Genetics of obesity

Genetic association of adrenergic receptor alpha 2A with obesity and type 2 diabetes

OBJECTIVE

The sympathetic nervous system (SNS) is linked to glucose, lipid, and protein metabolism. The α2A -adrenergic receptor (ADRA2A) is involved in the SNS and mediates inhibition of insulin secretion and lipolysis. The association of ADRA2A single-nucleotide polymorphisms (SNPs) with obesity and/or type 2 diabetes (T2D) was investigated.

DESIGN AND METHODS

Genotyping was performed in a case-control study of 1,177 Swedish individuals, including lean and obese subjects with normal glucose tolerance (NGT) and T2D patients. ADRA2A mRNA expression was measured in pancreatic islets isolated from T2D patients and nondiabetic subjects.

RESULTS

SNP rs553668 was associated with T2D in men (odds ratio [OR] = 1.47; 95% confidence interval [CI] = 1.08-2.01; P = 0.015) but this association was lost after adjusting for age and for body mass index (BMI). Associations were also detected when comparing obese NGT and lean NGT subjects (OR = 1.49; 95% CI = 1.07-2.07; P = 0.017), and in obese (OR = 1.62; 95% CI = 1.06-2.49; P = 0.026), but not in lean T2D. In women, multiple logistic regression regarding SNP rs521674 demonstrated an increased OR of 7.61 (95% CI = 1.70-34.17; P = 0.008) for T2D when including age as a covariant. Correcting for BMI removed the significant association. When age was included in the model, association also found when obese T2D patients were compared with lean NGT subjects (P = 0.041). ADRA2A mRNA expression in human pancreatic islets was detectable, but with no statistically significant difference between the diabetic and the control groups.

CONCLUSIONS

ADRA2A genetic polymorphisms are mainly associated with obesity and possibly with T2D in a Swedish population.

Progress in understanding the role of leptin in the pathogenesis and treatment of chronic hepatitis C

Leptin is an adipokine that is abundantly expressed in adipose tissue and has multiple biological effects related to the development of human diseases, such as diabetes mellitus, obesity, metabolism syndrome, and cancer. Pegylated interferon plus ribavirin has been considered as fist-line therapy in patients with chronic hepatitis C (CHC). Because this therapy is associated with many side effects, further studies on the mechanism and treatment of CHC are needed. More and more studies have demonstrated that leptin plays an important role in the pathogenesis of CHC and provides a new target for the treatment of this disease. This paper reviews the recent advances in understanding the role of leptin in the pathogenesis and treatment of CHC.

Fiber, protein, and lupin-enriched foods: role for improving cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death globally (World Health Organisation, 2011). Many of the risk factors for CVD are modifiable, including overweight and obesity. Numerous strategies have been proposed to fight CVD, with a special focus being placed on dietary interventions for weight management. The literature suggests that two nutrients, fiber and protein, may play significant roles in weight control and hence cardiovascular health. Increasing both protein and fiber in the diet can be difficult because popular low-carbohydrate and high-protein diets tend to have considerably low-fiber intakes (Slavin, 2005). One approach to obtain both is to develop functional foods using unique ingredients. Lupin flour is a novel food ingredient derived from the endosperm of lupin. It contains 40-45% protein, 25-30% fiber, and negligible sugar and starch (Petterson and Crosbie, 1990). Research conducted to date reveals that lupin-enriched foods, which are naturally high in protein and fiber, may have a significant effect on CVD risk factors. This review explores whether there is a role for fiber-, protein-, and lupin-enriched foods in improving cardiovascular health.

Potentiation of abnormalities in myocardial metabolism with the development of diabetes in women with obesity and insulin resistance

BACKGROUND

Because studies in animal models of type-2 diabetes mellitus (DM) show that excessive myocardial fatty acid (FA) metabolism (at the expense of glucose metabolism) cause cardiac dysfunction, we hypothesized that women with DM would have more FA and less glucose myocardial metabolism than normal or even obese (OB) women.

RESEARCH DESIGN AND METHODS

Women who were lean volunteers (NV) (N = 14; age 35 ± 17 years, body mass index 23 ± 1 kg/m(2)), OB (N = 28;31 ± 6 years, BMI 39 ± 7 kg/m2), and DM (n = 22; 54 ± 11 years, BMI 38 ± 5 kg/m2) were studied. Cardiac positron emission tomography was performed for the determination of myocardial blood flow, oxygen consumption, FA and glucose metabolism. Cardiac work was measured by echocardiography and efficiency by the ratio of work to myocardial oxygen consumption.

