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.