Heritability of leptin levels and the shared genetic effects on body mass index and leptin in adult Finnish twins

Leptin resistance in children with in utero exposure to maternal obesity and gestational diabetes

BACKGROUND

Leptin resistance occurs with obesity, but it is unknown if individuals at risk for obesity develop leptin resistance prior to obesity.

OBJECTIVE

Investigate whether leptin resistance is independent of weight status in children at risk for obesity due to intrauterine exposure to maternal obesity or gestational diabetes mellitus (GDM).

METHODS

Mother-child dyads (N = 179) were grouped by maternal pregnancy weight and GDM status: (1) normal weight, no GDM; (2) overweight/obesity, no GDM; (3) overweight/obesity with GDM. Children (4-10 years) were further stratified by current body mass index (BMI) <85th or ≥85th percentile. Leptin resistance of children and mothers was calculated as fasting leptin/fat mass index. Two-way ANOVA was used to assess whether leptin concentrations and leptin resistance differed by current weight status or in utero exposure group, after adjusting for race, sex and Tanner stage.

RESULTS

Children with a BMI ≥85th percentile had more leptin resistance than those with a BMI <85th percentile (p < 0.001), but leptin resistance did not differ by in utero exposure. Similarly, leptin resistance in women was associated with weight status and not prior GDM.

CONCLUSIONS

Results suggest that leptin concentrations are associated with obesity but not risk for obesity based on in utero exposure to maternal obesity or GDM.

Quantile-specific heritability of sibling leptin concentrations and its implications for gene-environment interactions

"Quantile-dependent expressivity" occurs when the effect size of a genetic variant depends upon whether the phenotype (e.g., leptin) is high or low relative to its distribution. Leptin concentrations are strongly related to adiposity, whose heritability is quantile dependent. Whether inheritance of leptin concentrations is quantile dependent, and whether this explains the greater heritability in women than men in accordance with their greater adiposity, and explains other gene-environment interactions, remains to be determined. Therefore, leptin and leptin receptor concentrations from 3068 siblings in 1133 sibships from the Framingham Heart Study Third Generation Cohort were analyzed. Free leptin index (FLI) was calculated as the ratio of leptin to soluble leptin receptor concentrations. Full-sib (β_FS) regression slopes were robustly estimated by quantile regression with nonparametric significance assigned from 1000 bootstrap samples. The analyses showed β_FS increased significantly with increasing percentiles of the offspring's age- and sex-adjusted leptin distribution (P_linear = 0.0001), which was accelerated at the higher concentrations (P_quadratic = 0.0003). β_FS at the 90th percentile (0.418 ± 0.066) was 4.7-fold greater than at the 10th percentile (0.089 ± 0.032, P_difference = 3.6 × 10^-6). Consistent with quantile-dependent expressivity, the β_FS was greater in female sibs, which was attributable to their higher leptin concentrations. Reported gene-environment interactions involving adiposity and LEP, LEPR, MnSOD, PPARγ, PPARγ2, and IRS-1 polymorphisms were consistent with quantile-dependent expressivity of leptin concentrations. β_FS for leptin receptor concentrations and free leptin index also increased significantly with increasing percentiles of their distributions (P_linear = 0.04 and P_linear = 8.5 × 10^-6, respectively). In conclusion, inherited genetic and shared environmental effects on leptin concentrations were quantile dependent, which likely explains male-female differences in heritability and some gene-environment interactions.

Maternal biomarker patterns for metabolism and inflammation in pregnancy are influenced by multiple micronutrient supplementation and associated with child biomarker patterns and nutritional status at 9-12 years of age

Maternal nutritional status influences fetal development and long-term risk for adult non-communicable diseases. However, the underlying mechanisms remain poorly understood. We examined whether biomarkers for metabolism and inflammation during pregnancy were associated with maternal health and with child biomarkers and health at 9-12 years of age in 44 maternal-child dyads from the Supplementation with Multiple Micronutrients Intervention Trial (SUMMIT, ISRCTN34151616) in Lombok, Indonesia. Archived blood for each dyad from maternal enrollment, later in pregnancy, postpartum, and from children at 9-12 years comprised 132 specimens. Multiplex microbead immunoassays were used to quantify vitamin D-binding protein (D), adiponectin (A), retinol-binding protein 4 (R), C-reactive protein (C), and leptin (L). Principal component analysis (PCA) revealed distinct variance patterns, i.e. principal components (PC), for baseline pregnancy, bp.pc1.D↓A↓R↓ and bp.pc2.C↓L↑; combined follow-up during pregnancy and postpartum, dp-pp.pc1.D↑↓A↑R↑↓L↓ and dp-pp.pc2.A↑C↑L↑; and children, ch.pc1.D↑R↑C↑ and ch.pc2.D↓A↑L↑. Maternal multiple micronutrient (MMN) supplementation led to an association of baseline maternal bp.pc2.C↓L↑ with decreased post-supplementation maternal dp-pp.pc2.A↑C↑L↑ (p = 0.022), which was in turn associated with both increased child ch.pc1.D↑R↑C↑ (p = 0.036) and decreased child BMI z-score (BMIZ) (p = 0.022). Further analyses revealed an association between maternal dp-pp.pc1.D↑↓A↑R↑↓L↓ and increased child BMIZ (p = 0.036). Child ch.pc1.D↑R↑C↑ was associated with decreased birth weight (p = 0.036) and increased child BMIZ (p = 0.002). Child ch.pc2.D↓A↑L↑ was associated with increased child BMIZ (p = 0.005), decreased maternal height (p = 0.030) and girls (p = 0.002). A pattern of elevated maternal adiponectin and leptin in pregnancy was associated with increased C-reactive protein, vitamin A, and D binding proteins pattern in children, suggesting biomarkers acting in concert may have qualitative as well as quantitative influence beyond single biomarker effects. Patterns in pregnancy proximal to birth were more associated with child status. In addition, child patterns were more associated with child status, particularly child BMI. MMN supplementation affects maternal biomarker patterns of metabolism and inflammation in pregnancy, and potentially in the child. However, child nutrition conditions after birth may have a greater impact on metabolism and inflammation.