RESULTS

Fractional glucose uptake was comparable between NV and OB but lower in DM (P < .05 versus NV). Myocardial FA utilization and oxidation were both higher in DM compared with NV and OB (P < .0001). Myocardial FA utilization and oxidation had positive correlations with HOMA (R = 0.35, P = .005 and R = 0.40, P = .001, respectively) whereas fractional glucose uptake exhibited an inverse correlation (R = -.31, P = .01). Cardiac work and efficiency were similar among the three groups.

CONCLUSIONS

In women, the presence of OB and DM compared with OB alone is associated with a greater reliance on myocardial FA metabolism at the expense of glucose metabolism. These perturbations in myocardial metabolism are not associated in a decline left ventricular efficiency or function suggesting that the metabolic perturbations may precede an eventual decline left ventricular function as is seen in animal models of DM.

Il6 gene promoter polymorphism (-174G/C) influences the association between fat mass and cardiovascular risk factors

During the last decades, the prevalence of obesity has increased rapidly among young people. A polymorphism in the promoter region of the IL6 gene (-174G/C), has been previously reported to be involved in obesity and metabolic syndrome development. Therefore, the aim of the study was to examine whether the IL6-174G/C polymorphism influence the association of body fat with low-grade inflammatory markers and blood lipids and lipoproteins in Spanish adolescents. 504 Spanish adolescents participating in the AVENA study were genotyped for the-174G/C polymorphism of the IL6 gene. Anthropometric and body composition measurements were taken and blood samples were collected for plasma molecules determinations. No differences between genotypes were observed in anthropometric values, body composition measurements and plasma markers concentration. Physical activity level differ between genotypes with subjects carrying the C allele of the polymorphism being significantly (p<0.05) more active than GG subjects. The association between body fat mass and plasma glucose was influenced by the -174G/C polymorphism of the IL6 gene. Subjects carrying the C allele of the mutation seem to have higher values of lipoprotein (a) and C-reactive protein as their percentage of body fat mass increase. Our results suggest that this promoter polymorphism influences the association between adiposity and some plasma markers.

The ZEB1 transcription factor is a novel repressor of adiposity in female mice

Background

Four genome-wide association studies mapped an “obesity” gene to human chromosome 10p11–12. As the zinc finger E-box binding homeobox 1 (ZEB1) transcription factor is encoded by the TCF8 gene located in that region, and as it influences the differentiation of various mesodermal lineages, we hypothesized that ZEB1 might also modulate adiposity. The goal of these studies was to test that hypothesis in mice.

Methodology/Principal Findings

To ascertain whether fat accumulation affects ZEB1 expression, female C57BL/6 mice were fed a regular chow diet (RCD) ad libitum or a 25% calorie-restricted diet from 2.5 to 18.3 months of age. ZEB1 mRNA levels in parametrial fat were six to ten times higher in the obese mice. To determine directly whether ZEB1 affects adiposity, wild type (WT) mice and mice heterozygous for TCF8 (TCF8+/−) were fed an RCD or a high-fat diet (HFD) (60% calories from fat). By two months of age on an HFD and three months on an RCD, TCF8+/− mice were heavier than WT controls, which was attributed by Echo MRI to increased fat mass (at three months on an HFD: 0.517±0.081 total fat/lean mass versus 0.313±0.036; at three months on an RCD: 0.175±0.013 versus 0.124±0.012). No differences were observed in food uptake or physical activity, suggesting that the genotypes differ in some aspect of their metabolic activity. ZEB1 expression also increases during adipogenesis in cell culture.

Conclusion/Significance

These results show for the first time that the ZEB1 transcription factor regulates the accumulation of adipose tissue. Furthermore, they corroborate the genome-wide association studies that mapped an “obesity” gene at chromosome 10p11–12.

Expression of leptin in hepatic fibrosis and its relation with hepatic stellate cell activation

AIM: To investigate the expression of leptin in hepatic fibrosis and explore its correlation with the expression of TGF-β1 and α-SMA as well as its relation with the activation of hepatic stellate cells (HSC).

