Chondrodystrophy and Chondrodysplasia (CDPA/CDDY, IVDD)
Chondrodystrophy in dogs is a common trait identified in many dogs’ breeds, characterized by shortened length of the limbs, which is a result of early changes in the structure of growth plates. The short-legged phenotype is known by two names: chondrodystrophy and chondrodysplasia. Chondrodysplasia is also known as canine dwarfism. Word ”chondro” come from cartilage, and ”dysplasia” means an abnormal growth, while word ”dystrophy” means degeneration of the tissue, in this case, of the cartilage. Breeds known for having shorter than normal limbs are: Bulldogs, Corgis, Dachshunds, Bassett Hounds, Pugs, French Bulldogs, Pekineses, Lhasa Apsos, Shih Tzus, Beagles and many more.
Except shorter limbs than normal, other skeletal characteristics of chondrodystrophy include a lower jaw that may protrude further than normal, an unusually short upper jaw, and an over under bit with crooked teeth. Named short-legged breeds are also prone to intervertebral disc disease (IVDD), which impacts health of the affected animal. Based on the histopathological analysis of the short-legged breed puppies, that the short stature is a consequence of the defects in the process where cartilage is replaced with bone in the developing limb, which is known as the endochondral ossification.
Chondrodysplasia is caused by an FGF4-retrogene insertion in dog chromosome 18. This mutation explains short-legged phenotype in breeds such as Basset Hound, Pembroke Welsh Corgi, Dachshunds, West Highland White Terriers and Scottish Terriers. The mutation is inherited in an autosomal dominant pattern.
The chondrodystrophy is caused by a second FGF4 retrogene insertion on chromosome 12. This mutation is held responsible also for intervertebral disc disease (IVDD). Dogs in which this mutation has been identified are: Jack Russel Terriers, Dandie Dinmont Terriers, French Bulldogs, Chihuahua, Chinese Crested, Pekingese, Shih Tzu, Havanese, Coton de Tulear, Bishon Frise, Miniature and Toy Puddle, Beagle, Cavalier King Charles Spaniel, English Springer Spaniel, American Cocker Spaniel, Portuguese Water Dog, Nova Scotia Duck Tolling Retriever or Chesapeake Bay Retriever. Dogs that carry both mutations show a more drastic reduction of leg length. The affected breeds are in particular Basset Hounds, Dachshund, Welsh Corgi and Scottish terriers.
In breeds where both mutations are present, breeders can benefit from test results to implement breeding strategies to reduce incidence of CDDY, while retaining the short-legged phenotype conferred by CDPA.
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