Pima Indians as a model to study the genetics of NIDDM

Trends in Cardiovascular Health Metrics in Obese Adults: National Health and Nutrition Examination Survey (NHANES), 1988-2014

BACKGROUND

No study has quantified trends in the prevalence of cardiovascular disease risk factors and cardiovascular health metrics among obese people in the United States in recent years.

METHODS AND RESULTS

We examined the secular changes in cardiovascular health metrics and key cardiovascular disease risk factors among obese adults (aged ≥20 years) in the United States. We included 18 626 obese adults (body mass index ≥30) from the National Health and Nutrition Examination Survey (NHANES) III and NHANES 1999-2014. Among those obese adults, there were decreases in mean systolic blood pressure, diastolic blood pressure, and total cholesterol levels and increases in mean high-density lipoprotein cholesterol levels and mean hemoglobin A1c levels. Prevalence of blood pressure health and lipid health remained stable during the period 1988-2014, whereas prevalence of blood glucose health decreased significantly during this period. Prevalence of freedom from cardiovascular disease risk factors remained stable at ≈15% among the adult obese population during the period 1988-2014, whereas prevalence of presence of all 3 risk factors increased from 16.4% to 22.4% during this period, commensurate with a decline in those with 1 to 2 risk factors (from 69.6% to 62.4%).

CONCLUSIONS

During the past 3 decades, blood pressure health and blood lipid health remained stable or improved, whereas blood glucose health deteriorated among adult obese population. This resulted in an overall decrease in cardiovascular health status among obese adults and greater risk of type 2 diabetes mellitus. The data argue for interventions targeted to those obese persons who are metabolically unhealthy to stem rising rates of diabetes mellitus.

Cardiometabolic disease risk in metabolically healthy and unhealthy obesity: Stability of metabolic health status in adults

OBJECTIVE

To assess the stability of metabolic status and body mass index (BMI) status and their relative contribution to risk of diabetes, cardiovascular events, and mortality.

METHODS

A total of 14,685 participants from the Atherosclerosis Risk in Communities Study and 4,990 from the Coronary Artery Risk Development in Young Adults Study were included. People with healthy obesity (HO) are defined as those meeting all three indices of blood pressure, blood glucose, and blood lipids. People with unhealthy obesity crossed the risk threshold for all three criteria.

RESULTS

In both healthy and unhealthy subgroups, risks for coronary heart disease (CHD), stroke, and mortality were comparable among BMI status during a mean 18.7-year follow-up. When compared with HO, hazard ratios were increased for diabetes (5.56, 95% confidence interval [CI] 4.12-7.48), CHD (5.60, 95% CI 3.14-9.98), stroke (4.84, 95% CI 2.13-10.97), and mortality (2.6, 95% CI 1.88-3.61) in people with unhealthy obesity. BMI only moderately increased the risks for diabetes among healthy subjects. In the Coronary Artery Risk Development in Young Adults Study over 20 years, 17.5% of lean subjects and 67.3% of overweight subjects at baseline developed obesity during follow-up. Despite rising BMI, metabolic status remained relatively stable.

CONCLUSIONS

Metabolic status is relatively stable despite rising BMI. HO had lower risks for diabetes, CHD, stroke, and mortality than unhealthy subjects but increased diabetes risks than healthy lean people. Cardiometabolic risk factors confer much higher risk than obesity per se.

Diet, insulin resistance, and obesity: zoning in on data for Atkins dieters living in South Beach

Insulin resistance is a central pathogenic factor for the metabolic syndrome and is associated with both generalized obesity and the accumulation of fat in the omental and intramyocellular compartments. In the context of the current obesity epidemic, it is imperative to consider diets in terms of their ability to both promote weight loss and ameliorate insulin resistance. Weight loss under any dietary formulation depends on hypocaloric intake, and only moderate weight loss (5-10%) is sufficient to augment insulin sensitivity. However, increments in insulin sensitivity may be more directly related to loss of intramyocellular or omental fat rather than loss of total body weight per se. The widespread acceptance of popular low-carbohydrate high-fat diets (e.g. Atkins Diet, Zone Diet, South Beach diet) further underscores the need to evaluate dietary interventions regarding their safety and metabolic effects. These high-fat diets have been shown to be safe in the short term; however, their long-term safety has not been established. With respect to insulin sensitivity, diets enriched in saturated fats can induce insulin resistance, whereas fat substitution with monounsaturated fats can enhance insulin sensitivity. On the other hand, high-fiber, high-carbohydrate diets comprised of foods with low caloric density can similarly be used for effective weight reduction and to ameliorate insulin resistance. Although some data suggest that low-glycemic index diets are most advantageous in this regard, these effects may have more to do with increments in dietary fiber than differences in available carbohydrates. Popular low-carbohydrate, high-fat diets are being fervently embraced as an alternative to challenging modifications in lifestyle and intentional calorie reduction. Current data do not support such unbridled enthusiasm for these diets, particularly in relationship to high-fiber, high-carbohydrate diets emphasizing intake of fresh vegetables and fruits. Long-term studies to determine the efficacy and safety of both popular and experimental diets are warranted.

