Common Symptoms
Cone degeneration (German shorthaired pointer type) is an inherited eye disease affecting German shorthaired pointers. 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 a veterinary eye exam. Normal cone cell function can be seen on Electroretinogram (ERG) before six weeks of age, but becomes abnormal between 6 to 12 weeks of age and is completely absent in affected adult dogs signifying complete loss of Cone Cells. 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 Shorthaired Pointer
The Mutation of the CNGB3 gene associated with cone degeneration (German shorthaired pointer type) has been identified in German shorthaired pointers, although its overall frequency in this breed is unknown.
Testing Tips
Genetic testing of the CNGB3 gene in German shorthaired pointers will reliably determine whether a dog is a genetic Carrier of cone degeneration (German shorthaired pointer type). Cone degeneration (German shorthaired pointer 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 being a carrier of the CNGB3 gene. 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 shorthaired pointers 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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Komáromy AM, Alexander JJ, Rowlan JS, Garcia MM, Chiodo VA, Kaya A, Tanaka JC, Acland GM, Hauswirth WW, Aguirre GD. Gene therapy rescues cone function in congenital achromatopsia. Hum Mol Genet. 2010 Jul 1; 19(13):2581-93.
[PubMed: 20378608]
