Polycystic Kidney Disease

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What is the Disease?

In Polycystic Kidney Disease (or PKD) large numbers of fluid filled cysts develop in the kidneys. These cysts are tiny when the cat is born, but over several years they gradually grow, compressing the surrounding normal kidney tissue. The end result is kidney failure by the time is 7 -8 years old although occasionally it can happen as early as 2 – 3 years – unfortunately it will always be fatal.

The disease is caused by a defective gene in Persians and exotic short-haired breeds. Frighteningly, world wide estimates are that one third of cats of these breeds are affected. It may also be present in a small number of British Short-Haired cats due to out-crossing. The gene is a single dominant one. That means that every cat with the gene will have polycystic kidneys. Only one parent has to have the gene to pass it onto offspring. If both parents have the gene then any kittens that are unlucky enough to receive two copies of the gene will die in their mother’s uterus – this means that all affected cats will only have one copy.

Treatment

Cats with PKD will show no signs of illness until more than 70% of their kidneys have been destroyed by cysts. They will then start drinking more than usual, eating less and losing weight just like any other cat with kidney disease. Unfortunately there is no cure nor specific treatment for PKD – the cysts can’t be removed drained nor stopped from growing. We can reduce the workload on the kidneys by using low protein and phosphate diets and control secondary problems like high blood pressure. However, as the condition is progressive it is inevitable that these cats will die prematurely no matter what is done.

 

What can be done?

The reason PKD is so prevalent is because affected cats are completely normal until late middle age. A queen can have had several litters by this stage, while a stud tom can have sired hundreds or even thousands of kittens. As 50% of offspring from a mating where one of the parents has PKD, are affected, the result is a lot of sick cats. X-rays and blood tests are completely normal until renal failure starts, but fortunately ultrasound scanning can pick up PKD in 95% of affected cats once they are more than 10 months old, so animals can be checked before they are used for breeding.

The Feline Advisory Bureau (FAB) has set up the FAB PKD Screening Scheme based at Bristol Vet School, and now available throughout the country. The cats need to be microchipped for identification, and if they pass the painless and non-invasive scanning procedure, they are issued with an FAB PKD certificate. As the cysts can be very small a high quality ultrasound machine together with an experienced operator is needed – a list of vets who can carry out the test is available on the FAB website – see below.

All breeding stock should be scanned even if both parents have certificates; although the test is 95% effective, there is still a tiny risk of affected cats slipping through the net. If this is seen to have happened, FAB will investigate free of charge. The cost of the scan is extremely reasonable - £30 - £100 depending on where it is done, and once the certificate is issued, it last the cat’s lifetime. If every Persian, Exotic and British Short Hair breeder in the country followed the FAB scheme for PKD, the disease could be eliminated completely in a few years. However, just a few breeders not getting their cats scanned will keep this distressing disease going for ever. The moral of the story is ensure that you buy kittens of affected breeds, only from breeders who have FAB PKD certificates for all their adult cats.

Update

In 2004, FAB and Bristol Vet School launched a DNA gene test for PKD. This revolutionary test is based upon PCR technology and costs approximately £35 per cat. Your vet can send either a blood or cheek swab sample from your cat (which is still required to be identichipped) to Bristol, and the results are generally available in 3-4 weeks.