This is a very interesting thread.
The other day, having time on my hands, I searched for information about my cav's relatives. What I found is distressing. My cav has SM.
One of his litter mates is a successful show dog and is the father of other successful show dogs being used as studs by their proud owners. There are probably show quality bitches being bred as well.
Websites seldom show MRI results along with other health test results.
Hopefully his litter mate does not have SM.
Charlie's breeder was made aware of his condition when I sought information about his SM and how to take care of him. She doesn't MRI her dogs but I was expected to provide a copy of Charlie's MRI proving he is affected. He was not MRI'd. This probably means Charlie doesn't have SM to his breeder. And so it goes.