POLYCYSTIC KIDNEY DISEASE (PKD)
What is polycystic kidney disease?
Autosomal Polycystic Kidney Disease (PKD) is a progressive, inherited condition which causes multiple fluid filled cysts on the kidneys of Persians/Exotic cats & breeds with Persians/Exotics in their lines.
Cysts are present from birth, but start out small, slowly increasing in size. Cysts can range from very small to several centimetres in diameter. The increasing size of the cysts damage the normal kidney tissue, eventually causing kidney failure.
The number of cysts & the speed & size in which they grow varies from cat to cat. The average age of kidney failure in cats with PKD is 7 years, but some cats will suffer from kidney failure at an earlier age & some cats much later, and in fact succumb to something other than PKD.
How is PKD inherited?
Genetic studies in cats have shown that PKD in cats is autosomal (non sex linked gene) dominant. This means only one parent needs the gene to pass it onto the offspring. There is a 50% chance of a cat inheriting PKD if a parent has it. If a cat is genetically free of PKD it is not possible to pass it onto offspring.
What are the signs of PKD in cats?
- Weight loss
- Polyuria (excessive urination)
- Polydipsia (excessive thirst)
- Enlarged kidneys
- Ultrasound: Ultrasound diagnosis is 98% accurate after approximately 10 months of age. Ultrasound should be performed by a veterinarian skilled in the use of ultrasound.
- Genetic Test: A swab from inside the cheeks (buccal swab) is provided to a specialised laboratory for testing. This test is 100% accurate.
How is it treated?
There is no way to slow down the growth of the cysts & they can't be removed. As the kidneys begin to fail, they lose their ability to filter out toxins. To understand the treatment it is necessary to give a brief summary of how the kidney's work;
Kidneys help control blood pressure by releasing an enzyme called renin. When blood pressure drops and kidneys don’t receive enough blood, renin is released; causing blood vessels to contract (tighten). When blood vessels contract, blood pressure goes up.
- Kidneys filter waste products & excess water from the blood. The cleaned blood stays in the body & the waste products leave the body in urine.
- Stimulation of red blood cell production.
- They help maintain the proper balance of acid and minerals, including sodium, calcium, potassium and magnesium, in the blood.
Therefore helping reduce the level of toxins in the cat is important. Treatment is based on that of a cat with chronic renal failure & may include:
- Administration of fluids subcutaneously to treat dehydration.
- Prescription diet: Such a prescription diet contains a lower percentage of protein and less phosphorus than normal cat food. Cats need protein every day for growth, building muscles and repairing tissue. After the body uses the protein in the foods, a waste product called urea is made. Cats with kidney failure are not able to get rid of this urea normally. Damaged kidneys may not be able to remove phosphorus from the blood. This causes the level of phosphorus in the blood to become too high. A high blood phosphorus level may cause the cat to lose calcium from their bones.
- Phosphorus binders may be given. These come in tablet or capsule form.
- High blood pressure (hypertension): Medication may be prescribed if your cat's blood pressure is too high.
- Antacids & anti nausea medication.
- Erythropoeitine: The kidneys produce a hormone, erythropoietin, which instructs the bone marrow to produce red blood cells. Cats with kidney failure often have a low red blood cell count. Only the human form is available & some cats may eventually recognise this substance as foreign & antibodies will be created against it.
What is the likely outcome for a cat with PKD?
It really varies from cat to cat. How many cysts are present, how large they grow & how quickly they grow. A cat with only a few small & slow growing cysts may live to an old age & eventually die from something unrelated to PKD. Other cats may have numerous, large & quick growing cysts & die at an early age.
Is there a cure?
No, there isn't a cure for PKD. Breeders are advised to test their cats & if they are found to have PKD have them desexed.
Please Note: I do understand why some breeders have continued to use PKD positive cats in their breeding programs. Some lines are just too precious to lose. And in particular, when breeding colours as uncommon as chocolate and lilac, we need all of the different lines that we can get!! So, if you see a cattery that is NOT PKD negative and you are interested in a kitten from that cattery, just ask the breeder why it is they are working with PKD positive cats. Just because a cat is PKD positive doesn't mean he/she WILL die of PKD.