The insulin resistance syndrome (IRS) is characterized by a constellation of interrelated coronary heart disease (CHD) risk factors, including dyslipidemia, obesity, central obesity, elevated systolic blood pressure, and hyperinsulinemia. Factor analysis was used to investigate the clustering of these risk factors in individuals by examining the correlational structure among these variables. Data from 281 genetically unrelated nondiabetic women who participated in exam 2 (1979 to 1980) 23 However, the metabolic and physiological relationships among these multiple risk factors may mask important biological associations between aspects of the IRS and CHD. Thus, it may be appropriate to consider the risk factors of the IRS in aggregate, rather than independently, when evaluating CHD risk in an epidemiological study.Factor analysis provides a method for investigating interrelated variables. On the basis of the correlational structure of quantitatively measured variables, this method can be used to empirically describe the clustering of these variables. Simplifying the characterization of the IRS in this way may lead to new insights into the underlying mechanisms of the IRS and the association of the syndrome with risk of CHD.The purpose of this study was to use factor analysis to reduce the set of interrelated disorders of the IRS to a smaller number of uncorrelated composite variables, using data from a large sample of genetically unrelated, nondiabetic women. Methods SubjectsStudy subjects were participants in the second examination of the Kaiser Permanente Women Twins Study in Oakland, Calif. Examination 2 was conducted between 1989 and 1990, and included 704 subjects, 81% of the original cohort examined between 1979 and 1980. 8 -28 At the time of the second exam, each woman completed a health history questionnaire and underwent a physical examination that included anthropometric and laboratory measurements.Because data from twins in the same pair are not independent observations, the results presented here are based on one randomly selected twin from each pair, leaving the other half of the sample for validation. The average age of the women at

The San Luis Valley Diabetes Study was undertaken to determine the prevalence, risk factors, and complications of non-insulin-dependent diabetes mellitus in Hispanics and Anglos (non-Hispanic whites), using a geographically based case-control design. The study was conducted in two southern Colorado counties that include 43.6% Hispanic and 54.9% Anglo persons. Medical practice records were reviewed to identify medically diagnosed diabetics. Controls without diabetes were identified by a two-stage random sample of households. Diabetics (n = 343) and controls (n = 607) attended a clinic where an oral glucose tolerance test or current hypoglycemic therapy confirmed or diagnosed non-insulin-dependent diabetes mellitus. The age-adjusted prevalence of confirmed non-insulin-dependent diabetes mellitus was 21/1,000 in Anglo males and 44/1,000 in Hispanic males, accounting for non-response. For Anglo females, the prevalence was 13/1,000 compared with 62/1,000 for Hispanic females, accounting for nonresponse. Previously undiagnosed non-insulin-dependent diabetes mellitus was also higher among Hispanics. There was a 2.1-fold excess of confirmed non-insulin-dependent diabetes mellitus among Hispanic males and a 4.8-fold excess among Hispanic females, consistent with the excess non-insulin-dependent diabetes mellitus among Hispanics reported from comparable studies. Non-insulin-dependent diabetes mellitus is a major chronic disease problem for persons of Hispanic ethnicity.

Small, dense LDL is an integral feature of the insulin resistance syndrome. Nongenetic (ie, behavioral or environmental) factors are important for the expression of the phenotype and for its association with other heart disease risk factors.

Multiple factors may determine insulin resistance and the insulin resistance syndrome. The contributions of genes and environment to the distribution of fasting insulin levels and to the associations of fasting insulin with elements of the syndrome were evaluated in the second examination of the Kaiser Permanente Women Twins Study (Oakland, California, 1989-1990). Subjects included 556 white women (165 monozygous twin pairs, 113 dizygous pairs; 455 women with normal glucose tolerance, 75 with impaired glucose tolerance, and 26 with non-insulin-dependent diabetes by World Health Organization criteria). The intraclass correlation coefficients for log fasting insulin for monozygous and dizygous twin pairs were 0.64 and 0.40, respectively. After adjustment for age, behavioral factors, and body mass index, the estimated classic heritability was 0.53 (p = 0.003). Commingling analysis of fasting insulin indicated the presence of four distributions (p < 0.001), consistent with at least one, and perhaps two, genes influencing this trait. In an unmatched multiple regression model among women from monozygous twin pairs only, log fasting insulin was independently associated with body mass index (p < 0.0001), waist/hip ratio (p = 0.02), and glucose intolerance (p = 0.04), but not with triglycerides, high density lipoprotein cholesterol, or hypertension. After removal of genetic influences by analysis of monozygous intrapair differences, only body mass index (p < 0.0001) remained independently related to fasting insulin. The authors conclude that, in addition to significant genetic influences on fasting insulin, environmental or behavioral factors (particularly nongenetic variation in obesity) are important determinants of fasting insulin and the insulin resistance syndrome.