Summary

Aims

Evaluate discs large homolog 2 (DLG2) as a positional candidate gene for disposition index (DI) in the Insulin Resistance Atherosclerosis Family Study (IRAS-FS) African-American sample.

Methods

SNPs (n=193) were selected for genotyping in 580 African-American individuals using a modified tagging algorithm. Follow-up genotyping was carried out within regions associated with DI. A subset of highly associated, uncorrelated SNPs were used as covariates in the linkage analysis to assess their contribution to linkage.

Results

Evidence of association with DI was observed at the DLG2 locus (admixture-adjusted P=0.050-8.7×10-5) with additional signals observed in follow-up genotyping of 17 SNPs (P=0.033-0.0012). Inclusion of highly associated, uncorrelated SNPs as covariates in the linkage analysis explained linkage at the DLG2 locus (90.8cM) and reduced the maximal LOD score (72.0cM) from 4.37 to 3.71.

Conclusions

Evidence of association and an observed contribution to evidence for linkage to DI was observed for SNPs in DLG2 genotyped on the African-American individuals from the IRAS-FS. Although not the only gene in the region, these results suggest that variation at the DLG2 locus contributes to maintenance of glucose homeostasis through regulation of insulin sensitivity and β-cell function as measured by DI.

OBJECTIVE

To describe the 5-year change in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas.

RESEARCH DESIGN AND METHODS

Absolute change in VAT and SAT measured by abdominal computed tomography scans has been obtained at a 5-year interval from African Americans (n = 389) and Hispanic Americans (n = 844), aged 20–69 years, in 10-year age-groups.

RESULTS

Mean 5-year increases in VAT areas in women were 18, 7, 4, 0.4, and −3 cm2 for African Americans and 13, 7, 3, 1, and −15 cm2 for Hispanics, across the 5 age decades (trend not significant). Mean 5-year increases in SAT areas in women were 88, 46, 19, 17, and 14 cm2 for African Americans and 53, 20, 17, 12, and 1 cm2 for Hispanics, across the 5 age decades (P < 0.05 for both). Similar trends have been observed in men.

CONCLUSIONS

Accumulation of abdominal fat is greatest in young adulthood. These data may be useful in identifying subgroups at risk of type 2 diabetes.

Background

Several observational studies have recently suggested an inverse association of circulating levels of vitamin D with blood pressure. These findings have been based mainly on Caucasian populations; whether this association also exists among Hispanic and African Americans has yet to be definitively determined. This study investigates the association of 25-hydroxyvitamin D (25[OH]D) with blood pressure in Hispanic and African Americans.

Methods

The data source for this study is the Insulin Resistance Atherosclerosis Family Study (IRASFS), which consists of Hispanic- and African-American families from three U.S. recruitment centers (n=1334). A variance components model was used to analyze the association of plasma 25[OH]D levels with blood pressure.

Results

An inverse association was found between 25[OH]D and both systolic (β for 10 ng/mL difference= −2.05; p<0.01) and diastolic (β for 10 ng/mL difference= −1.35; p<0.001) blood pressure in all populations combined, after adjusting for age, sex, ethnicity and season of blood draw. Further adjustment for body mass index (BMI) weakened this association (β for 10 ng/mL difference= −0.94; p=0.14 and β for 10 ng/mL difference = −0.64; p=0.09, respectively).

Conclusions

25[OH]D levels are significantly inversely associated with blood pressure in Hispanic and African Americans from the IRASFS. However, this association was not significant after adjustment for BMI. Further research is needed to determine the role of BMI in this association. Large, well-designed prospective studies of the effect of vitamin D supplementation on blood pressure may be warranted.

BACKGROUND

We examined the relationship between visceral adipose tissue (VAT), independent of overall adiposity, and prevalent hypertension among adults enrolled in the Insulin Resistance Atherosclerosis (IRAS) Family Study. We also examined the role of insulin sensitivity (SI) upon hypertension. This was a cross-sectional epidemiological study in which African-American and Hispanic-American families were recruited from three clinical sites. The main outcome measure was prevalent hypertension, as defined by standardized protocol.

METHODS

The relationship between VAT and prevalent hypertension was examined in adjusted marginal models among 1,582 participants. All continuous variables were standardized.

RESULTS

A significant VAT by gender interaction prompted separate analyses for VAT according to gender. Further adjustment for SI was performed to determine its potential role in the VAT-hypertension relationship. The mean age (SD) of the sample was 41.3 (13.8) years, with a mean BMI (SD) of 28.7 (6.0) kg/m2. Women comprised 58.5% of the sample (N = 925), and Hispanic-Americans comprised 69.2% of the sample (N=1095). One in five participants (21.2%) had prevalent hypertension. In women, VAT was significantly associated with hypertension, independent of BMI (OR = 1. 49 p= 0.006). African-American women demonstrated increased odds of prevalent hypertension compared to Hispanic-American women (OR = 3.08, p <0.001). Among men, VAT was not associated with hypertension independent of BMI, and BMI explained a significant amount of the variation in hypertension.

Conclusions

A significant relationship may exist between VAT and hypertension among women, but not men. The relationship between VAT and hypertension in women was not associated with insulin resistance.