be due to an autosomal recessive gene. Some descendants with this physical trait appeared clumsy, somewhat uncoordinated and tended to walk on their hocks. They were referred for investigation because of their “quiet” mental state. Affected cats and healthy relatives were investigated at the University of California (UC)- Davis. Cats with neurological symptoms had enlarged brain ventricles (fluid filled cavities in the brain) and thinning of the grey and white matter, often with cysts and multiple midline and callosal malformations. This syndrome appears clinically mild despite the marked structural malformations of the forebrain. The mild appearance is because the forebrain (the “thinking” region) is less important than the mid-brain in normal feline function. Although they had normal sexual behaviour, affected females in the investigated group appeared to be infertile. The link between the neural abnormalities and external ear development was not identified, but the appearance of the ears serves as an important phenotypic marker for affected cats.
Keating MK, Sturges BK, Sisó S, Wisner ER, Creighton EK, Lyons LA. Characterization of an Inherited Neurologic Syndrome in Toyger Cats with Forebrain Commissural Malformations, Ventriculomegaly and Interhemispheric Cysts. Journal of Veterinary Internal Medicine. 2016;30(2):617-626. doi:10.1111/jvim.13836.


Type: impairing, polygenes (related to facial conformation)
Breeds: Persian/Himalayan, Exotic

Prognathia means the upper (maxilla) or the lower jaw (mandible) protrudes beyond the other. If the upper jaw protrudes, it is overbite/undershot jaw ("parrot" face). If the lower protrudes is is underbite/overshot jaw ("bulldog" jaw). Excessive prognathism may cause problems suckling or eating. Short-face breeds are also predisposed to twisted or misaligned jaws and overcrowded teeth due to the small jaw.


Type: cosmetic
Breeds: Siamese/Oriental, Burmese and derivative breeds

Originally common in Siamese cats, but now considered a fault. Caused by deformities of tail vertebrae, usually closer to tip than to base. May be single or multiple kinks. Rarely cause discomfort and are a cosmetic issue only, but may ocasionally reduce mobility of tail in vicinity of the kink.



Type: unknown, impairing/lethal
Breeds: Domestic Shorthair, Siamese

Symptoms at 6-12 months are weakness of hind limbs. Progresses to weakness of all 4 limbs, facial spasm, severe extensor contracture and atrophy of muscles.


Type: cosmetic
Breeds: any, ginger/cream cats

Benign skin defect causing hyper-pigmented (dark) spots up to 1 mm diameter, most visible on the nose leather and rims of the eyes and occasionally as black hairs in the coat. Initially believed to be sex-linked as it was observed in red/cream males, but I have reports (and photos) of ginger female cats that have developed dark spots ("freckles") over their lifetimes.


Type: Predisposition
Breeds: European Burmese (Britain, Australia and New Zealand)

A transient milky appearance develops on one (rarely both) eyes between 5 and 12 months old, sometimes recurring. This resolves within 1 - 3 days. After the age of 1 year no further instances occur. Blood from affected cats shows raised lipid levels, suggesting abnormal lipid metabolism. The American Burmese is genetically different and this has not been reported in that breed.


Type: Predisposition
Breeds: Munchkin

Lordosis causes a dip in the spine and compression in the chest and has been observed in Munchkins; there may be a breed predisposition.


Type: impairing, probably polygenes
Breeds: Abyssinian, Devon Rex, Bengal, Maine Coon

Best known in Devon Rex. The patella (kneecap) is displaced from its normal position either by force or spontaneously. Usually affects both hindlegs, leading to limping, bunny hopping or hind-limb collapse. May recur if the trochlear groove is shallow or malformed. Minor cases may correct itself and cause only temporary discomfort or it may require surgery if the condition recurs or causes lameness. Cats with luxating patella have a greater tendency to hip dysplasia than those without.


Type: suspected predisposition
Breeds: Persian

Signs include ascites (fluid-effusion in the belly), jaundice, hypergammaglobulinaemia, anorexia, fever and weight loss. The condition progresses through an active stage where bile ductules proliferate to a stage of progressive monolobular fibrosis that distorts the liver architecture and causes enlarged liver. The rate of progression varies. It may be mistaken for FIP.


Type: Autosomal recessive suspected, impairing/lethal
Breeds: Siamese

Siamese appear predisposed to mediastinal (thymic/thoracic) lymphoma (lymphosarcoma). Affected cats are often less than 2 years old and are FeLV negative. They often respond well to chemotherapy.


See: Gangliosidosis GM1, Gangliosidosis GM2, Mannosidosis

Lysosomal storage diseases affect the part of the cell that recycles chemicals, including the gangliosides; gangliosides are vital for normal brain cell function. The two types of Gangliosidosis relate to which ganglioside (GM1 or GM2) accumulates in lysosomes. Though symptoms are similar, they are due to separate mutations. 12 different Lysosomal Storage Diseases have been described in cats; some of these are caused by multiple mutations.

This account received from Tashia White-Sumner in March 2018 suggests one of the Lysosomal Storage Diseases. On February 15, 2018, Tashia’s daughter’s stray cat had a litter of six small kittens. The mother was inexperienced and needed human help. One kitten was absolutely tiny – about half the size of the others and looked unusual with an oddly shaped head – but was fully furred and didn't appear premature. She was tortie, the only “colourful” kitten in the litter. She didn’t start breathing until Tashia rubbed her chest to revive it. She remained the runt of the litter, not growing or filling out like her siblings. Tashia supplemented her feeds with KMR (Kitten Milk Replacer) and made sure she had some time alone with the mother cat in order to suckle. She did not gain weight, remaining drastically tiny and lethargic. At six days old, the whole litter was seen by the vet who suggested the kitten had a neurological or other organ issue and would be lucky to survive another two days. That night the runt stopped breathing but was revived with chest rubs, sugar water and KMR.