Quantitative trait linkage studies of diabetes-related traits

Genetic linkage methods for diseases with complex inheritance are based on assessment of allele sharing between affected relative pairs, but such methods have low power to detect genes with moderate effects. This may explain the difficulty in replication for many of the putative loci for type 2 diabetes. To enhance power to detect diabetes-susceptibility genes, some investigators have performed quantitative-trait linkage studies for diabetes-related traits, including measures of glycemia, insulin sensitivity, insulin secretion, obesity, lipidemia, and blood pressure. These linkage studies have not provided stronger or more consistent evidence for linkage than studies of diabetes affection status, but have identified several loci that may play an important role in the physiologic processes related to the development of type 2 diabetes.

Population isolates: their special value for locating genes for bipolar disorder

OBJECTIVES

Population isolates offer several advantages for those hoping to identify predisposition genes for bipolar disorder (BP). In this review article, the rationale for performing gene mapping studies in this type of population and the results of genetic mapping studies performed to date in population isolates are presented.

METHODS

This article begins with a brief review of the concepts involved in mapping genes for BP. The concept of populations that show some degree of historical isolation and their special utility for certain types of gene mapping is presented. Methods of statistical analysis particularly relevant for gene mapping of complex diseases like BP are presented. Finally, several BP gene studies conducted to date in several population isolates are reviewed.

RESULTS

Genetic mapping studies of BP have occurred thus far in several isolates or sub-isolates, including the Amish population, Costa Ricans, Finnish, and Canadians (in Quebec), and significant linkage scores have been identified in the latter three isolates.

CONCLUSIONS

Possible greater homogeneity and greater consistency of diagnosis are factors that have been cited in several studies of BP done in isolates to date. Another special advantage of working in certain types of population isolate is their appropriateness for using certain types of association or linkage disequilibrium-based approaches at both the genome screening and fine mapping stages. These tests include mapping by linkage disequilibrium analyses, an approach that allows mapping to occur at the population, rather than the pedigree, level.

Family and genetic studies of indices of insulin sensitivity and insulin secretion in Pima Indians

BACKGROUND

The present analyses were conducted to examine the extent to which insulin sensitivity and insulin secretion, assessed using simple indices derived from an oral glucose tolerance test, are influenced by genetic factors, and to assess whether these genetic factors overlap with those influencing susceptibility to type 2 diabetes in Pima Indians.

METHODS

Indices calculated from fasting and 2-h post-load insulin (I(0), I(120)) and glucose (G(0), G(120)) concentrations included insulin sensitivity index [ISI(0)=10(4)/(I(0).G(0))] and corrected insulin response [CIR(120)=I(120)/[G(120).(G(120)-70 mg/dl)]]. Heritability (h(2)) was determined using variance components methods in 1421 non-diabetic individuals from 446 sibships. Among 595 individuals in 186 sibships, genome-wide quantitative trait linkage analyses of ISI(0) and CIR(120) were conducted and affected-sibling analyses of diabetic siblings stratified by prediabetic measurements of ISI(0) and CIR(120) were also performed.

RESULTS

Both ISI(0) (h(2)=0.37+/-0.06) and CIR(120) (h(2)=0.25+/-0.07) were moderately heritable. Modest evidence for linkage with CIR(120) (logarithm of odds (LOD)=1.6) was observed on chromosome 1q in a region previously shown to have linkage with young-onset diabetes in Pimas. When diabetic siblings were stratified by CIR(120), evidence for linkage in this region was strongest (LOD=1.5) among those with a low CIR(120). Additional regions with modest evidence for linkage with ISI(0) were observed on chromosomes 9p (LOD=2.0) and 14p (LOD=1.7).

