Genetic and behavioral determinants of waist-hip ratio and waist circumference in women twins

Relationship between amounts of daily cigarette consumption and abdominal obesity moderated by CYP2A6 genotypes in Chinese male current smokers

BACKGROUND

Cigarette smoking is an important risk factor for abdominal obesity. However, the degree to which the CYP2A6 genotype moderates the relationship between smoking and abdominal obesity has not been established.

PURPOSE

This study aims to investigate whether or not the relationship between smoking quantity and abdominal obesity is influenced by CYP2A6 genotypes.

METHODS

Nine hundred fifty-four male current smokers were selected. A venous specimen was collected to test serum cotinine and CYP2A6 genotype, and all smokers were divided into heavy (>15 cigarettes/day) and light smokers (≤15 cigarettes/day).

RESULTS

Heavy smoking increased the risk of abdominal obesity (odds ratio (OR) = 1.57; 95% CI, 1.13-2.19) compared with light smoking. Furthermore, heavy smoking had a positive interactive effect with CYP2A6 poor metabolizer genotype on abdominal obesity (OR = 3.90; 95% CI, 1.25-12.18). Moreover, CYP2A6 poor metabolizer genotypes were associated with slower nicotine metabolism.

CONCLUSIONS

Heavy smoking may increase the risk of abdominal obesity-particularly in smokers with CYP2A6 poor metabolizer genotypes.

Association between type 2 diabetes genetic susceptibility loci and visceral and subcutaneous fat area as determined by computed tomography

Visceral fat accumulation has an important role in the development of several metabolic disorders, such as type 2 diabetes, dyslipidemia and hypertension. New genetic loci that contribute to the development of type 2 diabetes have been identified by genome-wide association studies. To examine the association of type 2 diabetes susceptibility loci and visceral fat accumulation, we genotyped 1279 Japanese subjects (556 men and 723 women), who underwent computed tomography for measurements of visceral fat area (VFA) and subcutaneous fat area (SFA) for the following single-nucleotide polymorphisms (SNPs): NOTCH2 rs10923931, THADA rs7578597, PPARG rs1801282, ADAMTS9 rs4607103, IGF2BP2 rs1470579, VEGFA rs9472138, JAZF1 rs864745, CDKN2A/CDKN2B rs564398 and rs10811661, HHEX rs1111875 and rs5015480, TCF7L2 rs7901695, KCNQ1 rs2237892, KCNJ11 rs5215 and rs5219, EXT2 rs1113132, rs11037909, and rs3740878, MTNR1B rs10830963, DCD rs1153188, TSPAN8/LGR5 rs7961581, and FTO rs8050136 and rs9939609. None of the above SNPs were significantly associated with VFA. The FTO rs8050136 and rs9939609 risk alleles exhibited significant associations with body mass index (BMI; P=0.00088 and P=0.0010, respectively) and SFA (P=0.00013 and P=0.00017, respectively). No other SNPs were significantly associated with BMI or SFA. Our results suggest that two SNPs in the FTO gene are associated with subcutaneous fat accumulation. The contributions of other SNPs are inconclusive because of a limitation of the sample power.

Twins of Mistaken Zygosity (TOMZ): Evidence for Genetic Contributions to Dietary Patterns and Physiologic Traits

Twin designs, comparing correlations in monozygotic (MZ) versus dizygotic (DZ) twins, have an extensive history. One major confounder in such studies is that MZ twins may share postnatal environmental influences more so than do DZ twins. To avoid such confounding, twins separated at or soon after birth have been studied, but their scarcity often makes this approach impractical. Another method has been to measure the degree of contact twins have maintained over time, and adjust the observed correlations. Here, we remove confounding by utilizing the discrepancy between biological and self-perceived zygosity to separate environmental from genetic sources of twin similarity. We analyzed dietary patterns and physiologic traits in 350 female twin pairs of the 1988 Kaiser Permanente Twin Registry. Among twin pairs, 175 were MZ by self-report and genetic testing (MZC), 136 were DZ by self-report and genetic testing (DZC), 30 were MZ by genetic testing but not by self-report (MZW), and 9 were DZ by genetic testing but not by self-report (DZW) but were excluded due to small sample size. For healthy food patterns, MZC and MZW intraclass correlations were similar and greater than for DZC, yielding positive and significant heritability estimates. For unhealthy food patterns, the MZC, MZW and DZC correlations were similar with no significant heritability. For physiologic traits, MZC and MZW correlations were similar and higher than those for DZC, indicating significant heritability, except for insulin for which MZW and DZC were similar and which showed modest heritability. Twins of mistaken zygosity (TOMZ) provides a useful approach to robust determination of heritability.

MicroRNA expression in abdominal and gluteal adipose tissue is associated with mRNA expression levels and partly genetically driven

To understand how miRNAs contribute to the molecular phenotype of adipose tissues and related traits, we performed global miRNA expression profiling in subcutaneous abdominal and gluteal adipose tissue of 70 human subjects and characterised which miRNAs were differentially expressed between these tissues. We found that 12% of the miRNAs were significantly differentially expressed between abdominal and gluteal adipose tissue (FDR adjusted p<0.05) in the primary study, of which 59 replicated in a follow-up study of 40 additional subjects. Further, 14 miRNAs were found to be associated with metabolic syndrome case-control status in abdominal tissue and three of these replicated (primary study: FDR adjusted p<0.05, replication: p<0.05 and directionally consistent effect). Genome-wide genotyping was performed in the 70 subjects to enable miRNA expression quantitative trait loci (eQTL) analysis. Candidate miRNA eQTLs were followed-up in the additional 40 subjects and six significant, independent cis-located miRNA eQTLs (primary study: p<0.001; replication: p<0.05 and directionally consistent effect) were identified. Finally, global mRNA expression profiling was performed in both tissues to enable association analysis between miRNA and target mRNA expression levels. We find 22% miRNAs in abdominal and 9% miRNAs in gluteal adipose tissue with expression levels significantly associated with the expression of corresponding target mRNAs (FDR adjusted p<0.05). Taken together, our results indicate a clear difference in the miRNA molecular phenotypic profile of abdominal and gluteal adipose tissue, that the expressions of some miRNAs are influenced by cis-located genetic variants and that miRNAs are associated with expression levels of their predicted mRNA targets.

