Exploring differences in adiposity in two U.S. Hispanic populations of Mexican origin using social, behavioral, physiologic and genetic markers: the IRAS Family Study.

OBJECTIVE: The census classification of Hispanic origin is used in epidemiological studies to group individuals, even though there is geographical, cultural, and genetic diversity within Hispanic Americans of purportedly similar backgrounds. We observed differences in our measures of adiposity between our two Mexican American populations, and examined whether these differences were attributed to social, behavioral, physiologic or genetic differences between the two populations. RESEARCH DESIGN AND METHODS: In the IRAS Family Study, we examined 478 Hispanics from San Antonio, Texas and 447 Hispanics from the San Luis Valley, Colorado. Associations with body mass index (BMI), visceral adipose tissue area (VAT), and subcutaneous adipose tissue area (SAT) using social, behavioral, physiologic and genetic variables were examined. RESULTS: Hispanics of Mexican origin in our clinic population in San Antonio had significantly higher mean BMI (31.09 vs. 28.35 kg/m2), VAT (126.3 vs. 105.5 cm2), and SAT (391.6 vs. 336.9 cm2), than Hispanics of Mexican origin in the San Luis Valley. The amount of variation in adiposity explained by clinic population was 4.5% for BMI, 2.8% for VAT, and 2.7% for SAT. After adjustment, clinic population was no longer associated with VAT and SAT, but remained associated with BMI, although the amount of variation explained by population was substantially less (1.0% for BMI). CONCLUSION: Adiposity differences within this population of Mexican origin can be largely explained by social, behavioral, physiologic and genetic differences.

A genome scan for fasting insulin and fasting glucose identifies a quantitative trait locus on chromosome 17p: the insulin resistance atherosclerosis study (IRAS) family study.

Plasma insulin and glucose concentrations are important quantitative phenotypes related to diabetes and the metabolic syndrome. Reports purporting to identify quantitative trait loci (QTLs) that contribute to the variation in fasting insulin and glucose concentrations are discrepant. As part of the Insulin Resistance Atherosclerosis Study (IRAS) Family Study, a genome scan was performed in African-American (n = 42) and Hispanic (n = 90) extended families to identify regions that may contain positional candidate genes for fasting insulin and fasting glucose (n = 1,604 subjects). There was significant evidence for linkage of fasting insulin to the short arm of chromosome 17 (logarithm of odds [LOD] = 3.30; 54 cM between D17S1294 and D17S1299, P = 1.0 x 10(-4)). The strongest evidence for linkage over all pedigrees for fasting glucose was also observed in this region (LOD = 1.44; 58 cM, P = 9.9 x 10(-3)). The results of this study provide impetus for future positional cloning of QTLs regulating insulin and glucose levels. Identifying genes in these regions should provide insight into the nature of genetic factors regulating plasma glucose and insulin concentrations.

Minimal model-based insulin sensitivity has greater heritability and a different genetic basis than homeostasis model assessment or fasting insulin.

Insulin resistance is an important risk factor for development of type 2 diabetes as well as other chronic conditions, including hypertension, cardiovascular disease, and colon cancer. To find genes for insulin resistance it is necessary to assess insulin action in large populations. We have previously measured insulin action in a large cohort of subjects (Insulin Resistance and Atherosclerosis Study [IRAS] Family Study) using the minimal model approach. In this study, we compare sensitivity from the minimal model (insulin sensitivity index [S(I)]) with the measure of insulin resistance emanating from the homeostasis model assessment (HOMA) approach. The former measure emerges from the glycemic response to endogenous and exogenous insulin; the latter is based solely on fasting measures of glucose and insulin. A total of 112 pedigrees were represented, including 1,362 individuals with full phenotypic assessment. Heritability of S(I) was significantly greater than that for HOMA (0.310 vs. 0.163) and for fasting insulin (0.171), adjusted for age, sex, ethnicity, and BMI. In addition, correlation between S(I) and either HOMA or fasting insulin was only approximately 50% accounted for by genetic factors, with the remainder accounted for by environment. Thus S(I), a direct measure of insulin sensitivity, is determined more by genetic factors rather than measures such as HOMA, which reflect fasting insulin.

