Abdominal visceral fat is associated with a BclI restriction fragment length polymorphism at the glucocorticoid receptor gene locus

Glucocorticoid receptor variants: clinical implications

Following exposure to stress, cortisol is secreted from the adrenal cortex under the control of the hypothalamic-pituitary-adrenal axis (HPA-axis). Central in the regulation of the HPA-axis is a two tied corticosteroid-receptor system, comprised of high and low affinity receptors, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), respectively. In addition, these corticosteroid receptors mediate the effects of cortisol during stress on both central and peripheral targets. Cortisol modulates gene-expression of corticosteroid-responsive genes, with the effect lasting from hours to days. Mutations in the GR-gene are being associated with corticosteroid resistance and haematological malignancies, although these mutations are relatively rare and probably not a common cause of these diseases. However, several GR-gene variants and single nucleotide polymorphisms (SNP) in the GR-gene have been identified which are relatively common in the human population. The GRbeta-variant, for example, has been proposed to influence corticosteroid-sensitivity and most evidence has been derived from the immune system and in particular asthma. With respect to polymorphisms, a BclI restriction fragment polymorphism and a Asp363Ser have been described, which not only influence the regulation of the HPA-axis, but are also associated with changes in metabolism and cardiovascular control. These associations of a GR-gene polymorphism with metabolism and cardivascular control, and also with the regulation of the HPA-axis, indicates an important underlying role of cortisol in the etiology of these complex disorders. Therefore, we propose that a common underlying defect in these complex disorders is a disregulation of the HPA-axis, especially during stress. The clinical implication is that the regulation of the HPA-axis should be envisioned as a primary target of new drugs for the treatment of stress-related disorders.

A genomewide linkage scan for abdominal subcutaneous and visceral fat in black and white families: The HERITAGE Family Study

Abdominal visceral fat (AVF), abdominal subcutaneous fat (ASF), and abdominal total fat (ATF) were measured using a computed tomography scan, both before (baseline) and after (post) a 20-week endurance exercise training protocol in the HERITAGE Family Study. Each of the baseline and response (post minus baseline) measures was adjusted for several covariates, including total fat mass, and responses to training were further adjusted for baseline levels. Multipoint variance components linkage analysis using a genomewide scan of 344 markers was conducted separately by race using race-specific allele frequencies. Several promising results (P < 0.0023) were obtained. For baseline AVF, the best evidence was on 2q22.1 and 2q33.2-q36.3 (including the IRS1 locus) in whites, with suggestive findings on 7q22.2-q31.3 (including the LEP locus) in blacks. Although several regions were indicated for baseline ASF, only 4q31.22-q32.2 and 11p15.4-p11.2 replicated the results of another study. For responses to training, promising results were limited to ASF and ATF primarily on 7q36.2 (including NOS3) in blacks, with suggestive regions (P < 0.01) on 1q21.2-q24.1 (S100A, ATP1A2, and ATP1B1), 10q25.2 (ADRA2A), and 11p15.5 (IGF2). In summary, the 4q and 11p regions have now been implicated in two independent studies for ASF; further research is warranted to identify the genes and mutations in these regions that are responsible for fat accumulation in the abdominal depot. Additional work in an independent sample is needed to verify the linkages for baseline AVF as well as the response measures.

The human obesity gene map: the 2001 update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

Central and peripheral glucocorticoid receptor function in abdominal obesity

Abdominal obesity seems to be associated with a moderately deranged feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis where central glucocorticoid receptors (GR) are involved. Therefore, functions of central and peripheral GR were compared in this study. Furthermore, since trinucleotide repeats in early exons of steroid hormone receptor genes influence transcription, and therefore may influence receptor density, this was also studied. Ten middle-aged men, 5 with abdominal obesity and 5 controls, were studied. The suppression of dexamethasone (dex) on serum cortisol was used in dose-response tests to assess the function of central GR. Abdominal adipose tissue biopsies were incubated and exposed to cortisol in different concentrations, and the function of the peripheral GR assayed as induction of lipoprotein lipase (LPL) activity. Aberrant expansion of exonic trinucleotide repeats in the first coding exon of the GR gene was studied by sequencing of genomic DNA. Results showed that men with abdominal obesity showed less inhibition of serum cortisol by dex, particularly at lower concentrations, while in the controls cortisol secretion was inhibited in an apparent dose-response manner. LPL activity in adipose tissue was lower in abdominal obese men than in controls. However, the sensitivity to cortisol was not different between the groups. There was no evidence for expansion of trinucleotide repeats. These results suggest that the central GR and the peripheral GR in adipose tissue exhibit functional differences in abdominal obesity.

Gly40Ser polymorphism of the glucagon receptor gene is associated with central adiposity in men

OBJECTIVE

To study the association between the Gly40Ser polymorphism of the glucagon receptor gene (GCG-R) and central adiposity.

RESEARCH METHODS AND PROCEDURES

Data from 985 working men (The Olivetti Heart Study) examined in 1994 were used in a cross-sectional design. A complete anthropometry was performed; body mass index and waist circumference were taken as measures of total and central adiposity, respectively. The GCG-R Gly40Ser polymorphism was characterized. Biochemical variables linked to energy metabolism were measured.