The Intricate Network of Adipokines and Stroke

Cerebrovascular disorders, particularly ischemic stroke, are one of the most common neurological disorders. High rates of overweight and obesity support an interest in the role of adipose tissue and adipose tissue releasing cytokines in inducing associated comorbidities. Adipokines can serve as a key messenger to central energy homeostasis and metabolic homeostasis. They can contribute to the crosstalk between adipose tissue and brain. However recent research has offered ambiguous data on the network of adipose tissue, adipokines, and vascular disorders. In our paper we provide a critical insight into the role of adipokines in evolution of ischemic stroke.

Significant association between body composition phenotypes and the osteocalcin genomic region in normative human population

Osteocalcin, a major inorganic component of bone matrix and marker of bone formation, is also involved in regulation of glucose and fat mass metabolism. However, much uncertainty remains about whether the above effect on fat mass has a genetic component. Our main aim was to test whether a variation of body composition phenotypes is associated with BGLAP genomic region variants. To achieve this aim, we used an ethnically homogeneous discovery sample of 230 families consisting of 1112 apparently healthy individuals (561 males and 551 females) of European origin. We conducted association analysis between six SNPs and five obesity-related phenotypes: plasma levels of leptin, anthropometrical fat mass (FM), principal component scores of eight skinfold (SK_PC) and nine circumference (CR_PC) measurements, and body mass index (BMI). Two powerful and robust tools were applied: the pedigree disequilibrium test and variance component models, taking into account both familial and genetic effects. Significant association results were observed for all phenotypes. The most significant results were observed between the haplotype composed of three SNPs (rs2758605-rs1543294-rs2241106) and BMI (p=8.07(-7)), and CR_PC (p=5.29(-5)). The association with BMI was tested and confirmed in our replication study, including 2244 unrelated adult US Caucasians, who were previously assessed for whole genome SNP data. In addition, we obtained an evidence of potential non-additive interactions between the above three SNPs concerning their association with BMI. Bioinformatics sources suggest that the aforementioned interaction could originate from different genetic loci in this region; however, ascertaining the exact circumstances requires a detailed molecular-genetic study.

Genetic variation within a metabolic motif in the chromogranin a promoter: pleiotropic influence on cardiometabolic risk traits in twins

BACKGROUND

The cardiometabolic syndrome comprised of multiple correlated traits, but its origin is incompletely understood. Chromogranin A (CHGA) is required for formation of the catecholamine secretory pathway in sympathochromaffin cells. In twin pair studies, we found that CHGA traits aggregated with body mass index (BMI), as well as its biochemical determinant leptin. METHODS Here we used the twin method to probe the role of heredity in generating such risk traits, and then investigated the role of risk-trait-associated CHGA promoter genetic variation in transfected chromaffin cells. Trait heritability (h(2)) and shared genetic determination among traits (pleiotropy, genetic covariance, ρ(G)) were estimated by variance components in twin pairs.

RESULTS

CHGA, BMI, and leptin each displayed substantial h(2), and the traits also aggregated with several features of the metabolic syndrome (e.g., insulin resistance, blood pressure (BP), hypertension, catecholamines, and C-reactive protein (CRP)). Twin studies demonstrated genetic covariance (pleiotropy, ρ(G)) for CHGA, BMI, and leptin with other metabolic traits (insulin resistance, BP, and CRP). We therefore investigated the CHGA locus for mechanisms of codetermination with such metabolic traits. A common functional variant in the human CHGA promoter (G-462A, rs9658634, minor allele frequency ~21%) was associated with leptin and CRP secretion, as well as BMI, especially in women; marker-on-trait effects on BMI were replicated across twin populations on two continents. In CHGA promoter/luciferase reporter plasmids transfected into chromaffin cells, G-462A alleles differed markedly in reporter expression. The G-462A variant disrupted predicted transcriptional control by a PPARγ/RXRα motif and costimulation by PPARγ/RXRα and their cognate ligands, differentially activated the two alleles. During chromatin immunoprecipitation, endogenous PPARγ bound the motif.

CONCLUSIONS

Multiple features of the metabolic syndrome are thus under joint (pleiotropic) genetic determination, with CHGA as one such contributory locus: a common polymorphism in the promoter (G-462A) of CHGA predicts such heritable metabolic traits as BMI and leptin. CHGA promoter variant G-462A was not only associated with such metabolic traits but also disrupted a PPARγ/RXRα motif and responded differentially to characteristic trans-activators of that motif. The results suggest novel links between the catecholaminergic system and risk for the metabolic syndrome as well as systemic hypertension.

