Genetic Welfare Problems of Companion Animals

Manx

Manx Syndrome

Related terms: spina bifida, myelodysplasia, spinal cord dysplasia, hydromyelia, spinal dysraphism, syringomyelia, spinal dysplasia

Outline:The genetic mutation that causes Manx (tail-less) cats also frequently causes severe disease consequences because of its effects on the development of the spine and spinal cord. The various forms of spina bifida which commonly occur lead to complications which can cause partial paralysis, prevent normal behaviours, cause incontinence, and lead to painful infections. Cats evolved to have tails and they use them for communication and balance. As long as people buy or wish to keep Manx cats the serious disease and welfare problems caused by the genetic mutation carried by all these cats will be perpetuated.

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Summary of Information

(for more information click on the links below)

1. Brief description

The term ‘Manx syndrome’ is used to describe a range of conditions seen in the Manx cat, associated with it’s characteristic feature – a shortened or absent tail Unfortunately this very obvious vertebral mutation is often linked to some severe developmental abnormalities elsewhere in the spinal cord leading to significant neurological disease (disease of the nervous system).

The commonest developmental problem seen in Manx cats is spina bifida. Spina bifida is a general term used to describe several conditions where the neural tube which forms the spinal cord fails to close and the arches of the vertebrae (bones of the spine) also fail to form completely.

Signs shown by Manx cats with spina bifida vary according to the severity of the spinal cord abnormality, but can include an abnormal “hopping” gait, plantigrade stance (with more of the hind leg on the ground than normal), urinary and faecal incontinence, and lack of sensation in the hind legs and around the perineum (the skin round the anus and urethra openings). Some cats can be so severely affected that the deformity is fatal.

2. Intensity of welfare impact

Some Manx cats have no signs of spinal cord problems, whilst others experience major welfare problems, such as lack of properly functioning hind limbs and urinary and faecal incontinence. Cats which are unable to control their bladder or bowels may be regularly soiled in urine and/or faeces which causes skin inflammation, irritation and infection. Those whose hind limbs do not function correctly are hindered in their ability to show a full range of normal behaviours.

Severely affected individuals may die during foetal development in the uterus or are euthanased at an early age.

3. Duration of welfare impact

Signs may be present at birth or appear in the weeks to months afterwards. Usually there is no effective treatment so the condition is life-long. Occasionally surgical treatment can be beneficial, although this can have its own welfare impacts.

4. Number of animals affected

Manx cats with spina bifida are common. “Rumpy” cats (completely tailless Manx cats) are most often affected (Kroll and Constantinescu 1994).

5. Diagnosis

Spina bifida is diagnosed using a combination of veterinary examination, x-rays, myelography and magnetic resonance imaging (MRI) scans.

6. Genetics

Tail-lessness in Manx cats is due to a mutant gene, labelled M which causes abnormal development of the coccygeal (tail) and sacral vertebrae (the sacrum is the area of the spinal cord in front of the tail.) All Manx cats are heterozygous for the Manx gene (i.e. Mm), which means they have one mutant M gene and one normal m gene. The mutant M gene is dominant to the normal m gene (Long 2006). Homozygous MM cats with two mutant genes are so abnormal they die early during foetal development, thus the Manx gene is described as a lethal gene (Long 2006).

7. How do you know if an animal is a carrier or likely to become affected?

Affected individuals are likely to be identified prior to leaving the breeders.  All new Manx kittens should be fully examined by a vet prior to purchase.

All Manx cats have the mutant gene, M, and could produce affected offspring.

8. Methods and prospects for elimination of the problem

Currently there is no programme to decrease the unwanted affects of the mutant M gene. The gene is intimately linked to the phenotype that characterises the Manx cat i.e. tail-lessness, so breeding Manx cats results in persistence of these welfare issues.

For further details about this condition, please click on the following:
(these link to items down this page)

• Clinical and pathological effects
• Intensity of welfare impact
• Duration of welfare impact
• Number of animals affected
• Diagnosis
• Genetics
• How do you know if an animal is a carrier or likely to become affected?
• Methods and prospects for elimination of the problem
• Acknowledgements
• References

1. Clinical and pathological effects

The Manx cat is well recognised as a tailless breed; unfortunately this very obvious vertebral mutation is often linked to some severe developmental abnormalities of the spinal cord elsewhere leading to neurological disease (disease of the nervous system).

