NIDDM GENES IN MICE - DELETERIOUS SYNERGISM BY BOTH PARENTAL GENOMES CONTRIBUTES TO DIABETOGENIC THRESHOLDS

We used mouse genetics to model how polygenic thresholds for the trans ition from impaired glucose tolerance (IGT) to NIDDM are reached. NON/ Lt and NZO/HI are inbred mouse strains selected for IGT and polygenic obesity, respectively. Their Fl male progeny consistently developed NI DDM. Genetic analysis of F2 males from both cross directions identifie d an NON-derived diabetogenic locus, Nidd 1, on chromosome (Chr) 4 nea r the leptin receptor. This locus was associated with reduced plasma i nsulin, increased non-fasted blood glucose, and lower body weight. Ano ther NON-derived diabetogenic locus on Chr 18 (Nidd2) that controls bl ood glucose was identified. An NZO-derived diabetogenic region on Chr 11 (Nidd3), possibly comprising two separate loci, reduced ability to sustain elevated plasma insulin and significantly reduced weight gain over time. Thus, the diabetogenic synergism between genetic loci from strains separately exhibiting subthreshold defects perturbing glucose homeostasis underscores the likely complexity of the inheritance of ob esity-associated forms of NIDDM in humans.We used mouse genetics to mo del how polygenic thresholds for the transition from impaired glucose tolerance (IGT) to NIDDM are reached. NON/Lt and NZO/HI are inbred mou se strains selected for IGT and polygenic obesity, respectively. Their Fl male progeny consistently developed NIDDM. Genetic analysis of F2 males from both cross directions identified an NON-derived diabetogeni c locus, Nidd 1, on chromosome (Chr) 4 near the leptin receptor. This locus was associated with reduced plasma insulin, increased non-fasted blood glucose, and lower body weight. Another NON-derived diabetogeni c locus on Chr 18 (Nidd2) that controls blood glucose was identified. An NZO-derived diabetogenic region on Chr 11 (Nidd3), possibly compris ing two separate loci, reduced ability to sustain elevated plasma insu lin and significantly reduced weight gain over time. Thus, the diabeto genic synergism between genetic loci from strains separately exhibitin g subthreshold defects perturbing glucose homeostasis underscores the likely complexity of the inheritance of obesity-associated forms of NI DDM in humans.