Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

French BulldogFrench Bulldog

Hemivertebrae

Related terms: Congenital vertebral anomalies, wedge vertebrae

Outline: French bulldogs commonly have deformities of the bones of the spine. These can lead to pressure on the spinal cord resulting in progressive pain and loss of hind limb function and incontinence.

 


Summary of Information

(for more information click on the links below)

1. Brief description

Hemivertebrae are bones of the spine that are abnormally shaped. Because of their abnormal shape these bones tend not to align correctly with their neighbouring bones in the spine. This can lead to instability and deformity of the spinal column, which in turn can lead to the spinal cord (or the nerves arising from it) becoming compressed (squashed) and damaged. This causes pain – which can be severe - wobbliness (ataxia) on the hind legs and can also cause loss of hind leg function and incontinence (inability to control passing urine or faeces). It appears that the disease is a consequence of selecting for the screw (curly) tail conformation of this breed.  Screw tail describes a tail which, in its relaxed position, is coiled, usually to one side. The most severely affected tails cannot be straightened at all, others can be manually straightened but relax back into the coiled position. The screw-tail shape is due to abnormal shape of tail bones but this abnormality can also affect other parts of the spine with serious consequences as outlined above.

2. Intensity of welfare impact

Pain from spinal cord compression (squashing) can be severe. Affected dogs can also lose function in their hind limbs and sometimes lose bladder and bowel control. Not all animals with hemivertebrae develop these signs; some have milder signs of ataxia or no signs at all.

Dogs with severe signs may need major surgical interventions, which have their own welfare impacts, and, despite this, some may not recover and need to be euthanized on humane grounds.

3. Duration of welfare impact

Young dogs are most commonly affected when problems associated with skeletal deformities develop as their skeleton grows. The skeletal deformity is permanent without surgery. The clinical signs associated with the condition can develop rapidly over days, or gradually over weeks and months. Severely affected individuals would, without surgery, have permanent major disability. Even where surgery is possible, some animals may have unacceptable levels of disability necessitating euthanasia.

Thus, this condition can severely limit both the quality and length of life.

4. Number of animals affected

A study of French bulldogs in the UK found that approximately 1% of the population surveyed were being treated by a vet for a spinal cord disorder and that they are significantly more likely to suffer from a spinal cord disorder than other breeds of dog (between 2 and 4.5 times more - (O’Neil et al. 2021).

5. Diagnosis

A diagnosis is made on examination and radiography (taking x-ray pictures).

6. Genetics

French bulldogs possess a genetic mutation that affects tissue development and causes the screw-tail deformity and produces hemivertebrae elsewhere in the spine.

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

All French bulldogs are prone to the problem because the breed has a screw-tail. Studies have found that up to 97% of all French bulldogs examined had one or more abnormal vertebrae. That a dog has no hemivertebrae can only be confirmed by taking x-rays of the spine.

8. Methods and prospects for elimination of the problem

The genetic mutation that causes screw-tail and hemivertebrae is recessive, i.e. two copies of the variant gene need to be present for hemivertebrae to occur. To reduce the occurrence of the condition, out-breeding needs to be done with dogs with straight tails, combined with selection for a straight tail, as this would contribute to eliminating this welfare problem.

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


1. Clinical and pathological effects

An understanding of the anatomy of the normal spine of the dog is useful in understanding this condition.

Hemivertebrae figure 1

Figure 1. The regions of the spine.

The spine or spinal column of dogs is made up of many bones called vertebrae, and it is divided into 5 different regions (Figure 1). 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 depending on breed. In French bulldogs and other screw-tailed dogs there are relatively few coccygeal vertebrae. Vertebrae are numbered within each region of the spine, starting from the head and working towards the tail, using a prefix to indicate the spine region. Thus, the first cervical vertebra is called C1, the second C2 and the first thoracic vertebra is T1 etc. Intervertebral discs are found between the vertebral bodies.

