Renal
Dysplasia:
An Update and Advice
for Breeders
on How to Use the Current Test
by JoAnn Gustafson
The American Shih Tzu Club Gene
Mapping Committee, of which I am a member, was formed to support scientific
research that would help eliminate hereditary Renal Dysplasia (RD, a
developmental disorder in which the kidneys fail to mature normally) in the
Shih Tzu. Since the committee began we have had the ultimate elimination of this
dread disease as our clear goal. Years have passed and the ultimate goal has not
been reached, but that does not mean that we have not made progress.
Puppies that are severely affected
by RD generally die of renal failure by the time they are 6 months old, and
therefore do not reach breeding age to pass along their defective genes.
Moderately and mildly affected dogs may live normal life spans with few or no
obvious signs of the disease, although its presence can be detected through the
performance of a wide wedge kidney biopsy-a major surgical procedure. The big
problem in eliminating the disease has always been how to identify the silent
carriers of RD, who tested normal on all of the previous (non-genetic) tests but
still carried at least one defective gene and could pass it along to their
offspring.
Two and a half years ago
scientists found what they felt was a significant step in the right direction
when they located a genetic marker linked to hereditary renal dysplasia, on a
string of DNA. This research, funded by the AKC Canine Health Foundation, the
ASTC, the Lhasa Apso Club of America, and the Soft-Coated Wheaten Terrier Club
of America, is being conducted at the University of Michigan under the direction
of Dr. George Brewer. The noninvasive linked marker test Dr. Brewer's
researchers developed is conducted on a sample of tissue that is collected by a
dog owner with the use of a cheek swab. The swab is then sent to VetGen for
processing. In addition to the linked marker test for RD in Shih Tzu, Lhasa
Apsos, and Soft-Coated Wheaten Terriers, VetGen also offers several other marker
tests for other diseases in various breeds. The VetGen linked marker test for
Copper Toxicosis, for example, has significantly reduced the number of
Bedlington Terriers affected by this disease.
Dr. Brewer has been very
supportive in talking to us about the research and the progress that has been
made in the last few years. The last report given by Dr. Brewer told us that the
first two sets of DNA strings had been sequenced, but they had not produced
the defective gene that they are looking for. The scientists then started
sequencing another set of DNA strings that are closely associated with the
kidney. At this time they have finished sequencing these two genes, and did not
find the gene defect. They now plan to use other DNA markers in the area to
locate the gene more closely.
With this in mind, I would like to
clear up some misconceptions that are floating around the dog world. First,
almost all of the defective genes discovered start out with a marker test. The
marker test is sometimes all that is ever found, so it should not be discarded
because it is not 100% accurate. As far as I know there is no basis to judge the
marker test for RD as a bad test or unusable for guiding the dog breeder in
producing litters of pups that would have a reduced chance of producing
offspring affected by hereditary renal dysplasia. Using the marker test until
the scientists can locate the defective gene seems to be one of the main tools
breeders can use to plan future breedings. The test is to be used as a tool to
receive the best information available to get the best product (healthy
puppies) delivered. It is not and never has been a 100% accurate test for the
disease itself.
I have had some breeders tell me
that if the dog had a marker then the dog would be 80% affected with RD. This is
not correct. You could have a dog with 1 or 2 markers (one marker can be
inherited from each parent) and the dog could never be affected with RD.
However, this does not mean that the dog is not a carrier that is able to pass
the disease along to its puppies. In fact, we know that there are dogs that have wedge-biopsied normal but have produced RD puppies. The 80% refers to
those dogs clinically affected with RD. For example: If you produced 100 puppies
and 10 of these puppies are affected with RD, then 8 of those (or 80% of the 10)
should have I marker or more. The other 90 puppies will live happy normal
lives. Our concern is then focused on those 10 puppies.
If you took the same 100 puppies
and all of these puppies had no markers, the percentage of RD dogs produced
would reduce to 2 puppies. It then only follows that the longer you breed
no-marker dogs to no-marker dogs the smaller the percentage would become. By
selectively eliminating those parents that produced the 2 puppies affected, it
would then be reasonable to expect that the next 100 puppies would not be
affected by RD. The unknown factor would be new bloodlines brought into the
breeding program. Remember that if the kennel involved has a history of
producing a high number of affected RD dogs then the percentages are adjusted to
reflect the increase.
The criticism I've heard from
breeders is that the test does not work. This statement is based on the factor
that there have been dogs with no markers that are affected by or have produced
RD. I have already explained why this occurs. It in no way reflects on the test.
Your dog has either zero, one, or two markers. The test is accurate in locating
these markers. In those dogs tested in kennels that are active in the testing
process, I have had no party contact me that could prove differently. The one
dog that was mentioned in another article seems to be the one that does not fit
the results expected. In the last 2 1/2 years I have tested over 40 dogs. All of
these dogs' test results came back as expected. I found only two times that the
results were not what I thought they would be. In both circumstances the mistake
was mine in not knowing the number of markers each parent had.
