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For many breeds of
dogs we still need breeding studies to prove or disprove inheritance in
certain cataractous breeds. Then using genetic/DNA studies (to demonstrate
carrier dogs, and affected animals months to years before the cataracts
develop), we can markedly reproduce the frequency of cataracts in many
breeds in the next several years.
Retinal Disorders
Thee three large and
important groups of retinal diseases in the dog, include Collie eye anomaly,
the retinal dysplasias, and the dysplasia and degeneration of the outer
retinal photoreceptors (broadly grouped as progressive retinal atrophy-PRA).
Collie eye anomaly (CEA)
\\as intensively investigated in the 1960s, and the results are still very
valid. Unfortunately this disorder has surfaced in other breeds, such as the
Shetland Sheepdog, Border Collie, Australian Shepherd, and recently the
Lancaster Heeler in England. Hence, the Collie eye anomaly 'label' may be
less appropriate since its presence has been discovered in additional
breeds. As the basic eye pathology is focal choroidal hypoplasia and
colobomas (optic disc/adjacent retina), perhaps these terms would be
suitable.
Unfortunately CEA in
the Collie breed is still too common, and we need to work ourselves out of
this hole! Ideally only normal eye animals should be used for breeding. As
this defect is present at birth (and easily detected at 6-8 weeks), it can
be quickly eliminated. But breeders have to decide this is a priority and
critical for the future of this breed! In the other breeds CEA is
considerably less frequent (less than 5%), and breeding of affected animals
and parents that have affected offspring should be discouraged. We should
not need to repeat the CEA story again!!
The retinal dysplasias
are becoming more common, and in certain breeds can cause visual impairment
and blindness. The multifocal retinal dysplasias affect the American Cocker
Spaniel, Beagle, Rottweiler, and Yorkshire Terrier; these diseases do not
cause blindness but should be eliminated. The total retinal dysplasias are
often associated with other ocular disorders, such as cataracts,
microphthalmia, retinal detachments and blindness, and affect the Labrador
Retriever, Golden Retriever, English Springer Spaniel, Bedlington Terrier,
Sealyham Terrier, Doberman Pinscher, and the Australian Shepherd. These
blinding retinal dysplasias are infrequent.
One strategy at this
time is to eliminate all affected animals, and affected/carrier parents as
breeding animals. This strategy could be applied to either the focal or
generalized forms of retinal dysplasia, or targeted to those generalized
forms that cause blindness. Genetic/ DNA tests are future goals that could
be applied to a much larger population to identify and removal any carriers.
The retinal
photoreceptor diseases (traditionally called progressive retinal
atrophy-PRA) are being investigated now with the molecular genetic approach.
Experience has demonstrated the process of 'discovery' is slow but
rewarding! Those breeds with a significant PRA problem include the Toy and
Miniature Poodle, Labrador Retriever, American Cocker Spaniel, Miniature
Schnauzer, and Papillon. Other breeds with PRA will undoubtedly be
investigated.
Considerable effort,
time and support have been directed at the photoreceptor diseases for the
past several years and we are making progress! For certain breeds (i.e.
Irish Setters and Cardigan Welsh Corgi) the highly specific gene mutation
tests are available. For Portuguese Water Dogs, Chesapeake Bay, Retrievers,
English Cocker Spaniels, and Labrador Retrievers genetic tests have been
developed (all with a marker-based test for prcd). The marker-based test of
prcd (genetic markers on the canine chromosome 9 usually indicates the
presence of the gene mutation) appears not as sensitive as those that detect
the actual gene mutation. Hence, dogs may demonstrate the marker genes but
not gene mutation (they will test as false positives). Nevertheless these
tests are useful at this time identifying these animals completely clear of
these diseases (they are not carriers or affected). The positive results
will be either affected, carriers, or false positives! Another test has been
recently developed for congenital stationary night blindness (CSNB) for
Briards. So our interpretations of these new genetic tests has to become
more sophisticated and is based on the exact type of genetic test used!
Summary
Fortunately the time
to address and markedly reduce the frequency of 'blinding' inherited eye
diseases in purebred dogs is at hand! Many technologies are available and
are interrelated. All of the national breed clubs should be sponsors and
actively support the Canine Eye Registry Foundation (CERF). Annual CERF eye
examinations of all breeding animals is very important, particularly when
certain eye diseases occur in later life. The annual CERF reports are
important monitors for all breeds and can measure either the increase or
decline of all eye diseases in a large population of dogs in America.
Continued careful
analysis of pedigrees for multiple generations is critical for the
development of eye diseases and their mode of inheritance. The development
of additional genetic/DNA tests to detect affected and carrier dogs, and the
life-long identification (by tattoos or microchips) of these dogs is
critical. The unimpeded exchange of information among breeders and
veterinary ophthalmologists can ensure our chance of success, shorten the
time for positive results, and control our costs!
