Friday, October 23, 2009

Gene Mapping: Opportunity to Improve Dog Breeds or to Breed Irresponsibly

I got a blast from a well-know breeder of Labrador retrievers. Turns out her line of champion Labs is riddled with PRA (Progressive Retinal Atrophy), a recessive, single-gene trait that is unfortunately common in some breeds. Dogs with two PRA genes become blind. With the new genetic test, she knows which of her dogs are PRA carriers, and she can "safely" breed them to PRA normals and thereby avoid producing blind puppies.

The canine genotype was usefully mapped in 2004. Work on this massive project extended from 1997 and continues today. Genes for some dog diseases have been identified and located. After the PRA gene was found, a test was developed to identify dogs who carry it.

A dog with two recessive PRA genes will become blind. Carriers with one recessive PRA gene will not be blind, but they will pass on the PRA gene to half of their offspring.

Being able to identify carriers could be used to reduce the frequency of the PRA gene in dog breeds. Before the PRA test was available, PRA blind dogs were not bred, but unaffected carriers were bred by unsuspecting owners. Breeding carriers kept the gene frequency high. Now, if carriers are identified and not bred, the number of PRA genes in a breed could be rapidly reduced and eventually eliminated from the breed.

On the other hand, a test to identify carriers has given unscrupulous breeders a new tool to avoid producing PRA blind puppies by breeding their PRA carriers to PRA normals. Half of the puppies will carry on the PRA gene to the next generation, and beyond. But, no matter, they think. None of the current puppies is blind.

The excuse for breeding PRA carriers is they have other splendid breed characteristics, which is doubtless true. They win championships in the show ring, because judges cannot see the genetic liabilities of carriers. Many conformation winners are probably PRA carriers and carriers of other genetic diseases.

Conformation shows are limited to reproductively intact animals, because show dogs are supposed to be the parent stock for the next generation of the breed. Show champions are the most frequently used stud dogs, who sire hundreds of puppies and whose genes are carried to thousands of puppies in future generations. If champion stud dogs carry genetic disorders, the gene frequencies of these disorders will be increased in future generations of the breed.

The health of a breed cannot be improved until breeders use new genetic information to reduce the frequency of genetic disorders, not to increase them by breeding carriers.

Here's an idea: Dogs in conformation shows, which are held to identify the best breeding stock, must have clearances for PRA, exercise-induced collapse, identified heart, eye, kidney, and skeletal disorders, and other genetic diseases as they are identified. Carriers should not be eligible to be shown as future breeding stock, because they should not be bred.

The AKC claims to care about the health of purebred dogs. Healthy breeds are not riddled with genetic disorders. The AKC can take a proactive stance to limit conformation shows to genetically sound dogs. Even if the have staight backs, fine chests, handsome heads, and so forth, dogs who carry genes for serious genetic disorders are not a credit to the breed.

I was blasted by a well-known Labrador kennel owner for suggesting she not breed her PRA carriers. Because famous breeders, such as this jewel, have huge influence with the AKC and its stable of judges and show organizers, nothing will change. As more genetic information becomes available about serious canine disorders, that information will not be used to improve the health of dog breeds, because influential breeders' dogs carry those genetic disorders.

In my opinion, the number one priority for popular dogs, such as Labrador retrievers -- the world's most frequent breed -- has to be health. 95% of Labs are family pets. People want a sound companion, who will live a healthy life. They do not deserve to lose a cherished pet to hidden genetic disorders that show up after two, five or even 10 years. The only way to assure a healthy breed is to breed responsibly to eliminate genetic disorders.

No comments:

Post a Comment