In an effort to discover new mouse models of cardiovascular disease using N-ethyl-N-nitrosourea (ENU) mutagenesis followed by high-throughput phenotyping, we have identified a new mouse mutation, C699Y, in the LDL receptor (Ldlr), named wicked high cholesterol (WHC). When WHC was compared with the widely used Ldlr knockout (KO) mouse, notable phenotypic differences between strains were observed, such as accelerated atherosclerotic lesion formation and reduced hepatosteatosis in the ENU mutant after a short exposure to an atherogenic diet. This lossof-function mouse model carries a single base mutation in the Ldlr gene on an otherwise pure C57BL/6J (B6) genetic background, making it a useful new tool for understanding the pathophysiology of atherosclerosis and for evaluating additional genetic modifiers regulating hyperlipidemia and atherogenesis. Further investigation of genomic differences between the ENU mutant and KO strains may reveal previously unappreciated sequence functionality. The incidence and progression of atherosclerosis remains a challenge for public health intervention and medical research strategies. Mouse models have been of great utility in meeting this challenge and have enabled systematic evaluation of genetic and environmental influences on the pathogenesis of this disease. Lipoproteins and their receptors play crucial roles in cholesterol homeostasis and, when functionally impaired, can accelerate atherogenesis. Mice with targeted mutations resulting in loss of function and those engineered for overexpression of apolipoproteins, their receptors, and key enzymes in lipid metabolism have been used extensively to investigate the complex etiology of atherosclerosis and to develop effective approaches to treatment (1-6). In addition to genetically engineered mouse models, chemical mutagenesis using N-ethyl-N-nitrosourea (ENU), which causes primarily single-nucleotide mutations, has produced numerous new mouse models for studying human disease. Many of these mutants carry a novel functional mutation in a known gene (7-11). For known genes, having multiple models with a variety of unique mutations allows a survey of phenotypic differences and functional annotation of genes and their products. Causative mutations in numerous ENU mutants identified from large-scale mutagenesis programs worldwide, collectively representing a broad spectrum of disease-related phenotypes, have yet to be identified, and still hold promise of revealing novel genes.Here we describe the identification and initial characterization of a new mouse model of high cholesterol and atherosclerosis generated using ENU mutagenesis and high-throughput phenotyping. Candidate gene sequencing identified a point mutation in the LDL receptor (Ldlr) gene. Comparison of this mutant with the well-characterized Ldlr knockout (KO) mouse model reveals certain phenotypic differences and supports it as a new tool for the study of familial hypercholesterolemia (FH) and atherosclerosis. METHODS Mice and husbandryNonmutagenized C57BL/6J (B...