kidney disease is a disease in which a large number of fluid
filled cysts form within the kidneys. These cysts are present
from birth in affected cats but they start off very small
and then gradually increase in size until eventually they
compromise the surrounding normal kidney tissue and cause
In cats polycystic
kidney disease is an inherited disease which is a particular problem in
Persians and Exotic Shorthairs although it is also present in some other breeds. It is inherited as an autosomal dominant trait so its full name is autosomal dominant polycystic kidney disease (AD-PKD). Most Persian breeders are aware of this potential problem for their cats and are testing their cats for the disease before using them for breeding. If breeders are able to avoid using affected cats in their breeding lines it should be possible to eradicate the disease from the breed. To help this process the Feline Advisory Bureau has set up an FAB PKD Negative Register to allow breeders and buyers of kittens to identify cats that have been accurately identified as being negative for AD-PKD.
is polycystic kidney disease?
Autosomal dominant polycystic
kidney disease (AD-PKD) is an inherited condition that causes
multiple cysts (pockets of fluid) to form in the kidneys.
These cysts are present from birth. They start out very small
but they grow larger with time and may eventually severely
disrupt the kidney; when that happens the kidney can no longer
work and kidney failure develops. The cysts usually grow quite
slowly, so most affected cats will not show any signs of kidney
disease until relatively late in life, typically at around
seven or eight years old, or even into older age. However, in some cats kidney failure
will occur at a much younger age and at the moment there is
no way of predicting how rapidly the disease will progress
in any particular cat.
common is PKD in cats?
Unfortunately AD-PKD has now become very common in some cat breeds.
Persians and Exotic Shorthairs have the highest incidence
of problems and studies around the world have shown that around
one in three cats from these breeds are now affected by the
disease. The recent widespread adoption of pre-breeding testing by Persian and Exotic Shorthair breeders in the UK does mean that here the incidence of the disease is dropping, but it still remains a common problem within these breeds. Other cat breeds that have been developed using Persian
bloodlines, and breeds that have allowed outcrossing to Persian
cats (eg, British Shorthairs) may also have a proportion of
affected cats, but in other unrelated breeds it is an extremely
rare condition. To find other information on PKD in other breeds click here...
How is PKD inherited?
is the result of a single, autosomal, dominant gene abnormality.
This means that:-
Every cat with the abnormal gene will have AD-PKD; there are no unaffected carriers of the gene.
cat with AD-PKD will have the abnormal gene, even if that
cat only has a few small cysts in its kidneys.
cat only needs one of its parents to be affected with
AD-PKD in order to inherit the abnormal gene.
breeding cat with AD-PKD will pass the disease on to a proportion
of its kittens, even if it is mated with an unaffected
Inheriting two copies of the abnormal gene (one from each parent, ie, being homozygous) causes such severe disease that the affected kitten dies before birth. All affected cats therefore carry one AD-PKD gene and one normal gene (ie, they are heterozygous).
How can I find out if my cat is affected?
Testing for AD-PKD can be done in two ways. A gene test is available which accurately identifies all cats with the abnormal gene. This test can be run on a blood sample, or on a mouth swab. The disease can also be identified by ultrasound scanning of the kidneys. In advanced disease the cysts are large and diagnosis is straightforward, but it can be very difficult to identify the 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 very high definition ultrasound probe and the cat must be at least 10 months old. Unfortunately this limits the availability of this method of testing, and so breeders now prefer to use the gene test which can be done at any age.
A note of caution: In humans there are at least six different genes that can cause different forms of PKD. It appears that AD-PKD in Persians and related breeds is all caused by the autosomal dominant gene defect, but other forms of PKD caused by a different, unrelated gene mutation may exist (in Persians, or in completely unrelated breeds); if so these other forms of PKD would not be detected by the AD-PKD gene test and diagnosis would have to be undertaken by ultrasound.
has PKD become so common?
doesn't usually cause kidney failure until quite late in life,
so an affected cat may have been used to produce a large number
of litters of kittens before it becomes ill itself.
PKD be cured?
there is no available treatment that will prevent the development
of kidney failure in a cat that is affected by PKD. The cysts
are present from birth and cannot be removed, nor can they
be prevented from growing.
kidney failure has actually developed, treatment can be used
to try to reduce the amount of work that the kidneys have
to do, and to try to reverse the secondary effects of renal
failure. Such treatment will improve the cat's quality of
life, but will not alter the underlying disease or stop the
cysts from growing larger.
all cats with PKD die of renal failure?
number of cysts present in each kidney, and the rate at which
the cysts grow, varies considerably from cat to cat. Severely
affected cats or cats with rapidly growing cysts will develop
renal failure at an early age, and will die from PKD. Most
affected cats will appear to be quite healthy until later in
life but will eventually succumb to renal failure and die
from PKD. Some cats with few cysts or slowly growing cysts
may remain healthy into old age, and may die from other conditions
before renal failure develops.
there is currently no way to predict how quickly the condition
will progress in an individual cat, and at what age renal
failure will occur.
can be done about PKD?
cats that carry the abnormal gene are affected with AD-PKD, and
affected cats can be identified before they reach breeding
age. This makes it relatively easy to eliminate the disease
from a breeding group; if all cats in the high-risk breeds
were to have their kidneys scanned or be gene tested before
they were used for breeding, and if affected cats were not
then used for breeding, then PKD could be eradicated from
those breeds in a single generation.
Finding an AD-PKD negative cat
The FAB PKD Negative Register provides a list of cats that have been accurately tested for AD-PKD either using the gene test, or by having their kidneys scanned by an FAB approved specialist ultrasonographer before the gene test became available.
Updated November 2008