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Canine Multifocal Retinopathy ...
Canine Multifocal Retinopathy is
referred to as CMR and is a recently identified eye disease that is
found in Cotons as well as several other breeds. It is
believed genetic and is considered to have a recessive
hereditability. In order for the disease to manifest in a dog,
each parent must contribute the gene mutation responsible for CMR.
A DNA test is available for CMR through OptiGen. As of April
2007 this test can be done by cheek swab.
What is it?
Canine Multifocal Retinopathy is an
eye disease that presents as lesions on the retina. Typically
there are several rounded
patches where the retina is elevated.
These lesions look like blisters and can be of varying size.
The lesions are normally seen in both eyes.
CMR tends to develop prior to four months of age and may progress
slowly, may appear to go away, and may appear to go away then
redevelop. Sometimes the retina heals with no lasting signs,
other times a retinal fold or blister may remain.
CMR in the Coton seems to have
more prominent and persistent lesions than the other breeds in which
it is seen. It is difficult to ascertain degrees of visual
impairment in animals and so it is uncertain/unknown what degree of
visual impairment CMR can cause. It appears that most dogs
with CMR are not visually impaired to the point of severe functional
affectivity. Whether this remains true into the future remains
to be seen. The progressiveness of the disease in any given
dog is unknown.
What about breeding?
There are three possible outcomes
to the DNA testing for CMR. A dog can test as being affected,
being a carrier, or being clear/normal. Dogs that are affected
are not typically used for breeding although, technically, breeding
an affected Coton to a clear/normal Coton would result in all the
puppies being carriers with no affected puppies (because they would
need a gene from both parents to be affected). Dogs
that are carriers and clear/normal are able to be used for breeding
however, it is imperative that carriers are only bred to a dog with
a clear/normal status. Other combinations are at high risk of
producing dogs affected with CMR. Ideally, through judicious
breeding, CMR should be able to be eradicated from the breed.
However, some breeders that feel that since CMR is not determined to
cause any vision problems, and is not progressive, that CMR is not a
problem in the breed and therefore testing is not necessary.
The flip side to this thinking is that gene mutations can always
mutate otherwise, and with retinal dysplasia and progressive retinal
atrophy present in the breed, at the present time there really is no
way of knowing whether there is any correlation between CMR and
other eye diseases. Each breeder must make choices they feel
are suitable for them. We at Cotonwind felt it was important
to test all of our dogs.
What does this mean for the buyer?
Breeders that test for CMR are
taking another step forward in the overall health of the Coton de
Tulear. Only through testing can breeders avoid doing high
risk breedings. If the CMR status of the two dogs being bred
is not known then there exists the risk that both dogs can be
carriers or affecteds, or a combination of both, thus risking
puppies that have CMR. When dealing with a breeder who tests,
buyers can be assured that their new puppy Coton does not have CMR.
Because it is still unknown to what degree CMR can affect a Coton,
and how CMR will manifest into the future, buyers should seek the
assurance of purchasing a puppy that has no possibility of having
CMR by purchasing from a breeder that has tested their dogs.
Further information regarding CMR and breeding strategies for dogs
with a
CMR status of affected or carrier, please visit the
Optigen website.
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