Genetic Mismatch in Laboratory Mice Threatens Research Reproducibility

A *Science* analysis of 611 samples from 341 mouse strains at the Mutant Mouse Research and Resource Centers (MMRRC) at the University of North Carolina found 47 % of strains genetically inconsistent with catalogued names, affecting common inbred lines such as C57BL/6 and A/J.

Nature

Inbred strains arise from 10–20 generations of brother-sister matings, producing a uniform genome. Introducing a targeted mutation requires backcrossing the donor onto the recipient and maintaining breeding records. The MMRRC, founded by the NIH in 1999 to preserve and share mouse strains developed by federally funded researchers, distributes these strains.

Nature

Fernando Pardo-Manuel de Villena, mouse geneticist at the University of North Carolina at Chapel Hill, led the study. Immunologist Daniel Rawle of the QIMR Berghofer Research Institute in Brisbane provided expertise on strain mislabeling. Both are co-authors of the *Science* paper.

Nature

Among the 341 strains examined, 47 % (about 160) showed genotype-name mismatches, as revealed by a genotyping platform designed to discriminate among mouse strains and detect background differences.

Nature

The authors note that mismatches can compromise reproducibility and undermine conclusions from disease models. Misidentified backgrounds may confound phenotypic interpretation; the 2022 granzyme A study illustrates how a mislabeled background can lead to false attribution of therapeutic effects.

Nature

The authors argue that the high rate of strain misidentification threatens reproducibility of preclinical research and may lead to erroneous conclusions about disease mechanisms; the 2022 granzyme A study, where a knockout strain was mistakenly linked to arthritis protection, exemplifies how background genetics can confound therapeutic insights. Accurate strain identification is essential for translating animal findings to human health.

Nature

The authors stress that the high prevalence of misidentification calls for genetic verification of repository stocks before use. The NIH’s original MMRRC mandate—to preserve and share accurately characterized strains—highlights the need for genetic fidelity across colonies.

Nature

Researchers noted challenges in achieving fully cleaned backgrounds; Pardo-Manuel de Villena described backcrossing as “Twenty generations is a long time and a lot of money.” Rawle warned that insufficient genetic knowledge “risk[s] misinterpreting how diseases actually work.” Backcrossing typically spans 10–20 generations and incurs substantial expense.

Nature

• “This study is another wake-up call for biomedical research. If we don’t fully understand the genetics of the mice we’re using, we risk misinterpreting how diseases actually work,” — Daniel Rawle, Immunologist, QIMR Berghofer Research Institute

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• “Twenty generations is a long time and a lot of money,” — Fernando Pardo-Manuel de Villena, Mouse Geneticist, University of North Carolina at Chapel Hill

Nature

The authors recommend routine genotyping to confirm strain identity before distribution or experimentation, aiming to reduce genetic blurring and support reproducible biomedical research.

Nature