Polycystic Kidney Disease in Cats

Polycystic Kidney Disease in Cats -10 important things you should know

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Summary of Information

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1. Brief description

Polycystic kidney disease (PKD) is characterised by the presence of multiple fluid-filled sacs or cysts in the kidneys. They can be present at birth but initially are microscopic and enlarge throughout life. The rate of growth varies but, at some stage, chronic renal failure (CRF) occurs as the enlarging cysts damage normal kidney tissue. Typical signs of PKD are those also associated with chronic renal failure reduced appetite, weight loss, increased thirst and urine volume, muscle weakness, vomiting, seizures (fits) and death.

2. Intensity of welfare impact

Renal failure causes malaise and inappetance and, in later stages, muscle weakness, vomiting and seizures. These are likely to cause unpleasant feelings of a moderate to severe intensity.  Treatment can help to control the disease but treatment can itself have adverse welfare consequences. For example, special diets may be of low palatability, frequent administration of tablets may be aversive, as may frequent travel to and from veterinary practices and veterinary interventions.

3. Duration of welfare impact

Most cats affected with PKD will have a normal life until signs of CRF occur. Once signs associated with CRF appear they will persist until death. This may be weeks or years. During this period the welfare impact will vary from mild to severe depending on the stage of disease and the effectiveness of any treatments.

4. Number of animals affected

PKD has been very common in Persian cats. Around 36-49% of all Persians have been reported to have the condition (Cannon et al 2001, Barrs et al 2001, Beck & Lavelle 2001, Barthez et al 2003, Cooper 2000, Bonazzi et al 2007.  Domanjko-Petri et al 2008, Bonazzi et al 2009). However, the number with the condition may be decreasing due to the effectiveness of ongoing control schemes. It is believed to be the commonest genetic disease in cats.

Breeds related to Persians: Himalayans, Exotic shorthairs, Ragdolls, and Chinchillas, have also been shown to be affected by the condition (Barrs et al 2001).

5. Diagnosis

The diagnosis of renal failure (CRF) rests upon clinical examination and the results of laboratory tests. The presence of the cysts in the kidneys can be detected by ultrasound examination which can indicate the presence, number and size of the cysts within each kidney. This method of detection is most sensitive when the cat is over 10 months of age. A genetic test is available which detects the presence or absence of the PKD1 genetic mutation that underlies the disease.

6. Genetics

The form of PKD detailed here is an autosomal dominant condition with variable penetrance (Biller et al 1990, Biller et al 1996). The affected gene is PKD1 (Lyons et al 1994).

7. How do you know if an animal is a carrier or likely to become affected?

In contrast to conditions caused by recessive genes, all cats with the gene will be affected and will go on to develop signs of the disease in due course. However, although strictly there is therefore no carrier state, the disease tends not to manifest until relatively late in life and often not until after breeding age. It is therefore necessary to use special tests to detect affected animals before breeding age. Both ultrasound examination after 10 months of age or use of the genetic test after weaning are reliable in identifying affected and unaffected animals and combining both has its advantages.

8. Methods and prospects for elimination of the problem

All cats that carry the abnormal gene are affected with AD-PKD and this makes it relatively easy to eliminate the disease from a breeding group. If all cats in the high-risk breeds were to have their kidneys scanned or be gene tested before they were used for breeding, and if affected cats were not then used for breeding, PKD could be eradicated in a single generation. This would, however, significantly decrease the number of cats within the Persian breed which could be bred from, and hence restrict their gene pool. Such a restriction could increase the risk of other diseases with genetic influences.

Brown persian cat relaxing on carpet
 Benjamin Torode / Getty Images

Cats are typically born with two fully functioning, bean-shaped kidneys that help filter toxins out of the blood. These little organs are very important to the health of your cat so when something is wrong with them, like in a cat with polycystic kidney disease, it’s a serious matter. Cat owners should know what signs to watch for in order to best monitor their cat’s health and to be able help to catch PKD in its early stages.

What is Polycystic Kidney Disease?

PKD, as polycystic kidney disease is often referred to, is a disease that forms small fluid pockets called cysts on a cat’s kidneys. These cysts are typically present from birth and may grow slowly or rapidly. As they cysts get larger and multiply, they make it increasingly more difficult for the kidneys to do their job and ultimately cause the kidneys to fail. PKD can have a large number of cysts or just one large one.

