The human obesity gene map: the 2000 update

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Association Between Body Fat Response to Exercise Training and MultilocusADRGenotypes

OBJECTIVE

To examine the contribution of adrenergic receptor (ADR) gene polymorphisms and their gene-gene interactions to the variability of exercise training-induced body fat response.

RESEARCH METHODS AND PROCEDURES

This was an intervention study that used a volunteer sample of 70 healthy, sedentary men (n = 29) and postmenopausal women (n = 41) 50 to 75 years of age, with a BMI < or = 37 kg/m2, from the Washington, DC, metropolitan area. Participants completed 6 weeks of dietary stabilization (American Heart Association diet) before 24 weeks of supervised aerobic exercise training. Diet was maintained throughout the intervention. Change in percent total body fat, percent trunk fat, and fat mass by DXA in ADR genotype groups (Glu12/Glu9 alpha2b-ADR, Trp64Arg beta3-ADR, and Gln27Glu beta2-ADR) at baseline and after 24 weeks of aerobic exercise training was measured.

RESULTS

In multivariate analysis (covariates: age, gender, and baseline value of phenotype), best fit models for percent total body and trunk fat response to exercise training retained main effects of all three ADR gene loci and the effects of each gene-gene interaction (p = 0.009 and 0.003, respectively). Similarly, there was a trend for the fat mass response model (p = 0.03). The combined genetic factors explained 17.5% of the overall model variability for percent total body fat, 22% for percent trunk fat, and 10% for fat mass.

DISCUSSION

The body fat response to exercise training in older adults is associated with the combined effects of the Glu12/Glu9 alpha2b-, Trp64Arg beta3-, and Gln27Glu beta2-ADR gene variants and their gene-gene interactions.

Genes on rat chromosomes 3, 5, 10, and 16 are linked with facets of metabolic syndrome

WOKW (Wistar Ottawa Karlsburg W) rats develop metabolic syndrome closely resembling human disorder. In crossing studies between disease-prone WOKW and disease-resistant DA (Dark Agouti) rats, several quantitative trait loci (QTLs) were mapped. To prove the in vivo relevance of QTLs, congenic DA.WOKW rats, briefly termed DA.3aW, DA.3bW, DA.5W, DA.10W, and DA.16W, were generated by transferring chromosomal regions of WOKW chromosomes 3, 5, 10, and 16 onto DA genetic background. Male (n=12) and female (n=12) rats of each congenic strain and their parental strain DA were characterized for adiposity index (AI), serum leptin, and serum insulin as well as serum cholesterol and serum triglycerides as single facets of metabolic syndrome at the age of 30 weeks. The data showed a significant higher AI for male and female DA.3aW and female DA.16W compared with DA. Serum leptin was significantly elevated in male and female DA.3aW, DA.10W, and DA.16W rats in comparison with DA. Rats of both sexes of DA.10W and female DA.16W showed significantly elevated serum insulin in comparison to DA. Female rats of all congenics had significantly higher serum cholesterol compared with DA, while males did not differ. Finally, triglycerides were only elevated in male DA.16W. The results demonstrate an involvement of WOKW chromosomes 3, 5, 10, and 16 in developing facets of the metabolic syndrome.

Association of G-2548A LEP polymorphism with plasma leptin levels in Tunisian obese patients

OBJECTIVES

The aim of this study was to examine the association of the G-2548A polymorphism of the human leptin gene (LEP) with body mass index (BMI), plasma leptin, insulin, and lipid parameters in a sample of Tunisian population.

DESIGN AND METHODS

Two hundred and twenty nine obese patients (BMI>or=30 kg/m(2)) were screened and compared to 251 normal weight subjects (BMI<25 kg/m(2)). The human leptin gene promoter G-2548A genotype was determined by polymerase chain reaction followed by a digestion with the restriction of endonuclease CfoI.

RESULTS

In the entire study sample, carriers of -2548A allele had significantly lower leptin levels than homozygous for -2548G allele (14.28+/-9.10 ng/mL vs. 18.27+/-12 ng/mL, p<0.001 respectively) adjusted for BMI and gender. In obese patients but not control, subjects carrying the -2548A allele exhibited lower leptin levels than those with GG genotype (16.96+/-8.27 ng/mL vs. 21.37+/-11.72 ng/mL, p=0.001 respectively) adjusted for BMI and gender. In this group, carriership of the -2548A allele was identified, by multiple linear regression models, as significant independent predictor for leptin levels variability. Separate analyses by gender revealed that only in obese women, the -2548A allele was found to be associated with lower leptin levels independently of BMI (p=0.004).

CONCLUSIONS

The present study showed that G-2548A LEP polymorphism is associated with lower leptin levels in Tunisian obese women.

Mutations in the beta1 adrenergic receptor gene and massive obesity in Japanese

Catecholamines strongly promote lipolysis and thermogenesis, and play a central role in the regulation of body fat content. The beta1 adrenergic receptor (BAR-1) is a major mediator of catecholamine-induced lipolysis and thermogenesis. To explore whether mutations in the BAR-1 gene contribute to morbid obesity in Japanese, we scanned for mutations in the coding sequence of the gene in 50 morbid obese [body mass index (BMI)>==35.0kg/m(2); 99.7th percentile] Japanese subjects. Direct DNA sequencing was performed following polymerase chain reaction (PCR) amplification. Two common polymorphisms, Gly49Arg and Arg389Ser, were detected in these subjects. The frequencies of these polymorphisms, as determined by PCR-restriction fragment length polymorphism (RFLP) analysis, showed no significant difference between 180 severely obese subjects (BMI>==30.0kg/m(2); 97th percentile) and 132 control (BMI<25.0kg/m(2)) subjects. This study represents the first investigations of genetic variations of BAR-1 in relationship to morbid obesity and suggests mutations in the BAR-1 coding sequence is not likely a major cause of morbid obesity at least in Japanese.

Online genetic databases informing human genome epidemiology

BACKGROUND

With the advent of high throughput genotyping technology and the information available via projects such as the human genome sequencing and the HapMap project, more and more data relevant to the study of genetics and disease risk will be produced. Systematic reviews and meta-analyses of human genome epidemiology studies rely on the ability to identify relevant studies and to obtain suitable data from these studies. A first port of call for most such reviews is a search of MEDLINE. We examined whether this could be usefully supplemented by identifying databases on the World Wide Web that contain genetic epidemiological information.

METHODS

We conducted a systematic search for online databases containing genetic epidemiological information on gene prevalence or gene-disease association. In those containing information on genetic association studies, we examined what additional information could be obtained to supplement a MEDLINE literature search.

RESULTS

We identified 111 databases containing prevalence data, 67 databases specific to a single gene and only 13 that contained information on gene-disease associations. Most of the latter 13 databases were linked to MEDLINE, although five contained information that may not be available from other sources.

CONCLUSION

There is no single resource of structured data from genetic association studies covering multiple diseases, and in relation to the number of studies being conducted there is very little information specific to gene-disease association studies currently available on the World Wide Web. Until comprehensive data repositories are created and utilized regularly, new data will remain largely inaccessible to many systematic review authors and meta-analysts.