Genetic variations in the CYP17A1 and NT5C2 genes are associated with a reduction in visceral and subcutaneous fat areas in Japanese women

Visceral fat accumulation has an important role in increasing the morbidity and mortality rates, by increasing the risk of developing several metabolic disorders, such as type 2 diabetes, dyslipidemia and hypertension. New genetic loci that are associated with increased systolic and diastolic blood pressures have been identified by genome-wide association studies in Caucasian populations. This study investigates whether single nucleotide polymorphisms (SNPs) that confer susceptibility to high blood pressure are also associated with visceral fat obesity. We genotyped 1279 Japanese subjects (556 men and 723 women) who underwent computed tomography for measuring the visceral fat area (VFA) and subcutaneous fat area (SFA) at the following SNPs: FGF5 rs16998073, CACNB2 rs11014166, C10orf107 rs1530440, CYP17A1 rs1004467, NT5C2 rs11191548, PLEKHA7 rs381815, ATP2B1 rs2681472 and rs2681492, ARID3B rs6495112, CSK rs1378942, PLCD3 rs12946454, and ZNF652 rs16948048. In an additive model, risk alleles of the CYP17A1 rs1004467 and NT5C2 rs11191548 were found to be significantly associated with reduced SFA (P=0.00011 and 0.0016, respectively). When the analysis was performed separately in men and women, significant associations of rs1004467 (additive model) and rs11191548 (recessive model) with reduced VFA (P=0.0018 and 0.0022, respectively) and SFA (P=0.00039 and 0.00059, respectively) were observed in women, but not in men. Our results suggest that polymorphisms in the CYP17A1 and NT5C2 genes influence a reduction in both visceral and subcutaneous fat mass in Japanese women.

Genetics and epigenetics of obesity

Obesity results from interactions between environmental and genetic factors. Despite a relatively high heritability of common, non-syndromic obesity (40-70%), the search for genetic variants contributing to susceptibility has been a challenging task. Genome wide association (GWA) studies have dramatically changed the pace of detection of common genetic susceptibility variants. To date, more than 40 genetic variants have been associated with obesity and fat distribution. However, since these variants do not fully explain the heritability of obesity, other forms of variation, such as epigenetics marks, must be considered. Epigenetic marks, or "imprinting", affect gene expression without actually changing the DNA sequence. Failures in imprinting are known to cause extreme forms of obesity (e.g. Prader-Willi syndrome), but have also been convincingly associated with susceptibility to obesity. Furthermore, environmental exposures during critical developmental periods can affect the profile of epigenetic marks and result in obesity. We review the most recent evidence for genetic and epigenetic mechanisms involved in the susceptibility and development of obesity. Only a comprehensive understanding of the underlying genetic and epigenetic mechanisms, and the metabolic processes they govern, will allow us to manage, and eventually prevent, obesity.

The genetics of obesity

Obesity is a result of excess body fat accumulation. This excess is associated with adverse health effects such as CVD, type 2 diabetes, and cancer. The development of obesity has an evident environmental contribution, but as shown by heritability estimates of 40% to 70%, a genetic susceptibility component is also needed. Progress in understanding the etiology has been slow, with findings largely restricted to monogenic, severe forms of obesity. However, technological and analytical advances have enabled detection of more than 20 obesity susceptibility loci. These contain genes suggested to be involved in the regulation of food intake through action in the central nervous system as well as in adipocyte function. These results provide plausible biological pathways that may, in the future, be targeted as part of treatment or prevention strategies. Although the proportion of heritability explained by these genes is small, their detection heralds a new phase in understanding the etiology of common obesity.

Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution

Waist-hip ratio (WHR) is a measure of body fat distribution and a predictor of metabolic consequences independent of overall adiposity. WHR is heritable, but few genetic variants influencing this trait have been identified. We conducted a meta-analysis of 32 genome-wide association studies for WHR adjusted for body mass index (comprising up to 77,167 participants), following up 16 loci in an additional 29 studies (comprising up to 113,636 subjects). We identified 13 new loci in or near RSPO3, VEGFA, TBX15-WARS2, NFE2L3, GRB14, DNM3-PIGC, ITPR2-SSPN, LY86, HOXC13, ADAMTS9, ZNRF3-KREMEN1, NISCH-STAB1 and CPEB4 (P = 1.9 × 10⁻⁹ to P = 1.8 × 10⁻⁴⁰) and the known signal at LYPLAL1. Seven of these loci exhibited marked sexual dimorphism, all with a stronger effect on WHR in women than men (P for sex difference = 1.9 × 10⁻³ to P = 1.2 × 10⁻¹³). These findings provide evidence for multiple loci that modulate body fat distribution independent of overall adiposity and reveal strong gene-by-sex interactions.

CCAAT/enhancer binding protein alpha, beta and delta gene variants: associations with obesity related phenotypes in the Leeds Family Study

OBJECTIVE

To identify novel polymorphisms in the genes encoding the transcription factors CCAAT/enhancer binding protein alpha, beta and delta ( CEBPA, CEBPB, CEBPD) and investigate associations between polymorphisms and obesity-related phenotypes.

METHODS

Denaturing high-performance liquid chromatography (HPLC) was used to screen for novel gene variants and polymorphisms were genotyped in stored DNA from participants of the Leeds Family Study (537 subjects from 89 families). Genotype and haplotype analyses were carried out in STATA and PBAT, respectively.

