BACKGROUND Cystinuria is an
inherited, metabolic disorder. The affected individual has an impaired
capacity for reabsorption of the amino acid, cystine, in the kidney
tubules. Because cystine is not reabsorbed by the kidneys, it becomes a
part of the kidneys’ product: urine. Therefore, cystinuric individuals
have an excess of cystine in their urine. Most of the time, this excess
cystine is simply excreted in the urine. Because cystine is one of the
sulfur-containing amino acids, the urine may have a characteristic
"rotten egg" odor.
As long as
cystine stays in solution in the urine, it will be excreted without
incident. It is when excessive cystine in the urine is not excreted
that it becomes problematic. Sometimes, cystine will precipitate, or
solidify, forming stones. You may also see stones referred to as
crystals, uroliths, or calculi; these are interchangeable terms.
Cystine stones can cause problems for the person or animal affected, by
blocking the urethra, bladder, or kidney. This results in prevention or
slowing of urination. There may be straining to pass the urine, and
there may be blood in the urine. Some individuals will pass the actual
stones, if they are small enough to be passed instead of causing
blockage. In severe cases, the blockages can lead to rupture of the
bladder or kidney, which may even be fatal.
TREATMENT There are three
methods of control for cystinuria.
Medical
management is a possibility, through the administration of drugs that
will help to dissolve the stones. The drugs will not prevent the stones
from forming; they will only assist in "shrinking" already formed
stones. Drugs also come with side effects, and may not be a wise course
of treatment for long term use.
Surgery may be
indicated, in certain individuals. Usually it has been found that the
stones removed during surgery will eventually reform later on,
necessitating further surgery or some other method of treatment.
Dietary
modification, with the accompanying alkalinization of the urine, is the
approach I recommend. The intent of this approach is to reduce the
likelihood of the stones forming in the first place. This way, there is
no need to surgically remove or medically shrink anything! It may seem
that if we simply avoided feeding anything with cystine in it to the
animal, that would solve the problem. Afterall, if there were no
cystine, we would not have to worry about it being reabsorbed.
Unfortunately, that is not the case. Cystine is not the "enemy," in
fact, it is an essential amino acid, meaning it must be a part of the
diet of a healthy individual. It is so necessary, that the body will
actually manufacture cystine out of other amino acids (methionine) if
the diet is deficient in cystine. So, we will always have to be
concerned with how best to rid the body of the cystine that cannot be
reabsorbed. Of course it also makes sense that feeding the lowest
cystine-containing sources of foods is a smart thing to do; we just
can’t expect to eliminate cystine from the diet completely.
GOAL
OF DIETARY MODIFICATION There are many
types of urine stones that can develop in people and animals. Cystine
stones behave differently from other types of urinary stones (for
example, struvite) in that they tend to form when their environment
(the urine) is acidic (low pH). Therefore, the goal in modifying the
diet of an affected individual is to alkalinize, or raise, the pH of
the urine. This creates an environment where the excess cystine will be
less likely to form into stones, and more likely to be excreted as part
of the urine solution.
How can we
control the pH of the urine? Well, the pH is largely influenced by the
diet consumed. Generally speaking, high-protein diets, based on large
quantities of meats, lead to acidic urine. Low-protein diets, based
more on plant materials, lead to alkaline urine. The ideal diet is
designed to balance the proportions of meat and vegetables, such that
the dogs’ requirement for protein is met, but not vastly exceeded.
Another way to
trick the urine into becoming more alkaline is to use what are called
buffering agents. These are substances that will react in the digestive
system and internal organs, to de-acidify, or "buffer" the urine
components. This results in maintaining the pH at a higher level,
thereby preventing stone formation. The most common buffer is
plain old baking soda (sodium bicarbonate). Some special forms of
vitamin C also serve to help control the urine pH.
CONCLUSION It is important
to understand, as best we can, what is going on inside the bodies of
our pets. This enables us to provide the best care we know how to give
to them. Cystinuria can be controlled and managed; it need not mean
illness or early death for your dog. It is not recommended to breed
affected dogs, since this is a genetic condition. There is current
research being conducted on cystinuric dogs, in an attempt to map the
genes responsible and perhaps find a way to prevent its inheritability
one day in the future.
This article written
by J. Boniface, (c) copyright 1998, all rights reserved.
reprinted with kind permission from Jennifer Boniface, MS Animal
Nutritionist
Owner, Aunt Jeni's Home Made www.auntjeni.com