Polymorphism in the PPARgamma2 and beta2-adrenergic genes and diet lipid effects on body composition, energy expenditure and eating behavior of obese women

In order to evaluate the effect of polymorphism in the PPARgamma2 and beta2-adrenergic genes and diet lipids on body composition, energy expenditure and eating behavior of obese women, 60 subjects were submitted to anthropometric, biochemical, dietary, molecular, basal and postprandial metabolism (indirect calorimetry) and eating behavior (visual analog scale) evaluation. Fat and saturated fatty acid (SFA) high diet was used to assess postprandial metabolism. The frequency of Pro12Pro/Gln27Gln, Pro12Pro/Gln27Glu, Pro12Pro/Glu27Glu and Pro12Ala/Gln27Glu genotypes was 35.71%, 30.37%, 23.21% and 10.71%, respectively. These values were not significant (p>0.05) for the dietary, anthropometric, biochemical and metabolic parameters. The Pro12Ala/Gln27Glu group was found to present greater energy used in postprandial period (EUPP). The presence of the PPARgamma2 gene variant, independent of beta2-adrenergic gene polymorphism, resulted in fat oxidation increase. Also, this group presented higher satiety, compared to the Pro12Pro/Gln27Gln group. The presence of the variant alleles in the PPARgamma2 gene suggests benefits in food intake control.

Review article: Obesity, waist-hip ratio and hunter-gatherers

Obesity is a rapidly growing global problem. It is not simply the result of eating too much, and not all types of obesity have the same significance. Obesity is in part genetic, and one particularly important genetic type of obesity is the tendency to 'truncal obesity',-that is, a raised waist-to-hip ratio. Such obesity is powerfully associated not only with a tendency to diabetes, but also to cardiovascular disease, ('Syndrome X'). Interestingly, this is the type of obesity seen in every hunter-gatherer (HG) population around the globe. Such people are intolerant of carbohydrate, especially refined carbohydrate, especially in the excessive amounts typically consumed in affluent societies. In such pure HG communities, rates of diabetes can be as high as 50%, when the 'Western' lifestyle is adopted. Many of us, however, share some of their genes and their carbohydrate intolerance-perhaps as many as 20 or 30% of the world's population. Pregnancy can uncover this characteristic, and obesity and glucose intolerance in pregnancy are rapidly burgeoning problems. Quite contrary to the common nutritional dogma of encouraging regular carbohydrates, it is suggested that pregnant women with a high waist-to-hip ratio should be strongly advised to adhere to a low-glycaemic-index diet. Additionally, many dietary interventions, some of them derived from observation of HG populations, are of proven benefit in reducing the expression of glucose intolerance and may well help in tackling the obesity epidemic.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

A genomewide search finds major susceptibility loci for gallbladder disease on chromosome 1 in Mexican Americans

Gallbladder disease (GBD) is one of the major digestive diseases. Its risk factors include age, sex, obesity, type 2 diabetes, and metabolic syndrome (MS). The prevalence of GBD is high in minority populations, such as Native and Mexican Americans. Ethnic differences, familial aggregation of GBD, and the identification of susceptibility loci for gallstone disease by use of animal models suggest genetic influences on GBD. However, the major susceptibility loci for GBD in human populations have not been identified. Using ultrasound-based information on GBD occurrence and a 10-cM gene map, we performed multipoint variance-components analysis to localize susceptibility loci for GBD. Phenotypic and genotypic data from 715 individuals in 39 low-income Mexican American families participating in the San Antonio Family Diabetes/Gallbladder Study were used. Two GBD phenotypes were defined for the analyses: (1) clinical or symptomatic GBD, the cases of cholecystectomies due to stones confirmed by ultrasound, and (2) total GBD, the clinical GBD cases plus the stone carriers newly diagnosed by ultrasound. With use of the National Cholesterol Education Program/Adult Treatment Panel III criteria, five MS risk factors were defined: increased waist circumference, hypertriglyceredemia, low high-density lipoprotein cholesterol, hypertension, and high fasting glucose. The MS risk-factor score (range 0-5) for a given individual was used as a single, composite covariate in the genetic analyses. After accounting for the effects of age, sex, and MS risk-factor score, we found stronger linkage signals for the symptomatic GBD phenotype. The highest LOD scores (3.7 and 3.5) occurred on chromosome 1p between markers D1S1597 and D1S407 (1p36.21) and near marker D1S255 (1p34.3), respectively. Other genetic locations (chromosomes 2p, 3q, 4p, 8p, 9p, 10p, and 16q) across the genome exhibited some evidence of linkage (LOD >or=1.2) to symptomatic GBD. Some of these chromosomal regions corresponded with the genetic locations of Lith loci, which influence gallstone formation in mouse models. In conclusion, we found significant evidence of major genetic determinants of symptomatic GBD on chromosome 1p in Mexican Americans.

Comparison of Gene Expression in Intra-Abdominal and Subcutaneous Fat: A Study of Men with Morbid Obesity and Nonobese Men Using Microarray and Proteomics

Extent of intra-abdominal fat had significant linear relations with six metabolic coronary risk factors: systolic and diastolic blood pressure, fasting blood concentrations of glucose, high density lipoprotein (HDL) cholesterol, triglyceride, and plasminogen activator inhibitor-1. Tumor necrosis factor-alpha and adiponectin can be biological mediators from the intra-abdominal fat to the metabolic coronary risk factors. Complementarily, we describe a new study that will analyze the gene expression in intra-abdominal and subcutaneous fat on mRNA and protein level using high throughput methods. The study will elucidate further whether intra-abdominal obesity is the common denominator for the different components of the metabolic syndrome.

An autosomal genome scan for loci influencing longitudinal burden of body mass index from childhood to young adulthood in white sibships: The Bogalusa Heart Study

OBJECTIVE

To examine genetic loci linked to a long-term burden and trend of obesity traits, such as body mass index (BMI), from childhood to adulthood.

DESIGN

: Longitudinal study using serial measurements of BMI from childhood.

SUBJECTS

A total of 782 unselected white siblings (representing 521 full and 39 half sib-pairs) from 342 families enrolled in the Bogalusa Heart Study.

MEASUREMENTS

A total of 357 microsatellite markers with an average spacing of 9.0 cM spanning the 22 autosomal chromosomes were typed. A quadratic growth curve was developed using a random effects model based on serial measurements of BMI from childhood to adulthood. The serial changes in BMI were measured in terms of long-term burden (area under the curve (AUC) divided by follow-up years) and the long-term trend (incremental AUC, calculated as total AUC-baseline AUC).

RESULTS

Heritability estimates of long-term measures were 0.78 for total AUC and 0.43 for incremental AUC. In a variance-component-based multipoint linkage analysis with SOLAR, linkage to the long-term measures of BMI was observed on chromosomes 1, 5, 7, 12, 13 and 18. For total AUC, LOD scores were 3.0 at 110 cM on chromosome 12, 2.9 at 26 cM and 2.4 at 52 cM on chromosome 7, and 2.2 at 126 cM on chromosome 5. For incremental AUC, LOD scores were 2.9 at 26 cM, 2.1 at 97 cM and 2.3 at 110 cM on chromosome 12, 2.2 at 69 cM on chromosome 7, 2.2 at 91 cM and 2.5 at 150 cM on chromosome 1, 2.0 at 119 cM on chromosome 5, 2.0 at 54 cM on chromosome 13 and 2.0 at 7 cM on chromosome 18. Several important obesity-related candidate genes are located in the regions or near the markers showing positive linkage.

