Cystinuria (Newfoundland type) is an inherited disease affecting kidney function in dogs. Cystine can be detected in the urine of dogs affected with Cystinuria (Newfoundland type) as early as two days of age, but symptoms may not appear until 6-8 months of age in males and even later in females. 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 Mutation of both copies of the SLC3A1 gene fail to reabsorb cystine allowing high 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. Both male and female dogs have increased amounts of cysteine in the urine, but obstruction of urine flow is more common in males due to differences in anatomy. 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.
Genetic testing of the SLC3A1 gene will reliably determine whether a dog is a genetic Carrier of cystinuria (Newfoundland type). Cystinuria (Newfoundland 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.
Casal ML, Giger U, Bovee KC, Patterson DF. Inheritance of cystinuria and renal defect in newfoundlands. J Am Vet Med Assoc. 1995 Dec 15;207(12):1585-9.
Henthorn PS, Liu J, Gidalevich T, Fang J, Casal ML, Patterson DF, Giger U. Canine cystinuria: polymorphism in the canine SLC3A1 gene and identification of a nonsense mutation in cystinuric Newfoundland dogs. Hum Genet. 2000 Oct; 107(4):295-303.