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Introduction
Familial Nephropathy (FN) is a
recessively inherited (Lees, Macdougall/Cattanach) renal disease
that has been recognized in the English Cocker for more than 50
years (Krook 162). FN is a form of "hereditary nephritis" (Lees
189) which refers to a group of glomerular diseases that are
linked to genetic collagen defects.
Onset of renal failure due to FN
typically occurs between six and 24 months of age (Lees 189).
Clinical signs may include polydipsia (drinks more), polyuria
(urinates more), weight loss, lack of appetite, vomiting, or
diarrhea. These symptoms are commonly associated with any type of
renal failure.
Structure/Function
The kidney is an organ made up of
hundreds of thousands of tiny structures called nephrons. Each
nephron consists of a glomerulus and a tubule. Blood flowing
through the kidney is filtered by the glomerulus, with the fluid
that is filtered out of the blood subsequently passing down the
length of the tubule. Cells that line the inner surface of the
tubule process the fluid as it flows along, reabsorbing certain
components of the fluid and excreting others. The fluid leaving
the tubule at the end of this process is urine, which is a
combination of water and waste products.
Dogs affected with FN have a genetic
defect within the glomerulus. This defective glomerulus lacks a
certain type of collagen that helps to hold the structure of the
filter together. As a result of this collagen defect, a chain
reaction of events takes place. Once the glomerulus begins to
loose its ability to function properly, blood proteins leak
through the defective filter into the urine. The glomerular
abnormality also leads to subsequent tubular damage, and the chain
of events eventually destroys the entire nephron. Nephrons that
are severely damaged or destroyed can’t be replaced.
Since the kidney serves as the main
waste-disposal system in the body, it is a master at
compensation. When one nephron dies, another takes over its
work. Over the course of time and with continual compensation the
number of functioning nephrons is greatly reduced. Once at least
75 percent of the nephron population is destroyed, end-stage renal
failure occurs. Since the disease is gradual and progressive,
affected dogs do not appear sick until very late in the course of
disease.
In the Beginning...
English Cockers affected with FN are
born with normally developed kidneys. Because they lack a certain
type of collagen, however, the kidneys begin to deteriorate while
the dogs are just a few months old. As glomerular damage
evolves, the kidneys will first allow protein (proteinuria) to
escape into the urine. Generally, while proteinuria persists, the
pup’s growth rate will slow down. Once the pup begins to spill
protein into the urine, the ability of the kidneys to
‘concentrate’ the urine will also diminish. Finally, as a result
of progressive nephron damage, the ability of the kidneys to
excrete waste products (eg, urea and creatinine) will become
impaired (Lees). As excretion of waste products by the kidneys
progressively diminishes, the severity of renal failure will
gradually worsen.
Sequence of Events
The sequence of events is always the
same, but the rate of disease progression varies for reasons that
are not fully understood (Lees). As a result, it is difficult to
give a specific age when to expect various stages of the disease
to take place. "For example, onset of proteinuria was at 5 to 8
months of age in 3 dogs in which it was carefully studied.
Because we can’t be sure that these 3 dogs are representative of
all FN-affected dogs, we are uncertain what age to say is the
oldest an FN-affected dog can be when it first has proteinuria.
Nonetheless, we suspect that all, or almost all, dogs with FN will
have proteinuria before a year of age. The age range for
occurrence of renal failure is 6 months to 2 years" (Lees).
Clinical Signs
One way to identify a pup that might
have FN is through observation. Breeders and owners can watch the
voiding patterns of young dogs. Make it a point to regularly
check the color of the urine. The first morning release (assuming
water hasn’t been available during the night) is probably best.
There should be good yellow color (well concentrated). A
youngster that lacks the ability to pass concentrated urine
repeatedly should be taken to a veterinarian for a complete
urinalysis. A test called a "specific gravity (SG)" should be
performed as well as an analysis for protein (proteinuria).
Usually, protein can be checked by using a color-coded plastic
strip (Bili-Labstix). This strip is merely dipped into a urine
specimen and the plastic strip changes color and is checked
against a chart on the side of the bottle the strips come in.
