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Do I Need to
Understand Genetics to Understand PKD?
That depends upon the extent that you want to
understand PKD. At the lowest level -- that PKD is an inherited disease that can be
largely eliminated by ultrasounding breeding stock and removing positives from your
breeding program -- there's probably no need to understand genetics.
However, if you're the type of person who wants to
understand as much about PKD as possible, then you will need to understand the genetic
terminology that frequents discussions about PKD. Understanding the following terms
should give you a good basis for understanding most of the PKD discussions:
- Allele
One of two or more forms of a gene which occupies
corresponding loci on a chromosome.
- Locus
A specific place or position on a chromosome.
Each gene has a specific locus on a specific chromosome. Plural: loci.
- Genotype
The specific genetic makeup of an individual.
The alleles located at one or more sites on chromosomes. The genetic info
carried by a pair of alleles determines one trait or characteristic.
The genetic makeup of an individual is represented
by a series of letters -- uppercase letters representing dominant alleles and
corresponding lowercase letters representing recessive alleles. In some cases, such
as the genes for tabby pattern, there are multiple recessives, with some of the recessives
actually being dominant to other recessives. But in most cases, and with PKD in
particular, there is a single dominant form of the gene, and a single recessive form.
Most PKD discussions use P to represent the dominant form of the
gene, and p to represent the recessive form. Since PKD is not sex
linked, each individual has two genes at the locus for PKD -- one from the mother and one
from the father. These genes may combine in one of three combinations: PP,
which is the homozygous positive genotype; Pp, which is the heterozygous positive genotype; and pp,
which is the homozygous negative genotype. Note, however, that many believe the homozygous positive PP is not viable
and either dies in utero or does not survive early kittenhood.
Note that for a autosomal *recessive* characteristic, the opposite is true
-- ZZ would represent a homozygous unaffected individual, Zz
would represent a heterogygous unaffected individual who was also a "carrier"
[the recessive z gene is masked by the dominant unaffected Z
gene], and zz would represent the affected individual.
- Phenotype
The visible characteristics or traits of an
individual. Can be affected by both genetic makeup and environmental factors.
Includes behavioral traits, anatomical traits, biochemical traits, and physiological
traits.
In cats, phenotypes would include descriptive
traits such as red vs. black vs. tortie; dilute vs. full colored; agouti vs. non-agouti,
white vs. colored; bicolor vs. non-bicolor; etc. For PKD, the two phenotypes are: 1.
positive / affected; and 2. negative / unaffected. Both the PP and Pp
genotypes result in a positive phenotype; only the pp genotype results in
a negative phenotype. Note, however, that many believe the homozygous positive PP is not viable
and either dies in utero or does not survive early kittenhood.
- Autosomal
Basically, autosomal means not sex linked.
An autosome is a chromosome that is not a sex chromosome. Thus,
one member of the chromosome pair is inherited from each parent, and the genes on that
chromosome are also in pairs, one from each parent. The traits caused by genes on an
autosome are called autosomal -- i.e., the genes are inherited from both parents,
and both sexes have equal chances of inheriting the trait.
Most genes are autosomal, and most hereditary disorders are the result of
a defective gene on an autosome. In cats, one example of a gene that is not
autosomal is the gene for orange/red color. This gene is carried only on the female
(X) chromosome.
- Dominant gene
Dominant genes express themselves in the individual's phenotype
regardless of whether it's allele is dominant or recessive.
- Recessive gene
Recessive genes express themselves in the phenotype only when in a
homozygous state, and cannot affect the phenotype in the presence of a more dominant
allele.
What is PKD?
PKD (Polycystic Kidney Disease) is a progressive, genetic disease of the
kidneys. It occurs in humans, cats, dogs, and other animals. PKD is
characterized by the presence of multiple cysts in each Kidney (i.e, bilateral).
(See also Is a Single Cyst in One Kidney Conclusive for PKD?
and Can Kidney Cysts be Caused by Something Other Than
PKD?, below).
Research at Ohio State University conducted by Dr. David Biller and his
associates indicates that these cysts are present from birth, but it remains to be proven
whether this is always the case. (Note however, that two sites with information on PKD in
humans -- the National Institutes of Health NIDDK National
Kidney and Urologic Diseases Information Clearinghouse website
and the WebPath
pathology website at the University of Utah School of Medicine indicate that in
humans, PKD cysts are not always present at birth.)
Can PKD be
Caused by the Other Factors Such as Food Additives or The Environment?
No. By definition, PKD is a genetic disease (see What Is PKD?, above). In addition, there is no evidence
I've seen or heard of that even links food additives, the environment, or anything else to
the growth rate of PKD cysts or the severity of PKD.
Note, however, that there is a related, and probably more appropriate
question that some ask: Can Kidney Cysts be Caused
by Something Other Than PKD?
How is PKD Inherited?
In humans, there are two modes of inheritance: autosomal dominant and
autosomal recessive (with at least two, and possibly three different autosomal dominant
forms of PKD caused by different genes at different loci). To date, only the
autosomal dominant form has been identified in cats.
To quote Dr. DiBartola, Professor of Veterinary Clinical Sciences at The
Ohio State University College of Veterinary Medicine, and Co-Editor of the Journal of
Veterinary Internal Medicine (one of the Dr. Biller's co-investigators and a co-author of
many of the published PKD research results):
"While it is true that we do not know yet the actual gene for PKD in
the Persian, there are some things to keep in mind:
(1) in our experience, all affected cats have had at least one affected
parent (this supports dominant inheritance)
(2) two affected cats CAN produce an unaffected cat (this RULES OUT recessive inheritance)
(3) the disease in humans (caused by either PKD1 or PKD2 gene defects) is known to be a
dominant trait
(4) the clinical course of the disease is very similar to ADPKD in humans
All of the above support BUT DO NOT PROVE simple dominant inheritance for
PKD in the Persian. The above findings were reported in Journal of Heredity Vol.
87 pages 1-5, 1996. I have no reason to suspect a polygenic trait at this point."
Stephen P. DiBartola, DVM, DACVIM (as forwarded to the
PKD-List by Marie Thiers, 10/20/98)
For additional possibilities, see the discusion of Mutations under Can Two Negative Parents Produce A Positive Offspring?,
below.
Can Two
Negative Parents Produce A Positive Offspring?
With Autosomal Dominant PKD, the only form of PKD so far identified and
confirmed in cats, two genetic negative parents cannot produce a
genetically positive offspring unless that offspring is a fresh mutation.
See the discussion on autosomal-dominant
inheritance below for further details.