CONCLUSION

Linkage evidence found in this study indicates that regions on these chromosomes might harbor genetic loci that affect the propensity to develop obesity from childhood.

Neuropeptides in hypothalamic neuronal disorders

A few examples of hypothalamic, peptidergic disorders leading to clinical signs and symptoms are presented in this review. Increased activity of corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus (PVN) and decreased activity of the vasopressin neurons in the biological clock and of the thyroxine-releasing hormone (TRH) neurons in the PVN contribute to the signs and symptoms of depression. In men, the central nucleus of the bed nucleus of the stria terminalis (BSTc) is about twice as large and contains twice as many somatostatin neurons as in women. In transsexuals this sex difference is reversed, pointing to a role of this structure in gender. Luteinizing hormone-releasing hormone (LHRH) neurons are formed in the fetal olfactory placade and migrate along the terminal nerve fibers into the hypothalamus. In Kallmann's syndrome the migration process of the LHRH (gonadotropin-releasing hormone) neurons is aborted, which explains the joint occurrence of hypogonadotropic hypogonadism and anosmia in this syndrome. In postmenopausal women, the neurons of the infundibular nucleus hypertrophy and become hyperactive because of the disappearance of the estrogen feedback and contain hyperactive peptidergic neurons. Climacteric flushes may be caused by hyperactivity of the neurokinin-B or LHRH neurons in this nucleus. The hypocretin (orexin) neurons in the perifornical area are involved in sleep. In narcolepsy with cataplexy, a loss of these neurons, probably due to an autoimmune process, is found. Obese subjects with a mutation in the gene that encodes for leptin, the preproghrelin gene, or the alpha-melanocyte-stimulating hormone (alpha-MSH) gene have been described. Decreased numbers and activity of the oxytocin neurons in the PVN may be responsible for the absence of satiety in Prader-Willi syndrome. Moreover, a glucocorticoid receptor polymorphism is associated with obesitas and dysregulation of the hypothalamus-pituitary-adrenal axis. In contrast, two single nucleotide polymorphisms (SNPs) of the AGRP gene have been associated with anorexia nervosa.

Metabolic and psychosocial effects of minimal invasive gastric banding for morbid obesity

Obesity is considered a primary risk factor for cardiovascular disease and related mortality. The current study aimed to investigate the efficacy of minimal invasive gastric banding (GB) surgery for reducing caloric intake in morbid obesity, and to analyze the effects of weight loss on body composition and metabolic and psychosocial outcomes. Twenty-six adult severely obese patients (mean body mass index [BMI], 48.1 kg/m(2); range, 42 to 56) underwent adjustable silicone laparoscopic GB. Nine additional obese patients who declined surgery were treated with metformin (2 g daily) and served as a small additional group (BMI, 50.5 kg/m(2); range, 41 to 68). Presurgery and 17 +/- 2.2 months postoperatively, body composition (fat mass [FM], lean body mass [LBM], body water) and serum parameters (lipids, glucose, thyrotropin-stimulating hormone [TSH]) were determined. Quality of life (QoL) was evaluated by a standardized self-rating questionnaire (Short Form-36 [SF-36]), and supplemented by measures of physical complaints and psychological distress. After GB, weight loss was 21 +/- 14.9 kg (14%, P <.001). It was associated with a decrease in FM by 14 +/- 8.6 kg (18%, P <.001), LBM by 4 +/- 2.7 kg (5%, P <.001), body water by 4 +/- 3.4 L (7%, P <.01), systolic blood pressure by 16 +/- 26.3 mm Hg (10%, P <.05), total cholesterol by 0.69 +/- 1.29 mmol/L (12%, P <.05), and low-density lipoprotein cholesterol (LDL-C) by 0.38 +/- 0.39 mmol/L (10%, P <.05). Highly significant interactions between surgery and time were noted for weight (P <.005), BMI (P <.005), and FM (P <.007, analysis of variance [ANOVA]). Preoperatively, 14 of 26 patients (54%) had high fasting blood sugar levels (type 2 diabetics) and 11 (42%) had impaired glucose tolerance, whereas postoperatively, for baseline glucose levels a trend to decrease was noted. Neither malabsorption nor anemia was observed. QoL improved after GB; in particular, physical functioning and well being increased (P <.01), and somatic complaints (eg, dyspnea and heart complaints, pain in legs and arms) markedly decreased (P =.008). In the metformin group, neither relevant weight loss nor a significant decrease of biochemical values was observed. Minimal invasive GB is a successful therapeutic tool for reducing FM in morbidly obese patients. Weight loss resulted in improved metabolic parameters, suggesting a lowered atherogenic risk.

A study of linkage and association of body mass index in the Old Order Amish

Obesity is thought to have a genetic component with the estimates of heritability ranging from 0.25-0.40. As part of an ongoing study of obesity in the Old Order Amish, seven two- and three-generation families (157 individuals) were assessed for 21 traits related to obesity, including body mass index (BMI) and BMI-percentile (a standardized distribution of BMI adjusted for age and sex). Genotyping was performed using a panel of 384 short-tandem repeat markers. In this sample, the estimates of heritability ranged from 0.16-0.31 for BMI and from 0.40-0.52 for BMI-percentile. Model-independent linkage analysis identified candidate regions on chromosomes 1, 5, 7, 8, and 11. Given that several markers on 7q were significant for both BMI and BMI-percentile (P < or = 0.001) and that the structural locus for leptin was located on 7q, this region was considered to be the primary candidate region. Subsequent typing of additional flanking markers on 7q corroborated the original findings. Tests of intrafamilial association for alleles at markers in this candidate region were significant at similar levels. Although there is some evidence for linkage and association in the region containing leptin, there appears to be stronger evidence for linkage (P < or = 0.001) and association (P < or = 0.00001) with BMI in a region 10-15 cM further downstream of leptin, flanked by markers D7S1804 and D7S3070 with peak values from D7S495-D7S1798. Evidence from linkage and association studies suggests that this region (D7S1804-D7S3070) may be responsible, at least in part, for variation in BMI and BMI-percentile in the Old Order Amish.

The peroxisome proliferator-activated receptor alpha L162V mutation is associated with reduced adiposity

OBJECTIVE

To determine the contribution of the peroxisome proliferator-activated receptor alpha (PPARalpha) L162V mutation to the variation of several indexes of body fatness obtained from healthy adults who participated in the Quebec Family Study.

RESEARCH METHODS AND PROCEDURES

The PPARalpha L162V mutation was determined by a mismatch polymerase chain reaction method. Adiposity phenotypes were obtained by standardized anthropometric measurements, underwater weighing technique, and computed tomography.