RESULTS

The GCG-R Gly40Ser variant was present in 37 individuals only in heterozygous form and was significantly associated with anthropometric indices of central adiposity, accounting for age and body mass (odds ratio for waist circumference > 94 cm; 95% confidence interval: 3.14, 1.26 to 7.81), whereas no difference between the two groups was found with regard to biochemical indices of insulin resistance or plasma leptin levels.

DISCUSSION

The Gly40Ser polymorphism of the GCG-R gene is associated with central adiposity independently from total body mass in men.

Genetics of abdominal visceral fat levels

The purpose of this review is to explore the evidence accumulated thus far that suggests a genetic component to the observed variation in abdominal visceral fat (AVF) levels. The precise determination of AVF levels in humans is limited to methods such as computerized tomography and magnetic resonance imaging; thus, few studies have examined the role of genetic factors on this phenotype. Evidence from the Québec Family Study (QFS) and the HERITAGE Family Study indicates that between 50-55% of the variance in AVF levels, adjusted for total fatness, is attributable to genetic factors. Additionally, a major gene hypothesis for AVF was supported in the both the QFS and HERITAGE Family Study. However, after adjustment for total fat mass the support for a major gene was reduced, suggesting that a major gene which affects fat mass may also affect AVF either directly (pleiotropy), or indirectly. The search for candidate genes that may impact AVF levels is in its infancy, and few candidate genes have been identified. However, the glucocorticoid receptor (GRL), ss3 adrenergic receptor (ADRB3), and fatty acid binding protein 2 (FABP2) genes have been significantly associated with AVF or intra-abdominal fat levels in humans. In addition, three quantitative trait loci obtained from crosses of mice, the Do2, Mob4, and Qbw1 loci have been linked with mesenteric or abdominal fat and are thus considered positional candidate genes for AVF levels. The search for candidate genes or random genetic markers associated with AVF levels is a challenging prospect. However, given the significant heritability of this phenotype, the quest remains promising. Am. J. Hum. Biol. 11:225-235, 1999. Copyright 1999 Wiley-Liss, Inc.

Interactions among the glucocorticoid receptor, lipoprotein lipase and adrenergic receptor genes and abdominal fat in the Québec Family Study

OBJECTIVE

To investigate whether interactions between glucocorticoid receptor (GRL), lipoprotein lipase (LPL) and adrenergic receptor (ADR) gene markers contribute to individual differences in indicators of adiposity and abdominal obesity, including visceral fat level.

DESIGN AND SUBJECTS

Cross-sectional study; 742 individuals from the phase 2 of the Québec Family Study cohort.

MEASUREMENTS

Total body fat assessed by hydrodensitometry and the sum of six skinfolds. Abdominal fat areas measured by computed tomography and adjusted for age, sex and total fat mass in all analyses. GRL Bcl I, alpha 2A-ADR Dra I and beta 2-ADR Ban I markers were typed by Southern blot, and other markers by polymerase chain reaction technique.

RESULTS

It is confirmed that the 4.5 kb allele of the GRL BclI polymorphism is associated with a higher amount of abdominal visceral fat (AVF) depot (P for trend<0.001) independent of the level of total body fat. Furthermore, the alpha 2-ADR Dra I variant is associated with lower cross-sectional areas of abdominal total (P=0.003) and subcutaneous (P=0.012) adipose tissue. Gene-gene interactions between GRL and alpha 2-ADR genes affecting overall adiposity (P=0.016) as well as between GRL and beta 2-ADR genes (P=0.049) having influence on total abdominal fat levels were observed. When the three genes were considered together in the same analysis, significant interactions having influence on overall adiposity (P=0.017), abdominal total (P=0.032) and visceral fat (P=0.002) were observed. About 1-2% of the total variation in total fatness and abdominal fat was explained by these gene-gene interactions.

CONCLUSION

There is an association between the GRL BclI polymorphism and increased AVF levels independent of the level of total body fat. The alpha 2-ADR DraI variant is associated with a lower cross-sectional area of abdominal total fat. Numerous interactions between GRL and ADR markers on overall adiposity and total abdominal fat as well as between GRL, LPL and ADR genes on overall adiposity, abdominal total and visceral fat suggest that the genetic architecture of body fat content and adipose tissue distribution is complex although some genes, like GRL, may have ubiquitous effects.

Association of estrogen receptor and glucocorticoid receptor gene polymorphisms with sporadic breast cancer

We have utilized a cross-sectional association approach to investigate sporadic breast cancer. Polymorphisms in 2 candidate genes, ESRalpha and GRL, were examined in an unrelated breast cancer-affected and age-matched control population. Several polymorphic regions within the ESRalpha gene have been identified, and some alleles of these polymorphisms have been found to occur at increased levels in breast-cancer patients. Additionally, variations in GRL have the potential to disrupt cell transcription and may be associated with cancer formation. We analyzed 3 polymorphisms, from codons 10 (TCT to TCC), 325 (CCC to CCG) and 594 (ACA to ACG) of ESRalpha, and a highly polymorphic dinucleotide repeat, D5S207, located within 200 kb of the GRL. When allelic frequencies of the codon 594 (exon 8) ESR polymorphism were compared between affected and unaffected populations, a significant difference was observed (p = 0.005). Results from the D5S207 dinucleotide repeat located near GRL also indicated a significant difference between the tested case and control populations (p = 0.001). Allelic frequencies of the codon 10 and codon 325 ESR polymorphisms were not significantly different between populations (p = 0.152 and 0.181, respectively). Our results indicate that specific alleles of the ESR gene (alpha subtype) and a marker for the GRL gene locus are associated with sporadic breast-cancer development in the tested Caucasian population and justify further investigation of the role of these and other nuclear steroid receptors in the etiology of breast cancer.

