Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

German Shepherd Dog (Alsatian)

German Shepherd Dog (Alsatian)

Degenerative Myelopathy

Related terms: Degenerative radiculomyelopathy, chronic degenerative radiculomyelopathy (CDRM), German shepherd dog myelopathy

Outline: Degenerative myelopathy is a progressive, incurable, disease of the nerves of the spinal cord which causes gradual loss of mobility and loss of feeling in the limbs. Affected dogs become paralysed first in the hind limbs and then in the forelimbs. The condition, which appears to be quite common in German Shepherd dogs, does not cause pain but they are unable to behave or function normally which is likely to have a detrimental impact on their welfare.


Summary of Information

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1. Brief description

Degenerative myelopathy (DM) is a fatal, chronic, progressive, degenerative disease of the spinal cord of several breeds of dog, including the German Shepherd dog (GSD). There is no treatment for this disease and in time it leads to complete paralysis in all limbs (tetraparesis). Euthanasia is usually opted for before the disease progresses to this stage.

In DM there is a slow, progressive degeneration of an outer layer of tissue of the spinal cord (the white matter) in the thoracic (chest) section of the spine with loss of myelin and axons (Shell 2008). This degeneration appears to be due to the presence of excessive amounts of damaging reactive oxygen species molecules (ROS): biochemicals that react with and damage the components of cells, causing oxidative or free radical injury. High numbers of ROS occur with this condition, due to a mutation in the gene which codes for the production of the superoxide dismutase-1 (SOD1) enzyme, which is produced by cells to help break down ROS and limit any damage they might cause (Awano et al 2009).

The first signs of DM are classically seen at around 8 to 9 years of age and involve hindlimb ataxia (swaying when moving). As the disease progresses, hindlimb weakness occurs, leading to an inability to stand and then complete hindlimb paralysis. Most owners elect for euthanasia, once significant paralysis or paraplegia has occurred; however, if allowed to progress, the disease will ascend up the spinal cord to affect the forelegs leading to tetraplegia (inability to use all four limbs) (Awano et al 2009).

There is currently no effective treatment for this disease or its effects, though physiotherapy can help some dogs stay mobile for longer.

2. Intensity of welfare impact             

DM is a non-painful disease (Cherubini et al 2008, Shell 2008), however, the dog may be caused distress by its progressive inability to move normally. Normal maintenance behaviours, such as scratching, comfort shifting of the body, urinating/defaecating become difficult or impossible as the disease progresses and nursing-care needs rapidly increase. Pressure sores and painful ulcerations may occur secondary to hindlimb paralysis unless there is scrupulous care by the owners.

3. Duration of welfare impact

This disease usually appears in dogs from 8 or 9 years of age (Cherubini et al 2008, Rusbridge no date), however, animals as young as 6 months can be affected (Cherubini et al 2008).

Once the condition appears it is progressive and fatal. The majority of owners have their dogs euthanased within a year of diagnosis (Awano et al 2009).

4. Number of animals affected

Considered a common problem of older GSDs by veterinary surgeons; the exact percentage of GSDs affected is currently unknown although researchers at Missouri University suggest that a relatively high proportion of individuals have the predisposing mutated gene and many will go on to manifest the disease. From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are German Shepherd Dogs (Alsatians) (Lucy Asher, 2011, personal communication), we estimate that the UK population size of this breed may be around 400,000. 

In one study 2% of all GSDs presented at USA veterinary teaching hospitals were found to be affected (Coates et al 2007). If, on the basis of this, we estimate prevalence at 2%, then the number of affected animals in the UK may be about 8000.

5. Diagnosis

A definitive diagnosis of DM can only be made at post-mortem with microscopic examination of the spinal cord (Cherubini et al 2008). A tentative diagnosis of DM, whilst the dog is alive, can be made by a veterinary surgeon through elimination of all other possible causes of the signs. This may well involve diagnostic procedures including radiographs, blood tests, analysis of the cerebrospinal fluid (the fluid around the spinal cord and brain) and computerised tomography (CT) or magnetic resonance imaging (MRI) scans.

6. Genetics

A gene connected to a greatly increased risk for developing DM has been recently identified. This mutated gene has been categorised as autosomal recessive with incomplete penetrance; this means that to develop the disease an animal has to have inherited one copy of the gene from each parent but even then it may not go on to develop the symptoms of the disease (Awano et al 2009).

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

DNA testing can now be undertaken to identify animals at risk of developing the disease and carrier animals, who have a copy of the mutated gene but which are unaffected by the disease themselves. All animals should ideally be tested prior to purchase and breeding.

8. Methods and prospects for elimination of the problem

Currently there is no scheme in place to try and eradicate DM from the GSD breed in the UK, although in the USA the University of Missouri and the Orthopedic Foundation for Animals offers a test for the condition.