To have a clear understanding of the clinical problems seen as part of the Manx anomaly knowledge of normal cat anatomy and development is needed. The spine or spinal column of cats is made up of many bones, called vertebrae and it is divided into 5 different regions. There are 7 bones in the neck (cervical) region, 13 in the chest (thoracic) region, 7 in the lower back (lumbar) region and 3 fused together to form the sacrum (at the hips). Lastly, there are the tail (coccygeal) bones, and their number varies but it’s normally between 18 and 20 (Hudson and Hamilton 1993). Vertebrae are numbered according to the region of the spine they reside in and starting from the head working towards the tail. The first cervical vertebra is C1, the second C2, and the first thoracic vertebra is T1, etc.

Vertebrae are complicated bones. The body (largest part) of each vertebra is positioned ventrally (towards the lower side). Dorsal (towards the back of the cat) to the vertebral body is an opening with walls of bone called the vertebral canal. This is formed during development, from the fusing of two vertebral arches arising from each vertebral body that join together dorsally. The spinal cord passes through the vertebral canal and provides a neurological connection between the brain and the peripheral nerves. The vertebral canal protects the spinal cord which is very delicate. A pair of spinal nerves emerges between each vertebrae and these form peripheral nerves conveying sensation from, and signals to control the movement to all parts of the body (other than the head).

The regions of the spinal cord are labelled according to the regions of the spinal column. There are 8 cervical segments (including one in front of the first cervical vertebra), 13 thoracic segments, 7 lumbar segments, three sacral segments and about 7 caudal (coccygeal) segments. These segments are named in a similar way to the vertebrae ie C1, T1, and L1 etc. Because of differing growth rates between the spine and the spinal cord, the spinal cord ends at about the level of the L7 vertebra in normal cats. As, in the cat, the spinal cord is shorter than the vertebral column the various spinal cord segments do not necessarily sit within their corresponding vertebrae e.g. S2 cord segment is located within the L6 vertebrae in normal cats (Hudson and Hamilton 1993).

Tail-lessness in Manx cats is due to a mutant, autosomal dominant gene, labelled M, which causes abnormal development of the coccygeal and sacral vertebrae. All Manx cats are heterozygous for the Manx gene (i.e. Mm). Homozygous MM cats with two mutant genes are so abnormal they die early during development in the uterus, thus the Manx gene is described as a lethal gene (Long 2006). Those that are homozygous for the normal gene (ie those that are mm) have tails and are therefore, by definition, although born to Manx parents, are not Manx cats

The mutant M gene has variable expression and so individuals have variable degrees of tail-lessness. The four types described by Deforest and Basrur (1979) include:

• Rumpy cats – These have no coccygeal vertebrae.
• Rumpy-riser cats – These have several (1 – 7) coccygeal vertebrae fused in an upright position.
• Stumpy cats – These have 2-14 coccygeal vertebrae and may appear severely kinked due to abnormalities in their shape. These cats have some movement in their tail and can move it from side to side (which is impossible for rumpy-risers).
• Normal cats (or “Longie” Cats as described by Long 2006) which have a longer tail despite having the M gene (ie being Mm).

All animals in the first three categories have abnormal vertebrae (Deforest and Basrur 1979).

The development of the vertebrae in the foetus is intimately associated with the development of the spinal cord. During the early development of the embryo, the tissue that will form the spinal cord and brain, called the neural tube, forms from an invagination (inward folding) of an outer layer of tissue called the ectoderm. (In the early embryo there are three tissue layers). This invaginated fold then curls to form a complete tube, which breaks free of the surface tissue and sinks to form the neural tube and later the nervous tissue. Once the tube has formed, the mesoderm (the middle layer of the original three layers of tissue) divides into serial segments called somites, which in turn split into three regions. The region nearest the middle-line of the foetus (the sclerotome) forms vertebrae next to the neural tube (Kroll and Constantinescu 1994).

The Manx anomaly gene causes an abnormality in the ectodermal tissue that affects the spinal cord and vertebral arch (Bailey 1975).

Deforest and Basrur (1979) postulate that this underlying defect of the developing nervous system results in aberrant development of the vertebral column in Manx cats. Thus, although the cats have been breed for changes in their vertebral column i.e. tail-lessness, the gene, in fact, brings this about through abnormal spinal cord and vertebral arch development. So it is unsurprising that spinal cord abnormalities are often present. It is these problems of the spinal cord that cause the severe clinical and welfare problems of Manx cats.