The body of each vertebra is positioned ventrally (towards the lower side). Dorsal (towards the back of the dog) to the vertebral body, each vertebra forms a hollow tube of bone called the vertebral canal. Through this tube created by the column of vertebral canals the spinal cord passes, connecting the base of the brain with peripheral nerves. This tube of bone protects the spinal cord (Figure 2). The spinal cord is made up of delicate nerve tissue which transmits the messages between the brain and other parts of the body (excluding the head).

Hemivertebrae figure 2

Figure 2. Diagram showing the shape of normally-formed vertebrae in the spinal column and how the spinal cord runs through them.

Each vertebral body develops in the foetus from two separate parts which fuse together and then ossify (turn to bone). Hemivertebrae occur when this fusing process fails to happen correctly so that the vertebral body of one or more vertebra is malformed and wedge-shaped (LeCouteur and Child 1995). Often the fusion or ossification is asymmetrical (Jeffery et al2007). The malformations vary, with the apex of the wedge pointing dorsally, ventrally or medially (towards the middle of the animal) across the midline (LeCouteur and Child 1995). These abnormally-shaped vertebrae often lead to alterations and deformities in the shape of the spine such as kyphosis (curving upwards of the central spine), scoliosis (deviation to the side in the central spine) or lordosis (curving downwards in the central spine; LeCouteur and Child 1995). This angulation of the spine is often moderate to severe and can lead to displacement of the vertebrae (LeCouteur and Grandy 2000).  The upward curvature of the spine (kyphosis) seems to be a particularly significant factor in the development of clinical signs (De Decker et al. 2024). The deformity or instability in the spinal column can then narrow the vertebral canal, compressing and damaging the spinal cord, and this can lead to serious clinical signs (LeCouteur and Child 1995). This spinal deformity and the consequential clinical signs often progress as the dog grows or, sometimes, happen secondary to mild trauma because of the spinal column instability (LeCouteur and Grandy 2000).

Hemivertebrae figure 3

Figure 3. Abnormal development of vertebral bodies results in formation of hemivertebrae.  

Unlike the normal shape of vertebrae shown in Figure 2, in which the opposing faces of adjacent vertebrae are at right angles to the line of the spine, wedge shaped vertebrae as shown here can lead to distortion of the spine with health and welfare effects.

Hemivertebrae figure 4

Figure 4. Radiograph of a hemivertebra in the thoracic region of a Pug. The wedge shaped vertebra has caused lordosis of the spine, which in turn can cause compression and damage to the spinal cord. (Image property of Helen McDonald, to whom we are grateful for permission to reproduce it here).

Hemivertebrae can occur in any breed but are most common in brachycephalic, screw-tailed dogs such as French bulldogs (also English bulldogs and Boston terriers). This is because the kinked tails that many find desirable in these breeds result from hemivertebrae in the tail region of the spine and these breeds have genes that tend to cause the formation of hemivertebrae elsewhere in the spinal column as well as in the tail (LeCouteur and Grandy 2000, Mansur et al. 2018). Recent studies have demonstrated a prevalence of hemivertebrae in French bulldogs between 75% and 100% (see De Decker et al. 2024). The commonest region of the spine to be affected by hemivertebrae, in French bulldogs, is the chest (the thoracic area; LeCouteur and Child 1995, Mansur et al. 2018, Moses et al. 2024, De Decker et al. 2024).

Hemivertebral abnormalities commonly occur without clinical sign of disease (Done et al 1975). However, if the spinal cord becomes damaged or compressed, signs appear. A survey of 16,000+ French bulldogs under veterinary treatment in the UK found that spinal cord disorders occur in the breed approximately three times more frequently than in other breeds of dog (O’Neil et al. 2021). Signs include posterior paresis (abnormal functioning of the hindlimbs), muscle wastage, an abnormal shape to the back and back pain. If the problem is severe then the dogs can lose all use of their hind legs and can have urinary and faecal incontinence (inability to control passing urine or faeces; Mauler et al. 2014). Signs can be gradual or rapid in onset and are usually progressive (Colter 1993) In a number of cases, however, signs may be mild and non-progressive and stabilise once the dog has stopped growing at about 9 months of age (Jeffery et al. 2007), though the deformity will remain. In these cases, no treatment may be necessary. In the majority of cases the clinical signs are progressive (around 85% of the time – Mauler et al. 2014) and if not treated  will result in the loss of movement in their hind legs (see De Decker et al. 2024).

