Genotypic and Phenotypic Dissection of Canine Hip Dysplasia

A pedigree based on greyhounds and dysplastic Labrador Retrievers will be expanded to find genetic markers associated with the genetic mutations that cause hip dysplasia (HD). Several measures of the inherited traits of the dysplastic hip, age, distraction index, dorsolateral subluxation score and Orthopedic Foundation for Animals hip score, will be used to maximize the chance of finding genetic markers. The heritability, mode of inheritance, and predictability of these measures for HD will be determined.

Results

In the experimental cross breed and Labrador Retriever pedigrees we studied, the dorsolateral subluxation score serves as the most accurate single predictor of subsequent hip arthritis but when combined with the Norberg angle, an improved estimate is obtained. Hip dysplasia is caused by mutations in multiple genes (maybe as many as a dozen chromosomes contribute to the appearance of the hip on a radiograph). These hip dysplasia genes act in both an additive manner, in which the cumulative effect of all the genes underlies the radiographic appearance of the hip. Some genetic loci improve hip quality and some are detrimental. In addition, there are also dominant loci. Now we will narrow the chromosomal regions that contain these genes so as to be in position to assess candidate genes that may harbor the mutations that contribute to hip quality. To do this, we are acquiring DNA samples and hip radiographs on as many pure breed dogs as we can. By discovery of the contributing mutations, the design of genetic tests is now possible that will enable us to screen for dogs both susceptible and resistant to hip dysplasia. This information will further allow us to follow hip development more closely in susceptible pups and introduce strategies to prevent secondary hip arthritis and to develop new treatments.

Co-sponsored with the Morris Animal Foundation, Grant Number: D99CA-001

Rory J. Todhunter, BVSc, PhD
Cornell University