| Polycystic kidney disease (PKD)
is an inherited kidney disease which has become very common in
Persian cats and Exotic Shorthairs and has also been introduced to some other breeds, eg, British Shorthairs. Many cat breeders are aware
of the problem and have been taking steps to eradicate the gene
defect from their breeding lines.
When the disease was first recognised the only practical way to identify the affected cats was by ultrasound scanning of the kidneys but a gene test is now available for AD-PKD that has now become the test of choice for many breeders. A cheek swab or blood sample can be taken from cats of any age and the sample is then posted to one of the reputable laboratories offering this test.
Ultrasound scanning remains a good screening test for the disease too, especially for breeds where the gene test has not been verified. In advanced disease the cysts are large and diagnosis is straightforward, but it can be very difficult to identify cysts in young cats (ie, before breeding age) so for pre-breeding diagnosis the scan must be undertaken by a specialist veterinary ultrasonographer using a high definition ultrasound probe and the cat must be at least 10 months old.
A note of caution: In humans there are at least six different genes that can cause different forms of PKD. It appears that PKD in Persians and related breeds is all caused by the autosomal dominant gene defect (AD-PKD), but other forms of PKD caused by a different, unrelated gene mutation may exist (in Persians, or in completely unrelated breeds) and if so these other forms of PKD would not be detected by the AD-PKD gene test.
The
gene test
The
gene test is currently available in the UK at:
The
tests can be run on a blood sample, or on a sample of cheek cells
(known as a buccal swab) collected by swabbing the cat's mouth.
Cats
can be tested at any age, but if pre-weaning kittens are being
tested it must be done using a blood sample rather than a cheek
swab. This is because nursing kittens will have traces of the
queen's DNA in their mouth, and this could cause a false test
result. However, collection of cheek swabs is significantly less
stressful for the cat, or kitten, than collection of a blood sample,
so it may be preferable to wait until the kitten is weaned, so
that testing can be done using a cheek swab.
FAB PKD Negative Register
The FAB PKD Negative Register is now available to view by clicking here. The register allows breeders and owners to look up negative cats - useful for breeders who have perspective owners asking about the AD-PKD status of parents of kittens and for finding breeding cats.
Cats that have screened negative for AD-PKD by either ultrasound scanning or by the gene test (with a microchip number on the sample and result), can be listed on the FAB PKD Negative Register.
Anyone having their cat gene tested can go on the Register as long as the swab is taken by a vet and the cat's microchip number is recorded by the vet on the sample at the time of submission to the laboratory. Breeders who wish their gene-tested cats to be eligible for inclusion on the FAB PKD Negative Register must follow the procedures outlined below.
How
to have your cat tested if you want negative results to go on the FAB PKD Negative Register
- Contact your local vet, let them know you want to have your cat(s) gene tested and make an appointment to see the vet.
- Take your cat(s) to your local vet to be microchipped and sampled (buccal swab or blood sample). Your vet will need to have a laboratory submission form for one of the UK laboratories offering the test. These forms can be downloaded from the labs' websites (www.bristol.ac.uk/vetpath/lvd/lvd.htm or www.aht.org.uk/pdf/perpkdformv2.2.pdf). If our local practice has not previously been involved with the AD-PKD gene testing of cats they may not have copies of these forms, but you can download and print copies yourself by following the link above. You will need one copy of the form for each cat that is to be tested.
- You and your vet will need to complete all the relevant sections of the laboratory submission form. Make sure that your vet records your cat's microchip number on the sample pot at the time of collection of the sample. This is essential if you wish your cat to be included on the FAB PKD Negative Register.
- Your vet will post the samples to the laboratory and the results will be faxed and posted to the veterinary
practice. Ensure that your vet passes on to you a copy of each Submission Form, as well as a copy of each
results form.
- When you receive the results from your vet, any negative results can be included on the FAB PKD Negative Register. You will need to make copies of both the submission form and the results form and submit them to the FAB, at the address below, along with a cheque to cover the administration fee. The current administration fee is £4 per cat, or £3 if two or more cats owned by the same breeder are submitted at the same time.
NB: If you want to go on the FAB PKD Negative Register but wish to use
the UC Davis Laboratory in the USA, you will
still need to get your vet to take a sample and record your cat's microchip number on the sample at the time of collection. Then when completing the UC Davis laboratory submission form your vet will need to ask the laboratory to write the microchip number on the result sheet.
How to have your cat tested if you do not want negative results to go on the FAB PKD Negative Register
If you do not want your negative cats to be advertised on the FAB PKD Negative Register you do not need to have them microchipped. You can still follow the other steps outlined above, or you may prefer to collect a buccal swab sample yourself. Langford Diagnostic Laboratories and the laboratory at UC Davis in America will accept samples submitted by owners. To post the samples appropriate packing of the sample is required. A customs declaration form should be completed for samples destined for America.
Making
use of the results of a genetic test
Screening
for AD-PKD allows accurate identification of affected cats so that
an informed decision can be taken as to whether or not the cat
should be used for future breeding. If the cat is found to be
negative then there is no problem, however if the cat is positive
a number of other factors may need to be considered. The affected cat may
come from a particularly valuable breeding line or it may be free
of some of the other congenital or familial problems which affect
Persian cats and so may have a valuable role to play in maintaining the breed. A further concern is that by avoiding breeding
from all AD-PKD positive Persians there will inevitably be increased
in-breeding between the remaining AD-PKD negative cats and this may bring other problems to the fore.
If
there are enough good reasons to use a particular affected cat
for breeding, enough to outweigh the certainty that it will pass
AD-PKD on to a proportion of its offspring, then it may be appropriate
to mate that cat to cat known to be free of AD-PKD. On average 50%
of the offspring will be affected by AD-PKD, but a number of AD-PKD
negative kittens would also be expected and these could then be
used as future breeding stock so as to maintain the desired breeding
line, although there will remain the moral dilemma of what to
do with the AD-PKD positive kittens that have been produced by this
mating.
Updated November 2008
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