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Polycystic kidney disease (PKD) is an inherited disease that affects the kidneys. It is seen in Persians, Persian-related breeds, and cats with Persian ancestry. PKD is thought to be the most prevalent inherited disease in cats, and various studies and surveys have reported between 36 - 49% of Persians are affected by PKD. However it is believed that this prevalence is now decreasing due to the availability of a genetic test for the disease and concerted efforts by breeders to reduce the prevalence of the disease amongst their breeding stock.
PKD is transmitted as an autosomal dominant trait. This means that an affected cat inherits the disease from only one affected parent. There are no “carriers” as such; however the disease has variable expression, meaning some cats can be severely affected, while others may have very mild or occasionally even no clinical signs of disease. The severity of illness in a parent has no relation to the severity of illness that may occur in his/her offspring.
PKD causes the formation of cysts within the kidney. Initially these cysts are very small, but they increase in size over time, and when they become very large they squeeze against and damage the normal kidney tissue, leading to kidney failure. The rate that the cysts enlarge varies between individuals, and also can vary in the one cat at different times. It is the size of the cysts that determines the degree of illness caused by the PKD. Most cats develop kidney failure between 3 - 10 years of age, with the average age being 7 years. Severely affected cats may develop kidney failure earlier than this, while some cats may have small cysts in their kidneys that never become large enough to cause renal failure.
Renal failure is a progressive condition that is ultimately fatal. Affected cats will lose weight, have increased thirst and increased volumes of urine, and may lose their appetite. As the disease progresses cats become increasingly unwell, and become weak, lethargic and anorexic, and may develop vomiting, mouth ulcers and possibly diarrhoea. Signs of chronic renal failure are managed with medications and dietary modification, however cats will reach a point where euthanasia will be required, and this may occur within weeks or years of the onset of kidney failure. The only treatment available for PKD is kidney transplant, which is of limited availability at the current time.
PKD is diagnosed either by ultrasound of the kidneys to demonstrate cysts, or by a DNA test to detect the presence or absence of the causative PDK1 mutation. The genetic test can be performed on young kittens, but does not give any information about the severity of the disease that they may develop. Ultrasound examination is recommended to be carried out as well as DNA testing, as there are occasionally cases of polycystic kidney disease that are not caused by the PDK1 mutation. These cats will have cysts in their kidneys, but will be negative on genetic testing. Also, ultrasound examination can document the size of renal cysts, and repeat scanning can also document disease progression. Occasionally cats may have cysts in other locations, such as the liver, as well as the kidneys.
Urogenital (Associated with the Urinary and Genital Tracts)
Base Substitution C>A
Low-Moderate. This disease can cause some discomfort and/or dysfunction in the affected animal. It does not generally affect life expectancy.
Mode of Inheritance:
Autosomal Dominant with Incomplete Penetrance
1. Genetic (DNA) testing performed on all kittens at any age (e.g. 8 - 17 weeks) 2. Ultrasound screening of kidneys - recommended at 10 months of age for maximal sensitivity
Lyons et al (2004) J am. Soc neprhol 15:2548-2555