i thought it was the genes that did not communicate with each other, the genes that dictate the size of the brain are from one type of dog and the genes that dictate the skull size from a different type of dog and they dont speak the same language, the skull size is from a lap dog, and the brain size from a toy spaniel (or similair) when they were first breed. Bruxilles griffons are also bred from toy spaniels and share the same problems. so depending on your cavs original ancestors, if they have toy spaniel genes for brain size and skull size they wont have any problem and will be larger dogs, if they have lap dog genes for skull size and brain size they will also be ok. I assume by now there are so many variations and such a mixture thats why there is a variation in size from 5kg to 16 kg.
As for why some dogs with cm has syptoms and other dont, i put that down to the actual difference in brain size and skull size from a slight variation to a vast difference making the malforation larger, i assume a larger malforation allows more fluid into the spine canal which causes problems before i starts to pool and make shrinxes. This is what ive come to assume reading from animal trust sites. di
What's the difference between a new husband and a new dog? After a year, the dog is still excited to see you.