Canine Skeletal Dysplasia

Amy Young, Jeanne Ryun, and Danika Bannasch
Partial funding provided by the AKC Canine Health Foundation

Chondrodysplasia is a category of skeletal dysplasia caused by abnormalities of the growth or development of bone or cartilage that result in distinct dwarf characteristics. Certain dog breeds, such as Basset Hounds, Dachshunds, and Corgis, have traditionally been classified as chondrodysplastic and are fixed for the phenotype. Chondrodysplasia has been described as a disease that segregates in several breeds, including Alaskan Malamutes, Norwegian Elkhounds, and Great Pyrenees. Although the clinical and morphological symptoms in these breeds are often similar, the molecular mechanisms leading to the phenotype are poorly understood.
We have identified a disease in Chesapeake Bay Retrievers, Newfoundlands, and Nova Scotia Duck Tolling Retrievers that resembles chondrodysplasia but does not appear to be as severe. We have classified it generally as skeletal dysplasia. This phenotype is characterized by asynchronous growth of the radius and ulna, leading to bowing of the radius and valgus of the front limbs. In extreme cases, the phenotype is so debilitating that some owners elect to euthanize their dogs. There appears to be considerable phenotypic variation within breeds and dogs that appear to be normal may actually be mildly affected. This complicates the construction of phenotypically-based pedigrees.

As a result of the difficulties encountered in obtaining accurate phenotypes, we have adopted a candidate gene approach to begin to address the molecular basis of this condition. Due to the similarity of our phenotype to the classic chondrodysplastic phenotype, the same set of candidate genes is under investigation in all breeds included in our study. The candidate genes are being sequenced in Chesapeake Bay Retrievers, Newfoundlands, Nova
Scotia Duck Tolling Retrievers, Basset Hounds, Dachshunds, Pembroke and Cardigan Welsh Corgis, and Pekinese. The identification of the molecular basis of skeletal dysplasia could lead to the development of a DNA test. Such a test would enable breeders to select against the disease phenotype and ultimately eradicate it from breeds that segregate the disease.