Copyright 2002-2011 Sarah Hartwell

Smaller than usual cats occur for several reasons - some genetic, some hormonal and some environmental. Dwarfism is a term which covers numerous conditions resulting in undersized individuals. It usually results from a combination of genetic factors and endocrine (hormone) malfunction. Some forms are caused by early injury e.g. physical damage to the pituitary or thyroid gland. Dwarf or stunted individuals can also result from malnutrition and chronic illness in early life. I am aware that some terms are now considered more politically correct than others, however political correctness is a human consideration and not a feline one.


Those seeking miniature cats (often known as "teacup cats") should be warned that not all petite cats are dwarf or miniature. The normal size range for cats is around 5 lbs to over 12 lbs and cats at the lower end of this spectrum are not necessarily miniatures. I have seen some advertisements claiming that cats under 10 lbs are miniature, when in fact they fall well within the normal size range! In the past, cats at the lower end of the size range were homed or sold as pets, particularly in the Persian breed where a massive, cobby build is required by the breed standard. The modern trend for miniature cats means that less scrupulous breeders charge high prices for runty or under-sized cats and some "breeding programmes" are little more than kitten mills. Genuine miniature cats come from breeding lines where the trait has been, or is being, fixed by selective breeding and where the cats are a consistently small size due to genetic mutation or to progressive downsizing. Genuine breeders pay strict attention to health, hygiene and to the homes their cats are adopted into. Reputable breeders limit the number of litters produced each year to ensure the health of the female cats and will take great care to avoid excessive inbreeding (damaging to the immune system) and to widen their gene pools.

Note: This is a work in progress and is not intended to be an authoritative work. During its research I found many contradictions in texts relating to the various forms of dwarfism in other species, including dwarfism in humans. Although I have tried to resolve these inconsistencies, these may result in inconsistencies or inaccuracies in this article. There is currently little data available specifically about feline dwarfism.


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Forms of Dwarfism
Dwarfism / Midgetism and Health
Appendix: Other Dwarfing Conditions


Miniature and Midget Cats Recorded in History
Miniature Cats in the Random-Bred Population


Modern Dwarf Breeds
Modern Miniature Breeds
Buying Mini Cats
Breeding Mini Cats
Appendix: Simple Mendelian Inheritance

PAGE 4: Short-legged Breeds and Mutations


Genetic dwarfism usually involves a bone disorder where the bones do not grow and develop normally. These are called skeletal dysplasias or chondrodystrophies. In humans, there are over 200 conditions causing stunted growth (possibly as many as 400 conditions) and over 100 known skeletal dysplasias; of which achondroplasia is the most commonly seen. Achondroplasia dwarfism is also found in cats. It is likely that other dysplasias also occur in cats, having subtly different dwarfing effects.

Achondroplasia Dwarfism (True Dwarfism, Genetic Dwarfism, Chondrodysplasia)

The most common (and easily recognisable) form is achondroplasia dwarfism which shortens the long bones of the limbs while leaving the trunk (body) unchanged. Achondroplasia dwarfism is characterised by abnormal body proportions. Achondroplasia dwarfism is the result of a dominant genetic trait affecting the hormones which control bone growth. Typically, the growth of the limbs is stunted, while the size of the trunk and mental capacity are normal.

The condition causes abnormally short and deformed limbs; this is most noticeable in short-legged dog breeds where the limbs are bowed or twisted. It also typically produces a large head with undershot (bulldog) jaw and crowded, misaligned teeth. Other cranial problems may occur due to the abnormal head shape. The limbs are frequently bowed which may result in poorly articulating joints. The vertebrae may also be affected. Although most affected cats are mentally normal, their abnormal body proportions may result in slow development in early kittenhood. The large head may result in kittens being delivered by caesarian section as they are unable to pass through the birth canal. Stuck kittens are likely to die and would likely cause the mother to die.

