Polycystic Kidney Disease
What is It?
Polycystic Kidney Disease, known as PKD, is an autosomal dominant genetic disease of the kidneys which is passed on by one or both parents - siblings may be unaffected. PKD affects around 6% of all cats, but appears to be more common in Persian cats, British Shorthairs and others with Persian ancestry. One of our Persians, Harpsie (in the washbasin), has PKD. The distinguishing characteristic of PKD is that cysts are present, usually on both kidneys, and as the cat gets older, these cysts often increase in size and multiply until eventually kidney function is diminished. The cat then develops CRF and eventually dies.
Symptoms
PKD is usually asymptomatic, but a PKD cat may exhibit polydipsia (increased thirst). If the disease progresses so far that CRF results, then the usual CRF symptoms will be present. Most cats with PKD appear to develop CRF around the age of 5 - 7 years but seriously affected cats with multiple cysts can fall ill as young as two. Stress or infection can accelerate this disease.
Much depends how badly the kidneys are affected - Harpsie above has PKD yet he is almost 14 years old and not yet in renal failure. He does, however, get frequent kidney infections; these are relatively common in PKD cats because the bacteria can burrow deep into the cysts. Many PKD cats show a slight heart murmur and slightly swollen kidneys before CRF develops, and male PKD cats are often susceptible to FLUTD (feline lower urinary tract disorder).
Quite often PKD cats die from other causes before reaching CRF status. For those where the PKD does develop into CRF, then the usual CRF symptoms will be apparent, and the usual treatments can be used. CRF itself is generally considered not to be a painful disease. Unfortunately, this may not apply to cats who progress to severe end stage PKD: these cats may suffer pain from the cysts growing rapidly and occasionally rupturing. Sadly, nothing can be done for this, but you do need to watch for this occurring in a PKD cat.
Diagnosis
The University of California at Davishas identified the gene mutation that causes PKD, and is now offering genetic testing at a cost of US$40 per cat. The test can be run as soon as a kitten is 8-10 weeks old and is almost 100% accurate. You can obtain the sample yourself, it is obtained by non-invasive means so your vet does not need to be involved. Details of how to apply for the test can be found
here. You will be sent the results via e-mail.
Veterinary Diagnostics Center in Ohio offers a similar test for US$48.
In the UK the test is offered by the
Animal Health Trust (click on Science, then choose Genetics, Cat, Feline Genetic Services, PKD) in Newmarket at a cost of £30 or by the
University of Bristol (click on Downloads on the left, then click on Polycystic Kidney Disease PCR submission form) for £35.
The only other way to diagnose PKD properly is via an ultrasound of the kidneys. Ultrasound is a reasonably accurate method of diagnosis if it is undertaken by somebody skilled in sonography, and ideally with experience of PKD kidneys. Repeated scans may need to be taken if the cat is very young as the cysts may not be visible at that time; it is often hard to detect PKD in cats less than nine months old. Cysts are rare in cats but not all cysts are necessarily PKD; research is still being done in this area. Some PKD cats may also show cysts in their liver.
If you have a Persian cat suspected of having HCM and are planning to have the heart examined by ultrasound, I would recommend having the cat's kidneys examined by ultrasound at the same time in order to rule out PKD. This was how we discovered that Harpsie has PKD - the cardiologist checked his kidneys when he checked his heart. So far Harpsie shows no signs of CRF, although the cysts in his kidneys are growing.
Treatments
PKD is incurable (though see the links further in this section regarding research into two drugs which appear to slow the progression of the disease) and sadly, there are very few treatments available.
Potassium citrate/citric acid intake improves renal function in rats with polycystic kidney disease (199
Tanner GA
American Society of Nephrology 9 pp1242-48 indicated that potassium citrate may help PKD rats; it is not known if this also applies to cats, but potassium citrate is an ingredient in Royal Canin's Persian catfood.
A soy protein diet may also help. Try to ensure that your cat leads a stress free life, free of infection and toxicity.
If the PKD develops into CRF, then the usual CRF treatments can be used. CRF itself is generally considered not to be a painful disease. Unfortunately, this may not apply to cats who progress to severe end stage PKD: these cats may suffer pain from the cysts growing rapidly and occasionally rupturing. Sadly, nothing can be done for this.
The PKD Foundationreports on a drug called OPC31260 which appears to retard cyst production and thus progression of the PKD in humans. Trials are continuing. No studies appear to have been performed on cats as yet.
Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease (2004) Torres VE, Wang X, Qian Q, Somlo S, Harris PC, Gattone VH 2nd
Natural Medicine 10(4) pp363-4 reports on the use of OPC-31260 in mice.
Effectiveness of vasopressin V2 receptor antagonists OPC-31260 and OPC-41061 on polycystic kidney disease development in the PCK rat (2005)
Wang X,
Gattone V 2nd,
Harris PC,
Torres VE Journal of the American Society of Nephrology 16(4) pp846-51 reports on research on rats into OPC-31260 and another drug called OPC-41061.
PKD Websites
Autosomal Dominant Polycystic Kidney Disease in Persian Cats is an informative article by US vets Biller DS, DiBartola S and Lagerwerf WJ.
PKD FAQs- this site gives a good overview of PKD.
PKD Links - this site has many links about PKD, including the main scientific references.
PKD List- a support list for people with cats with PKD, where you can obtain feedback on research into this disease and support on living with PKD. There are primarily breeders on this list, so much of the discussion concerns research and diagnosis rather than treatment.
If a vet said that about one of my beloved fluffies I would be a bit concerned to say the least!
