Autosomal dominant polycystic kidney disease (AD-PKD) is a genetic condition in cats that can cause kidney disease and progressive kidney failure. It is an inherited disease, meaning it is passed from affected adult cats to their kittens. And it is more prevalent in certain breeds, such as the Persian. It is potentially fatal, but the good news is that with careful breeding it may be possible to eliminate it.
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What is autosomal dominant polycystic kidney disease (AD-PKD)?
AD-PKD is caused by an abnormal gene. This causes small cysts (holes filled with fluid) to form in the kidneys, and these cysts get larger over time. The cysts disrupt the structure of the kidneys; and can cause the kidneys to stop functioning well, leading to progressive kidney failure. This can be a rapid, or very slow progression. The cysts start very small and then get bigger. This means the disease is usually not symptomatic until the cat is an adult, or even an older adult.
How do cats get AD-PKD?
Polycystic kidney disease is an inherited condition, caused by a gene abnormality and passed from parent cat to kitten. It is caused by an autosomal dominant gene. This means that it affects both male and female cats; it can be passed on even if only one parent cat has the disease.
All cats who have this abnormal gene passed to them by their parents will develop AD-PKD at some stage. But most will not develop any symptoms until they are adults, as the cysts are small enough in kittens not to stop the kidneys from working. This means that affected cats may breed, and indeed have many litters, before the disease becomes apparent.
What are the symptoms of polycystic kidney disease?
Cats with the AD-PKD abnormal gene usually begin to show symptoms of kidney failure at any time from about 3 years to 10 years. Symptoms commonly include increased thirst, increased urination (volume or frequency), vomiting, weight loss, reduced appetite and constipation. Occasionally the signs may include blood in the urine or urinating in odd places.
Is this condition treatable?
The cysts cause considerable damage to the kidneys, which eventually leads to kidney failure. This is ultimately fatal. There is no known cure. Although there are some methods of managing kidney disease to partially alleviate symptoms and improve quality of life and longevity.
Which cats are prone to AD-PKD?
The cat breeds at a high risk of polycystic kidney disease are the Persian, British Shorthair and Exotic Shorthair. A study in the U.K. in 2001 showed that the prevalence of AD-PKD in Persian cats was around 49% at the time; a hugely high number and therefore a very worrying statistic.
Persian cats are found in the bloodlines of several other cat breeds, resulting in a moderate risk in cats such as Burmillas, Chinchillas and Himalayans.
Can you test for polycystic kidneys?
There are methods of testing for AD-PKD, and indeed, it is highly recommended in at-risk breeds. If cats who have tested negative for polycystic kidney disease are bred together, the defective gene is not present to be passed on, and the kittens are guaranteed not to develop this often-fatal condition. Therefore, if all cats from at-risk breeds are screened before breeding, and only those that test negative are bred, the condition should disappear, or at least be greatly reduced.
An ultrasound scan of the kidneys can be performed to look for cysts. However this can only be done after 10 months, as before that time the cysts might be too small to spot. However, it is now possible to test for the AD-PKD gene mutation using a blood sample or cheek swab; which is much more convenient. Kittens who are still having milk from their mothers must have the blood sample. But older kittens and adult cats can have a cheek swab, which is much less stressful for all, and therefore most cats are tested once weaned.
Should I get my cat tested?
If you own a cat which isn’t purebred – a moggy – or a breed that isn’t considered at risk of polycystic kidney disease, then there is no need to test them, unless there is a family history of the disease. If you own a Persian, British or Exotic Shorthair, or one of the breeds known to be more a risk, then you might want to consider testing for two reasons. Firstly, to find out if your cat may suffer from this condition – although there is no treatment, there are management strategies that can be put into place.
Secondly, if you are considering breeding from your cat then testing is strongly recommended. There is now an AD-PKD register, where breeders can register their cats as negative once they have been tested, allowing a healthier gene pool for the breed to flourish. This has been very successful, with a clear decline over recent years in the number of AD-PKD positive cats.
Summing up
Polycystic kidney disease is a genetic condition which is slowly progressive and can eventually cause kidney failure and death. Due to its inherited nature, the disease is strongly linked to certain breeds such as the Persian and British and Exotic Shorthairs. Testing cats of these breeds for AD-PKD before breeding is strongly recommended to try and reduce the prevalence of the condition, a strategy that appears to already be working well.
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