Genetics of adipose tissue biology

Adipose tissue morphology and release of free fatty acids, as well as peptide hormones, are believed to contribute to obesity and related metabolic disorders. These adipose tissue phenotypes are influenced by adiposity, but there is also a strong hereditary impact. Polymorphisms in numerous adipose-expressed genes have been evaluated for association with adipocyte and clinical phenotypes. In our opinion, some results are convincing. Thus ADRB2 and GPR74 genes are associated with adipocyte lipolysis, GPR74 also with BMI; PPARG and SREBP1, which promote adipogenesis and lipid storage, are associated with T2D and possible adiposity; ADIPOQ and ARL15 are associated with circulating levels of adiponectin, ARL15 also with coronary heart disease. We anticipate that the use of complementary approaches such as expression profiling and RNAi screening, and studies of additional levels of gene regulation, that is, miRNA and epigenetics, will be important to unravel the genetics of adipose tissue function.

Association of adipokines with blood pressure in rural Chinese adolescents

Previous research has demonstrated that adipokines influence blood pressure (BP). Limited data exist in healthy adolescents, who are in a critical period for preventing the development of high BP. This study investigated the association of leptin, adiponectin and the leptin-to-adiponectin ratio (LAR) with BP in rural Chinese adolescents. This report included 1245 adolescents (average body mass index: 19.3 kg m(-2)) aged 13-21 years from an established twin cohort. We examined gender-specific associations between plasma adipokines and BP, with adjustment for measures of adiposity and insulin resistance (IR). We estimated the genetic contribution to adipokines using the twin design and Cholesky decomposition models. There was no correlation between leptin and adiponectin levels. Leptin was positively associated with systolic blood pressure (SBP) in males and diastolic blood pressure in females, but the association disappeared after adjusting for adiposity and IR. LAR was positively associated with SBP (β(s.e.): 1.94(0.45)), P<0.01), adiponectin was negatively associated with SBP (β(s.e.): -2.18(0.63)), P<0.001) only in males, and such associations were independent of adiposity and IR. A test of gender × adiponectin interaction was significant (P=0.01). Heritability estimation showed that both environmental and genetic factors contribute to variance in adipokines. In these relatively lean Chinese adolescents, leptin was positively associated with BP in both genders, but was adiposity/IR dependent. Adiponectin was negatively associated with SBP in males, independent of adiposity/IR.

Parent-offspring transmission of adipocytokine levels and their associations with metabolic traits

Adipose tissue secreted cytokines (adipocytokines) have significant effects on the physiology and pathology of human metabolism relevant to diabetes and cardiovascular disease. We determined the relationship of the pattern of these circulating hormones with obesity-related phenotypes and whether such pattern is transmitted from parent to offspring. A combined total of 403 individuals from 156 consenting Saudi families divided into initial (119 families with 123 adults and 131 children) and replication (37 families with 58 adults and 91 children) cohorts were randomly selected from the RIYADH Cohort study. Anthropometrics were evaluated and metabolic measures such as fasting serum glucose, lipid profiles, insulin, leptin, adiponectin, resistin, tumor necrosis factor alpha (TNFα), activated plasminogen activator inhibitor 1 (aPAI1), high sensitivity C-reactive protein (hsCRP) and angiotensin II were also assessed. Parent-offspring regressions revealed that with the exception of hsCRP, all hormones measured showed evidence for significant inheritance. Principal component (PC) analysis of standardized hormone levels demonstrated surprising heritability of the three most common axes of variation. PC1, which explained 21% of the variation, was most strongly loaded on levels of leptin, TNFα, insulin, and aPAI1, and inversely with adiponectin. It was significantly associated with body mass index (BMI) and phenotypically stronger in children, and showed a heritability of ∼50%, after adjustment for age, gender and generational effects. We conclude that adipocytokines are highly heritable and their pattern of co-variation significantly influences BMI as early as the pre-teen years. Investigation at the genomic scale is required to determine the variants affecting the regulation of the hormones studied.

Tracking of leptin, soluble leptin receptor, and the free leptin index during weight loss and regain in children

OBJECTIVE

To investigate changes in leptin and soluble leptin receptor (SLR) concentrations, and in the free leptin index (FLI) during weight loss and subsequent weight regain; and to ascertain whether these indices remain stable in the rank of the distribution in repeated measures (tracking) during perturbations of weight in obese children.

DESIGN AND MEASUREMENTS

In a longitudinal study, 115 obese children were examined during a 12- week weight loss programme and 28 months of follow-up. Height, weight, body composition, Tanner stages, testicular size, time of menarche, and concentrations of leptin and SLR were measured at baseline, on days 14, 33, and 82, and from months 10, 16, and 28.

RESULTS

During weight loss, leptin decreased and the SLR increased. During weight regain, leptin increased and the SLR decreased. The partial correlation coefficients expressing the relationship between leptin and SLR were significant in girls during both weight loss and weight regain, whereas in boys they were much weaker and not significant. Leptin, SLR and FLI exhibited individual-specific levels (tracking) during weight loss and regain in boys and girls. The observed tracking seemed stronger during weight loss than during weight regain. The observed tracking was independent of both baseline body mass index (BMI) standard deviation score (SDS) and pubertal development at baseline and of subsequent changes in BMI SDS and puberty stages.

CONCLUSION

Leptin and the SLR exhibit tracking during weight loss and regain, which indicates individual stability in the leptin system despite challenges of weight.

