They've got their knickers in a twist over at the Stop the BBC Making Another PDE Facebook site over something I said when I was being interviewed by Victoria Stilwell last week.
But of course they're wrong. What I pointed out in the podcast was that there are different forms of PRA in different breeds, caused by different mutations. There's cord1 (found in some Dachshunds and English Springers), prcd (found in a lot of breeds, including Cocker Spaniels, Golden Retrievers, Labradors and Tollers), rcd1 (Irish Setters), rcd2 (Smooth and Rough Collies), rcd3 (Welsh Corgi), rcd4 (Gordon + Irish Setters),Type A (Miniature Schnauzer) and X-linked (Samoyed).
All these mutations are recessive, meaning that both parents must carry and pass on the mutation to their puppies for the pups to be affected.
Obviously, if you mate a Golden Retriever with a Labrador, there's a risk to the resulting pups.
But you can mate two carriers (or even affecteds) of two different breeds that don't carry the same form of PRA - eg a Springer to a Cocker - and the pups will not be affected (although of course could be carriers so one would have to test for both mutations if you breed on).
The only exception to this is with a dominant form of PRA found in Bullmastiffs and Mastiffs.
So thank you for the suggestion that I talk to Optigen. Of course I have - and to the Animal Health Trust which has found so many of the other PRA mutations (and is still working on others).