In the Munchkin; these short limbs are the distinguishing feature of the breed and the other deformities associated with achondroplasia are avoided (as far as possible) by careful selective breeding, avoiding breeding those individuals which have spine or chest deformities. Although achondroplasia is typically associated with a large or abnormal head, Munchkins do not seem to suffer this effect and therefore may have a different condition with similar physical effects rather than true achondroplasia. The Munchkin trait is more likely to be pseudochondroplasia or hypochondroplasia.

Achondroplasia also occurs at random in the feline population due to mutation hence the occasional report of short-legged cats (Kangaroo Cats and Squittens Revealed). It occurs in varying degrees, ranging from "nearly normal" to crippling with all legs severely deformed. The forelegs are usually more severely affected than the hindlegs. In animals this form of dwarfism ranges from mildly disabling to crippling or lethal (stillborn). In Munchkins, homozygous embryos apparently die early in the pregnancy and are reabsorbed, decreasing the litter size compared to litter size in most other breeds.

Other Dysplasias

There are probably other dwarf conditions in cats, although they may not have not been identified as distinct from the Munchkin mutation. It is likely that many, or most, are reabsorbed during pregnancy, are stillborn or die in kittenhood before any dwarf mutation is detected. The following are examples of dysplasias seen in other species.

In Dexter cattle there is a form of dwarfism which causes short-legged individuals. Occasionally "bulldog calves" are born. Bulldog calves are usually stillborn or die soon after birth. They are dwarfed with large heads, cranial deformities and other skeletal abnormalities. There may be gross deformities of the skull.

A hereditary recessive form of achondroplasia is found in some sheep breeds. Known as "Spider Syndrome", it is related to abnormal transformation of cartilage to bone. Normally, as an animal grows, the cartilage at the end of the long bones grows and expands and is transformed into bone (calcified). In Spider Syndrome sheep, some cartilage is transformed to bone, but adjacent areas of cartilage are not. This causes skeletal abnormalities, particularly the splay-leggedness which gives the condition its name. The portion of the leg below the knee/hock protrudes outward at 30-45 degrees. There is usually S-shaped curvature to the spine, a pronounced humped back over the rib cage and the whole muzzle curves to one side. Spider Syndrome lambs often have long necks and legs and a shallow body.

Midgetism (Pituitary Dwarfism, Hyposomatotrophism, Growth Hormone Deficiency; Panhypopituitarism)

Midgetism is quite different from achondroplasia dwarfism and it is caused by malfunctioning pituitary gland not producing enough growth hormone (hypopituitary dwarfism) before sexual maturity. In a few cases, the hormone is produced but the body fails to respond to it. This can have a knock-on effect on other glands which affect growth and development. The pituitary gland is the body's "master gland" and if it malfunctions, it can result in other metabolic disorders such as hypothyroidism, hypoadrenocorticism and diabetes.

Midget cats stop growing during kittenhood and, depending on which hormones are and are not being produced, may retain some juvenile characteristics such as soft (kitten-like) fur, kitten-like proportions (though the legs may become deformed due to abnormal bone growth) and a high-pitched mew. Midgetism produces a small individual with normal or near-normal proportions except for the head, which may appear relatively large when compared to the body. The relationship of head to body proportions approximates that of normal kittens. The lack of growth hormone during kittenhood means that bone sutures (the "cracks" which allow growth of some bones) fuse too early preventing further growth. Typically, a pituitary dwarf stops growing in kittenhood but retains normal body proportion and mental capacity.

According to some texts, pituitary dwarfs have normal sexual development and are capable of reproduction although they may be unable to carry a normal-sized foetus to full term. Other texts state that pituitary dwarfs are often sexually immature and cannot reproduce. Some texts contain contradictory information on the matter of sexual maturity and reproduction in midgets. Those which do not become sexually mature probably have panhypopituitarism, where not only growth hormone but also other pituitary hormones are deficient.

In humans, midgetism is caused by a dominant gene. In German Shepherd dogs it is a recessive trait. Although cats with features indicative of midgetism have been reported, little is known about the genetics. In addition, damage to the pituitary gland during early life may also cause non-hereditary midgetism.