Signs of Polycystic Kidney Disease in Cats

Symptoms

  • Increased thirst
  • Increased urination
  • Nausea
  • Vomiting
  • Decreased appetite
  • Weight loss
  • Lethargy
  • Blood in the urine
  • High blood pressure

It is impossible to distinguish the symptoms of polycystic kidney disease from other kidney diseases, but these signs are still important to look for. An increase in thirst and urination, a decrease in appetite, weight loss, vomiting, high blood pressure, blood in the urine, and overall lethargy can all be symptoms of PKD. Any changes from what is normal for a cat could be an indication of disease and should be discussed with your veterinarian.

Causes of Polycystic Kidney Disease

Polycystic kidney disease is an inherited disease in cats, so it is passed from cat to cat at birth. It is thought that about 40 percent of Persians have this form of renal disorder, but it may also affect Himalayans, British Shorthair, and other cat breeds that were originally bred from Persians. It is rare in cats that have no Persian ancestry. PKD is due to a mutated gene called PKD1, but what exactly causes this gene mutation is unknown.

Treatment

There is no cure for polycystic kidney disease, but you can manage the symptoms. Depending on how early in the disease progression PKD is identified, the treatment plan and longevity of the cat will vary. Antibiotics, anti-inflammatories, omega-3 fatty acids, pain medications, appetite stimulants, fluid therapy, dietary plans, and other treatments may be utilized. Drainage of the cysts may be performed but this is only a temporary answer as the cysts will simply refill with fluid.

Monitoring the progression of the disease may be done with the use of X-rays, ultrasounds, blood rechecks, blood pressure measurements, and the observation of symptoms. Once kidney failure has occurred, the decision to euthanize a cat with polycystic kidney disease is often discussed with the veterinarian.

How to Prevent Polycystic Kidney Disease

The best way to prevent polycystic kidney disease in cats is to practice selective breeding. Screening Persians and other at-risk breeds for the presence of PKD1 should be done prior to breeding, and any cats that test positive for this gene should not be bred.

Regular monitoring of kidney function is also recommended for Persians and cats who have Persian ancestry. Even though you cannot prevent your cat from developing polycystic kidney disease, you may be able to slow the progression of the disease by managing the symptoms.

Diagnostic Processes

The best way to definitively diagnose polycystic kidney disease is through the use of ultrasound. This will allow a veterinarian to visualize the cysts on the cat’s kidneys. In advanced PKD, the cysts are sometimes able to be felt during a physical examination, but in the earlier stages of the disease they won’t be palpable. Cats are usually around seven years of age when they start showing symptoms of PKD, but they will have had it since birth and the signs of the disease can appear at any time during their life.

polycystic_kidney_disease_2018-02

Laboratory testing can also aid in diagnosing a cat with kidney disease, but these tests won’t identify that there are cysts, only problems with kidney function. Blood tests can measure waste materials and other levels to check how well the kidneys are working, blood pressure measurements can check for hypertension, and X-rays can be performed to look at the size of the kidneys. These are all useful tools to help manage the disease.

A special genetic test is also available from the University of California in Davis to screen a cat for polycystic kidney disease. This test uses cotton swabs to collect DNA from inside a cat’s mouth and then looks for the PKD1 gene. This test only provides a positive or negative result and does not tell you the severity or progression of the disease, though.

ultrasound_cat

Has your cat been diagnosed with polycystic kidney disease? You are not alone. Polycystic kidney disease in cats (PKD) is one of the most common feline genetic diseases. It is widely described in Persian and related cats, but also, sporadically, in other cat breeds (Nivy et al, 2015 & Volta et al, 2009).

PKD is diagnosed in approximately 38% of Persian cats worldwide, which accounts for about 6% of all cats (Lyons et al, 2014). The disease is characterized by a formation of small fluid-filled cysts in the kidneys and may lead to kidney failure. An autosomal dominant mutation in the PKD1 gene has been identified as a cause for this condition.

Background information

Polycystic kidney disease in cats is an inherited condition characterized by the formation of fluid-filled cysts in the kidney, and sometimes liver and pancreas (Lee et al, 2015). Cysts are non-functioning formations filled with fluid which can vary in a wide range of sizes. PKD in cats coincides with the same condition described in humans.

This disease is associated with disrupted cilia-mediated signaling caused by a defect in a polycystin-1 protein (PC1). PC1 is a membrane-bound protein expressed in primary cilia, thread-like organelles present on the surface of the most body cells. The exact mechanism of the cyst formation remains unclear, but it is thought to be linked to the disrupted signaling through the cilia caused by the deficiency of the PC1 (Halvorson et al, 2010).