The commonest developmental problem seen in Manx cats is spina bifida. Spina bifida is a general term used to describe several conditions in which the neural tube which forms the spinal cord fails, to varying degres, to close, and the vertebral arches also fail to form completely.

There are various types of spina bifida and spinal cord abnormalities that can occur (Kroll and Constantinescu 1994) and each is associated with particular clinical and welfare issues:

• meningeal dysplasia (abnormal formation of the meninges – the tissue wrapping the spinal cord)
• spinal cord dysplasia, also called myelodyplasia (Hopkins 1992), in which there is a malformation of the spinal cord that may include any or all of the following:
  • absent or duplicated central canal in the spinal cord (in nwhich a canal runs through the centre of the spinal cord);
  • hydromyelia (dilated central canal);
  • syringomyelia (the formation of cavities – spaces-  in the spinal cord);
  • abnormal distribution or migration of gray matter (one of the tissue types of the spinal cord);
  • absence of the ventral median fissure (ie absence of a feature of the shape of the normalspinal cord) (Shell 2003a).
• sacrocaudal dysgenesis – an absence of the sacral and caudal spinal cord segments (Shell 2003b)
• Spina bifida occulta  a localised defect involving incomplete formation of one or more vertebral arch. The overlying skin is normal and the cat is clinically normal (Kroll and Constantinescu 1994).
• Spina bifida manifesta is the form of the condition in which signs of nervous system abnormalities are present.
• Spina bifida cystic  - a defect of the vertebral arch with herniation (ballooning out) of the meninges (the membrane which covers the spinal cord) from the spinal canal through the defect (also called meningocele) or with herniation of the meninges and parts of the spinal cord (called meningomyelocele). Meningomyeloceles usually lead to severe signs of spinal cord problems.
• Spina bifida aperta - the spinal cord is open to the surface of the skin. There is great risk of infection of the spinal cord leading to severe illness and deterioration.

Rumpy Manx cats often lack sacral and sometimes even lumbar vertebrae and often have parts of the spinal cord missing (spinal cord dysgenesis) (Kroll and Constantinescu 1994).

Signs seen in Manx cats with spina bifida and spinal cord dysgenesis vary according to the severity of the spinal cord abnormality at birth, but include those outlined below.

• A plantigrade hind limb stance and gait (Hopkins 1992) in which the cat stands and walks on all of the area from the hock to the toe (like a human) instead of on its toes as usual. This is due to partial paralysis of the hind limbs. Normal rapid locomotion is impossible for these cats without “hopping” (Deforest and Basrur 1979). A hopping, rabbit-like gait is common in Manx cats (Kroll and Constantinescu 1994). The cats may appear to be crouching, and have less coordination than normal cats.
• Lack of sensation in the skin around the perineum (Deforest and Basrur 1979).
• Urinary incontinence (inability to control the release of urine) and secondary urinary tract infections.
• Faecal incontinence (inability to control the release of faeces), with distension of the colon (megacolon), and sometimes the whole abdomen, due to constipation. Constipation has many causes in cats but here it is due to compromised ability to expel faeces because of loss of nerve function. Faeces accumulate and distend the colon and abdomen. Soiling of the perineal skin is seen secondary to faecal and urinary incontinence.
• Rectal prolapse, where some of the rectum protrudes and prolapses through the anus (Deforest and Basrur 1979).
• More severely affected individuals have abnormalities along the spine such as a meningomyelocele which is detected as a dorsal midline lump covered by membrane (Kroll and Constantinescu 1994). These may or may not be covered by the skin, and those which are open may leak CSF (cerebrospinal fluid – the fluid that bathes the spinal cord and brain) (Evans 1985). Serious infections easily occur in these individuals leading to rapid depression, general ill health and lethargy and pyrexia (high temperature), more severe neurological signs and death.

Sometimes more severe clinical signs develop in the weeks to months after birth due to “tethering” of the spinal cord. In these individuals the spinal cord is abnormally attached to the vertebral canal. As the cat grows the spinal cord is stretched and damaged leading to progressive sensory and motor impairment in the hind legs and incontinence (Kroll and Constantinescu 1994). The latter signs are due to abnormalities of the sensory and motor nerves of the hind limbs, bladder, bowel and perineal region (Kroll and Constantinescu 1994). They are most often seen in Rumpy cats.

