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DNA tests for Cystinuria in dogs.
What is Cystinuria?
Cystine, an amino acid, is one of the building blocks of proteins. Amino acids are part of
a normal animal's diet and are absorbed through the intestine. Although they are filtered
through the kidney, amino acids are normally reabsorbed (nearly 100%) by special kidney
transporters and are not lost in the urine.
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In dogs with Cystinuria, the kidney transporter for cystine is defective. In acid urine,
cystine precipitates to create crystals, which may further precipitate to form calculi
(stones) in the kidney and bladder. These calculi can cause serious illness including complete
urinary blockage, which is a medical emergency. Because male dogs have a narrower urethra than
female dogs do, male dogs are more likely to become completely blocked. In this case, the
urinary bladder may greatly distend and rupture if not properly managed. Urine may then back
up into the kidneys, and the resultant pressure on the kidney may cause cell death and kidney
failure. Without appropriate and immediate care, such complications can lead to death.
Cystinuria is generally treated with compounds that bind cystine and prevent formation of
crystals. In humans the most common drugs of choice are 2-mercaptopropionylglycine (MPG) and
D-penicillamine. There is little information available on effective dosages for dogs. One study
indicated that affected Newfoundlands require higher dosages of MPG than other dogs with
Cystinuria. D-penicillamine was found to be of minimal benefit in reducing cystine calculi.
This may relate to the fact that Newfoundlands suffer from a form of the disorder that is more
severe than those we see in other breeds. Treatment with MPG can, in some cases, result in
dissolution of cystine calculi, therefore eliminating the need for surgical removal of the
stones. Unfortunately, some Newfoundlands are poorly responsive to medical treatment, they
suffer from recurring urinary dysfunction and require surgery to resolve urinary calculi.
A DNA test for Cystinuria
Breeds at risk
Breeding policy
Testing for Cystinuria
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