Elimination of a recessive gene with incomplete penetrance from a breed is not straightforward if its prevalence is high because removing all carrier animals, that possess a copy of the gene, may significantly affect the number of animals suitable to breed from, and hence the size of the gene pool. To avoid such a problem, careful breeding of carrier animals to known healthy non-carrier individuals is recommended (Bell 2010), with slow replacement of carrier breeding animals with non-carriers over time.


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1. Clinical and pathological effects

Degenerative myelopathy is a fatal, chronic, progressive, degenerative disease of the spinal cord, affecting several breeds of dog including the GSD. In time, it leads to complete paralysis in all limbs (tetraparesis).

To understand the disease process some knowledge of the anatomy of the spinal cord and nervous system is needed. The nervous system is comprised of the central nervous system – the brain and spinal cord – and the peripheral nerves, which connect to the spinal cord throughout its length. The brain is the nervous system’s information processing centre, analogous in function to a computer. It receives messages from sensors throughout the body (sensory functions), processes this information, decides what changes need to occur and then sends out messages to glands and muscles to make these changes (motor functions).

The spinal cord’s function is to act as the switch board, helping transmit sensory messages from the body to the brain and motor messages from the brain back to the body. The spinal cord runs along the length of the spine, which protects it. The spine is divided into 5 different regions – cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic) and coccygeal (tail). The spinal cord is similarly split into regions and correspondingly labelled.

The spinal cord is comprised of two major types of tissue: white and grey matter. The white matter contains the axons – long wire-like fibres - of the sensory and motor neurons that carry nerve impulses either to or from the brain, the grey the cell bodies of the neurons. The axons of the motor neurons, that start in the brain, are often called the upper motor neurons (UMNs), and their connections with the cell bodies of the nerves cells that go on to form the peripheral nerves (the lower motor neurones LMNs). To increase the speed with which axons can transmit their impulse (the electrical message that they carry), they are insulated (much like electrical wires in our homes). The insulating layer is called the myelin sheath and it is because of its fat content, that the tissues of the spinal cord that it makes up appear white.

In DM there is a slow, progressive degeneration of the white matter of the thoracic section of the spinal cord, with loss of both myelin and axons (Shell 2008). Abnormal structures called cytoplasmic inclusions are also observed within the diseased tissue when it is examined under the microscope (this can only be done at post mortem) (Rusbridge no date).

The degeneration of the spinal cord tissue appears to be caused by the action of excessive amounts of damaging reactive oxygen species molecules (ROS): biochemicals that react with and damage the components of cells, causing oxidative or free radical injury. High numbers of ROS occur with this condition, due to a mutation in the gene which codes for the production of the superoxide dismutase-1 (SOD1) enzyme, which is produced by cells to help break down ROS and limit any damage they might cause (Awano et al 2009). DM in dogs is comparable to amyotrophic lateral sclerosis (ALS) a progressive, neurodegenerative disease of humans (Awano et al 2009). Prior to the discovery of the SOD1 gene mutation, possible causes of DM were suggested as genetic, nutritional (Averill 1973, Williams et al 1985), or immunological (Barclay and Haines 1994, Waxman et al 1980).

The first signs are typically seen at around 8 to 9 years of age and involve hindlimb ataxia (swaying when moving). This may be asymmetrical (worse on either the right or left side). The dog may also have difficulty getting up and its hindlimb nails may become scuffed to the point of bleeding. DM has an insidious (gradual) onset and can easily be misdiagnosed as hip dysplasia or other orthopaedic problems, which are also common in GSDs. Unlike many other of these conditions, DM seems painless (Cherubini et al 2008). Owners may notice the hindlegs crossing over as the dog walks. In this stage of the disease, it is mainly the UMNs of the spinal cord that are affected, along with sensory nerves. Spinal reflexes, when tested, often seem to be intact but the dog seems to be unable to sense exactly where the hindlimbs are or place them accurately - hence the scuffing of the nails and ataxic gait.

With progression of the disease, loss of motor functions and signs of LMN dysfunction manifest in the hindlimbs. These show as weakness leading to inability to stand and paralysis in the hindlimbs. In time, the muscles of the hindlegs waste away. Most owners elect for euthanasia once paraplegia has occurred; however, if allowed to progress, the disease will ascend up the spinal cord to affect the forelegs leading to tetraplegia (loss of use of all four limbs) (Awano et al 2009). The rate at which the disease progresses is often not uniform rather it is characterised by periods of slow progression followed by rapid changes (Cherubini et al 2008). Urinary and faecal incontinence may occur (Shell 2008) and trauma to nails and the hindlimbs or pressure sores may occur secondary to the paresis (loss or impaired movement), paralysis and incontinence.

