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Cone Degeneration, Achromatopsia
Achromatosis relates to a deficiency of pigmentation in the tissues or lack of staining power in a cell or tissue. 2
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 condition referred to as achromatopsia, total color blindness, day-blindness or rod monochromacy has been extensively described. 4
Cones are light-sensitive structures in the vertebrate eye. They are found throughout retina and are concerned with discrimination of color and visual acuity. There are three types of cone cells each containing a different iodopsin and each giving maximum response when stimulated by the blue, green and red. A pigment defect in one or more of the types of cone cells can lead to color blindness.
Breeds Affected by Achromatopsia
Cone degeneration (CD) is an autosomal recessive canine disease that occurs naturally in the Alaskan Malamute
, Miniature Poodle
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.
Signs of Cone degeneration
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 normal throughout life. It is similar to human achromatopsia, a heterogeneous autosomal recessive disorder (caused by more than one factor). 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.
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
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Canine Eye Diseases and Vision Disorders
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