Chondrodystrophy (CDDY) predisposes dogs to intervertebral disc disease (IVDD)

Katariina Mäki, PhD

Chondrodystrophic dogs have an extra copy of a growth factor gene known as the CDDY retrogene. This retrogene causes a dog to have a hereditary disorder of bone growth and ossification. The disorder predisposes dogs to intervertebral disc disease (IVDD) and herniation, a painful condition with a high mortality rate.

What are the effects of CDDY on intervertebral discs?

In most chondrodystrophic dogs, degeneration of the intervertebral discs typically begins in the first year of life (Hansen 1952).

As the dog grows older, the degeneration continues. The gelatinous core of the intervertebral disc hardens and calcifies, reducing its ability to absorb shocks and protect the spine from the forces acting on it.

As they degenerate, the discs also calcify. In dogs with degenerated discs, there is a high risk of herniation into the spinal canal and even rupture. All this is referred to as intervertebral disc disease (IVDD).

In non-chondrodystrophic dogs, disc degeneration occurs much later in life. This degeneration is a normal phenomenon associated with ageing.

Symptoms of disc herniation

The symptoms of disc herniation are the result of spinal cord and nerve damage. A herniated disc exerts pressure on the spinal cord, which can result in pain and paralysis.

Some dogs exhibit symptoms on a single occasion, whereas others experience recurring symptoms. In the most severe cases, a disc herniation can result in permanent spinal cord damage and euthanasia (Lappalainen 2021).

Predisposing factors for disc herniation

In addition to chondrodystrophy-related disc degeneration, disc herniation is also influenced by factors related to the dog’s conformation and environmental factors. It is likely that genes of minor influence also play a role.

One such gene may be the retrogene on chromosome 18 (CDPA; Batcher ym. 2019).

The risk of herniation is associated with obesity, size, and the length of the dog’s back (Packer et al. 2013). In high-risk breeds, even a moderate degree of overweightness increases the risk (Packer et al. 2013). In this study population, 46% of Miniature Dachshunds were found to be overweight, with 13% exhibiting a substantial degree of overweight.

The longer the back, the higher the risk of IVDD. The probability of the disease was 0.30 for Miniature Dachshunds when the ratio between body length and withers height equalled 1.1, compared to 0.68 when the ratio equalled 1.5 (Packer et al. 2013).

Packer et al. (2013) also demonstrated that a smaller skeletal structure was a significant risk factor for IVDD.

Consequently, the authors propose that selection for longer backs and miniaturisation should be discouraged in high-risk breeds in order to reduce the risk.

Treatment of herniated discs

The treatment of herniated discs may be undertaken via either a conservative management approach or surgical intervention.

Conservative treatment includes complete rest, anti-inflammatory drugs and physiotherapy.

The recommended treatment for recurrent or persistent pain and paralysis is surgical removal of the herniated disc material pressing on the spinal cord.

The prognosis is typically favourable, although recovery from severe paralysis can take a long time. Even in dogs that have undergone surgical intervention, the disease can recur (Lappalainen 2021).

Certain dog breeds are more susceptible to IVDD than others

Studies of animal hospital data have revealed that certain dog breeds are significantly more susceptible to IVDD than others. These include the Beagle, Cocker Spaniel, Pekingese, Lhasa Apso, Dachshund, Pembroke Welsh Corgi, French Bulldog and Shih Tzu (Brown et al. 2017).

According to Swedish insurance company Agria’s statistics, the risk of disc and/or vertebral-related morbidity is greatest in Pekingese, Miniature Dachshund, Greater Swiss Mountain Dog, French Bulldog, Basset Hound, and Standard Dachshund breeds. The Greater Swiss Mountain Dog is affected for reasons other than chondrodystrophy (Get a GRIHP on Dachshunds, DogWellNet.com).

A study by Mayousse et al. (2017) found that during the time of surgical treatment of IVDD, French Bulldogs were on average younger (4.1 years) than dogs of other breeds. Batcher et al. (2019) proposed that this may be attributed to a combined effect of the chromosome 12 FGF4 retrogene and the DVL2 variant in the French Bulldog.