Stable genes and changing environments: body mass index across adolescence and young adulthood

The transition between adolescence and young adulthood is a developmentally sensitive time where children are at an increased risk for becoming overweight and developing obesity. Twin studies have reported that body mass index [BMI] is highly heritable, however, it remains unclear whether the genetic influences are sex-limited and whether non-additive genetic influences contribute to body mass index [BMI] during these ages. In the current report, we examined self-reported data on BMI in same [n = 2,744] and opposite-sex [n = 1,178] siblings participating in the National Longitudinal Study on Adolescent Health [Add Health]. To investigate whether the same or different genes contributed to BMI for both sexes, we fit quantitative sex-limited genetic models to three waves of data collection. At each of the three Waves of assessment, models that included additive genetic, individual-specific environment, and no sex-limited genetic influences fit the data most parsimoniously. Heritable effects on BMI at each of the three Waves were large for both sexes and ranged between .75 and .86. While genetic contributions across the ages were highly correlated, longitudinal analyses indicated that the relevant individual-specific environmental influences on BMI in adolescence and young adulthood change sizably. These results underscore the importance of understanding early genetic influences on BMI and highlight the role environmental experiences have at later ages when new genetic influences appear to make a small contribution to individual variation in BMI.

Leptinemia and its association with stroke and coronary heart disease in the Jackson Heart Study

BACKGROUND

To examine the association of increased plasma leptin concentration with prevalent stroke and coronary heart disease (CHD) and to examine the genetic contributions of leptin to this association in the Jackson Heart Study cohort.

METHODS

A cohort of 5170 participants aged 21-84 years who underwent Exam I during 2000-2004 was analysed. Odds ratios (OR) of prevalent stroke and CHD were calculated using a logistic regression model adjusted for age, smoking, hypertension and waist circumference (WC). Variance component analysis was used to partition the phenotypic variance of leptin into the polygenic and environmental components.

RESULTS

The prevalence of stroke and CHD was 4.04% and 5.85% in women, and 4.88% and 8.92% in men, respectively. Body mass index (BMI) and WC were highly correlated with leptin both in men and women. In multivariate analysis stratified by sex, leptin was significantly associated with stroke (OR = 1.97, 95% CI = 1.21-3.21) in women after adjustment for age, smoking, systolic blood pressure, BMI and WC (P = 0.0079). No significant association was observed in men. Heritability of sex-, age-adjusted log-transformed leptin for this cohort was 38.0% and 37.8% after further adjustment for WC and hypertension, respectively. In addition, a sibship effect was also found to be significant and explained 12.2% of the total variance of leptin (P = 0.007).

CONCLUSION

There is a significant association of leptin with stroke in women, which is partly influenced by the genetic factor. The findings suggest that leptinemia is an independent risk factor for stroke in African American women.

An integrated expression phenotype mapping approach defines common variants in LEP, ALOX15 and CAPNS1 associated with induction of IL-6

Interleukin-6 (IL-6) is an important modulator of inflammation and immunity whose dysregulation is associated with a number of disease states. There is evidence of significant heritability in inter-individual variation in IL6 gene expression but the genetic variants responsible for this remain to be defined. We adopted a combined approach of mapping protein and expression quantitative trait loci in peripheral blood mononuclear cells using high-density single-nucleotide polymorphism (SNP) typing for ∼2000 loci implicated in cardiovascular, metabolic and inflammatory syndromes to show that common SNP markers and haplotypes of LEP (encoding leptin) associate with a 1.7- to 2-fold higher level of lipopolysaccharide (LPS)-induced IL-6 expression. We subsequently demonstrate that basal leptin expression significantly correlates with LPS-induced IL-6 expression and that the same variants at LEP which associate with IL-6 expression are also major determinants of leptin expression in these cells. We find that variation involving two other genomic regions, CAPNS1 (encoding calpain small subunit 1) and ALOX15 (encoding arachidonate 15-lipoxygenase), show significant association with IL-6 expression. Although this may be a subset of all such trans-acting effects, we find that the same ALOX15 variants are associated with induced expression of tumour necrosis factor and IL-1beta consistent with a broader role in acute inflammation for ALOX15. This study provides evidence of novel genetic determinants of IL-6 production with implications for understanding susceptibility to inflammatory disease processes and insight into cross talk between metabolic and inflammatory pathways. It also provides proof of concept for use of an integrated expression phenotype mapping approach.

Association of plasma leptin concentrations with adiposity measurements in rural Chinese adolescents

CONTEXT

There is evidence that leptin is involved in the etiology of obesity-related cardiovascular disease in adults. This raises the question of whether leptin levels in adolescence are indicative of adiposity-related cardiovascular risk.

OBJECTIVE

This study investigated gender-specific patterns of plasma leptin during adolescence, assessed which adiposity measurements are most strongly associated with plasma leptin, and estimated to what degree leptin-adiposity associations are influenced by genetic factors.

METHODS

Plasma leptin concentrations were determined using a sandwich immunoassay. Associations between plasma leptin and several adiposity measurements were examined using generalized estimating equations. Genetic contribution to leptin-adiposity association was estimated by Cholesky decomposition models using twin design.

RESULTS

Plasma leptin levels were higher in females than males at all Tanner stages. In females, body mass index, waist circumference, fat mass index (FMI), and percentage body fat (%BF) had similar associations with leptin levels. In males, %BF and FMI were more strongly associated with leptin levels than body mass index and waist circumference. In both males and females, percentage trunk fat had the weakest association with leptin among the five adiposity measures. Shared genetic factors account for more than 80% of the phenotypic correlation between %BF and leptin.

CONCLUSIONS

We found gender differences in leptin levels and leptin-adiposity associations. In both genders, leptin levels were strongly associated with %BF and FMI, particularly in males. Shared genetic factors contributed largely to the phenotypic correlation between leptin and %BF. Our findings underscored the importance of further investigation of leptin as a biomarker of adiposity in adolescents.