The N363S polymorphism of the glucocorticoid receptor: potential contribution to central obesity in men and lack of association with other risk factors for coronary heart disease and diabetes mellitus

Considerable evidence suggests that diabetes mellitus and hypertension are influenced by genetic factors. Studies in humans have associated glucocorticoid receptor (GR) polymorphisms with high blood pressure, insulin sensitivity, body mass index, increased visceral fat, and variations in tissue-specific steroid sensitivity. The N363S polymorphism of the GR results in an asparagine to serine amino acid substitution in a modulatory region of the receptor. Phosphorylation of serine residues in this region has been shown to enhance transactivation of GR responsive genes. The aim of this study was to investigate the association between the 363S allele and risk factors for coronary heart disease and diabetes mellitus in a population of European origin living in the northeast of the United KINGDOM: Blood samples from 135 males and 240 females were characterized for 363 allele status. The overall frequency of the 363S allele was 3.0%, 23 heterozygotes (7 males and 16 females) but no 363S homozygotes were identified. The data show a significant association of the 363S allele with increased waist to hip ratio in males but not females. This allele was not associated with blood pressure, body mass index, serum cholesterol, triglycerides, low-density lipoprotein and high-density lipoprotein cholesterol levels, and glucose tolerance status. The results of this study suggest that this GR polymorphism may contribute to central obesity in men. Further studies are required to elucidate the properties of GR(363S) at a molecular level.

Do stress reactions cause abdominal obesity and comorbidities?

'Stress' embraces the reaction to a multitude of poorly defined factors that disturb homeostasis or allostasis. In this overview, the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system have been utilized as objective measurements of stress reactions. Although long-term activation of the sympathetic nervous system is followed by primary hypertension, consequences of similar activation of the HPA axis have not been clearly defined. The focus of this overview is to examine whether or not repeated activation of these two stress centres may be involved in the pathogenesis of abdominal obesity and its comorbidities. In population studies adrenal hormones show strong statistical associations to centralization of body fat as well as to obesity. There is considerable evidence from clinical to cellular and molecular studies that elevated cortisol, particularly when combined with secondary inhibition of sex steroids and growth hormone secretions, is causing accumulation of fat in visceral adipose tissues as well as metabolic abnormalities (The Metabolic Syndrome). Hypertension is probably due to a parallel activation of the central sympathetic nervous system. Depression and 'the small baby syndrome' as well as stress exposure in men and non-human primates are followed with time by similar central and peripheral abnormalities. Glucocorticoid exposure is also followed by increased food intake and 'leptin resistant' obesity, perhaps disrupting the balance between leptin and neuropeptide Y to the advantage of the latter. The consequence might be 'stress-eating', which, however, is a poorly defined entity. Factors activating the stress centres in humans include psychosocial and socioeconomic handicaps, depressive and anxiety traits, alcohol and smoking, with some differences in profile between personalities and genders. Polymorphisms have been defined in several genes associated with the cascade of events along the stress axes. Based on this evidence it is suggested that environmental, perinatal and genetic factors induce neuroendocrine perturbations followed by abdominal obesity with its associated comorbidities.

Evidence for a major gene influence on abdominal fat distribution: the Minnesota Breast Cancer Family Study

Abdominal fat has been shown to be an important risk factor for many chronic conditions, including diabetes, heart disease, and breast cancer. The objective of this study was to provide evidence for a major gene influence on the ratio of waist to hip circumference (WHR), a measurement commonly used in large scale studies to indicate the presence of abdominal fat. Segregation analysis was conducted on three subsets of families from the Minnesota Breast Cancer Family Study. One analysis was conducted among families with WHR measurements on all women. Two additional analyses were conducted on subsets of women stratified on menopausal status. Multiple regression analysis was used to identify factors associated with WHR expressed as a continuous trait. Complex segregation analyses were performed on the continuous trait of WHR and the covariates identified in the regression analysis. In the analysis of all women, all hypotheses were rejected. Among premenopausal women, the environmental hypothesis with no heterogeneity between generations fit the data best (P = 0.85). However, among postmenopausal women, the requirements for conclusion of the presence of a major gene were met. All non-Mendelian hypotheses were rejected (P < 0.0001), but the additive hypothesis was not rejected (P = 0.19) and provided the best fit to the data. The putative major gene identified by this model accounted for 42% of total phenotypic variance in WHR among these postmenopausal women. The allele for high WHR had a frequency of 27%. These findings support the hypothesis that the distribution of abdominal fat in postmenopausal women is under genetic control.