RESULTS

For all adiposity phenotypes, subjects carrying the V162 allele had lower values compared with L162 homozygotes (HMZs) [BMI (kg/m(2)): 27.8 +/- 7.6 vs. 26.0 +/- 5.6, p < 0.05; percentage body fat: 28.5 +/- 10.7 vs. 25.7 +/- 10.1, p < 0.05; waist circumference (cm): 89.0 +/- 18.1 vs. 85.7 +/- 15.8, p = 0.07; total computed tomography abdominal fat areas (cm(2)): 406 +/- 221 vs. 359 +/- 192, p = 0.15; means +/- SD for L162 HMZs vs. V162 carriers, respectively]. Differences in cross-sectional abdominal adipose tissue areas and waist circumference were abolished after adjustment for total body fat mass. Similar trends were observed when results were analyzed by gender, although associations seemed stronger in women. The odds ratio of having a BMI above 30 kg/m(2) reached 1.77 (1.02; 3.07, 95% confidence intervals) for L162 HMZs. This risk could be considered marginal on an individual basis, but because 85% of the subjects are affected by this small risk, the impact on the population is important.

DISCUSSION

The PPARalpha V162 allele is associated with reduced adiposity and has a substantial population-attributable risk.

The human obesity gene map: the 2002 update

This is the ninth update of the human obesity gene map, incorporating published results through October 2002 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and various animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. For the first time, transgenic and knockout murine models exhibiting obesity as a phenotype are incorporated (N = 38). As of October 2002, 33 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and the causal genes or strong candidates have been identified for 23 of these syndromes. QTLs reported from animal models currently number 168; there are 68 human QTLs for obesity phenotypes from genome-wide scans. Additionally, significant linkage peaks with candidate genes have been identified in targeted studies. Seven genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 222 studies reporting positive associations with 71 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. 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. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

Weight control and the management of obesity after menopause: the role of physical activity

BACKGROUND

Postmenopausal women have an increased tendency for gaining weight. The declines of endogenous estrogen, together with physical inactivity, are probably the major causes of this phenomenon. Postmenopausal overweight and obesity leads to increased rates of hypertension, diabetes mellitus, coronary artery disease, and all cause mortality. Additional consequences may include hormone-dependent cancer, gallstones, nephrolithiasis, and osteoarthritis. Weight loss can reverse many of these complications, reduce the number and dosages of medications used, and improve longevity. This difficult task requires lifestyle modification.

OBJECTIVES

To review the current information about the effects of physical activity on postmenopausal weight gain and its consequences and to provide basic strategies to treat obesity during the menopause transition.

METHODS

A Medline search together with a manual search of selected articles.

CONCLUSION

Several options for weight loss are available, yet lifestyle modification is essential in managing postmenopausal obesity and overweight. While this demands dietary and behavioral changes, a major element of this modification is regular physical activity, which reduces obesity-related morbidity and mortality. The amendment to a healthier lifestyle is achievable at the postmenopausal years. All medical personnel should advocate against overweight and obesity and provide tools for their management.

A genome-wide scan for body mass index among Nigerian families

OBJECTIVE

Interest in mapping genetic variants that are associated with obesity remains high because of the increasing prevalence of obesity and its complications worldwide. Data on genetic determinants of obesity in African populations are rare.

RESEARCH METHODS AND PROCEDURES

We have undertaken a genome-wide scan for body mass index (BMI) in 182 Nigerian families that included 769 individuals.

RESULTS

The prevalence of obesity was only 5%, yet polygenic heritability for BMI was in the expected range (0.46 +/- 0.07). Tandem repeat markers (402) were typed across the genome with an average map density of 9 cM. Pedigree-based analysis using a variance components linkage model demonstrated evidence for linkage on chromosome 7 (near marker D7S817 at 7p14) with a logarithm of odds (LOD) score of 3.8 and on chromosome 11 (marker D11S2000 at 11q22) with an LOD score of 3.3. Weaker evidence for linkage was found on chromosomes 1 (1q21, LOD = 2.2) and 8 (8p22, LOD = 2.3). Several candidate genes, including neuropeptide Y, DRD2, APOA4, lamin A/C, and lipoprotein lipase, lie in or close to the chromosomal regions where strong linkage signals were found.

DISCUSSION

The findings of this study suggest that, as in other populations with higher prevalences of obesity, positive linkage signals can be found on genome scans for obesity-related traits. Follow-up studies may be warranted to investigate these linkages, especially the one on chromosome 11, which has been reported in a population at the opposite end of the BMI distribution.

Interacting genetic loci on chromosomes 20 and 10 influence extreme human obesity

Obesity is a multigenic trait that has a substantial genetic component. Animal models confirm a role for gene-gene interactions, and human studies suggest that as much as one-third of the heritable variance may be due to nonadditive gene effects. To evaluate potential epistatic interactions among five regions, on chromosomes 7, 10, and 20, that have previously been linked to obesity phenotypes, we conducted pairwise correlation analyses based on alleles shared identical by descent (IBD) for independent obese affected sibling pairs (ASPs), and we determined family-specific nonparametric linkage (NPL) scores in 244 families. The correlation analyses were also conducted separately, by race, through use of race-specific allele frequencies. Conditional analyses for a qualitative trait (body mass index [BMI] >/=27) and hierarchical models for quantitative traits were used to further refine evidence of gene interaction. Both the ASP-specific IBD-sharing probability and the family-specific NPL score revealed that there were strong positive correlations between 10q (88-97 cM) and 20q (65-83 cM), through single-point and multipoint analyses with three obesity thresholds (BMI >/=27, >/=30, and >/=35) across African American and European American samples. Conditional analyses for BMI >/=27 found that the LOD score at 20q rises from 1.53 in the baseline analysis to 2.80 (empirical P=.012) when families were weighted by evidence for linkage at 10q (D10S1646) through use of zero-one weights (weight(0-1)) and to 3.32 (empirical P<.001) when proportional weights (weight(prop)) were used. For percentage fat mass, variance-component analysis based on a two-locus epistatic model yielded significant evidence for interaction between 20q (75 cM) and the chromosome 10 centromere (LOD = 1.74; P=.024), compared with a two-locus additive model (LOD = 0.90). The results from multiple methods and correlated phenotypes are consistent in suggesting that epistatic interactions between loci in these regions play a role in extreme human obesity.

Long-term divergent selection on fatness in mice indicates a regulation system independent of leptin production and reception

Divergent selection in mice on fatness over 60 generations produced a fat (F) and a lean (L) line, having about 22% and 4% body fat, respectively. To elucidate the importance of the leptin regulatory feedback loop in the genetic changes produced by this selection, Lep(ob) and Lepr(db) mutations causing leptin production and leptin receptor deficiency, respectively, were introgressed individually into both lines by repeated backcrossing. The fat amount increased significantly in homozygotes for Lep(ob) or Lepr(db) in both lines, for example, in F and L males from 8.5 to 18.8 and 17.2 g (P<0.001) and from 1.25 to 18.0 and 12.7 g (P<0.001), respectively. Line differences were, however, mostly maintained after introgression. Concentrations of circulating leptin were relatively independent of the original lines but heavily dependent on the introgressed genotype. Introgression of leptin production and receptor deficiencies had separate effects from long-term selection, indicating that the genes responsible for the line divergence must act independently of the leptin regulatory system. Energy budget analysis indicated that the major line differences were in the level of energy expended on physical activity, and these differences were preserved following introgression, suggesting that multiple pathways regulate fatness, which may be independently responsive to intervention.