While working at a cat shelter in Essex. England in the 1990s, I came across two dwarfed cats, probably pituitary dwarfs, where the cat was "compact" with only slightly shortened legs and a short body. The size was approximately that of a 4 month old kitten. Overall, both cats were thick-set and the head was slightly large and best described as "rounded". One cat was a pregnant farm cat,the other was a pet. Because of the risk of a large (i.e. normal sized) kitten becoming wedged in the birth canal the farm cat was aborted and spayed. The second such cat was a bad-tempered spayed female pet who was also tailless. Both cats were alert, active and mentally normal. The farm cat was extremely sweet-natured while the pet cat was a bad-tempered individual.

Cretinism (hypothyroid dwarfism)

Cretinism is a type of dwarfism accompanied by mental retardation and physical distortion and is caused by insufficient of thyroid hormone in early life. It is usually due to birth defect (missing, malformed on non-functioning thyroid gland) or by early damage to the thyroid gland. Cretinism seriously retards an affected kitten's physical and mental development, leading to stunted growth, poor skin tone, misshapen (flattened) muzzle, pot belly and general physical and mental lethargy. Cretinism is well documented in humans, and its treatment with thyroxine, is well-documented. It has been artificially induced in laboratory animals and may occur naturally although individuals are unlikely to survive.

Congenital hypothyroidism has been seen in Abyssinian cats; the kittens grew more slowly and remained small with kitten-like features and the typical goitre.


Small size can also be an inherited characteristic of a breed e.g. Singapura is not dwarfism or midgetism since the individuals in such groups are physiologically normal. In cat shelter work I have come across a number of adult cats which appear to be simply "small" and not actually dwarfs. Miniature cats are small, but normally proportioned, cats.

Miniaturisation by progressive downsizing is neither dwarfism nor midgetism, but is the result of always breeding from the smallest individuals in a population. In most animals there is a natural variation in size - a few unusually large individuals, a few undersized ones and the majority being "normal size". Some simply turn out smaller than other due to the interaction of various genes. By breeding only from the smallest individuals, it is possible to create a population of undersized animals. In nature, this occurs naturally where the environment is such that the smaller animals have an advantage over the larger ones e.g. not requiring as much food. Over many generations they become progressively smaller until eventually a minimum size is reached; any smaller and the offspring are too fragile to survive. Shetland ponies and Falabellas are examples of progressive miniaturisation.

Miniaturisation can also occur spontaneously in a single generation by mutation of genes which govern size. The gene most often implicated in normally formed, but miniature, cats is one which affects the asp count on the asp gene. Such a mutation could halve or double the body mass of an animal by changing the asp count by one unit. It does not appear to affect body proportions or general health. The brains and other organs of asp-miniature cats contain approximately half the number of cells compared to the same organs in normal sized cats because in a normal sized cat the asp count is one unit larger i.e. there has been one additional cellular division cycle. One would expect asp-miniatures to weigh half as much as a normal sized cat, however natural variation (governed by numerous other genes [polygenes, modifiers] and also by environment) means they are likely to range from one-third to two-thirds the size of a normal cat. The cases of "Treker" (Persian) and "Cotie" and "Scamp" are consistent with this type of mutation.

In dogs, a single mutant gene could explain the range of sizes, according to a study published in 2007 (Elaine Ostrander, National Human Genome Research Institute, Bethesda, US; Dr Carlos Bustamante, a member of the research team from Cornell University, Ithaca, US; Science journal). Researchers found that small dogs had the same mutation in a gene that influences size. The mutant gene is absent from most large dog breeds. The small breeds studied shared a mutatnt form of the insulin-like growth factor 1 (IGF-1) gene known to influence size in mice and humans. The mutant gene is present in some larger dogs; in those cases some other genetic factor must somehow override the mutant IGF-1 gene. The mutant form of IGF-1 causing small size probably arose more than 10,000 years ago.