Based on all information available to date on PKD in felines, the most
likely reasons for reports of a positive offspring from two negative parents are: one or
both parents are "false negatives" -- i.e., they are genetically positive but
for one reason or another showed no signs of cysts when ultrasounded; or the offspring
itself is a "false positive" -- i.e., the offspring is genetically negative, but
for one reason or another was diagnosed with apparent cysts when ultrasounded. See
the discussion of False Negatives and False Positives for
more details.
Another possible explanation for a positive offspring from two negative
parents is that one or both of the cats identified as a parent is really not the biologic
parent, and that the biologic parent is actually a PKD positive cat. While we all
hope mis-identification of parents doesn't happen, unfortunately it does happen on
occasion.
Yet another explanation for a positive offspring from two negative parents
would be a second form of PKD in cats -- Autosomal Recessive PKD. Autosomal
Recessive PKD does exist in humans, but is a childhood onset disease
that is almost always fatal before the individual reaches adulthood. It is theorized
that if Autosomal Recessive PKD exists in cats, it would work the same as in humans --
i.e., few if any affected cats would live to adulthood. While to date, this is just
a theory, Dr. DiBartola, professor of Veterinary Clinical Sciences at The Ohio State
University notes:
"PKD in very young kittens resembling RECESSIVE PKD has been reported
in the veterinary literature. See Crowell WA, Hubbell JJ and Riley JC. Polycystic
renal disease in related cats. J Am Vet Med Assoc 175: 286-288, 1979. While
there is no genetic proof that this manuscript describes ARPKD, it is likely. The
cats in this paper died at around 6 weeks of age as I recall and had SEVERE renal cystic
disease."
Stephen P. DiBartola, DVM, DACVIM (from a private e-mail
11/2/98)
From our own cattery experience, however, I suspect even this example may
have been from autosomal dominant PKD (ADPKD). In August, 1993, we had an otherwise
healthy 4 day old kitten die. Necropsy concluded the kitten had died from acute
renal failure precipitated by severe polycystic kidneys (the "swiss cheese"
look). His dam is one of our ADPKD positive cats (PKD confirmed via ultrasound, and
must be dominant because she's produced negative offspring from breedings to a positive
male), but the sire was neutered and placed as a pet several years ago. So unless
this queen has both ADPKD and autosomal recessive ARPKD (a condition which has
been created in mice strains), our early kitten death was caused by ADPKD.
(Note that this might also be an example of a homozygous
positive who survived birth, but died as a very young kitten.). And in
September, 1997, necropsy confirmed severe cysts on a 4 month old kitten we had euthanized
due to classic signs of renal failure. This kitten was initially diagnosed with
kidney problems during a physical exam at 12 weeks, when palpation revealed that both
kidneys were greatly enlarged and seemed to have irregular surfaces. In this case,
the sire was diagnosed as PKD free by Dr. Biller when 4 years of age, but the mother was
petted out shortly after we euthanized the kitten, and has not been tested for PKD.
Finally, a positive could result from a new mutation -- either of the same
gene as other PKD positives, or of an enitrely different gene. In discussing human
autosomal dominant PKD, the National Institutes of Health NIDDK National
Kidney and Urologic Diseases Information Clearinghouse website
contains the following information:
"Either the mother or father can pass it along, but new mutations may
account for one-fourth of new cases. In some rare cases, the cause of autosomal dominant
PKD occurs spontaneously in the child soon after conception--in these cases the parents
are not the source of this disease."
So at least in humans, ADPKD does exist even where neither parent is PKD
positive -- sometimes from new mutations and rarely from post-conception spontaneous
occurances. Since NIH specifically calls these cases ADPKD, which is by definition
genetic, these positive humans would be able to pass on their disease to their children.
Although similar positives have not yet been documented cats, it is at least possible
that similar exceptions do exist in our feline population.
In any case, thus far there have been no actual cases of a
positive offspring from two negative parents that have been confirmed and documented
for Dr. Biller, so there is no reason to believe that Autosomal Recessive PKD exists in
cats. However, there is also virtually no way to rule out the possibility
that one or more cases will be found sometime in the future. Unfortunately, in
science, it is extremely difficult to prove that something does not
exit.
What's the Difference
between Autosomal Dominant and Autosomal Recessive?
Autosomal Dominant genes express themselves when present. Autosomal
Recessive genes will only express themselves when in the homozygous state -- i.e., both
genes in the gene pair are the recessive gene form. Thus, recessive genes can be
"carried" by those whose phenotype does not exhibit the gene characteristic,
while dominant genes cannot be "carried".
According to Mosby's Medical & Nursing Dictionary, autosomal-dominant inheritance is "a
pattern of inheritance in which the transmission of a dominant gene on an autosome causes
a characteristic to be manifested. Males and females are affected with equal
frequency. Affected individuals have an affected parent (unless the condition is the
result of a fresh mutation). Half of the children of a heterozygous affected parent
are affected. All of the children of a homozygous affected parent are
affected. Normal children of an affected parent do not carry the trait."
In comparison, Mosby's defines autosomal-recessive
inheritance as "a pattern of inheritance in which the transmission of a
recessive gene on an autosome results in a carrier state if the person is heterozygous for
the trait and in the affected state if the person is homozygous for the trait. Males
and females are affected with equal frequency. Affected individuals have unaffected
parents who are heterozygous for the trait. One fourth of the children of two
unaffected heterozygous parents are affected. All of the children of two homozygous
affected parents are affected. The children of a couple in which one parent has the
trait and the other does not are all carriers who show no effect of the trait."
Examples of dominant genes in cats include full color, white spotting
(bicolor), and inhibitor (smoke/silver).
Do PKD
Positive Homozygotes Exist?
To date, there is no proof whether PKD positive homozygotes (PP)
exist or not. We may not know the answer to this question until a DNA test is
available and that test has been used on a significant number of PKD positive cats.
However, Dr. DiBartola, Professor of Veterinary Clinical Sciences at The
Ohio State University says:
"In all likelihood, the homozygous state (PP) for
ADPKD probably is not viable. No human homozygotes have ever been detected and recent work
using so-called "knockout" mouse models of PKD1 (Dr Zhou at Harvard) and PKD2
(Dr Somlo at Albert Einstein in NY) (in which the researchers genetically target and
inactivate a gene) has shown that mouse embryos homozygous for mutations in PKD1 or PKD2
have severe abnormalities in kidneys and other organs with branching tubular epithelial
structures (e.g. biliary tree, pancreas) that preclude survival. Thus it is VERY UNLIKELY
that homozygotes live ex utero."
Stephen P. DiBartola, DVM, DACVIM (from a private e-mail
11/2/98)
Anecdotally, however, I have had reports from two separate well known
breeders who believe they may have examples of homozygous positive cats. Both are
males who have produced multiple litters, and all offspring tested to date have been
positive. In both cases, there are offspring who have not been, and probably never
will be tested. In one case, the suspect cat is neutered and still living, while in
the other case, the suspect cat died of PKD related kidney failure as an adult.