Every other day she would crash in the same way (this suggests she could not lay down any energy reserves). She would only take drops of formula at a time. She slowly grew in size but did not lay down any fat and remained just all skin and bones. At 9 days old she weighed 59g, which was much higher than her birth weight. On day ten she was up to 67g, but dropped back down to 63g and fluctuated a gram back and forth from day 11 until day 14, never weighing any heavier than 67g. Whiskers appeared on day 10, eyes opened on day 12, but she died on day 14.

kitten with suspected lysosomal storage disease

On day 12 the inexperienced mother broke the tip of the kitten’s tail which turned black but did not fall off before the kitten died. At this point the kitten received supplementary feeds every 30 minutes in addition to suckling from the mother cat and from another lactating cat. The vet still suspected neurological issues but could not perform any tests on such a tiny kitten. The kitten cried and was a fighter during her 14 day life, but could not maintain her own body temperature. Despite warmth and intensive care she died around midnight on the 14th day. She had been noted as being yellow that day when she was normally grey on her feet pads (jaundice, indicating liver problems, again a metabolic issue). Her abdomen had a dark spot that was not there previously and she was having regular bowel movements. A week previously, the side of her stomach had swollen while eating and then went back down; it never did this again.

The photos show her at 12 days old with her brother. Her brother is small for his age but the tortie kitten is only about half his size. The vet also suggested a possible placenta issue which would have caused her to waste away in the womb instead of receiving proper nutrition, but her inability to gain weight, maintain her own body temperature, lay down fat or store glucose, in combination with the oddly shaped head, indicates a metabolic disorder.


Type: predisposition
Breeds: Siamese

Compared to non-Siamese, Siamese females are at twice the risk of mammary carcinoma and are likely to develop it at a younger age. Males are sometimes affected.


Type: lethal, autosomal recessive
Breeds: Persian

A lysosomal storage disease. Mannosidosis is an enzyme deficiency that affects the central nervous system. Results in accumulation of large sugar molecules in the brain, kidney and liver. Most kittens with mannosidosis are either stillborn or die at birth. Those that survive usually show symptoms during the first few days or weeks. Symptoms are general apathy, inability to stand properly and diarrhoea, progressing to tremor and ataxia (inco-ordination). The voice becomes weaker and an enlarged liver causes a swollen belly. There may be bizarre behaviour/dementia, corneal and lens opacification and retarded growth, ending in premature death. Age of onset and rate of progression of symptoms are variable reflecting variable degree of enzyme deficiency.


Type: Deferred lethal (semi-lethal), autosomal incomplete dominant with high penetrance
Breeds: Manx, Cymric and derivative breeds
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals. In spite of available veterinary and research literature, some North American breeders deny the existence of Manx syndrome and blame poor breeding. Manx syndrome is well recognised and is used as a laboratory model for human spina bifida.

Homozygous Manx die before birth and are resorbed, mummified, aborted or stillborn. Stillborn kittens show gross abnormalities of the central nervous system. All surviving Manx are heterozygotes. Heterozygous Manx are affected to a greater or lesser degree. The most visible effect is shortening of the tail, varying from complete absence through to partial tail; different lengths can occur in a single litter. Some Manx die before 12 months old and exhibit skeletal and organ defects. In severe cases, spina bifida occurs due to malformed spinal canal. Syndrome includes sacrocaudal dysgenesis, megacolon and constipation, rectal prolapse, congenital urinary tract defects, spina bifida, hopping gait (hind legs not moving independently). Manx syndrome is a neural tube defect affecting the entire vertebral column. Vertebrae at the front end may be shorter than normal. Those at the hind end are fewer in number and some may be fused. The pelvis may be malformed and fused and the anal opening may be narrow, causing constipation (evident at weaning). The spinal cord may terminate prematurely causing poor hindlimb control.

To reduce the likelihood of homozygous kittens, breeders should not breed two tailess Manxes together. Problems can be avoided by breeding tailess cats with tailed ones; this is reducing the occurrence of Manx syndrome. In one study Manx syndrome affected one fifth of Manx cats, mostly tailless. Cats with partial tails may be prone to painful arthritis of the tail and in the US, the partial tails are often amputated (the prevalence of arthritis is disputed).


Type: predisposition
Breeds: Siamese

Two distinct forms of cutaneous mast cell tumours have been recognised in cats: mastogenic and histiocytic (less common). Siamese cats appear to be three times more likely than other breeds to develop mast cell tumours with males at slightly more risk.


Type: impairing, mode undetermined
Breeds: Siamese and related breeds

Some cases of megaoesophagus appear to have a hereditary link. The oesophagus is dilated and peristalsis impaired so that swallowed food may be regurgitated. This becomes apparent after weaning. The condition can be managed by elevating the food bowl so that gravity assists in getting food into the stomach. If untreated, weight loss and malnutrition are likely. The condition is also called eosophageal achalasia, oesophageal dilatation, oesophageal hypomotility and oesophageal neuromuscular disease.


Type: lethal, autosomal recessive
Breeds: Burmese

Fatal herniation of meninges (brain sac) and brain tissues and is apparent in newborn kittens as soft swellings on the forehead and face. of the newborn. It was initially linked to the round-headed American Burmese, but affected kittens have been born to Burmese cats with relatively long skulls.


Type: Unknown, impairing/lethal
Breeds: Domestic Shorthair, Maine Coon, Siamese

Progressive hind-limb weakness from 2-5 months old.


Type: deferred lethal, autosomal recessive

Abnormal facial features, retarded growth, large paws, poor growth and progressive hind-limb paralysis. Flat, broad face, hypertelorism (abnormally wide-set eyes), frontal bossing, small ears, thickened upper and lower eyelids. Dilated pupils, retinal degeneration leading to blindness. Tickened skin, especially on the back of the neck. Severely deformed spinal column, fused vertebrae, hip dysplasia, abnormally shaped skull and generalised decreased bone opacity. Differentiated from mucopolysaccharidosis by blood and urine tests. Affected cats die within the first few days to first 7 months of life, often due to upper respiratory disease or cardiac failure.


Type: lethal, autosomal recessive

An enzyme deficiency that causes grossly abnormal neurons in the brain and spinal cord. The facial profile of affected cats is altered: short, broad nose, depressed nasal bridge, prominent forehead, small ears and opacity of the cornea. The affected cat sits crouched with spread forelegs. The cervical vertebrae unusually wide, asymmetrical and frequently fused. The breast-bone (sternum) is unusually concave. Enlarged liver and spleen may cause a swollen belly. Though the gene behaves as a recessive (lethal in homozygous cats), the enzyme deficiency can also be detected in heterozygous cats, allowing carriers to be screened out of breeding programmes.


