Related terms: spina bifida, myelodysplasia, spinal cord dysplasia, hydromyelia, spinal dysraphism, syringomyelia, spinal dysplasia
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.
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.
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.
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.
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).
Spina bifida is diagnosed using a combination of veterinary examination, x-rays, myelography and magnetic resonance imaging (MRI) scans.
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.
Causes & Pathological Affects
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).
Information & Content Courtesy of Universities Federation for Animal Welfare