CONCLUSIONS

The present analyses suggest that insulin sensitivity and insulin secretion are influenced by genetic factors in Pima Indians. The linkage analyses suggest that the putative diabetes-susceptibility gene on chromosome 1q affects insulin secretion. Published in 2001 by John Wiley & Sons, Ltd.

Subcutaneous abdominal adipocyte size, a predictor of type 2 diabetes, is linked to chromosome 1q21--q23 and is associated with a common polymorphism in LMNA in Pima Indians

Large subcutaneous abdominal adipocyte size (s.c. abd. AS) is associated with insulin resistance and predicts type 2 diabetes in Pima Indians. Because type 2 diabetes is familial, we aimed to determine whether mean s.c. abd. AS is also familial and if so, to identify chromosomal regions linked to this measure. Body composition (hydrodensitometry) and mean s.c. abd. AS (fat biopsy) were measured in 295 Pima Indians (179 with normal, 80 with impaired, and 36 with diabetic glucose tolerance) representing 164 nuclear families. Mean s.c. abd. AS, adjusted for age, sex, and percentage body fat was a familial trait (heritability h(2) = 0.48, P < 0.0001). A genome-wide autosomal scan revealed suggestive evidence for linkage (LOD 1.73) of adjusted mean s.c. abd. AS to chromosome 1q21--q23, a region containing LMNA, the gene encoding for the nuclear envelope proteins lamin A/C. Rare mutations in LMNA were recently shown to underlie familial partial lipodystrophy (FPLD), a syndrome characterized by regional loss of adipose tissue, insulin resistance, and glucose intolerance. A common (allelic frequency 0.43) single nucleotide polymorphism (silent 1908C --> T substitution) in exon 10 of LMNA (GenBank X03444) was associated with reduced age-, sex- and percentage body fat-adjusted mean s.c. abd. AS [0.80 +/- 0.17 (CC), 0.76 +/- 0.15 (CT), 0.73 +/- 0.16 (TT) microg lipid/cell, P < 0.05 for CC vs TT]. These findings indicate that approximately half of the variance in mean s.c. abd. AS can be attributed to familial factors and that genetic variation in LMNA might not only underlie rare cases of FPLD, but may also contribute to variation in adipocyte size in the general population.

Molecular scanning for mutations in the insulin receptor substrate-1 (IRS-1) gene in Mexican Americans with Type 2 diabetes mellitus

BACKGROUND

Insulin receptor substrate-1 (IRS-1) is an endogenous substrate for the insulin receptor tyrosine kinase, which plays an important role in insulin signaling. Mutations in the IRS-1 gene are associated in some populations with obesity and Type 2 diabetes.

METHODS

To determine whether variation in the IRS-1 gene contributes to genetic susceptibility to insulin resistance and Type 2 diabetes in Mexican Americans, the entire coding region of the IRS-1 gene was screened for variation in 31 unrelated subjects with Type 2 diabetes using single-stranded conformational polymorphism analysis (SSCP) and dideoxy sequence analysis. Variants encoding amino acid substitutions were genotyped in 27 unrelated nondiabetic Mexican Americans and in all family members of subjects containing these variants, and association analyses were performed. To trace the ancestral origins of the variants, Iberian Caucasians and Pima Indians were also genotyped.

RESULTS

Eight single base changes were found: four silent polymorphisms and four missense mutations (Ala94Thr, Ala512Pro, Ser892Gly and Gly971Arg). Allele frequencies were 0.009, 0.017, 0.017 and 0.043, respectively. There were no significant associations of any of these variants with diabetes, glucose or insulin levels during an oral glucose tolerance test, or with body mass index (BMI) in Mexican American families except for a modest association between the Ala94Thr variant and decreased BMI (30.4 kg/m(2) vs 24.0 kg/m(2); p=0.035). None of these four missense mutations were detected in Pima Indians. In Iberian Caucasians, neither Ala94Thr nor Ser892Gly were detected, and Ala512Pro was detected in only 0/60 diabetic patients and 1/60 nondiabetic controls. Gly971Arg was relatively more common in Iberian Caucasians with 12/58 diabetic patients and 7/60 nondiabetic controls being heterozygous for this variant (p=0.21 for comparison between diabetic and nondiabetic subjects).

