That is the 64,000 dollar question and since we have not cured human health issues yet I doubt we will cure dog issues much sooner. The diseases consist of a very complex DNA strains that run in the millions and a lot is how they match up. It is the great scientific mystery as to how or even what contributes to what and how.
Unless we get exact DNA test that would allow something to be eliminated it is and will remain a crap shoot. We test in the hopes of some devine revelation that will prevent that DNA strain from picking the wrong genes out of the millions it has to choose from.
I say that partly because in humans they have found 24 genes so far that contribute to DCM. Our gene pool is not big enough to sustain a healthy population if we could eliminate all dogs with even half those genes.