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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 homework.
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 with you, you have no way of knowing what those
disease genes are.
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?
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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, Tijdschrift voor
Diergeneeskunde, April 1991).
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
have shown little 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.gdcinstitute.org/) 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.
Additionally, in 2001, OFA began offering customers
the option of sharing all results openly on their web site, both unaffected and affected.
OFA reports a strong increase in the number of people taking advantage of this option.
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.
In the summer of 2002, GDC closed all of its
registries except the Eye and Tumor registries, and in early 2003 merged its database
with OFA. OFA has done a major upgrade of its web site to make gathering information
on family groups of dogs much easier.
What can you do?
- Register your dogs in an open registry and urge
every breeder you know to register also. If you register with OFA, choose
the full disclosure option.
- Learn enough basic genetics so that you know AT
LEAST how single recessive modes of inheritance work.
- 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 and the AKC
and strongly urge them to actively promote the use of open registries. Urge
your health committee to promote use of the full disclosure option at
OFA.
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Further Reading:
For specific information on breeding methods and genetic disease, start with these books:
- Control of Canine Genetic Diseases; George A. Padgett,
DVM, Howell Book House, New York, 1998
- Genetics of the Dog; Malcolm B. Willis, Howell Book
House, New York, 1989
- Genetics for Dog Breeders; 2nd edition, 1992, Roy
Robinson, Butterworth/Heinemann
- Several very good articles on basic genetics for dog breeding:
http://www.canine-genetics.com/
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