This should answer your question:
Shunts can be either congenital--a condition the animal was born with--or acquired--a condition that developed later in life. Congenital shunts are generally diagnosed in animals less than one year old.
Acquired shunts can occur at any age and are often caused by liver disease.
Refer to this link:
Yorkshire Terriers: Health issues in Yorkies Breeders should be aware of.