METHODS: Forty healthy male SD rats were randomly divided into normal control group and carbon tetrachloride treatment group. The rats were given a subcutaneous injection of either vehicle or carbon tetrachloride, and sacrificed at weeks 2, 4 and 6 after the injection, respectively. The mRNA and protein expression of leptin, TGF-β1 and α-SMA was assayed by reverse transcription-polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry, respectively.

RESULTS: Leptin, TGF-β1 and α-SMA were lowly expressed in normal liver tissues. After injection of carbon tetrachloride, the expression of leptin, TGF-β1 and α-SMA began to increase at week 2 and was significantly higher at weeks 4 and 6 (P < 0.05), showing a gradually rising trend. The expression of leptin was positively correlated with that of TGF-β1 and α-SMA (r = 0.668 and 0.570, respectively; both P < 0.05).

CONCLUSION: The expression of leptin, TGF-β1 and α-SMA increases with the development of hepatic fibrosis. Leptin is probably involved in the activation of HSCs and the synthesis of extracellular matrix (ECM) in the development of hepatic fibrosis.

Triplet repeat in the Repin1 3'-untranslated region on rat chromosome 4 correlates with facets of the metabolic syndrome

BACKGROUND

Congenic and subcongenic rat strains confirmed the quantitative trait loci (QTLs) for facets of the metabolic syndrome between 60.53 and 77.11 Mb on chromosome 4. The analysis of candidate genes in this region favoured the replication initiator 1 (Repin1) characterized by a SNP in the coding region and a triplet repeat (TTT) in the 3'-untranslated region (3'UTR).

METHODS

We analysed nine rat strains (BB/OK, SHR, F344, BN, DA, LEW, hHTg, WOKW, and their founders WOK-F) and four wild rats on DNA (sequencing) and RNA level (gene expression in blood, liver, subcutaneous, and epididymal adipocytes). In addition, the rats were phenotypically characterized in order to link the rat phenotype to genotype differences in the QTL on chromosome 4.

RESULTS

Wild rats were heterozygous for the SNP (C/T), whereas all the inbred strains were homozygous. The shortest triplet repeat was found in SHR (5) and the highest was found in hHTg and WOKW (11), which developed metabolic disorders. The repeat number correlated with most phenotypic traits studied. Using linear multiple regression analysis with repeat size as the dependent variable and considering all the data of this study, it was clearly demonstrated that not only VLDL cholesterol and serum insulin but also the expression of Repin1 in the liver is significantly associated with the repeat size of the 3'UTR.

CONCLUSIONS

It is concluded that the triplet repeat expansion in 3'UTR is involved in metabolic alterations as found in hHTg and WOKW rats and that the functional unknown gene, Repin1, could be a novel candidate gene for the development of facets of the metabolic syndrome.

Constitutive traffic of melanocortin-4 receptor in Neuro2A cells and immortalized hypothalamic neurons

Melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that binds alpha-melanocyte-stimulating hormone (alpha-MSH) and has a central role in the regulation of appetite and energy expenditure. Most GPCRs are endocytosed following binding to the agonist and receptor desensitization. Other GPCRs are internalized and recycled back to the plasma membrane constitutively, in the absence of the agonist. In unstimulated neuroblastoma cells and immortalized hypothalamic neurons, epitopetagged MC4R was localized both at the plasma membrane and in an intracellular compartment. These two pools of receptors were in dynamic equilibrium, with MC4R being rapidly internalized and exocytosed. In the absence of alpha-MSH, a fraction of cell surface MC4R localized together with transferrin receptor and to clathrin-coated pits. Constitutive MC4R internalization was impaired by expression of a dominant negative dynamin mutant. Thus, MC4R is internalized together with transferrin receptor by clathrin-dependent endocytosis. Cell exposure toalpha-MSH reduced the amount of MC4R at the plasma membrane by blocking recycling of a fraction of internalized receptor, rather than by increasing its rate of endocytosis. The data indicate that, in neuronal cells, MC4R recycles constitutively and that alpha-MSH modulates MC4R residency at the plasma membrane by acting at an intracellular sorting step.

