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Feline Polycystic Kidney Disease

| October 16, 2010

Feline Polycystic Kidney Disease

Feline Polycystic Kidney Disease

Introduction

Polycystic kidney disease (PKD) is an inherited kidney disease that occurs mainly in the Persian cat. The condition was first reported in 1967, but actual study into this renal disease did not begin until 1990. Polycystic kidney disease results in chronic renal failure after a variable course of time. The gene for PKD is an autosomal dominant gene that will result in disease if it is present, even if inherited only from one parent.

Polycystic kidney disease resembles autosomal dominant polycystic kidney disease (ADPKD) in humans, which is a very common genetic disorder that occurs in 1 in 200 to 1 in 1000 people. The disease occurs in all races and affects as many as 5 million people worldwide. In the United States the disease is one of the most common causes of end stage renal disease and accounts for approximately 10% of patients on dialysis.

In both cats and humans polycystic kidney disease is a slowly progressive disease. The main problem is the presence of cysts within the tissue of the kidneys. The cysts are present from birth and can vary from less than one millimetre to several centimetres in size, with older cats/humans having larger and more numerous cysts. With time these cysts grow and progressively enlarge which results in swelling of the kidney with a subsequent reduction in the kidneys’ ability to function properly. The ultimate end is kidney failure.

Approximately 45% of humans with ADPKD will develop renal failure by the age of 60, but the age of onset can range from 2 to 80 years. The age at which renal failure develops in Persian cats with PKD is also variable with the average age of onset of renal failure in affected cats being 7 years, with a range of 3 to 10 years. The onset of renal failure is related to environmental and genetic factors. In humans, identified risk factors are high blood pressure, multiple pregnancies, and urinary tract infections. As all these conditions occur in the cat it thus likely that they can also be risk factors.

Clinical signs

Polycystic kidney disease is a disease that shows up later in life with enlarged kidneys and kidney dysfunction occurring at an average age of 7 years. Some of the clinical signs that an affected cat may show include depression, lack of or reduced appetite, excessive thirst, excessive urination, and weight loss. There is a marked difference in when and how quickly individual cats succumb, with the possibility of this developing late enough in life that the cat can die of other causes before kidney failure. However, kidney failure is certain when the cysts can grow and cause problems. Although rare cysts can also occur in other organs such as the liver and uterus.

Diagnosis

The easiest way to diagnose PKD is by ultrasound, which can identify the disease very early in its course. All that is required is that the fur on the mid-ventral abdomen is clipped and a short time period for imaging to detect the possible presence of cysts. The whole process only takes a few minutes, with usually no sedation needed. It is very important that experienced personnel and proper equipment is used to perform the ultrasound. Ultrasound diagnosis is 98% accurate after the cat is approximately 10 months of age.

The gene responsible for ADPKD in humans has been localized but as yet, not in the cat and thus a DNA-test for cats is not currently available.

Therapy

There is no specific treatment for this disease. Treatment is similar to treatment of chronic kidney failure of any cause. This treatment includes moderate dietary protein restriction using high biological value protein, dietary phosphorus restriction, providing fresh drinking water at all times, use of phosphate binders, and if necessary, treatment of the anaemia, acid-base imbalance, and gastric signs.

Prevention

As PKD is the result of an autosomal dominant gene, it is relatively easy to track and eliminate from the breeding population. If a cat is PKD positive, then it must be either heterozygous (inherited the gene from one parent) or homozygous (inherited the gene from both parents). Remember that because the gene is dominant both heterozygous and homozygous cats will have evidence of PKD.

As mentioned above the simplest way to diagnose PKD is by ultrasound, thus all breeding animals should have an ultrasound to detect the possible presence of kidney cysts. The quickest way to eliminate the problem is to neuter or spay the affected individuals and only breed from PKD-negative cats as a PKD-negative cat is also genetically PKD-free. If a particular breeding stud or queen is extremely valuable, there is still a possibility to produce PKD-negative kittens. To achieve this, one parent has to be PKD-negative and the other parent heterozygous in its gene.

If the gene carrying the defect for PKD is represented by A, then an unaffected cat will be aa; a heterozygous affected cat Aa; and a homozygous affected cat AA. With this in mind the following are mating possibilities:

  • Heterozygous affected cat (Aa) mated with a homozygous affected cat (AA) will result in all the offspring being affected.
  • Heterozygous affected cat (Aa) mated with an unaffected cat (aa) will result in 50% of the offspring being affected.
  • Homozygous affected cat (AA) mated with an unaffected cat (aa) will result in all of the offspring being affected.
  • Two heterozygous affected cats (Aa) mated will result in 75% of the offspring being affected.

Conclusion

It is theorised that PKD is far more common in Persians than is currently diagnosed. With more study and published information about the disease, breeders and veterinarians can work together to establish PKD-free breeding programs. In this manner this genetic health problem can be eliminated.

Ultrasound view of an affected kidney showing a few cysts. The cysts appear as “black” holes in the tissue of the kidney

Ultrasound view of an affected kidney showing a few cysts. The cysts appear as “black” holes in the tissue of the kidney

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Cross section of a normal kidney

Cross section of a normal kidney

Cross section of an affected kidney with a few cysts

Cross section of an affected kidney with a few cysts

Cross section of a severely affected kidney showing multiple=

Copyright & Credit:

Source: Dr Remo Lobetti
BVSc (Hons) MMedVet (Med) Dipl. ECVIM (Internal Medicine) Veterinary Specialist Physician

Bryanston Veterinary Hospital
6 Ballyclare Drive
Bryanston
Johannesburg

Tel: +27 11 706-6023/4/5
Fax: +27 11 706-5801
Emergencies: +27 11 706-6023e
Mail: bvh@global.co.za

Photo copyright and courtesy:  Barry Newcombe – www.flickr.com

Category: Feline Health, Feline Health and Care, Feline Resources

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