RESULTS

Twenty-five polymorphisms were identified; 11 in CEBPA, 12 in CEBPB and 2 in CEBPD. Several allelic variants were associated at a nominal 5% level with waist-to-hip ratio (-919G>A in CEBPA, -412G>T and 646C>T in CEBPB), leptin (1558G>A in CEBPA, -1051A>G and 1383T>- in CEBPB) and adiponectin (1382G>T and 1903G>T in CEBPB). Effects of CEBPA and CEBPB allelic variants were independent, but variants within each gene were in linkage disequilibrium. Several associations were observed between other obesity-related traits and allelic variants in CEBPA and CEBPB, but not CEBPD.

CONCLUSION

These findings suggest that common allelic variants in CEBPA and CEBPB could influence abdominal obesity and related metabolic abnormalities associated with type 2 diabetes and cardiovascular disease in healthy White Northern European families, although results require independent confirmation.

The impact of a population-based multi-factorial lifestyle intervention on alcohol intake: the Inter99 study

PURPOSE

To investigate the effect of screening and five years of multi-factorial lifestyle intervention on changes in alcohol intake in a general population.

METHODS

The study was a pre-randomized intervention study on lifestyle, Inter99 (1999-2006), Copenhagen, Denmark. Participants in the intervention group (n=6 091) had at baseline a medical health examination and a face-to-face lifestyle counselling. Individuals at high risk of ischemic heart disease were repeatedly offered both individual and group-based counselling. The control group (n=3 324) was followed by questionnaires. Alcohol intake was measured by questionnaires. Changes were analysed by multilevel analyses.

RESULTS

Binge drinking decreased both in men and women at three and five-year follow-ups (men: five-year: net-change:-0.13; p=0.03; women: five-year: net-change:-0.08; p=0.04). Furthermore, in women the ratio between wine and total alcohol was increased compared with the control group at five-year follow-up (net-change: 0.04; p<0.01). In men with a high intake of alcohol (>21 drinks per week) the effect on total alcohol intake was maintained at five-year follow-up (net-change: -3.7; p=0.01). No significant effects were found in women on total alcohol intake.

CONCLUSION

Multi-factorial lifestyle intervention, including low intensity alcohol intervention, improved long-term alcohol habits in a general population.

Genome-wide association scan meta-analysis identifies three Loci influencing adiposity and fat distribution

To identify genetic loci influencing central obesity and fat distribution, we performed a meta-analysis of 16 genome-wide association studies (GWAS, N = 38,580) informative for adult waist circumference (WC) and waist-hip ratio (WHR). We selected 26 SNPs for follow-up, for which the evidence of association with measures of central adiposity (WC and/or WHR) was strong and disproportionate to that for overall adiposity or height. Follow-up studies in a maximum of 70,689 individuals identified two loci strongly associated with measures of central adiposity; these map near TFAP2B (WC, P = 1.9x10(-11)) and MSRA (WC, P = 8.9x10(-9)). A third locus, near LYPLAL1, was associated with WHR in women only (P = 2.6x10(-8)). The variants near TFAP2B appear to influence central adiposity through an effect on overall obesity/fat-mass, whereas LYPLAL1 displays a strong female-only association with fat distribution. By focusing on anthropometric measures of central obesity and fat distribution, we have identified three loci implicated in the regulation of human adiposity.

Raised adolescent body mass index predicts the development of adiposity and a central distribution of body fat in adulthood: a longitudinal study

OBJECTIVE

To test the hypothesis that adolescent body mass index (BMI) tracks into adulthood and can be used as a predictor of obesity and/or central adiposity in adulthood.

METHOD

A prospective cohort study following up 111 female and 84 male subjects who participated in dietary and anthropometric surveys when aged 12 years (in 1979-1981) and 33 years (in 2000-2001). At both time points, height and weight were measured and BMI calculated. At 33 years, waist circumference (WC) and hip circumference were also measured and waist-to-hip ratio (WHR) calculated.

RESULTS

In the male and female participants, BMI at 12 years was associated significantly with BMI at 33 years (R = 0.58 and 0.53, respectively, both p < 0.01) and WC at 33 years (R = 0.58 and 0.53, both p < 0.01). The probability of being an obese adult increased with rising adolescent BMI: normal weight male (BMI < 20.89 kg/m(2)) and female subjects (BMI < 21.20 kg/m(2)) at 12 years had a 20% and a 7% chance of being obese at 33 years, respectively; the probabilities for obese male (BMI > or =25.58 kg/m(2)) and female subjects (BMI > or =26.05 kg/m(2)) were 83 and 64%. The corresponding probability of becoming centrally obese (measured by WC) increased from 17 and 16% in male and female subjects of a normal weight to 58 and 59% in those being obese.

CONCLUSIONS

Adolescent BMI is a good predictor of adult BMI and WC and the likelihood of becoming obese and/or centrally obese in adulthood.

Role of shared genetic and environmental factors in symptoms of depression and body composition

BACKGROUND

Both obesity and lean mass have been correlated with symptoms of depression.

OBJECTIVE

To investigate the contribution of genetic and environmental factors in the co-occurrence of obesity and lean mass with symptoms of depression.

METHODS

Individuals were 2383 participants of the Erasmus Rucphen Family study. Symptoms of depression were assessed using the Center for Epidemiologic Studies Depression Scale and the Hospital Anxiety and Depression Scale. Anthropometric and dual-energy X-ray absorptiometry total body scans were obtained for the assessment of body composition. The role of shared genetic and shared environmental factors was quantified by estimating genetic and environmental correlations between symptoms of depression and measures of body composition.