A Brief Update of Glucocorticoid Receptor Variants and Obesity Risk

Excess body fat, obesity, is one of the most common disorders in clinical practice. Obese individuals are at increased risk for physical ailments, such as type 2 diabetes, coronary heart disease, hypertension, and several types of cancer. The location of the body fat is a major determinant of the degree of excess morbidity and mortality due to obesity. More specifically, the amount of subcutaneous truncal or abdominal fat, and the amount of visceral fat located in the abdominal cavity independently predicts obesity-related adverse health outcomes. The obesity gene map shows putative loci on all chromosomes except Y. More than 300 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. These genes can be divided into two broad categories: (a) rare gene variants that have a strong influence, and (b) common gene variants that have a weaker influence on obesity phenotypes. Studies in humans have suggested a positive association between obesity, hypertension, and insulin resistance, with alleles at the glucocorticoid receptor gene. In this article, we will estimate the risk by which such gene polymorphism mediates a role in obesity.

Approaching the shared biology of obesity and depression: the stress axis as the locus of gene-environment interactions

Obesity and depression are serious public health problems and also constitute cardiovascular disease risk factors. Research organizations have called for efforts to explore the interrelationship between obesity and depression. A useful starting point is the fact that in both disorders there is dysregulation of stress systems. We review molecular and clinical evidence indicating that the mediators of the stress response are a key locus for gene-environment interactions in the shared biology of depression and obesity. Scientific milestones include translational paradigms such as mice knockouts, imaging and pharmacogenomic approaches that can identify new therapeutic strategies for those burdened by these two afflictions of contemporary civilization. Perspectives for the future are promising. Our ability to dissect the underpinnings of common and complex diseases with shared substrates will be greatly enhanced by the Genes and Environment Initiative, the emerging Large Scale Studies of Genes and Environment in Common Disease, and the UK Biobank Project.

Low-carbohydrate diets affect energy balance and fuel homeostasis differentially in lean and obese rats

In parallel with increased prevalence of overweight people in affluent societies are individuals trying to lose weight, often using low-carbohydrate diets. Nevertheless, long-term metabolic consequences of those diets, usually high in (saturated) fat, remain unclear. Therefore, we investigated long-term effects of high-fat diets with different carbohydrate/protein ratios on energy balance and fuel homeostasis in obese (fa/fa) Zucker and lean Wistar rats. Animals were fed high-carbohydrate (HC), high-fat (HsF), or low-carbohydrate, high-fat, high-protein (LC-HsF-HP) diets for 60 days. Both lines fed the LC-HsF-HP diet displayed reduced energy intake compared with those fed the HsF diet (Zucker, -3.7%) or the HC diet (Wistar rats, -12.4%). This was not associated with lower weight gain relative to HC fed rats, because of increased food efficiencies in each line fed HsF and particularly LC-HsF-HP food. Zucker rats were less glucose tolerant than Wistar rats. Lowest glucose tolerances were found in HsF and particularly in LC-HsF-HP-fed animals irrespective of line, but this paralleled reduced plasma adiponectin levels, elevated plasma resistin levels, higher retroperitoneal fat masses, and reduced insulin sensitivity (indexed by insulin-induced hypoglycemia) only in Wistar rats. In Zucker rats, however, improved insulin responses during glucose tolerance testing and tendency toward increased insulin sensitivities were observed with HsF or LC-HsF-HP feeding relative to HC feeding. Thus, despite adverse consequences of LC-HsF diets on blood glucose homeostasis, principal differences exist in the underlying hormonal regulatory mechanisms, which could have benefits for B-cell functioning and insulin action in the obese state but not in the lean state.

The polygenetically inherited metabolic syndrome of WOKW rats is associated with insulin resistance and altered gene expression in adipose tissue

BACKGROUND

Wistar Ottawa Karlsburg W (RT1u) rats (WOKW) develop a complete metabolic syndrome closely resembling the human disease. The aim of this study was to characterize the phenotype of adipose tissue in WOKW rats with regard to adipocyte metabolism, insulin resistance, and gene expression and thus to define the phenotype more precisely.

METHODS

Glucose metabolism, insulin sensitivity, and gene expression of key adipocyte genes, including adiponectin, interleukin 6 (Il6), 11 beta-hydroxysteroid dehydrogenase (11beta Hsd), peroxisome proliferator-activated receptor gamma (Ppar gamma), forkhead box O1 (Foxo1), glucose transporter 4 (Glut4), CCAAT/enhancer binding protein (C/ebp alpha), and fatty acid synthase (Fasn) were characterized in adipocytes from epididymal and subcutaneous fat depots of 28-week-old male WOKW rats and Dark Agouti (DA) controls.