A genome-wide scan for abdominal fat assessed by computed tomography in the Québec Family Study

To identify chromosomal regions harboring genes influencing the propensity to store fat in the abdominal area, a genome-wide scan for abdominal fat was performed in the Quebec Family Study. Cross-sectional areas of the amount of abdominal total fat (ATF) and abdominal visceral fat (AVF) were assessed from a computed tomography scan taken at L4-L5 in 521 adult subjects. Abdominal subcutaneous fat (ASF) was obtained by computing the difference between ATF and AVF. The abdominal fat phenotypes were adjusted for age and sex effects as well as for total amount of body fat (kilogram of fat mass) measured by underwater weighing, and the adjusted phenotypes were used in linkage analyses. A total of 293 microsatellite markers spanning the 22 autosomal chromosomes were typed. The average intermarker distance was 11.9 cM. A maximum of 271 sib-pairs were available for single-point (SIBPAL) and 156 families for multipoint variance components (SEGPATH) linkage analyses. The strongest evidence of linkage was found on chromosome 12q24.3 between marker D12S2078 and ASF (logarithm of odds [LOD] = 2.88). Another marker (D12S1045) located within 2 cM of D12S2078 also provided evidence of sib-pair linkage with ASF (P = 0.019), ATF (P = 0.015), and AVF (P = 0.0007). Other regions with highly suggestive evidence (P < 0.0023 or LOD > or =1.75) of multipoint linkage and evidence (P < 0.05) of single-point linkage, all for ASF, included chromosomes 1p11.2, 4q32.1, 9q22.1, 12q22-q23, and 17q21.1. Three of these loci (1p11.2, 9q22.1, and 17q21.1) are close to genes involved in the regulation of sex steroid levels, whereas two others (4q32.1 and 17q21.1) are in the proximity of genes involved in the regulation of food intake. This first genome-wide scan for abdominal fat assessed by computed tomography indicates that there may be several loci determining the propensity to store fat in the abdominal depot and that some of these loci may influence the development of diabetes in obese subjects.

Clustering of metabolic abnormalities in obese individuals: the role of genetic factors

The objective of this paper is to review the current evidence in support of genetic factors underlying the clustering of components of the metabolic syndrome in obese individuals. It has become clear that individual features of the metabolic syndrome are partially determined by familial factors some of which are unique to a given component and others that are shared among several features. A few candidate genes, encoding proteins of glucose, insulin and lipid metabolism, lipolytic cascade, fatty acid intestinal absorption, glucocorticoid metabolism, haemostasis and blood pressure, have been associated with a clustering of metabolic abnormalities, although the functional significance of these associations remains to be established. Furthermore, genetic polymorphisms, such as those detected at several lipoprotein metabolism loci, can modulate the relationships between different components of the metabolic syndrome. An overfeeding study conducted on identical twins has demonstrated that genetic factors play an important role in the responsiveness to changing energy balance conditions. Leptin receptor, beta2 adrenergic receptor and glucocorticoid receptor gene polymorphisms have been associated with an augmented clustering of metabolic abnormalities in response to overfeeding. Gene-gene interaction effects between markers of the alpha2A, beta2 and beta3 adrenergic receptor genes on components of the metabolic syndrome have been described. Genetic factors also seem to modify the responsiveness of metabolic syndrome features to endurance training. A growing understanding of the genetic architecture of the metabolic syndrome may help in the prevention of this condition. The reduction of excess body fat, the most common clinical feature among the cluster of metabolic abnormalities, should be the focus of the prevention and treatment of the metabolic syndrome.

The human obesity gene map: the 2000 update

This report constitutes the seventh update of the human obesity gene map incorporating published results up to the end of October 2000. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci uncovered in human genome-wide scans and in cross-breeding experiments in various animal models, and association and linkage studies with candidate genes and other markers are reviewed. Forty-seven human cases of obesity caused by single-gene mutations in six different genes have been reported in the literature to date. Twenty-four Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different quantitative trait loci reported from animal models currently reaches 115. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 130 studies reporting positive associations with 48 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

Programming other hormones that affect insulin

The metabolic syndrome is associated with a marked increase in risk of type 2 diabetes and atherosclerotic vascular disease (AVD). The mechanism responsible for the metabolic syndrome is uncertain, but recent evidence suggests that a combination of low birth weight and adult obesity is associated with a markedly increased prevalence. Insulin resistance is the cardinal feature of the metabolic syndrome. Several hormones, have modes of action that either potentiate or reduce the biological actions of insulin and, therefore, attenuate or induce insulin resistance. Since insulin action may be modified, these hormones potentially contribute to the pathogenesis of the metabolic syndrome. The purpose of this review is to discuss programming of hormones that modulate insulin action. The review focuses on two major endocrine pathways: (i) glucocorticoid hormone action; and (ii) the growth hormone (GH)-insulin-like growth factor (IGF-1) axis, and discusses mechanisms linking abnormal activity of these pathways with reduced early growth, adult obesity and the metabolic syndrome.

Subcutaneous and visceral adipose tissue: their relation to the metabolic syndrome

Methods for assessment, e.g., anthropometric indicators and imaging techniques, of several phenotypes of human obesity, with special reference to abdominal fat content, have been evaluated. The correlation of fat distribution with age, gender, total body fat, energy balance, adipose tissue lipoprotein lipase and lipolytic activity, adipose tissue receptors, and genetic characteristics are discussed. Several secreted or expressed factors in the adipocyte are evaluated in the context of fat tissue localization. The body fat distribution and the metabolic profile in nonobese and obese individuals is discussed relative to lipolysis, antilypolysis and lipogenesis, insulin sensitivity, and glucose, lipid, and protein metabolism. Finally, the endocrine regulation of abdominal visceral fat in comparison with the adipose tissue localized in other areas is presented.

