Cystinuria
Cystinuria is a condition passed down through families in which stones form in
the the kidney, ureter, and bladder. Cystinuria is caused by excessive levels of an amino acid called cystine in the urine. After entering the kidneys, most cystine normally dissolves and goes back into the bloodstream. But individuals with cystinuria have a genetic defect that interferes with this process. As a result, cystine builds up in the urine and forms crystals or stones, which may get stuck in the kidneys, ureters, or bladder.
Different forms of the disease, designated type I and non-type I in cystinuric humans, can be distinguished clinically and biochemically, and have been associated with mutations in genes.
Cystinuria has been recognized in more than 60 breeds of dogs and a severe form, resembling type I cystinuria, has been characterized in the Newfoundland breed.
Dogs that form cystine stones leading to clinical signs (blockage) before the age of 1 year suffer from the type of cystinuria caused by a mutation in both copies of the rBAT gene. Conversely, for breeds in which cystine stone formation does not occur in the first year of life, mutations in the rBAT gene have not been found. Cystinuria in Mastiffs and English Bulldogs (two breeds in which cystinuria is more common than other breeds) does not appear to be caused by mutations in either rBAT or in an additional gene known to cause cystinuria in humans.
Not all dogs with cystinuria develop urolithiasis (a condition characterized by formation of stones). The calculi (stones) usually occur in younger animals, with a mean age of 4.8 years. Dachshunds are the most common breed to develop cystine uroliths. Cystine uroliths (stones) are usually small, smooth, yellow brown to yellow green. They can be radiopaque or radiolucent depending upon their size.
TREATMENT
Cystine uroliths can be surgically removed or medically dissolved. Medical management includes:
- feeding a protein restricted diet low in methionine such as UD
- increasing water intake will dilute the crystals but salt should not be administered as increased sodium may increase urine cystine excretion
- increasing urine pH > 7.5 will increase solubility of crystals. Potassium citrate is preferred over sodium bicarbonate due to sodium's effect on increasing urine cystine.
- D-penicillamine changes cystine to more soluble form. It is dosed at 10-30 mg/Kg divided BID. One author suggests this dose to be intolerable by many patients and advocates a dose of 10 mg/Kg. D-penicillamine delays wound healing, so avoid use immediately postoperative if calculi are surgically removed. Alpha-mercaptopropionylglycine (MPG) - has fewer side effects which appears to be more effective than D-penicillamine but is not approved yet for use in dogs. Dr. Osborne at the University of Minnesota has had success in dissolving cystine calculi using Hills UD and 2 MPG. [2]
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
Adapted from:
1. The Veterinary Formulary By Yolande M. Bishop
2. CVM Course Websites Washington State University, Pullman, WA
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