von Willebrand's Disease &
Your Breeding Program
Appeared In CMTC Newsletter "Thumbprints"
December, 1998.
Prepared by Amanda Kelly
As many Manchester breeders will know von Willebrand's
Disease (or vWD) is one of the diseases affecting Manchester Terriers currently
being targeted on a wide scale by breeders. New procedures in detecting the
presence of this disease have made selecting suitable breeding stock very easy
and virtually risk free when utilized correctly.
Canine von Willebrand' s Disease, first reported in 1970,
is an inherited deficiency of one of the clotting factors of the blood (von
Willebran' s Factor or vWF). The disease is quite similar to hemophilia but can
appear in either males or females. Dogs affected by vWD can have symptoms
ranging from very mild to severe or lethal. Symptoms include: prolonged bleeding
from toe nails cut too short, hemorrhage from even minor surgical procedures,
hematomas, lameness, stillbirth or early death of newborn puppies, intestinal
bleeding, nose-bleeds, etc. These symptoms can be further aggravated by
stressful situations.
Genetically, each dog carries two genes controlling
production of vWF, one inherited from each parent. Each normal gene is capable
of producing 50% of the total amount of vWF produced by a cell, for a total of
100%. Manchester Terriers, along with Dobe rman Pinschers and Poodles, are prone
to Type 1 vWD, meaning that even diseased genes are capable of producing a small
amount of the vWF produced by a normal gene -- typically 5-10%. Because of this,
Manchesters are not prone to as severe problems with bleeding and clotting as
some oth er breeds. This is not to say that affected Manchesters are not at
risk, simply that they are not likely to die from a bleeding toe nail or a nose
bleed, or to suffer from spontaneous bleeding as has been known to happen in
Type 3 breeds for example.
Until recently the only way to test for the presence of
vWD was through the use of a protein-based test called a vWD Factor Assay. This
test measured the amount of vWF the dog was able to produce and compared it to
the 'normal amount' found in a dog presumed to be clear of the disease. The dogs
were then classified accordingly with the higher reading being considered more
desirable in a breeding program. The problem with the Factor Assay test was that
many variables could affect the resulting readings, in cluding thyroid hormone
levels, condition of the liver, menstrual cycles, improper blood handling and
variations within the protein-based tests themselves.
Researchers at Michigan State University, the University
of Michigan and a company called VetGen have now discovered a way to detect the
presence of the gene mutation causing von Willebrand\rquote s Disease through
the use of a simple DNA test. The test has several advantages over the old
method, the most important of which is accuracy. Because the test looks at the
individuals DNA each dog needs to be tested only once in its life. Results are
not subject to change due to any variables affecting the dog -- no matter how
many times the dog is tested the results will always be the same. Results can be
obtained within two weeks and the sample DNA is collected by simply swabbing the
inside of the dog's mouth using the soft-bristle brush provided in the test kit.
The brush can then be returned to VetGen' s labs through regular mail.
Another important feature of thi s test is the definitive
results it offers, classifying each dog as Clear, Carrier or Affected. Because
vWD is a recessive trait in Manchester Terriers both copies of the gene present
must be disease genes in order for the dog to be "affected" by vWD
(i.e. exhibit symptoms). In this case any puppies an affected dog produces will
carry at least one disease gene for vWD. When only one copy of the disease gene
is found the dog is classified as a "carrier." Though the individual
will not exhibit symptoms of the disease its puppies will inherit the disease
gene approximately 50% of the time. Dogs possessing no copies of the disease
gene are classified as "clear" of the disease and will never pass on a
disease gene. These simple classifications will now allow the breeder to make
informed decisions concerning vWD when planning breedings.
Data from the several hundred Manchester Terriers that
have been tested show that only approximately 1% are classified as
"affected" and 10-11% as "carrier." This is very encouraging
news, eventually we hope to be able to eliminate vWD from the breed forever,
though this will have to be done with care. It is important to note when
evaluating your breeding program and your dogs' vWD results that researchers
like Patrick Venta, PhD of the College of Veterinary Medicine at Michigan State
University "do not believe that it is in the best interest of the breed to
limit the gene pool by breeding only clear to clear." This does not negate
the importance of controlling and eliminating the disease, it simply puts it in
perspective. It is, obviously, not advisable to plan any breeding in which
affected animals will be produced.
It should also be noted by those considering testing their
breeding stock that many North American kennels now require DNA test results
before breeding to or buying from a fellow fancier.