Obesity and cortisol

Cortisol in obesity is a much-studied problem. Previous information indicates that cortisol secretion is elevated but that circulatory concentrations are normal or low, suggesting that peripheral disappearance rate is elevated. These studies have usually not taken into account the difference between central and peripheral types of obesity. Recent studies using saliva cortisol have indicated that the problem is complex with both high and low secretion of cortisol, perhaps depending on the status of the function of the hypothalamic-pituitary-adrenal gland axis. A significant background factor seems to be environmental stress. The results also suggest that the pattern of cortisol secretion may be important. Other neuroendocrine pathways are also involved, including the central sympathetic nervous system, the gonadal and growth hormone axes, and the leptin system. In concert, these abnormalities seem to be responsible for the abnormal metabolism often seen in central obesity. Several associated polymorphisms of candidate genes may provide a genetic background. Cortisol conversion to inactive metabolites may be a factor increasing central signals to secretion and may add to the increased secretion of cortisol induced by centrally acting factors. Perinatal factors have been found to be involved in the pathogenesis of obesity and its complications. The mechanism involved is not known, but available information suggests that programming of the hypothalamic-pituitary-adrenal axis may be responsible.

Genetic factors, perceived chronic stress, and the free cortisol response to awakening

Recent studies have demonstrated that the free cortisol response to awakening can serve as a useful index of hypothalamus-pituitary-adrenal axis (HPA) activity. This endocrine marker is rather consistent, shows good intraindividual stability across time and appears to be able to uncover subtle changes in HPA regulation. The present twin study investigated genetic factors as sources of the interindividual variation of the cortisol awakening response. Furthermore, the relationship between psychological variables and morning cortisol levels was studied. On two consecutive days saliva samples were collected 0, 30, 45 and 60 minutes after awakening in 52 monozygotic and 52 dizygotic twin pairs. Moreover, samples were obtained at 0800, 1100, 1500 and 2000 h. ('short day-time profile'). Additionally, the participants filled out questionnaires assessing chronic stress load, self-esteem and self-efficacy.Heritability estimates of h(2)=0.40 for the mean increase and of h(2)=0.48 for the area under the response curve indicate a significant impact of genetic factors on cortisol levels after awakening. However, no genetic influence on the short day-time profile could be observed. Furthermore, several aspects of perceived chronic stress, namely 'worries', 'social stress' and 'lack of social recognition' were significantly associated with the awakening cortisol response. The evidence for a medium-sized, yet distinct genetic influence on cortisol levels after awakening is discussed with regard to a potential clinical relevance of genetic determinants of HPA (re)activity. In line with several recent studies, the present findings further support the view that the cortisol awakening responses is consistently enhanced under chronic stress conditions.

A glucocorticoid receptor gene marker is associated with abdominal obesity, leptin, and dysregulation of the hypothalamic-pituitary-adrenal axis

OBJECTIVE

Abdominal obesity has a key role in the pathogenesis of prevalent and serious diseases and has been shown to be associated with an altered hypothalamic-pituitary-adrenal (HPA) axis function, which is regulated by endocrine feedback mediated via hippocampal glucocorticoid receptors (GR).

RESEARCH METHODS AND PROCEDURES

We examined the HPA axis function by repeated salivary samples for the assessment of cortisol, as well as other endocrine, anthropometric, metabolic, and circulatory variables in middle-aged Swedish men (n = 284). With the restriction enzyme BclI, variants of the GR gene (GRL) locus were identified and two alleles with fragment lengths of 4.5 and 2.3 kilobases (kb) were detected.

RESULTS

The observed frequencies were 40.1% for the 2.3- and 2.3-kb, 46.2% for the 4.5- and 2.3-kb, and 13.7% for the 4.5- and 4.5-kb genotypes. The larger allele (4.5 and 4.5 kb) was associated with elevated body mass index (BMI; p < 0.001), waist-to-hip circumference ratio (p = 0.015), abdominal sagittal diameter (p = 0.002), leptin (p < 0.001), and systolic blood pressure (borderline, p = 0.058). The 4.5- and 4.5-kb allele was associated with leptin after adjustment for BMI. Moreover, salivary cortisol values, particularly after stimulation by a standardized lunch (p = 0.040 to 0.086), were elevated in the men with the larger allele.

DISCUSSION

These results indicate that there is an association between a deficient GR function, defined as a poor feedback regulation of the HPA axis activity, and a polymorphic restriction site at the GR gene locus. An abnormal control of HPA axis function due to genetic alterations may contribute to the pathogenesis of abdominal obesity.

The metabolic syndrome--a neuroendocrine disorder?

Central obesity is a powerful predictor for disease. By utilizing salivary cortisol measurements throughout the day, it has now been possible to show on a population basis that perceived stress-related cortisol secretion frequently is elevated in this condition. This is followed by insulin resistance, central accumulation of body fat, dyslipidaemia and hypertension (the metabolic syndrome). Socio-economic and psychosocial handicaps are probably central inducers of hyperactivity of the hypothalamic-pituitary adrenal (HPA) axis. Alcohol, smoking and traits of psychiatric disease are also involved. In a minor part of the population a dysregulated, depressed function of the HPA axis is present, associated with low secretion of sex steroid and growth hormones, and increased activity of the sympathetic nervous system. This condition is followed by consistent abnormalities indicating the metabolic syndrome. Such 'burned-out' function of the HPA axis has previously been seen in subjects exposed to environmental stress of long duration. The feedback control of the HPA axis by central glucocorticoid receptors (GR) seems inefficient, associated with a polymorphism in the 5' end of the GR gene locus. Homozygotes constitute about 14% of Swedish men (women to be examined). Such men have a poorly controlled cortisol secretion, abdominal obesity, insulin resistance and hypertension. Furthermore, polymorphisms have been identified in the regulatory domain of the GR gene that are associated with elevated cortisol secretion; polymorphisms in dopamine and leptin receptor genes are associated with sympathetic nervous system activity, with elevated and low blood pressure, respectively. These results suggest a complex neuroendocrine background to the metabolic syndrome, where the kinetics of the regulation of the HPA axis play a central role.

