Common Symptoms
Cone degeneration (German shepherd type) is an inherited eye disease affecting German shepherd dogs. Affected dogs develop day blindness (blindness in bright light) and Photophobia (light sensitivity) between 8 to 12 weeks after birth due to degeneration of cells in the eye called cone photoreceptors which are responsible for vision in bright light. Affected dogs have normal vision in low light and structures of the inner eye appear normal on eye exam. The cells responsible for vision in low light called Rod photoreceptors are not affected and thus, affected dogs will still be able to see normally in low light throughout life.
Breed-Specific Information for the German Shepherd Dog
The Mutation of the CNGA3 gene associated with cone degeneration (German shepherd type) has been identified in German shepherd dogs, although its overall frequency in this breed is unknown.
Testing Tips
Genetic testing of the CNGA3 gene will reliably determine whether a German shepherd dog is a genetic Carrier of cone degeneration (German shepherd type). Cone degeneration (German shepherd type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the CNGA3 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. German shepherd dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
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Tanaka N, Dutrow EV, Miyadera K, Delemotte L, MacDermaid CM, Reinstein SL, Crumley WR, Dixon CJ, Casal ML, Klein ML, Aguirre GD, Tanaka JC, Guziewicz KE. Canine CNGA3 Gene Mutations Provide Novel Insights into Human Achromatopsia-Associated Channelopathies and Treatment. PLoS One. 2015 Sep 25;10(9):e0138943.
[PubMed: 26407004]
