Cystinuria is an inherited disorder caused by a defective transport of the amino acid cystine in the kidney tubules. Normally, cystine is filtered in the kidney and reabsorbed within the tubules, resulting in little cystine in the urine. Dogs with Cystinuria do not properly reabsorb the cystine (and a few other amino acids) in the kidney tubules, causing the urine to contain abnormally high levels of cystine. Cystine is insoluble in neutral pH or acidic urine, so excess urinary cystine results in the formation of crystals, which in turn can lead to formation of cystine calculi (stones) in the kidney and/or the bladder.
Dogs suffering from Cystinuria suffer repeated urinary tract inflammations, and are at risk for urinary blockage, which can, if not treated promptly, lead to kidney failure, bladder rupture, and death.
The average age of onset of clinical signs attributable to Cystinuria is about 4.8 years, but in Newfoundlands, signs appear as early as 6 months to 1 year, suggesting that Newfoundlands suffer from a more severe form of the disorder than other breeds.
Treatment of the Disease
Cystinuria in humans and dogs is generally treated with compounds that bind cystine and prevent crystal formation. The two most common drugs of choice are 2-mercaptopropionylglycine (MPG) and D-penicillamine. Little information is available on effective dosages for Newfoundlands, however, at least one study indicated that affected Newfoundlands require higher dosages of MPG than other dogs with Cystinuria. D-penicillamine was found to be of minimal benefit in reducing cystine calculi. This may relate to the fact that Newfoundlands suffer from a more severe form of the disorder than other breeds. Treatment with MPG can, in some cases, result in dissolution of cystine calculi, therefore eliminating the need for surgical removal of the stones. Unfortunately, some Newfoundlands are poorly responsive to medical treatment, suffering from recurring bouts of urinary dysfunction, and, oftentimes, requiring surgery to resolve urinary calculi