The human obesity gene map: the 1999 update

This report constitutes the sixth update of the human obesity gene map incorporating published results up to the end of October 1999. Evidence from the rodent and human obesity cases caused by single gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTL) uncovered in human genome-wide scans and in crossbreeding experiments with mouse, rat, pig and chicken models, association and linkage studies with candidate genes and other markers is reviewed. Twenty-five human cases of obesity can now be explained by variation in five genes. Twenty Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models reaches now 98. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 89 reports of positive associations pertaining to 40 candidate genes. Finally, 44 loci have linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all autosomes, with chromosomes 14 and 21 showing each one locus only. The number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes continues to increase and is now well above 200.

Association and linkage analyses of glucocorticoid receptor gene markers in essential hypertension

Suggestive evidence has been obtained in a "4-corners" study for involvement of the glucocorticoid receptor gene (GRL) in genetic variation in blood pressure. Therefore, we tested markers at the GRL locus for association and linkage with essential hypertension (HT). For the association study, we used a well-characterized group of 129 white Australians of Anglo-Celtic extraction who had HT, a strong family history of HT (2 parents with the disease), and early-onset moderate-to-severe disease. Controls were 195 normotensive white subjects whose parents were normotensive past the age of 50 years. For the linkage study, we used 175 sibling pairs of similar ancestry. The case-control groups were genotyped for an Asn363Ser variant in exon 2, a G/T variant in intron 4, and a microsatellite marker (D5S207) tightly linked (<200 kb) to GRL. For the groups as a whole, no association or linkage was observed after analysis of data by a variety of statistical tests. Analysis of sibling-pair data gave an exclusion score of -3.8 for the logarithm of the odds for linkage, indicating significant nonlinkage. However, in females, weak association of the intron 4 polymorphism with HT (P=0.03), as well as with systolic and diastolic blood pressure in all subjects (P=0. 04 and 0.03), was observed, and in the case of the D5S207 marker, association with HT was apparent in males (P=0.0001). Thus, although our results provide no overall support for GRL in HT etiology, apparent gender-specific associations could exist in this genomic region, possibly reflecting correlated occurrence with (an)other metabolic syndrome disorder(s).

Hypothalamic origin of the metabolic syndrome X

The conspicuous similarities between Cushing's syndrome and the Metabolic Syndrome X open up the possibility that hypercortisolemia is involved also in the latter. Salivary cortisol is possible to measure during undisturbed conditions including perceived stressful events during everyday life. Such measurements clearly show that normally regulated cortisol secretion is associated with excellent health in anthropometric, metabolic, and hemodynamic variables. Upon perceived stress cortisol secretion is increased and followed by the Metabolic Syndrome X (insulin resistance, abdominal obesity, elevated lipids, and blood pressure). In a minor part of the population a defect, "burned-out" cortisol secretion, occurs with decreased sex steroid and growth hormone secretions, and strong, consistent associations with the Metabolic Syndrome X. Psychosocial and socioeconomic handicaps with tendencies to abuse and depressive-anxious mood changes are consistently associated. The feedback control of cortisol secretion by central glucocorticoid receptors (GR) is blunted, and the function of the GR is abnormal. This corresponds to a polymorphism early in the GR gene locus, which is also associated with abdominal obesity and insulin resistance and is found in 14% of the Swedish male population. We suggest that the Metabolic Syndrome X is due to a discretely elevated cortisol secretion, discoverable during reactions to perceived stress in everyday life. This is based on environmental factors and expressed with different impact depending on genetic susceptibility.

Neuroendocrine perturbations as a cause of insulin resistance

Insulin resistance is followed by several prevalent diseases. The most common condition with insulin resistance is obesity, particularly when localized to abdominal, visceral regions. A summary of recent reviews on the pathogenesis of systemic insulin resistance indicates that major factors are decreased insulin effects on muscular glycogen synthase or preceding steps in the insulin signalling cascade, on endogenous glucose production and on circulating free fatty acids (FFA) from adipose tissue lipolysis. Contributions of morphologic changes in muscle and other factors are considered more uncertain. Newly developed methodology has made it possible to determine more precisely the neuroendocrine abnormalities in abdominal obesity including increased cortisol and adrenal androgen secretions. This is probably due to a hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, amplified by inefficient feedback inhibition by central glucocorticoid receptors, associated with molecular genetic defects. Secondly, secretion of gender-specific sex steroid hormones becomes inhibited and the sympathetic nervous system activated. At this stage the HPA axis shows signs of a 'burned-out' condition, and cortisol secretion is no longer elevated. Cortisol counteracts the insulin activation of glycogen synthase in muscle, the insulin inhibition of hepatic glucose production and the insulin inhibition of lipolysis in adipose tissue, leading to the well-established systemic insulin resistance caused by excess cortisol. This is exaggerated by increased free fatty acid mobilization, particularly with a concomitant elevation of the activity of the sympathetic nervous system. Furthermore, capillarization and fiber composition in muscle are changed. These are the identical perturbations responsible for insulin resistance in recent reviews. The diminished sex steroid secretion in abdominal obesity has the same consequences. It is thus clear that insulin resistance may be induced by neuroendocrine abnormalities, such as those seen in abdominal obesity. These endocrine perturbations also direct excess fat to visceral fat depots via mechanisms that are largely known, indicating why abdominal obesity is commonly associated with insulin resistance. This possible background to the most prevalent condition of insulin resistance has been revealed by development of methodology that allows sufficiently sensitive measurements of HPA axis activity. These findings demonstrate the power of neuroendocrine regulations for somatic health.

