HERITABILITY OF FACTORS OF THE INSULIN-RESISTANCE SYNDROME IN WOMEN TWINS

The insulin resistance syndrome (IRS) is characterized by a combinatio n of interrelated coronary heart disease (CHD risk factors, including low high-density lipoprotein cholesterol (HDL-C) levels, obesity and i ncreases in triglyceride (TG), blood pressure, small low-density lipop rotein particles (LDL), and both fasting and postload plasma insulin a nd glucose. Using factor analysis, we previously identified 3 uncorrel ated factors that explained 66% of the variance among these variables, based on data from women participating in examination 2 of the Kaiser Permanente Women Twins Study in Oakland, CA during 1989-1990. The fac tors were interpreted as: 1) body mass/fat distribution, 2) insulin/gl ucose, and 3) lipids: TG, HDL-C, LDL peak particle diameter. In this a nalysis, heritability of each of the factors was estimated based on da ta from 140 monozygotic and 96 dizygotic pairs of non-diabetic women t wins. Heritability estimates were calculated using the classical appro ach, the analysis of variance (ANOVA) approach, and the maximum likeli hood approach. For the body mass/fat distribution factor heritability estimates suggest moderate genetic influences: 0.61 (P < 0.001), 0.14 (P > 0.05), and 0.71 (P < 0.001), respectively. The insulin/glucose fa ctor appeared to be highly heritable, with estimates of 0.87, 0.92, an d 0.57 (all P < 0.001), respectively. The heritability estimates for t he lipid factor were moderate and consistent across methods: 0.25 (P < 0.10), 0.32 (P < 0.05), and 0.30 (P < 0.05), respectively. These resu lts are consistent with genetic influences on each of the 3 ''factors, '' and suggest that both genetic and environmental effects are involve d in the clustering of IRS risk factors. (C) 1997 Wiley-Liss, Inc.