ANIMAL MODELS OF HUMAN DISEASE Vet Pathol 45:939–940 (2008) Editorial: Best Pathology Practices in Research Using Genetically Engineered Mice

The recent advent of high-throughput transgenic and gene targeting technologies has accelerated the generation of new genetically engineered mouse (GEM) lines for research and testing. As an example, the International Mouse Knockout Con-sortium has proposed to systematically mutate every gene in the mouse genome, thereby creating more than 20,000 new embryonic stem cell lines from which null mutant (‘‘knockout’’) mice can be made to explore gene function in vivo.2,4,6 An enormous number of mice will need to be characterized in the coming decades if this remark-able resource is to yield a rich harvest of scientific information. The recent explosion in the use of GEM i