RESULTS

WOKW rats display decreased insulin-stimulated glucose uptake and decreased insulin sensitivity during lipogenesis and lipolysis in isolated adipocytes. The severe insulin resistance predominantly in epididymal adipose tissue of WOKW rats is associated with a 10-fold decrease in adipocyte adiponectin gene expression, decreased Ppar gamma, but increased Foxo1 gene expression compared to DA rats.

CONCLUSIONS

Insulin resistance in adipose tissue is associated with altered adipocyte gene expression in WOKW rats, additionally completing the picture of the metabolic syndrome in this animal model. This fact not only qualifies the WOKW rat for further detailed analysis of genetic determinants of metabolic syndrome but also highlights its suitability for pharmacological research.

Pathophysiology of dyslipidaemia in the metabolic syndrome

The insulin resistance/metabolic syndrome is characterised by the variable coexistence of hyperinsulinaemia, obesity, dyslipidaemia, and hypertension. The pathogenesis of the syndrome has multiple origins, but obesity and sedentary lifestyle coupled with diet and still largely unknown genetic factors clearly interact to produce the syndrome. Dyslipidaemia, the hallmark of the metabolic syndrome, includes increased flux of free fatty acids, raised triglycerides, apolipoprotein B, and small dense low density lipoprotein, and decreased high density lipoprotein cholesterol. The widely prevalent nature of the metabolic syndrome emphasises the importance of its diagnosis and treatment. This review analyses the clinical and dynamic features of this syndrome in the aspect of dyslipidaemia and its management.

Childhood obesity. Treatment options

The prevalence of child and adolescent overweight and obesity is rapidly increasing and is associated with morbidity, both medical and psychosocial. Obesity is unlikely to resolve spontaneously. It is important that health professionals can assess obesity and initiate an action plan. The evidence base for what works best in the management of child and adolescent overweight and obesity is limited. It is uncertain whether protocols from clinical research trials can be translated into primary care. Dietary change, with an emphasis on lower fat intake and smaller portion size, should be commenced. There should be an increase in physical activity and a decrease in sedentary behaviours, combined with behavioural change and parental involvement. These are the elements of a lifestyle intervention. In the severely obese adolescent with obesity-related co-morbidity, the use of very low-energy diets and anti-obesity agents could be considered. Bariatric surgery may be indicated in carefully selected, older, severely obese adolescents.

N/A

N/A

Genome-wide scan of resistin mRNA expression in omental adipose tissue of baboons

INTRODUCTION

The hormone resistin was recently discovered in adipose tissue of mice. Functional tests suggest a role for resistin in the regulation of insulin sensitivity. However, human studies have reported controversial results on the metabolic function of this hormone.

METHODS

A 1 g omental adipose tissue biopsy was obtained from 404 adult baboons. Resistin mRNA expression was assayed by real-time, quantitative RT-PCR, and univariate and bivariate quantitative genetic analyses were performed, via the variance decomposition approach. A genome scan analysis was conducted using resistin mRNA abundance in omental adipose tissue as a quantitative phenotype.

RESULTS

A significant heritability of h2 = 0.23 (P = 0.003) was found for resistin mRNA abundance in omental adipose tissue. A genome scan detected a quantitative trait locus for resistin expression with an LOD score of 3.8, in the region between markers D19S431 and D19S714, corresponding to human chromosome 19 p13. This chromosomal region contains genes related to insulin resistance phenotypes, such as resistin, insulin receptor, angiopoietin-like 4 protein and LDL receptor.

CONCLUSIONS

Individual variation in resistin mRNA expression has a significant genetic component, and a gene or genes on chromosome 19 p13 may regulate resistin mRNA levels in baboon omental adipose tissue.

Aetiology of obesity: a striving after wind?

The current global epidemic of obesity is fuelled by a constant, unidirectional adverse effect on energy balance that exceeds the adaptive capacity of the system. The individual response to this environmental pressure is under the control of a variety of genes, which not only interacts with environmental factors but also with one another. Since the discovery that adipocytes may produce and secrete hormones, the adipose tissue has taken on increasing importance in the regulation of energy balance. Indeed, the pathogenesis of obesity, once regarded as so obvious and simple, is becoming one of the most complex in medical practice. From a clinical perspective, obesity is associated with a remarkably broad spectrum of health complications and, over the years, obesity-related mortality has consistently increased. From a theoretical viewpoint, the growing complexity of factors affecting the liability to obesity, the inconsistency of scientific results, the lack of consensus among scientists, and so forth, obstruct our efforts to unravel the aetiology of obesity. Is the field of obesity research merely a striving after wind, and nothing more?

