What is Cystinuria in dogs?

Cystinuria in dogs is an autosomal recessive disease that results in the condition where the dog is unable to properly reabsorb a number of amino acids including cystine from the urinary system. Normally, there is a low concentration of these amino acids in the urine but a dog with this condition has a high concentration of these amino acids in the urine. Cystine is normally absent from the urine. This results in the formation of cystine crystals in the kidneys or bladder. These stones can become larger and form stones that can go on to block various parts of the urinary tract. Cysinuria also affects humans and the maned wolf in South America. Cystinuria in dogs also seems to affect male dogs more than their female counterparts.

Genetics of Cystinuria in dogs

Cystinuria in dogs is a result of mutations in the SLC3A1 and SLC7A9 genes that code for proteins to allow the proper reabsorption of the amino acids from the urine. As an autosomal recessive trait, Cystinuria in dogs must be inherited from both parents who are either carriers or affected dogs. Carriers of Cystinuria do not normally show any symptoms of the disease due to its recessive expression.

What is the severity of Cystinuria in dogs?

Cystinuria in dogs is considered to be of medium severity as it is not often a fatal disease in treated dogs but does cause discomfort and pain to the affected dogs. It may be fatal and certainly much more painful in untreated affected dogs as the stones block the urinary tract.

What are the symptoms of Cystinuria in dogs?

Symptoms of Cystinuria in dogs will start at different times between males and females due to their differences in anatomy. Male dogs are affected earlier than females with the typical onset of symptoms beginning between 6 to 14 months of age. Female dogs tend to present the same symptoms at about a year older than the males. Common symptoms of Cystinuria in dogs include frequent urination, failure to urinate and straining to urinate. These symptoms are all the result of blockages in the urinary system caused by the formation of cystine stones. Other symptoms may also include dull aches, vomiting, nausea and the presence of blood in the urine (Hematuria). Aside from the pain the stones cause while in the bladder or kidneys, there is acute pain in passing the stone during urination.

Diagnosis of Cystinuria in dogs

Diagnosis of Cystinuria in dogs is often performed via a urine test for the presence of cystine in the urine. X-rays and Ultrasound scans of the bladder and kidneys to visibly see the cystine stones in largely unsuccessful as they are much harder to spot compared to calcium oxalate stones as they have a fuzzy appearance on X-ray. Blood tests can also be part of diagnostic testing for Cystinuria in dogs but DNA Disease Screening is quite definitive in confirming affected dogs as well as screening breeding dogs for carrier or clear status.

Treatment of dogs with Cystinuria

Treatment of dogs with Cystinuria will depend on the stage of the condition and whether there are stones present. Also the size of any stone present will affect the decision as to which treatment option would be best. Pre-stone forming dogs can be treated with drug therapy in combination with dietary changes that limit the amount of protein and salts. Blasting the kidney or bladder stones with sound waves (Extracorporeal shock wave lithotripsy) can be used to break large stones into sizes small enough for the dog to pass during urination. Surgery is often the last resort but may be necessary if the previously mentioned methods are unsuccessful.
Recent research work since 2010 at the University of Houston by Jeffery Rimer suggests that the use of L-cystine dimethylester may work in preventing the formation of the stones.

References

Crane C, Turner A (1956) Amino acid patterns of urine and blood plasma in a cystinuric Labrador dog. Nature. 177(4501):237-8.
Ahmed, K.; Dasgupta, P.; Khan, M. S. (2006). “Cystine calculi: Challenging group of stones”. Postgraduate Medical Journal 82 (974)
Brons AK, Henthorn PS, Raj K, Fitzgerald CA, Liu J, Sewell AC, Giger U. SLC3A1 and SLC7A9 mutations in autosomal recessive and dominant canine cystinuria: A new classification system. J Vet Intern Med. 2013 Nov;27(6):1400-8
D Bannasch and PS Henthorn (2009). “Changing Paradigms in Diagnosis of Inherited Defects Associated with Uroliths”. Veterinary Clinics of North America. Small Animal Practice 39 (1): 111–125
Joly, Dominique; Rieu, Philippe; méJean, Arnaud; Gagnadoux, Marie-France; Daudon, Michel; Jungers, P. (1999). “Treatment of cystinuria”. Pediatric Nephrology 13 (9): 945–50.
Lui J-L, Van Hoeven M, Seng AS, Giger U, Henthorn P (2004). Molecular and Biochemical Heterogeneity of Cystinuria in dogs. 2nd International Conference “Advances in Canine & Feline Genomics”.
Rimer, J. D.; An, Z.; Zhu, Z.; Lee, M. H.; Goldfarb, D. S.; Wesson, J. A.; Ward, M. D. (2010). “Crystal Growth Inhibitors for the Prevention of L-Cystine Kidney Stones Through Molecular Design”. Science 330 (6002): 337–41