While these reports are certainly not conclusive, and all anecdotal reports need
to be taken with a degree of skepticism, in my opinion they are at least suggestive
that homozygous positives may not only exist ex utero, but may also survive kittenhood and
become active breeders.
Note that if homozygote positives do not survive until breeding age, this
will disturb the normal distribution of positives and
negatives in the surviving population. If homozygote positives die
early (before sexual maturity), then PP x PP, PP
x Pp and PP x pp breedings would never
occur. Only Pp x Pp, Pp x pp,
and pp x pp breedings would occur. And the PP
offspring from Pp x Pp breedings would die early,
meaning that instead of 25% PP, 50% Pp, and 25% pp,
only the 50% Pp and 25% pp would survive to be
tested. In this case the phenotypes of the survivors would be 66% positive and 33%
negative, rather than the 75% positive and 25% negative that would occur if homozygous
positives do survive.
Is PKD Sex Linked?
Based on Dr. Biller's research, and reports from more than 5,000
ultrasounds worldwide since April, 1998, PKD does not appear to be sex linked.
Therefore, males and females can both have PKD, and can both pass PKD on to their
offspring.
Is PKD Only a Problem
for Persian Breeders?
No. Although PKD appears to be more prevalent among Persians
(including Himalayans) and Exotics, ultrasound results to date have also found PKD in
American Curls, American Shorthairs, Siamese and Scottish Folds, as well as Household
Pets, Domestic Shorthairs, and Feral cats. An Oriental Shorthair was also diagnosed
with PKD as the result of a necropsy.
Test results from many breeds are not available, and even for those which
are available, most are so few in number as to be inconclusive what the eventual results
will be. However, about 7% of the 172 non-Persian and non-Exotic cats tested to date
have been positive, vs. about 37% of the Persians and Exotics.
How is PKD
Diagnosed?
Currently, the best method to diagnose PKD in living cats is by
ultrasounding the kidneys. Other radiological modalities have been used, but have
proven to be generally less accurate and more costly. However, even the most skilled
sonographer using the best equipment cannot be 100 percent accurate in diagnosing PKD via
ultrasound, since the resolution afforded by ultrasound is not sufficient to detect very
small cysts.
Histopathological examination of frozen sections of the kidneys is
virtually 100% accurate, but typically cannot be done on live cats. In humans, I've
seen references to examining biopsy specimens using histopathology, but have never heard
of this being done on cats. However, if a nephrectomy is done on a diseased kidney
(removal of the kidney), which does occur in cats, the removed kidney could certainly be
examined by histopathology.
How Accurate is
Ultrasound?
In Dr. Biller's study (sometimes referred to as "the Ohio
study"), Dr. Biller was able to diagnose cats at 10 months of age with 98% accuracy
(as determined by eventual histopathology exams after natural death or euthanasia). Given
the many variables in real-world testing (the skill, training and experience of the
sonographer; the ultrasound equipment; etc.), my personal opinion is that the real-world
accuracy will be somewhat lower -- perhaps in the 90% to 95% range.
Dr. DiBartola notes that in Dr. Biller's and his paper in the Journal
of Heredity, 1996:
"…ultrasound exam had a sensitivity of 75% and specificity of
100% at 16 weeks of age and a sensitivity of 91% and specificity of 100% at 36 weeks of
age," where "sensitivity = true positive/(true positive +false negative) [i.e.,
how frequently positive results occur in animals with the disease] and specificity = true
negative/(true negative + false negative) [i.e., how frequently negative results occur in
animals without the disease]. In terms of recommendations, I would advise people
wait until their cats are 6 to 9 months of age to increase accuracy of
ultrasonography."
Stephen P. DiBartola, DVM, DACVIM (from a private e-mail
11/2/98)
In any case, the best results will be achieved when using highly skilled,
well trained sonographers with considerable experience diagnosing PKD from
ultrasounds. Evidence to date suggests that sonographers, including many local vets,
who have minimal skills using ultrasound, have little training on the proper use and
interpretation of ultrasounds, and/or have little or no experience diagnosing PKD from
ultrasounds, tend to have proportionately lower accuracy rates. A number of breeders
have therefore chosen to rescan their cats with a more qualified sonographer -- frequently
with significantly different results than initially reported.
Another factor in the accuracy of ultrasound in diagnosing PKD is the
equipment itself, although Dr. Biller is consistent in his position that equipment is much
less important that the skill, training, and experience of the sonographer doing the test.
According to Dr. Biller, a skilled, well-trained, experienced sonographer should be
able to find cysts down to 1mm in size using an ultrasound equipped with a 5 MHz
transducer and 256 gray scale.
What
Ultrasound Equipment Should be Used to Test for PKD?
Like Radar and Sonar, Ultrasound uses the echoes of sound waves to produce
images. In the case of Ultrasound, these sound waves are transmitted through a
transducer, and partially reflected back to the transducer by the body's tissue.
Human hearing is typically in the frequency range under 18,000 Hz (18 kHz). Bats and
whales use frequencies in the range of 100 kHz. In contrast, Ultrasound uses
frequencies above 1 MHz (1,000,000 Hz). The higher the frequency, the shorter the
wave length, and the shorter the wave length, the greater the resolution of the
image. However, longer wave lengths are able to penetrate deeper into the
subject. Until very recently, 10 MHz was thought to be the upper limit of ultrasound
in clinical applications, so most of the equipment in common use utilizes transducers in
the 1.8 MHz to 10 MHz range, with many multi-frequency transducers available. In the
last year or so, transducers up to 14 MHz have been released by most manufacturers, while
20 MHz transducers are available from at least one manufacturer (based on info
available from Manufacturer's web sites). These higher frequency transducers
are not in common use yet, and as with most new technology, are still rather
expensive. Most transducers currently being used are probably 3.5, 5.0 or 7.5
MHz. The lower frequency transducers are more than adequate for most purposes,
particularly in human medicine and large animal veterinary practice.
Dr. Biller has said that the equipment is much less important than the
skill, training, and experience of the sonographer, and that a skilled, well-trained and
experienced sonographer should be able to detect cysts as small as 1 mm in diameter using
an ultrasound equipped with a 5 MHz transducer and a 256 gray scale. However, even
Dr. Biller recommends a 7.5 MHz or higher frequency transducer, with a 256 gray
scale.
Higher frequency equipment will definitely provide higher resolution
pictures, and in the hands of a skilled and experienced sonographer, should allow for
detecting cysts smaller than 1 mm.
