Cat - Polycystic Kidney Disease (PKD)

What is polycystic kidney disease?

Polycystic kidney disease (PKD) is an inherited condition in cats, 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.

All cats that are affected by PKD have cysts in their kidneys, but the number of cysts present, and the rate at which the cysts grow is very variable. 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 7 or 8 years old, however in some cats kidney failure will occur at a much younger age while in other cats kidney failure will not develop until into old age. At the moment there is no way of predicting how rapidly the disease will progress in any particular cat.

Can PKD be cured?

Unfortunately there is no treatment that will prevent or delay 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.

How can I tell if my cat has polycystic kidney disease?

It can be very difficult to identify PKD in its early stages when the cysts are very small. At this stage in the disease the kidneys will be working normally and the cat will show no outward signs of the disease. Even if your cat is regularly examined by your vet the kidneys will feel normal on palpation (feeling them through the body wall), they will look normal on an x-ray, and blood and urine tests will not show any abnormalities. Diagnosis at this early stage is most commonly achieved by examining the cat's kidneys using a high definition ultra-sound scanner to look for evidence of fluid filled cysts within the kidneys. Recently a DNA test has also been developed that can identify affected cats. The test can be performed on either a blood sample or cheek swab. It has the advantage of being more accurate and does not need the expertise required for an ultrasound scan.

Once the cysts have grown large enough to disrupt kidney function signs of kidney failure will develop. Common signs of kidney failure include weight loss, poor appetite, increased thirst and increased urine production and occasionally vomiting. At this stage your vet may detect that the kidneys feel abnormal on palpation, and blood and urine tests will indicate that the kidneys are not working properly. Even at this advanced stage an ultrasound scan is still the best way to confirm that the kidney failure is due to PKD rather than any other form of kidney disease.

How common is PKD in cats?

Unfortunately PKD has now become very common in some cat breeds. Persian cats have the highest incidence of problems and studies around the world and in the UK have shown that around 1 in 3 Persian cats are now affected by the disease. Other cat breeds that have been developed using Persian bloodlines, like Chinchillas and Exotics, also have a significant proportion of affected cats, but in other unrelated breeds it is a rare condition.

How is PKD inherited?

PKD is the result of a single, autosomal, dominant gene abnormality. This means that:-

• Every cat with the abnormal gene will have PKD, there are no unaffected carriers of the gene.
• Every cat with PKD will have the abnormal gene and can pass the gene onto its kittens, 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 PKD in order to inherit the abnormal gene and be affected itself.
• Every breeding cat with PKD will pass the disease on to a proportion of its kittens, even if it is mated with an unaffected cat.

What can be done about PKD?

PKD has become very common in some breeds of cat because it 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. Many cat breeders are now aware of this problem, and are trying to identify affected cats at a young age, before they have been used for breeding.

The Feline Advisory Bureau (FAB) has now set up a nationwide screening program to identify which cats are affected and to allow breeders to make informed decisions about which cats to use for future breeding. The FAB screening program involves either an ultrasound examination of the cats kidneys by one of a panel of approved, highly qualified veterinary ultrasonographers, or a DNA test. A FAB approved certificate stating the result of the scan or DNA test for that particular cat is then issued.

Anyone who is planning to buy a Persian cat or kitten should make sure that the cat, or both of its parents, have been checked by an experienced ultrasonographer using a high quality ultrasound machine, or had the DNA test before they buy the cat.

More information about PKD and the FAB PKD Screening Scheme is available from the FAB Office (Feline Advisory Bureau, Taeselbury, High St., Tisbury, Wiltshire, SP3 6LD. Tel 01747 871872) or on the FAB website