Retrospective analysis on the occurrence of kidney cysts in mice in a central animal facility in the years 2009-2019.

Kidney cysts in humans are mainly caused by inheritable polycystic kidney disease. Although they are a regular finding in laboratory mice, their occurrence upon dissection has not been systematically investigated, yet. Therefore, the aim of this report was to investigate on prevalence, phenotype and aetiology of spontaneously occurring kidney cysts in mice by retrospectively analysing the laboratory-receipt tables of the in-house laboratory of a central animal facility in North Rhine-Westphalia, Germany, years 2009-2019. A percentage of 0.4% of dissected mice displayed kidney cysts, with more male than female animals affected and average age equal to that of all dissected animals. Preliminary report in half of the cases was distended abdomen, and a few individuals displayed additional pathologic alterations of kidneys, most commonly dilated renal pelvis, or extrarenal comorbidities. Kidney cysts occurred independently of a renal phenotype of the transgenic strain or presence of infectious agents in health monitoring. To conclude, kidney cysts were characterized as harmless for affected mice but, as inheritability is suggested according with the literature, affected animals should be excluded from breeding.