RESULTS

Phenotypic correlations between body composition and symptoms of depression ranged from -0.08 to 0.08. Heritability estimates for body composition ranged from 0.40 to 0.46 (P<0.001) in women and from 0.35 to 0.51 (P<0.001) in men, and heritability estimates for depression scores were higher in women (0.34 and 0.37) than in men (0.13 and 0.21). No consistent genetic correlations between measures of body composition and symptoms of depression were found. We did find a significant consistent environmental correlation between depression scores and lean mass index (environmental correlation=-0.23 for Center for Epidemiologic Studies Depression Scale and -0.31 for Hospital Anxiety and Depression Scale).

CONCLUSION

In our study, there is no evidence that the co-occurrence of symptoms of depression and body composition result from a common genetic pathway.

Genetic and environmental influences on factors associated with cardiovascular disease and the metabolic syndrome

The relative influence of genetics and the environment on factors associated with cardiovascular disease (CVD) and metabolic syndrome (MetS) remains unclear. We performed model-fitting analyses to quantify genetic, common environmental, and unique environmental variance components of factors associated with CVD and MetS [waist circumference, blood pressure, fasting plasma glucose and insulin, homeostatic model assessment of insulin resistance (HOMA-IR), and fasting plasma lipids] in adult male and female monozygotic twins reared apart or together. We also investigated whether MetS components share common influences. Plasma cholesterol and triglyceride concentrations were highly heritable (56-77%, statistically significant). Waist circumference, plasma glucose and insulin, HOMA-IR, and blood pressure were moderately heritable (43-57%, statistically significant). Unique environmental factors contributed to the variance of all variables (20-38%, perforce statistically significant). Common environmental factors contributed 23, 30, and 42% (statistically significant) of the variance of waist circumference, systolic blood pressure, and plasma glucose, respectively. Two shared factors influenced MetS components; one influenced all components except HDL cholesterol, another influenced only lipid (triglyceride and HDL cholesterol) concentrations. These results suggest that genetic variance has a dominant influence on total variance of factors associated with CVD and MetS and support the proposal of one or more underlying pathologies of MetS.

Considerations regarding the genetics of obesity

The genetics of human body fat content (obesity) are clearly complex. Genetic and physiological analysis of rodents have helped enormously in pointing to critical molecules and cells in central nervous system and "peripheral" pathways mediating the requisite fine control over the defense of body fat. Human and animal studies are consistent with inferences from evolutionary considerations that the strengths of defenses against fat loss are greater than those against gain. Many of the genes participating in these pathways have reciprocal effects on both energy intake and expenditure, though different genes may have primary roles in respective responses to weight gain or loss. Such distinctions have important consequences for both research and treatment strategies. The body mass index (BMI) is a useful gross indicator of adiposity, but more refined measurements of body composition and energy homeostasis will be required to understand the functional consequences of allelic variation in genes of interest. Phenotypes related to energy intake and expenditure-which clearly are the major determinants of net adipose tissue storage-are not salient when individuals are in energy balance (weight stable); measurements obtained during weight perturbation studies are likely to provide more revealing phenotypes for genetic analysis. The advent of high-density genome-wide scans in large numbers of human subjects for association analysis will revolutionize the study of the genetics of complex traits such as obesity by generating substantial numbers of powerful linkage signals from smaller genetic intervals. Many of the genes implicated will not have been previously related to energy homeostasis (e.g., recent experience with FTO/FTM as described below), and will have relatively small effects on the associated phenotype(s). The mouse will again prove useful in determining the relevant physiology of these new genes. New analytic tools will have to be developed to permit the necessary analysis of the gene x gene interactions that must ultimately convey aggregate genetic effects on adiposity.

[Obesity and risk factors for the development of chronic non-transmissible diseases among consumers in a foodservice unit]

This study aimed to assess nutritional status and risk factors for chronic non-transmissible diseases in 1,252 factory employees in Santa Catarina State, Brazil. The following variables were studied: nutritional status, waist circumference, blood pressure, blood glucose levels, age, and schooling. Overweight and obesity were observed in 45% and 10% of the sample, respectively, with a significant association between nutritional status and gender, but not between nutritional status and schooling, adjusted for age. The proportion of high waist circumference was 33%, with a significant difference between genders. High systolic blood pressure (SBP) and diastolic blood pressure (DBP) were present in 18% and 11% of the employees, respectively, with a significant association between genders after adjusting for age. Type II diabetes mellitus was diagnosed in 2% of the sample and altered glucose levels in 4%. After adjusting for age, the only variables significantly associated with waist circumference were SBP and DPB. The results allowed the implementation of preventive and educational activities to improve employees' quality of life and productivity.

Anthropometry, carbohydrate and lipid metabolism in the East Flanders Prospective Twin Survey: heritabilities

AIMS/HYPOTHESIS

We determined the genetic contribution of 18 anthropometric and metabolic risk factors of type 2 diabetes using a young healthy twin population.

METHODS

Traits were measured in 240 monozygotic (MZ) and 138 dizygotic (DZ) twin pairs aged 18 to 34 years. Twins were recruited from the Belgian population-based East Flanders Prospective Twin Survey, which is characterised by its accurate zygosity determination and extensive collection of perinatal and placental data, including information on chorionicity. Heritability was estimated using structural equation modelling implemented in the Mx software package.

RESULTS

Intra-pair correlations of the anthropometric and metabolic characteristics did not differ between MZ monochorionic and MZ dichorionic pairs; consequently heritabilities were estimated using the classical twin approach. For body mass, BMI and fat mass, quantitative sex differences were observed; genetic variance explained 84, 85 and 81% of the total variation in men and 74, 75 and 70% in women, respectively. Heritability estimates of the waist-to-hip ratio, sum of four skinfold thicknesses and lean body mass were 70, 74 and 81%, respectively. The heritability estimates of fasting glucose, fasting insulin, homeostasis model assessment of insulin resistance and beta cell function, as well as insulin-like growth factor binding protein-1 levels were 67, 49, 48, 62 and 47%, in that order. Finally, for total cholesterol, LDL-cholesterol, HDL-cholesterol, total cholesterol:HDL-cholesterol ratio, triacylglycerol, NEFA and leptin levels, genetic factors explained 75, 78, 76, 79, 58, 37 and 53% of the total variation, respectively.