Genetic and environmental influences on adiponectin, leptin, and BMI among adolescents in Taiwan: a multivariate twin/sibling analysis

Circulating levels of leptin and adiponectin are closely associated with obesity. However, it is not known whether there are common shared genes or environment exerting influences on the levels of leptin, adiponectin, and BMI. We aimed to assess the relative contribution of genes and environment to adiponectin, leptin, and BMI individually as well as simultaneously to the three measures. Our subjects included a total of 228 twin/sibling pairs aged 12 to 18 (130 monozygotic twins, 68 dizygotic twins and 30 sibling pairs) were recruited from the middle schools. Multivariate analyses were applied to twin/sibling data using structural equation modeling. The results showed that intraclass correlations for adiponectin, leptin and BMI were higher in the MZ twins than those in the DZ/SP group. The relative contribution of genes to adiponectin (39%) was comparable to those of shared environment (40%). In contrast, leptin and BMI were influenced mostly by genes (74% and 89%, respectively). The multivariate genetic analyses showed that a latent factor underlying the three measures was identified, with BMI being equivalent to this latent factor. The BMI-dependent genetic factor explains only 15% and 34% of variation of adiponectin and leptin, respectively. These data indicate a differential contribution of genetic factors for the variation of adiponectin, leptin and BMI. More importantly, only a small portion of the genetic influences on adiponectin and leptin was attributed to BMI. Our findings provided more insight into the complex regulation of adiponectin and leptin in obesity.

Leptin, insulin, and obesity-related phenotypes: genetic influences on levels and longitudinal changes

This study estimated the genetic and environmental determinants of plasma leptin and insulin levels and of obesity-related phenotypes. Included in this analysis were family members from 80 families living in kibbutz settlements, who participated in two examinations 8-10 years apart. We estimated that polygenes explained 30-50% of the adjusted leptin and insulin levels and 30-70% of the anthropometric phenotypes. This study demonstrated a significant genetic influence on longitudinal changes in leptin and BMI (h(2) = 0.45) and small-to-moderate heritability estimates for changes in insulin and other obesity-related phenotypes. In bivariate genetic analyses, we observed positive genetic correlations between leptin and anthropometric phenotypes, suggesting that shared effects of the same sets of loci account for 20-30% of the additive genetic variance in these pairs of variables. Shared genetic factors also account for 20-25% of the additive genetic variance in insulin-anthropometric pairs of variables.

Common genetic components of obesity traits and serum leptin

To estimate common and distinct genetic influences on a panel of obesity-related traits and serum leptin level in adults. In a cross-sectional study of 625 Danish, adult, healthy, monozygotic, and same-sex dizygotic twin pairs of both genders, we carried out detailed anthropometry (height, weight, waist and hip, and skin-fold thickness, body composition assessment by bioimpedance (fat mass and fat-free mass), and measurement of serum leptin level. Bivariate variance component analyses estimated the additive genetic correlations between these measurements. The genetic correlations between the traits for overall fatness (BMI and fat mass index, kg/m(2)) were 0.94 in men and 0.98 in women, and their correlations with the various local fatness measures ranged from 0.49 to 0.83 in men and from 0.70 to 0.87 in women. The correlations between the truncal measures (waist circumference and truncal skin folds) and between the peripheral measures (hip circumference and peripheral skin folds) were 0.57 and 0.47 in men and 0.71 and 0.70 in women, respectively. The correlations between the truncal and peripheral measures ranged between 0.49 and 0.72 in men and between 0.61 and 0.82 in women. For leptin vs. the various measures of overall and local fatness the correlations ranged from 0.54 to 0.74 in men and from 0.48 to 0.75 in women. All correlations were significantly <1.00. The study supports control of overall fat mass and peripheral and truncal fat mass by both shared and different genetic components, which suggests that it is important to distinguish between the different phenotypes in the search for genes involved in the development of obesity.

Genotype-phenotype associations in obesity dependent on definition of the obesity phenotype

OBJECTIVE

In previous studies of associations of variants in the genes UCP2, UCP3, PPARG2, CART, GRL, MC4R, MKKS, SHP, GHRL, and MCHR1 with obesity, we have used a case-control approach with cases defined by a threshold for BMI. In the present study, we assess the association of seven abdominal, peripheral, and overall obesity phenotypes, which were analyzed quantitatively, and thirteen candidate gene polymorphisms in these ten genes in the same cohort.

METHODS

Obese Caucasian men (n = 234, BMI >or= 31.0 kg/m(2)) and a randomly sampled non-obese group (n = 323), originally identified at the draft board examinations, were re-examined at median ages of 47.0 or 49.0 years by anthropometry and DEXA scanning. Obesity phenotypes included BMI, fat body mass index, waist circumference, waist for given BMI, intra-abdominal adipose tissue, hip circumference and lower body fat mass (%). Using logistic regression models, we estimated the odds for defined genotypes (dominant or recessive genetic transmission) in relation to z-scores of the phenotypes.

RESULTS

The minor (rare) allele for SHP 512G>C (rs6659176) was associated with increased hip circumference. The minor allele for UCP2 Ins45bp was associated with increased BMI, increased abdominal obesity, and increased hip circumference. The minor allele for UCP2 -866G>A (rs6593669) was associated with borderline increased fat body mass index. The minor allele for MCHR1 100213G>A (rs133072) was associated with reduced abdominal obesity. None of the other genotype-phenotype combinations showed appreciable associations.