Type: impairing, autosomal recessive
Breeds: Siamese

A lysosomal storage disease due to an enzyme deficiency; can be treated using bone marrow transplants. Affected cats have slow growth, a short, broad nose, depressed nasal bridge, widely spaced eyes and small ears. The face has a flattened appearance. The eyelids appear to be narrow, the upper lid is swollen and drooping. The cornea of the eye is slightly opaque. The vertebral column is deformed, especially the cervical, thoracic and lumbar regions. Signs evident from 6-8 weeks as the kitten adopts a crouching gait. Joints may be painful and hindlimbs weak due to compression of the spinal cord within the backbone. Bony changes progress until around 9 months old and may stabilise. There are changes within major organs and white blood cells. The enzyme deficiency can be detected in heterozygous cats, allowing carriers to be screened out of breeding programmes. There are 2 biochemically distinct forms of Mucopolysaccharidosis caused by different mutations of the same gene, but the disease is very similar or identical.

Note: There are 2 forms of Mucopolysaccharidosis VI (MPS VI) in cats: the more severe L476P mutation identified in cats from Italy and North America and the milder, very widespread D520N mutation. These are inherited independently of each other. L476P homozygotes have dwarfism and facial dysmorphia. D520N (MPS VI Mild) homozygotes have normal growth and appearance and are unaffected by disease UNLESS they also carry the L476P (MPS VI Severe) mutation. Cats with one D520N and one L476P have normal growth and appearance and only mild MPS VI signs. Both mutations are in the ARSB gene.

Cherisse from Idaho, USA, provided these photos of Myrtle, a 3 month old black female kitten with apparent midgetism and Mucopolysaccharides 6. She has a minor cleft palate, nasal issues, weeping eyes, an undershot jaw and dwarfism in her front legs. She also has a cranial deformity with bulbous, protruding eyes. She is, nevertheless, active and happy and is on a semi-liquid diet due to her facial conformation.


Type: deferred lethal, autosomal recessive

Observed in 2 feral kittens from an inbred colony in California. Cause stunted growth, short limbs, paralysis of limbs, fusion of bones, clouded eyes, tendency to upper respiratory infections and early death (in the 2 reported cases, one died aged 21 months, one at 7 months). It has also been reported in a domestic shorthair cat in Switzerland and in in Michigan, USA. A further case occurred in Trenton, Ontario. A 3-month old, female farm kitten presented with weakness in her rear legs. Compared to an unaffected littermate, she was small for her age, had a rounded head, hollow chest and hind limb paralysis. She was not in pain and pulled herself along with her forelegs. By 6 months old all four limbs were paralysed and her corneas became opaque. X-rays found spinal abnormalities and enlarged organs. Diagnosis was MPS VII, but analysis found it to be a new spontaneous mutation.


Type: Sex-linked, X chromosome
Breeds: Domestic Shorthair

Dystrophin-deficient muscular dystrophy. Progressive and histopathologically resembles human Duchenne/Becker muscular dystrophy except for the lack of fat infiltration and the presence of prominent hypertrophy of both muscle fibres and muscles groups in the feline form. Affects predominantly male cats. Muscles large but very weak. May have problems swallowing due to large tongue and poor function of oesophagus. No cure, but cats can be managed except in severe cases.


Type: impairing, genetic predisposition
Breeds: Abyssinian, Somali

These breeds show a predisposition to developing myasthenia gravis, an auto-immune nerve condition. Cats become reluctant to exercise and develop muscular weakness, progressive stiffness, crouching gait, weak neck, muscle tremors and often a barely audible voice. The affected cat will eventually collapse onto its chest with the head to one side of the front paws. Medication is possible, but there is a danger of recurrence and of death from aspiration pneumonia.


Type: Predisposition
Breeds: Abyssinian, Somali, Siamese

MAC is a slow-growing bacterium. Disseminated MAC infection (disease similar to TB) found in 10 young Abyssinians and 1 Somali cat aged 1 - 5 years, all Australia or North America. Cats had weight loss, but good appetite, difficult breathing and/or coughing and enlarged lymph nodes. Hair clipped to allow blood tests re-grew slowly or not at all. 3 Siamese from father-daughter matings were affected; signs included anorexia, weight loss, lethargy, fever, pale mucous membranes, enlarged lymph nodes and spleen. All deteriorated in spite of antibiotics and were euthanized. May indicate poor immune response and predisposition to certain mycobacterial infections.


Type: suspected autosomal recessive
Breeds: any

Muscle spasm and stiffness, stiff awkward gait with out-turned feet and poor flexing of joints. Muscles unusually large. Eyelid/facial spasms when startled. Stiffness is worse in cold or on wakening. If affected kittens are startled they may stiffen and fall onto their side (like the famous "fainting goats"). Jaw does not fully open so there may be problems eating.


Type: predisposition
Breeds: Siamese

Reports suggest Siamese cats are more prone to nasal cavity tumours, possibly due to the elongated nose. However the popularity of Siamese cats may be the reason they are over-represented. Siamese have an anecdotal predisposition to nasal polyps based on the association between nasal polyps and asthma in humans.


Type: suspected autosomal recessive, impairing/lethal
Breeds: Domestic Shorthair

Progressive weakness with rapid staccato gait and tremors, starting from 6 months old.


Type:inheritance mode undetermined
Breeds : Noted in a family of domestic shorthairs

Degenerative neurological disorder similar to feline hereditary neuroaxonal dystrophy (FHND) syndrome, but later onset (6-9 months) and is not associated with abnormal coat colour (Chediak-Higashi). Begins with hindlimb ataxia/paralysis, progressive worsening with hind limb muscle atrophy. Noted in domestic shorthairs among siblings from several litters from the same female barn cat; cats presented for study ranged up to 3 years of age.


Type: impairing
Breeds: Snowshoe

Onset is 4-8 months old. Signs are intermittent hind limb weakness with significant muscle loss; the condition becomes progressively more debilitating.


