What is polycystic kidney disease?
Polycystic kidney disease or 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. Initially they are very small but they grow larger over time and may eventually disrupt kidney function resulting in kidney failure.
"The number of cysts and the rate at which the cysts enlarge varies between cats."
All cats with polycystic kidney disease have cysts in their kidneys, but the number of cysts and the rate at which the cysts enlarge varies between cats. In most cats, the cysts enlarge slowly and affected cats will not show any signs of kidney disease until later in life, typically around seven or years of age. In some cats, kidney failure will occur at a much younger age while in other cats kidney failure will not develop at all. There is currently no way of predicting how rapidly the disease will progress in a particular cat.
What causes polycystic kidney disease?
Polycystic kidney disease (PKD) is an inherited disease. Unfortunately, PKD has become very common in certain cat breeds.
"Persian cats have the highest incidence of PKD."
Persian cats have the highest incidence of PKD. Studies have shown that the disease affects around one-third of Persian cats. Breeds such as Chinchillas and Exotics, that have been developed using Persian bloodlines, also have a significant number of affected cats. In the majority of other cats, especially mixed breeds, it is a rare condition.
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. Even if the cat only has a few small cysts in its kidneys or has no clinical signs, it can still pass the genetic defect onto its kittens, even when mated with an unaffected, healthy cat. A cat only needs one of its parents to be affected with PKD in order to inherit the abnormal gene and be affected itself.
How is PKD diagnosed?
The diagnosis is based on breed, medical history, clinical signs, blood and urine tests and ultrasound evaluation of the kidneys.
"Early diagnosis is imperative for all potential breeding cats..."
Special radiographic dye studies may also be used in certain situations. Early diagnosis is imperative for all potential breeding cats; PKD is best diagnosed in these cases by an experienced ultrasonographer.
If you are interested in purchasing a Persian kitten, it is very important that you verify that it is not carrying the PKD gene. Since PKD is normally unapparent until middle age, you should ask for a complete genealogy and results of ultrasound evaluation of both parents.
What is the treatment for PKD?
There is no specific treatment for PKD. Special diets, fluid therapy and medications to reduce nausea and vomiting and to block the absorption of phosphorus are often used to treat the symptoms of kidney failure (for further details, see our handout on Chronic Renal Failure).