How do I screen for and manage polycystic kidney disease in Persian cats?

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Genetic testing is the gold standard for PKD screening in Persian cats and can be performed from birth, while ultrasound is a reliable alternative when genetic testing is unavailable, with sensitivity of 96.2% and specificity of 91% at 10–14 weeks of age.8 For genetic diagnosis, the causative mutation is a cytosine-to-adenine transversion (c.10063C>A) in exon 29 of the polycystin-1 (PKD1) gene, and PCR-based assays detect this mutation reliably from birth onward.310 Genetic testing eliminates the age-dependent false-negative rate of ultrasound: in one comparison, ultrasound detected only 18.6% of affected cats while genetic testing identified 48.6% in the same population, with the discrepancy concentrated in cats aged 4 months to 3.5 years whose cysts were too small to resolve sonographically.3 When ultrasound is used, age-based cyst-count criteria must be applied — a single cyst threshold is not sufficient across all age groups.12 The validated criteria are: ≥1 cyst in cats up to 15 months of age; ≥2 cysts in cats aged 16–32 months; ≥3 cysts in cats aged 33–49 months; and ≥4 cysts in cats aged 50–66 months.12 Cats must be at least 16 weeks old before ultrasound screening is attempted.3 For each additional year of age, the probability of detecting cysts on ultrasound increases approximately 2.62-fold, reflecting progressive cyst enlargement over time.5 Combining ultrasound with genetic testing is the most complete screening strategy. Agreement between the two methods is high (Cohen's kappa 0.85), but each modality catches cases the other misses: in one cohort, three cats with renal cysts were negative on standard PCR-RFLP yet confirmed heterozygous by DNA sequencing, indicating that sequencing should follow a negative PCR result in a cat with sonographic cysts.8 Prevalence in Persian and Persian-related cats is high across multiple regions, ranging from 23.1% by genetic testing in western Mexico10 to 31.3–36.8% by ultrasound in Iran15 and 46.8–48.6% by molecular met