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In this section details of:
Research Information
- New DNA Test - Genetic
Inheritance of PRA
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| Dr Cathryn Mellersh and colleagues at The Animal Health
Trust in England have recently identified and reported
a mutation that causes PRA in Miniature Longhaired Dachshunds.
Dr. Mellersh has found that the mutation is not restricted
to Dachshunds and The University of Missouri has investigated
the frequency of this mutation in English Springer Spaniels
primarily from North America. |
| The mutation is a risk factor for the development
of PRA in English Springer Spaniels: Most of the dogs
that were tested in the USA as "affected" are
considered to have normal eyesight by their owners. Some
of these dogs may develop PRA as they get older; however,
there are many examples of old English Springer Spaniels
that DNA test "affected" but, have subtle, if
any, visual impairment. |
| On the other hand, 95% of the English Springer Spaniels
with clinically recognized PRA test "affected."
Erroneous diagnoses or a second rare form of PRA may account
for the 5% of English Springer Spaniels with PRA that
do not test "affected." |
| The USA study implies that the likelihood of developing
PRA is approximately 20 times higher for English Springer
Spaniels testing "affected" than it is for other
English Springer Spaniels. This is strong evidence that
testing "affected" is a major risk factor for
PRA in English Springer Spaniels and indicates that the
prevalence of English Springer Spaniel PRA can be reduced
by breeding programmes that select away from the mutant
gene. This can be accomplished by giving highest preference
to breeding stock that test "normal," intermediate
preference to dogs that test "carrier" and lowest
preference to dogs that test "affected." |
| Although we believe that English Springer Spaniel breeders
should make efforts to reduce PRA in future generations
of their line, we also believe that if the mutation is
so common in the Breed, overly aggressive elimination
of dogs testing affected or carrier from breeding consideration
could have an overall detrimental effect on the Breed
and could devastate successful breeding programmes. |
| A realistic approach when considering which English
Springer Spaniels to select for breeding would be to consider
dogs with the mutation to have a fault just as lack of
working ability, poor top line, or imperfect gait would
be considered faults. |
| Dogs that test "affected" with two mutant
copies of the PRA gene should be considered to have a
worse fault than "carriers" with only one mutant
copy. English Springer Spaniel breeders could then continue
to do what conscientious breeders have always done: make
their selections for breeding stock in light of all of
the dogs' good points and all of the dogs' faults. Using
this approach over several generations should substantially
reduce the prevalence of PRA while continuing to maintain
or improve those qualities that have made English Springer
Spaniels so popular. |
One problem with this approach
is that the clinical consequences of testing "affected"
are, as yet, poorly defined. Thus, it is hard for breeders
of English Springer Spaniels to determine how much priority
should be given to selecting away from the mutation. To
better understand the clinical consequences, we will continue
to assess clinical eye examinations (BVA/ECVO & AHT)
and other relevant medical records of the dogs that are
tested.
When the results of these studies become available, they
will be posted at this Website. |
- · A DNA test for PRA in the English Springer
Spaniel is now available at the Animal Health Trust.
- · The AHT will require cheek swabs for the
DNA test.
- · The cost of each test is £50 (including
VAT). This includes the cost of the cheek swab sampling
kit. A 20% discount is offered if 20 or more samples
are sent in together in a single batch for testing.
- · Animal Health Trust DNA Testing Form can
be downloaded from the AHT website at www.aht.org.uk.
Kits for taking cheek swabs are available by phoning
08700 509144 or via email to swab.request@aht.org.uk.
- · Further information can be obtained by
emailing dna.testing@aht.org.uk.
- · Samples should be sent together with a
completed DNA Testing Form and payment for each sample
to
Genetic Services,
Animal Health Trust,
Lanwades Park,
Kentford,
Newmarket,
Suffolk CB8 7UU.
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- · For most tests offered by the AHT, 100
- 200 samples are routinely handled per month and
turnaround time is usually a few weeks. However, this
may take longer during very busy periods.
- · Owners of all samples that the AHT has
actively used in the research that has led to the
development of this DNA test will be entitled to the
genetic results of those samples free of charge in
an email. The AHT will make a charge of £5.00
if the owner would like a certificate.
For samples to have been used in the research, they
must be from affected dogs, or closely related to
affected dogs.
All the samples that have been sent previously to
the AHT will not have all been used, if they do not
fall into the above categories.
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Dr Gary Johnson
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Dr Cathryn Mellersh
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