Total body fat and abdominal visceral fat response to exercise training in the HERITAGE Family Study: evidence for major locus but no multifactorial effects

The familial etiology of the response in total fat mass (FM) and abdominal visceral fat (AVF) to 20 weeks of exercise training was investigated in families participating in the HERITAGE Family Study. AVF (measured by computed tomographic scanning) and FM (measured by underwater weighing techniques) were assessed at baseline (in a sedentary state) and after 20 weeks of exercise training. The response AVF (AVFdelta) and response FM (FMdelta) were computed as the simple delta values (posttraining - baseline) and adjusted for the effects of sex, generation, and a polynomial in age using multiple regression analysis. To index the AVF response independently of the response in FM and the initial level of visceral fat, the AVFdelta was also adjusted for age and baseline AVF (AVFB) and FMdelta. Familial correlation analysis was used to investigate the multifactorial familial effects (polygenic and/or familial environmental), and segregation analysis was used to search for major gene effects. For the age-adjusted AVFdelta, a putative recessive locus accounting for 18% of the variance (q2 = 1%) was detected. Adjusting AVFdelta for AVFB and FMdelta slightly increased the percentage of variance accounted for (to 26%, q2 = 3%) but did not radically alter the pattern of the parameter estimates. For FMdelta, a putative dominant locus accounting for 31% of the variance (q2 = 49%) was noted. In conclusion, the results were consistent across methods in suggesting that there is little evidence of a multifactorial heritability for either AVFdelta or FMdelta. Rather, the familial etiology of the response to exercise training appears to be primarily due to putative major genes (a recessive locus for AVFdelta and a dominant locus for FMdelta). In addition, a pleiotropic/oligogenic system underlying these variables was inferred. That is, the putative loci for FMdelta and/or AVFB also may impact the AVFdelta, with an additional independent major locus effect on AVFdelta after the former influences have been removed.

Abdominal obesity increases overnight cortisol excretion

Although plasma and 24 h urinary free cortisol (UFC) levels are normal in obese subjects, pharmacological investigations have identified minor hypothalamo-pituitary-adrenal axis differences in patients with abdominal body fat distribution (A-BFD) vs peripheral BFD (P-BFD). Using recent tools such as saliva cortisol or overnight urinary free cortisol upon creatinine ratio (UFC/UC) determinations, we have investigated a population of obese females according to their body fat distribution. In-patients subjects (no.=82) were subjected to routine biochemical testing, 24 h and overnight UFC/UC, basal and post-1 mg overnight dexamethasone-suppressing test plasma and saliva cortisol determinations. Central obesity defined by a waist-to-hip ratio (WHR) >0.85 was found in 64% of the subjects vs 87% when defined by waist girth (WG) corrected for age. Despite identical body mass index, A-BFD subjects were more prone to hypertension using both classifications and had higher triglycerides (WHR classification) or higher triglycerides, cholesterol and glycemia (WG classification). Plasma cortisol levels were similar but saliva cortisol levels were lower in the A-BFD group using the WG classification. The 24 h UFC/UC were similar but the overnight UFC/UC were higher in the A-BFD group using the WHR classification. These mild differences in cortisol nocturnal secretion and free cortisol indexes in subjects with different body fat mass distribution suggest that their hypothalamo-pituitary-adrenal axis has a spontaneously subtly different regulation.

Hypothalamic arousal, insulin resistance and Type 2 diabetes mellitus

AIMS

Type 2 diabetes mellitus (DM) develops when insulin resistance overcomes the capacity of compensatory insulin secretion. Insulin resistance may be induced via psychoneuroendocrine pathways, a possibility which has received little previous attention.

METHODS

We have used salivary cortisol measurements to monitor the activity of the hypothalamic-pituitary-adrenal (HPA) axis, the major controller of hormones involved in the regulation of peripheral insulin sensitivity under everyday conditions. The influence of external challenges, as well as the sensitivity of feedback regulation, were followed in randomly selected middle-aged population samples.

RESULTS

In health there is a rhythmicity of cortisol secretion, with a high plasticity and efficient feedback control. In contrast, a group of subjects were identified with a flat, rigid day curve and poor feedback control, who showed consistent abnormalities in stress-related cortisol secretion, including inhibited secretions of sex steroids and growth hormone; insulin resistance; abdominal obesity; elevated leptin levels; hyperglycaemia; dyslipidaemia and hypertension with elevated heart rate. The endocrine abnormalities are probably responsible for the anthropometric and metabolic abnormalities. The circulatory perturbations seem to be induced by a parallel activation of the central sympathetic nervous system suggesting an 'hypothalamic arousal syndrome', gradually developing into an independent risk for disease. An associated cluster of environmental factors, including psychosocial and socio-economic stress, traits of depression and anxiety, alcohol consumption and smoking, all factors known to activate hypothalamic centres, has been identified. A polymorphism of the glucocorticoid receptor gene, with 13.7% homozygotes in the male Swedish population, parallels receptor dysfunction, and may be responsible for the associated insulin resistance, central obesity and hypertension.