Type: undetermined

A lysosomal storage disease seen in Siamese. Results in progressive degeneration of the brain, blindness (with retinal atrophy) and seizures. Ceroid-lipofuscin pigment is deposited within neurons of the central and peripheral nervous systems. Unlike the human form, neuronal ceroid-lipofuscinoses, pigment deposition appears restricted to neural tissues.


Type: lethal, dominant
Breeds: Ojos Azules

The gene causing Ojos Azules blue eyes is lethal in the homozygous state. Individuals with 1 copy of the mutant gene have vivid blue eyes, a flattened tail tip and often white tail tip/paws. Kittens with 2 copies have gross deformities and cannot survive.


Type: impairing, autosomal recessive
Breeds: Abyssinian

Characterised by "onion-like" swellings on the hairs, usually at the tip, but may occur along the hair shaft. The swelling is just visible to the naked eye. The coat is lustreless and feels rough when stroked. The swelling is due to enlargement of the inner core of medulla cells. Apparently caused by a single recessive gene mutation since onion-haired cats can be born to normal-coated parents. Historically (early 1900s) there have been reports of "broken-coated" cats, these may have exhibited the onion-hair trait.


Type: dominant, impairing
Breeds: Scottish Fold and derivative breeds

The Fold mutation affects the cartilage, the most visual sign being the folded ears. All Scottish Folds have variable degrees of painful degenerative joint disease; there is fusing of the tail, ankles and knees. This causes lameness, reluctance to jump, stiff stilted gait, short misshapen lower limbs, swelling of foot region and short thick inflexible tails. Homozygotes are most severely affected. Heterozygotes have a milder form of the condition. As a result, the bree is not accepted by several cat fancies.


Type: predisposition
Breeds: Persian/Himalayan, anecdotally in Scottish Fold

Otitis externa (infection of external part of ear canal) is generally common, but Persians may have a predisposition. The popularity of Persian cats may also mean they are over-represented in surveys of the condition. Anecdotally, the Scottish Fold was considered susceptible to ear infection due to its ear conformation.


Type: Predisposition
Breeds: Munchkin

Pectus affects the chest/ribcage and has been observed in Munchkins; there may be a breed predisposition.


Type: lethal, autosomal dominant
Breeds: Birman

Causes abnormal segmentation of the nuclei of granulocytes (one of the several forms of white blood cell). Heterozygotes are healthy, but may have leucocyte abnormalities. Homozygotes may die in utero or early in life and may have skeletal dysplasias.


Type: undetermined
Breeds: Burmese, Siamese

Symptoms of a heritable form of peripheral vestibular disease in Burmese are apparent at birth or soon after: head tilt, poor balance, flickering eye movements and ataxia, sometimes deafness. In Siamese, signs developed at 3-4 weeks old, usually improving by 3-4 months old.


Type: impairing
Breeds: Himalayan/Colourpoint Persian, Persian, possibly British Shorthair and other colourpoints (particularly blue-points)

The abdominal cavity directly communicates with the pericardium (sac around the heart). Persians and Colourpoint Persians (Himalayans) appear predisposed to this. Anecdotally, blue self and blue-points are at an increased risk.


Type: Polygenes
Breeds: Persian, Colourpoint Persian/Himalayan, Exotic

"Persian syndrome" describes the various problems that may accompany the short-muzzled head shape of Persian and related breeds. The syndrome includes absent, deformed, narrow or non-draining tearducts (causing tears to flow down the face); narrow nasal passages causing breathing difficulties (some Persians become mouth-breathers); twisted, undershot or overshot jaw and eyelid problems such as entripion (rolled inwards) or coloboma (notch in lower eyelid due to abnormal facial plates) and a predisposition to corneal problems. It may include high palate (causing suckling problems). The short muzzle may cause problems in feeding, with cats appearing to flick food upwards. Along with anecdotally reported food sensitivities in Persians, the flattened face has led to "Persian formulation" dried foods which also have a kibble shape/size suited to the breed's facial conformation. The most severely affected was the extremely dome-headed, short-faced Peke Faced Persian caused by a gene mutation. The Peke Faced Persian is no longer bred, but the trend to extreme (or ultra) typing produces cats with similar appearance and problems.


Type: undetermined
Breeds: undetermined, possibly Sphynx (2015)

Pink-eyed dilution was reported by NB Todd NB in 1961. "A pink-eyed dilution in the cat" (Journal of Heredity 52, pg 202). The usual type of dilution found in cats is blue dilution which turns black into grey. A second type of dilution seen in some mammals is "pink-eyed dilution" which gives a bluish-tan/fawn coat and also depigments the eye, giving a pink or ruby appearance. According to Todd, this has been reliably reported only once in cats when a pink-eyed female with a light tan coat was produced. None of her kittens survived so pink-eyed dilution in cats seemed to have been lost. In 2015, a pink-eyed Sphynx kitten of unidentifiable colour appeared in Australia. It matched the description of bluish-tan/fawn colour as well as having gold irises with ruby red pupils. Genetic testing at UC Davis was unable to identify its colour, but ruled out the known dilution and albinism genes.


Type: lethal, autosomal dominant
Breeds: Persians, Exotic Shorthairs and derivative breeds

In one form of PKD, kittens are born with enlarged abdomens and death occurs at 6-7 weeks old. Post mortem showed enlarged kidneys, comprising dilated cystic channels, and cystic bile ducts of the liver. In the most common form of PKD, kidneys enlarge with age, kidney function deteriorates and kidney disease occurs between 3 and 10 years old. Kidney cysts are evident through ultrasound scans by 8-10 month old; cats with multiple cysts in both kidneys are confirmed with PKD. Those with fewer cysts should receive regular checks. Severely affected cats may show signs of kidney failure at 2-3 years old, while others show no symptoms until old age. PKD cats should not be bred, but can continue to live as pets while they remain healthy though their lifespan will be shortened. Kidney transplantation can extend their lifespan. Other breeds may have PKD, but the differing symptoms indicate different mutations.


Type: Related to Polycystic Kidney Disease
Breeds: Persians, Exotic Shorthairs and derivative breeds

Some cats affected by Autosomal Dominant Polycystic Kidney Disease develop fluid filled cysts in the liver; the cysts may be large and may cause enlarged liver and abdomen, but liver function is usually normal.