The first case was when a litter
of 5 pups was tested and all of the pups had 2 markers. After I peeled myself
off the ceiling, I started to research what went wrong. The mother had 2 markers
and was bred to what I believed was a no marker male. The male was purchased
from another breeder who supplied a copy of his no marker certificate from
VetGen. I then contacted VetGen to confirm the certificate. I was told that the
number on the certificate did not match the name of the dog listed on my copy.
Because of the confidentially procedures that VetGen has, I could find out
nothing else. I then went back to the breeder. The end result was that I
discovered I had received a falsified certificate from the breeder. The copy of
the certificate had been altered to reflect a no marker dog, but in reality the
dog had 2 markers.
The second time is when I thought
I had bred a 1 marker bitch to a no marker male and came up with four I marker
pups. Come to find out we had never tested the bitch for some reason and had
somehow convinced ourselves that she had one marker when she really had two. So
you can see that not paying attention to some details can cost you a lot of time
and money. But the end result is this: the test is accurate. It is how you are
using the test- that will make the difference.
In my case, in the initial 26 dogs
tested three years ago I had 2 dogs that had no markers, and one of those was
neutered and in a pet home. Of the 26 dogs tested only 15 resided in my kennel.
So out of the 15, I had 1 with no marker, 5 with two markers, and 9 with one
marker. In order to keep the other good qualities present in the genetic makeup
of the dogs with one or two markers, I decided to breed the marker dogs with a
no marker male and keep pups that had no markers or I marker (depending on the
bitch bred). At present we have found homes for all of the 2 marker dogs and
kept some of their 1 marker offspring. We now have 3 males with no markers and 5
females with no markers. We have kept one seasoned male with I marker (since he
has a long history of producing healthy pups from a lot of different bitches)
and four females with 1 marker. The plan is to place at least two of the 1
marker females this year when those are replaced with their offspring that have
no markers. None of the 4 males that I have are related, which allows us to keep
a large gene pool for the next five to ten years of breeding. I am hoping that
when Dr. Brewer discovers the defective gene I will be able to keep 80% or more
of my dogs by breeding all no marker dogs. For those of you that are not
testing, be prepared to eliminate 80% or more of your dogs if and when the gene
is discovered.
My recommendations to people that
call me wanting to start showing or breeding dogs is to buy only no marker dogs.
Why start a breeding program already in the hole? If you have dogs, get them
tested. Tests can be purchased in large numbers for as little as $99.00 per
test. Be sure you know what dogs have what markers and breed accordingly. You
can eliminate some of the testing expense by just knowing what markers each dog
carries. Don't be afraid to breed your 2 marker dogs--just be sure you are
breeding them to no marker partners. All the pups produced will have 1 marker
and no testing is necessary.
If you want to breed to that good
looking male that is being advertised and the owner has not tested the dog, then
send a no marker bitch. Test those pups, the results will give you a very good
idea what the stud’s marker status is. With a whole litter of I marker pups, the
stud is probably carrying 2 markers. A litter that has 1 and zero marker pups
likely means that the stud is carrying I marker, and a litter of no marker pups
means you have hit the jackpot and the stud could be a no marker male.
Partner up with another breeder
and trade dogs. I have traded for one of my no marker males and also for a
non-related no marker female. If you are buying or trading, be sure you get
the original copy of the VetGen certificate. A written release from the owner
to get information from VetGen on the certificate should also be requested.
Always assume that the dogs you have that are not tested have 2 markers and
breed accordingly. I am always leery of those breeders that say "I don't test
because I have never had a problem." If they have not had a problem then they
have been very lucky, but I know that they have had pups die at birth or soon
after for unknown reasons. Can they be sure that these were not RD affected
puppies? I would rather deal with someone that admits they are trying and allows
that there could be a problem than to go about raising and showing dogs with
an "it won't strike me" attitude. (It WILL strike, eventually.)
The last item is that those people
that are testing should be registering their dogs on the OFA register as no
marker dogs. This would help other breeders find puppies or studs for future
litters.
Most of our members have supported
the research and supported the testing program. There are still a few that
want to degrade the efforts made. This test is the best science we have at
present, so it would be a shame to ignore it. Ignoring the issue does not make
the problem disappear. It will only ensure that we continue to reproduce the
hidden defective gene. Be sure you are doing all you can to produce not only a
beautiful dog for the show ring but a dog that can produce healthy show dogs and
pets for the future.
Please continue to support this
research- not only with your donations, but by testing your dogs. If we all do
our part, we will all get to the winners circle together.
JoAnn Gustafson
This article
originally appeared in the American Shih Tzu Club
magazine. It was reprinted with the permission of the author.
Also see the page
on Markers & Pets!
There is a Yahoo
Group for support and info with dogs with kidney and bladder problems, if you
are looking at this page because you have a dog with problems, go to:
http://groups.yahoo.com/group/K9KidneyDiet/ and sign up!
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