Homeostasis model assessment of insulin resistance in relation to the incidence of cardiovascular disease: the San Antonio Heart Study.

OBJECTIVE: The prospective association between insulin levels and risk of cardiovascular disease (CVD) is controversial. The objective of the present study was to investigate the relationship of the homeostasis model assessment of insulin resistance (HOMA-IR), as well as insulin levels, with risk of nonfatal and fatal CVD over the 8-year follow-up of the San Antonio Heart Study. RESEARCH DESIGN AND METHODS: Between 1984 and 1988, randomly selected Mexican-American and non-Hispanic white residents of San Antonio participated in baseline examinations that included fasting blood samples for glucose, insulin, and lipids, a glucose tolerance test, anthropometric measurements, and a lifestyle questionnaire. Between 1991 and 1996, 2,569 subjects who were free of diabetes at baseline were reexamined using the same protocol. RESULTS: Over the follow-up period, 187 subjects experienced an incident cardiovascular event (heart attack, stroke, heart surgery, angina, or CVD death). Logistic regression analysis indicated that risk of a CVD event increased across quintiles of HOMA-IR after adjustment for age, sex, and ethnicity (P for trend <0.0001; quintile 5 vs. quintile 1, odds ratio [OR] 2.52, 95% CI 1.46-4.36). Additional adjustment for LDL, triglyceride, HDL, systolic blood pressure, smoking, alcohol consumption, exercise, and waist circumference only modestly reduced the magnitude of these associations (P for trend 0.02; quintile 5 vs. quintile 1, OR 1.94, 95% CI 1.05-3.59). Furthermore, there were no significant interactions between HOMA-IR and ethnicity, sex, hypertension, dyslipidemia, glucose tolerance (impaired glucose tolerance versus normal glucose tolerance), or obesity. The magnitude and direction of the relationship between insulin concentration and incident CVD were similar. CONCLUSIONS: We found a significant association between HOMA-IR and risk of CVD after adjustment for multiple covariates. The topic remains controversial, however, and additional studies are required, particularly among women and minority populations.

Prevalencia de diabetes e intolerancia a la glucosa en una población urbana de nivel económico bajo / Prevalence of type II diabetes and impaired glucose tolerance in a low income urban population

Se presentan los resultados de un estudio epidemiológico en población abierta, en medio urbano, de nivel económico bajo, con el propósito de establecer la prevalencia de diabetes mellitus tipo II (DM) e intolerancia a la glucosa (IG) en este sector de la población. Se seleccionó una zona equivalente a un área geoestadística básica, de acuerdo al Instituto Naccional de Estadística, Geografía e Informática. Se obtuvo un plano de la colonia con sus 39 manzanas. Se seleccionaron aleatoriamente empleando el paquete estadístico Systat. Se enumeraron todos los hogares de cada manzana, listando a todos sus habitantes y definiendo como elegibles a los que tuvieran 35 a 64 años de edad que no estuvieran embarazadas. Se entrevistó en el domicilio a todos los elegibles. Se investigó si padecían o no DM. Después se les invitó a realizarse un exàmen físico con curva de tolerancia a la glucosa. El total de habitantes en la zona fue de 4411. De estos 931 resultaron elegibles: 452 hombres (48.5 porciento) y 479 mujeres (51.5 porciento). La taza de respuesta de la encuesta domiciliaria fue 91.7 porciento y la del exámen físico 69.8 porciento utilizando los criterios de diagnóstico recomendados por la Organización Mundial de la Salud, la taza cruda de prevalencia de DM fue: en hombres 10.6 porciento y en mujeres 14.8 porciento. La taza cruda de prevalencia de IG en hombres resultó 12.8 porciento y en mujeres 12.3 porciento. Estos datos manifiestan que nuestra población tiene un alto grado de susceptibilidad a la DM e IG: ubican en nuestro país entre las poblaciones con mayor prevalencia de DM.