Type 2 diabetes in humans is not a single gene disorder but a multifactorial disease caused by the interaction of multiple genes and environmental factors. Recombinant inbred (RI) strains are a powerful tool for analyzing not only single genetic traits but also multifactorial genetic traits. By using the SMXA RI mice, we genetically dissected diabetes-related traits (BMI, nonfasting blood glucose concentration, and blood glucose concentration during intraperitoneal glucose tolerance tests). For minimizing the variation of glucose tolerance in each strain, all mice were fed the high-carbohydrate diet and subjected to phenotypic and genetic analyses. The parental strains, SM/J and A/J, were nondiabetic, and the differences of the mean values of diabetes-related traits were small. In contrast, an impaired glucose tolerance was observed in (SM × A)F1 mice, and marked differences in diabetes-related traits were observed in 19 SMXA RI strains. In particular, several SMXA RI strains showed markedly impaired glucose tolerance and hyperglycemia. Quantitative trait locus (QTL) analysis revealed a locus on chromosome (Chr) 10 contributing significant effect on nonfasting blood glucose concentration, as well as six diabetes-related loci on four chromosomes with suggestive evidence of linkage with diabetes-related phenotypes. The A/J-derived QTLs on Chr 2 and 18 and an SM/J-derived QTL on Chr 10 contributed to the impairment of glucose tolerance and/or the increase of blood glucose concentration. The present study indicates that QTLs derived from parental SM/J and A/J genomes, both of which are nondiabetic, interact in the RI genomes, leading to the development of hyperglycemia and diabetic phenotypes. Genetic dissection of this kind of diabetogenesis will increase our understanding of the complex gene-gene interaction and mode of inheritance in human type 2 diabetes.
Address correspondence and reprint requests to Fumihiko Horio, Graduate School of Bioagricultural Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. E-mail:.
Received for publication 4 April 2002 and accepted in revised form 23 September 2002.
Chr, chromosome; IPGTT, intraperitoneal glucose tolerance test; LOD, logarithm of odds; QTL, quantitative trait locus; RI, recombinant inbred.