Canine Hyperuricosuria (HUU)

URIC ACID EXCRETION/ CANINE HYPERURICOSURIA/ HUU

This is a problem which has recently been discovered in the HWV.  Affected dogs excrete uric acid which can lead to the formation of urinary calculi (stones) which sometimes require surgery to remove.  

A gene mutation has been found to cause this which has a recessive mode of inheritance.  This means that both of the pair of genes the dog has have to be the mutated gene to be affected by the disorder.   DNA testing can classify dogs as either clear (not carry the mutated gene at all), a carrier (carry one copy of the mutated gene) or affected (carry two copies of the mutated gene).  It should be noted that not all dogs who are genetically “affected” will become affected by the problem.   Neither clear or carrier dogs will develop the disorder.

When dogs are mated each parent passes on one copy of the gene to form a pair with the gene passed on from the other parent.  Clear dogs cannot pass on the mutated gene so none of their progeny will be affected.  Carrier dogs pass on the mutated gene in an average of 50% of cases and affected dogs will pass on the mutated gene 100% of the time.

Therefore on average the matings below will produce puppies in the proportion:

Clear x Clear = 100% Clear
Clear x Carrier = 50% Carrier, 50% Clear
Clear x Affected = 100% Carrier
Carrier x Carrier = 25% Clear, 50% Carrier, 25% Affected
Carrier x Affected = 50% Carrier, 50% Affected
Affected x Affected = 100% Affected

Key points to note:

• The Kennel Club has now (2017) recognised the condition in HWV so any HWV who are tested through a recognised laboratory will have their status logged against them on their KC records, just like hip scoring.
• The only genetic status with the potential to have clinical problems is “affected”.  Neither “clear” or “carrier” dogs will ever develop this particular condition although any dog could go on to produce stones for other reasons.
• Not all HWV who have an “affected” genetic status will become clinically affected by the problem.  Any dogs known as genetically “affected” can be monitored more closely for signs of a problem.
• HWV of any genetic status can safely be used in breeding programs.  As long as one parent is genetically “clear” there is no risk of producing puppies who will be affected.  The other parent can safely be “affected”, “carrier” of “clear”.
• Whilst there are still a high number of “affected” and “carrier” dogs in the gene pool, for the sake of genetic diversity it would be wise to still use these dogs within breeding programs.
• Symptoms of urate stones revolve around difficulty or discomfort urinating, frequent urination or leakage and blood in urine although many dogs have no symptoms at all.
• Treatment of stones often involves a change to a low purine diet and an increase in fluid intake, however, stubborn stones may require more aggressive treatment/surgery.  Dogs who are prone to forming stones can usually be managed with a special low purine diet.  Always be guided by your veterinarian.

We very much hope that everyone involved in breeding the HWV will join us in trying to eradicate the problem and testing so they can employ informed mating decisions.