CONCLUSIONS

Ala94Thr, Ala512Pro and Ser892Gly mutation are rare in the populations studied. Gly971Arg, is more common in Mexican Americans and Caucasians, but is not a major contributor to genetic susceptibility to Type 2 diabetes.

Potential interactions of zinc in the neuroendocrine-endocrine disturbances of diabetes mellitus type 2

An accumulation of evidence implicates leptin, insulin, glucocorticoids, proopiomelanocortin (POMC), and neuropeptide Y (NPY) interactions as being integral to metabolic control associated with neuroendocrine-endocrine functioning. Dysfunction of neuroendocrine-endocrine interactions contributes to the metabolic disturbances of diabetes mellitus type 2 (DM-2). Since Zn has a direct impact on the healthy functioning of hormonal and neuropeptide balance, it is possible that altered Zn status and metabolism in DM-2 are involved in some of the metabolic dysfunctions of DM-2.Key words: zinc, insulin, leptin, neuropeptide Y, glucocorticoids, proopiomelanocortin (POMC), diabetes, obesity.

An autosomal genomic scan for loci linked to type II diabetes mellitus and body-mass index in Pima Indians

Genetic factors influence the development of type II diabetes mellitus, but genetic loci for the most common forms of diabetes have not been identified. A genomic scan was conducted to identify loci linked to diabetes and body-mass index (BMI) in Pima Indians, a Native American population with a high prevalence of type II diabetes. Among 264 nuclear families containing 966 siblings, 516 autosomal markers with a median distance between adjacent markers of 6.4 cM were genotyped. Variance-components methods were used to test for linkage with an age-adjusted diabetes score and with BMI. In multipoint analyses, the strongest evidence for linkage with age-adjusted diabetes (LOD = 1.7) was on chromosome 11q, in the region that was also linked most strongly with BMI (LOD = 3.6). Bivariate linkage analyses strongly rejected both the null hypothesis of no linkage with either trait and the null hypothesis of no contribution of the locus to the covariation among the two traits. Sib-pair analyses suggest additional potential diabetes-susceptibility loci on chromosomes 1q and 7q.

Evidence for defects in the trafficking and translocation of GLUT4 glucose transporters in skeletal muscle as a cause of human insulin resistance

Insulin resistance is instrumental in the pathogenesis of type 2 diabetes mellitus and the Insulin Resistance Syndrome. While insulin resistance involves decreased glucose transport activity in skeletal muscle, its molecular basis is unknown. Since muscle GLUT4 glucose transporter levels are normal in type 2 diabetes, we have tested the hypothesis that insulin resistance is due to impaired translocation of intracellular GLUT4 to sarcolemma. Both insulin-sensitive and insulin-resistant nondiabetic subgroups were studied, in addition to type 2 diabetic patients. Biopsies were obtained from basal and insulin-stimulated muscle, and membranes were subfractionated on discontinuous sucrose density gradients to equilibrium or under nonequilibrium conditions after a shortened centrifugation time. In equilibrium fractions from basal muscle, GLUT4 was decreased by 25-29% in both 25 and 28% sucrose density fractions and increased twofold in both the 32% sucrose fraction and bottom pellet in diabetics compared with insulin-sensitive controls, without any differences in membrane markers (phospholemman, phosphalamban, dihydropyridine-binding complex alpha-1 subunit). Thus, insulin resistance was associated with redistribution of GLUT4 to denser membrane vesicles. No effects of insulin stimulation on GLUT4 localization were observed. In non-equilibrium fractions, insulin led to small GLUT4 decrements in the 25 and 28% sucrose fractions and increased GLUT4 in the 32% sucrose fraction by 2.8-fold over basal in insulin-sensitive but only by 1.5-fold in both insulin-resistant and diabetic subgroups. The GLUT4 increments in the 32% sucrose fraction were correlated with maximal in vivo glucose disposal rates (r = +0.51, P = 0.026), and, therefore, represented GLUT4 recruitment to sarcolemma or a quantitative marker for this process. Similar to GLUT4, the insulin-regulated aminopeptidase (vp165) was redistributed to a dense membrane compartment and did not translocate in response to insulin in insulin-resistant subgroups. In conclusion, insulin alters the subcellular localization of GLUT4 vesicles in human muscle, and this effect is impaired equally in insulin-resistant subjects with and without diabetes. This translocation defect is associated with abnormal accumulation of GLUT4 in a dense membrane compartment demonstrable in basal muscle. We have previously observed a similar pattern of defects causing insulin resistance in human adipocytes. Based on these data, we propose that human insulin resistance involves a defect in GLUT4 traffic and targeting leading to accumulation in a dense membrane compartment from which insulin is unable to recruit GLUT4 to the cell surface.

