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Rod Cone Dysplasia Type 2 -PRA        rcd2-PRA Test      Code 106

For breeds: Collie

Background:  “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.

 

rcd2 mutation identified:  After many years of study at Cornell University by scientists in the laboratory of Drs. Greg Acland and Gus Aguirre, the mutation causing rcd2 was identified (1).  This work was supported prior to 2006  by the Morris Animal Foundation and also by continued contributions of the Collie Health Foundation.

 

OptiGen DNA Test for rcd2- PRA identifies dogs as being Normal, Carrier, or Affected with rcd2. The rcd2 DNA test requires special techniques compared to the other DNA tests that OptiGen offers, so it  typically takes 1-2 weeks longer to obtain rcd2 test results.  Blood samples, cheek swabs or semen samples are all acceptable sources of DNA for the rcd2 test.

 

Breeding recommendations:  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 two Carrier parents can show quite a variation from the expected results.

Expected results for breeding strategies using the OptiGen rcd2 test

Parent 1

Status

Parent 2 Status

Normal/Clear

Carrier

Affected

Normal/Clear

All = Normal/Clear

1/2 = Normal/Clear

1/2 = Carrier

All = Carrier

Carrier

1/2 = Normal/Clear

1/2 = Carrier

1/4 = Normal/Clear

1/2 = Carrier

1/4 = Affected

1/2 = Carrier

1/2 = Affected

Affected

All = Carrier

1/2 = Carrier

1/2 = Affected

All = Affected


 

Benefits & Limits to All Genetic Testing: Many Collie breeders already make use of OptiGen’s services to test their dogs for Collie Eye Anomaly (CEA), and so they are aware of the great advantage that genetic testing offers. With informed breeding practices, breeders can immediately avoid producing dogs that are affected with specific diseases. Since genetic testing can be done at any age, each dog’s genetic status can be known even before clinical disease signs are recognized. Over several generations of selection away from the disease gene, breeders can eliminate a disease gene completely from their line.

BUT, there are basic limits for all genetic tests. Any DNA test is only able to identify a specific change in DNA (e.g. a mutation) that is being tested. For example, the rcd2 DNA test detects one specific mutation in the RD3 gene and the CEA test detects a specific mutation in a different gene.  Both mutations cause eye diseases but the DNA tests can only detect the specific type of mutation for which it is designed.  The rcd2 test will not identify any other forms of PRA that may occur.  At this point we are not aware of other forms of PRA that occur in the Collie but many breeds do have multiple types of PRA to contend with and this is a possibility in any breed.

Collies already tested for CEA by OptiGen: OptiGen may be able to do the rcd2 test on samples that previously were sent for another test (e.g. for CEA testing or Long Term Storage). OptiGen retained many frozen samples that were previously submitted, and these may be available for rcd2 testing. You may order the rcd2 test online on a stored sample.

 References:

1. Kukekova AV, Goldstein O, Johnson JL, Richardson MA, Pearse-Kelling SE, Swaroop A, Friedman JS, Aguirre GD, Acland GM. 2009. Canine RD3 mutation establishes rod-cone dysplasia type 2 (rcd2) as ortholog of human and murine rd3. Mamm. Genome 20 (2):109-123.


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Tel: 607 257 0301 · Fax: 607 257 0353 · email: genetest@optigen.com or optigen@clarityconnect.com
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