Type: predisposition
Breeds: Siamese

Siamese have a predisposition to intestinal polyps (benign growths on stalks in the lining of the small intestine, most often associated with signs of intestinal obstruction). Studies suggest predisposition to intestinal polyps in cats of Asian ancestry and castrated males and a possible familial incidence was reported in Siamese. Anecdotally, Siamese have a predisposition to nasal polyps.


Type: autosomal dominant with incomplete penetrance, usually cosmetic, occasionally impairing,
Breeds: randombred, Manx. Maine Coon, Pixie-Bob, American Polydactyl and recently developed polydactyl breeds
Notes: Considered impairing under the 1995 European Convention for the Protection of Pet Animals. Many registries consider polydactyly impairing; the impairing form of polydactyly is associated with radial hypoplasia, the benign form is cosmetic only

Anatomically, the extra digits range from being pads of soft tissue (no bone or bones not connected to rest of foot), through to complete functioning digits complete with claws. Visual appearance varies from thumb-cats to cats with enlarged paws, but no thumbs ("hamburger feet"). Hind feet are hardly ever affected unless the front feet are affected. The "thumb-cat" form where the dew-claw is converted into a thumb is benign, with occasional problems such as fused claws on the extra toes. The "hamburger feet" form, where the extra toes are 3-jointed and there is no distinct thumb, has been associated with Radial Hypoplasia (Twisty Cat syndrome, impairing). X-rays can determine the structure of the additional toes and potential RH carriers can be screened out of breeding programmes.


Type: impairing, autosomal dominant
Breeds: Siamese/Oriental, Domestic Shorthair (particularly white cats)

Porphyrins are haem precursors that arise in the bone marrow. An enzyme deficiency causes excessive porphyrins in the blood, viscera, teeth, bones, urine and faeces. Teeth become unusually discoloured (teeth and bones may become pinkish) and the urine turns bloody. These symptoms are usually evident at an early age. Under UV light, the porphyrins in the teeth and bones result in bright pinkish-red fluorescence. A severe macrocytic hypochromic anaemia, enlarged liver and/or spleen and uraemia may occur. A second form of porphyria had the additional affects of anaemia and lethargy, but the mode of inheritance was not known. An old Thai breed called Ninlaret, described as having black teeth, eyes, claws and tongue may be a description of hereditary porphyria.


Type: unknown, impairing
Breeds: Himalayan/Colourpoint Persian, Birman.

Porto-systemic shunt is an aberrant blood vessel from the intestines that bypasses the liver so that toxins are not removed from the blood. This causes neurological signs (e.g. bizarre behaviour, fits, temporary blindness) usually present by 6 months of age. Clinical signs from around 10-12 weeks old, typically presenting with intermittent visual disturbances, dilated pupils, poor co-ordination, behavioural changes e.g. aggression, fits, lethargy, depression, gastrointestinal upsets, excessive salivation and occasionally stunted growth. Colourpoint Persians appear predisposed. Also found at random in both pedigree and randombred cats. Anecdotal evidence that Birman cats are predisposed to porto-systemic shunt.


Type: Predisposition
Breeds: Siamese

Priapism is the persistent and painful erection of the penis. it has been observed in the Siamese more than in other cats and in both castrated and entire cats that attempted to mate an oestrus female. If may require surgical removal of the penis.


Type: cosmetic/impairing, autosomal recessive (may also be dominant forms)

Results in perfectly proprotioned small (teacup, miniature) cats as opposed to the Munchkin mutation. Not fully understood and there may be multiple genetic mutations producing this effect. It does not appear to affect health or lifespan. Opinions are divided as to whether miniatures cats are in any way impaired/disadvantaged by their stature.


Type: impairing, autosomal dominant
Breeds: Abyssinian

Retinal dystrophy found in Abyssinian cats in the UK. Retinal abnormalities evident in retinas from age of 2 weeks. Development of both rod and cone photoreceptors is retarded and abnormal. Photoreceptors remain rudimentary and degenerative changes are noticeable at 4.5 weeks of age, beginning in the central retina and proceeding towards the periphery. It is usually noticed at 8-12 weeks of age and preceded by marked dilatation of the pupils, impairment of the pupillary light reflex and nystagmus.


Types: impairing, retinal dystrophy is autosomal dominant in Abyssinian/Somali; rod-cone degneration is recessive in Abyssinian/Somali; PRA recessive in Persian
Breeds: Abyssinian, Somali, Bengal, Persian

The rod and cone cells in the retina are aberrant or degenerate. Rods usually degenerate first, leading to night blindness. When cones also degenerate, blindness progresses and becomes total. Two forms of Progressive retinal atrophy have been identified in Abyssinians: autosomal dominant retinal dystrophy (Rdy) and the more common recessive rod-cone degeneration. Rdy is apparent at 4 weeks old with dilated pupils and flickering eye movements (nystagmus). Retinal degenerations is visible on examination at 8-12 weeks and blindness usually occurs by 1 year old. Symptoms of rod-cone degeneration occur at 18-24 months old and night blindness progresses to total blindness over the next 2 - years. A form of PRA has been seen in middle-aged Bengals. Early-onset recessive PRA reported in Persians; pupil reflex to light deteriorated from 2 weeks old with total blindness by 16 weeks. There are anecdotal reports of retinal degeneration in Siamese cats.


Type: impairing
Breeds: any, but predisposition in Siamese/Oriental

A malfunction of the lower opening of the stomach diagnosable by xrays following a barium meal. Symptoms of pyloric stenosis begin after weaning and are persistent, sometimes violent, vomiting, usually after a meal. The inability to retain food results in poor growth and stunting. There appears to be a genetic component to the condition, but the mode of inheritance is unknown. With other related gastric dysfunctions, affected cats usually show symptoms around 6 months old: regurgitating food, vomiting and weight loss. The oesophagus may be dilated (megaoeasophagus) and may have abnormal gastric tissue (gastric heterotopia). The stomach may be distended and slow in passing food into the intestine.


