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| Collie Eye Anomaly |
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What is Collie Eye Anomaly (CEA)?
CEA is a disorder of the deep structures of the eye that affects collie breeds around the world. The four main changes are:
• Inadequate development of the choroids, a thin layer of blood vessels that delivers oxygen and nutrients to the retina (called hypoplasia of the choroids or chorioretinal dysplasia);
• Coloboma - a cleft or defect of the optic disc or adjacent areas;
• Staphyloma - an area of thinning in the sclera which is adjacent to the choroids; and
• Retinal detachment with or without hemorrhage - a complication associated with the other defects.
The CEA/CH genetic test provides the life-long genetic status of a dog for this disease. In conjunction with genetic testing, an eye exam by a veterinary ophthalmologist is recommended before 8-9 weeks of age, with annual eye exams thereafter. The eye exam will give you information about mild versus severe CEA/CH disease among affected dogs. Annual eye exams are always recommended for all dogs of all breeds. Clinical exams detect a wide variety of eye problems, both genetic and non-genetic.
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Expected Results of Breeding Strategies for Inherited Recessive Diseases
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Parent 1
Genotype
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Parent 2 Genotype
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Normal
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Carrier
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Affected
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Normal
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All = Normal
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1/2 = Normal
1/2 = Carriers
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All = Carriers
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Carrier
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1/2 = Normal
1/2 = Carriers
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1/4 = Normal
1/2 = Carriers
1/4 = Affected
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1/2 = Carriers
1/2 = Affected
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Affected
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All = Carriers
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1/2 = Carriers
1/2 = Affected
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All = Affected
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The table shows the desirable breedings (gray-shaded boxes) which have at least one parent that is Normal by the OptiGen CEA/CH test. All other breedings are at risk of producing pups affected with CEA/CH.
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PRA (Progressive Retinal Atrophy)
Rcd2 Background of Disease: “Collie PRA”, or rod-cone dysplasia type 2 (rcd2), is a form of retinal degeneration that has been a health concern in rough and smooth collies for decades. In this disease, an abnormal development (dysplasia) of the rods and cones (the light sensitive cells in the eye) leads to an early onset of night blindness that is typically apparent by the time pups are 6 weeks of age. In most cases, the rcd2-Affected dog is completely blind by the time it is 1 year old.
Inheritance of rcd2: Collie breeders and researchers knew for many years that Collie PRA/rcd2 is inherited in an autosomal recessive manner. In order for disease to occur, two copies of the mutation must be present. Carriers do not show disease but are able to pass the disease on to offspring. The table below shows the predicted outcome of different matings when the rcd2 status of each parent is known. It should be kept in mind that these predictions are statistical in nature. A Carrier will pass the mutation on to half of its offspring on average. The larger the population that one examines, the more closely the predicted outcome will fit the actual outcome. A single litter of pups (a small population) produced by a Carrier parent can show quite a variation from the expected results.
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Expected results for breeding strategies using the OptiGen rcd2 test
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Parent 1
Status
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Parent 2 Status
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Normal/Clear
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Carrier
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Affected
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Normal/Clear
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All = Normal/Clear
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1/2 = Normal/Clear
1/2 = Carrier
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All = Carrier
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Carrier
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1/2 = Normal/Clear
1/2 = Carrier
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1/4 = Normal/Clear
1/2 = Carrier
1/4 = Affected
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1/2 = Carrier
1/2 = Affected
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Affected
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All = Carrier
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1/2 = Carrier
1/2 = Affected
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All = Affected
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