Had Gatsby's breeder had bloodwork done before breeding him to make sure he couldn't pass on any genetic condition to his offspring? Was everything normal then?   
As the others have said, at this point all you can do is wait to see what the necropsy said. Even if his sire did die of a genetic kidney condition, it doesn't mean Gatsby inherited it.    
Gatsby's been neutered, right? Never sired puppies himself?        |