• Manx cats with a short deformed tail i.e. stumpies, are prone to arthritis in the joints between the deformed tail bones. This can be very painful (Feline Advisory Bureau).
• Exencephally, in which the skull development is incomplete and the brain lies partially outside the skull, and kyphoscoliosis, which is dorsal and lateral curvature of the spinal column (Evans 1985).

Occasionally surgery of the spine can be helpful to treat some forms of the disease in affected cats. Constipation problems may be treated medically with some success. But, generally, no effective treatment for these problems is available.

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2. Intensity of welfare impact

Some Manx cats appear normal, apart from their short tails, and show no signs of spinal cord dysfunction. Others have major abnormalities of the spine and spinal cord as outlined above which result in lack of proper functioning of the hind limbs and urinary and faecal incontinence. These individuals may be regularly soiled in urine and/or faeces which cause skin inflammation, irritation and infection and which requires constant nursing care. Affected individuals are unable to move freely which affects their ability to behave normally. Spina bifida does not cause pain unless there is spinal cord infection. Stumpy cats are prone to painful arthritis in their abnormal tail stumps.

Severely affected individuals cannot lead normal lives and are usually euthanased at an early age. Individuals with spina bifida aperta may get spinal cord infections leading to a rapid severe illness often causing pain and death.

“It must be remembered that the unique appearance of the Manx actually constitutes the relatively normal end of a spectrum of genetically controlled characteristics that include serious and potentially lethal abnormalities” (Kitchen et al 1972 as cited by Kroll and Constantinescu 1994).

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3. Duration of welfare impact

Abnormalities may be apparent from birth; otherwise, signs appear over weeks to months as the cat develops and grows (Kroll and Constantinescu 1994). Usually these problems are untreatable and if severe the animal is likely to become ill and die of complications unless euthanased. Life expectancy is severely reduced in affected individuals. Less severely affected individuals may cope in a protected environment with close attention from their owners. Occasionally surgical treatment may help.

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4. Number of animals affected

Spina bifida is common in Manx cats.. Deforest and Basrur (1979) state “the Manx breeder soon discovers that a considerable percentage of kittens suffer from severe congenital abnormalities”. In their study they reported 7 out of 44 kittens recorded were affected (16%); all of these were rumpies. Rumpies are often clinically affected (Evans 1985), and have an increased juvenile mortality (Kroll and Constantinescu 1994), though they may be the most desirable individuals to breeders and owners (if unconcerned about welfare issues) as they are completely tailless. Breeders often have affected kittens euthanased in early life so that potential owners only see the more healthy individuals.

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5. Diagnosis

Detection of the various forms of abnormality that can be caused by the genetic mutation is not always easy. An expert examining an affected individual may be able to feel an abnormality in the caudal or sacral vertebral area. A dimple in the skin may be seen in the lumbosacral region indicating an underlying meningocele (Kroll and Constantinescu 1994). A vet may also detect abnormalities in spinal reflexes which indicate spinal cord abnormalities. Radiography (x-rays) will show the bony defects and a myelograph (an x-ray taken after special dye has been injected into the space around the spinal cord) or an MRI (magnetic resonance imaging) scan is needed to confirm the type and extent of the spinal cord abnormalities (Kroll and Constantinescu 1994).

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6. Genetics

Tail-lessness in Manx cats is due to a mutant, autosomal dominant gene M which causes abnormal development of the coccygeal and sacral vertebrae. All Manx cats are heterozygous for the Manx gene (i.e. Mm), which means they have one mutant M gene and one normal m gene each inherited from a parent. The M gene is a mutant form of the normal gene m and is dominant to it (Long 2006). Homozygous MM cats with two mutant genes are so abnormal they die early during foetal development in the uterus, thus the Manx gene is described as a lethal gene (Long 2006).

The variable expression of the mutant M gene in heterozygous (Mm) individuals  gene is due to the actions of other genes which influence its effects (Long 2006).  These modifying genes are currently unidentified. Robinson (1993) suggests the variation in expression is only partly genetic in origin. The heritability has been estimated to be in the region of 0.40 ± 0.11 (Robinson, 1993), ie around 40% is due to the modifying genes and the rest due to other, presumably, environmental factors.