Gene-environment interactions in the pathogenesis of type 2 diabetes mellitus: lessons learned from the Pima Indians

The comprehensive longitudinal studies of diabetes conducted in the Pima Indians of Arizona over the last 30 years indicate that both genetic and environmental factors play a critical role in the pathogenesis of the disease. Pre- and postnatal exposures as well as diet and physical activity in adulthood markedly affect risk of developing NIDDM in this population. In addition, the high prevalence of diabetes in the Pimas relative to other populations and the familiality of the disease and its precursors, strongly suggest a substantial genetic basis. Interactions between genes and the environment are obviously important in the pathogenesis of NIDDM, but it remains unclear exactly how these interactions occur and how to adequately account for these effects when searching for genes contributing to diabetes. The realization that gene-environment interactions are significant, and may be the dominant mechanism increasing susceptibility to NIDDM, should encourage further investigations. Future progress in studying the genetics of NIDDM and other complex diseases will come not only from technical advances currently in development, but also from advances in understanding the pathophysiology of the disease and the role of gene-environment interactions, and a renewed emphasis on careful clinical characterization of subjects participating in these studies.

An autosomal genomic scan for loci linked to prediabetic phenotypes in Pima Indians

Type 2 diabetes mellitus is a common chronic disease that is thought to have a substantial genetic basis. Identification of the genes responsible has been hampered by the complex nature of the syndrome. Abnormalities in insulin secretion and insulin action predict the development of type 2 diabetes and are, themselves, highly heritable traits. Since fewer genes may contribute to these precursors of type 2 diabetes than to the overall syndrome, such genes may be easier to identify. We, therefore, undertook an autosomal genomic scan to identify loci linked to prediabetic traits in Pima Indians, a population with a high prevalence of type 2 diabetes. 363 nondiabetic Pima Indians were genotyped at 516 polymorphic microsatellite markers on all 22 autosomes. Linkage analyses were performed using three methods (single-marker, nonparametric multipoint [MAPMAKER/SIBS], and variance components multipoint). These analyses provided evidence for linkage at several chromosomal regions, including 3q21-24 linked to fasting plasma insulin concentration and in vivo insulin action, 4p15-q12 linked to fasting plasma insulin concentration, 9q21 linked to 2-h insulin concentration during oral glucose tolerance testing, and 22q12-13 linked to fasting plasma glucose concentration. These results suggest loci that may harbor genes contributing to type 2 diabetes in Pima Indians. None of the linkages exceeded a LOD score of 3.6 (a 5% probability of occurring in a genome-wide scan). These findings must, therefore, be considered tentative until extended in this population or replicated in others.

The metabolic significance of leptin in humans: gender-based differences in relationship to adiposity, insulin sensitivity, and energy expenditure