New 3-D Ultrasound, when commonly available, will also provide an increase
in diagnostic accuracy by better differentiating between cysts and normal kidney
structures. However, it is unlikely that even the most state-of-the-art equipment
will substitute for the skill, training, and experience of a top-notch sonographer.
Can Any Vet Test
for PKD?
Although anyone with access to ultrasound equipment and minimal knowledge
of ultrasound can do the testing, the quality and accuracy of the test results
appear to be directly proportional to the skill, training, and experience of the
sonographer doing the testing.
Ultrasound testing can be expensive (as high as $275 US per cat in some
private practices, and $25 to $50 US per cat in special PKD "Clinics").
Many breeders have had to re-test their cats after learning that the results from
an inexperienced sonographer were inaccurate. Since the cost is relatively high, and
accurate results are very important when used either as the basis for future breeding
decisions or as the basis for PKD free sales, we strongly recommended that testing be done
only by sonographers who have in-depth training in ultrasound techniques and considerable
experience detecting kidney cysts and diagnosing PKD.
In order of preference, we suggest looking for a veterinary radiologist
first, then a veterinary internal medicine specialist, and then a competent ultrasound
technician with in-depth veterinary experience and/or human PKD experience.
Radiologists who are members of the American College of Veterinary Radiologists (ACVR) can
be located using Directory link at the
ACVR website. We suggest
checking the ACVR box, but not checking any of the other search criteria boxes. In
particular, don't check the Ultrasound box under "Membership In:", since many of
the members who are skilled in ultrasound may not be members of the Ultrasound Society.
Based on the experiences of many breeders, we feel that local
veterinarians, despite good intentions and with some exceptions, are not typically good
choices for PKD testing. Before using a local veterinarian, verify that they are
well-trained in using the equipment and both trained in and experienced in diagnosing PKD.
What are False
Negatives and False Positives?
False Negatives are cases where an individual is diagnosed negative, but
is in actuality positive. False negatives can be caused by the use of the wrong
equipment (too little resolution to detect cysts which better equipment would have clearly
shown), or because the sonographer was not skilled enough in using the equipment, or had
not been trained sufficiently in the use and interpretation of ultrasounds, or had
insufficient experience in diagnosing PKD by ultrasound.
However, even with the best equipment and best sonographers, some false
negatives will occur simply because of the inherent limitations of ultrasound. All
ultrasound equipment has a limited resolution (higher wave-length transducers have better
resolution than lower wave-length transducers), so any cyst that is smaller than the
capabilities of the equipment to resolve cannot be differentiated from the surrounding
kidney tissue. Even Dr. Biller himself reported 2% false negatives during his study
(from cysts that were too small to resolve via ultrasound).
False positives occur when an individual is diagnosed as positive but is
really negative. False positives would typically arise from one of two causes:
The sonographer diagnosed something as a cyst that was not a cyst.
According to Dr. DiBartola in a private e-mail, "False positives occurs when
inexperienced ultrasonographers mistake normal medullary tissue for cysts (because the
renal medulla normally is less echogenic than the renal cortex)." Dr. DiBartola
goes on to say that this problem "should not occur if the ultrasonographer is
experienced and knowledgeable. I prefer to see only board-certified radiologists
doing this type of exam."
the sonographer did find cysts, but those cysts were not caused by
PKD.
To date, I've seen nothing that would indicate any rate for false
positives, nor have I seen anything that would suggest that false positives occur with any
significant frequency. I suspect that most, if not all, false positives are due to
unskilled, poorly trained, and/or inexperienced sonographers. Dr. Biller did not
report any false positives from his study.
Is a Single Cyst in One
Kidney Conclusive for PKD?
Absent any other information, the classic answer is "no, PKD is
bilateral and requires multiple cysts". However, evidence suggests that cysts
from other causes are relatively rare. So particularly for Persians, Exotics and
other cats with direct Persian lineage, if either parent is positive, or if there are
positive offspring from a negative mate, or even if the cat in question is young
(certainly under 1 year, and perhaps even up to two years), it would be wisest to consider
the cat "questionable" or even "probable", not use the cat for
breeding immediately, and rescan the cat closer to two years of age.
To quote Dr. Biller, the acknowledged expert on feline PKD and Associate
Professor Department of Clinical Sciences College of Veterinary Medicine Kansas State
University :
"I use to believe that PKD meant bilateral. But I'm not
sure that is true. I think that maybe histologically it is true but that maybe we
are not seeing cysts bilaterally. I also have seen some cats with unilateral
disease(cysts). I have had the chance to follow one of these cats and have seen
positive offspring when bred to a negative female. So I am getting ready to do a
large study and see if cysts are in other non Persian cats. That may let me know if
benign cysts exist in Persians. This is a constantly changing situation. As I
learn and see new things daily."
David S. Biller, DVM, DACVR (as forwarded to the PKD List by
BJ Fox, 10/21/98)
Can Kidney
Cysts be Caused by Something Other Than PKD?
Yes. However, cysts in non-Persian cats are relatively rare,
regardless of the cause. So the current theory is that almost all cysts found in
Persians and related breeds will be PKD cysts. Dr. Biller will be conducting research to help establish exactly how frequently cysts are
found in non-persian cats. This study should help us understand the frequency of
non-PKD kidney cysts in Persians, and possibly even provide clues about how they can be
differentiated from PKD cysts using ultrasound.
Since PKD cysts occur in the renal cortex and medulla, cysts that are
outside the cortex and medulla areas of the kidneys can almost certainly be diagnosed as
non-PKD cysts. However, as Susan Little, DVM, notes in a recent issue of Persian
News:
"... in breeds at risk (Persians and relatives), the most common
cause of cysts by far is PKD, especially if there is a family history. So we put
together the ultrasonographic appearnce of the cysts plus the cat and its family
history."
Susan Little, DVM (Persian News, Vol. 9, No. 5, p. 17)
Known causes of kidney cysts that I've run across reviewing available
on-line literature include trauma and infection. However, contrairy to the
suggestions of some folks, I've found absolutely no documentation to support the
belief that BHT, Ethoxiquin, other food additives, environmental pollution, etc. can cause
kidney cysts (or for that matter, cysts anywhere else in the body) in cats, humans, or any
other animal.
Is PKD Confined to
Certain Lines?
No, at least not in Persians. PKD positives have been found in
virtually all major lines of Persians. However, it is at least possible that a few
lines with very small gene pools, particularly if they are not descended from the
hand-full of pre-potent cats upon which many of today's Persians owe their lineage, may
not have PKD in those lines.
However, it is also important to note that virtually all major lines of
Persians have PKD negative cats too.
Is PKD Linked to Certain
Colors?
No. All evidence to date suggests that there is no relationship
between a cat's color and the presence or frequency of PKD.