CONCLUSIONS/INTERPRETATION

Genetic factors explain the greater part of the variation in traits related to obesity, glucose intolerance/insulin resistance and dyslipidaemia.

Adult weight gain and central obesity in women with and without a family history of breast cancer: a case control study

Adult weight gain and central obesity can increase breast cancer risk. We determined the prevalence of adult weight gain and central obesity amongst women with a family history (FH) as compared to women with a population risk to determine whether adiposity could contribute to their increased risk. Adult weight gain, waist and waist:hip ratio (WHR) were determined amongst 475 women (aged 20-60 years) attending a regional FH breast cancer risk clinic, compared to 312 age matched women at population risk. Patterns of adult weight gain did not differ between women with and without a FH of breast cancer. The majority of weight gain occurred between the ages of 20 and 40 in both groups. Mean (sd) weight gain for women aged >40 years with a FH was 8.9 (10.3) kg compared to 9.1 (10.6) kg for controls (p = 0.85). Women with a FH had a significantly greater waist and WHR than controls. Mean (sd) waist was 83.7 (13) cm compared to 81.6 (11.3) cm for controls (p < 0.01). Mean (sd) WHR was 0.82 (0.1) compared to 0.80 (0.1) for controls (p < 0.01). FH of breast cancer was an independent predictor of having a WHR of >0.85; odds ratio (95% CI) = 1.42 (1.01-2.01) (p = 0.044). Significant weight gain between the ages of 20 and 40 and the prevalence of central obesity amongst FH women suggest the need for weight management within FH clinics.

Linkage and potential association of obesity-related phenotypes with two genes on chromosome 12q24 in a female dizygous twin cohort

Obesity is a multifactorial disorder with a complex phenotype. It is a significant risk factor for diabetes and hypertension. We assessed obesity-related traits in a large cohort of twins and performed a genome-wide linkage scan and positional candidate analysis to identify genes that play a role in regulating fat mass and distribution in women. Dizygous female twin pairs from 1,094 pedigrees were studied (mean age 47.0+/-11.5 years (range 18-79 years)). Nonparametric multipoint linkage analyses showed linkage for central fat mass to 12q24 (141 cM) with LOD 2.2 and body mass index to 8q11 (67 cM) with LOD 1.3, supporting previously established linkage data. Novel areas of suggestive linkage were for total fat percentage at 6q12 (LOD 2.4) and for total lean mass at 2q37 (LOD 2.4). Data from follow-up fine mapping in an expanded cohort of 1243 twin pairs reinforced the linkage for central fat mass to 12q24 (LOD 2.6; 143 cM) and narrowed the -1 LOD support interval to 22 cM. In all, 45 single-nucleotide polymorphisms (SNPs) from 26 positional candidate genes within the 12q24 interval were then tested for association in a cohort of 1102 twins. Single-point Monks-Kaplan analysis provided evidence of association between central fat mass and SNPs in two genes - PLA2G1B (P = 0.0067) and P2RX4 (P = 0.017). These data provide replication and refinement of the 12q24 obesity locus and suggest that genes involved in phospholipase and purinoreceptor pathways may regulate fat accumulation and distribution.

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.

Twin study of genetic and environmental influences on adult body size, shape, and composition

OBJECTIVE

To investigate the genetic and environmental influences on adult body size, shape, and composition in women and men, and to assess the impact of age.

MATERIALS AND METHODS

In this cross-sectional study of 325 female and 299 male like-sex healthy twin pairs, on average 38 y old (18-67 y), we determined zygosity by DNA similarity, and performed anthropometry and bioelectrical impedance analysis of body composition. The contribution to the total phenotypic variance of genetic, common environment, and individual environment was estimated in multivariate analysis using the FISHER program. Further, these variance components were analysed as linear functions of age.

RESULTS

In both women and men genetic contributions were significant for all phenotypes. Heritability for body mass index was 0.58 and 0.63; for body fat%, 0.59 and 0.63; for total skinfolds, 0.61 and 0.65; for extremity skinfolds 0.65 and 0.62; for truncal skinfolds, 0.50 and 0.69; for suprailiac skinfolds, 0.49 and 0.48; for waist circumference, 0.48 and 0.61; for hip, 0.52 and 0.58; for lean body mass/height2, 0.61 and 0.56; and for height, 0.81 and 0.69, respectively. There was no strong evidence of common environmental effects under the assumptions of no nonadditive effect. The pattern of age trends was inconsistent. However, when significant there was a decrease in heritability with advancing age.

DISCUSSION

These findings suggest that adult body size, shape, and composition are highly heritable in both women and men, although a decreasing tendency is seen with advancing age.

Central and total obesity in middle aged men and women in relation to lifetime socioeconomic status: evidence from a national birth cohort

STUDY OBJECTIVE

To investigate the influence of social class in childhood, young adulthood and middle age, and intergenerational mobility, on adult central and total obesity.

DESIGN

Prospective, population based, birth cohort study.

PARTICIPANTS AND SETTING

1472 men and 1563 women born in 1946 in England, Scotland, and Wales.

OUTCOME MEASURES

Waist-hip ratio, waist-height ratio, waist circumference, and body mass index at age 53 years.