Obesity and cancer

Large prospective studies show a significant association with obesity for several cancers, and the International Agency for Research on Cancer has classified the evidence of a causal link as 'sufficient' for cancers of the colon, female breast (postmenopausal), endometrium, kidney (renal cell), and esophagus (adenocarcinoma). These data, and the rising worldwide trend in obesity, suggest that overeating may be the largest avoidable cause of cancer in nonsmokers. Few obese people are successful in long-term weight reduction, and thus there is little direct evidence regarding the impact of weight reduction on cancer risk. If the correlation between obesity and cancer mortality is entirely causal, we estimate that overweight and obesity now account for one in seven of cancer deaths in men and one in five in women in the US.

Adiposity signals, genetic and body weight regulation in humans

Numerous signals convey information about body fat status from the periphery to the brain areas that control energy homeostasis so that, throughout life, body weight remains nearly stable. These signals mainly originate, either from the adipose tissue, like leptin and to a lesser extent interleukin 6, or from the pancreas, like insulin and amylin. These factors circulate in proportion to body fat mass and they are referred to as "adiposity signals". It is well established, at least for leptin and insulin, that they enter the brain from the plasma where they induce/repress a network of important neuropeptide regulators of energy intake and expenditure. Beside these endocrine signals, a growing amount of literature show data relative to adipocyte-derived molecules, most of them belonging to the cytokine family, like IL6, TNFalpha, IL8, IL10 whose secretion also correlates with body fat mass and that may locally regulate fat mass expansion. Others, like adiponectin, are negatively correlated with body fat mass. These "adiposity molecules" have already been involved in insulin resistance associated with obesity and inflammatory process. They may participate to a complex inter organ dialogue. In this review, we will synthesize data relative to the role played by insulin, leptin and amylin, either alone or through a cross talk, in "energy level sensing" at the brain level. Furthermore, we will develop how "adiposity molecules" through their paracrin and/or autocrin action may contribute to maintain fat mass expansion, therefore representing new adiposity molecules per se. Lastly, since any distortion in the metabolic circuitry of energy homeostasis is susceptible to lead to a pathological status like obesity, the impact of known genetic polymorphisms in genes encoding the adiposity signals will be discussed.

Research issues in genetic testing of adolescents for obesity

Obesity is often established in adolescence, and advances are being made in identifying its genetic underpinnings. We examine issues related to the eventual likelihood of genetic tests for obesity targeted to adolescents: family involvement; comprehension of the test's meaning; how knowledge of genetic status may affect psychological adaptation; minors' ability to control events; parental/child autonomy; ability to make informed medical decisions; self-esteem; unclear distinctions between early/late onset for this condition; and social stigmatization. The public health arena will be important in educating families about possible future genetic tests for obesity.

Genómica de la regulación del peso corporal: mecanismos moleculares que predisponen a la obesidad

Obesity has become a worldwide public health problem which affects millions of people. Substantial progress has been made in elucidating the pathogenesis of energy homeostasis over the past few years. The fact that obesity is under strong genetic control has been well established. Twin, adoption and family studies have shown that genetic factors play a significant role in the pathogenesis of obesity. Human monogenic obesity is rare in large populations. The most common form of obesity is considered to be a polygenic disorder. New treatments are currently required for this common metabolic disease and type 2 diabetes. The identification of physiological and biochemical factors that underlie the metabolic disturbances observed in obesity is a key step in developing better therapeutic outcomes. The discovery of new genes and pathways involved in the pathogenesis of such a disease is critical to this process. However, identification of genes that contribute to the risk of developing the disease represents a significant challenge since obesity is a complex disease with many genetic and environmental causes. A number of diverse approaches have been used to discover and validate potential new genes for obesity. To date, DNA-based approaches using candidate genes and genome-wide linkage analysis have not had a great success in identifying genomic regions or genes involved in the development of these diseases. Recent advances in the ability to evaluate linkage analysis data from large family pedigrees (using variance components-based linkage analysis) show great promise in robustly identifying genomic regions associated with the development of obesity. Studying rare mutations in humans and animal models has provided fundamental insight into a complex physiological process, and has complemented population-based studies that seek to reveal primary causes. Remarkable progress has been made in both fronts and the pace of advance is likely to accelerate as functional genomics and the human genome project expand and mature. Approaches based on Mendelian and quantitative genetics may well converge, and ultimately lead to more rational and selective therapies.