Because Manx cats have to be tail-less (to some degree - see above) they are all heterozygous and do not “breed-true” i.e. when Manx cats are bred some kittens (about a quarter) will be genetically mm and will therefore have normal tails (and will avoid all of the disease conditions described above) – but they will not be called Manx cats.

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7. How do you know if an animal is a carrier or likely to become affected?

All Manx cats (i.e. those cats that have the tail abnormality) carry the mutant gene M and could therefore produce affected offspring and are thus carriers of the gene. It might be thought that as stumpy cats are less likely to have signs of disease themselves, breeding from them is less likely to produce rumpy individuals (which are more likely to have forms of the disease). However, this is not the case as it is the effects of the unknown modifying genes and environmental factors that determine if the individual will be a rumpy (or other form) and these cannot be currently tested for or identified prior to mating.

The disease is perpetuated by breeding Manx (tail-less) cats. Cats evolved to have tails and they use them for communication and balance. As long as people buy or wish to keep Manx cats the serious disease and welfare problems caused by the genetic mutation carried by all these cats will be perpetuated.

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8. Methods and prospects for elimination of the problem

Manx breeders may breed Manx cats i.e. Mm individuals to “normal” mm individuals to avoid the production of severely affected MM foetuses that die before birth. However this practice does not avoid the possible production of affected Mm individuals.

Currently, as far as we are aware, there is no programme to decrease the unwanted affects of the mutant M gene. The gene is intimately linked to the phenotype that characterises the Manx cat ie tail-lessness, so breeding Manx cats maintains the persistence of the diseases caused by the mutant gene with their adverse welfare consequences. FAB (www.fab.org) suggests that due to informed breeding practices the occurrence of problems is reduced, however evidence for this has not been identified. Breeding of Manx cats and the long-haired type (Cymric) seems to have greatly decreased in the UK, in recent years (http://www.danzantemanx.com). In the future, if the genes and environmental factors which affect the M gene’s expression were to be identified then it might be possible to develop methods to help reduce the adverse effects of the Manx gene. However, the ethics of continuing a breed whose characteristic is based on such a damaging gene should be seriously considered and reviewed.

Tailed individuals (not referred to as Manx cats), who are mm homozygous, produced from Manx cat breeding do not possess the mutant gene, are free from the condition and can be bred safely.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section.

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10. References

Bailey C (1975) An embryologic approach to the clinical significance of congenital vertebral and spinal abnormalities. Journal of the American Animal Hospital Association 11: 426-434

Danzante manx (2010) Homepage. (On-line). Available at http://www.danzantemanx.com. Accessed 7.12.2010

Deforest M and Basrur P (1979) Malformations and the Manx Syndrome in Cats. Canadian Veterinary Journal 20 304-314

Evans RJ (1985) The Nervous System. In: Feline Medicine and Therapeutics. Editors E. Chandler, C, Gaskell, & A Hilbery Blackwell scientific publications: London, pp 38

Feline Advisory Bureau (FAB) Available at http://www.fabcats.org/breeders/inherited_disorders/manx.php. Accessed 7.12.2010

Hopkins A (1992) Feline Neurology Part 2: Diseases of the spinal cord, peripheral nerves and neuromuscular system. In Practice, 14 111-117

Hudson L and Hamilton W (1993) Atlas of Feline Anatomy for Veterinarians. W.B Saunders Company: Philadelphia, USA. pp 30.

Kitchen H, Murray R and Cockrell B (1972) Animal model for human disease; spina bifida, sacral dysgenesis and myelocele. American Journal of Pathology 66 203-206

Kroll R and Constantinescu G (1994) Congenital Abnormalities of the Spinal Cord and Vertebrae. In: Consultations in Feline Medicine 2. Editor J. August. W.B Saunders Company: Philadelphia, USA. pp 413

Long S (2006) Veterinary genetics and reproductive physiology. A textbook for veterinary nurses and technicians. Butterworth Heinemann: London. pp 18

Robinson R (1993) Expressivity of the Manx Gene in Cats. Journal of Heredity. 84 170-172

Shell L (2003a) Myelodysplasia (Spinal Dysraphism) (on-line) Available at http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1023. Accessed 30.11.10

Shell L (2003b) Sacrocaudal Dysgenesis. (On-line) Available at http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1024.  Accessed 30.11.10

© UFAW 2011