MAIN RESULTS

Father's social class at participant's age 4 years was inversely associated with adult central and total obesity at age 53 years in men and women. For example, the mean difference of waist-hip ratio (95% confidence intervals) between father's professional social class I and unskilled manual social class V was 2.6% (0.7 to 4.6) for men and 2.5% (0.5 to 4.4) for women. The effect of father's social class remained after adjustment for participant's own social class in young adulthood and middle age. Both adult social classes were inversely related to obesity among women, but not men, after adjustment for childhood circumstances. Upwardly mobile men and women were less obese than participants remaining in their father's social class and their levels of obesity tended to be between the class they left and the class they joined.

CONCLUSIONS

The effect of social class on adult obesity differed according to the stage in the life course at which social class was measured, and gender. Childhood circumstances had enduring influences on adult obesity, although our results on intergenerational mobility indicate potential reversibility of early life disadvantage.

Alcohol drinking patterns differentially affect central adiposity as measured by abdominal height in women and men

Alcohol drinking in light-to-moderate amounts has been associated with reduced coronary heart disease (CHD) risk. However, there is evidence that the way people consume alcohol (drinking pattern) may affect risk. Central adiposity, a known CHD risk factor may be one mechanism in the pathway between alcohol consumption and CHD risk. Our study examined whether various drinking patterns differentially affect fat distribution, particularly abdominal fat in women and men. In a randomly selected population-based cohort (n = 2343), 35-79 y old, we assessed drinking pattern as reported for the past 30 d, including beverage type and amount, frequency of consumption, percentage of time drinking while eating and number of drinks consumed/drinking day. Central adiposity was determined using an abdominal caliper to measure supine height of the abdomen. Current drinkers tended to have smaller abdominal heights than nondrinkers (women, P < 0.0001; men, P = 0.0559). For drinking pattern, frequency was inversely associated, but drinking intensity (drinks/drinking day) was positively associated with central adiposity in women (P trend for frequency, 0.0007; intensity, 0.0010) and men (P trend for frequency, 0.0005; intensity, 0.0004), even when age, education, physical activity, smoking status and amount of alcohol (g) were included in the models. When frequency and intensity were considered together, daily drinkers of <1 drink/drinking day had the smallest mean abdominal height measures with the largest measures in less than weekly drinkers who consumed 4 or more drinks/drinking day. These results support the hypothesis that drinking pattern affects the distribution of body fat, an important CHD risk factor.

Genetic and environmental influences on body-fat measures among African-American twins

OBJECTIVE

To investigate the genetic and environmental influences on body-fat measures including waist circumference (WC), waist-to-hip ratio (WHR), and body mass index (BMI) among African-American men and women.

RESEARCH METHODS AND PROCEDURES

Measurements were taken as part of the Carolina African American Twin Study of Aging. This sample currently comprises 146 same-sex African-American twins with an average age of 50 years (range, 22 to 88 years). This analysis included 26 monozygotic and 29 dizygotic men and 45 monozygotic and 46 dizygotic women. Maximum likelihood quantitative genetic analysis was used.

RESULTS

In men, additive genetic effects accounted for 77% of the variance in WC, 59% in WHR, and 89% in BMI. In women, additive genetic effects accounted for 76% of the variance in WC, 56% in WHR, and 73% in BMI. The remaining variance in both men and women was attributed to unique environmental effects (WC, 21%; WHR, 36%; BMI, 11% in men and WC, 22%; WHR, 38%; BMI, 27% in women) and age (WC, 2%; WHR, 5% in men and WC, 2%; WHR, 6% in women). When BMI was controlled in the analysis of WC and WHR, it accounted for a portion of the genetic and environmental variance in WHR and over one-half of the genetic and environmental variance in WC.

DISCUSSION

There are both genetic and environmental influences on WC, WHR, and BMI, and independent of BMI, there are genetic and environmental effects on WC and WHR among both genders. The results from this African-American twin sample are similar to findings among white twin samples.

[Waist-to-hip ratio and dietary factors in adults]

OBJECTIVES

To assess the association between diet factors and abdominal fat accumulation.

METHODS

A household survey carried out in the city of Rio de Janeiro during 1995-1996. The usual diet of a sample of 2,441 individuals (42.8% men and 57.2% women), aged 20 to 60 years, was investigated using a food frequency questionnaire and data about height, weight, waist and hip perimeter was collected. The cut-off points for inadequate waist-to-hip ratio (WHR) for men and women were 0.95 and 0.80, respectively.

RESULTS

Inadequate WHR was positively associated with age, cigarette smoking, body mass index, and inversely associated with education level, income and leisure physical activity in both men and women (p<0.05). Inadequate WHR was not associated with lipids, carbohydrates and total fiber intake. Positive association was found with inadequate WHR and spirits consumption among menopause women (p<0.001), and the consumption of four or more glasses of beer per day in men (p<0.001).

CONCLUSION

In agreement with other studies, alcohol intake was associated with abdominal fat accumulation.

Segregation analysis of waist circumference, hip circumference and waist-to-hip ratio in the Korean Nationwide Family Study

AIM

A central distribution of adipose tissue is frequently associated with cardiovascular disease and its risk factors. In this study, we investigated environmental, familial and genetic influences on waist circumference (WC), hip circumference (HC) and waist-to-hip ratio (WHR) in 2507 members of 435 families who had participated in the Korean Nationwide Health Examination Survey.

METHOD

Maximum likelihood methods were used to fit several genetic and nongenetic models of inheritance to these data to determine whether an unobserved Mendelian major gene could explain the familial distribution of WC, HC and WHR. Adjustments for age, age(2), body mass index, smoking, alcohol consumption and exercise were carried out separately for males and females by multiple regression procedures for WC, HC and WHR phenotypes prior to segregation analysis. Regression models were used to test genetic and non-genetic models in these 435 families.

RESULTS

Segregation analysis did not provide statistical evidence of a major gene controlling either HC or WHR. Mendelian single-locus models with two underlying genotypic distributions were best supported by these data on WC, and this putative major gene explained the 22.4% of variance in adjusted WC.