What
are the Symptoms of PKD?
PKD itself has no symptoms. Only when PKD has progressed to the
point of causing renal failure will symptoms occur, and those symptoms will be those
associated with renal failure, and not PKD specific.
According to Dr. Susan Little, Bytown Cat Hospital, Ottawa, Canada:
"Many cats with PKD will never develop kidney failure so they will
have no physical symptoms at all. Their routine blood tests will be normal.
Other cats will develop kidney failure, depending on the severity of their disease and how
rapidly the cysts grow. The symptoms of chronic kidney failure are the same,
regardless of the cause in cats. Weight loss, poor appetite, increased thirst,
increased urination, lack of energy, vomiting - these are all common signs. We have
to remember that symptoms only appear when 2/3 of kidney function is already lost - until
then, the cat will appear normal. As well, routine blood testing cannot detect
kidney failure until 2/3 of function is lost - before that, blood tests will be normal.
The exception to this is a sensitive blood test for kidney function called the
iohexol clearance test."
Susan Little DVM, DABVP (Feline) (as posted to the PKD List by
Marie Thiers, 11/1/98)
Is PKD Fatal? If
So, Is It Always Fatal?
If a normal cat lived forever, PKD cats would eventually progress to the point where
renal failure occurs, and would eventually die of renal failure. However, in real
life, it is believed that most PKD cats actually die from something other than renal
failure due to PKD. So the practical answer to this question is no, most PKD
positive cats will not die from PKD. However, as Dr. DiBartola notes in a private
e-mail, in the Ohio study he and Dr. Biller reported "the mean age of renal failure
is 7 years in affected cats (range 3 to 10 years of age)." Dr. DiBartola also
notes that "In humans with ADPKD, approximately 50% of affected people have end-stage
renal disease by age 60. PKD1 is associated with a more severe clinical course than
is PKD2. Humans with PKD1 have end-stage renal disease by 54-59 years of age whereas
those with PKD2 have end-stage renal disease by 66-72 years of age." However,
in the cats diagnosed by ultrasound during the spring, summer and fall of 1998, there have
been numerous cases of much older PKD positive cats reported, some with very mild
affliction. One case in particular I remember was a 13 year old female with two very
small cysts in one kidney and one small cyst in the other. In our own case, one of
our positive males is was 7+ years of age when ultrasounded in mid-July 1998. He had
a single 8.5 mm cyst in one kidney, and two cysts in the other (the larger of which was 5
mm). According to Dr. Jonathan Shiroma, our Columbus, Ohio based radiologist, he
will probably never show any signs of renal failure, and should live a normal life.
One of the main problems with PKD deaths is that you can't predict which
positive cat will live a full life and which will die. Or even which will die from PKD
related complications at 15 vs. which will die from PKD at 2 years. So far, Dr. Biller and
other experts have not been able to identify why the disease progresses quickly in some
cats, and slowly in others. All they know is that this is the way it happen.
So the ones that die could be ones that were attributed to "fading kitten
syndrome". Or they could be the ones that were petted out and you lost track of the
owners over the years. Or they could be the ones they died of a cardiac problem at age
three -- before the renal problem surfaced. Or the ones your vet said died of
FUS, or just about anything else, for that matter. Or, you could just be lucky
and have never had a serious case of PKD -- one that would eventually compromise
the cat's health.
How Long Do
Cats Live?
You'd think that would be a simple question, with a simple answer. Unfortunately,
every source I've found gives different information:
- The oldest cat I've seen reference to lived 36 years.
Britanica Online says the lifespan of a
domestic cat in captivity is 21 years (in context, this seems to be the maximum age of the
vast majority of otherwise healthy cats!!!).
The Tidycat website once indicated that the average Russian Blue lives 18 years (I couldn't find a reference to persian
lifespan).
One the VetInfo
website, Dr. Mike Richards says the average lifespan of a cat is 10 to 18 years.
On the HomeArts
Ask the Vet website, Dr. Pamela Abney, billed as a consultant to the American
Association of Veterinary Medical Colleges, says "Indoor cats live an average of 16
to 18 years."
In a recent Persian News, Susan Little, DVM, says "Cats are
considered geriatric between eight and ten years of age, and ... the average feline age is
considered to be 12-15 years." (Persian News, Vol.9,No.5,
pg 17)
One general consensus I've found is that indoor cats tend to live longer
than outdoor cats, so whatever the true average lifespan for a cat, I suspect that an
indoor cat would be at the upper end of any range given. I should also note that
I've found several references to the fact that small dogs tend to live longer (16 - 18
yrs.) than larger dogs (10 - 12 yrs.). The range in dog size is, of course much
greater than for cats, but if the same held true for cats, since Persians are normally
medium to large cats, one would expect their lifespan might be less than that of smaller
cats such as the Russian Blue.
At any rate, from everything I've seen, I think its safe to assume that
the average lifespan of a Persian, kept indoors, should be at least 10 years, and that
those that live 18 years or more are pushing the upper limits of a cat's lifespan and are,
therefore, not an average example of the breed.
Is There
a Cure for PKD -- Or at Least a Treatment?
There is currently no known cure for PKD, in cats or in humans. While a Kidney
Transplant may eliminate the cysts and allow a particular individual to live symptom free,
the underlying genetic makeup for that individual is still one of a PKD positive, and that
individual can still pass the disease on to its offspring. Similarly, dialysis can
replace the function of failed kidneys, but does not change the underlying disease state.
There are also no clinically proven treatments that will eliminate or reduce the cysts
in either human or feline PKD positives. In humans, the best that can be done is to
treat some of the symptoms (see the National Institutes of Health NIDDK National
Kidney and Urologic Diseases Information Clearinghouse website
for details). However, as far as we're aware, there is currently no evidence, one
way or the other, that these same types of treatments will offer any relief to a feline
PKD positive (except that we know Tylenol cannot be safely used on cats). If you
decide to try something experimentally, we suggest careful coordination with your own
veterinarian.
Still in the research phase, there are at least three potential treatments that have
shown positive results in PKD positive animals:
- a soy
protein diet, as reported at the 9th Annual Conference on PKD (see
note below).
- treatment with Potassium Citrate,
as reported by the American Society of Nephrology, July 1, 1998
.
- the use of a specific therapeutic drug to block the activity
of a common growth factor receptor (epidermal growth factor
receptor, or EGFR), a significant reduction in both cyst growth and prolongation of
lifespan can be achieved in an animal model of ARPKD. Since EGFR has previously been
show to be overproduced in both ADPKD and ARPKD, there is hope that this treatment may not
only prove beneficial for ARPKD, but for ADPKD too. In the latter case, it might
also be beneficial for feline ADPKD patients. Again, from the 9th Annual Conference
on PKD (see note below).