Leptin is an adipocyte-derived hormone that interacts with a putative receptor(s) in the hypothalamus to regulate body weight. The relationship of leptin to metabolic abnormalities associated with obesity together with hormonal and substrate regulation of leptin have not been extensively studied. Therefore, 116 subjects (62 men and 54 women) with a wide range of body weight [body mass index (BMI), 17-54 kg/m2] were characterized on a metabolic ward with regard to body composition, glucose intolerance, insulin sensitivity, energy expenditure, substrate utilization, and blood pressure. Eighty-five of the subjects had normal glucose tolerance (50 men and 35 women), and 31 had noninsulin-dependent diabetes mellitus (12 men and 19 women). In both men and women, fasting leptin levels were highly correlated with BMI (r = 0.87 and r = 0.88, respectively) and percent body fat (r = 0.82 and r = 0.88, respectively; all P < 0.0001). However, men exhibited lower leptin levels at any given measure of obesity. Compared with those in men, leptin levels rose 3.4-fold more rapidly as a function of BMI in women [leptin = 1.815 (BMI)-31.103 in women; leptin = 0.534 (BMI)-8.437 in men] and 3.2 times more rapidly as a function of body fat [leptin = 1.293 (% body fat)-24.817 in women; leptin = 0.402 (% body fat)-3.087 in men]. Hyperleptinemia was associated with insulin resistance (r = -0.57; P < 0.0001) and high waist to hip ratio (r = 0.75; P < 0.0001) only in men. On the other hand, during the hyperinsulinemic euglycemic clamp studies, hyperinsulinemia acutely increased leptin concentrations (20%) only in women. There was no correlation noted between fasting leptin levels and either resting energy expenditure or insulin-induced thermogenesis in men or women (P = NS). In stepwise and multiple regression models with leptin as the dependent variable, noninsulin-dependent diabetes mellitus did not enter the equations at a statistically significant level. The data indicate that there are important gender-based differences in the regulation and action of leptin in humans. Serum leptin levels increase with progressive obesity in both men and women. However, for any given measure of obesity, leptin levels are higher in women than in men, consistent with a state of relative leptin resistance. These findings have important implications regarding differences in body composition in men and women. The observation that serum leptin is not related to energy expenditure rates suggests that leptin regulates body fat predominantly by altering eating behavior rather than calorigenesis.

Microsatellite hybrid capture technique for simultaneous isolation of various STR markers

The microsatellite hybrid capture technique was designed to enrich simultaneously for various microsatellite repeats from a genomic clone. It is illustrated in this report that different repeat motifs, including polymorphic ones, can be efficiently isolated in a single experiment. In principle, this technique can be applied to any type of genomic clones to facilitate the isolation of informative markers for fine mapping of subchromosomal regions of interest, and for linkage and association studies of candidate genes for which no polymorphic markers are available yet.

A novel (TA)n polymorphism in the hexokinase II gene: application to noninsulin-dependent diabetes mellitus in the Pima Indians

Hexokinase II, one member of a family of structurally similar enzymes that catalyze the phosphorylation of glucose in the 6-position, has been suggested to play a role in the pathophysiology of noninsulin-dependent diabetes mellitus (NIDDM). The gene for hexokinase II, HK2, has been previously mapped to human chromosome 2p13 by fluorescence in situ hybridization, and two-point linkage analysis has placed it near the locus for transforming growth factor alpha, TGFA. We now report the characterization of a (TA)n polymorphism in intron 12 of HK2. Using multipoint analysis of CEPH family genotypes, we have determined the most likely locus order to be cen-D2S169-[D2S286-HK2]-[D2S145-D2S291]-[+ ++D2S45-D2S101-TGFA]-tel. As HKII is a candidate gene that could contribute to the manifestation of insulin resistance and NIDDM, we genotyped 1152 Pima Indians, a Native American tribe that has the highest reported prevalence of NIDDM in the world. Although we did not detect any linkage or association of HK2 with insulin resistance or NIDDM in the Pima Indians, the polymorphism and detailed mapping of HK2 described in this report should prove useful in the assessment of the role of this gene in the predisposition to NIDDM in other populations.

Characterization of Japanese families with early-onset type 2 (non-insulin dependent) diabetes mellitus and screening for mutations in the glucokinase and mitochondrial tRNA(Leu(UUR)) genes

Genetic linkage studies of families with early-onset type 2 diabetes have facilitated the identification of diabetes-susceptibility genes. In order to assess the feasibility of using linkage approaches to identify genes responsible for the development of type 2 diabetes in Japanese subjects, we examined our clinical records for multigenerational families suitable for genetic studies. We identified 16 families in which at least one subject was diagnosed with type 2 diabetes before 25 years of age. Seven of these families had a pattern of inheritance consistent with a diagnosis of maturity-onset diabetes of the young (MODY) and nine families showed a complex pattern of inheritance of type 2 diabetes with transmission of diabetes-susceptibility genes from both parents. The glucokinase and mitochondrial tRNA(Leu(UUR)) genes were screened for mutations in at least one affected subject from each family in order to assess the contribution of mutations in these genes to the development of the diabetes. No mutations were found, which suggests that the diabetes in these families resulted from mutations in other genes.