Polycystic 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 kidney failure.

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.

What 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.

How 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?

AD-PKD 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.
• Every cat with AD-PKD will have the abnormal gene, even if that cat only has a few small cysts in its kidneys.
• A cat only needs one of its parents to be affected with AD-PKD in order to inherit the abnormal gene.
• Every breeding cat with AD-PKD will pass the disease on to a proportion of its kittens, even if it is mated with an unaffected cat.

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.

Why has PKD become so common?

PKD 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.

Can PKD be cured?

Unfortunately 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.

Once 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.

Do all cats with PKD die of renal failure?

The 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.

Unfortunately 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.

What can be done about PKD?

All 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