At even a more preliminary stage of research, the 9th Annual
Conference on PKD (see note below) also noted PKD physician and researcher, Jared Grantham, MD, has
identified very specific
lipids present in PKD cyst fluid that stimulate fluid secretion and inflammation in
PKD. If researchers can find a way to modify these lipids, this might offer a way to
slow or eliminate cyst growth and preserve renal function in PKD patients.
While none of these research efforts have yet progressed to the point of clinical
trials in humans, much less been tested on cats, they do indicate the level of activity
toward finding treatments for PKD, and someday, perhaps even a cure. And they do
give us reason to hope that these or other treatments for cats with PKD will be available
at some point in the future.
Note: from a old
news article on PKD Cure web site;
when last checked, I could no longer find this article on the web site.
I Don't Understand
All These Percentages. How Do You Figure Out the Expected Outcome From a Particular
Breeding?
The possibilities for offspring are determined by paring the possible genetic
contributions from each parent. Since PKD is autosomal, each parent has two genes at
the PKD locus, and the sperm can carry either of the father's genes, and the ovum can
carry either of the mother's genes. The easiest way to depict this is with the
checkerboard, or Punnett square. This is really a simple 2 x 2 table, where the
heading for each column represents one gene possibility from the sperm, and the row
headings represent one gene possibility for the ovum. The intersection of each
column/row combination represents one genotype possibility for the offspring.
For PKD, these possibilities are as follows. In each case, the first parent
discussed is depicted as the sire in the accompanying chart; however, the sire and dam's
genes can be switched without affecting the results.
Note that the homozygous positives may not actually
survive to breeding age, but are included in this discussion for theoretical consistency
and completeness:
If the genotype of one parent is PP and the other is Pp,
then 50% of the offspring will be PP, and 50% will be Pp
(phenotypically, 100% will be positive):
| |
Sire's Contribution
(Genotype of Sperm) |
|
| P |
P |
Dam's Contribution
(Genotype of Ovum) |
P |
PP |
PP |
} Offspring |
| p |
Pp |
Pp |
If the genotype of one parent is PP and the other is pp,
then all the offspring will be Pp (phenotypically, 100% will be
positive):
| |
Sire's Contribution
(Genotype of Sperm) |
|
| P |
P |
Dam's Contribution
(Genotype of Ovum) |
p |
Pp |
Pp |
} Offspring |
| p |
Pp |
Pp |
If the genotype of both parents is Pp,
then 25% of the offspring will be PP, 50% will be Pp,
and 25% will be pp (phenotypically, 75% positive and 25% negative):
| |
Sire's Contribution
(Genotype of Sperm) |
|
| P |
p |
Dam's Contribution
(Genotype of Ovum) |
P |
PP |
Pp |
} Offspring |
| p |
Pp |
pp |
If the genotype of one parent is Pp and the other is pp,
then 50% of the offspring will be Pp and the other 50% will be pp
(phenotypically, 50% positive and 50% negative):
| |
Sire's Contribution
(Genotype of Sperm) |
|
| P |
p |
Dam's Contribution
(Genotype of Ovum) |
p |
Pp |
pp |
} Offspring |
| p |
Pp |
pp |
If the genotype of both parents is pp, then 100%
of the offspring will be pp (phenotypically, 100% negative):
| |
Sire's Contribution
(Genotype of Sperm) |
|
| p |
p |
Dam's Contribution
(Genotype of Ovum) |
p |
pp |
pp |
} Offspring |
| p |
pp |
pp |
Of course, in real life, the percentages will seldom be
exactly what you'd expect, just as the number of males and females in any population are
not exactly even. Part of the reason is simply the sample size. The smaller the
sample size, the more you should expect it to deviate from expectations. Conversely,
the larger the sample size, the closer you should expect it to resemble expectations.
In the case of PKD, there may be other factors at work, including:
how pervasive the PKD gene is in the total population;
the more "PKD free" pockets or gene pools that have existed in the past, the
less pervasive the disease will be today
whether or not homozygous positives exist in our
breeding population; there is considerable speculation that all or most homozygous positives die in utero, at
birth, or early in life. If homozygote positives die early (before sexual maturity), then PP
x PP, PP x Pp and PP x
pp breedings would never occur. Only Pp x Pp,
Pp x pp, and pp x pp
breedings would occur. And the PP offspring from Pp x Pp
breedings would die early, meaning that instead of 25% PP, 50% Pp,
and 25% pp, only the 50% Pp and 25% pp
would survive to be tested. In this case the phenotypes of the survivors would be
66% positive and 33% negative, rather than the 75% positive and 25% negative that would
occur if homozygous positives do survive.
Why Are Some Catteries
Unscathed by PKD?
Based on all available information, not many Persian catteries of any size have zero
positives, at least unless they've already tested and eliminated positives from their
breeding program. So if "unscathed" means "no PKD positives",
the answer is that not many catteries are unscathed. And because we've
never been able to identify PKD positives before, the only reason any cattery would be
unscathed is pure, blind luck. Those catteries just lucked into not
buying or acquiring any PKD positive breeding stock.
On the other hand, if "unscathed" means "no deaths from PKD", I
expect that almost all catteries with more than a few cats that have been breeding for
more than 5 years have had some deaths due to PKD, even if they don't realize it.
After all, as one of our on-line vets pointed out, the very fact that PKD is asymptomatic
for most of a cat's life, and then manifests itself as renal failure (indistinguishable
from any other cause of renal failure without necropsy), obscures the very existence of
PKD to most breeders.
Are
There Catteries That Truly Do Not Have A PKD Problem? If So, Why?
Yes, there are probably some catteries that have no PKD positives in their breeding
stock.
Why? Because PKD is a genetic disease, not a communicable disease. So any cattery lucky
enough to have only PKD negative foundation stock AND never bring in a PKD positive cannot
produce PKD positive cats, and thus will be a PKD free cattery.
However, the only way to know you don't have a problem is to test
your cats.
Won't A Breeder Know
Whether They Have a PKD Problem Or Not?
Not necessarily, although I guess the answer depends in part on how each breeder
defines "Problem". Some would say that producing any PKD positive cats is
a problem. Others would argue that PKD is really only a problem if cats are dying
from PKD.
Of course, then the question becomes "How many have to die before it becomes a
problem?" I'm not sure that question can be answered except by each individual.