Dachshund is the most extensively researched breed

IVDD has been studied most extensively in Dachshunds. Bruun et al. (2020) reported that approximately one in five (18%) Danish Dachshunds exhibited severe symptoms, with one in three of these cases resulting to euthanasia. When all symptomatic dogs were included, the disease was found to affect one in four (26%) Dachshunds.

In a Danish veterinary master’s thesis (Mørck Andersen & Marx 2014), the prevalence of IVDD was estimated to be 16.0% in wire-haired Dachshunds, 17.4% in long-haired Dachshunds and 21.6% in smooth-haired Dachshunds.

The risk of disc herniation was found to be significantly higher in “pet” dogs compared to working dogs. Of the dogs with a history of hernia, 44% had been euthanized due to the condition.

In the wire-haired population, not all dogs are homozygous for the CDDY; heterozygous dogs also exist. These are dogs that carry only one copy of the CDDY, as opposed to the two copies typically observed in other dogs in the breed. This may result in a slightly lower morbidity rate compared to other Dachshund varieties.

The broader implications of intervertebral disc disease

Disc herniation is a painful condition. Dogs susceptible to herniated discs may exhibit multiple herniations in different vertebral discs throughout their lifetime (Mayhew et al. 2004).

The condition is associated with a high mortality rate, and the cost of surgical treatment is considerable. Long-term aftercare has the potential to negatively impact the quality of life of the affected dog. The conservative treatment, which involves several weeks of exercise restriction and cage rest, is highly restrictive for the dog, causing both psychological and physical well-being problems.

Several dog breeds with the CDDY retrogene are particularly popular. Consequently, there are millions of dogs on the planet that are susceptible to disc disease. The health and economic consequences of disc disease are considerable (Brown et al. 2017).

In their 2020 publication, Bruun and colleagues posit that breeding programmes must be employed to forestall the occurrence of the disease in at-risk breeds.

As Brown et al. (2017) correctly conclude, prevention of disease through breeding and eradication has the potential for far-reaching benefits beyond those achievable through advances in surgical or medical therapy.

Our next article deals with breeding against IVDD – stay tuned!

References

Batcher et al. 2019. Phenotypic effects of FGF4 retrogenes on intervertebral disc disease in dogs. Genes 10:435. doi: 10.3390/genes10060435

Brown et al. 2017. FGF4 retrogene on CFA12 is responsible for chondrodystrophy and intervertebral disc disease in dogs. Proc. Natl. Acad. Sci. USA. 114: 11476–11481. doi: 10.1073/pnas.1709082114.

Bruun et al. 2020. Breeding schemes for intervertebral disc disease in dachshunds: Is disc calcification score preferable to genotyping of the FGF4 retrogene insertion on CFA12? Canine Genet. Epidemiol. 7:18.

Hansen 1952. A pathologic-anatomical study on disc degeneration in dog, with special reference to the so-called enchondrosis intervertebralis. Acta Orthop. Scand. Suppl. 11: 1–117. doi: 10.3109/ort.1952.23.suppl-11.01.

Lappalainen 2021. Selkänikamien välilevyjen rappeutuminen ja välilevykalkkeutumat (Degeneration and calcification of the intervertebral discs). www.kennelliitto.fi.

Mayhew et al. 2004. Risk factors for recurrence of clinical signs associated with thoracolumbar intervertebral disk herniation in dogs: 229 cases (1994-2000). J. Am. Vet. Med. Assoc. 225: 1231-1236.

Mayousse et al. 2017. Prevalence of neurological disorders in French bulldog: A retrospective study of 343 cases (2002–2016). BMC Vet. Res. 13: 212.

Mørck Andersen and Marx 2014. Diskusprolaps hos gravhunde: Incidens studie og follow-up studie på rygfotografering og brugen af K-status og indekstal. Veterinært Kandidatspeciale. Det Sundhedsvidenskabelige Fakultet, Københavns Universitet.

Packer et al. 2013. How long and low can you go? Effect of conformation on the risk of thoracolumbar intervertebral disc extrusion in domestic dogs. PLoS One 8, e69650.