What is Cystinuria?

Cystine is an amino acid and an end product of the protein metabolism. Normally it is absorbed in the small intestine after being filtered through the kidneys and reabsorbed into the blood stream.

In dogs with cystinuria the tubules in the kidney fail to reabsorb cystine and it is passed into the urine.

The excess of cystine in the urine can then lead to the formation of crystals or stones in the bladder, kidneys or ureters.

Which dogs are affected?

Cystinuria is an autosomal recessive inherited disorder. In other words both sexes can pass it on and in order to pass on the disease the dog has to have inherited two mutant genes ie one from each parent.

A dog inheriting one normal gene and one mutant will be a carrier of the disease but will not show any symptoms itself. Carriers will however pass the mutant gene on to any offspring.

Other breeds can and do get cystinuria however Newfoundland dogs seem to show symptoms much earlier than other breeds and as young as 5 months of age in some cases. Newfoundlands appear to be affected by a more severe form of the disease than other breeds.

Male and females are both affected by this disease however due to the fact that males have longer and narrower urethras, they are more likely to be affected more quickly and more severely than females.

What are the signs and symptons?

• Repeated urinary tract infections.
• Blood stained urine – haematuria.
• The presence of crystals in the urine.
• Urinary retention – the dog is trying to pass urine but is unable to do so. THIS IS A VETERINARY EMERGENCY AND REQUIRES IMMEDIATE ATTENTION. In extreme cases of urinary retention the bladder can rupture. There is also the danger that urine will back up from the bladder into the kidneys causing kidney failure.
• There may be a characteristic rotten eggs smell to the urine of an affected dog. This is due to the fact that cystine is the chief sulphur containing compound of the protein molecule.

What can be done to prevent passing this on to future generations?

There is a breed specific DNA test for Newfoundlands. The test will show whether the dog is clear, affected or a carrier.

The test requires a buccal [mouth] swab and takes approximately ten days to complete.

Testing kits are available from Veterinary Diagnostics Centre from www.vetdnacenter.com. The price for the test is quoted in American dollars per sample.

You can also get testing done by Genomia Laboratories. The cost for using Genomia is per one test or five or more samples for a reduced rate per test. Results are ready in a week. Contact www.genomia.cz.

It is strongly recommended that ALL breeding stock is tested before mating.

Cystinuria does affect other breeds and in particular Mastiffs. However, the abnormal gene found in Newfoundlands is normal in Mastiffs. Therefore there is another abnormal gene causing cystinura in Mastiffs and it has yet to be discovered.

What can be done if a dog already has the condition?

The condition can be diagnosed with a nitroprusside urine spot test. This test requires a small amount of the dog's urine and it can accurately identify a cystinuric dog. Your Vet will most likely use this test for diagnostic purposes.

A special low protein diet will be prescribed by the vet and regular monitoring of the dog’s condition will be required. The dog will need to be regularly monitored for urinary tract infections and for any signs of urinary retention. It is possible to remove crystals and stones from the bladder surgically but they tend to form again.