For breeders, here's a very interesting site that tells which congenital defects purebreeds are known to have. Although, the Yorkie line seems to have its share of problems I really thought it would be higher than it is. Poodles have a lot more listed under their category.
To use the site, scroll down to breed listings, find the breed your interested in, it will list those defects prone to that breed, then scroll down and read what each default is.
http://www.webhometown.com/mr/dog_gen.html