Yorkshire terriers have almost a 36 times greater risk of developing shunts than all other breeds combined. This is a leading doctor in the livershunt disease. I know a fellow yorkie owner who flew to Tennessee to see Dr Tobias. She is the best and specializes in this disease. here is the site. Lots of good info
http://www.vet.utk.edu/clinical/sacs/shunt/faq.shtml
Good luck!