In severely affected individuals, the only solution is major surgery of the spine to attempt stabilisation and to stop the spinal cord being compressed. This is not straightforward, needs specialist veterinary treatment, and may not always be successful. Some dogs that are completely paralysed in their hind legs may not recover use of them after surgery.

Paralysed dogs have long-term care needs which many owners find difficult, and some dogs will be euthanized because of this. It is an ethical dilemma whether these permanently paralysed dogs should be euthanized or if their quality of life may be sufficient to justify supported living with paralysis and incontinence. The welfare of the dog must be paramount in making this decision.

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2. Intensity of welfare impact

Some dogs with hemivertebrae suffer no apparent ill effects; however, others have major welfare problems such as pain, loss of function of the hindlimbs, and incontinence. Pain from spinal cord compression can be significant, severe, and difficult to control using drugs.

Along with pain, the spinal cord damage in severely affected individuals leads to the need for rapid veterinary treatments including major surgery. Though some dogs recover, surgical treatment is a major intervention, and many animals have a prolonged recovery during which veterinary staff and owners need to carry out extensive treatment and nursing which interfere with the dog’s life and daily routine. Some animals do not recover and will need to be euthanized.

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3. Duration of welfare impact

The condition usually first manifests in young growing dogs and worsens as growth proceeds. In a case study by Jeffery et al. (2007), all three dogs described were less than 7 months of age. Though some may be mildly affected, all affected animals will have permanent deformity unless surgical intervention is used. The disease problems can develop rapidly over hours or more gradually. Though some dogs with hemivertebrae do not develop signs, others develop severe problems which will not improve unless surgical intervention occurs. Some dogs with severe signs may not improve after surgery and will need to be euthanized to prevent further suffering.

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4. Number of animals affected

A study of French bulldogs in the UK found that approximately 1% of the population surveyed were being treated by a veterinarian for a spinal cord disorder and that this breed is significantly more likely to suffer from a spinal cord disorder than other breeds of dog (between 2 and 4.5 times more; O’Neil et al. 2021). As the population of the 16,000+ French bulldogs surveyed was significantly younger than the other dog breeds included (a median age of 1.5 compared to 4.5 years), the number treated for the condition would be expected to increase as the population demographic shifts and ages .

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5. Diagnosis

The condition may be suspected in any French bulldog with spinal deformity or with the characteristic clinical signs because it is commonly seen within the breed. A key factor in the development of the clinical signs is the severity of the upward curvature of the spine (De Decker et al. 2024). A diagnosis can be made using plain and contrast radiography (x-rays, with or without injection around the spinal cord of dye, which shows up on the x-ray), however, Jeffery et al. (2007) recommend MRI (magnetic resonance imaging) scans prior to surgery to help decide on exact surgical requirements.

The presence of hemivertebrae seen on x-rays may also be a confusing finding. Older French bulldogs may have spinal disease from other causes and detection of hemivertebrae may make diagnosis of the real cause difficult.

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6. Genetics

French bulldogs possess a genetic mutation that affects tissue development and causes the screw-tail deformity and in producing hemivertebrae elsewhere in the spine.

Whole genome sequencing and association has identified a frameshift mutation in a gene that is involved in controlling development of tissues in the embryo - the DISHEVELLED 2 gene (DVL2) (Mansour et al 2018). The mutation makes an altered protein that affects an important cell-cell communication system crucial for tissue development.

This variant is recessive, i.e. two copies of the variant DVL2 gene need to be present for hemivertebrae to occur. All of the French bulldogs assessed in this study possessed this variant allele, i.e. were homozygous for DVL2 variant (Mansour et al. 2018).