Dr. Gelatt's work is
supported by the following grant from the AKC Canine Health Foundation:
No. 1607: Hereditary and DNA Studies in Cataracts in the Bichon Frise
(Supported in part by the Bichon Frise Club of America
Biographical
Profile
Kirk N. Gelatt,
VMD, graduated from Pennsylvania State University (Penn State), and
the School of Veterinary Medicine University of Pennsylvania (VMD; 1965). He
received his ophthalmology training at Penn supported by a National
Institutes of Health research fellowship. Dr. Gelatt has served as a faculty
member at three additional veterinary schools: Kansas State University (1967
- 70); University of Minnesota (1970 - 76); and the University of Florida
(1976 to present).
Dr. Gelatt's more than
three decades of work in academia has included didactic and clinical
teaching to more than 2,700 veterinary students, and training 34 residents
and postdoctoral fellows in comparative ophthalmology. He has presented more
than 240 professional talks nationally and internationally. He has published
more than 150-refereed articles, 50 abstracts, 90 nonrefereed articles, 45
book chapters, and seven books. He serves as the editor for the reference,
Veterinary Ophthalmology, the "gold standard" for this discipline.
The third edition of Veterinary Ophthalmology with 37 chapters and 45
different authors was released in January 1999. Dr. Gelatt's research
interests have concentrated on the canine glaucomas, inherited cataracts in
the dog, clinical pharmacology of drugs that change intra-ocular pressure,
and ophthalmic surgeries.
Dr. Gelatt is one of
eight veterinarians of the organizing committee that chartered the American
College of Veterinary Ophthalmologists in 1970. He served in the different
offices of ACVO, and was President in 1997-78. He currently serves as editor
and chief of the new journal, Veterinary Ophthalmology, the official journal
of the ACVO.
Dr. Gelatt has
received the University of Minnesota Phi Zeta Research Award (1976), the
Ralston Purina Research Award (1979), Alumni Award of Merit, University of
Pennsylvania (1990), Gaines-Cycle-"Fido" Research Award (1991), North
American Veterinary Conference Founding Award (1993), Daniel's Senior
Clinical Investigator Award (1994), Bourgelatt International Award from the
British Small Animal Veterinary Association (1995), and the American Kennel
Club's Career Achievement Award (I 998). Dr. Gelatt was promoted in 1998 at
the University of Florida to "Distinguished Professor of Comparative
Ophthalmology."
Dr. Gary Johnson
is on the faculty in the Department of Veterinary Pathobiology in the
College of Veterinary Medicine at the University of Missouri. He has a
Bachelors Degree from Augsburg College, a Ph.D. from Kansas State University
and a DVM from the University of Minnesota. He has postdoctoral training
from Johns Hopkins University and the New York State Department of Health.
His early research was on bleeding diseases of dogs. For the last ten years
his research has focused on the use of DNA markers to study inherited
diseases and quantitative traits in dogs and cattle. Dr. Johnson is a
breeder and exhibitor of Irish Terriers.
George J.
Brewer, MD, went to undergraduate school (Pharmacy) at Purdue
University, and to medical school at Indiana University and the University
of Chicago. He did residency training at the University of Chicago, and then
did a postdoctoral fellowship in Human Genetics at the University of
Michigan. He has been on the faculty at the University of Michigan since
1967, and is a Professor of Human Genetics and a Professor of Internal
Medicine.
Dr. Brewer's research
has involved human genetic diseases, such as sickle cell anemia and Wilson's
disease (human copper toxicosis). Over the last fifteen years he has worked
extensively in the molecular genetics of canine diseases, such as copper
toxicosis, von Wildebrand's disease, renal dysplasia, hip dysplasia,
cataract, epilepsy and others. He is one of the founders of VetGen, LLC, an
Ann Arbor-based company offering a variety of DNA tests for canine diseases
and traits.
Gregory M.
Acland is a veterinary ophthalmologist at the James A. Baker
Institute for Animal Health, in the College of Veterinary Medicine of
Cornell University. His research is undertaken as part of the Center for
Canine Genetics and Reproduction directed by Dr. Gustavo Aguirre. Current
projects include collaborative efforts to identify the genes for PRA in
multiple breeds, for cone degeneration in Alaskan Malamutes, Collie Eye
Anomaly, and several forms of cataract; and to evaluated potential therapies
for inherited retinal degenerations. Dr. Acland is funded by the American
Border Collie Association, the AKC Canine Health Foundation, the Baker
Institute PRA/CEA Fund, The Foundation Fighting Blindness, and the National
Eve Institute (Grant EY06855). |