Pleiotropic relationships between cortisol levels and adiposity: The HERITAGE Family Study

OBJECTIVE

To investigate familial basis for the relationship between cortisol adiposity at baseline and their training responses.

RESEARCH METHODS AND PROCEDURES

Bivariate correlation and segregation analyses were employed between cortisol and several adiposity measures [body mass index, fat mass (FM), fat-free mass, percentage of body fat (% BF), abdominal visceral fat (AVF), abdominal subcutaneous fat (ASF), and abdominal total fat (ATF)] from 99 white families and 105 black families.

RESULTS

In both races, significant inverse phenotypic correlations were generally observed between cortisol and adiposity measures at baseline but not for training responses. Significant cross-trait familial correlations were found for cortisol with abdominal fat (ASF, AVF, ATF) and overall body adiposity (FM, % BF) measures at baseline, which accounted for 14% to 20% of the phenotypic variance in whites. The cross-trait correlations were not significant for baseline phenotypes in blacks, perhaps because of the small sample size. A bivariate segregation analysis showed evidence of polygenic pleiotropy for cortisol with both abdominal fat and overall adiposity measures that accounted for 14% to 17% of the phenotypic covariance, but major gene pleiotropy was not suggested in whites. However, when ASF, AVF, and ATF were additionally adjusted for FM, no familial cross-trait correlations or polygenic pleiotropy between cortisol and the abdominal fat measures remained.

DISCUSSION

Evidence was found for polygenic pleiotropy but not for pleiotropic major gene effects between cortisol and overall adiposity in whites. However, the covariation of cortisol with abdominal fat phenotypes is dependent on concomitant polygenic factors for total-body fat.

Dopamine transporter genotype as a risk factor for obesity in African-American smokers

OBJECTIVE

To assess the association between a polymorphism related to dopamine function, dopamine transport (SLC6A3), and obesity in smokers.

RESEARCH METHODS AND PROCEDURES

Logistic regression was used to assess the relationship between this genetic polymorphism and obesity (body mass index > or = 30 kg/m(2)) from a sample of 510 smokers who smoked at least 10 cigarettes per day and who were participating in a study designed to examine genetic and nongenetic predictors of response to a pharmacological treatment.

RESULTS

The likelihood of obesity in African Americans (N = 90) with the 10/10 SLC6A3 genotype was 5.16 times that of African Americans with 9/9 or 9/10 SLC6A3 genotypes (odds ratio = 5.16, confidence interval = 1.60 to 16.65). There was no association of the SLC6A3 genotype with obesity for non-Hispanic whites (N = 420).

DISCUSSION

These results suggest that variants of the dopamine transporter gene may be related to obesity in African-American smokers. Possible mechanisms responsible for the association between dopamine transport and obesity in African-American smokers are discussed.

Prevalence of attention deficit/hyperactivity disorder among adults in obesity treatment

BACKGROUND

Bariatric patients showing poor "focus" during treatment more often failed to lose weight or maintain reduced weight. Evaluation of these patients identified a number having attention deficit/hyperactivity disorder (ADHD), evidently a potent factor limiting successful weight control. After searches found no published reports describing comorbid ADHD and obesity, this report was conceived to begin exploring the prevalence and characteristics of these patients.

METHOD

Clinical records of 215 patients receiving obesity treatment during 2000 were reviewed. Data collected and analyzed included age, sex, beginning and ending body mass index (BMI), number of clinic visits, months of treatment, and diagnostic category (ADHD, some ADHD symptoms, non-ADHD). DSM-IV criteria were used, except age of onset was modified to <= 12 years.

RESULTS

Whole sample ADHD prevalence was 27.4% (CI:21.1,32.9), but 42.6% (CI: 36.3% to 48.9%) for BMI >= 40. Mean weight loss among obese patients with ADHD (OB+ADHD) was 2.6 BMI (kg/m2) vs. 4.0 for non-ADHD (NAD) (p < 0.002). For BMI >= 40, OB+ADHD had BMI loss 2.9 vs. 7.0 (NAD) (p < 0.004). OB+ADHD had more clinic visits, with a trend toward longer treatment duration.

CONCLUSIONS

ADHD was highly prevalent among obese patients and highest in those with extreme obesity. Comorbid obesity and ADHD symptoms rendered treatment less successful compared to NAD counterparts. Reasons for the comorbidity are unknown, but may involve brain dopamine or insulin receptor activity. If replicated in further studies, these findings have important implications for treatment of severe and extreme obesity.

Familial resemblance of body mass index and familial risk of high and low body mass index. A study of young men in Sweden

OBJECTIVE

Male familial correlations in body mass index (BMI) were studied using a large nationwide dataset of Swedish military conscripts examined at age 18-19 y.

DESIGN

Record linkage was performed between Sweden's Military Service Conscription Register and the Multiple-Generation Register, enabling the identification of 92 869 families containing at least two brothers. Data on BMI at conscription was available for 196 743 sons and for 19 972 fathers. Pairs of relatives were used to estimate Pearson correlation coefficients for BMI, and to examine whether there are BMI intervals that show particularly strong familial resemblance.

RESULTS

All biological family relations showed highly significant correlations for BMI: 0.28 (95% CI 0.27-0.29) for father-son pairs; 0.36 (0.35-0.37) for full-brothers, 0.21 (0.18-0.24) for maternal half-brothers, and 0.11 (0.08-0.14) for paternal half-brothers. Also, a significant correlation, of 0.06 (0.01-0.11), was found for non-biological quasi father-son relations. Full-brothers were more similar with respect to BMI at age 18 than father-son pairs, and maternal half-brothers were more similar than paternal half-brothers. The familial risk of having BMI values above or below various cut-offs was found to be equally strong for low BMI as for high BMI values.

CONCLUSION

The almost twice as strong BMI correlation between maternal half-brothers as between paternal half-brothers illustrates the importance of factors of non-additive genetic origin, to the familial aggregation of BMI. The significant BMI association found between biologically unrelated individuals from the same family emphasizes that assortative mating (and regional clustering) should be taken into account when the heritability of BMI is estimated.

A prospective study of the role of depression in the development and persistence of adolescent obesity

BACKGROUND

Adolescent obesity is a strong predictor of adult obesity, and adult obesity has been associated with depression, especially in women. Studies have also suggested an association between depression in adolescence and higher body mass index (BMI) in adulthood. Whether depression leads to obesity or obesity causes depression is unclear.

OBJECTIVE

To determine in longitudinal analyses whether depressed mood predicts the development and persistence of obesity in adolescents.

METHODS

A prospective cohort study of 9374 adolescents in grades 7 through 12 who completed in-home interviews for the National Longitudinal Study of Adolescent Health. Assessments were made at baseline (1995) and at follow-up 1 year later. Depressed mood was assessed with the Center for Epidemiologic Studies Depression Scale. BMI (kg/m2) was calculated from self-reported height and weight. BMI percentiles and z scores were computed using the 2000 Centers for Disease Control and Prevention growth charts. Obesity was defined as BMI > or =95th percentile, overweight as BMI > or =85th percentile and <95th percentile, and normal weight as BMI <85th percentile. A parental respondent gave information on household income, parental education, and parental obesity.

