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.

In male Mastiff, Continental, English, French and Olde English Bulldogs, we test for the marker which has strong association with the occurrence of Cystinuria. Only intact males which are tested homozygous for the marker are known to show symptoms of the disease. Females are not known to show symptoms. Due to high occurrence of the disease it is not recommended to remove carriers from breeding to avoid compromising the gene pool, but carrier should only be bred with clear animals. In affected dogs which are showing symptoms of the disease, castration can alleviate symptoms.

Cystinuria is a well-known hereditary metabolic disorder that leads to the formation of urinary stones and urinary obstruction. It has now been described in over 70 breeds. New studies have shown that this disease is very heterogeneous in terms of inheritance, mutation, frequency, severity, treatment and symptoms. A distinction is now made between the following subtypes of cystinuria affecting the different breeds:

The designation of type I cystinuria is used when the disease shows autosomal recessive inheritance, Type II when inheritance is autosomal dominant, and Type III for sex-limited/androgen-dependent inheritance (PH, UG, unpublished data). Additional types can be assigned if found. Specific mutations within each type should lead to phenotypes that are sufficiently similar that the same medical management and breeding advice applies to all cases within that type. Involvement of the SLC3A1 gene is indicated by adding - A, and similarly addendum of - B indicated involvement of mutations in SLC7A9.

• Newfoundland, Landseer, Labrador: Type I -A - autosomal recessive inheritance
• Miniature Pinscher: Type II - B - autosomal dominant inheritance
• Australian Cattle Dog: Type II - A - dominant inheritance
• Mastiff, Bulldogs, Kromfohrländer and Irish Terrier: Type III - androgen-dependent expression.

The type III genetic test is currently available for the variant which is known to be associated with symptoms of the disease in the Mastiff, Continental, English, French and Olde English Bulldog breeds since December 2016, however, there is currently no test available for Kromfohrländer and Irish Terrier. We test for a marker which is strongly associated with the occurrence of cystinuria. Type III Cystinuria affects only intact male dogs which have two copies of the cystinuria marker (cy/cy). Castration can alleviate the symptoms. Bitches do not show any symptoms but pass on the mutation to offspring.

Prevalence: between 8 and 16% of the dogs are genetically affected, while the carrier rate is between 32 and 50%. Targeted breeding reduces the frequency of the marker associated with the disease and is therefore desirable. Due to the high frequency of the gene, it is advisable that carriers should not taken out of breeding in order maintain the diversity of the gene pool. Dogs (Males or Females) tested Carriers (N/cy) should only be bred with clear dogs (N/N). Bitches tested genetically affected (homozygous for the mutation) (Cy/Cy) should not be removed from breeding but should only be bred with clear dogs (N/N). Mating with free animals is possible without any problems. The Laboklin team will be happy to answer any further questions you may have.