Polycystic kidney disease(PKD)

Autosomal dominant polycystic kidney disease (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?

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.

How can I find out if my cat is affected?

Testing for 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.

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.


Interpretation of test results:

A Normal AD-PKD genetic test result means that the cat does not have the respective genetic mutation.

An Affected AD-PKD genetic test result means that the cat has one normal and one mutant copy of the PKD1 gene. Presence of the mutant PKD1 gene has been strongly associated with polycystic kidney disease.