Stunted Growth

Stunted growth can also be caused by non-inherited factors such as environmental factors such as poor nutrition during the main growth stage of the animal. Although the animal carries all the genes for normal size, the environment prevents it from reaching that size. Metabolic disorders and some congenital defects (birth defects) can cause the individual to simply stop growing. Chronic illness or acute illness in kittenhood can both result in stunted growth. Another stunting condition is porto-systemic shunt where an aberrant arrangement of blood vessels causes the liver to be bypassed. In some cases this is operable, but in others it is managed using medication (though life expectancy is reduced). The smallest kitten in a large litter has to compete for food against stronger siblings and may not get enough food to grow fully.

In September 2011, Cherisse from Idaho, USA, provided these photos of Myrtle, a 3 month old black female kitten with apparent midgetism and Mucopolysaccharides 6. Myrtle showed up as a stray at a humane society in Boise, Idaho, USA. 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. At 3 months of age she weighed just over 2 lbs and cannot be spayed due the risk of dying under anesthesia. She was adopted by Cherisse, a vet assistant, at a smaller animal shelter in Nampa, Idaho, USA. While it is sad that Myrtle will not live much longer, she is lively, playing and interacting with my other cats just as any normal kittens of the same age. She cannot eat solid foods due to her facial deformity, and is on a strict diet of canned Wellness brand wet food with 2 tablespoons of water mixed in for added moisture. She also cannot drink water, and gets all of her hydration through her canned food.

Other Forms of Dwarfism

The appendix at the end of this article lists a number of conditions known to cause dwarfism in humans and which are potential causes of dwarfism in cats.


Current dwarf and miniature breeds are described as healthy for the most part. As with any full size cats, some individual miniature cats may exhibit health problems although these will not be representative of the breed as a whole.

I received a report in March 2002 of a supposed breed called the Asian Miniature Cat. The correspondent, a veterinary technician, believed this to be a discontinued breed due to health problems. The breed apparently suffered from mental retardation, bad teeth formation (possibly due to a misshapen head), fused vertebrae and joints and also chronic bladder stones. It was sweet natured, mentally dim and resembled a bear cub when walking. This sounds like one-off genetic dwarf since dwarfism produces a compact, short-bodied cat, often with a disproportionately large head and possibly other abnormalities. I am not aware of any formally developed Asian Miniature Cat breed and it may be the result of an individual breeding dwarf cats together with crippling results for the offspring. Achondroplasia is variable in its effects (alternatively there may be mimic conditions which are not currently distinguished from achondroplasia). The descriptions sounds typical of the more severe form of achondroplasia dwarfism. No reputable cat breeder would wish to produce kittens which such severe defects.

I have also received an isolated report of a miniature Persian which had giardia (intestinal parasite), Ringworm, Horner's sydrome (neurological disorder affecting cranial nerves and characterised by eye abnormalities; can be congenital, or caused by trauma or infection) and luxation of patellas (slipping kneecaps requiring corrective surgery). This is not necessarily representative of the breed since those same conditions also occur in full-size cats of different breeds and in random-bred cats.

Notes: Giardia is an intestinal parasite carried by up to 10% of cats with no symptoms; a recently infected cat or an infected cat which becomes stressed may show symptoms. Ringworm is also carried asymptomatically by many longhaired cats. Horner's Syndrome is due to lesions in areas of the brain and may be due to bacterial or viral infection or to head injury as well as to inherited causes; symptoms include drooping eyelid(s), exposed third eyelid and pupils of different sizes. Luxating patellas may also occur due to injury; if there is an inherited component to the condition there are a number of different genes involved which makes it unpredicatable. It is known to be hereditary in Devon Rexes. These allegations, and others have been found to originate from a single disgruntled individual who has posted (often anonymously) to a variety of forums and boards with an ever-varying list of "late manifesting" ailments against anindividual breeder's cats. They should not be regarded as representative of the breed.

Kittening and rearing kittens proved to be a problem in miniature Siamese. There was high kitten mortality and the mothers seemed unable to produce adequate milk for their offspring. Bonnie Arnold's miniature Persians were originally cause for concern (until the genetics were better understood) because a miniature mother might produce a full size kitten - a 3 lb mother with a 4 oz kitten (which might rapidly outgrow its mother) would not be an ideal situation. Because of the small size, spay surgery may have to be delayed even beyond the 6 months stage to ensure that the cats are robust enough for anaesthesia and surgery.