I'm not even sure I can answer that for myself. But I do have a few clues:
- I suspect that if I had just spent 20 grand campaigning the best cat I'd ever bred, only
to have that cat die at 2 years. old from renal failure precipitated by PKD, then one
preventable case of PKD would be too much
- I suspect that if I had just spent three grand (probably money I really didn't
have to spare) on a new male with just the qualities needed to raise our breeding program
to the next level, and that cat died shortly thereafter from PKD, then one
preventable case of PKD would be too many
- I suspect that if I'd watched one of my cats die the horrible death that *some* PKD cats
will experience, then one preventable case of PKD would be too
many.
Most PKD positives won't die from PKD related causes.
But since no one knows ahead of time -- particularly without testing -- which
cats will die and which won't, let's suppose it's just bad luck when its your PKD
positive that dies. Do you really want to take the risk that its
your campaign cat, or your new stud, or your pillow partner?
Particularly when its relatively easy to reduce that risk
substantially by testing your breeders, then using the knowledge gained from those tests
to improve breeding decisions and reduce the incidence of PKD?
See the answer to the following question for additional discussion on this subject.
Are
There Catteries That Have PKD Positive Cats, But Don't Realize They Have
PKD? If So, Why?
Definitely.
There are undoubtedly many reasons why this could occur, including the following:
- PKD expresses itself differently in each cat. And, based on the best information
available, it appears that most PKD positive cats die from other reasons -- not
from End Stage Renal Failure resulting from PKD. So it is entirely possible to
have PKD positives and never have a cat exhibit the signs of renal failure, much less die
from PKD.
- PKD can only be detected by ultrasound or necropsy. Most if not all PKD cases
would be picked up on necropsy with histopathology, if that were routinely done.
But most breeders don't even routinely do gross necropsies. Fewer still have
histopathology done unless they are looking for something specific (like FIP).
- PKD itself is asymptomatic. Only when PKD progresses to the point of causing Renal
Failure will symptoms occur, and then the symptoms are indistinguishable from renal
failure caused by other kidney disease or injury.
- While PKD has been described in research literature since the '60s, and has undoubtedly
been around much longer, few breeders or veterinarians have really looked for cases of PKD
until this year (1998).
- Many breeders tend to pet out their breeding stock by the age of 5 or 6 years of age (or
alternatively, place them in other catteries). Because Autosomal Dominant PKD tends
to be a "late onset" disease, it's quite possible that a breeder may have
inadvertently "passed the problem" on to a pet owner or another breeder before
there is any sign of a problem.
At the Columbus, Ohio PKD Clinic in August, 1998, a breeder/veterinarian mentioned that
when the PKD issue was first raised, she said to herself "I don't have a problem. I'm
a vet. I'd know if my cats had PKD or any other disease." When she finally
tested "just to prove I was right", she found out how wrong she was.
Our own vet said "You don't have a problem -- I wouldn't waste the money
testing". After all, we'd done gross necropsies on virtually *all* our deaths
for many years, and complete histopathology whenever the gross exam indicated further work
was needed. In all those years, we only had three cases of renal failure, two of which
were diagnosed as PKD (a newborn [2 to 4 days old], and a four month old. In both
cases, we altered the suspected parent before producing any more litters. Yet
unfortunately, when we finally tested, 35% of our cats were positive, including both our
foundation male and our primary female. Unknowingly, we'd bred them together many times,
keeping the best of most litters. As it turned out, we don't have a negative male out of
either of these parents, most of the Grands we've bred are positive, and half of all the
Grands we currently own are positive. Yet our vet was sure we didn't have a
problem, and so were we.
Are
There Breeders Who Know Deep Down That They Have A PKD Problem, But Won't Admit
It -- Even to Themselves?
The simple answer is yes, absolutely. It's always easier to deny a problem than to face
it -- at least, in the short term.
However, I suspect that most of us have been in denial about a health problem at some
time or another -- whether its our own problem, a loved one's problem, or our cattery's
problem. For most of us, its very difficult to accept that we've unknowingly been
breeding cats with potential health problems, and have innocently sold cats with those
same problems to other breeders and to the pet-buying public. So while we can
empathize with those in denial, we do need to work toward educating them and convincing
them that testing is the beginning of a solution, not the end of life as they know it.
Are There Catteries That
Have Tested For PKD and Have Reported No PKD Positive Cats?
There's a useful web site which reports statistics on PKD testing to date.
Although I'm sure there are many catteries who, for one reason or another, have chosen not
to report their results, I find this the best source of information currently
available. Taking the stats for US Catteries through 10/8/98 and using MS Excel to
manipulate the data, I came up with the following information:
- Slightly less than one half of the US cats tested are included in the Cattery stats
(1547 vs. 3545), so either many catteries haven't reported, or many catteries reported
only some of those tested to Barb.
- The US catteries who have reported their stats have a
significantly lower rate of positives than the total statistics indicate, which means that
those that have not reported have a significantly higher rate of positives:
| |
|
|
|
|
|
|
Total
Tested |
#
Positive |
%
Positive |
|
Cats reported by US catteries: |
1547 |
469 |
30.32% |
|
Cats not reported by US catteries: |
1998 |
836 |
41.84% |
|
All US Cats reported |
3545 |
1305 |
36.81% |
|
|
|
|
|
- Based on those US catteries reporting, the smaller the number of cats tested, the lower
the percentage of positives:
| |
|
|
|
|
# Cats Tested |
% Positive |
# Catteries, Total Tested |
|
More than 20: |
32.43% |
(14 catteries, 407 cats total) |
|
13 to 20: |
31.72% |
(34 catteries, 536 cats total) |
|
6 to 12: |
27.94% |
(55 catteries, 494 cats total) |
|
1 to 5: |
26.36% |
(33 catteries, 110 cats total) |
|
|
|
|
|
or |
|
|
|
|
|
|
|
More than 12: |
32.03% |
(48 catteries, 943 cats total) |
|
12 or Less: |
27.65% |
(88 catteries, 604 cats total) |
|
|
|
|
- Based on those US catteries reporting, the more cats tested, the less of being PKD free:
| |
|
|
|
|
# Cats Tested |
% with
Positives |
Catteries w/o Positives
vs. Total Catteries |
|
More than 12: |
00.00% |
( 0 out of 48 catteries) |
|
6 to 12: |
14.55% |
( 8 out of 55 catteries) |
|
1 to 5: |
42.42% |
(14 out of 33 catteries) |
I suspect (i.e., no proof whatever) that many of the smaller catteries have
tested with their own vets, and that there may be a higher percentage of false negatives
in that group, so the differences between small and large catteries may not be as marked
as the figures above indicate. And, of course, we don't know about the catteries large or
small that have tested but have not reported their results. But one
thing is pretty clear based on the results to date -- very few catteries with more than 12
cats are truly PKD free unless they have tested and eliminated the positives from their
breeding program.
