UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Chondrodystrophy (CDDY and IVDD Risk) and Chondrodysplasia (CDPA)

Chondrodysdrophy (CDDY) is a trait that defines many dog breeds and is characterized by reduction of long bone length (shorter legs) as a consequence of early changes in the structure of growth plates. CDDY can also impact health of animals through an abnormal process that causes premature degeneration of the intervertebral discs. Two retrogene insertions of functional fibroblast growth factor 4 (FGF4) explain short-legged phenotypes of dogs. FGF4 gene is involved in many biological processes including bone development.

The first insertion discovered (Parker et al 2009) is an FGF4-retrogene insertion in dog chromosome 18 (FGF4-18). This FGF4-18 insertion explains a short-legged phenotype known as chondrodysplasia (CDPA) in breeds such as Basset Hound, Pembroke Welsh Corgi, Dachshunds, West Highland White Terriers and Scottish Terriers. CDPA inheritance is considered to follow am autosomal dominant mode.

The Chondrodysdrophy (CDDY) mutation was recently discovered by researchers in the Bannasch Laboratory at the University of California, Davis (Brown et al. 2017) as a second FGF4-retrogene insertion in dog chromosome 12.  CDDY includes a short-legged phenotype and abnormal premature degeneration of intervertebral discs leading to susceptibility to Hansen’s type I intervertebral disc disease (IVDD). The intervertebral disc, which sits between vertebrae, is composed of an outer fibrous basket (annulus fibrosus) made of 70% collagen and an inner gel-like layer called the nucleus pulposus. These structures allow for flexibility of the vertebral column. In Chondrodystrophic breeds, premature calcification of the nucleus pulposus at early age (from birth to 1 year of age) results in degeneration of all discs in young dogs. These abnormal discs are predisposed to herniation into the spinal canal where the inflammation, and hemorrhage can cause severe pain and neurological dysfunction (myelopathy) termed Intervertebral Disc Disease or IVDD. IVDD has high mortality rate and high cost of surgical and medical veterinary care.

CDDY is inherited as a semi-dominant trait for height, meaning that dogs with 2 copies of the mutation are smaller than dogs with only 1 copy. With respect to IVDD, the inheritance follows a dominant mode, meaning that 1 copy of the FGF4-12 mutation is sufficient to predispose dogs to IVDD. Dogs that have both FGF4-12 and FGF4-18 show a more drastic reduction of leg length.  One area of current investigation is how CDDY and CDPA might work in concert to increase the risk of IVDD.

The Veterinary Genetics Laboratory offers a combined test for CDDY and CDPA for breeds that have long and short leg phenotypes. CDDY and CDPA occur in many breeds. Testing for these mutations can help breeders determine if CDDY is present among breeding stock and to identify dogs at risk for IVDD. 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.

CDDY variant has been found in breeds such as: Basset Hound, Beagle, Bichon Frise, Cardigan Welsh Corgi, Cavalier King Charles Spaniel, Chesapeake Bay Retriever, Chihuahua, American Cocker Spaniel, Coton de Tulear, Dachshund, Dandie Dinmont Terrier, English Springer Spaniel, French Bulldog, Jack Russell Terrier, Nova Scotia Duck Tolling Retriever, Pekingese, Pembroke Welsh Corgi, Poodle (Miniature and Toy), Portuguese Water Dog, Scottish Terrier, Shih Tzu. This is not a complete list of breeds. Research on the distribution of this mutation across breeds is ongoing.

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Results reported as:

Chondrodystrophy (CDDY and IVDD Risk)
N/N No copies of CDDY mutation.
N/CDDY 1 copy of CDDY mutation. Dog is short-legged and at risk for IVDD.
CDDY/CDDY 2 copies of CDDY. Dog is short-legged and at risk for IVDD.

Chondrodysplasia

N/N No copies of CDPA mutation.
N/CDPA 1 copy of CDPA. Dog is short-legged.
CDPA/CDPA 2 copies of CDPA. Dog is short-legged.

References:

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. 2009. An expressed fgf4 retrogene is associated with breed-defining chondrodysplasia in domestic dogs. Science 325(5943):995-8. doi: 10.1126/science.1173275.

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, Danika L. Bannasch. 2017. FGF4 retrogene on CFA12 is responsible for chondrodystrophy and intervertebral disc disease in dogs. http://m.pnas.org/content/early/2017/10/09/1709082114.
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL