Canine hyperuricosuria (HUU)

When levels of uric acid in the urine are too high (hyperuricosuria, or HUU), dogs can become prone to the formation of bladder and kidney stones, which can also lead to urinary blockages in male dogs. 

HUU is caused by a failure to properly break down and excrete chemicals called purines. Normally, when purines are broken down, they form a harmless waste product called allantoin. Dogs with HUU produce uric acid when they metabolize purines. Excess uric acid forms urate stones in the bladder (and sometimes in the kidneys), leading to bladder irritation or blockage. 

Urate stones

Urate stones are minerals that solidify in the bladder. They can be small and sandy, more gravel-like, or even form as a larger, single stone. Urate stones are more common in male dogs than females, likely due to differences in anatomy.

Signs of Urate Stones

HUU itself does not cause problems, but the resulting bladder stones can be deadly. These stones may rub against the walls of the bladder, leading to inflammation or cystitis.   Common signs of cystitis include frequent urination, urinating in abnormal locations, blood in the urine, straining to urinate, and recurrent bacterial infections. The stone may also get lodged in the urethra preventing urine from passing through. When there is a blockage, additional signs include lethargy, pain, vomiting, and failure to eat. 

Urinary blockage is a medical emergency and dogs who are blocked should be evaluated by a veterinarian immediately. The blockage can lead to increased levels of potassium and other metabolic waste in the blood, kidney damage, and within days, death. A total obstruction of the urethra is fatal if not treated promptly.

Treatment of Urate Stones

Treatment involves removing the urate stones from the urethra. This can be done by attempting to flush the stones back into the bladder with a catheter (known as urohydropropulsion). There they can either be removed surgically (cystotomy), or broken up with lithotripsy (breaking down stones with ultrasonic waves or lasers). Dogs which have a urethral obstruction that cannot be unblocked or are recurrent stone formers may require surgery to form a new permanent opening to the urethra (scrotal urethrostomy).

Prevention of Urate Stones

Dogs with a history of bladder stones will need routine monitoring, including urine tests and x-rays of the bladder. They may be placed on a therapeutic diet to help prevent future stone formation. Increasing a dog’s water intake may also help keep their urine dilute and reduce the risk of stones. 

HUU is an autosomal recessive condition, meaning that a dog needs to inherit two copies of the mutation for the condition to be expressed. This would result when both parents are either carriers or affected. Unaffected dogs who are carriers can produce affected puppies.

Breeds at Risk

This condition is common in Dalmatians, Bulldogs and Black Russian Terriers, although any dog can develop HUU.

All Dalmatians are considered homozygous, meaning they have two copies of the mutation that causes HUU. HUU has become fixed in the population and all Dalmatians will be at risk for the formation of urate stones. Backcrossing Dalmatians with Pointers has allowed for the production of dogs with the Dalmatian appearance who are clear or carriers for HUU (sometimes referred to as LUA, or Low Uric Acid Dalmatians). As of 2011, backcrossed/LUA Dalmatians are allowed to be registered with the AKC and entered into their stud books.

Resources

VCA: Urate Bladder Stones in Dogs

Genetic Welfare Problems of Companion Animals: Dalmatian Hyperuricosuria (HUU)

VIN: The Genetic & Molecular Basis of Urate Calculi Formation in Dalmatians

Bannasch, D., Safra, N., Young, A., Karmi, N., Schaible, R. S., & Ling, G. V. (2008). Mutations in the SLC2A9 gene cause hyperuricosuria and hyperuricemia in the dog. PLoS genetics, 4(11), e1000246.

Karmi, N., Brown, E. A., Hughes, S. S., McLaughlin, B., Mellersh, C. S., Biourge, V., & Bannasch, D. L. (2010). Estimated frequency of the canine hyperuricosuria mutation in different dog breeds. Journal of veterinary internal medicine, 24(6), 1337-1342.