CONCLUSIONS

This is the first detailed examination of psychoneuroendocrinological processes in the natural environment on a population basis in relation to somatic health. The results suggest that an hypothalamic arousal syndrome, with parallel activation of the HPA axis and the central sympathetic nervous system, is responsible for development of endocrine abnormalities, insulin resistance, central obesity, dyslipidaemia and hypertension, leading to frank disease, including Type 2 DM. We suggest that this syndrome is probably based on environmental pressures in genetically susceptible individuals.

Linkage analysis of glucocorticoid and beta2-adrenergic receptor genes with blood pressure and body mass index

Glucocorticoids and catecholamines exert important effects on cardiovascular physiology and metabolism. Variants of the glucocorticoid receptor gene (GRL) and the beta2-adrenergic receptor gene (ADRB2) have been associated with high blood pressure and obesity. These genes are close on human chromosome 5q31-5q32, and we undertook a linkage analysis of this region in 264 families from the general population in relation to systolic and diastolic blood pressure, body mass index, weight, height, and pulse rate. All family members were genotyped at four microsatellite loci (D5S207, D5S210, D5S519, and D5S119) located on chromosome 5q31-5q33.3. Using quantitative identity-by-descent sibling pair linkage analysis, we found that at no loci was genetic similarity associated with phenotypic similarity for systolic and diastolic blood pressure, body mass index, weight, height, or pulse rate. Although it is not possible to exclude the influence of specific combinations of certain GRL and ADRB2 polymorphisms, the absence of significant linkage in our population argues against a role for GRL or ADRB2 in physiological variation of blood pressure and body mass index.

The Nutrition Society Medical Lecture. Obesity: from molecules to man

Obesity is now a major public health problem in both developed and developing countries. In the UK over 16% men and 17.5% women are obese, an increase of more than 100% since 1980. However, interventions to prevent and treat obesity are hampered by an inadequate understanding of the aetiology of this condition. The present paper considers the current state of knowledge regarding the causes of obesity, including some of the genetic, metabolic, behavioural and environmental factors which influence energy balance. The present paper comprises The Nutrition Society Medal Lecture and focuses in particular on the research carried out at the MRC Dunn Nutrition Centre in Cambridge. It argues that despite decades of intensive research there is relatively little evidence of genetic or metabolic defects to explain the majority of cases of human obesity. Instead we must look to behavioural and/or environmental factors which may be underpinning the current epidemic of obesity.

The human obesity gene map: the 1998 update

An update of the human obesity gene map incorporating published results up to the end of October 1998 is presented. Evidence from the human obesity cases caused by single gene mutations; other Mendelian disorders exhibiting obesity as a clinical feature; quantitative trait loci uncovered in human genome-wide scans and in crossbreeding experiments with mouse, rat, and pig models; association and case-control studies with candidate genes; and linkage studies with genes and other markers is reviewed. The most noticeable changes from the 1997 update is the number of obesity cases due to single gene mutations that increased from three cases due to mutations in two genes to 25 cases due to 12 mutations in seven genes. A look at the obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes are found on all but chromosome Y of the human chromosomes. Some chromosomes show at least three putative loci related to obesity on both arms (1, 2, 3, 6, 7, 8, 9, 11, 17, 19, 20, and X) and several on one chromosome arm only (4q, 5q, 10q, 12q, 13q, 15q, 16p, and 22q). The number of genes and other markers that have been associated or linked with human obesity phenotypes is increasing very rapidly and now approaches 200.

Abdominal obesity

The application of magnetic resonance imaging and computed tomography to obesity research has changed the focus from body mass and skinfold thickness to abdominal fat mass and visceral adiposity. Intra-abdominal fat constitutes less than 20% of total body fat but is a major determinant of fasting and postprandial lipid availability because of its physiological (lipolytic rate and insulin resistance) and anatomical (portal drainage) properties. High levels of serum free fatty acids, as a result of abdominal obesity, cause excessive tissue lipid accumulation and contribute to dyslipidaemia, beta cell dysfunction, and hepatic and peripheral insulin resistance. An individual's risk of non-insulin dependent diabetes mellitus and cardiovascular disease relates closely to the inheritance of central obesity and susceptibility to tissue lipotoxicity.

The human obesity gene map: the 1997 update

An update of the human obesity gene map incorporating published results up to October 1997 is presented. Evidence from Mendelian disorders exhibiting obesity as a clinical feature; single-gene mutation rodent models; quantitative trait loci uncovered in human genome-wide scans and in crossbreeding experiments with mouse, rat, and pig models; association and case-control studies with candidate genes; and linkage studies with genes and other markers is reviewed. All chromosomal locations of the animal loci are converted into human genome locations based on syntenic relationships between the genomes. A complete listing of all of these loci reveals that all but chromosome Y of the 24 human chromosomes are represented. Some chromosomes show at least three putative loci related to obesity on both arms (1, 2, 6, 8, 11, and 20) and several on one chromosome arm only (3p, 4q, 5q, 7q, 12q, 13q, 15q, 15p, 22q, and Xq). Studies reporting negative association and linkage results are also listed, with the exception of the unlinked markers from genome-wide scans.