CONCLUSION

If replicated in independent studies with focus on the specific phenotypes, our explorative studies suggest significant associations between some candidate gene polymorphisms and distinct obesity phenotypes, predicting beneficial and detrimental effects, depending on compartments for body fat accumulation.

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.

Leptin: a potential biomarker for childhood obesity?

Leptin, a hormone made by adipocytes, is an important circulating signal for the regulation of body weight. A review of the scientific literature (PubMed Search 1994 to 2005) for studies examining the relationship among leptin, pediatric obesity and the impact of exercise intervention programmes on leptin concentrations are summarized. The potential utility of leptin as a biomarker for identifying children at risk of obesity is discussed. This literature review demonstrated that (1) leptin directly interacts with the hypothalamus for energy balance regulation; (2) the measurement of free, bound and total leptin as well as soluble leptin receptor concentration are critical for our understanding of obesity in children; and (3) leptin concentration may be an important factor for determining intervention programme responsiveness in pediatric obesity.

Polymorphisms of the low-density lipoprotein receptor-related protein 5 (LRP5) gene are associated with obesity phenotypes in a large family-based association study

BACKGROUND

The low-density lipoprotein receptor-related protein 5 (LRP5) gene, essential for glucose and cholesterol metabolism, may have a role in the aetiology of obesity, an important risk factor for diabetes.

PARTICIPANTS AND METHODS

To investigate the association between LRP5 polymorphisms and obesity, 27 single-nucleotide polymorphisms (SNPs), spacing about 5 kb apart on average and covering the full transcript length of the LRP5 gene, were genotyped in 1873 Caucasian people from 405 nuclear families. Obesity (defined as body mass index (BMI) >30 kg/m(2)) and three obesity-related phenotypes (BMI, fat mass and percentage of fat mass (PFM)) were investigated.

RESULTS

Single markers (12 tagging SNPs and 4 untaggable SNPs) and haplotypes (5 blocks) were tested for associations, using family-based designs. SNP4 (rs4988300) and SNP6 (rs634008) located in block 2 (intron 1) showed significant associations with obesity and BMI after Bonferroni correction (SNP4: p<0.001 and p = 0.001, respectively; SNP6: p = 0.002 and 0.003, respectively). The common allele A for SNP4 and minor allele G for SNP6 were associated with an increased risk of obesity. Significant associations were also observed between common haplotype A-G-G-G of block 2 with obesity, BMI, fat mass and PFM with global empirical values p<0.001, p<0.001, p = 0.003 and p = 0.074, respectively. Subsequent sex-stratified analyses showed that the association in the total sample between block 2 and obesity may be mainly driven by female subjects.

CONCLUSION

Intronic variants of the LRP5 gene are markedly associated with obesity. We hypothesise that such an association may be due to the role of LRP5 in the WNT signalling pathway or lipid metabolism. Further functional studies are needed to elucidate the exact molecular mechanism underlying our finding.

Genetic pleiotropy between asthma and obesity in a community-based sample of twins

BACKGROUND

Asthma and obesity are common conditions that are strongly associated. This association might be due to shared genetic or environmental causes.

OBJECTIVE

We sought to determine whether a shared genetic cause is responsible for the association between asthma and obesity and to estimate the magnitude of shared genetic cause.

METHODS

The analyses were performed with 1001 monozygotic and 383 dizygotic same-sex twin pairs within the University of Washington Twin Registry. The presence of asthma was determined by self-report of a physician diagnosis of asthma, and body mass index (BMI) was calculated by using self-reported height and weight. Obesity was defined as a BMI of 30 or greater. The association between asthma and BMI was assessed by means of mixed-effects ordinal regression. Twin correlations examined the association of asthma and obesity. Univariate and bivariate structural equation models estimated the components of variance attributable to genetic and environmental effects.

RESULTS

A strong association between asthma and BMI was identified in the sample population (P < .001). Substantial heritability was detected for asthma (53%) and obesity (77%), which is indicative of additive genetic influences on each disorder. The best-fitting model of shared components of variance indicated that 8% of the genetic component of obesity is shared with asthma.

CONCLUSION

The covariation between obesity and asthma is predominantly caused by shared genetic risk factors for both conditions.

Genetic regulation of the variation of circulating insulin-like growth factors and leptin in human pedigrees

Recent literature has shown that circulating levels of insulin-like growth factor I (IGF-I) and/or IGF binding proteins (IGF-BPs) may be of importance in the risk assessment of several chronic diseases including cancer, cardiovascular disease, diabetes mellitus and so on. The present study examined the extent of genetic and environmental influences on the populational variation of circulating IGF-I and IGF-BP-1 in apparently healthy and ethnically homogeneous white families. The plasma levels of each of the studied biochemical indices were determined by enzyme-linked immunoassay in 563 individuals aged 18 to 80 years. Quantitative genetic analysis showed that the IGF-I variation was appreciably attributable to genetic effects (47.1% +/- 9.0%), whereas for IGF-BP-1, only 23.3% +/- 7.8% of the interindividual variation was explained by genetic determinants. Common familial environment factors contributed significantly only to IGF-BP-1 variation (23.3% +/- 7.8%). In addition, we examined the covariations between these molecules and between them and IGF-BP-3 and leptin that were previously studied in the same sample. The analysis revealed that the pleiotropic genetic effects were significant for 2 pairs of traits, namely for IGF-I and IGF-BP-3, and for IGF-BP-1 and leptin. The bivariate heritability estimates were 0.21 +/- 0.04 and 0.15 +/- 0.05. The common environmental factors were consistently a significant source of correlation between all pairs (barring IGF-I and leptin) of the studied molecules; they were the sole predictors of correlation between IGF-I and IGF-BP-1, and between IGF-BP-1 and IGF-BP-3. Our results affirm the existence of specific and common genetic pathways that in combination determine a substantial proportion of the circulating variation of these molecules.

