PROJECT SUMMARY/ABSTRACT This P01 proposal offers a fresh approach to understanding the genetics of an extremely important polygenic autoimmune disease: type 1 diabetes (T1D), which affects nearly three children out of every thousand in North America, and many more around the world. T1D occurs with variable penetrance in Non-Obese Diabetic (NOD) mice, which exhibit a phenotype remarkably similar to that of human patients. Both environmental and genetic factors determine penetrance, but most of the influential mutations and the genes they affect remain unknown. We have developed a powerful technology platform that permits instantaneous identification of point mutations that cause phenotype. Using this platform, we have already identified two spontaneous mutations that cause high and low frequency of disease development in the NOD/NckH and NOD/NckL sublines, respectively. Noting that these sublines, isolated by selective breeding over a period of only seven years, had approximately the same mutational distance from one another as one finds in a pedigree of ENU mutagenized mice as compared to the parental reference strain, we performed a pilot study in which mice were mutagenized on the NOD/NckH background. In a sample of 14 pedigrees, we unambiguously identified twelve ENU-induced mutations with modifying effects on T1D: some accelerating the disease and others suppressing it. Stressing the precision of these studies, which do not merely identify intervals or candidates, but resolve the exact nucleotide change responsible for T1D modification, we propose to expand our efforts, analyzing 21,000 coding/splicing mutations for modifier effects over a period of five years. Our preliminary work suggests that T1D is “balanced on a knife’s edge” from a genetic point of view. Mutations in many genes are clearly capable of influencing T1D development, since randomly induced coding/splicing mutations affecting approximately 1% of the mouse genome caused unambiguous modifier phenotypes. We expect to identify scores if not hundreds of individual modifier mutations during the period of funding. Some of these will have important new facts to tell us about what it takes to develop T1D. Concentrating on those modifier mutations that show large effect sizes, may be amenable to targeting with therapeutic drugs, and/or are particularly surprising in light of what we presently know about T1D pathogenesis, we will rigorously verify causation by re-creating the mutations and/or deleting the causative genes on clean backgrounds (NOD/NckH or NOD/NckL devoid of ENU-induced mutations). We will then systematically examine the mechanism of phenotype modification, both at the level of cellular immuno-pathogenesis, and at the level of molecular pathogenesis. Ultimately, we hope to understand how T1D can be prevented or driven into remission, and we expect many new insights to emerge from the studies planned. A close collaboration between the Bach/Chatenoud group, with its great ...