RESULTS

At baseline, 12.9% were overweight, 9.7% were obese, and 8.8% had depressed mood. Baseline depression was not significantly correlated with baseline obesity. Among the 9.7% who were obese at follow-up, 79.6% were obese at baseline, 18.6% were overweight at baseline, and 1.8% were normal weight at baseline. Having depressed mood at baseline independently predicted obesity at follow-up (odds ratio: 2.05; 95% confidence interval: 1.18, 3.56) after controlling for BMI z score at baseline, age, race, gender, parental obesity, number of parents in the home, and family socioeconomic status. This finding persisted after controlling further for the adolescents' report of smoking, self-esteem, delinquent behavior (conduct disorder), and physical activity. After controlling for all these same factors, depressed mood at baseline also predicted obesity at follow-up among those not obese at baseline (odds ratio: 2.05; 95% confidence interval: 1.04, 4.06) and follow-up BMI z score among those obese at baseline (beta = 0.11; standard error beta = 0.05). In contrast, baseline obesity did not predict follow-up depression.

CONCLUSIONS

Depressed adolescents are at increased risk for the development and persistence of obesity during adolescence. Understanding the shared biological and social determinants linking depressed mood and obesity may inform the prevention and treatment of both disorders.

Position of the American Dietetic Association: weight management

It is the position of the American Dietetic Association that successful weight management to improve overall health for adults requires a lifelong commitment to healthful lifestyle behaviors emphasizing sustainable and enjoyable eating practices and daily physical activity. Americans are increasing in body fat as they become more sedentary. Obesity has reached epidemic proportions and health care costs associated with weight-related illnesses have escalated. Although our knowledge base has greatly expanded regarding the complex causation of increased body fat, little progress has been made in long-term maintenance interventions with the exception of surgery. Lifestyle modifications in food intake and exercise remain the hallmarks of effective treatment, but are difficult to initiate and sustain over the long term. The dietitian can play a pivotal role in modifying weight status by helping to formulate reasonable goals which can be met and sustained with a healthy eating approach as outlined in the Dietary Guidelines for 2000. Any changes in dietary intake and exercise patterns which decrease caloric intake below energy expenditure will result in weight loss, but it is the responsibility of the dietitian to make sure the changes recommended are directed toward improved physiological and psychological health. A thorough clinical assessment should help define possible genetic, environmental, and behavioral factors contributing to weight status and is important to the formulation of an individualized intervention. The activation of treatment strategies is often limited by available resources and cost. Reimbursement by third party payers for services is limited. Health care dollars are consumed for treatment of weight-related diseases. Public policy must change if the obesity epidemic is to be stopped and appropriate weight management techniques activated.

Allelic variants in the GABA(A)alpha6 receptor subunit gene (GABRA6) is associated with abdominal obesity and cortisol secretion

INTRODUCTION

Cortisol is involved in the regulation of adipose-tissue differentiation, function and distribution, and in excess causes abdominal obesity. At the level of the brain, cortisol secretion is partly controlled by gamma-aminobutyric acid (GABA), which is the major inhibitory neurotransmitter in the vertebrate brain, and acts by binding to GABA(A) receptors.

METHOD

We examined the potential impact of a 1519T>C polymorphism in the GABA(A)alpha6 receptor subunit (GABRA6) gene on obesity and obesity-related phenotypes as well as circulating hormones, including salivary cortisol in 284 unrelated Swedish men born in 1944. The subjects were genotyped by using PCR amplification of the 3' non-coding region of the GABRA6 gene followed by digestion with the restriction enzyme AlwNI.

RESULTS

The frequency of allele T was 0.54 and 0.46 for allele C. Carriers for the T allele (n=211) had borderline significantly higher waist-to-hip ratio (P=0.094) and abdominal sagittal diameter (P=0.084) compared to homozygotes for the C allele (n=56). The homozygotes for the T allele had, in comparison to heterozygotes, significantly (P=0.004-0.024) higher mean cortisol levels at 11:45 am, and 30, 45 and 60 min after a standardized lunch and, finally, at 5:00 pm. In addition, T/T subjects had significantly (P=0.031) higher diurnal cortisol secretion compared to T/C subjects. Other hormones, glucose and serum lipids were not different across the genotype groups.

CONCLUSION

These findings suggest a role of the 1519T>C polymorphism in GABRA6 in the predisposition to hypercortisolism and perhaps abdominal obesity. The pathophysiology may involve various environmental factors, particularly stress, that destabilize the GABA-hypothalamic-pituitary-adrenal systems in those with genetic vulnerability.

A major predisposition locus for severe obesity, at 4p15-p14

Although the predisposition to morbid obesity is heritable, the identities of the disease-causing genes are largely unknown. Therefore, we have conducted a genomewide search with 628 markers, using multigenerational Utah pedigrees to identify genes involved in predisposition to obesity. In the genomewide search, we identified a highly significant linkage to high body-mass index in female patients, at D4S2632, with a multipoint heterogeneity LOD (HLOD) score of 6.1 and a nonparametric linkage (NPL) score of 5.3. To further delineate the linkage, we increased both the marker density around D4S2632 and the size of our pedigree data set. As a result, the linkage evidence increased to a multipoint HLOD score of 9.2 (at D4S3350) and an NPL score of 11.3. Evidence from almost half of the families in this analysis support this linkage, and therefore the gene in this region might account for a significant percentage of the genetic predisposition to severe obesity in females. However, further studies are necessary to clarify the effect that this gene has in males and in the general population.

Human leptin locus (LEP) alleles and BMI in Samoans

OBJECTIVES

Because of their location in known candidate gene regions for obesity the associations between six microsatellite markers (D2S2170, D2S144, D2S1268, D2S1788, D2S1348 and a tetranucleotide repeat in the 3' UTR of the LEP locus) and body mass index (BMI) were studied in adult Samoans.

DESIGN

The study was designed to detect differences in the proportion of alleles at the six microsatellite markers between two groups of adult Samoans at the extremes of the longitudinal BMI distribution.

SUBJECTS AND MEASUREMENTS

The 181 unrelated Samoan participants were 25-55 y of age, reported that all four grandparents were Samoan, resided in American Samoa (AS) or Samoa (S) and were without diagnosed hypertension or type 2 diabetes. Initial statistical analysis was based on chi(2) tests of independence between marker allele frequencies and BMI status at each marker. The association of individual alleles with BMI status was tested by aggregating a marker's allelic data into a two-by-two contingency table and applying a two-tailed version of Fisher's exact test, with a Bonferroni correction to account for the multiple testing implicit in the procedure.

RESULTS

There were no significant differences in allele frequencies at any of the markers between AS and S, as expected from our prior population genetic analyses. Only the LEP gene 3'-tetranucelotide repeat was associated (P<0.006) with BMI status. The distribution of the marker alleles at the LEP locus was significantly associated with the BMI groups (P<0.01), due to the low frequency of allele 226 in the high BMI group. The same pattern of association was found in sub-group analyses with low BMI individuals from AS and high BMI individuals from S.