The prevalence of the PKD among Persian and Persian related cats is around 36-49,5%. The disease has also been reported in domestic shorthair cats, British Shorthair cats, Ragdolls, Burmillas, Himalayans, Scottish Folds and one Chartreux cat (Volta et al, 2009).Polycystic kidney disease in cats

Polycystic kidney disease in cats

The cysts themselves won’t hurt the cats, but they can damage the kidneys and disrupt their normal functioning. As the cysts grow and multiply, they gradually replace the kidney tissue and disrupt their healthy functioning. The kidneys are the two bean-shaped organs of the renal system and are involved in the filtration of the blood.

Kidneys help maintain the homeostasis in the kitty’s body by filtration and excretion of the waste products from the blood, regulating acid-base balance, electrolyte levels, water levels and blood pressure. Kidneys also produce erythropoietin which is necessary for erythropoiesis (production of erythrocytes).

Because kidneys utilize so many important functions, the disrupted function of kidneys, such as in PKD, may result in numerous health complications. To learn more about the function of the kidneys please read our article about the Chronic Kidney Disease.

Genetics

A single nucleotide mutation in exon 29 of the polycystin-1 (PKD1) gene has been identified as a cause of feline PKD (Lyons et al, 2012). The mutation is inherited in an autosomal dominant mode, meaning that every cat who inherits at least one mutated copy of the gene (allele) is affected. Two unaffected cats will always give unaffected offspring.

If an affected heterozygote is crossbred with a healthy cat, there is a 50% chance for each kitten to be affected too. If two affected heterozygotes are crossbred, then there is a 75% chance for each kitten to inherit PKD. And finally, affected homozygotes (carriers of two mutated alleles) will always give affected offspring.

Polycystic kidney disease in cats is inherited in an autosomal dominant mode

Symptoms and diagnosis

Clinical presentation of PKD often include fever, polyuria (increased urination) and polydipsia (increased water intake), anorexia and weight loss, enlarged and painful kidneys, dehydration, lethargy and depression.

Pale mucous membranes, low body condition score, anaemia, leucocytosis and azotaemia have been recorded too (Nivy et al, 2015). PKD diagnosis involves physical examination, ultrasound and genetic testing. Genetic tests allow pre-symptomatic diagnosis and early treatment.

Treatment and prognosis

Because this is an irreversible and progressive disease, the prognosis is guarded (Volta et al, 2009). There is no treatment which can reverse PKD, but there are treatments which may help maintain and prolong the health and functioning of the cat’s kidney.

These treatments are not PKD specific though and are used in therapies of various kidney diseases. They include increased water intake, special diets, potassium and/or calcium supplements, kidney transplantation, aspiration of the fluid build-up and more.

Note: It is not recommended to breed the carriers in order to prevent the progression of the condition to the offspring. A genetic test is now available for the detection of the mutation.Polycystic kidney disease in cats

Polycystic kidney disease in cats

PKD is a common and serious genetic disease. Persian and related cats are considered to be under a higher risk from PKD and are often recommended candidates for DNA tests. It is important to remember that all cats of all other breeds can be affected as well.

Citations:

1. Halvorson CR, Bremmer MS, Jacobs SC. (2010). Polycystic kidney disease: inheritance, pathophysiology, prognosis, and treatment. Int J Nephrol Renovasc Dis. 3:69-83. PMID: 21694932

2. Lee YJ, Chen HY, Hsu WL, Ou CM, Wong ML. (2015). Diagnosis of feline polycystic kidney disease by a combination of ultrasonographic examination and PKD1 gene analysis. Veterinary Record. 67:614-17 doi: 10.1136/vr.c4605

3. Lyons LA (2012). Genetic testing in domestic cats. Molecular and Cellular Probes: 1-7. doi:10.1016/ j.mcp.2012.04.004

4. Lyons LA, Biller DS, Erdman CA, Lipinski MJ, Young AE, Roe BA, Qin B, Grahn RA. (2014) Feline Polycystic Kidney Disease Mutation Identified in PKD1. JASN. 15(10):2548-2555. doi: https://doi.org/10.1097/01.ASN.0000141776.38527.BB

5. Nivy R, Lyons LA, Aroch I, Segev G. (2015). Polycystic kidney disease in four British shorthair cats with successful treatment of bacterial cyst infection. Journal of Small Animal Practice. 56:585-89. doi: 10.1111/jsap.12327