Though there is less definitive evidence that the following problems are inherited, they do tend to show up in certain breeds, including the Yorkshire terrier. Only retinal dysplasia might be reported to and followed by any of the disease registries.

Idiopathic Polyarthritis

Idiopathic simply means “of unknown origin.” Though most common in large dogs, this disorder is also frequently seen in Chihuahuas, toy poodles, and Yorkshire terriers. Idiopathic polyarthritis is characterized by stiffness or lameness, along with fever that does not respond to antibiotics, anorexia, and a general depression. These symptoms cycle from hardly noticeable to worsening and back again. A course of glucocorticoids given for several months usually provides effective control.

Hemorrhagic Gastroenteritis

Toy dogs are said to appear predisposed to this serious disorder. Formerly normal, healthy dogs, generally two to four years old, suddenly have an acute attack of bloody diarrhea and vomiting. Though nothing may have changed in daily routine or diet, the problem is thought to result from a hypersensitivity reaction.

Supportive treatment should be started immediately. Food and water are withheld while fluid therapy and antibiotics are given. When food is reintroduced, the diet should use a protein source new to the dog, mixed with rice. Most dogs respond well, though up to 15 percent have repeated episodes.

Color Dilution Alopecia

The Yorkshire terrier's blue-black color lies at the root of this condition. The DNA portion that changes black to blue, “coat color phenotype dd,” is also responsible for coat problems. Affected pups are born with normal coats, but they begin to show problems as they approach one year of age. They can develop follicular seborrhea (dandruff), folliculitis, and progressive hypotrichosis (less hair than normal) in the blue-coated areas.

Retinal Dysplasia

Several types of retinal dysplasia exist, but the one to which the Yorkshire terrier is susceptible is inherited as a recessive trait. This consists of incorrect development of the focal areas of the retina. Depending on the extent and placement of the malformation, there could be no symptoms or the dog could have impaired central vision.

Idiopathic Epilepsy

Though other breeds are more afflicted and show a more definite genetic component, the Yorkshire terrier also falls victim to epilepsy of unknown cause. Diagnosis consists of eliminating other possible causes of seizures. Treatment has improved greatly, and the prognosis is fairly good.