CONCLUSION

Future linkage studies may be worthwhile to further clarify the mechanisms controlling WC.

Physical activity and energy intake selectively predict the waist-to-hip ratio in men but not in women

BACKGROUND

The waist-to-hip ratio (WHR) has emerged as an important risk factor for several chronic diseases, but little quantitative information exists about its relation with energy intake and expenditure in men and women.

OBJECTIVE

We examined the relative role of energy intake and physical activity as determinants of WHRs in men and women, after adjustment for body mass index (BMI) and other likely confounding factors.

DESIGN

In the context of the European Prospective Investigation into Cancer and Nutrition (EPIC), 16433 women and 11520 men aged 30-82 y, apparently healthy and from all over Greece, were examined between 1994 and 1999. Anthropometric measurements were taken, a validated semiquantitative food-frequency questionnaire was administered, and time-weighted occupational and leisure activities were assessed. The WHR was regressed, separately for men and women, on energy intake and energy expenditure after age and BMI were controlled for.

RESULTS

Results for women and men differed. In women, neither energy intake nor energy expenditure was associated with the WHR in any way other than that mediated through BMI. In contrast, in men, higher energy intakes and higher energy expenditures were associated significantly, and largely independently of BMI, with higher and lower WHRs, respectively.

CONCLUSIONS

Because the WHR is an important predictor of several cardiovascular and other chronic diseases, documentation of a strong effect of physical activity on the WHR selectively in men may provide a partial explanation of how the effect of physical activity is mediated and why physical activity is more effective in men than in women in reducing disease risk.

Human obesity: an evolutionary approach to understanding our bulging waistline

The unique worldwide spread of the human species and the remarkably long post-reproductive survival show that our genome permits excellent adaptation to vastly different environments. Moreover, the main scourges of later age, namely malignant growths and atherosclerosis, appear in humans later than in shorter-living animals. In recent years, excess weight and obesity have become mass phenomena with a pronounced upward trend in all developed countries. However, despite the detrimental effects of being overweight, these populations live longer than ever, which in part may be explained by the availability of better medical treatment. The prevalence and predicted further spread of obesity can be understood in the light of evolution. In all animal species energy metabolism is asymmetric with energy accumulation ('thrifty genotype') being the necessary condition of survival during hard times. For humans, which are no different to other animals in this respect, this genetic programming was necessary for survival because during the course of history, including the recorded history in the more developed Middle East, Europe or China, there was never a long period of uninterrupted food abundance, whereas famines were regular and frequent. Therefore fat accumulation, when food was available, meant survival at times of shortage, while the possible detrimental effects of overindulgence in food and being overweight expressed in unrealistically old age were irrelevant. It is the central, mostly intra-abdominal fat (in both humans and animals) that is more medically important than the subcutaneous truncal fat, and the accumulation of both types of fat is conditioned by high food consumption; therefore it is a historic novelty for human populations. In contrast, lower-body fat in human females is unique in the animal kingdom: it is much less metabolically active, it is of much lower pathologic significance than central fat, and it is programmed to be mobilized mostly during pregnancy and lactation. In view of all this, norms of desired weight should be based on hard mortality and morbidity statistics and not on theoretical, esthetic or fashion considerations. By this criterion, the upper limit of desirable weight is likely to be body mass index (BMI) 27 or 28, but specified for different populations (sex, race, ethnic origin); moreover, with aging, the detrimental effects of obesity diminish and finally disappear. Risks of other pathologies related to obesity (e.g. diabetes, hypertension and coronary disease) are also population-specific. However, total fatness, measured by BMI, is insufficiently sensitive as a risk factor, and fat distribution (upper-body versus low-body type, as reflected by waist circumference and waist:hip ratio) plays at least as prominent a role. Therefore the detailed norms, not yet available, should take into account both general obesity and fat distribution and be specific for different populations. Since long-term weight loss in adults is rarely achievable, public health measures should be aggressively directed at the prevention of obesity from childhood.

[Factors associated with abdominal obesity among childbearing-age women]

OBJECTIVE

To investigate variables potentially associated with abdominal obesity among childbearing-age women.

METHODS

A total of 781 women were studied based on data from the Nutrition and Health Survey conducted in 1996 in the municipality of Rio de Janeiro, Brazil. Abdominal obesity was defined as waist girth (WG) > 80 cm or waist:hips girth ratio (WHR) > 0.85. Statistical analysis involved calculation of central trend measures. Calculating the odds ratio using multivariate logistic regression tested the association between abdominal obesity and BMI, age, parity, and tobacco use.

RESULTS

The highest frequencies of abdominal obesity were observed in women over 35 years of age and those with two or more children (50.7%). OR showed the effect of interaction between parity and age for WG>80 cm when only the effect of these two variables was controlled. Based on the logistic regression models, the study showed that when the population was categorized into women with and without overweight, schooling was the only factor associated with WHR, while the association with age and parity disappeared for WG>80 cm.

CONCLUSIONS

Abdominal obesity in this population group is independent of age and parity when adjusted by relative weight, with overall adiposity and schooling as the greatest determinant. Having more schooling meant having a smaller WHR. It is crucial to implement strategies to prevent the development of obesity in childbearing-age women.

Familial aggregation of central obesity in Southern Indians

BACKGROUND

High prevalence of diabetes in South Asians is associated with a pronounced tendency to abdominal obesity. This intermediate quantitative trait may be more amenable than type 2 diabetes to genetic linkage studies.

OBJECTIVES

To derive a measure of central obesity independent of total adiposity and adjusted for factors under environmental influence, and to estimate the genetic contribution to familial aggregation of this trait.

SUBJECTS AND METHODS

A total of 1,295 individuals from 300 families were studied in a community-based cross-sectional study in Chennai, India. Central fat was measured using sagittal abdominal diameter, and adjusted for age, BMI and body fat percentage measured by impedance. Intra-sibship correlations were calculated for adjusted sagittal abdominal diameter and a comparison variable, adjusted body fat percentage.

