CMR1 - Canine multifocal retinopathy type 1

Canine multifocal retinopathy (CMR) is a hereditary eye disease.

There is a specific form of canine multifocal retinopathy called CMR1. This disease is caused by C73T mutation in exon 2 of VMD2 gene. The mutation causes forming of premature stop codon in position 25 (R25X). Breeds that are affected with CMR1 are: Great Pyrenees, English Mastiffs, Bullmastiffs, Cane Corso, Dogue sde Bordeaux, English Bulldog, American Bulldog, Pero se Presa Canario and Australian shepherds.

CMR symptoms are very similar to Best macular dystrophy disease (BMD) in humans. BMD and CMR are retinal disorders caused by mutation in VMD2 gene (Vitelliform Macular Dystrophy 2 Gene). VMD2 gene is coding a protein bestrophin which is responsible for right forming of pigment epithelium in retina. Mutations in VMAD2 gene cause pigment epithelium athrophy which is leading to serious damage of sight.

CMR disease usually arises before 4th month of age in an affected puppy. Clinically, rose-grey coloured lesions are remarkable in retina. These lesions are of different size and shape and are occured in both eyes of affected individual. Total blindness usually comes in higher age.

CMR1 is an autosomal recessive disorder. The disease affects dogs with P/P (positive / positive) genotype only. Dogs with P/N (positive /negative) genotype are clinically without any symptoms. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

References:

Karina E. Guziewicz, Barbara Zangerl, Sarah J. Lindauer, Robert F. Mullins, Lynne S. Sandmeyer, Bruce H. Grahn, Edwin M. Stone, Gregory M. Acland, and Gustavo D. Aguirre: Bestrophin Gene Mutations Cause Canine Multifocal Retinopathy: A Novel Animal Model for Best Disease. Invest. Ophthalmol. Vis. Sci., May 2007; 48: 1959 - 1967.

Keiko Miyadera et al.: Genetic and phenotypic variations of inherited retinal diseases in dogs: the power of within- and across-breed studies ; Mamm Genome (2012)