Quick Summary
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Phenotype: Affected dogs typically begin to show vision deficits in low light (night blindness) as early as 6 weeks of age and can be completely blind by 6-8 months. Ophthalmoscopic abnormalities, such as excessively shiny tapetal appearance (tapetal hyperreflectivity), reduced retinal vascularization and pale optic nerve, can be found around 3-4 months of age.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, RCD2 = Rod-cone dysplasia type 2
Breeds appropriate for testing: Collie, Smooth Collie, Rough Collie, Old-Time Scotch Collie
Explanation of results:
• Dogs with N/N genotype are expected to not have rod-cone dysplasia type 2 (rcd2). They cannot transmit this RCD2 allele to any of their offspring.
• Dogs with N/RCD2 genotype have one copy of this RCD2 allele and are expected to not have rod-cone dysplasia type 2 (rcd2) but are carriers. They will transmit this RCD2 allele to 50% of their offspring. Matings between two carriers of RCD2 may, on average, produce 25% of puppies with rod-cone dysplasia type 2 (rcd2).
• Dogs with RCD2/RCD2 genotypes are homozygous for this RCD2 allele and will display signs of rod-cone dysplasia type 2 (rcd2).
Sample Collection
Dog DNA tests are carried out using cells brushed from your dog's cheeks and gums. Only VGL-provided cytology brushes are accepted for this test. Brushes will be sent to you by mail for no additional charge.
We recommend waiting until puppies are at least three weeks old before testing.
Step-By-Step:
- Make sure the dog has not had anything to eat or drink for at least 1 hour prior to collecting sample.
- When swabbing puppies, isolate each puppy from the mother, littermates and any shared toys for 1 hour prior to swabbing. Puppies should not have nursed or eaten for 1 hour prior to collecting sample.
- If collecting samples from more than one dog, make sure to sample one dog at a time and wash your hands before swabbing another dog.
- Label brush sleeve with name or ID of dog to be sampled.
- Open brush sleeve by arrow and remove one brush by its handle.
- Place bristle head between the dog’s gums and cheek and press lightly on the outside of the cheek while rubbing or rotating the brush back and forth for 15 seconds.
- Wave the brush in the air for 20 seconds to air dry.
- Insert brush back into sleeve.
- Repeat steps 5 - 8 for each unused brush in sleeve on a fresh area of cheek and gums. Make sure to use and return all 6 brushes sent by the VGL.
- Do not seal brushes in sleeve.
- Place all samples in an envelope and return to the address provided.
ATTENTION:
- Do not collect saliva/drool – the key to obtaining a good sample is getting cheek cells on the swab
- Do not rub swab on the dog’s tongue or teeth – this will result in poor quality sample
- Do not collect a sample from a puppy that has recently nursed – the mother’s genetic material can rub off on the puppy’s mouth and contaminate the sample
Rod-cone dysplasia type 2 (rcd2) is a type of early-onset retinal degeneration found in collie breeds. Affected dogs typically display vision deficit in low light (commonly referred to as night blindness) as early as 6 weeks of age. Degeneration of the retina progresses over the next few months, resulting in functional blindness at around 6-8 months of age. Ophthalmoscopic abnormalities such as excessively shiny tapetal appearance (tapetal hyperreflectivity), reduced retinal vascularization, and pale optic nerve, can be seen around 3-4 months of age.
This disorder is caused by an insertion in the retinal degeneration 3 gene (RD3) and inherited as an autosomal recessive trait, meaning that two copies of the RCD2 allele must be present for the dog to develop disease.
Testing recommendations: DNA testing for rod-cone dysplasia type 2 can determine the genetic status of dogs. Dogs with one copy of the RCD2 variant are normal but are carriers. Matings between two carrier dogs may, on average, produce 25% of puppies with rod-cone dysplasia type 2.