This strip will test for several things other than protein. A pup
with a low specific gravity and excess protein (++) in the urine
should be tested using a more specific test. This test, a
‘protein-creatinine ratio,’ will provide a better estimate of the
amount of protein in the urine. A complete urinalysis should also
be done to identify other urinary problems that may be present. A
positive dip-stick for protein does not necessarily indicate that
the dog has renal disease or will develop FN. It’s merely an
indication that a more thorough evaluation is needed. Not all
young-age renal failure in this breed is FN; however, the symptoms
are the same.
End Stage
Once it is established that a young
dog is consistently passing dilute urine with protein, serum
chemistry tests should be performed. Such tests will only show
significant elevations in specific areas once 75% of both kidneys
are destroyed. Elevations in BUN (blood urea nitrogen),
creatinine, and inorganic phosphorus suggest kidney disease.
These findings coupled with a low urine specific gravity and
proteinuria signal end-stage renal disease.
When the serum chemistry tests show
"abnormally high levels of urea (BUN), creatinine, and other
non-protein nitrogenous substances, a laboratory term called
Azotemia is used to identify these specific abnormal levels
(Barrett 1753)."
Generally, once the BUN reaches
approximately 120 mg/dl, the dog only has a few weeks before
critical illness sets in. When these animals become critically
ill, they will not eat. If they do eat, they usually vomit. They
may go for two or three days without food, loosing more weight.
They will drink a tremendous amount of water and urinate even
more. Sometimes there will be an ammonia odor from the mouth.
Since the dog sleeps on the ear leathers, this ammonia odor may be
apparent on the ear furnishings. The dog will become very weak,
and may tremble as if it’s cold. They loose the ability to
regulate their body temperature. Since the kidney’s are no longer
able to filter the body’s waste products, and regulate many
important functions essential for life, the animal is essentially
poisoning itself with its own waste products.
Perhaps one of the most frequent
questions asked by owners with a young dog in failure is how will
they know when it’s time to say good-bye. Despite being in the
critical stage of renal failure, these youngsters can always
manage to wag their tail and greet family members, not with the
usual exuberance, but the effort is there until the end. When the
time comes to say good-bye you’ll know…
Those that have lost a dog to FN
will tell you the loss is more profound with this disease process
than any other they’ve experienced. It’s something no one wants
to experience. Through the efforts of Dr. George Lees and his
research team, hopefully in the very near future the mutation will
be found. This will enable the development of a mutation-based
DNA test that will unequivocally identify carrier animals.
Currently, a research fund has been
set-up at the Texas A&M Development Foundation to honor the memory
of Arthur B. Ferguson. Arthur expressed a desire to help
researchers find a means to end this disease. Appropriately
titled, Arthur B. Ferguson Memorial Fund for English Cocker
Spaniel Kidney Disease Research. Donations to this fund can be
made in the following manner; 1) Make the check payable to: Texas
A&M Development Foundation; 2) In the "For" space write: Ferguson
Memorial Fund; 3) Send your check to: Dr. George E. Lees Small
Animal Medicine & Surgery, College of Veterinary Medicine, Texas
A&M University, College Station, TX 78843-4474. Donations to the
Memorial are the only means we have right now to continue the
research until a new grant can be secured. This fund is classified
a 501-C3 tax contribution. Join the fight to end FN in our breed.
Addi Pittman, Chairperson
ECSCA Health Education
Works Cited
Lees, George. Personal
correspondence. 25 Sept , 1999.
Lees, George E. et al. "Early
Diagnosis of Familial Nephropathy in English Cocker Spaniels.
Journal of the American Animal Hospital Association. May/June
1998, Vol. 34: 189-195.
The Cocker Spaniel Club. "Familial
Nephropathy (FN) of Cocker Spaniels. An advisory leaflet for all
Cocker owners." September 1986.
Krook, Lennart. "The Pathology of
Renal Cortical Hypoplasia in the Dog. Nord. Vet.-Med. 1957, 9,
161-176.
Barrett, Ralph E. "Textbook of
Internal Veterinary Medicine." Azotemia and Proteinuria. Section
11, Chapter 21, 141-145.
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