There is currently no effective treatment (Cherubini et al 2008, Rusbridge no date) although physiotherapy has been shown to prolong the time some dogs can remain mobile (Kathmann et al 2006).

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2. Intensity of welfare impact

DM is itself not a painful disease (Cherubini et al 2008, Shell 2008); however, affected dogs may be caused distress by being unable to function or behave as normal. Trauma may also occur to nails and the skin of the hind limbs as sensation and loss of function progresses. Once paralysed, these dogs have long-term care needs which many owners find difficult and some dogs will be euthanased because of this. Deciding whether these dogs should be euthanased or if they have enough quality of life to justify being supported with paralysis and possible incontinence is an ethical dilemma – some dogs and owners do seem to manage successfully with ‘hindlimb carts’ which support the rear of the dog, for a period of time.

Ultimately, when earlier euthanasia is declined, DM leads to an inability to carry on any kind of normal life and finally to death.

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3. Duration of welfare impact

Degenerative myelopathy usually appears in dogs from 8 or 9 years of age (Cherubini et al 2008, Rusbridge no date), however, animals as young as 6 months can be affected (Cherubini et al 2008).

The condition is progressive from the start although the rate of progression of the disease may not be uniform. Most owners of affected dogs elect to have them euthanased within 12 months of the onset of signs, often when they become paraplegic. Deterioration to death can take over 3 years (Awano et al 2009).

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4. Number of animals affected

Degenerative myelopathy was first identified in GSDs. The commonest cause of progressive hindlimb dysfunction in older, large-breed dogs (Wheeler 1989), it was originally thought to only affect GSDs, this is now known not to be the case. Wahl et al (2008) consider it a major genetic disease afflicting GSDs.

The exact percentage of GSDs to be affected is currently unknown although researchers at Missouri University suggest that a relatively high proportion of individuals from the following breeds: GSD, Boxer, Pembroke corgi, Chesapeake Bay retriever and Rhodesian ridgeback have the predisposing mutated gene and that many of these genetically-affected individuals will go on to manifest the disease. (see: http://www.caninegeneticdiseases.net/DM/ancmntDM.htm), In one study 2% of all GSDs presented at USA veterinary teaching hospitals were found to be affected (Coates et al 2007).

From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are German Shepherd Dogs (Alsatians) (Lucy Asher, 2011, personal communication), we estimate that the UK population size of this breed may be around 400,000.  If, on the basis of the above, we estimate prevalence at 2%, then the number of affected animals in the UK may be about 8000.

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5. Diagnosis

A definitive diagnosis of DM can only be made after death by microscopic examination of the spinal cord (Cherubini et al 2008). A tentative diagnosis of DM, whilst the dog is alive, can be made by a veterinary surgeon through elimination of all other possible causes of the signs. This will include the need for a full physical and neurological examination (examination of the nervous system by means of tests to check out the health of various nerve pathways). It may also include blood tests, spinal x-rays including myelography (x-rays after injection of a dye into the spinal canal), analysis of cerebrospinal fluid (the fluid that bathes the brain and spinal cord), CT (computed tomography) scans and MRI (magnetic resonance imaging) scans, the most useful diagnostic test for imaging the brain and spinal cord. The tentative diagnosis is made if the results of all tests including the MRI scans are normal, though the CSF analysis may reveal a high level of protein (Cherubini et al 2008).

As DM is most often seen in older dogs it is not uncommon for them to have concurrent disease which often will cause abnormalities on these tests and may complicate the diagnostic process. For example it is relatively common for an older GSD to have hip dysplasia (to which they are also predisposed) and/or other changes which show on the spinal x-rays including spondylosis deformans, lumbosacral spondylosis, narrowed intervertebral disc spaces, spinal arthritis, and lumbosacral stenosis (Shell 2008). It is also possible for osteoarthritis of the hips or spine to develop secondary to DM due to uneven weight bearing in the hindlimbs as the disease progresses (Cherubini et al 2008). It is the veterinary surgeon’s role to decide which diagnostic changes are significant and whether the dog has several concurrent diseases.

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6. Genetics

Recently a gene connected to the development of DM has been identified. Dogs which are homozygous for the mutated gene SOD1, i.e. those that have two copies of the mutated gene are at high risk of developing DM (Awano et al 2009). Currently, not all the animals identified with a pair of the abnormal genes have developed the disease. It is not known if they will go on to develop the disease later or if other unknown risk factors are necessary for disease development in these individuals (College of Veterinary Medicine, University of Missouri, no date). Animals with one abnormal gene appear to be healthy carriers i.e. they themselves remain healthy but can pass the abnormal gene on to offspring. The problem has therefore been categorised as an autosomal recessive disorder with incomplete penetrance i.e. not all genetically affected animals develop the disease (Awano et al 2009).