10: Management of obesity

Obesity has reached epidemic proportions in Australia, with 67.5% of men, 52.1% of women and 19%-23% of children and adolescents being overweight or obese. Genetically predisposed individuals are especially vulnerable to developing obesity in the highly obesogenic environment of 21st century Australia. Obesity causes or contributes to many comorbidities, including type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, non-alcoholic steatohepatitis, orthopaedic problems and polycystic ovary syndrome. Management in the individual requires their complete co-operation and should be tailored to individual needs and complications. Management of obesity in children should consider the family context and involve the parents. All treatment strategies must involve lifestyle modification, with a reduction of energy intake and an increase in physical activity. Some patients may also require the assistance of drug therapy or bariatric surgery.

What have rare genetic syndromes taught us about the pathophysiology of the common forms of obesity?

Obesity is a central feature for several congenital syndromes, including Prader-Willi, Angelman, Bardet-Biedl, Cohen, Alström, and Börjeson-Forssman-Lehmann syndromes, and Albright's hereditary osteodystrophy. Although a role for the central nervous system, including the hypothalamus-pituitary axis, has been suggested for the etiology of obesity in these syndromes, the pathophysiologic pathways are as yet not well defined, and in many cases may identify currently unknown mechanisms. Nevertheless, many of the causative genes and unusual mechanisms, including parental imprinting of genes and complex patterns of inheritance, have been identified. We review the latest advances in understanding congenital syndromes in which obesity is purely genetic, drawing on comparisons to genetic studies of obesity in the human population as well as to those in experimental and agricultural animal models. An understanding of the genetic basis for these syndromes will provide a more comprehensive picture of the mechanisms that control food intake and energy balance in humans.

An obesity-related locus in chromosome region 12q23-24

Obesity is a growing health problem in the U.S. As a complex trait, obesity involves multiple genes and gene-gene and gene-environment interactions that contribute to its pathogenesis. Here we report significant linkage from a scan of a large sample segregating extreme obesity and normal weight. We have used 382 microsatellite markers in 1,297 individuals from 260 European-American families. We conducted nonparametric linkage (NPL) analyses for dichotomous BMI (using BMI >/=27, >/=30, >/=35, and >/=40 kg/m(2)) using Genehunter. We also analyzed quantitative traits (BMI, percentage of fat, and waist circumference) by the family regression method using Merlin_regress. We found evidence for linkage on chromosome 12 (125 cM, D12S2070, logarithm of odds [LOD] 3.79, P = 0.00001 for percentage of fat; LOD 2.98, P = 0.0001 for BMI; and LOD 2.86, P = 0.00014 for waist circumference) by family regression analyses. Adding three additional markers to the intervals flanking the chromosome 12 peak yielded an LOD score of 4.08 (P = 0.00001) for percentage of fat at 116 cM and LOD scores of 3.57 (P = 0.00003) and 3.05 (P = 0.00009) for BMI and waist circumference, respectively, at 125 cM. We also obtained other suggestive linkages on chromosomes 2, 3, 7, 8, 9, 12, 13, and 21. Our results suggest multiple loci that could influence obesity, particularly a locus in chromosome region 12q23-24.

Obesity wars: molecular progress confronts an expanding epidemic

The worldwide prevalence of obesity is increasing at an alarming rate, with major adverse consequences for human health. This "obesity epidemic" is paralleled by a rapid and substantive increase in our understanding of molecular pathways and physiologic systems underlying the regulation of energy balance. While efforts to address the environmental factors that are responsible for the recent "epidemic" must continue, new molecular and physiologic insights into this system offer exciting possibilities for future development of successful therapies.