CONCLUSION

These findings indicate that the leptin 3'-tetranucleotide repeat is associated with high BMI in adult Samoans, with allele 226 having a low frequency in the high BMI group.

Association between a variant at the GABA(A)alpha6 receptor subunit gene, abdominal obesity, and cortisol secretion

In the present study, we examined the potential impact of a T-to-C substitution at nucleotide 1519 of the GABA(A)alpha6 receptor subunit gene (GABRA6) on obesity and obesity-related phenotypes as well as circulating hormones, including salivary cortisol, in 284 unrelated Swedish men born in 1944. The subjects were genotyped by using PCR amplification followed by digestion with the restriction enzyme AlwNI. The frequency of allele T was 0.54 and that of allele C was 0.46. Carriers for the T allele (n = 211) had higher waist-to-hip ratio (p = 0.094) and abdominal sagittal diameter (p = 0.084) compared to homozygotes for the C allele (n = 56). The homozygotes for the T allele had, in comparison to heterozygotes, significantly (p = 0.004-0.024) higher mean cortisol levels at 11:45 am; at 30, 45, and 60 min after a standardized lunch; and finally at 5:00 pm. In addition, T/T subjects had significantly (p = 0.031) higher diurnal cortisol secretion compared to T/C subjects. Leptin, insulin, and glucose were not different across the genotype groups. In conclusion, these findings suggest a role of the point substitution (T-to-C) at nucleotide 1519 of GABRA6 in the predisposition to hypercortisolism and perhaps abdominal obesity. The pathophysiology may involve various environmental factors, particularly stress, that destabilize the GABA-hypothalamic-pituitary-adrenal systems in those with genetic vulnerability.

Familial resemblance for plasma leptin: sample homogeneity across adiposity and ethnic groups

OBJECTIVE

Previous studies show a wide range in the percentage of variance in leptin levels attributable to genetic factors. These studies differ markedly with respect to ethnicity, study design, and statistical methodology. Therefore, the purpose of this study was to investigate heterogeneity hypotheses across ethnic groups and by adiposity level, using the same statistical methods.

RESEARCH METHODS AND PROCEDURES

Samples included black vs. white (HERITAGE Family Study) and random vs. obese (Québec Family Study) individuals from 432 families (1432 individuals). Heritability for leptin, alternatively adjusted for age and sex and then for age, sex, and adiposity was estimated with the use of familial correlations. Heterogeneity in the magnitude of the familial resemblance between samples and the effect of adjusting for adiposity was explored.

RESULTS

Heritability did not vary across samples stratified by adiposity level or ethnic group or across adjustment schemes. Maximal heritability, the percentage of additive phenotypic variability due to all familial sources, was 32%.

DISCUSSION

Whereas leptin and adiposity were highly correlated within individuals, removing the effects of adiposity did not significantly alter the magnitude of the familial component for leptin. Moreover, this effect did not vary as a function of ethnicity (black vs. white) or adiposity level. Thus, no evidence for heterogeneity was detected. However, a comparison among previous studies raises questions concerning possible genetic heterogeneity in other ethnic groups in which complex interactions among leptin, adiposity, and diabetes status may be important.

Association between obesity and a polymorphism in the beta(1)-adrenoceptor gene (Gly389Arg ADRB1) in Caucasian women

INTRODUCTION

Genetic variants affecting adrenoceptors have been suggested to influence body fatness. A putative gain-of-function polymorphism in the beta(1)-adrenoceptor was recently discovered (Gly389Arg ADRB1). We examined the association between Gly389Arg ADRB1 and obesity status in a large cohort of well-characterized individuals.

METHODS

First, a large cohort of 931 Caucasian women (55.0+/-12.2 y) were genotyped for Gly389Arg ADRBbeta1 and we examined the association of the Arg allele with body weight and BMI (Gly/Gly, n=54; Gly/Arg, n=360; Arg/Arg, n=517). To further examine phenotypes regulating energy balance and body fatness, we examined the contribution of the Arg allele to body composition (DEXA), fat distribution (CT scan), resting energy expenditure, energy and macronutrient intake, maximal oxygen capacity, and physical activity in a subsample of 214 women from the main cohort that had been carefully characterized (Gly/Gly, n=19; Gly/Arg, n=82; Arg/Arg, n=113).

RESULTS

In the entire cohort (n=931), allele frequencies were 0.25 and 0.75 for the Gly and Arg alleles, respectively. In this cohort, we found that each Arg allele was associated with greater body weight of 2.91 kg (P=0.01) and BMI of 0.86 kg/m(2) (P=0.05). Accordingly, in the subsample of women, each Arg allele was associated with greater fat mass (3.71 kg; P=0.008). Other phenotypes were not significantly associated with the presence of the Arg allele.

CONCLUSIONS

This is the first study to investigate the relationship between the Gly389Arg ADRB1 variant and obesity. We found that the Arg allele is associated with greater body weight and BMI in Caucasian women due to a greater fat mass.

Genetics of eating and its relation to obesity

Humans show remarkable variability in their eating styles. Reasons for this variability are poorly understood, but carry important implications for the onset of obesity and its comorbidities. Although it is well established that genes influence obesity, genetic influences on human eating patterns have received less attention. Dramatic increases in the prevalence of obesity justify additional research into the genetics of eating style. This review highlights what is known about the genetics of food preferences and selection in humans. Data from family and twin studies suggest a moderate genetic contribution to eating style, with clear environmental effects emerging as well. Select studies show support for gene-environment interactions and common genetic bases for certain dietary patterns, obesity, and/or metabolic complications. Genetically informative designs that infuse innovative behavioral measures may help explain individual differences in eating styles and hopefully promote more effective obesity treatments.

A genomewide linkage scan for quantitative-trait loci for obesity phenotypes

Obesity is an increasingly serious health problem in the world. Body mass index (BMI), percentage fat mass, and body fat mass are important indices of obesity. For a sample of pedigrees that contains >10,000 relative pairs (including 1,249 sib pairs) that are useful for linkage analyses, we performed a whole-genome linkage scan, using 380 microsatellite markers to identify genomic regions that may contain quantitative-trait loci (QTLs) for obesity. Each pedigree was ascertained through a proband who has extremely low bone mass, which translates into a low BMI. A major QTL for BMI was identified on 2q14 near the marker D2S347 with a LOD score of 4.04 in two-point analysis and a maximum LOD score (MLS) of 4.44 in multipoint analysis. The genomic region near 2q14 also achieved an MLS >2.0 for percentage of fat mass and body fat mass. For the putative QTL on 2q14, as much as 28.2% of BMI variation (after adjustment for age and sex) may be attributable to this locus. In addition, several other genomic regions that may contain obesity-related QTLs are suggested. For example, 1p36 near the marker D1S468 may contain a QTL for BMI variation, with a LOD score of 2.75 in two-point analysis and an MLS of 2.09 in multipoint analysis. The genomic regions identified in this and earlier reports are compared for further exploration in extension studies that use larger samples and/or denser markers for confirmation and fine-mapping studies, to eventually identify major functional genes involved in obesity.

