Feline polycystic kidney disease, or PKD, is one of the most common inherited diseases in cats and one of the clearest success stories for genetic testing in the cat world. Fluid-filled cysts form in the kidneys from birth and grow over the years, slowly replacing healthy tissue until the kidneys fail, usually in middle or older age. Because the disease is caused by a single dominant variant in most affected cats, a simple DNA test identifies them as kittens, and breeders who test have been able to cut its frequency sharply.
Key facts
- Feline PKD is autosomal dominant: one copy of the PKD1 variant is enough to cause cysts.
- The variant, a C>A change in exon 29 of PKD1 that creates a premature stop codon, was identified by Lyons and colleagues in 2004.
- It is most common in Persians and related breeds (Exotic Shorthair, Himalayan, British Shorthair and others with Persian ancestry); published Persian prevalence has ranged from about 36% to 49% depending on country and period.
- The DNA test detects the variant; ultrasound detects the cysts. Some cats with cysts do not carry the known variant, so the two methods complement each other.
What PKD does to the kidneys
In PKD, small cysts are present in the kidneys of affected kittens and grow and multiply with age. Cats are usually normal for years. Signs, when they appear, are those of chronic kidney disease: drinking and urinating more, weight loss, poor appetite, vomiting, lethargy and a poor coat. The age at which kidney function fails varies widely, from a few years to old age, and some affected cats live a normal lifespan. Cysts can also form in the liver.
There is no treatment that removes the cysts or stops them growing. Management focuses on supporting kidney function, as for any cat with chronic kidney disease, under a veterinarian's care: diet, hydration, monitoring blood pressure and kidney values, and treating complications.
The genetics: one copy is enough
Most inherited diseases that breeders test for are recessive. PKD is not. The causative variant in PKD1, the gene for the protein polycystin-1, is autosomal dominant: a cat with one copy develops cysts. This has two practical consequences.
- An affected cat bred to a clear cat is expected to pass the variant to about half of the kittens.
- There are no "healthy carriers" to worry about. A cat that tests negative for the variant cannot pass it on.
Cats with two copies of the variant appear to be extremely rare, and it is thought that this genotype is lethal before birth.
Which breeds are affected
The PKD1 variant spread through Persian bloodlines, and its frequency in Persians was very high before testing became routine. Studies have reported prevalence in Persians of about 49% in the United Kingdom and 36% in Slovenia. Because the Persian was used to develop or improve many other breeds, the variant is also found in Exotic Shorthairs, Himalayans, British Shorthairs, Scottish Folds, Selkirk Rex and other breeds with Persian ancestry, as well as in non-pedigree cats. Thanks to widespread testing, breeders in many countries now report far lower frequencies than in the early 2000s.
DNA test or ultrasound?
There are two ways to screen cats for PKD, and they answer slightly different questions.
| PKD1 DNA test | Ultrasound scan | |
|---|---|---|
| What it detects | The known PKD1 variant | Visible kidney cysts |
| Sample | Cheek swab or blood | Scan by an experienced veterinarian |
| Age | Any age, including young kittens | Most reliable from about 10 months; early scans can miss small cysts |
| Limitation | Misses PKD caused by other, unknown variants | Depends on equipment, operator and age; cysts from other causes can confuse |
Studies comparing the two methods have found good agreement in Persians, but not perfect agreement. A 2009 study of Persian and Exotic Shorthair kittens scanned and genotyped at about 10 to 14 weeks reported ultrasound sensitivity of 96.2% and specificity of 91% against the genetic result, and its authors recommended using ultrasound together with genetic testing. A 2010 study found cats with cysts on ultrasound that did not carry the known exon 29 variant, which suggests other causes of polycystic kidneys in some cats. For most breeders of Persian-type cats, a negative DNA test is the main screening tool, with ultrasound added when a cat has kidney problems or in breeds where the known variant may not explain all cases.
PKD and HCM: the two common cat gene tests
PKD is often discussed together with hypertrophic cardiomyopathy (HCM), the most common heart disease in cats. The situation is different: two HCM variants in the MYBPC3 gene are known in the Maine Coon (A31P) and the Ragdoll (R820W), but most cats with HCM do not carry either, and echocardiography by a veterinary cardiologist remains the standard screening tool. Our Finnish guide to HCM in cats covers the condition in more detail. Genoscoper's own cat test page notes that its feline testing moved to another Finnish laboratory in 2013.
Frequently asked questions
At what age can a kitten be tested for PKD?
The DNA test can be done at any age, because the result does not change. Ultrasound is more reliable from about 10 months, when cysts are larger.
Can a cat with PKD live a normal life?
Many can for years. How quickly kidney function declines varies a lot between cats. Regular veterinary checks of kidney values and blood pressure help catch problems early.
If my cat tests negative, can it still get kidney disease?
Yes. Chronic kidney disease is common in older cats for many reasons. A negative PKD1 test only means the cat does not have the known inherited form.
Should non-Persian cats be tested?
For breeds with Persian ancestry, yes, it is widely recommended before breeding. For other breeds, ask the breed society or your veterinarian whether the test is relevant.
Sources
- Lyons LA, et al. (2004). Feline polycystic kidney disease mutation identified in PKD1. Journal of the American Society of Nephrology 15:2548–2555.
- Bonazzi M, et al. (2009). Comparison between ultrasound and genetic testing for the early diagnosis of polycystic kidney disease in Persian and Exotic Shorthair cats. Journal of Feline Medicine and Surgery. PubMed 19046910.
- Domanjko-Petrič A, et al. (2008). Polycystic kidney disease: a review and occurrence in Slovenia with comparison between ultrasound and genetic testing. Journal of Feline Medicine and Surgery. PubMed 17988914.
- Lee YJ, et al. (2010). Diagnosis of feline polycystic kidney disease by a combination of ultrasonographic examination and PKD1 gene analysis. Veterinary Record. PubMed 21257442.
- OMIA, University of Sydney: Polycystic kidney disease, PKD1-related (cat).