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Canine Multifocal Retinopathy 2

Canine Multifocal Retinopathy 2 (CMR2) is an eye disorder that can cause retinal decay which may impact vision, but very rarely results in blindness.

Key Signs

Retinal degeneration

Age of Onset

0 to 2 yrs

Juvenile onset

Inheritance

Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

High likelihood

At risk dogs are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with CMR2

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about CMR2

Typically, the first ocular fundus changes in CMR2 can be diagnosed by the age of four months. In many cases, the lesions may appear to heal or even go away, sometimes leaving no evidence or only a wrinkle at the site of the healed lesion. In almost all cases, lesions from CMR2 do not progress significantly over time, so there is generally no reduction in eyesight though more serious cases could exhibit vision impairment. Very seldom is the patient completely blinded. The lesions noted in CMR2 in Coton de Tulears tend to be more severe and persist longer than the lesions noted in breeds affected by the other CMR.

Monitor fundus changes for evidence of healing and monitor patient for any signs of visual impairment.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to develop. A carrier dog with one copy of the CMR2 mutation can be safely bred with a clear dog with no copies of the CMR2 mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the CMR2 mutation. A dog with two copies of the CMR2 mutation can be safely bred with a clear dog. The resulting puppies will be all carriers with one copy of the CMR2 mutation. Puppies in a litter which is expected to contain carriers should be tested prior to breeding. Please note: It is possible that disease signs similar to the ones caused by the CMR2 mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene BEST1
Variant G>A
Chromosome 18
Coordinate 54,476,143

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Guziewicz, K. E., Slavik, J., Lindauer, S. J. P., Aguirre, G. D., & Zangerl, B. (2011). Molecular consequences of BEST1 gene mutations in canine multifocal retinopathy predict functional implications for human bestrophinopathies. Investigative Ophthalmology and Visual Science, 52(7), 4497–4505. View the article

Guziewicz, K. E., Zangerl, B., Lindauer, S. J., Mullins, R. F., Sandmeyer, L. S., Grahn, B. H., Stone, E. M., Acland, G. M., & Aguirre, G. D. (2007). Bestrophin gene mutations cause canine multifocal retinopathy: A novel animal model for best disease. Investigative Ophthalmology and Visual Science. View the article