Polycystic kidney disease

What it is

Polycystic kidney disease (PKD) is an inherited disorder caused by a variant of the PKD1 gene, which encodes polycystin 1, a protein of the cilia of renal tubular cells. It is inherited as an autosomal dominant trait: one copy of the variant is enough for the cat to be affected, and the homozygous form is considered lethal before birth. From birth there are small fluid-filled cysts in the cortex and medulla of both kidneys; over the years they increase in number and size, compress and replace functional renal tissue and lead to chronic kidney disease. The rate of progression varies widely between cats. Some cats also have cysts in the liver.

Who it affects

Persians and breeds derived from or crossed with them: Exotic Shorthair, Himalayan, British Shorthair, among others. Prevalence in Persians was high before genetic testing and has fallen in breeding populations where testing has been used. The cysts are present from an early age, but kidney failure usually appears in middle-aged adult cats, although some develop it earlier and others never do.

Anatomy involved

• Kidneys: enlarged, with an irregular, lumpy outline, and cysts of variable size (from millimetres to several centimetres) in the cortex and medulla; between them, interstitial fibrosis and inflammation.
• Liver: biliary cysts in a proportion of affected cats, usually without clinical consequences.

Clinical signs

For years there are no signs. As renal function is lost, the signs of chronic kidney disease appear: polyuria and polydipsia, weight and appetite loss, vomiting, lethargy, dehydration and a poor coat. On palpation the kidneys may feel large and irregular. Systemic hypertension, haematuria and cyst infection can occur.

Diagnosis

• Renal ultrasound: shows anechoic, round, thin-walled cysts in both kidneys; it is a good screening method, and its reliability increases with the cat's age.
• Genetic test for the PKD1 variant on a blood or cheek swab sample: detects carrier cats at any age, before they are used for breeding.
• Blood work and urinalysis: creatinine, SDMA, urine specific gravity, urine protein:creatinine ratio and blood pressure to stage the kidney disease using the IRIS system.

Treatment

No treatment prevents the cysts from growing. Chronic kidney disease is managed according to the IRIS stage: renal diet, hydration, control of hypertension and proteinuria, phosphate binders, antiemetics and appetite stimulants. Infected cysts need antibiotics and sometimes drainage. The most effective measure is prevention: genetic or ultrasound testing of breeding cats and not breeding from affected cats. The prognosis depends on how quickly the cysts progress and on the stage of kidney disease.

Key studies

• Lyons et al. (2004) identified the causal variant, a stop mutation in exon 29 of PKD1. It was present in heterozygous form in all 48 affected cats examined (41 Persians, a Siamese and breeds crossed with Persians) and in no unaffected cat; no homozygous cat was found, which supports the view that the homozygous form is lethal before birth.
• Barthez et al. (2003), ultrasound screening of 310 healthy cats in France: prevalence was 41.8% in Persians and 39.1% in Exotic Shorthairs, with no difference between males and females.
• Bonazzi et al. (2009), 70 Persian and Exotic Shorthair kittens examined by ultrasound and genetic test at 10–14 weeks. Ultrasound had 96.2% sensitivity and 91% specificity, and agreement with the genetic test was high (kappa 0.85). Some cats with cysts were negative on the genetic test, so the authors recommend using both.
• Guerra et al. (2019), 82 genotyped Persian cats examined by ultrasound, from which age-based criteria were derived: one cyst is enough for the diagnosis up to 15 months of age, two are needed from 16 to 32 months, three from 33 to 49 months and four from 50 to 66 months.
• Enomoto et al. (2025), retrospective cohort of 300 cats carrying the PKD1 variant in Japan. Life expectancy at birth was about 12.7 years, with survival of 95.1% at 5 years and 61.3% at 10 years; 16% progressed to uraemia. Survival began to fall clearly at 6 to 7 years of age.
• Ukawa et al. (2026), data from 110,325 insured cats and 61,968 genotyped cats in Japan. 77.8% of cats with cystic kidneys carried the classic variant, so other variants also cause the disease. Between 2019, when routine testing of kittens began, and 2022, the frequency of carriers fell by 42.6% across 14 breeds without an increase in inbreeding.