The study reports the identification of 410 lethal genes and 198 subviable genes from 1,751 knockout mouse lines generated by the International Mouse Phenotyping Consortium (IMPC). Using a standardized, high-throughput phenotyping pipeline incorporating 3D imaging, the researchers identified novel phenotypes for previously uncharacterized genes and additional phenotypes for genes with known mutant phenotypes. They found that incomplete penetrance and variable expressivity are common, even on a defined genetic background. Human disease genes were enriched for essential genes identified in the screen, providing a novel dataset for prioritizing and validating mutations from clinical sequencing. The study highlights the importance of systematic, standardized approaches to mouse phenotypic analysis for genome-wide functional annotation. It emphasizes the need for careful standardization of allele design, genetic background, and phenotyping protocols to ensure reproducibility. The IMPC aims to generate a comprehensive catalog of gene function through systematic generation and phenotyping of a genome-wide collection of gene knockouts in the mouse. The results provide novel insights into gene function, new models for inherited disorders, and new understanding of the role of essential genes in human diseases. The study also identifies novel lethal phenotypes, including cardiovascular defects, craniofacial malformations, and abnormalities in limb and tail development. It reveals that genes causing lethality in the mouse are enriched in disease genes, and that human orthologs of mouse essential genes show evidence of purifying selection in the human population. The study further identifies genes associated with human diseases, including metabolic and storage syndromes, mitochondrial complex deficiencies, and syndromes caused by disruption of basic processes such as replication or translation initiation. The study also highlights the importance of high-resolution imaging techniques, including optical projection tomography (OPT), microcomputed tomography (micro-CT), and high-resolution episcopic microscopy (HREM), for identifying and characterizing phenotypes. These techniques provide cost-effective, high-throughput approaches to the collection of phenotype data, including quantitative volumetric analysis. The data are available to the community via the IMPC portal, facilitating further analysis and enrichment of phenotype calls. The study also discusses the importance of automated image analysis for identifying mutant anatomical phenotypes that are statistically beyond wildtype variation. It highlights the value of the IMPC data in assigning function to novel, previously uncharacterized genes. The study also discusses the importance of open access to mouse models and data for reducing duplication of effort and accelerating discovery. The study concludes that the IMPC effort has provided a rich resource with impact for many scientific communities, and that the systematic approach to phenotyping and unrestricted access to data and mouse models provided by the IMPC promises to fill large gaps in our understanding of mammalian gene function.The study reports the identification of 410 lethal genes and 198 subviable genes from 1,751 knockout mouse lines generated by the International Mouse Phenotyping Consortium (IMPC). Using a standardized, high-throughput phenotyping pipeline incorporating 3D imaging, the researchers identified novel phenotypes for previously uncharacterized genes and additional phenotypes for genes with known mutant phenotypes. They found that incomplete penetrance and variable expressivity are common, even on a defined genetic background. Human disease genes were enriched for essential genes identified in the screen, providing a novel dataset for prioritizing and validating mutations from clinical sequencing. The study highlights the importance of systematic, standardized approaches to mouse phenotypic analysis for genome-wide functional annotation. It emphasizes the need for careful standardization of allele design, genetic background, and phenotyping protocols to ensure reproducibility. The IMPC aims to generate a comprehensive catalog of gene function through systematic generation and phenotyping of a genome-wide collection of gene knockouts in the mouse. The results provide novel insights into gene function, new models for inherited disorders, and new understanding of the role of essential genes in human diseases. The study also identifies novel lethal phenotypes, including cardiovascular defects, craniofacial malformations, and abnormalities in limb and tail development. It reveals that genes causing lethality in the mouse are enriched in disease genes, and that human orthologs of mouse essential genes show evidence of purifying selection in the human population. The study further identifies genes associated with human diseases, including metabolic and storage syndromes, mitochondrial complex deficiencies, and syndromes caused by disruption of basic processes such as replication or translation initiation. The study also highlights the importance of high-resolution imaging techniques, including optical projection tomography (OPT), microcomputed tomography (micro-CT), and high-resolution episcopic microscopy (HREM), for identifying and characterizing phenotypes. These techniques provide cost-effective, high-throughput approaches to the collection of phenotype data, including quantitative volumetric analysis. The data are available to the community via the IMPC portal, facilitating further analysis and enrichment of phenotype calls. The study also discusses the importance of automated image analysis for identifying mutant anatomical phenotypes that are statistically beyond wildtype variation. It highlights the value of the IMPC data in assigning function to novel, previously uncharacterized genes. The study also discusses the importance of open access to mouse models and data for reducing duplication of effort and accelerating discovery. The study concludes that the IMPC effort has provided a rich resource with impact for many scientific communities, and that the systematic approach to phenotyping and unrestricted access to data and mouse models provided by the IMPC promises to fill large gaps in our understanding of mammalian gene function.