Genetics & Dwarfism

Lesson Contents:

 


Little Leg Genetics

There are two separate, common genetic “mutations” that produce the short-legged phenotype characteristic of many dog breeds.

  1. Chondrodysplasia (CDPA) is a genetic trait that cause a premature closure of the ulna growth plate, which causes the radius to grow in a “curved” manner, resulting in shortened legs and angular limb deformity.  This postural deviation can manifest with varying degrees of severity (1).

    Commonly Affected Breeds: Scottish Terriers, West Highland Terrier, Cairn Terrier, Glen of Imaal Terrier (2)(3)(4).


  2. Chondrodystrophy (CDDY) is a genetic trait that results in shortened long bones and abnormal vertebral discs prone to premature disc degeneration (5).  Dogs carrying this genetic mutation are thought to suffer from intervertebral disc disease, and can experience back pain even in the absence of disc herniation (6)(7).

    Commonly Affected Breeds: Beagles, French Bulldogs, Spaniel breeds (4)

 

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What is a “Dwarf” Dog?

Dwarfism is defined as having a short stature that results from a genetic or medical condition.  Disproportionate dwarfism is characterized by changes in body proportions which may be visible as short limbs when compared to body length.

Dwarf dog breeds such as the Dachshund, Basset Hound, Corgi, Dandie Dinmont Terrier, and Pekingese are thought to have both Chondrodysplasia and Chondrodystrophy.

Dogs can also be affected by unintentional dwarfism, which may be caused by genetics, hormone deficiencies, inadequate nutrition, and more.  Dogs effected by these unintentional forms of dwarfism should have veterinarian approval before beginning an exercise program.

 

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Structural Function

Dwarf dogs share common structural limitations, regardless of their specifically bred purpose.  Short legs can be beneficial for digging, crawling through tunnels, sniffing close to the ground, and herding.

However, these same short legs can also impede a dog’s speed, jumping capabilities, joint alignment, and spinal health.

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Role of Targeted Exercise

Improving joint alignment can help to decrease the risk of discomfort, osteoarthritis, and other joint concerns throughout the kinetic chain (8).

 

Keeping a dog’s spine stable, appropriately mobile, and in good alignment may decrease the risk of back pain flare ups and concerns (9).

 

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Conclusion:

Many dog breeds have been intentionally bred with the genetic mutations that cause shortened limbs.  In some cases, dwarfism is an unintentional result relating to genetics, nutrition, or other health concerns.

Functional spinal stability and joint alignment are important for all dogs, but prioritizing these components is especially important for dwarf dogs who may be more predisposed to certain concerns.

 

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References:

(1): Gustafsson, Kristina. (2015).  Genetics and phenotypes of Chondrodysplasia (Achondroplasia) across domestic animal species. Svent Istvan University Faculty of Veterinary Science Budapest.
(2) UC Davis Veterinary Medicine Veterinary Genetics Labratory Chondrodystrophy (CDDY and IVDD) and Chondrodysplasia (CDPA)
(3) Danika Bannasch, DVM, PhD: Chondrodystrophy, Functional Breeding Podcast
(4) Dickinson PJ, Bannasch DL. Current Understanding of the Genetics of Intervertebral Disc Degeneration. Front Vet Sci. 2020 Jul 24;7:431. doi: 10.3389/fvets.2020.00431. PMID: 32793650; PMCID: PMC7393939.
(5) Brown, E.A., Dickinson, P.J., Mansour, T., Sturges, B.K., Aguilar, M., Young, A.E., Korff, C., Lind, J., Ettinger, C.L., Varon, S., Pollard, R., Brown, C.T., Raudsepp, T., & Bannasch, D.L. (2017). FGF4 retrogene on CFA12 is responsible for chondrodystrophy and intervertebral disc disease in dogs. Proceedings of the National Academy of Sciences of the United States of America, 114(43), 11476-11481.
(6) Thompson K, Moore S, Tang S, Wiet M, Purmessur D. The chondrodystrophic dog: A clinically relevant intermediate-sized animal model for the study of intervertebral disc-associated spinal pain. JOR Spine. 2018 Mar;1(1):e1011. doi: 10.1002/jsp2.1011. Epub 2018 Mar 28. PMID: 29984354; PMCID: PMC6018624.
(7) Batcher K, Dickinson P, Giuffrida M, Sturges B, Vernau K, Knipe M, Rasouliha SH, Drögemüller C, Leeb T, Maciejczyk K, et al. Phenotypic Effects of FGF4 Retrogenes on Intervertebral Disc Disease in Dogs. Genes. 2019; 10(6):435. https://doi.org/10.3390/genes10060435
(8) Knapp JL, Tomlinson JL, Fox DB. Classification of Angular Limb Deformities Affecting the Canine Radius and Ulna Using the Center of Rotation of Angulation Method. Vet Surg. 2016 Apr;45(3):295-302. doi: 10.1111/vsu.12460. Epub 2016 Mar 24. PMID: 27011252.
(9) Hart L. Exercise therapy for nonspecific low-back pain: a meta-analysis. Clin J Sport Med. 2006 Mar;16(2):189-90. doi: 10.1097/00042752-200603000-00042. PMID: 16603894.