| What does this mean to
the Chesapeake breeder? Due to the late onset of the
disease, breeders were unaware of a PRA-affected dog
in their stock, until it was diagnosed well after reproductive
age had been reached, when it might already have produced
many puppies, all of which were obligate carriers. Breeders
were unaware of "hidden" carriers in their stock, until
a carrier was unwittingly mated to another carrier or
to an affected dog not yet showing signs of the disease,
and the resulting puppies began to show symptoms at
age 4 or 5 or 6 years. The only tool was pedigree
analysis, but without extensive data on many individuals,
this was not very useful. No one ever set out to breed
a PRA affected dog, but it happened. The test provides
a huge step forward, as we can now identify those individuals
who are totally free of the disease, and breed any Chesapeake
safely to them.
Quoting from OptiGen's material,
"The OptiGen prcd test identifies a fingerprint of
markers on canine chromosome 9, immediately adjacent
to the prcd locus. This test yields three possible marker
patterns for any dog tested. The test can be done reliably
at any age, and the results are exactly accurate. That
is, the test result will never change with age, and
will be the same whenever it
is repeated."
"Certain results from applying this test are exactly
true, with no ambiguities in interpretation."
1." All dogs yielding Pattern A are homozygous normal.
The result is certain, and can be determined from birth.
No Pattern A dog will ever pass the prcd mutant gene
to a pup. No pup of a Pattern A dog can be affected
with prcd - regardless of the status of the other parent...
2.No dogs yielding Pattern A or B will ever develop
prcd.
The result is certain and can be determined from birth.
Thus, for dogs at risk from family history of developing
PRA, you can identify which dogs can not be affected...
3.All prcd affected dogs yield Pattern C.
The only dogs at risk of developing prcd are Pattern
C Dogs. The result is certain, and can be used to eliminate
possible incorrect or uncertain clinical diagnoses.
If a dog is considered "suspicious" of PRA, or diagnosed
as affected, then it must be Pattern C for it to be
truly affected with prcd. If it is either Pattern A
or Pattern B, then it can not be affected with prcd."
(OptiGen)
Thus, all dogs yielding Pattern A are homozygous normal.
They inherited two "normal" genes, one from each parent,
and do not carry the mutant gene which causes PRA. They
are "genetically clear" of PRA. They will never pass
the mutant prcd gene on to a pup. They will never develop
the disease, nor will any of their offspring become
affected, regardless of the status of the other parent.
In general, Pattern B dogs are carriers of the prcd
gene, though a small percentage are not (and, unfortunately,
that percentage can't be estimated as yet, but it is
small.) Additionally, all Pattern C dogs must be considered
as high risk for developing PRA, though again a small
percentage will be carriers only and not affected. These
ambiguities are
caused by the possible presence of a "false positive
allele" marker which is indistinguishable from the true
disease allele at this time. (An "allele" is one form
of a gene.) However, ALL dogs of Patterns B and C can
safely be bred to Pattern A dogs, with no possibility
of those puppies being affected with PRA. No dog need
be removed from the gene pool because it is PRA-affected,
a known or suspected carrier, or of unknown status.
Before this test, the only way to select against PRA
was to eliminate affected dogs and carriers from breeding
stock as they were discovered, which meant eliminating
the many great qualities these dogs had to offer. With
the test, they may be safely bred to tested clears (Pattern
A dogs), as none of the puppies of such breedings can
go blind from PRA. Thus any Chesapeake can pass on its
superior characteristics, and contribute to the diversity
of the gene pool.
Gradually over generations, by testing progeny retained
for breeding and breeding carriers only to genetically
normal individuals, selection can be aimed away from
the disease, without losing many other qualities we
prize in our brown dogs. And, by using the test, no
breeder need fear devastating news from a heartbroken
owner of a newly diagnosed
PRA-affected dog, produced unwittingly from his bloodline.
OptiGen is ready to begin testing Chesapeakes on May
1. The test currently costs $260 per dog and there is
a special litter rate. Further information on submitting
a blood sample is available on their website (http://www.optigen.com)
as well as the application form which can be submitted
on-line (preferred to insure accuracy of your information)
or
downloaded. You may also call OptiGen at 607-257-0301
for a form, or request one by e-mail at genetest@optigen.com.
Updated information will be added to the site on May
1 to include the Chesapeake test. With summer approaching,
please pay careful attention to the instructions for
shipping blood samples in hot weather. At this time,
the result of tests will be reported to the dog's owner
in confidence. The ACC is considering a future registry
policy for listing results.
We can look at this test as "Phase 1", as research
is ongoing to develop a second generation test by identifying
the actual mutant gene itself, or by finding a marker
which distinguishes the "false positive allele" from
the true disease allele. Success in either of these
areas will eliminate the uncertainties currently applying
to dogs testing Patterns B and C. OptiGen is storing
all blood samples for two years, so they will be available
for re-testing when this research is successful. The
ACC should continue with projects to help fund this
further research. However, being able to
identify those Chesapeakes which are genetically clear
of prcd will allow breeders to be confident that they
will not produce dogs affected with the disease, doomed
to go blind from PRA in the prime of life.
We will be bringing you further information on the
test and new developments from OptiGen on the Internet,
in mailings, and in the ACC Bulletin. In the meantime,
please, if you have any questions direct them to me,
rather than the scientists in Ithaca who are continuing
research towards locating the actual mutant gene. I
will be acting as liaison with
Dr. Aguirre and OptiGen, and will quickly provide accurate
answers from them, and post the information here, and
in the Bulletin. You can e-mail me at suecone@interactive.net,
or call 973-994-4444.
This test would never have become a reality without
the concerned and generous owners of PRA- affected and
carrier Chesapeakes, who selflessly volunteered their
dogs for the research which made it possible. They have
done a wonderful service for our beloved breed.
Sue Cone
PRA Project Leader |
