TEST for rod-cone dysplasia type 2 (rcd2) in Collies
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.
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 and a manuscript describing the finding has been submitted for publication (Kukekova, Goldstein et al., 2008). This work was supported prior to 2006 by the Morris Animal Foundation and also by continued contributions of the Collie Health Foundation. The rcd2 DNA test (patent pending) is able to identify with complete accuracy whether a dog has no copy (is Normal), has 1 copy (is a Carrier) or has 2 copies of the mutation (is Affected).
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.
OptiGen DNA Test for rcd2/Collie PRA: A patent for rcd2 is pending and owned by Cornell University which granted OptiGen permanent and exclusive licensing rights to make the test immediately available to the public. The rcd2 DNA test will identify 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.
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 rcd2 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.
Ordering the rcd2 Test: The rcd2 test is done on a small sample of blood obtained by your veterinarian or on a cheek swab or semen sample. Please read the paragraphs below, and then read "Instructions and Information" to learn about ordering a test, shipping a sample and prices.
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. We hope this will help owners to obtain the new rcd2 test more easily. You may order the rcd2 test online on a stored sample. If the frozen sample is still available at OptiGen we will run the test on that. If an insufficient frozen sample remains to run the rcd2 test, we will contact you to request a new sample. Link to "Order Test” and complete the order form as usual. Be sure to indicate that this dog's sample is already at OptiGen by selecting "Blood sample is already at OptiGen under a long-term storage agreement." Mark this choice even if you did not specifically pay for Long-Term Storage.
Multiple Tests for Collies not tested previously by OptiGen: There is a discounted price for ordering multiple tests on one sample (rcd2 and CEA). See the price list for current pricing.
Note: A manuscript describing the rcd2 mutation and its physiological significance has been submitted (Kukekova et al.). A patent for these tests is pending and owned by
Page last updated October 29, 2008
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