Aims/hypothesis: Hyperinsulinaemia and insulin resistance usually precede clinical hyperglycaemia and Type 2 diabetes. Thus, plasma insulin concentrations and insulin resistance are important quantitative traits associated with risk of Type 2 diabetes, and represent key measures for genetic analysis of the syndrome.
Methods: We carried out a genome-wide search for loci related to plasma insulin concentrations and insulin resistance in 330 extended, community-based pedigrees from the Framingham Heart Study. Normalized deviates of the standardized residuals of plasma insulin concentrations in the fasting state, 2 h after oral glucose challenge and as a measure of insulin resistance were used in linkage analysis with the variance components model implemented in the computer program SOLAR.
Results: The results suggest susceptibility loci influencing plasma concentrations of fasting insulin and insulin resistance on chromosomes 11 (LOD 2.43 at 85 cM close to D11S2002) and 17 (LOD 1.8 at 60 cM, close to D17S784); and susceptibility loci influencing 2-h plasma insulin concentrations on chromosomes 9 (LOD 2.8 at 80 cM, close to D9S922) and 19 (LOD 1.8 at 66 cM, close to D19S245). The results of the analysis of 1000 simulations of the trait and an unlinked marker suggest that in a genome scan of 401 markers fewer than one LOD score over 1 would be due to Type 1 error, and be a false positive.
Conclusion/interpretation: We conclude that these suggestive regions for quantitative pre-diabetic insulin traits could contain major loci in the pathogenesis of Type 2 diabetes.