Achromatopsia 2 in Labrador Retrievers and Labradoodles

Achromatopsia-2 or day blindness is a rare inherited disease of the retina which affects the development of the cones. The cones are photoreceptor cells in the retina that enable colour and high-acuity vision. Therefore, achromatopsia is associated with reduced visual acuity, photophobia (light blindness), colour blindness and impaired daylight vision. A painful reaction to light may also be observed. Symptoms can be seen in puppies as young as 8 to 12 weeks of age.

The cause of the disease in Labrador Retrievers is a deletion in exon 7 (c.1931_1933del) in the gene for CNGA3, the alpha subunit of the CNG ion channel, which is important for signal transmission in the photoreceptors of the retina.

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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References:

Tanaka, N., Dutrow, E.V., Miyadera, K., Delemotte, L., MacDermaid, C.M., Reinstein, S.L., Crumley, W.R., Dixon, C.J., Casal, M.L., Klein, M.L., Aguirre, G.D., Tanaka, J.C., Guziewicz, K.E. : Canine CNGA3 gene mutations provide novel insights into human achromatopsia-associated channelopathies and treatment. PLoS One 10:e0138943, 2015. Pubmed reference: 26407004.