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. Initially, they are very small, but they grow larger over time and may eventually disrupt kidney function, resulting in kidney failure.
All cats with PKD 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 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.
Cysts may also develop in other organs, particularly the liver and pancreas. This condition can also lead to the development of cardiac abnormalities.
What causes polycystic kidney disease?
Polycystic kidney disease is an inherited disease and has become common in certain cat breeds. Persian cats have the highest incidence of PKD. Studies have shown that the disease affects around one-third of Persian cats. Breeds that have been developed using Persian bloodlines (e.g., Himalayan, Scottish Fold, British Shorthair, Chartreux, Exotic Shorthair, Burmilla, and Siberian Neva Masquerade) are commonly affected as well. In most other cats, especially mixed breeds, the condition is rare.
"Polycystic kidney disease is an inherited disease and has become common in certain cat breeds."
PKD is the result of a single autosomal dominant gene abnormality. This means that every cat with the abnormal gene will have PKD. There is no sex predilection for this condition, meaning that both males and females can be affected. All cats with the PKD gene, even those with only a few small cysts or those with no clinical signs, will pass the genetic defect onto their kittens, even if mated with an unaffected, healthy cat. In other words, a cat only needs one of its parents to be affected with PKD to inherit the abnormal gene.
It should also be noted that some cats with PKD have been found to be negative for PKD gene mutation, meaning that there may be other mutations that cause PKD in the cat.
What are the clinical signs of polycystic kidney disease?
Affected cats may present for typical signs of renal failure such as drinking and urinating a lot, not eating, weight loss, and vomiting.
How is polycystic kidney disease diagnosed?
The diagnosis is based on breed, medical history, clinical signs, blood and urine tests, genetic testing, and ultrasound evaluation of the kidneys. Special radiographic dye studies may also be used in certain situations.
Blood tests will reveal increased levels of waste products normally eliminated by the kidneys, possible anemia (low numbers of red blood cells), and electrolyte abnormalities. An examination of the cat’s urine will likely reflect renal dysfunction (inability to properly concentrate their urine, protein in the urine, abnormal cells in the urine sediment). X-rays may show an enlarged kidney that may be irregular in shape. Ultrasound examination is usually the best imaging tool for this condition, as the cysts are readily apparent using this diagnostic device. The cysts are visible from an early age, well before any signs of renal failure might develop.
"Ultrasound examination is usually the best imaging tool for this condition..."
How is polycystic kidney disease treated?
There is no specific treatment for PKD, as the disease causes similar clinical signs to those seen in cats with chronic kidney disease (CKD). Therapeutic 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 the handout “Chronic Kidney Disease in Cats”). Periodic recheck examinations and follow-up diagnostic testing are recommended to monitor the progress of the disease, thereby allowing for appropriate treatment modifications.
What should I do if I am interested in purchasing a kitten with Persian bloodlines?
If you are interested in purchasing a Persian kitten or one with Persian bloodlines listed in this handout, it is very important to verify that it is not carrying the PKD gene. Genetic testing for PKD is available (from several companies in both North America and Europe) to check if a cat has the defective PKD gene, and therefore will develop the condition. Consult your veterinarian for details about this testing.