Cystinuria is a condition where a very specific type of bladder stone – cystine stones – are formed. These stones can cause blockage, which is a life-threatening emergency that needs immediate veterinary care.
Cystinuria means “cystine in the urine.” Cystine is an amino acid, which are the building blocks of proteins, and thus necessary to the body. When the kidney filters substances out of the blood to make urine, cystine, as well as all other amino acids, are reabsorbed from the urine back into the blood. This reabsorption doesn’t happen in those afflicted with cystinuria, so the cystine, as well as three other amino acids—ornithine, lysine, and arginine, the four of which are referred to as COLA—build up in the urine. For the other amino acids, nothing comes of this, but with cystine, crystals can form. The crystals can form stones that can lodge anywhere in the urinary tract but commonly end up in the bladder in dogs. These stones can cause urinary blockage, which is a life-threatening condition if left untreated.
Cystinuria has been diagnosed in more than 92 dog breeds, as well as mixed breeds, according to the Urolith Center at the University of Minnesota, which maintains a database of the stones it analyzes. It accounts for about 1% of stones submitted to the Center, yet in Deerhounds, 90% (nine out of ten) of the samples submitted for the breed in 2009-2010 were cystine, by far the largest percentage in any breed of dog (“Recent Shifts in the Global Proportions of Canine Uroliths,” by J. P. Lulich, C. A. Osborne, H. Albasan, L. A. Koehler, L. M. Ulrich, and C. Lekcharoensuk. Veterinary Record, April 6, 2013).
In Deerhounds, only intact adult male Deerhounds appear to be affected by cystinuria. It is uncommon for young Deerhounds to have a urinary obstruction: although dogs as young as two years of age have blocked, usually it is dogs between the ages of four and eight that become symptomatic, and dogs as old as ten have formed stones. With such a late age of onset, this means that stone formers may have been bred before it is known they have this disease.
No one is exactly sure why it is that only intact adult males are affected. It is assumed that testosterone plays a role, but exactly what the role is has not yet been discovered. One positive aspect of this is that neutering appears to prevent stone formation, so can be used on cystinuric Deerhounds to prevent a recurrence. This is a huge step forward, because historically dietary management did little to prevent stones from forming in dogs with that tendency.
There is a urinary screening test for cystinuria, called the Nitroprusside (NP) test, which is run by the University of Pennsylvania, but the testing results from Deerhounds are not straightforward. Some dogs initially test negative, only to test positive or form stones in subsequent years. Some dogs test positive, yet never seem to have a problem. A couple of dogs have tested negative shortly after cystine crystals were found in their urine during a routine urinalysis. According to the most recent SDCA health survey, approximately 30% of male dogs test positive, and approximately 80% of the dogs that test positive will go on to form stones, so the test can help owners identify some dogs that are at risk of forming stones. Yet without a good understanding of the causes of the variable test results, breeders are at a loss as to how to use the test when making breeding decisions. Stone formers should be neutered to prevent a recurrence, but with 30% of dogs testing positive, there is concern that the gene pool is going to be adversely affected if all dogs with a positive test are eliminated as breeding stock. However, owners of intact male Deerhounds are encouraged to NP test their dogs to help the cystinuria research at Penn.
Currently, it is recommended that you observe your intact male dog a couple of times a day, every day, to make sure that he is peeing normally. Any sign of an infection should be checked out promptly, and if there is any change in behavior or other sign that your dog is blocked or having trouble urinating, call your veterinarian immediately or go to an emergency clinic if it’s after hours, as this is an emergency situation that cannot wait.