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

All French bulldogs are prone to the problem because the breed has a screw-tail. Studies have found that between 90-100% of all French bulldogs examined had one or more abnormal vertebrae, with more than 90% possessing thoracic (back) vertebral malformation (Mansur et al. 2018, Moses et al 2024).

Without x-ray images of the spine, absence of hemivertebrae cannot be definitely confirmed. However, a mature animal without signs has a lower chance of developing clinical problems than a puppy who has yet to undergo a period of significant growth.

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8. Methods and prospects for elimination of the problem

The genetic mutation that causes screw-tail and hemivertebrae is recessive. To reduce the occurrence of the condition, out-breeding (i.e. crossing with straight tailed dogs) combined with selection for a straight tail would contribute to eliminating this welfare problem.

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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 and to Hazel Bentall BVSc MRCVS for her comments on it.

 

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10. References

Colter S (1993) Congenital anomalies of the spine. In Bojrab M (Ed) Disease mechanism in Small Animal Surgery. 2nd Ed. London: Lippincott, Williams and Wilkins

Done S, Drew R and Robins G (1975) Hemivertebra in the dog: clinical and pathological observations. Veterinary Record 96: 313

De Decker S, Rohdin C and Gutierrez-Quintana R (2024) Vertebral and spinal malformations in small brachycephalic dog breeds: Current knowledge and remaining questions. The Veterinary Journal, 304 https://doi.org/10.1016/j.tvjl.2024.106095.

Jeffery N, Smith P and Talbot C (2007) Imaging findings and surgical treatment of hemivertebrae in three dogs. Journal of the American Veterinary Medical Association 230: 532-536

Lackmann F, Forterre F, Brunnberg L, Loderstedt S. Epidemiological study of congenital malformations of the vertebral column in French bulldogs, English bulldogs and pugs. Vet Rec. 2021; e509. https://doi.org/10.1002/vetr.509

LeCouteur R and Child G (1995) Diseases of the spinal cord. In Ettinger S and Feldman E (Eds) Textbook of veterinary internal medicine. 4th Ed. Philadelphia: WB Saunders Company

LeCouteur R and Grandy J (2000) Diseases of the spinal cord. In Ettinger S and Feldman E (Eds) Textbook of veterinary internal medicine. 5th Ed. Philadelphia: WB Saunders Company

Mauler DA, De Decker S, De Risio L, Volk HA, Dennis R, Gielen I, Van der Vekens E, Goethals K and Van Ham L. (2014), Signalment, Clinical Presentation, and Diagnostic Findings in 122 Dogs with Spinal Arachnoid Diverticula. J Vet Intern Med, 28: 175-181. https://doi.org/10.1111/jvim.12241

Mansour TA, Lucot K, Konopelski SE, Dickinson PJ, Sturges BK, Vernau KL, et al. (2018) Whole genome variant association across 100 dogs identifies a frame shift mutation in DISHEVELLED 2 which contributes to Robinow-like syndrome in Bulldogs and related screw tail dog breeds. PLoS Genet 14(12): e1007850. https://doi.org/10.1371/journal.pgen.1007850

Moses WB, Moses IA, Moses EA and Moses PA (2024). Prevalence and classification of congenital thoracic vertebral body abnormalities in neurologically normal brachycephalic ‘screw‐tail’ dog breeds in referral practice in Australia. Australian Veterinary Journal. https://doi.org/10.1111/avj.13361

O’Neill DG, Packer RM, Francis P, Church DB, Brodbelt DC and Pegram C (2021). French Bulldogs differ to other dogs in the UK in propensity for many common disorders: a VetCompass study. Canine Genet Epidemiol 8, 13  https://doi.org/10.1186/s40575-021-00112-3

 

© UFAW 2024


Credit for main photo above:

http://depositphotos.com/11051798/stock-photo-french-bulldog-standing-on-the.html

©Depositphotos.com/muro

 

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