Gene expression profile of omental adipose tissue in human obesity

The aim of the present study was to gain insight into the pathophysiology of obesity by comparing the pattern of gene expression of omental adipose tissue of obese and lean volunteers using DNA microarrays. Omental adipose tissue biopsies were obtained by laparoscopic surgery from six male patients (44.2+/-6.3 yr). RNA was extracted and pooled for the obese (BMI: 37.3+/-2.5 kg/m2) and lean (BMI: 23.4+/-0.8 kg/m2) groups. From the total number of genes analyzed (1,152 well-characterized human genes), 41% were expressed at sufficient levels in human adipose tissue for detection in the microarray experiments, finding that 89 genes were up-regulated while 64 were down-regulated at least twofold in the omental adipose tissue obtained from obese patients. We found a general tendency to blunt lipolysis inducer genes and a global down-regulation of genes encoding growth factors. Moreover, an up-regulation in the expression of several mitogen-activated protein kinases (MAPKs) was observed. The down-regulation of genes involved in lipolysis activation may be involved in the etiopathogenesis of obesity. In addition, down-regulation of growth factors and the up-regulation of MAPKs may indicate an attempt to restrain adipocyte proliferation and differentiation. Furthermore, obesity is accompanied by an altered expression in omental adipose tissue of genes involved not only in energy homeostasis but also in quite diverse biological functions, such as immune response. The genomic approach underlines the importance of adipose tissue beyond energy metabolism.

GAD2 on chromosome 10p12 is a candidate gene for human obesity

The gene GAD2 encoding the glutamic acid decarboxylase enzyme (GAD65) is a positional candidate gene for obesity on Chromosome 10p11-12, a susceptibility locus for morbid obesity in four independent ethnic populations. GAD65 catalyzes the formation of gamma-aminobutyric acid (GABA), which interacts with neuropeptide Y in the paraventricular nucleus to contribute to stimulate food intake. A case-control study (575 morbidly obese and 646 control subjects) analyzing GAD2 variants identified both a protective haplotype, including the most frequent alleles of single nucleotide polymorphisms (SNPs) +61450 C>A and +83897 T>A (OR = 0.81, 95% CI [0.681-0.972], p = 0.0049) and an at-risk SNP (-243 A>G) for morbid obesity (OR = 1.3, 95% CI [1.053-1.585], p = 0.014). Furthermore, familial-based analyses confirmed the association with the obesity of SNP +61450 C>A and +83897 T>A haplotype (chi(2) = 7.637, p = 0.02). In the murine insulinoma cell line betaTC3, the G at-risk allele of SNP -243 A>G increased six times GAD2 promoter activity (p < 0.0001) and induced a 6-fold higher affinity for nuclear extracts. The -243 A>G SNP was associated with higher hunger scores (p = 0.007) and disinhibition scores (p = 0.028), as assessed by the Stunkard Three-Factor Eating Questionnaire. As GAD2 is highly expressed in pancreatic beta cells, we analyzed GAD65 antibody level as a marker of beta-cell activity and of insulin secretion. In the control group, -243 A>G, +61450 C>A, and +83897 T>A SNPs were associated with lower GAD65 autoantibody levels (p values of 0.003, 0.047, and 0.006, respectively). SNP +83897 T>A was associated with lower fasting insulin and insulin secretion, as assessed by the HOMA-B% homeostasis model of beta-cell function (p = 0.009 and 0.01, respectively). These data support the hypothesis of the orexigenic effect of GABA in humans and of a contribution of genes involved in GABA metabolism in the modulation of food intake and in the development of morbid obesity.

Genetic and environmental aspect of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous syndrome determined in most patients by the association of two main factors: hyperandrogenism and insulin resistance. These characters are probably independent of each other and seem to be inherited by several different mechanisms. In some patients homozygous gene alteration has been found but in most patients PCOS seems to be determined by the association of gene polymorphisms that are common in the general population but alone are unable to determine phenotypic consequences. Alteration of genes that regulate the initial steps of ovarian steroidogenesis is probably the main causal factor of hyperandrogenism. Insulin resistance may be the result of many different gene alterations including insulin receptor substrate (IRS)-1 and 2, calpain-10 and peroxisome proliferator-activated receptor gamma(PPARgamma). Some polymorphisms may be protective against other gene alterations. Insulin sensitivity is also modified by socioeconomic and cultural factors that influence quantity and quality of food and energy expenditure. However, even eating behavior and weight response to food intake may be under genetic regulation. Different combinations of multiple gene polymorphisms and of environmental factors explain the heterogeneity of PCOS.