Achromatopsia in German Shepherds

Achromatopsia-2, or day blindness, is a rare inherited disease of the retina in which cone development is impaired. Cones are the photosensitive cells of the retina that allow for colour and sharp vision. Achromatopsia is associated with reduced visual acuity, photophobia (light blindness), colour blindness and impaired day vision. A painful reaction to light may also be observed. Symptoms can be observed in puppies as young as 8 to 12 weeks of age.

The cause of the disease in German Shepherds is a missense mutation (c.1270C>T) of the gene for CNGA3, the alpha subunit of the CNG ion channel, important for signal transduction 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.

.

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.