Type: autosomal recessive, impairing
Breeds: Somali, Abyssinian, Singapura, domestic shorthair

Pyruvate kinase is an enzyme necessary within red blood cells for them to produce energy to survive. Deficiency causes reduced red blood cells lifespan and usually intermittent, mild (often sub-clinical) or gradual anaemia although rapid, life-threatening anaemia can occur. Usually not detected until cat is quite old and has already been bred. Gene screening is available to detect carriers.


Type: cosmetic/impairing
Breeds: twisty Cat, some polydactyls
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals

Affected cats have unusually short front legs, normal length hind limbs and are otherwise normal. Their gait resembles that of a ferret and they tend to sit back like a squirrel or kangaroo. This has been reported several times since the 1940s and is known to be inherited. A form in the late 1990s was perpetuated as the "Twisty Cat" and was associated with a gene that causes a form of polydactyly in its less severe form. In badly affected cats the forelegs were twisted with the long bones either severely shortened or absent. It has also been termed Foreleg Micromelia. Where polydactyly is a desirable breed trait, a x-ray can determine whether the cat has the normal (benign) form or the form associated with mildly expressed Radial Hypoplasia. The latter should not be bred.


Breeds: see below

There are differences between breeds in terms of litter sizes and health.
Siamese/Orientals tend to have longer pregnancies while Korats and Persians/Himalayans may have shorter pregnancies.
Burmese, Tonkinese and Siamese tend to have larger litters (on average) while Persian, Birman and Somali tend to have smaller litters.
Maine Coons tend to have larger kittens (on average) while Korats tend to have lighter weight kittens.
Manx and Munchkin may have smaller litters due in-utero deaths associated with the mutation: homozygous Manx is lethal while heterozygous kittens may have spina bifida.
Birthing problems (dystocia) are more common in cats with extreme head shape, particularly Persian and Siamese cats, or narrow/unusually formed pelvises (Manx). These result in kittens become stuck in the birth canal.
The highest levels of kitten mortality are found in Persian cats as a result of birthing problems.
The Peke-Faced Persian (a mutation found in Red Persians) is no longer bred due to the need for casearian births and difficulty suckling as a result of the abnormally high palate.
Other causes of kitten death include: Flat Chested Kitten syndrome (Burmese), craniofacial deformity (American Burmese), pericardial-peritoneal hernia (British Shorthair).


Type: cosmetic, both autosomal dominant and recessive forms exist
Breeds: various Rex breeds, LaPerm

Fur of affected kittens and adults has varying degrees of wave, ringletting, curliness or woolliness depending on type and length of fur. Some rex mutations cause curled or absent whiskers and may have patchy baldness or temporary baldness before growing the curled adult coat. Numerous rex mutations have been reported, some are spontaneous mutations. Many of the apparently spontaneous mutations are identical to existing rex types and some may be due to carried recessives resurfacing.


Type: cosmetic, probably polygenes
Breeds: American Ringtail, other cats at random

The ringtail condition is characterised by the tail looping upwards over the back, forming a loop and lying against one or other flank. The tail is mobile and is held this way when the cat is at rest. In the past, some affected kittens with tightly curled tails have undergone tail amputation for fear of arthritis in later life.


Type: Autosomal recessive, cosmetic/impairing
Breeds: Persian, Himalayan, Exotic

Symptoms observable in young kittens as progressive skin scaling and greasy seborrhoea affecting the whole body. Anti-seborrhoea shampoos can be used (with care - may be toxic if not completely removed from coat/skin).


Type: impairing, autosomal recessive
Breeds: Seen in Oriental cat, test-breeding found it undesirable due to brain abnormalities

A small-eared male Oriental catfrom Italy went to the USA to introduce small, rounded ears into the Toyger breed to improve the tiger-like appearance. Test breeding with unrelated female domestic cats and the F1 offspring showed the trait to be autosomal recessive (not sex-linked). Short-eared females showed normal sexual behaviour, but never conceived when mated to short-eared males, carrier males or completely unrelated males. The foundation male was (obviously) fertile as were carrier males and females.

unusual ear shapes

The short-eared kittens were “clumsy” and MRI scans found them to have marked ventricular dilatation and associated anomalies. 20 related Oriental-derived crossbred Toyger cats weres from the breeding programme were donated to UC Davis for study. Seven were clinically healthy carriers and 13 were cats showing neurological signs, short ear phenotype and complex brain anomalies (“affected cats”). MRI scans were performed on all of the cats. Following diagnostic studies, the cats were destroyed and their brain anatomy was studied. The affected cats had structural brain abnormalities such as ventriculomegaly, cysts and multiple midline and callosal malformations. The affected cats had varying degrees of dilated ventricles (fluid filled regions of the brain) and thinning of the cerebral cortex. The affected cats did not have the normal pattern of ridges and furrows on the brain surface – these were much shallower and had an abnormal pattern. The degree of shallowness corresponded to how severely the cat was affected. These congenital brain defects were found to underlie the neurologic signs observed in those cats selectively bred for the short ear phenotype.

The study was documented in Characterization of an Inherited Neurologic Syndrome in Toyger Cats with Forebrain Commissural Malformations, Ventriculomegaly and Interhemispheric Cysts, MK Keating, BK, Sturges, S Siso, ER Wisner, EK Creighton, LA Lyons, in J Vet Intern Med. 2016;30(2):617–626.


Type: Impairing, autosomal recessive

Sparse-fur is characterised by marked alopecia and a thin straggly, rough coat. The guard hairs are short and deformed; down hairs are few or absent. Whiskers are contorted. There is also reddish-brown exudate forming a crust around the eyes, nostrils and mouth and often on the chest and stomach. The eyelids become thickened, inflamed and prone to infection.


Type: impairing, autosomal recessive
Breeds: Devon Rex
Note: Not to be confused with another condition known as spasticity that is properly called Cerebellar Hypoplasia (CH) and caused by a viral infection in the mother that crosses the placental barrier and affects brain development in kittens.