In any breed (and in random-bred cats), congenital problems can occur due to unpredictable hidden recessive genes (see The Pros and Cons of Inbreeding) or groups of genes (polygenes), while other health problems occur due to environmental conditions later in life. Although most miniatures are by no means fragile, their smaller size means they are more at risk of damage from minor knocks than are full size individuals - in a fight with a full-size cat, a small individual is likely to come off worse.

The black kitten in the background is only a few weeks younger than the white kitten. Even allowing for slight age difference and perspective, its growth is quite markedly stunted and it will never reach a normal size. It was the only survivor of a random-bred litter and suffered chronic digestive problems.

During rescue work, I handled a random-bred miniature cat which never grew beyond the size of a 12 week kitten; it had suffered horrendous problems with anorexia and diarrhoea during kittenhood; the littermates died as a result (despite veterinary intervention) and the survivor was left with digestive problems which in turn suggested that its midgetism was either caused by or linked to metabolic problems affecting the digestive tract. It was never in the best health and could not undergo neutering surgery. It had a severely reduced life expectancy. Again, this was an isolated case and being born to strays there was no way of knowing if its condition was genetic, a developmental disorder (non-inherited birth defect) or illness-induced. A metabolic disorder stunting growth was strongly suspected.

In the case of dwarfed randombred "Tellie" (born to a feral mother), the dwarfism is accompanied by permanent respiratory problems, weeping eyes and a deformity of the palate; these indicate some cranial deformites affecting the eyes, nose and mouth. These may be linked to Tellie's dwarfism, due to other effects of inbreeding or may be due to his poor start in life.


In general, there is inadequate research into feline dwarfism. There are probably many more forms of dwarfism than are formally recognised, visual impression alone being insufficient to identify which form the cat has. As far as vets are concerned, many dwarf cats present with no health problems while others have problems ranging from mild to severe. At present, there is a great deal of guesswork involved in dealing with dwarf cats and each must be investigated as an individual. Only when the different dysplasias can be distinguished will it be possible to say which conditions (affecting skeleton and/or internal organs) are definitively linked to the cat's dwarfism.

When dwarf cats are encountered, X-rays, body scans and blood tests can be used to look for skeletal effects, internal abnormalities and abnormal hormone levels respectively. This can identify why a cat is undersized. Identification of the underlying cause is not always possible since some causes do not leave easily detectable physical traces; some individuals are small due to natural variation and there are also a multitude of genetic mutations which have yet to be encountered or identified!


Many conditions have multiple names while some genetically different conditions have a similar appearance and may be mistaken for each other. Some disorders have a range of effects and are not primarily associated with dwarfism. This list is based mainly on human data and only a subset of these conditions have been identified in cats. There is the possibility that others do occur but are not identified because the affected kittens may be reabsorbed during pregnancy, be stillborn or die early (and the bodies may be eaten by the mother). Such conditions are generally only noted in pedigree and pure-bred cats and for two reasons: firstly inbreeding causes normally hidden recessive genes to be exhibited and secondly (and perhaps most important) breeders are far more likely to investigate abnormal kittens and to ask for an autopsy on kittens which die early.

Achondroplasia: This is the classical form of dwarfism and, in humans, the most common form. A number of other genetic mutations produce almost identical effects e.g. hypochondroplasia, pseudoachondroplasia. True achondroplasia results in an enlarged head; pseudoachondroplasia does not. Although the Munchkin's condition is termed achondroplasia, the head size is normal and it may ultimately prove to be a different mutation. The occurrence dwarf cats with cranial abnormalities also suggest that different genes are at work. Dwarfism is not common enough in cats for a distinction to be made between these conditions.