So this brings me back full circle. Are there catteries that really have no
PKD problem? Quite probably, but not very many. Are there catteries that think
they don't have a problem? Definitely, though if they test, most will find they too have
PKD.
What
Affects The Number of PKD Positive Cats In a Breeding Program?
The only thing that affects the number of PKD Positives in any
particular breeding program are the number:
- The number of PKD positives cats you've purchased or otherwise acquired
over the years that are still in your breeding program.
- The number of PKD positives that you breed and keep.
- Whether any positives are homozygous or heterozygous. (Note that homozygous positives may not exist ex
utero, or may not survive until breeding age.)
The number of PKD positives you breed, assuming you have some positives
to start with, is partly a product of luck (as with any other breeding percentages), but
primarily a factor of how you breed your positives and negatives:
- all offspring from even one homozygous positive parent will be positive;
if both parents are homozygous positive, all offspring will also be homozygous positive
- breeding heterozygous positive to heterozygous positive produces, on the
average, 75% positives (though some believe the homozygotes die in utero, at birth, or
shortly thereafter, in which case 67% of the survivors would be positive)
- breeding heterozygous positive to negative produces, on the average, 50%
positives and 50% negatives
- breeding negative to negative produces all negatives, so if you don't
have any PKD positive breeders to begin with, or breed only PKD negatives, you won't
produce any PKD positives
Is Spaying or Neutering Harmful to the PKD Positive
Cat?
I'm not aware of any evidence that spaying or neutering would put a PKD
positive cat at any more risk than any other cat, unless the cat was already in kidney
failure. However, since certain anesthesia agents can be nephrotoxic, in my opinion
it would be best not to use these agents in any cat with known kidney problems, including
PKD.
According to Dr. Susan Little, Bytown Cat Hospital, Ottawa, Canada:
"I cannot see how spaying would have any effect, positive or
negative, on the progression of PKD. If a cat is already in early kidney failure, the
stress of anesthesia and surgery could certainly precipitate a crisis, however. This is
true of kidney failure due to any cause."
Susan Little DVM, DABVP (Feline) (as
posted to the PKD List by Marie Thiers, 11/1/98)
In our Columbus, Ohio PKD Clinic, Dr. Biller did mention
that PKD in cats seems to progress in spurts, but that so far, we had not been able to
identify what causes these spurts to start/accelerate or stop/decelerate. If
stress turns out to be one of the causes, then I suspect the stress of any surgery,
including spaying or neutering, could precipitate a spurt. But then, so could
cycling, breeding, or even being placed into a pet home, since all these are known
stressors.
Is PKD Associated
with Cysts in Other Organs Such As the Liver and/or Ovaries?
According to Dr. Susan Little, Bytown Cat Hospital, Ottawa, Canada:
"… a few cats with PKD also have cysts elsewhere, such as in the
liver and the reproductive tract. Livers can have cystic disease that is not related to
PKD."
Susan Little DVM, DABVP (Feline) (as
posted to the PKD List by Marie Thiers, 11/1/98)
Researching PKD on the web, I have seen references to human PKD being
linked to both cysts in other organs and to a certain type of cerebral aneurysm.
However, so far, I haven't seen any indication that similar links have been established
for feline PKD.
Is Dr Biller going to do further studies?
To quote Dr. Biller himself:
"I am getting ready to do a large study and see if cysts are in other non Persian
cats. That may let me know if benign cysts exist in Persians."
David S Biller, DVM, DACVR (as forwarded
to the PKD List by BJ Fox, 10/21/98)
At the Columbus PKD clinic, Dr. Biller mentioned this study, which he
said will also involve 4 or 5 other radiologists. I don't remember all the details, but I believe
each participating radiologist will scan the kidneys of the next 400 or so non-Persians
they treat (until 2000 total are scanned), and provide the results to Dr. Biller, who will
correlate the information.
From listening to and talking to Dr. Biller, I suspect he and other
radiologists would like to do much more research, if the funding were
there. But I also personally suspect that for Dr. Biller himself, with
his full time faculty position at Kansas State College of Veterinary Medicine, traveling
to various PKD clinics almost every weekend, and a wife and kids to take care of too,
there's currently not much band-width available to handle additional research.
I'm Just Learning About
PKD. Right Now, I'm a Little Skeptical About The Whole Thing. When I Ask
Questions to Find Out More, Why Don't I Ever Get The Answers I Need? And Why
Are The Answers I Do Get So Nasty Sometimes?
Like many, we were skeptical at first, and did go through the
tedious process of trying to make sense of all this myself -- both in trying to decide
whether to test or not, and later in trying to deal with the test results. And we got our
share of flames because of some of the questions we asked and some of the positions we
took.
However, in our experience, most knowledgeable breeders are more than willing to help
others through the process of deciding what to do. But the process will go much
smoother if you understand, and can avoid, a few major obstacles:
- Some folks ask their questions in what appears to be a belligerent way;
regretfully, some of us who are trying to make sense of the whole mess can be caught off
guard and react poorly. Once all parties begin to communicate instead of criticizing, we
can usually answer any questions that arise.
- Sometimes, questions are very clear to the person asking the question, but are not very
clear (or mean something entirely different) to those trying to respond. This always adds
an element of confusion to the discussion, and the person who originally asked the
question eventually feels their questions aren't being answered. And again, with good
communications, the problem can be quickly surmounted.
- Other times, our answers may be clear to us, but are not very clear to the person who
asked the question. Again, establishing good, non-combative communications is the link to
getting understandable, accurate as possible answers. So politely ask again if the
answer you get doesn't make sense, or doesn't meet your needs. But make sure the
person you ask understands your question, and you understand their answer.
- There have been times (hopefully in the past) when many of us have felt "under
attack" by those who don't believe in testing and/or think the whole PKD issue is
"much ado about nothing". Consequently, I'm afraid many of us -- myself
included -- occasionally, and often incorrectly, see some questions as an
"attack", and sometimes respond with a counter-attack. Even when none is
necessary. Hopefully, as more folks test and we feel less under attack, we'll all feel a
little less defensive and our responses will be less defensive as a result.
- Finally, many folks assume there are answers to all their questions.
Unfortunately, in many cases there are no answers. In other cases, there are answers, but
they aren't the answers the questioner is looking for. Sometimes, when there is no
answer, the only responses to that question are opinions. Most of us, I suspect, have
developed our own theories/opinions to fill in the missing pieces in our puzzles.
Some are willing to share their opinions, others aren't. But in any case, where there is
an absence of facts, questions often elicit different (and even contradictory) opinions
from different people. And I think that's really a healthy sign that we're all
trying to understand the issues and deal with them as best we can.
So if those who are honestly looking for answers will be patient, and understand that
we are trying the best we can to help, you'll eventually get the answers you need.
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|
