Hyperuricosuria

What is hyperuricosuria?

Hyperuricosuria (HUU) is the excessive excretion of uric acid in the urine. This condition can cause the formation of stones in the bladder or kidneys (uroliths), which is uncomfortable and painful. The stones are difficult to treat and often require surgical removal. The condition can become life threatening in males if the urinary tract becomes blocked. Hyperuricosuria can occur in any breed, but is most commonly seen in Dalmatians, Bulldogs, and Black Russian Terriers.

Inherited as an autosomal recessive condition, a causative genetic mutation was identified at UC Davis in the laboratory of Dr. Danika Bannasch. A DNA test is available. Dogs that carry two copies of the mutation are susceptible to bladder/kidney stones. Dalmatians have two copies of the mutation, but “low uric acid” dogs derived from Dalmatian x Pointer backcrosses provide a means for breeders to reduce the incidence of the disease and maintain the breed characteristics.

What are the clinical signs of hyperuricosuria?

Clinical signs of HUU can include difficulty urinating, frequent urination, blood in the urine, and urinating in unusual places. Some affected dogs show no clinical signs.

How is hyperuricosuria diagnosed?

Hyperuricosuria can be diagnosed by ultrasound (urate stones are typically not visible on x-rays) or urine sediment analysis. The available DNA test may be used to differentiate between urate stones caused by hyperuricosuria and other conditions such as portosystemic shunts and hepatic microvascular dysplasia.

How is hyperuricosuria treated?

Small stones may be flushed out with a urinary catheter. The removal of larger stones often requires surgery. Affected dogs can be maintained on low purine diets to prevent the formation of stones. Increased water intake is also often recommended. The medication allopurinol may be prescribed in some cases.

What is the prognosis for hyperuricosuria?

The prognosis for HUU depends on the size and number of stones. Some affected dogs never show clinical signs, whereas others may require surgery to resolve obstructed urinary tracts.

How can hyperuricosuria be prevented?

Breeders can use DNA testing for the HUU mutation as a tool for selection of mating pairs to avoid producing affected dogs. Since HUU is inherited as an autosomal recessive disease, an affected dog receives one copy of the mutation from its mother and one copy from its father. Dogs with one copy of the HUU mutation are unaffected, but can pass the disease to their offspring. If two HUU carriers are bred to each other, there is a 25% chance of producing affected offspring.

Dietary management is essential to prevent stones in affected dogs that have previously shown clinical signs.

For more information:

UC Davis Veterinary Genetics Laboratory - Canine Hyperuricosuria genetic testing

Bannasch D, N Safra, A Young, N Karmi, RS Schaible and GV Ling. 2008. Mutations in the SLC2A9 Gene Cause Hyperuricosuria and Hyperuricemia in the Dog. PLoS Genetics 4(11): e1000246.

Karmi N, EA Brown, SS Hughes, B McLaughlin, CS Mellersh, V Biourge, and DL Bannasch. 2010. Estimated Frequency of the Canine Hyperuricosuria Mutation in Different Dog Breeds. J Vet Intern Med 24(6):1337–1342.

Karmi N, Safra N, Young A, Bannasch DL. 2010. Validation of a urine test and characterization of the putative genetic mutation for hyperuricosuria in Bulldogs and Black Russian Terriers. Am J Vet Res 71(8):909-914.

*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.