Common Symptoms
Cystinuria (Labrador retriever type) is an inherited disease affecting kidney function in dogs. The SLC3A1 gene codes for a protein that allows the kidneys to transport cysteine and other amino acids from the urine. Normal kidneys reabsorb the Amino Acid cystine so that only small amounts pass into the urine, while dogs with mutations of both copies of the SLC3A1 gene fail to reabsorb cystine allowing large amounts to pass into the urine, hence the name cystinuria. Cystine can form crystals and/or stones in the urinary tract, which can block the ureters or Urethra and stop the normal flow of urine. Affected male dogs typically present with symptoms related to cysteine bladder stones at 6 to 14 months of age, however female dogs tend to develop symptoms later than males. Symptoms of disease include straining to urinate, frequent urination of small volumes or inability to urinate. In Labrador Retrievers, males and females are equally affected with excess cysteine in the urine, but obstruction of urine flow is more common in males due to differences in anatomy and females tend to develop stones about a year later than males on average. Dogs with cystinuria often have recurrent inflammation of the urinary tract and if not treated, urinary stones can cause urinary tract infections, kidney failure and even death.
Testing Tips
Genetic testing of the SLC3A1 gene will reliably determine whether a dog is a genetic Carrier of cystinuria (Labrador retriever type). Cystinuria (Labrador retriever type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the SLC3A1 gene mutation. Reliable genetic testing is important for determining breeding practices. Because not all affected dogs will have clinical signs associated with cystinuria, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
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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.
[PubMed: 24001348]
