How to Select Against Genetic Disease
with Knowledge, Not Hope
By George Packard
High anxiety about genetic
diseases comes with the territory for anybody who is considered to be a responsible
breeder these days. In fact, if you are breeding dogs, and you aren't worried about
genetic disease, you'd better hold off on that next mating until you've done your
Canine geneticists estimate that the average purebred dog is
carrying at least 4-5 defective genes. To put it another way, when you are looking at that
gorgeous champion with normal hips you are also looking at a dog who is carrying the genes
that can cause several types of genetic disease. And unless his owner has a detailed
genetic pedigree on this dog and is willing to share it, you have no way of knowing what
those disease genes are.
Canine geneticists estimate that the
average purebred dog is carrying at
least 4-5 defective genes.
That champion may be carrying a recessive gene for PRA, and if he's
bred with a bitch who is also carrying the PRA gene, the disease will show up in the
puppies. And even though he has normal hips, he may be carrying some of the recessive
genes involved in hip dysplasia. If you mate him with a bitch who is normal but also
carrying recessive genes for dysplasia, you'll suddenly find yourself, heartbroken and
bewildered, with dysplastic puppies.
"I'm not worried," you may say, "because soon we'll
have DNA tests that will solve these problems."
That's all well and good if researchers have developed a test for
the single gene disease your line is troubled by. But if that test doesn't exist, are you
willing to wait five or ten years for your turn to come? And that's assuming you'll
persevere as a breeder beyond the six-year average when most people give up, often because
they can't seem to stop producing puppies with genetic diseases. Of course, we are only
talking about tests for single gene diseases. Most of the severe diseases like hip and
elbow dysplasia, cancer and epilepsy, are polygenic, caused by the complex interplay of
many genes, and no researchers have come close to developing a polygenic gene test.
Are you willing to wait 20 years for a gene test for hip dysplasia?
Are you willing to watch another 30 years go by with no significant decrease in hip
dysplasia among purebred dogs?
Breeders in Sweden in 1976 weren't willing to wait, and so they set
up an open registry and started screening all their dogs. By 1989 they had achieved a 50
percent decrease in moderate to severe hip dysplasia in almost all breeds ("Breeding
Healthier Dogs in Sweden": Ake Hedhammar, Tijdschriftvoor Diergeneeskunde, April
What is the secret of this astonishing success? Nothing more
profound than the fact that each breeder made it his or her business to find out where the
carriers and affecteds were in a dog's close family, siblings, half-sibs, offspring,
parents and parents' siblings. Using relatively simple methods, they could then predict
the risk of inheritance of defective genes in any mating.
A few breed clubs in the US have shown similar successes with
targeted genetic diseases. But the majority of our purebred dog breeders, and the major
institutions that support them such as AKC and OFA, have shown little or no interest in
using open registries combined with proven breeding methods to reduce genetic diseases.
Times are changing, however. In 1990 GDC (Institute for Genetic
Disease Control in Animals - www.vetmed.ucdavis.edu/gdc/gdc.htm ) established an
international all-breed open registry based on the success of the Swedish model. In the
following decade thousands of breeders began to register their dogs and to make breeding
decisions in accord with the knowledge of where the carriers and affecteds were in a
particular dog's family.
Recently, GDC started an advocacy campaign to call for the
widespread use of open registries and appropriate breeding methods. The strong response
they are getting from breeders throughout the purebred community confirms that the demand
for open registries is increasing rapidly.
But the reality is that no open registry, whether it is the
international GDC registry, or an open registry set up by a breed club, can be useful
until it contains significant number of dogs registered in close family groups. Detractors
of the open registry concept point to this weakness but ignore the fact that even without
enough information in an open registry, breeders can still make progress against genetic
disease by doing the legwork themselves.
What can you do?
-- Register your dogs in an open registry and urge every breeder you
know to register also.
-- Do whatever you have to do to find out where affecteds and
carriers are among a dog's siblings, offspring and other close relatives.
-- Don't breed to a dog whose owner will not supply that
information. Screen as many of your own dogs as possible, and supply that information to
buyers and breeders.
-- Contact your breed's health committee, the AKC and OFA and
strongly urge them to actively promote the use of open registries.
-- Urge your health committee to put GDC on the list of approved
For specific information on breeding methods and genetic disease,
start with these books:
Click here for more Canine Health, Breeding & Genetics
Several very good articles on basic genetics for dog breeding can be
found at the following Web site. Click the link below:
The Canine Diversity
Project - Genetics & Diversity
(c) 2001 George Packard)
The above is the full text of a new article which
states the basic case for open registries and is a good, short introduction for breeders
or owners who are just becoming acquainted with the issues. Please feel free to post this
article or to submit it to your breed club newsletter.
Permission for noncommercial electronic distribution
granted. Contact author at firstname.lastname@example.org
for permission to reprint.
GDC [the Institute for Genetic Disease Control in
Animals] is a public-benefit nonprofit organization working for the health of companion
GDC, PO Box 222
Davis, CA 95617
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