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

DNA testing can now be performed to identify animals at risk of developing the disease and carrier animals. All animals should be tested prior to purchase and breeding. Currently this test is only available from the University of Missouri and the Orthopedic Foundation of America (OFA) in the USA. Without DNA testing, individuals at risk of developing DM in later life cannot be identified.

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8. Methods and prospects for elimination of the problem

Currently there is no scheme in place to try to eradicate DM from the GSD breed in the UK, although in the USA the University of Missouri and the Orthopedic Foundation for Animals offers a test that can identify the condition and individuals at high risk of developing the disease and/or who are unaffected by the disease but can pass it on (carriers). The researchers who developed this test believe that careful use of it could help decrease the incidence of DM in affected breeds although they feel this occurs slowly, over many generations (College of Veterinary Medicine, University of Missouri, no date).

Elimination of a recessive gene with incomplete penetrance from a breed is not straightforward if its prevalence is high because removing all carrier animals, that possess a copy of the gene, may significantly affect the number of animals suitable to breed from, and hence the size of the gene pool. Careful breeding of carrier animals to known healthy non-carrier individuals is recommended (Bell 2010), with slow replacement of carrier breeding animals with non-carriers over time.

If, as suspected, the mutated gene is common in GSDs, halting breeding from all carrier animals may significantly affect the number of animals suitable to breed from, and hence the size of the gene pool. This could lead to excessive inbreeding and the appearance of other unwanted genetic diseases (of which there are many). To avoid such a problem, the careful breeding of carrier animals with non-carriers, either from within the breed or from outside the breed, seems necessary. To enable the elimination of the gene whilst minimising the risks of other genetic problems emerging due to greater levels of inbreeding, Bell (2010) recommends that, over time, breeders slowly replace carrier breeding animals with non-carriers.

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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

Averill DR (1973) Degenerative myelopathy in the aging German Shepherd dog: Clinical and pathologic findings. Journal of the American Animal Hospital Association 162: 1045-1051

Awano T, Johnson GS, Wade CM,  Katz ML, Johnson GC, Taylor JF, Perloski M, Biagi T, Baranowska I., Long S, March PA, Olby NJ, Shelton GD, Khan S, O’Brien DP, Lindblad-Toh K  and Coates JR (2009) Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proceedings of the National Academy of Science 106: 2794–2799

Barclay KB and Haines DM (1994) Immunohistochemical evidence for immunoglobulin and complement deposition in spinal cord lesions in degenerative myelopathy in German shepherd dogs. Canadian Veterinary Journal of Research 58: 20-24

Bell J (2010) Genetic Testing and Genetic Counseling in Pet and Breeding Dogs. World Small Animal Veterinary Association World Congress Proceedings, Geneva 2-5th June 2010

Cherubini G, Lowrie M and Anderson J (2008) Pelvic limb ataxia in the older dog 1. Assessment and non-painful conditions. In Practice 30: 386-391

Coates JR, March PA, Oglesbee M, Ruaux CG, Olby NJ, Berghaus RD, O’Brien DP, Keating JH, Johnson GS and Williams DA (2007) Clinical Characterization of a Familial Degenerative Myelopathy Pembroke Welsh Corgi Dogs Journal of  Veterinary Internal Medicine 21: 1323–1331

College of Veterinary Medicine, University of Missouri (no date) Degenerative Myelopathy. (On-line). Available at http://www.caninegeneticdiseases.net/DM/ancmntDM.htm.  Accessed 21.12.2010.

Kathmann I, Cizinauskas S, Doherr MG, Steffen, F and Jaggy A (2006) Daily controlled physiotherapy increases survival time in dogs with suspected degenerative myelopathy. Journal of Veterinary Internal Medicine 20: 927-932

Rusbridge C (no date) Degenerative Myelopathy (On-line) available at http://www.veterinary-neurologist.co.uk/degenerative_myelopathy.htm. Accessed 10.12.10

Shell L (2008) Degenerative Myelopathy (Degenerative Radiculomyelopathy). (On-line) Available at http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1737.  Accessed 10.12.10

Wahl J, Herbst S, Clar L, Tsai K and Murphy K (2008) A review of hereditary diseases of the German shepherd dog. Journal of Veterinary Behaviour 3: 255-265

Waxman FJ, Clemmons RM and Hinrichs DJ (1980) Progressive myelopathy in older German Shepherd dogs: Presence of circulating supressor cells. Journal of Immunology 124 1216-1222

Wheeler S (1989) Neurological deficits in multiple limbs. In: Manual of Small Animal Neurology editor S.J. Wheeler. British Small Animal Veterinary Association, Cheltenham 175

Williams DA, Prymak C and Baugham J (1985) Tocopherol (vitamin E) status in canine degenerative myelopathy. Proceedings of the American College of Veterinary Internal Medicine 3: 154

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