Acrodysplasia with exostoses (acrodysplasia type V, trichorhinophalangeal dysplasia type II, trichorhinophalangeal syndrome type II, Ttichorhinophalangeal syndrome with exostoses, Langer-Giedion syndrome, Giedion-Langer syndrome): Genetic condition characterised by distinctive facial and cranial features. In humans these include mild/moderate dwarfism, large protruding ears, a bulbous nose, sparse hair, mild microcephaly (small-headedness) and often with mental retardation.

Acromesomelia (acromesomelic dysplasia): Characterized by short arms, legs, and fingers, and a slightly enlarged head.

Bulldog Syndrome: Noted in Dexter Cattle and always lethal. Affected offspring have gross cranial deformities and other skeletal abnormalities. Individuals are either stillborn or die soon after birth.

Chondroectodermal dysplasia (Mesoectodermal dysplasia, Ellis-van Creveld syndrome): A short-limb dwarfism associated with polydactyly, abnormal development of nails and often with congenital heart defects. Probably recessive as it is prevalent in inbred populations.

Congenital adrenal hyperplasia: A wide-ranging endocrine condition with serious medical problems. Afflicted individuals may grow faster initially, but will become smaller adults.

DeMorsier's syndrome (septo optic dysplasia, optic-nerve hypoplasia): A dwarfing condition and pituitary-gland disorder that also affects vision and brain function.

Diastrophic dysplasia (DD): This was once thought to be a form of achondroplasia. It is a form of short-limbed dwarfism accompanied by serious orthopaedic problems. In humans it may be associated with cleft palate, clubfeet, deformed hands, cauliflower ears and respiratory problems in early life. Kittens with cleft palates are unable to suckle and generally die, so this condition is unlikely to be diagnosed in cats.

Flat-Chested Kitten Syndrome: This syndrome is typified by a flat chest or compressed chest which, in severe cases, causes breathing difficulties and displacement of internal organs, ultimately leading to poor growth and death. Mildly afflicted individuals recover fully.

Focal mucopolysaccharidosis (acromicric dysplasia, geleophysic dysplasia, geleophysic dwarfism): Characterised by short limbs, small hands and feet and (in humans) a genial facial appearance. Associated with heart/breathing problems, overall delayed development and ear infections. Two types of mucopolysaccharidosis are seen in cats - these are described later.

Hypochondrogenesis: Characterised by short body, short limbs, large head where the jaw may be small and the forehead enlarged (in humans the face appears oval or egg-shaped). Associated with cleft palate and severe respiratory distress due to the small rib cage. Most affected individuals die soon after birth; survivors are generally found to have spondyloepiphyseal dysplasia congenita which has a similar appearance. In kittens, cleft palate would prevent suckling and lead to death, so this condition is unlikely to be diagnosed.

Hypochondroplasia: Visually this looks like milder form of achondroplasia, but genetically it is different. The effects are less pronounced than achondroplasia and there are fewer associated health problems. In species where dwarfism is poorly documented, it may be misclassified as achondroplasia.

Hypothyroid: A lack of thyroid hormone results in poor growth and dwarfed cats which retain kitten-like features.

Jeune's syndrome (asphyxiating thoracic dystrophy): Potentially lethal form of dwarfism characterised by respiratory and kidney complications. In kittens this would probably prove lethal and therefore not be identified.

McCune-Albright syndrome: Precocious-puberty condition (affects mostly females) typified by bone, endocrine, and skin abnormalities. Varies from lethal, through severe to benign and almost entirely asymptomatic.

Metaphyseal chondrodysplasia, McKusick-type (cartilage-hair hypoplasia, CHH): A form of short-limb dwarfism associated with fine, sparse hair, impaired immunity and anaemia.

Metatropic dysplasia: Similar to, and often confused with, Kniest syndrome.

Metatropic dysplasia type II (Kniest syndrome, Kniest dysplasia): Similar to spondyloepiphyseal dysplasia congenita (SEDc) and spondyloepimetaphyseal dysplasia, Strudwick (SEMD).

