Genome-wide scans reveal quantitative trait Loci on 8p and 13q related to insulin action and glucose metabolism: the San Antonio Family Heart Study

Type 2 diabetes is a complex disease that arises from physiological disruptions of the body's sensitivity to insulin and ability to metabolize glucose. Multipoint linkage analyses for insulin sensitivity phenotypes were conducted in 1,280 Mexican Americans from 41 families who participated in the San Antonio Family Heart Study. A significant linkage signal (logarithm of odds [LOD] = 2.98) affecting corrected insulin response to glucose was detected on chromosome 13q between D13787 and D13S252, in the region where the MODY-4 gene has previously been mapped. Another signal on chromosome 13 was observed at D13S285 (LOD = 1.86), where the insulin receptor substrate 2 gene resides. Significant linkage (LOD = 3.09) for insulin response to glucose was found on chromosome 8 between D8S1130 and D8S1106, near the lipoprotein lipase and macrophage scavenger receptor genes. Multipoint analysis of abdominal skinfold with an LOD of 2.68 showed signals in the same region. There was also suggestive evidence for linkage of quantitative insulin sensitivity check index and fasting glucose to a previously reported location at D9S301 (LOD = 2.19). These results indicate that chromosomal locations on 8p and 13q might harbor genes that affect a variety of insulin- and glucose-related phenotypes that contribute to the observed variations in these important risk factors for diabetes in Mexican Americans.     

Linkage analysis of a composite factor for the multiple metabolic syndrome: the National Heart, Lung, and Blood Institute Family Heart Study

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.     

Genome-wide and fine-mapping linkage studies of type 2 diabetes and glucose traits in the Old Order Amish: evidence for a new diabetes locus on chromosome 14q11 and confirmation of a locus on chromosome 1q21-q24

We conducted a genome scan using a 10-cM map to search for genes linked to type 2 diabetes in 691 individuals from a founder population, the Old Order Amish. We then saturated two regions on chromosomes 1 and 14 showing promising linkage signals with additional markers to produce a approximately 2-cM map for fine mapping. Analyses of both discrete traits (type 2 diabetes and the composite trait of type 2 diabetes and/or impaired glucose homeostasis [IGH]), and quantitative traits (glucose levels during a 75-g oral glucose challenge, designated glucose 0-180 and HbA(1c)) were performed. We obtained significant evidence for linkage to type 2 diabetes in a novel region on chromosome 14q11 (logarithm of odds [LOD] for diabetes = 3.48, P = 0.00005). Furthermore, we observed evidence for the existence of a diabetes-related locus on chromosome 1q21-q24 (LOD for type 2 diabetes/IGH = 2.35, P = 0.0008), a region shown to be linked to diabetes in several other studies. Suggestive evidence for linkage to glucose traits was observed on three other regions: 14q11-q13 (telomeric to that above with LOD = 1.82-1.85 for glucose 150 and 180), 1p31 (LOD = 1.28-2.30 for type 2 diabetes and glucose 120-180), and 18p (LOD = 3.07, P = 0.000085 for HbA(1c) and LOD = 1.50 for glucose 0). In conclusion, our findings provide evidence that type 2 diabetes susceptibility genes reside on chromosomes 1, 14, and 18.     

Quantitative trait loci on chromosome 8q24 for pancreatic beta-cell function and 7q11 for insulin sensitivity in obese nondiabetic white and black families: evidence from genome-wide linkage scans in the NHLBI Hypertension Genetic Epidemiology Network (HyperGEN) study

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.