Low frequency of melanocortin-4 receptor (MC4R) mutations in a Mediterranean population with early-onset obesity

BACKGROUND

Melanocortin-4 receptor (MC4R) mutations have been reported as the most common single genetic cause of obesity in some populations and it has been suggested that they may be responsible for more than 4% of early-onset obesity.

OBJECTIVES

To verify the presence of mutations of the MC4R coding region in children from southern Italy with early-onset obesity.

SUBJECTS AND METHODS

Two-hundred and eight unrelated obese children and adolescents were included in the study. The average age at obesity onset was 4.5+/-2.6 y. MC4R coding region was screened using both single-strand conformation polymorphism (SSCP) analysis and denaturing high-performance liquid chromatography (DHPLC). Automatic sequencing of PCR products of all individuals that showed an aberrant SSCP and/or DHPLC pattern was performed.

RESULTS

One novel missense mutation and one previously described polymorphism (Vall03Ile) were identified. The missense mutation C142T, resulting in the substitution of proline with serine at codon 48, within the first MC4R transmembrane domain, was detected at the heterozygous state in a 15-y-old obese girl (body mass index (BMI)=35 kg/m(2)) who has been obese since she was 8 y old. The mutation co-segregated with the obesity phenotype for over three generations and was not found in the control population.

CONCLUSIONS

Our data show MC4R obesity causing mutations in less than 0.5% of the patients (ie 1 out of 208 patients) and therefore indicate a low prevalence of MC4R variants in the obese population from southern Italy. The specific genetic background of the Mediterranean population could make it difficult for MC4R mutations to produce an essentially polygenic trait such as common obesity, at least during childhood.

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.

Deconstructing and reconstructing obesity-induced diabetes (diabesity) in mice

Obesity-driven type 2 diabetes (diabesity) involves complex genetic and environmental interactions to trigger disease. Here, we combine variable numbers of known quantitative trait loci (QTL) for obesity and diabetes contributed by New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt) strains in the form of 10 interval-directed recombinant congenic strains (RCS), with NON/Lt as the background strain, to dissect the genetic interactions involved. All 10 RCS gain significantly more weight than the NON parental strain, but none are as obese as the parental, diabetes-prone NZO. Diabetes development in these RCS at F12 ranges between 0 and 100%, depending on genetic constitution. RCS-2, -1, and -10 represent a step-wise increase in numbers of specific diabetogenic QTL, resulting in a step-wise increase in diabetes incidence. RCS-10 recreates the 100% incidence seen in (NZOxNON)F1 males, but with less weight gain. Similarly, RCS-6, -7, -8, and -9 represent diabetes-prone strains with different combinations of diabetogenic QTL. RCS-3, -4, and -5 represent obese strains that do not transit to diabetes. Because these obesity and diabetes syndromes reflect different collections of QTL, rather than null mutations in the leptin or leptin receptor genes, they are extremely relevant as models for the polygenic obesity/diabesity syndromes in humans.

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.

Role of genetics in osteoporosis

Osteoporosis is a disease characterized by fragile bones and high susceptibility to low-trauma fractures. It is a serious health problem, especially in elderly women. Bone mineral density (BMD) has been employed most commonly as the index for defining and studying osteoporosis. BMD has high genetic determination, with heritability ranging from 50 to 90%. Various gene-mapping approaches have been applied to identify specific genes underlying osteoporosis, largely using BMD as the study phenotype. We review here the genetic determination of osteoporosis as defined by BMD and discuss a fundamental issue we encounter in genetic research in osteoporosis: the choice of phenotype(s) to study. We briefly summarize and discuss advantages and disadvantages of various approaches used in genetic studies of osteoporosis. Finally, we review and discuss the current status for mapping and identification of genes for osteoporosis. We focus on linkage studies in humans and quantitative trait loci mapping in mice to supplement the already extensive reviews of association studies made by many investigators for candidate genes.

O futuro da epidemiologia genética de características complexas

A epidemiologia genética evoluiu de um enfoque em estudos sobre doenças mendelianas raras para a análise genética de características complexas. Com o advento de informações sobre a completa seqüência de genes ao longo do genoma humano e de outros organismos, o interesse da epidemiologia genética em desvendar a natureza dos fatores que influenciam essas características se tornou primordial. São apresentados os principais métodos empregados no estudo de doenças complexas bem como suas principais vantagens e desvantagens. Discute-se a importância na determinação da amostra e o uso de fenótipos e marcadores genéticos apropriados. Como exemplo das estratégias citadas tomamos o estudo de índice de massa corporal (BMI) para ilustrar um fator genético principal localizado no cromossomo 7. Em uma discussão sobre tendências no estudo de ligação, embora reconhecendo que famílias e genealogias continuarão sendo o foco principal das amostras, discute-se alguns novos e eficientes tipos de amostragem (como por exemplo, controles não-relacionados) em que amostras de conjunto de DNA serão universalmente empregadas. O reconhecimento da heterogeneidade genética entre estudos e sua interpretação será uma das mais importantes características no futuro das análises de características complexas.

Strategies for the Management of Patients with Obesity

The prevalence of overweight and obesity is increasing worldwide. During the last two decades, the prevalence of adults in the higher body mass index (BMI) categories in the US has increased the most, as much as 300% for those with a BMI above 40kg/m2. In children and adolescents, a doubling of the prevalence of severe overweight poses a serious health risk to future generations of young adults who may develop chronic diseases normally associated with aging. The simple definition of obesity, an imbalance between energy intake and energy expenditure, ignores the complexity of, and largely unknown interactions between, genes, food intake and physical activity, which together determine bodyweight and fat distribution. Although the etiology and manifestations of overweight and obesity are complex, the assessment of overweight and obesity requires only an accurate measurement of bodyweight, height and abdominal circumference, as well as a history and physical examination attuned to the morbidities that commonly accompany overweight and obesity such as diabetes mellitus, hypertension, dyslipidemia and sleep apnea. The treatment of patients with overweight and obesity continues to be based on changes to diet and physical activity. Simple behavior modification techniques are within the reach of busy clinicians. The additional use of available bodyweight reduction medications can reliably lead to a 5 to 10% reduction from initial bodyweight, a loss that has been shown to provide significant health benefit. The use of meal replacements has also been shown to be effective and is probably an under-appreciated treatment resource. Surgery is the most successful treatment for those with severe obesity and should be discussed as an option for those in the appropriate bodyweight categories. Because societal trends favor the greater intake of calorie-dense foods and less physical activity to accomplish the activities of daily life, the future of obesity treatment will require the development of bodyweight reduction medications that work by a variety of mechanisms to decrease food intake or increase energy expenditure. Such medications should not be viewed as a 'crutch' but rather as a 'helping hand' that enable people to better adhere to a healthier lifestyle.

Rat genetics: attaching physiology and pharmacology to the genome

During the past five years, the Rat Genome Project has been rapidly gaining momentum, especially since the announcement in August 2000 of plans to sequence the rat genome. Combined with the wealth of physiological and pharmacological data for the rat, the genome sequence should facilitate the discovery of mammalian genes that underlie the physiological pathways that are involved in disease. Most importantly, this combined physiological and genomic information should also lead to the development of better pre-clinical models of human disease, which will aid in the development of new therapeutics.