Spasticity is a hereditary muscular disorder found in the Devon Rex. Symptoms usually develop between 4-7 weeks though some show no symptoms until 12-14 weeks and are progressive until around 6 months. Severity varies and cat may deteriorate. After 6- months symptoms remain stable or progress more slowly. Generalized muscle weakness, especially head and neck muscles, protruding shoulder blades, high-stepping forelimb gait. The kitten is active but holds its shoulder blades high and its neck arched downwards. When resting, the body lies flat with the head held to one side. During exercise they tire easily, the head bobs, the shoulder blades protrude, stride shortens and there are muscle tremors before the affected cat collapses onto its chest with the head to one side of the forepaws. The arched neck interferes with feeding and drinking. There are usually short periods (measured in days) of apparent normality. The condition worsens with age and the cat rests more often, either lying flat with the head to one side or leaning against an upright object. Otherwise the cat remains active and its condition can be managed by adapting its environment. Symptoms may be worsened during illness, stress, excitement or cold temperature. When resting they may sit on haunches with forelimbs resting on a raised object. Food may be regurgitated (may be inhaled resulting in pneumonia). The abnormal head posture result in swallowing difficulties (a common cause of death).


Type: lethal, autosomal recessive
Breeds: Abyssinian

The cause is anomalous tissue occurring in the central nervous system. Initial symptoms are exhibited around 8-12 weeks old. A tremor progresses to head-nodding and swaying of the body. Movement is slow, clumsy and the kitten falls often. The sense of direction is impaired and the cat may have seizures when handled. The appetite is normal, but feeding is messy due to increasing tremor.


Type: lethal, autosomal recessive
Breeds: Siamese

A lysosomal storage disease caused by an enzyme deficiency. Manifests as a nervous diease. Signs apparent from 3-4 months old. Affected kittens lose interest in their surroundings, lose their appetites, develop a tremor, poor balance and later ataxia. Other signs can include splayed legs, high-stepping walk, plantigrade stance (hock-walking) and moderate enlargement of the liver and spleen. Sometimes there is stereotypic chewing. There is progressive paralysis and most cats die before 1 year old. Although inherited as a recessive trait, heterozygous cats can be detected by biochemical analysis and screened out of breeding programmes. A variant form with mild or no central nervous system signs has been seen in Siamese cats: a 6 month old Siamese with ataxia and head tremor was possibly reported as neurovisceral sphingomyelinosis. It showed familial incidence, the mode of inheritance was unknown, but a sibling had died after exhibiting similar signs.


Type: lethal/deferred lethal, autosomal dominant

See Manx Syndrome. Some breeders dispute that Spina Bifida is caused by the same gene that causes Manx taillessness and assert that they are linked genes.


Type: autosomal recessive, impairing
Breeds: Maine Coon

Similar to human spinal muscular atrophy. Symptoms begin at 15-17 weeks of age: fine muscle tremors and rippling of muscles, with progressive muscular weakness starting in the hindlimbs although cats seem to stabilize and have reasonable quality of life in supportive environment.


Type: cosmetic/impairing, autosomal dominant with variable expression

The usual form, as suggested by its common name (lobster foot), is a central cleft in one or both front paws. This may be accompanied by missing digits, fused digits, fused claws and/or abnormal foot pads. The foot bones are abnormal, but the cat's movement is rarely impaired apart from its ability to climb. The hind feet are usually unaffected. The gene is dominant, but few split-footed cats are seen in the population. This indicates variable expression (interaction with other genes) with many genetically split-footed cats appearing normal or having only minor effects. Can also occur through in utero exposure to toxins. Various forms known as hypodactyly, ectrodactyly and syndactyly depending on the conformation of the foot.

SPONGIFORM DEGENERATION (LEUKOENCEPHALOPATHY) (distinct from Feline Spongiform Encephalopathy)

Type: unknown, lethal
Breeds: Egyptian Mau, Persian, Birman

The formation of holes, mostly in the white matter of the brain, but can affect grey matter and spinal cord. Some forms due to exposure to toxins, but possible hereditary form seen in Egyptian Mau kittens. Affected kittens were smaller than littermates. Also seen in 4 month old Persian kitten and some closely inbred Birman kittens. Symptoms seen at a few weeks to a few months of age. Hindlimb ataxia and high-stepping gait progresses to depression, inactivity and fits. Diagnosis is based on post mortem examination of brain. In contrast, Feline Spongiform Encephalopathy (FSE, mad cat disease) manifests later in life due to toxins or prions.


Type: cosmetic/impairing, recessive

Occurred in inbred colony in 2006. Kittens in 3 different litters had sticky fur, sticky eyes and keratitis, possibly herpetic. Saliva was normal. Bathing, eye drops and and lysine supplements were used to control the condition.


Type: cosmetic/impairing, probably polygenes
Breeds: Siamese and other colourpointed breeds
Note: Considered impairing under the 1995 European Convention for the Protection of Pet Animals

Due to disruption of the visual pathways causing the cat to squint to compensate. Although associated with Siamese (it has been called the "Siamese squint"), it has been bred out of many lines. It may occur at random in any breed. Some kittens have mild squints that self-correct as they grow. Convergent squint is common in colourpoint cats along with nystagmus (sideways flickering eye movement). These result from abnormal routing of optic nerve fibres in the embryo; too many fibres are routed to the wrong side of the brain and the cat squints to compensate. Melanin is required for the correct routing of optic nerve fibres between the eye to the brain. It appears to be due to polygenes and only manifests when sufficient of those genes are inherited (threshold character) though or a monogene with incomplete penetrance has been posited.


Type: impairing, sex-linked

This defect may have a genetic cause (disruption to a gene on the X chromosome) or may be a developmental defect. Some apparently normal female cats fail to reach sexual maturity and are found to be feminized males. A mutated gene on the X chromosome disrupts development of normal male secondary sex structures and causes the male embryo to develop as a female, albeit a sterile female.


Type: impairing/lethal, autosomal recessive
Breeds: Birman

Affected kittens are born hairless and, additionally, have no thymus gland. The resulting immune deficiency gives increased risk of infection and death.


Type: mode of inheritance not determined, usually lethal
Breeds: possible predisposition in Siamese/Oriental

Found in non-pedigree cats and in a number of different breeds, including Siamese and Oriental cats. Affected kittens become ill at 3-5 weeks old, stop feeding, become weak and usually die within a few days. They have fast breathing, fast heart rates and may have hind limb paralysis. Usually affects whole litter. On examination, the blood resembles strawberry milkshake due to raised lipoproteins and low iron levels. It appears to be a problem in lipoprotein lipase (LPL) metabolism - the kittens are consuming high levels of fat (in milk), but cannot properly metabolise it. Those that are treated (blood transfusion and hand-reared on low fat diet) and survive have reduced LPL activity, but no clinical disease. The associated anaemia is less well understood and may be due to weakened kittens less able to cope with parasites.


