Cystinuria 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.

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