RESULTS

Among individuals free of diabetes, intra-sibship correlations were 0.48 for adjusted sagittal abdominal diameter and 0.14 for adjusted body fat percentage.

CONCLUSIONS

Even after adjustment for possible assortative mating, these results are consistent with a heritability exceeding 90% for a trait defined as abdominal fat accumulation adjusted for total adiposity, sex and age. Linkage studies of abdominal obesity that map one or more of the genes underlying this high heritability are therefore a possible route to identifying genes for type 2 diabetes in South Asians.

Major gene effect on subcutaneous fat distribution in a sedentary population and its response to exercise training: The HERITAGE Family Study

Complex segregation analysis of baseline subcutaneous fat distribution and the change in response to exercise training (post-training minus baseline indices) was performed in a sample of 482 individuals from 99 Caucasian families who participated in the HERITAGE Family Study. The sum of skinfold (SF) thicknesses at eight sites, and the waist and hip circumferences were measured at baseline and after completing a 20-week exercise training program. The trunk-to-extremity ratio (TER) was calculated by dividing the sum of skinfold thicknesses at four trunk sites (subscapular + suprailiac + abdominal + midaxillary) by the sum of skinfold thicknesses at four extremity sites (triceps + biceps + medial calf + thigh). While SF was used to assess total subcutaneous adiposity, TER and the ratio of the waist-to-hip circumferences (WHR) were used to characterize subcutaneous fat distribution. Baseline TER and WHR were age-adjusted and age-SF-adjusted within four sex-by-generation groups. The changes of SF, TER, and WHR in response to training were adjusted for age effects alone and for the effects of age and baseline values. Baseline SF was influenced by a multifactorial component (30%) plus a major effect that may be environmental in origin accounting for 47% of the variance. Baseline TER was influenced by a multifactorial component (18%) and a major codominant gene (q(2) = 0.10), which accounted for 56% of the variance. The major gene effect was independent of total subcutaneous adiposity. Baseline WHR was regulated by a major codominant gene (q(2) = 0.15), which accounted for 48% of the variance. However, this major gene effect for baseline WHR should be interpreted with caution, given the estimates of the tau's under the general model. No familial effect was found for the changes in response to training for these subcutaneous adiposity and fat distribution phenotypes. Am. J. Hum. Biol. 12:600-609, 2000. Copyright 2000 Wiley-Liss, Inc.

Inheritance of the waist-to-hip ratio in the National Heart, Lung, and Blood Institute Family Heart Study

OBJECTIVE

Considering that waist-to-hip ratio (WHR) is a simple anthropometric measure of obesity and is a better predictor of coronary heart disease than body mass index (BMI), the genetic underpinnings of WHR are of interest. The inheritance pattern of WHR, before and after adjustment for BMI (WHR-BMI), was investigated in 2713 individuals from 1038 nuclear families in the National Heart, Lung, and Blood Institute Family Heart Study (NHLBI-FHS).

RESEARCH METHODS AND PROCEDURES

Waist and hip measurements were taken twice, and the means of the measurements were used to calculate the WHR. Adjustments for age were carried out separately by sex, using stepwise multiple regression procedures for WHR and WHR-BMI phenotypes. Segregation analysis was applied using the unified model as implemented in the computer program POINTER.

RESULTS

For age-adjusted WHR, the segregation results suggested an additive major gene that accounts for 35% of the phenotypic variance, and approximately 30% of the sample are homozygous for the "high" genotype. The results for age- and BMI-adjusted WHR were also compatible with a major gene; however, the multifactorial model provided the most parsimonious fit to the data.

DISCUSSION

Although the genetic mechanisms for several obesity traits have been studied, tests of Mendelian segregation on this simple anthropometric measure (WHR) have not been reported previously. This study provides evidence for the presence of a major gene for age-adjusted WHR, suggesting that it is an appropriate trait for further genetic analysis, especially because it has strong predictive value and probably relates biologically to cardiovascular risk.

Familial aggregation of amount and distribution of subcutaneous fat and their responses to exercise training in the HERITAGE family study

OBJECTIVE

Investigate the familial aggregation of amount and distribution of subcutaneous fat and their changes in response to endurance training.

RESEARCH METHODS AND PROCEDURES

A total of 483 sedentary subjects from 99 nuclear families were recruited, trained for 20 weeks of exercising on cycle ergometers, and measured before and after training for the following indicators of subcutaneous fat and fat distribution: trunk fat (TRUNK = sum of abdominal, subscapular, suprailiac, and midaxillary skinfolds), extremity fat (EXTREM = sum of biceps, triceps, thigh, and calf skinfolds), subcutaneous fat (SF8 = sum of the eight skinfolds), the trunk to extremity skinfolds ratio adjusted for SF8 (TER) and waist girth adjusted for body mass index (WAIST). The familial aggregation of the age- and sex-adjusted baseline phenotypes and their responses to training (delta) after adjustment for the baseline values was investigated using a familial correlation model.

RESULTS

Significant familial aggregation was observed for all the phenotypes measured at baseline and for deltaTRUNK and deltaWAIST. Transmissibility estimates reached about 30% to 35% for TRUNK, EXTREM, and SF8 and 50% for TER and WAIST. The transmissibilities of the response phenotypes were lower, ranging from 0% for deltaWAIST to 21% for deltaTRUNK and the pattern of familial correlations suggested a greater within- than between-generation resemblance in the response.

DISCUSSION

This study suggests that the amount and distribution of subcutaneous fat strongly aggregates in families, whereas the response to exercise training is characterized by a moderate and more complex pattern of familial resemblance. We conclude that familial/genetic factors are more important in determining the amount and distribution of subcutaneous fat than their responses to exercise training.