What is cystinuria?

Cystinuria is a genetic defect in the kidney tubules. Normal kidneys filter the amino acid cystine and do not allow it to go into the urine. In dogs with cystinuria, this filtering action fails, and cystine passes into the urine, where it can form crystals and/or stones (uroliths). If stones form, they can block the urethra and obstruct urinary flow, especially in males.

Are dogs born with cystinuria?

Dogs who have this defect are born with it, although it can take years to cause symptoms - or never cause any.

Do all dogs with cystinuria form stones?

No. According to the Textbook of Internal Veterinary Medicine, "Not all cystinuric dogs form uroliths; therefore, cystinuria is a predisposing rather than a primary cause of cystine urolith formation. In a study of five generations of offspring from one Scottish terrier, only one of six cystinuric males formed uroliths."

Do females get cystinuria?

Yes, but in most breeds it's much more common in males. Some breeds, such as Scottish Deerhounds, have yet to identify even one female who has it, whereas in the Newfoundland, it is common in both males and females.

Is there a genetic test for cystinuria?

At this time, there is a DNA test available for cystinuria only in Newfoundlands and Labrador Retrievers.

What is the mode of inheritance?

In Newfoundlands and Labrador Retrievers, cystinuria is an autosomal recessive trait. In other breeds, the mode of inheritance is unknown, and in most breeds does not appear to be autosomal recessive. Research is ongoing at the University of Pennsylvania to discover the mode of inheritance in, and develop genetic tests for, cystinuria in other breeds. More info here.

Can cystinuria be controlled by diet, supplements, or medications?

Although a reduced-protein diet is usually prescribed for this condition, the actual experiences of people who have attempted to prevent stone formation with diet have not been positive. And while it is hard for cystine stones to form in alkaline urine (dog urine is normally acidic), maintaining a constant alkaline urine with diet or supplements is difficult, and can lead to the formation of other types of stone. Furthermore, since cystine stones do not dissolve in alkaline urine, if the urine goes into acidity even briefly, stones can form and will not dissolve just because alakaline urine is achieved shortly thereafter. Most of us with dogs with cystinuria have had bad experiences and poor outcomes from relying on diet and supplementation to prevent stone formation in our stone-forming dogs.

The use of medications has been more successful. The drug Thiola is effective in preventing stone formation in many dogs, with few reported side effects. In fact, the single most frequently reported "side effect" is the depletion of the owner's bank account, especially for owners of large or giant breed dogs. Thiola is also an "orphan drug," and can be hard to obtain. Information on getting thiola is available from the FDA.

There is another drug that is easier to obtain and somewhat less expensive, cupramine (d-Penicillamine). This drug is associated with more side effects, but if your dog tolerates it, it might be a better choice.

Is there anything else I can do?

Although it seems very extreme to some, many of us with cystinuric, stone-forming male dogs have had a procedure done on them called a "scrotal urethrostomy." In a nutshell, this is a surgery that redirects the dog's urethra away from the penis and out a new, surgically-created opening in front of the scrotum. This enables male dogs to more easily pass small stones, and can help prevent urinary blockage, the main risk from this condition. While it's not impossible they will still obstruct, it reduces the chances substantially. This surgery is not to be undertaken lightly, however. More info on diet, supplements, medication, and surgical options here.

Will this condition shorten my dog's life?

If your dog does not die of complications of his cystinuria, such as obstruction, recurrent infections, or surgical complications, no. Many dogs, including stone formers and those who have had serious health problems when their condition was first diagnosed, have lived not just normal but longer-than-normal lives.

For more in depth discussion of these issues, follow the indicated links within the FAQ, or join the Canine Cystinuria email list and review the archives, which contain lots of information from a personal perspectives of many dog owners. Also, an additional "Frequently Asked Questions" section is available on the website of the Mastiff Club of America, with general as well as breed-specific information.