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Recent studies have demonstrated the importance of sex effects on the underlying genetic architecture of insulin-related traits. To explore sex-specific genetic effects on fasting insulin, we tested for genotype-by-sex interaction and conducted linkage analysis of fasting insulin in Hypertension Genetic Epidemiology Network families. Hypertensive siblings and their first-degree relatives were recruited from five field centers. We performed a genome scan for quantitative trait loci influencing fasting insulin among 1,505 European Americans and 1,616 African Americans without diabetes. Sex-stratified linear regression models, adjusted for race, center, and age, were explored. The Mammalian Genotyping Service typed 391 microsatellite markers, spaced roughly 9 cM. Variance component linkage analysis was performed in SOLAR using ethnic-specific marker allele frequencies and multipoint IBDs calculated in MERLIN. We detected a quantitative trait locus influencing fasting insulin in female subjects (logarithm of odds [LOD] = 3.4) on chromosome 2 at 95 cM (between GATA69E12 and GATA71G04) but not in male subjects (LOD = 0.0, P for interaction = 0.007). This sex-specific signal at 2p13.2 was detected in both European-American (LOD = 2.1) and African-American (LOD = 1.2) female subjects. Our findings overlap with several other linkage reports of insulin-related traits and demonstrate the importance of considering complex context-dependent interactions in the search for insulin-related genes. [ABSTRACT FROM AUTHOR]

Genome-wide linkage scans were carried out using a multipoint variance components method in white and black families of the NHLBI Hypertension Genetic Epidemiology Network (HyperGEN) study to identify quantitative trait loci (QTLs) for pancreatic beta-cell function and insulin sensitivity estimated through the newly released nonlinear computer version of homeostasis model assessment 2. Participants fasting <8 h, with diagnosed type 2 diabetes, or taking blood glucose or blood lipid-lowering medications were excluded. Both phenotypes were adjusted separately by race and sex for the effects of age, BMI, and field center before linkage scans using 370 microsatellite markers were performed. A total of 685 white families (1,180 sibpairs) and 773 black families (775 sibpairs) were evaluated as well as subsets including 267 obese white families (757 sibpairs) and 427 obese black families (599 sibpairs) identified through tree-linkage analyses using interacting covariates of age, sex, and BMI. For beta-cell function in the obese white families, significant (logarithm of odds [LOD] score >3.6) evidence supporting linkages was detected on chromosome 8q24 at D8S1179 (135 cM, LOD score 4.2, empirical P = 0.002) and at D8S1128 (140 cM, LOD score 3.7, empirical P = 0.003). In addition, two regions supported linkage for insulin sensitivity index in the obese black families on chromosome 7q11 at D7S3046 (79 cM, LOD score 3.0, empirical P = 0.018) and on chromosome 6q26 at D6S1277 (173 cM, LOD score 3.0, empirical P = 0.018). Reducing clinical heterogeneity using obesity data and improved estimates of beta-cell function and insulin sensitivity may have permitted identification of a QTL on chromosome 8q24 for beta-cell function in the presence of estimated insulin resistance and a QTL on chromosome 7q11 for insulin sensitivity. These regions replicate previous reports for type 2 diabetes-associated traits. [ABSTRACT FROM AUTHOR]

Type 2 diabetes susceptibility is determined by multiple genetic and environmental factors. Genome-wide linkage scans have localized common regions, possibly harboring susceptibility genes on chromosomes 1, 2, 12, and 20. Variability in linkage findings underscores the probable genetic heterogeneity of type 2 diabetes. Thus, we conducted a genome scan of diabetes status using maximum likelihood methods that model affection status by a liability threshold model. Hypertensive sibships and their offspring and/or parents in the Hypertension Genetic Epidemiology Network study were recruited from five field centers. The diabetes phenotype was derived using the World Health Organization criteria and adjusted for race/study center, age, age2, sex, and with and without percent body fat. In total, 567 diabetic participants were identified in 437 families. Variance component linkage analysis was performed among 1,545 Caucasians and 1,608 African Americans using race-specific marker allele frequencies. We detected a quantitative trait loci (QTLs) influencing diabetes variance (logarithm of odds = 3.4) on chromosome 22, which overlaps a positive type 2 diabetes finding among Canadian Oji-Cree Indians. We also observed suggestive evidence for linkage on chromosomes 1, 2, 5, 8, 14, 17, and 19. The identification and replication of type 2 diabetes QTLs will bring us closer to the detection of functional genes that influence diabetes susceptibility. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated significant genetic and phenotypic correlation underlying the clustering of traits involved in the multiple metabolic syndrome (MMS). The aim of this study was to identify chromosomal regions contributing to MMS-related traits represented by composite factors derived from factor analysis. Data from the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study were subjected to a maximum likelihood-based factor analysis. These analyses generated an MMS factor that was loaded by BMI, waist-to-hip ratio, subscapular skinfold, triglycerides, HDL, homeostasis model assessment index, plasminogen activator inhibitor-1 antigen, and serum uric acid. Genetic data were obtained for 2,467 subjects from 387 three-generation families (402 markers, the NHLBI Mammalian Genotyping Service) and 1,082 subjects from 256 sibships (243 markers, the Utah Molecular Genetics Laboratory). Multipoint variance components linkage analysis (GENEHUNTER version 2.1) of the MMS factor was conducted in the combined marker set sample. The greatest evidence for linkage was found on chromosome 2, with a peak LOD of 3.34 at 240 cM. Suggestive linkage was also observed for regions on chromosomes 7, 12, 14, and 15. In summary, a genomic region on chromosome 2 may contain a pleiotropic locus contributing to the clustering of MMS-related phenotypes.

Elevated blood glucose levels are the hallmark of type 2 diabetes as well as a powerful risk factor for development of the disease. We conducted a genome-wide search for diabetes-related genes, using measures of glycemia as quantitative traits in 330 pedigrees from the Framingham Heart Study. Of 3,799 attendees at the 5th Offspring Study exam cycle (1991--1995), 1,461, 1,251, and 771 men (49%) and women provided information on levels of 20-year mean fasting glucose, current fasting glucose, and HbA(1c), respectively, and 1,308 contributed genotype data (using 401 microsatellite markers with an average spacing of 10 cM). Levels of glycemic traits were adjusted for age, cigarette smoking, alcohol and estrogen use, physical activity, and BMI. We ranked standardized residuals from these models, created normalized deviates from the ranks, and used the variance component model implemented in SOLAR (Sequential Oligogenic Linkage Analysis Routines) to evaluate linkage to normalized deviates as quantitative traits. We found peak evidence for linkage to 20-year mean fasting glucose levels on chromosome 1 at approximately 247 cM from p-telomere (pter) (multipoint logarithm of odds [LOD] 2.33) and on chromosome 10 at approximately 86 cM from pter (multipoint LOD 2.07); to current fasting glucose levels on chromosome 1 at approximately 218 cM from pter (multipoint LOD 1.80) and on chromosome 10 at approximately 96 cM from pter (multipoint LOD 2.15); and to HbA(1c) levels on chromosome 1 at approximately 187 cM (multipoint LOD 2.81). This analysis of unselected European Caucasian pedigrees suggests localization of quantitative trait loci influencing glucose homeostasis on chromosomes 1q and 10q. Findings at approximately 187--218 cM on chromosome 1 appear to replicate linkage reported in previous studies of other populations, pointing to this large chromosomal region as worthy of more detailed scrutiny in the search for type 2 diabetes susceptibility genes.