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Cystinuria in
Dogs
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Cystine is a
naturally occurring amino acid produced by the dog's body. In normally
functioning kidneys the cystine is filtered out of the urine in the
tubules of the kidneys resulting in very little cystine in the urine.
Cystinuria is an
inherited genetic defect in which the kidney is not able to process and
transport a basic amino acid, cystine, correctly in the kidney
tubules. This causes abnormally high levels of cystine in the
urine. Cystine is insoluble in neutral pH or acidic urine, so
excess urinary cystine results in formation of cystine crystals, which
in turn can lead to formation of cystine calculi (stones) in the kidney
and/or bladder over time. This can lead to recurrent or frequent
urinary tract infections and causes painful urination especially in
males. Males, because of their anatomy are at risk of a blockage
by a stone. Cystinuria does occur in females as well. This
is a life-threatening condition and requires surgery.
Affected dogs are born with this condition
but in most cases it takes many years before things get bad enough that
we notice it and it will vary greatly from dog to dog. Puppies
born with the condition may not developed cystinuria until they
are mature. That is not to say the puppies may not have trouble with
kidney stones even at a young age. Factors such as overall
health, other presenting genetic or congenital problems or even kidney
and bladder infections can make this situation more problematic at
younger ages.
Symptoms of kidney stones or cystinuria in dogs include painful and
frequent attempts to urinate, blood in the urine and a very foul
"rotten egg" smell to the urine because of the high cystine levels. The
dogs may become very despondent or walk with their backs arched since
the pain is localized in the kidney area. Vets can do a simple urine
test to look for any trace of the amino acid cystine in the urine.
Canine Cystinuria is typically diagnosed through the identification of
characteristic crystals in the urine. Cystine can be identified in the
urine of an affected dog in as early as 2 days of age using a
nitroprusside spot test or paper chromatography; either of these tests
can be used to further confirm a suspected case of Cystinuria. While
the nitroprusside spot test can detect affected dogs, it will not
determine whether a dog carries a gene for Cystinuria. A dog carrying
only one copy of the mutated cystinuria gene (carrier) would display no
symptoms of disease, but could potentially produce affected offspring
if bred to another carrier or affected dog. Until recently, the
nitroprusside spot test was the only available means of testing for
Cystinuria. A DNA-based diagnostic test for the detection of Canine
Cystinuria in Newfoundlands is now available. This test employs the
latest advances in DNA technology to specifically target the gene
associated with this disease, ensuring 100% accuracy of detection. This
DNA test can definitively diagnose affected animals, as well as
carriers of the mutated gene. By selectively identifying carriers of
Cystinuria, breeders can effectively remove these animals from their
breeding programs and eventually eradicate this disease from their
lines.
Treatment can include several different options. If the dog is
diagnosed with the condition but has no presenting conditions such as
the kidney stones, problems with urination or signs of pain and
discomfort a special diet that is very low in protein can help reduce
the risks of stones occurring. Special supplements can also be used to
buffer the urine and keep the cystine from clumping to form stones. In
cases where stones have already occurred they will need to be
surgically removed from the bladder to prevent possible obstruction of
the urinary tract. When a blockage of the urinary tract has already
happened a processed known as hydropulsion can be used to push the
stone back up into the bladder where it can be removed.
In cases where surgery is not possible there are some new drugs
available that can be given to the dog to try to break down the stones.
These drugs are rather risky and very expensive are not typically
advised unless there are no other options. In some males a surgical
procedure is used to re-route the urinary tract to a small, surgically
developed opening beside or just to the front of the scrotum, more like
the female dogs urinary opening, to prevent the problem of stone
lodging in the smaller urinary tube of the penis.
Cystinuria has been
reported in many breeds (and mixed breeds) of dogs. The average
age of onset of clinical signs attributable to Cystinuria in dog breeds
is about 4.8 years, but in Newfoundlands, signs appear as early as 6
months to 1 year, suggesting that the Newfoundland breed suffers from a
more severe form of the disorder than do other breeds. Recurrence of
calculi following surgical removal also occurs much more rapidly in
Newfoundlands than in other breeds.
