"We have to put aside the 'all or nothing' notion. There is a variable degree of susceptibility for the disease," he explains.
"If the dog has a DI above .3, the susceptibility of having hip dysplasia increases—but that doesn't mean it's a guarantee
that the dog will develop the condition."
To achieve genetic control of CHD, researchers say, an accurate test must minimize false-negative diagnoses that mistakenly
permit the breeding of dogs that carry genes coding for CHD. Particularly for a late-onset disease such as CHD, dogs remaining
in the gene pool must not only be free of obvious signs of CHD at the time of evaluation (2 years for OFA) but ideally should
not be susceptible to the osteoarthritis of CHD that occurs later in life.
"We don't want people to think that if the dog is at risk that it isn't breedable," Smith says. "But if we can tighten the
gene pool and only breed dogs that are better than the average, it can make a difference."
The study was conducted by Smith, Michelle Y. Powers, Georga T. Karbe, Thomas P. Gregor, Pamela McKelvie, William T. N. Culp
and Hilary H. Fordyce of the Department of Clinical Studies at Penn Vet. Culp is currently with the School of Veterinary Medicine
at the University of California, Davis.
The study was funded by the University of Pennsylvania, the National Institutes of Health, The Seeing Eye Inc., the Morris
Animal Foundation and Nestle Purina Co. The article was published in the Journal of the American Veterinary Medical Association.
Smith, who is the inventor, and the University of Pennsylvania, which holds the patent, have a financial interest in the PennHIP