Morquio-Brailsford syndrome (Morquio syndrome, MPS-IV, mucopolysaccharidosis): A mucopolysaccharidosis (MPS) disease, caused by the body's inability to produce certain enzymes. In cats, MPS-I and MPS-6 have been recorded, both causing facial deformities (short broad nose with depressed nasal bridge) and spinal deformities

Multiple epiphyseal dysplasia (MED): Not usually noticed at birth, but in juveniles it causes unexplained pain in the hips, knees, and/or ankles and mild dwarfism.

Neuroaxonal dystrophy: A lethal disorder which causes degeneration of main neurons in the brain and progressive incoordination; it also reduces the body size but the kittens do not survive into adulthood.

Osteodysplastic primordial dwarfism (primordial dwarfism): Causes extremely short stature and, in humans, bird-like facial features.

Osteogenesis imperfecta (OI): A brittle bone disease. In humans, there are four types of OI; Type III being a dwarfing condition and also associated with hearing loss.

Pituitary dwarfism (growth-hormone deficiency, hypopituitary dwarfism, hypopituitarism, pituitary dwarfism, panhypopituitarism): Body proportions are preserved resulting in a midget individual. Panhypopituitarism means absence of all pituitary hormones; in this case, sexual development does not occur, juvenile features are retained and life expectancy is reduced. Deficiency of only the growth hormone prevents growth, but the affected individual matures sexually as normal.

Precocious puberty: Early growth is often faster than normal, sexual development occurs early, after which growth slows so that the adult size may be small.

Progeria (Huntington-Gilford progeria syndrome (Huntington-Gilford syndrome): A rare genetic disease that causes ageing at several times the normal rate. One of its effects is profound short stature.

Pseudoachondroplasia: Mimics achondroplasia in some ways, but is a different condition entirely. A short-limb dwarfism, but in this case, the head size and facial features are unaffected. It is associated with osteoarthritis and other orthopaedic problems.

Rhizomelic chondrodysplasia punctata (RCP): A very severe form of dwarfism with profound delays in developmental and physical growth.

Russell-Silver syndrome (Silver-Russell syndrome, Russell syndrome, Silver syndrome): Affected individuals are of low birth-weight and may have a poor appetite. The condition causes small stature and (in humans) a small, triangular face, low-set ears and incurved fifth fingers. Low birth-weight kittens with poor appetite would be unlikely to survive so the condition might go unnoticed should it occur in cats.

Spondyloepimetaphyseal dysplasia, Strudwick (SEMD , SMD): This is genetically different from spondyloepiphyseal dysplasia congenita (below) but has indistinguishable characteristics.

Spondyloepiphyseal dysplasia congenita (SEDc, SED): This causes in moderate to severe small stature and is associated with clubfeet, a cleft palate, barrel-chest and other orthopaedic problems. It is considered one of the most common forms of dwarfism in humans. Cleft palate would prevent kittens from suckling.

Spondyloepiphyseal dysplasia tarda (SEDT, X-linked spondyloepiphyseal dysplasia tarda, X-SEDT): A sex-linked variant of SED carried on the X chromosome, which means it affects males (who only have one X chromosome) more often than it affects females. Females must inherit two copies of the gene in order to be affected. Mild dwarfism.

Spider Syndrome: Causes irregular calcification of cartilage so that legs become distorted at the knee/hock joints and the affected individual develops a splay-legged stance. In addition the spine is affected, causing hunchback and a long neck. Noted in some sheep breeds.

Thanatophoric dwarfism: A lethal form of dwarfism that results in death at birth or shortly thereafter..

Turner syndrome: The absence of all or part of one sex chromosome causes Turner syndrome, which affects only females (since an embryo having a Y chromosome but no X chromosome will not develop, but one with only a single X chromosome will develop into an apparent female). Individuals are physically female and are small in size, do not develop sexually (therefore infertile). It may be associated with mental dullness, skeletal abnormalities, heart, kidney and thyroid problems and thyroid dysfunction. If this condition does occur in cats, it might go unnoticed unless those associated effects draw attention to it or unless an otherwise normal female proves infertile.



