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Canine chondrodysplasia (CDPA), colloquially known as canine dwarfism, is a hereditary condition characteristic of purebred dogs, causing abnormal cartilage development and shortening of long bones. Affected dogs characteristically have a normal-sized trunk but noticeably shorter limbs. Additional cranial changes associated with CDPA include protruding lower jaw, unusually short upper jaw, and under or overbite with crooked teeth. Crooked spine and breathing problems often complicate everyday life. Parker et al (2009) found that dogs with clinically diagnosed CDPA have an insertion of fibroblast growth factor 4 (FGF4) retrogene on chromosome 18. The protein coded by the FGF4 gene is involved in early cartilage and bone development. The condition is expressed as autosomal dominant, meaning that inheriting a single copy of the aberrant gene is sufficient for the animal to develop the symptoms.
Breeds with a high prevalence of CDPA are:
Chondrodystrophy (CDDY) is another form of canine dwarfism caused by a different insertion of FGF4 retrogene on chromosome 12 with autosomal dominant mode of inheritance. Chondrodystrophic dogs also possess shortened long bones and prematurely calcified intervertebral discs. Along with many complications caused by the short-legged phenotype, affected dogs have a high propensity for the development of Hansen’s type I Intervertebral Disc Disease (IVDD).
The IVDD is described as premature calcification of the nucleus pulposus, the inner core of the vertebral disc composed of water and a network of collagen fibers. This elastic structure works as a cushion that allows flexibility of the vertebral column. This enables the vertebral column to withstand forces of compression and torsion without damaging the disc. In chondrodystrophic dogs, the nucleus pulposus is gradually replaced by chondrocyte-like cells, forming chondroid metaplasia. Premature calcification of the nucleus pulposus causes the disc to be less able to adjust to compressions and twists. The nucleus pulposus can then herniate through the protective layer (annulus fibrosus) and leak into the spinal canal. This inflames the nerve roots next to the disc, causing severe pain and neurological dysfunction or paralysis. IVDD is a degenerative disease and premature calcification can start in dogs that are less than a year old.
IVDD is quite prevalent in many dog breeds, such as:
Owning a chondrodysplastic and/or chondrodystrophic dog is more about awareness and preparation since there are no known effective treatments. If your dog shows signs of discomfort or pain it is recommended to seek veterinary consultation. Currently, there is no concrete scientific evidence that chondrodystrophic dogs should be restricted from running, jumping, or other movements to prevent IVDD. The disease is genetic and will occur regardless of the activity. If one wishes to own a chondrodystrophic breed, there is a need to educate oneself on the genetic disease(s) your dog may possess.
Emily A. Brown, Peter J. Dickinson, Tamer Mansour, Beverly K. Sturges, Miriam Aguilar, Amy E. Young, Courtney Korff, Jenna Lind, Cassandra L. Ettinger, Samuel Varon, Rachel Pollard, C. Titus Brown, Terje Raudsepp, and Danika L. Bannasch
FGF4 retrogene on CFA12 is responsible for chondrodystrophy and intervertebral disc disease in dogs Proc Natl Acad Sci U S A. 2017 Oct 24; 114(43): 11476–11481. [PMID: 29073074].
Parker HG, VonHoldt BM, Quignon P, Margulies EH, Shao S, Mosher DS, Spady TC, Elkahloun A, Cargill M, Jones PG, Maslen CL, Acland GM, Sutter NB, Kuroki K, Bustamante CD, Wayne RK, Ostrander EA. An expressed fgf4 retrogene is associated with breed-defining chondrodysplasia in domestic dogs. Science. 2009 Aug 21;325(5943):995-8. doi: 10.1126/science.1173275. Epub 2009 Jul 16. PMID: 19608863; PMCID: PMC2748762.