Heritability of free and receptor-bound leptin in normal twins

Free and receptor-bound leptin may be regulated by different mechanisms. Genes that influence the concentration of these fractions may have an important functional bearing. We determined circulating leptin receptor concentrations, bound as well as free leptin concentrations, and body composition in 24 monozygotic (MZ) and in 22 dizygotic (DZ) twin pairs. Bound leptin and leptin receptor concentrations were inversely correlated with body fat content. Free leptin concentrations were directly correlated with body fat content. The correlations in age- and sex-adjusted free leptin, bound leptin, and leptin receptor concentrations were higher between MZ twins than between DZ twins. Adjusted heritability (h2) estimates were 0.28 for free leptin, 0.73 for bound leptin, and 0.55 for leptin receptor. The genetic correlation with body fat was −0.58 for the leptin receptor, −0.20 for bound leptin, and 0.93 for free leptin. Our data are consistent with a strong genetic influence on leptin receptor and bound leptin and a weaker genetic influence on free leptin concentrations. The same genes that lower bound leptin and leptin receptor concentrations may increase fat mass or vice versa.

No difference in serum leptin concentrations between urban-dwelling Austronesians and Non-Austronesians in Papua New Guinea

Pacific Islands populations can be broadly divided into Austronesians (AN) and Non-Austronesians (NAN); obesity and type 2 diabetes are prevalent in the former, although leptin levels in both groups have seldom been investigated. Thirty-seven (20 male and 17 female) adult pairs, matched by age and percent body fat, from AN-speaking Balopa and NAN-speaking Huli, all of whom migrated to settle in Port Moresby, the capital of Papua New Guinea, were selected for comparison of their serum leptin concentrations. The Balopa did not differ significantly from the Huli in age (30.5 +/- 9.7 and 30.0 +/- 8.7 years for males, 33.7 +/- 8.9 and 34.1 +/- 7.5 years for females, respectively) or percent body fat (19.4 +/- 5.6 and 18.8 +/- 4.6 for males, 34.1 +/- 6.2 and 33.3 +/- 5.0 for females), although the BMI of females was lower in the Balopa (26.4 +/- 4.9) than in the Huli (29.7 +/- 4.7) (P = 0.02). In both ethnic groups, females had markedly higher leptin concentrations than males, but there was no significant inter-group difference in males (3.5 +/- 2.6 and 3.1 +/- 4.7 ng/ml, P = 0.14) or females (22.7 +/- 12.9 and 19.7 +/- 11.9 ng/ml, P = 0.40), after controlling for lifestyle factors and serum lipids. Multiple regression analysis revealed that significant predictors of leptin concentration were % body fat (beta = 0.58), sex (male, 0; female, 1; beta = 0.27), and smoker status (non-smoker, 0; smoker, 1; beta = -0.15) (R(2) = 0.80), implying that the leptin concentration was primarily determined by lifestyle-derived body fatness. In conclusion, the NAN populations do not endogenously differ in leptin status from the AN populations, who have been recognized as a typical group with a "thrifty" genotype.

Stability and change of volume and intensity of physical activity as predictors of hypertension

AIMS

Controversy exists concerning intensity of physical activity and risk of hypertension. Also, the association between long-term changes in physical activity and hypertension is poorly known. Therefore we investigated how the stability and change of volume and intensity of physical activity are associated with the risk of hypertension in Finnish men and women.

METHODS

A total of 3,931 men and 4,381 women responded to three questionnaires on health and lifestyle. Baseline data were gathered from two questionnaires, in 1975 and 1981. The subjects were 24-51 years of age, healthy, and non-hypertensive at baseline (1981). At the end of the follow-up, in 1990, the subjects responded to a third questionnaire, according to which we assessed the cumulative incidence of hypertension between 1982 and 1990.

RESULTS

The cumulative incidence of hypertension from 1982 to 1990 was 10.2% in men and 8.0% in women. In men, the risk of hypertension was higher among those who were persistently not participating in vigorous physical activity (i.e. in both 1975 and 1981) (odds ratio, 1.60; 95% confidence interval, 1.15 to 2.24; p=0.006) than among those persistently participating, when all confounding factors were adjusted for. Among those participating in vigorous activity only in 1975 or in 1981 the risk was not significantly increased compared with those participating persistently. Volume of physical activity was not associated with hypertension. In women, there was no association between physical activity and incidence of hypertension.

CONCLUSIONS

Compared with inactivity, persistent vigorous physical activity predicts a low risk of hypertension in men.

Association of leptin levels with obesity and blood pressure: possible common genetic variation

OBJECTIVE

To ascertain the extent to which relationships between obesity (OB) and blood pressure (BP) can be explained by an individual's leptin plasma levels.

DESIGN

Pedigree-based cross-sectional study in an apparently healthy population of European origin.

SUBJECTS

The study sample is comprised of 90 nuclear and more complex families totaling 210 male and 213 female subjects aged 18-75 y, randomly recruited in Bashkorstan Autonomic region, Russia.

MEASUREMENTS

Various fatness and fat distribution traits (including nine circumferences (CRCs), and eight skinfolds (CKFs) by anthropometry), blood pressure, and plasma leptin levels (by ELISA kits).

