Well, it's all good to say that a genetic component must be there, but no one really knows for sure. We all believe there is a genetic component, but none has ever been identified; it just seems to be what makes the most sense given the evidence. But we don't know if it's really there or how it actually works.
Just me, perhaps, but I think it is interesting to note that there was almost no HD in Golden Retrievers before the advent of commercial dog food in the depression and WWII years. Prior to that, it was almost unheard of in the breed. Undiagnosed maybe? No one knows. But the rate of HD appearance skyrocketed in the late 40s and early 50s, and seemed to reach a high in the 80s, which tracks the use of commercial dog food. Now, we have no more evidence for that than we do a genetic component, but it's an interesting correlation. (Correlation does not necessarily mean causation, though.) It's also noteworthy that dogs raised on better quality food seem to have a lower rate of HD, though that too is hard to say for sure because there have been no studies done on that.
I think Julie is probably right about a combination of some sort of genetic predisposition combined with some sort of environmental trigger being the most likely cause. But we still don't really know. What's taken as conventional wisdom is just that; it's not science.
The fact that we don't seem to be able to breed it out altogether implies a genetic factor. That makes sense. It may be that whatever set of genes makes a Golden a Golden also gives some level of predisposition for HD. Otherwise, you'd think we'd have been able to breed it virtually out, by now. So, my own guess is that all
Golden Retrievers, no matter how carefully bred, have some predisposition for HD, because my own belief is that HD is linked to the essence of what makes a Golden Retriever. But again, that's just my belief. The truth is that we all have beliefs, but no one really knows for sure. Yet.
Edited to add: Oops. Sorry, I didn't mean to hijack the thread. I just got carried away.