Type: mode of inheritance not determined
Breeds: Birman

Seen in several litters of Birman kittens. Kittens begin to tremble and shake at around 10 days old (when they start moving around). They worsen through weaning, but recover completely from 12 weeks onwards. The trembling kittens must be held still in order to eat properly. Possibly of metabolic origin.


Type: impairing, presumed autosomal recessive

There is a continuous, whole body, tremor commencing at 2-4 weeks old. Affected kittens roll and bob in an undulating fashion and the tail weaves in circles (possibly attempting to balance the kitten). The trembling only stops when the affected animal is completely at rest or is held firmly. Unlike virally induced cerebellar hypoplasia (cerebral palsy) the cerebellum is normal.


Type: cosmetic/impairing, possibly dominant with incomplete penetrance
Breeds: Abyssinian, Cornish Rex, associated with short-muzzled breeds as side effect of the short face

An unusually high incidence of umbilical hernia was found in some Swedish lines of Abyssinian though the mode of inheritance was not determined. A dominant with incomplete penetrance was suspected. The hernia is a secondary effect of defective musculature of the abdominal wall. Protrusion of intestine/abdominal organs through abdominal wall near the umbilicus (belly button). Ranges from minor to severe (abdominal wall partly or wholly absent). Seen at random in any breed or random-bred and can be due to in utero exposure to toxins. Claimed to be more common in short-muzzled (brachycephalic) breeds where it may be due to a short-muzzled queen pulling the umbilical cord while trying to bite through it. Incidence of umbilical hernia in a family of Cornish Rex suggested monogenic trait, but was more likely polygenic with the cats reaching a threshold (sufficient polygenes) to manifest the defect. Apart from the Cornish Rex and Abyssinian cases, a genetic link has not been established except as possible side effect of short muzzle.


Type: impairing

One form of urolithiasis (formation of urinary calculi) was found to have a familial tendency in kittens born to brother-sister matings. The disease did not respond to treatment, including surgery. No environmental factors were found and the affected cats were otherwise healthy. There may be a genetic predisposition to form urinary calculi.


Type: Undetermined
Breeds: Sphynx, Devon Rex

Observed in Sphynx and a similar condition observed in 5 Devon Rex. Abnormal amounts of mast cells in the skin causing an itchy symmetrical red-brown rash on neck, body and limbs. Hives or blisters occur if scratched. Crusting and seborrhoea may be present on the trunk and chest. Mastocytes and eosinophiles were found in the dermis. The condition tended to come and go and could be alleviated by prednisolone or essential fatty acids. As the Devon Rex was used in the development of the Sphynx, it is not surprising that both breeds are affected.


Type: impairing (lethal if not controlled in individuals)

Some Singapura females are unable to give birth naturally due to the uterus not contracting strongly enough to expel the kitten(s). Caesarian sections may be required; if not treated when the female is in labour the kitten and the queen may die. This condition traces to one of the foundation cats.


Type: impairing

Seen in true albino animals (pink-eyed) and also in the Siamese (a form of albinism). An unusually high number of visual nerves from the retina were misrouted to the wrong side of the brain. A lesser degree of misrouting is seen in cats with Chediak-Higashi syndrome.


Type: autosomal recessive, impairing
Breeds: Devon Rex

Deficiency of vitamin K-dependent blood-clotting factors (II, VII, IX, and X). Observed in 3 Devon Rex cats. Oral treatment with vitamin K1 resulted in normal levels of clotting factor.


Type: Predisposition, more common in females
Breeds: Siamese and other colourpointed cats

Bilateral periocular leukotrichia temporarily causes pale spectacles around the both eyes, often resulting from some type of stress: pregnancy, illness or dietary deficiency. Unilateral periocular (around-the-eye) depigmentation in Siamese has also been associated with Horner’s syndrome, eye/upper respiratory tract infection. The pale colour is a result of the Siamese form of albinism; the markings are temperature sensitive with only the paler regions being pigmented. Inflammation raises the temperature, leading to temporary or permanent lightening of the fur in that area.


Type: impairing
Breeds: Persians and derivative short-nosed breeds

Weeping eyes can be due to injury, entropion (eyelid turned inwards), blocked tear-ducts or foreign object. It is also associated with excessively short nose due to facial distortion resulting in blocked or absent nasolacrinal canals or lacrinal duct. This is probably polygenically inherited due to changed skull shape. Afflicted cats should not be bred from. Surgery may improve many cases.


Type: Dominant (white spotting, epistatic solid white)
Breeds: any that permit white or parti-colour individuals

The lack of pigmentation in white cats and coloured cats with white ears and noses makes them prone to squamous cell carcinoma (SCC) tumours on areas where skin is more exposed to UV in sunlight: ear, nose-tip, eyelid, lips. Commences as ulcer and becomes black and crusty requiring surgical removal where possible. Prevention through use of sun-block or keeping cat out of strong sunlight.


Type: cosmetic, autosomal dominant
Breeds: American Wirehair

The wirehair mutation is characterised by coarse, curled hair and is currently only seen in one breed.


Type: genetic link possible
Breeds: Devon Rex

Fungal infection of the nail beds; possible genetic predisposition due to excessive sebum or poor immune response towards the yeast. Colombo et al (2007) found Malassezia in 100% of Devon Rex cats studied compared to 42% of Persians and randombred shorthairs studied.


Vella, Carolyn M.; Shelton, Lorraine M.; McGonagle, John J.; Stanglein, Terry W.; "Robinson's Genetics for Cat Breeders and Veterinarians, 4th Edition", 1999, Butterworth-Heinemann; ISBN 0750640693

Alvarez, Becky. Femoral hypoplasia. Personal correspondence 2006.
Durrenberger, Jocelyne. (Metrowest Animal Awareness Society). Sticky Fur. Personal correspondence.