RESULTS

Adjustment for circulating leptin led to attenuation of the magnitude of correlations between OB and BP, regardless of trait pair and sex cohort. Some of these correlations became statistically nonsignificant. All familial effects were gone, and heritability estimates became virtually zero after adjustment of each of the OB traits and systolic blood pressure (SBP) in offspring for leptin values in parents.

CONCLUSION

BP and OB covariation is substantially mediated by circulating leptin levels. As a result, body fat has only a weak independent effect on BP variation after adjustment for leptin levels. Our findings also strongly suggest that genetic variation in body mass index, SKFs, and even body CRCs, as well as of SBP is due to genetic variation of leptin. Genetic variation of diastolic blood pressure in the present sample, however, shared very little with that of leptin.

Glucocorticoids contribute to the heritability of leptin in Scottish adult female twins

OBJECTIVE

The precise interactions between glucocorticoids and leptin are complex and poorly understood. The aim of the study was to investigate whether the glucocorticoid/leptin interaction is influenced by shared environmental or genetic factors.

DESIGN

We investigated the heritability of body mass index (BMI), circulating leptin and urinary glucocorticoid metabolites [tetrahydrocortisol (THF), alloTHF and tetrahydrocortisone (THE)] in 54 monozygotic (MZ) and 39 dizygotic (DZ) female twins. Analysis was performed using a structural equation modelling package Mx, developed by Neale.

RESULTS

Leptin and BMI showed substantial heritability (68.3% and 71.3%, respectively). Bivariate analysis indicated that the genetic determinants of BMI and leptin are partly shared. Total cortisol metabolites (THF + alloTHF + THE), the (THE + alloTHF)/THE ratio [a marker of 11beta-hydroxysteroid dehydrogenase (11HSD) activity] and the alloTHF/THF ratio (marker for 5alpha-reductase activity) followed an environmental pattern. The heritability of leptin was significantly lowered to 63.8% (P = 0.012) when values were corrected for the influence of total cortisol metabolites but unaffected by markers of 11HSD and 5alpha-reductase activity.

CONCLUSIONS

We confirm that the genetic influence on both BMI and the circulating leptin concentration is substantial and show that these genetic determinants are highly correlated. These genetic factors, which are more likely to be dominant than additive, can be modestly but significantly modified by urinary total cortisol metabolites implying an adrenal influence.

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.

Genetic variation of circulating leptin is involved in genetic variation of hand bone size and geometry

Leptin is secreted primarily by the adipocytes and plays an important role in the regulation of food intake and energy expenditure. In addition to its adipostatic function, it has been demonstrated that leptin directly enhances stromal cell differentiation to osteoblasts, and since such precursor cells are potential targets for leptin, the latter could possibly mediate the relationship between obesity and bone mass and size. To address this question, we studied phenotypic and genetic correlations between the circulating levels of leptin and hand bone size (BS) and geometry (BG) of the radiographic hand in a healthy and ethnically homogeneous sample of pedigrees. We also attempted to evaluate to what extent potential leptin/BS/BG correlations are modified by an individual's obesity traits, specifically his/her BMI. Our research has shown that leptin, BMI and the corresponding bone measures are clearly inherited traits (0.46+/-0.11, 0.35+/-0.16, 0.62+/-0.12 and 0.51+/-0.09, respectively). The bivariate variance component analysis revealed very strong and significant genetic and environmental correlations between circulating leptin and BMI ( r(G)=0.86+/-0.09, r(E)=0.75+/-0.05, P<0.001). Furthermore, genetic correlations between leptin and hand bone characteristics proved inverse and statistically significant ( r(G)=-0.35+/-0.01 and -0.45+/-0.10 for BS and BG, respectively), while corresponding environmental correlations were low ( r(E)=-0.14+/-0.15 and -0.07+/-0.14) and they could be constrained to zero without significant deterioration of the model fit to the data ( P>0.10). However, despite the extremely strong relationship between leptin and BMI, we failed to detect phenotypic or genetic correlations between BMI and our two hand bone measures. Thus our study provided evidence that plasma leptin levels may be statistically significant predictor of hand bone size and geometry, and may play a physiological role in maintaining bone mass as well as in regulation of hand bone proportions.

The human plasma proteome: history, character, and diagnostic prospects

The human plasma proteome holds the promise of a revolution in disease diagnosis and therapeutic monitoring provided that major challenges in proteomics and related disciplines can be addressed. Plasma is not only the primary clinical specimen but also represents the largest and deepest version of the human proteome present in any sample: in addition to the classical "plasma proteins," it contains all tissue proteins (as leakage markers) plus very numerous distinct immunoglobulin sequences, and it has an extraordinary dynamic range in that more than 10 orders of magnitude in concentration separate albumin and the rarest proteins now measured clinically. Although the restricted dynamic range of conventional proteomic technology (two-dimensional gels and mass spectrometry) has limited its contribution to the list of 289 proteins (tabulated here) that have been reported in plasma to date, very recent advances in multidimensional survey techniques promise at least double this number in the near future. Abundant scientific evidence, from proteomics and other disciplines, suggests that among these are proteins whose abundances and structures change in ways indicative of many, if not most, human diseases. Nevertheless, only a handful of proteins are currently used in routine clinical diagnosis, and the rate of introduction of new protein tests approved by the United States Food and Drug Administration (FDA) has paradoxically declined over the last decade to less than one new protein diagnostic marker per year. We speculate on the reasons behind this large discrepancy between the expectations arising from proteomics and the realities of clinical diagnostics and suggest approaches by which protein-disease associations may be more effectively translated into diagnostic tools in the future.

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.