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IMPORTANT ANNOUNCEMENT TO THE ENGLISH
SPRINGER SPANIEL WORLD WIDE COMMUNITY CONCERNING PROGRESSIVE RETINAL
ATROPHY RESEARCH
Dr Gary Johnson and Dr Cathryn Mellersh
have identified a DNA mutation that is a major risk factor for
development of Progressive Retinal Atrophy (PRA) in English Springer
Spaniels.
• A DNA test is available for breeders, along with information about
what the test can and cannot tell them.
• The percentage of English Springer
Spaniels testing as affected or carrier for this mutation is very high.
• It is likely to take several
generations to reduce the frequency of this mutation in the ESS
population.
• Additional research, funded by the
ESSFTA Foundation and the AKC Canine Health Foundation, has been
initiated to help answer the questions that remain unexplained by the
discovery of this mutation.
• Much more important information about
this discovery can be found in the PRA section of the
www.CanineGeneticDiseases.net website.
Dr Gary Johnson’s Animal Molecular
Genetics Laboratory at the University of Missouri-Columbia, in
collaboration with Dr Cathryn Mellersh of the Animal Health Trust in
England, has identified a mutation that is a major risk factor for
development of Progressive Retinal Atrophy (PRA) in English Springer
Spaniels (ESS). A DNA test for this mutation is now available for
concerned ESS breeders to help them make breeding choices that can
reduce the incidence of PRA in this breed. In the dogs tested during the
research, 80% of the English Springer Spaniels tested as affected or
carrier for this mutation, so it is important that breeders have a clear
understanding of what this test can and cannot tell them. It is very
likely to take several generations to reduce the frequency of this
mutation in the ESS population. Additional research has been initiated
to help answer the questions that remain unexplained by discovery of
this mutation.
THE DISCOVERY
Dr Mellersh recently published information on a mutation found to cause
a recessive cone-rod form of PRA in Miniature Longhaired Dachshunds. In
a limited survey, Dr. Mellersh also found the mutation to be present in
ESS. Because of this, Masters student, Xuhua Chen, from Dr Johnson’s
laboratory tested over 1100 ESS DNA samples and found that dogs that
inherited the mutation from both their sire and dam were approximately
20 times more likely to develop PRA compared to other ESS. Preliminary
electroretinogram (ERG) studies by Dr Kristina Narfstrom, Laboratory for
Comparative Ophthalmology, University of Missouri-Columbia, suggest that
ESS have a cone-rod form of PRA similar to that found in the Dachshunds.
It is important to note that there are
a large number of dogs that have tested as genetically affected, but are
reported as clinically normal by their owners. This is also similar to
the situation in Miniature Longhaired Dachshunds. With the wide range of
age of onset observed for PRA in ESS, it may be that many of these dogs
will develop symptoms eventually. It is also possible that that these
dogs have some loss of visual function that has not yet been detected by
the owner.
GOOD NEWS – BAD NEWS
The good news – a DNA test is now available. This test clearly
identifies dogs that are clear (have 2 normal copies of the gene), those
who are carriers (have one normal copy of the gene and one mutated copy
of the gene), and those who are at much higher risk for developing PRA
(have 2 mutated copies of the gene). Wise use of this test can reduce
the incidence of dogs at risk for PRA in future generations.
The bad news – only 20% of the
1100-plus ESS’s genotyped during the research tested as clear, or
normal. Thirty-eight percent tested as carriers, and 42% tested as
genetically affected. Obviously, eliminating all dogs testing as
affected from breeding programs will have a major impact on the breed,
and has the potential to devastate successful breeding programs.
Reducing the incidence of dogs at risk for PRA while maintaining genetic
diversity and positive qualities present in the breed is likely to be a
slow process and will take several generations.
Information about the benefits of this test, testing forms and
instructions, and suggestions for using the test to reduce the frequency
of PRA in this breed is available online in the PRA section of
www.CanineGeneticDiseases.net and at
www.aht.org.uk .
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