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In dealing with Pet Loss Grief and Pet Loss Support, there
are many resources on the site to help in dealing with the loss of our beloved
This Months May's News Letter
In Pet Wellness:
Progressive Retinal Atrophy
Progressive Retinal Atrophy (PRA), is an incurable hereditary eye disease
which, as the name implies, progressively attacks and destroys the retina
of the eye, causing blindness. The retina is essential to eyesight, for it
is here that a visual image is formed before being transmitted via the optic
nerve to the brain. A defect in an enzyme causes a chemical compound to form
that kills the cells in the retina.
PRA begins with night blindness, followed by gradual loss of day vision and,
eventually, total sightlessness. In some affected breeds, vision loss is
observed in puppies, and the dogs may become blind before or soon after maturity.
In other breeds, the disease can go undetected until the dog is
several years old and has passed the PRA gene to subsequent generations of
puppies. Like retinitis pigmentosa in humans, canine PRA is not one
disease but a group of related ones. All are characterized by malformation
or degeneration of the retinal visual cells. Most forms of PRA are caused
by different, autosomal recessive gene defects. This means that for offspring
to be affected, both parents must carry one copy of the same mutant
gene. Both parents could have normal eyesight, but have 1 gene for normal
enzyme production that is dominate over the 1 recessive gene for the
abnormal enzyme defect. In this case the parents would be considered carriers.
When a carrier is bred to another dog with 1 dominant normal gene and 1 recessive
abnormal enzyme defect gene (i.e., another carrier), 25% of the
offspring will be afflicted with PRA, 50% will be carriers like their parents,
and 25% will possess the normal 2 dominant correct enzyme genes.
If a dog afflicted with PRA is bred to another dog who is neither afflicted
nor a carrier, then all the offspring from that breeding will be carriers
(possessing 1 dominant normal enzyme gene and 1 recessive abnormal enzyme
gene). All of these offspring are then capable of producing PRA if
they are bred to another carrier or a PRA afflicted dog.
In some cases, breeders have resorted to producing "test litters"
as a means of identifying and removing all carriers and affected dogs from
their lines. The disease afflicts an estimated 80 breeds of dogs worldwide.
Research has achieved some success in developing a test for the defective
gene. Carriers of the mutant gene for one type of PRA in Irish Setters
can be detected with a new blood test developed at the Cornell College of
Veterinary Medicine. The unequivocal DNA blood test for rod-cone
dysplasia-1 (rcd-1) in Irish Setters gives researchers hope that similar tests
for other affected breeds will produce equally promising results.
Meanwhile, the best recourse of breeders and buyers alike is regular eye
checks by qualified veterinarians, and honest
disclosure of the problem when diagnosed. Until the method of detecting the
defective gene in Chesapeakes is available, buyers and breeders alike
must depend upon vigilance and careful research of pedigrees to reduce the
occurrence of PRA in the breed.
Until development of the first DNA test, PRA can only be detected by
electro- retinography testing and requires examination by a canine ophthalmologist.
Using special equipment the opthamologist will examine your dog's eyes for
a thinning of the retina, which causes the dog's eyes to be hyper-reflective.
They may also observe a paleness of the optic disk and a reduction of blood
vessels in the eyes. This test, which is available at
regional veterinary centers, identifies only dogs affected by
PRA - not the clinically normal animals that carry
one copy of the defective gene. Thus, a carrier can still be unknowingly used
in breeding. Responsible breeders will supply information on the eyes of
their dogs in the form of one or more of the following: eye examination reports
(preferably from veterinary ophthalmologists), electroretinogram (ERGs), and
examination forms for the Canine Eye Registry Foundation (CERF).
Often, the symptoms of the disease can go un-noticed by owners until it has
progressed significantly. Since the disease advances slowly, an afflicted
dog can adapt by depending more heavily on his sense of smell and hearing.
Often an afflicted dog can cope very well until total blindness occurs.
It is not unusual for owners of afflicted dogs to be unaware of the
problem until an eye examination is obtained.
Not all retinal degeneration is caused by genetic PRA. non-PRA retinal degeneration
does exist and can be distinguished in the early stages of
development from genetic PRA. When either type of retinal degeneration is
found in an advanced state (e.g., the retina in nearly totally degenerated)
it is not possible to distinguish between the two types by eye examination.
This is further reasoning for routine and periodic eye examinations. Also,
because the determination of PRA can be subjective and have significant consequences,
a second opinion would be a good idea.
PROGRESSIVE RETINAL ATROPHY
PRA is a descriptive term applied to retinal diseases that affect all breeds
of dogs. The same clinical signs are present in all PRA affected animals.
Affected animals will show night blindness and a progressive loss of day vision.
Many PRA cases can be diagnosed between three and five years of age.
It is during this age period subtle retinal changes can be noted by the experienced
ophthalmologist. Even though the same clinical signs will be present in all
PRA affected animals, the age of onset of disease differs from breed to breed.
The onset period is divided into three approximate age groups: early, middle,
and late. This late-onset form of the disease is now called Progressive Rod-Cone
Degeneration (PRCD). PRCD is inherited RECESSIVELY.
An affected animal can only be produced if both parents
are affected, both carry the defective gene, or one parent is affected and
the other carries. All the offspring of a PRA affected dog will carry ONE
PRA gene. The status of the second parent will determine whether the offspring
will be affected or carriers. Statistically, when two carriers are mated a
1:2:1 ratio (25% will be affected- i.e., 1 in 4, 50% will carry, 25% will
be genetically clear-1 in 4) will occur.
All breeding stock should have annual eye exams for life. There are other
ocular conditions that affect our breed. some of these conditions are: cataracts,
entropian, ectropion, distichiasis, dry eye(geriatric), persistent pupillary
membranes, and retinal dysplasia.
As always your Veterinarian is the best source of
treatment for questions or problems that may exist.
If you have any suggestions or comments or would like
to add to our "Monthly Newsletter",
mailto: CaroleMiller@In-Memory-Of-Pets.com>> Carole
mailto: JohnMingo@In-Memory-Of-Pets.com>> John
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Bless all who come to "In Memory Of Pets" in sharing loving feelings
for their beloved ones.
John, Carole and Staff
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