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Cone Degeneration, Achromatopsia
Segregation of the domestic dog population into separate breeds, driven by artificial selection for defined phenotypic and behavioral traits, has been marked by the emergence of inherited canine diseases that are often directly comparable to those observed in humans. In humans, a cd-like condition referred to as achromatopsia, total color blindness, day-blindness or rod monochromacy has been extensively described. [4]
Cone degeneration (cd ) is an autosomal recessive canine disease that occurs
naturally in the Alaskan Malamute, miniature poodles and German Shorthaired Pointer breeds, although this condition may exist in other breeds of dogs.[3] Canine cone degeneration (cd ) was first observed in an inbred strain of Alaskan Malamute dogs in 1960, and is inherited as an autosomal recessive trait (15). Cone-degenerate pups develop day-blindness and photophobia between 8 and 12 weeks postnatal, the age when retinal development is normally completed in dogs. Symptoms are present only in bright light; vision in dim light is normal. Affected dogs remain ophthalmoscopically normal throughout life.[4] It is similar to human achromatopsia, a heterogeneous autosomal recessive disorder. Both the canine disease and its human counterparts are characterized by day-blindness and absence of retinal cone function in adults.[2] You will know that your dog has day-blindness when you notice him colliding with obstacles in daylight.
In humans, achromatopsia is characterized by reduced visual acuity, pendular nystagmus, increased sensitivity to light (photophobia), day blindness, reduced or complete loss of color discrimination. All individuals with achromatopsia (achromats) have impaired color discrimination along all three axes of color vision.
Achromatopsia is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once an at-risk sib is known to be unaffected, the risk of his/her being a carrier is 2/3. Heterozygotes (carriers) are asymptomatic. Carrier testing for family members at risk for CNGA3 or CNGB3 mutations is available on a clinical basis once the mutations have been identified.[1]
References
1. Susanne Kohl, MSc, PhD, Herbert Jägle, MD, Lindsay T Sharpe, MA, MA, PhD, Dhabil (med)
Bernd Wissinger, MSc, PhD, Achromatopsia, Jan. 2006, gentests.org
2. Sidjanin DJ, Lowe JK, McElwee JL, Milne BS, Phippen TM, Sargan DR, Aguirre GD, Acland GM, Ostrander EA. Canine CNGB3 mutations establish cone degeneration as orthologous to the human achromatopsia locus ACHM3. Hum Mol Genet. 2002 Aug 1;11(16):1823-33.
3. Hurn SD, Hardman C, Stanley RG. Day-blindness in three dogs: clinical and electroretinographic findings. Vet Ophthalmol. 2003 Jun;6(2):127-30.
4. Duska J. Sidjanin, Jennifer K. Lowe, John L. McElwee1, Bruce S. Milne, Taryn M. Phippen, David R. Sargan, Gustavo D. Aguirre1, Gregory M. Acland, and Elaine A. Ostrander. Canine CNGB3 mutations establish cone degeneration as orthologous to the human achromatopsia locus ACHM3. Human Molecular Genetics, 2002, Vol. 11, No. 16 1823-1833
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
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