New Form of PRA - General Comments

1) As with most PRA the mode of inheritance is assumed to be autosomal recessive until proven otherwise. To date, we know that the parents of the affected dogs are not affected with PRA; also the dogs diagnosed with this new PRA are both male and female.

2) Remember with autosomal recessive mode of inheritance:
  • 16 unaffected pups would need to be produced from an unknown to a known carrier to have a high degree of confidence the unknown parent is a non-carrier.
  • 7 unaffected pups would need to be produced from an unknown to an affected to have a high degree of confidence the unknown parent is a non-carrier.

3) Looking back at our PWD history during the period of the discovery of prcd-PRA, a prominent stud dog from had produced 112 offspring (unknown to unknown) before producing an affected pup.

4) Carrier to carrier in theory produces 25% affected, 50% carrier, and 25% non-carrier. (The percentages in any affected litter might differ from statistical probabilities which are based on 1000 offspring.)

5) In the past our prcd-PRA was more widespread than JDCM and GM-1. JDCM/GM-1 affected pups did not live long enough to be bred but with the late onset prcd-PRA, some affected dogs were used for breeding before they became clinically symptomatic for PRA blindness.

6) Because this new form of PRA appears to be early in onset, most dogs should be detectable on an ECR/CERF exam if done yearly and just prior to breeding no earlier than age 2 years.

7) It is critical to the process of getting a genetic test for this new form of PRA to have as many dogs as possible (both companion and breeding dogs) examined by an ACVO vet for ECR/CERF exams.  CERF statistics for PWDs examined by ACVO vets for the past five years have bounced up and down. In 2007 the total number of PWDs was 1,414; 2008 it dropped to 1,358; 2009 there were only 735 and in 2010 it was way down to only 639 PWDs. In 2011 the number of dogs went back up to 1,262.  Please submit your forms to the ECR registry.

 
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