Multifocal Retinopathy type 3 (CMR3)

Canine Multifocal Retinopathy (CMR) is an inherited eye disease characterized by retinal degeneration. The clinical features are essentially the same as other forms of CMR (1 and 2), but the molecular mechanism is different. In the Lapinporokoira breed, the disease is caused by mutation c.1388del in the BEST1 gene.

In the retina, pigment epithelium atrophy, vacuolization, multiple detachments due to accumulation of fluid under the retina and the formation of yellow to pink blister-like lesions occur. These pathological changes lead to severe impairment of central vision and to complete loss of vision in old age.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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Reference:

Zangerl, B., Wickström, K., Slavik, J., Lindauer, S.J., Ahonen, S., Schelling, C., Lohi, H., Guziewicz, K.E., Aguirre, G.D. : Assessment of canine BEST1 variations identifies new mutations and establishes an independent bestrophinopathy model (cmr3). Mol Vis 16:2791-804, 2010. Pubmed reference: 21197113.