Familial resemblance for abdominal visceral fat: the HERITAGE family study

The HERITAGE Family Study: A Review of the Effects of Exercise Training on Cardiometabolic Health, with Insights into Molecular Transducers

The aim of the HERITAGE Family Study was to investigate individual differences in response to a standardized endurance exercise program, the role of familial aggregation, and the genetics of response levels of cardiorespiratory fitness and cardiovascular disease and diabetes risk factors. Here we summarize the findings and their potential implications for cardiometabolic health and cardiorespiratory fitness. It begins with overviews of background and planning, recruitment, testing and exercise program protocol, quality control measures, and other relevant organizational issues. A summary of findings is then provided on cardiorespiratory fitness, exercise hemodynamics, insulin and glucose metabolism, lipid and lipoprotein profiles, adiposity and abdominal visceral fat, blood levels of steroids and other hormones, markers of oxidative stress, skeletal muscle morphology and metabolic indicators, and resting metabolic rate. These summaries document the extent of the individual differences in response to a standardized and fully monitored endurance exercise program and document the importance of familial aggregation and heritability level for exercise response traits. Findings from genomic markers, muscle gene expression studies, and proteomic and metabolomics explorations are reviewed, along with lessons learned from a bioinformatics-driven analysis pipeline. The new opportunities being pursued in integrative -omics and physiology have extended considerably the expected life of HERITAGE and are being discussed in relation to the original conceptual model of the study.

Genetics of Obesity: What We Have Learned Over Decades of Research

There is a genetic component to human obesity that accounts for 40% to 50% of the variability in body weight status but that is lower among normal weight individuals (about 30%) and substantially higher in the subpopulation of individuals with obesity and severe obesity (about 60%-80%). The appreciation that heritability varies across classes of BMI represents an important advance. After controlling for BMI, ectopic fat and fat distribution traits are characterized by heritability levels ranging from 30% to 55%. Defects in at least 15 genes are the cause of monogenic obesity cases, resulting mostly from deficiencies in the leptin-melanocortin signaling pathway. Approximately two-thirds of the BMI heritability can be imputed to common DNA variants, whereas low-frequency and rare variants explain the remaining fraction. Diminishing allele effect size is observed as the number of obesity-associated variants expands, with most BMI-increasing or -decreasing alleles contributing only a few grams or less to body weight. Obesity-promoting alleles exert minimal effects in normal weight individuals but have larger effects in individuals with a proneness to obesity, suggesting a higher penetrance; however, it is not known whether these larger effect sizes precede obesity or are caused by an obese state. The obesity genetic risk is conditioned by thousands of DNA variants that make genetically based obesity prevention and treatment a major challenge.

Heritability estimation of 2D:4D finger ratio in a Chuvashian population-based sample

OBJECTIVES

The purpose of this study was to evaluate the familial correlations and heritability of 2D:4D ratio traits using a large population-based sample of ethnically homogeneous pedigrees from Chuvasha and Bashkortostan Autonomies of the Russian Federation.

METHODS

We calculated the familial correlations and performed a heritability analysis of 2D:4D ratio traits in a sample of 1541 subjects (803 men and 738 women, mean age 47.78 ± 16.89 years, range 18-90 years).

RESULTS

Familial correlations of 2D:4D ratio traits showed no significant correlation for spouses; however, parent-offspring (0.15-0.28, P < .001) and sibling correlations (0.13-0.38, P < .009) were found to be significant. Heritability (H² ) of visual classification of 2D:4D ratio was 0.36 for the left and 0.28 for the right hand; finger ratio was 0.55 and 0.66, respectively; the ray ratio was 0.49 and 0.59, respectively, thus indicating the existence of a clear familial aggregation of 2D:4D ratio variation in the Chuvashian pedigrees, which cannot be explained only by common environmental effects.

DISCUSSION

Results of our study suggest familial aggregations of finger ratio variation (for all traits) in Chuvashian pedigrees. No evidence of assortative mating was found.

Comprehensive identification of pleiotropic loci for body fat distribution using the NHGRI-EBI Catalog of published genome-wide association studies

We conducted a hypothesis-free cross-trait analysis for waist-to-hip ratio adjusted for body mass index (WHR_adjBMI ) loci derived through genome-wide association studies (GWAS). Summary statistics from published GWAS were used to capture all WHR_adjBMI single-nucleotide polymorphisms (SNPs), and their proxy SNPs were identified. These SNPs were used to extract cross-trait associations between WHR_adjBMI SNPs and other traits through the NHGRI-EBI GWAS Catalog. Pathway analysis was conducted for pleiotropic WHR_adjBMI SNPs. We found 160 WHR_adjBMI SNPs and 3675 proxy SNPs. Cross-trait analysis identified 239 associations, of which 100 were for obesity traits. The remaining 139 associations were filtered down to 101 unique linkage disequilibrium block associations, which were grouped into 13 categories: lipids, red blood cell traits, white blood cell counts, inflammatory markers and autoimmune diseases, type 2 diabetes-related traits, adiponectin, cancers, blood pressure, height, neuropsychiatric disorders, electrocardiography changes, urea measurement, and others. The highest number of cross-trait associations were found for triglycerides (n = 10), high-density lipoprotein cholesterol (n = 9), and reticulocyte counts (n = 8). Pathway analysis for WHR_adjBMI pleiotropic SNPs found immune function pathways as the top canonical pathways. Results from our original methodology indicate a novel genetic association between WHR_adjBMI and reticulocyte counts and highlight the pleiotropy between abdominal obesity, immune pathways, and other traits.

Physical Activity, Screen Time, and Dietary Intake in Families: A Cluster-Analysis With Mother-Father-Child Triads

Background: The co-occurrence of multiple health behaviors such as physical activity, diet, and sedentary behavior affects individuals' health. Co-occurence of different health behaviors has been shown in a large number of studies. This study extended this perspective by addressing the co-occurrence of multiple health behaviors in multiple persons. The objective was to examine familial health behavioral patterns by (1) identifying clusters of families with similar behavior patterns and (2) characterizing the clusters by analyzing their correlates.

Methods: Cross-sectional data were collected from 198 families (mother, father, and child). Mothers, fathers, and children completed questionnaires assessing health related behaviors (physical activity, consumption of “healthy” and “unhealthy” foods, and screen time), the perception of Family Health Climate (regarding physical activity and nutrition) and demographics. Twelve variables (four health behaviors of three family members) were included in a cluster analysis conducted with Ward's Method and K-means analysis. Chi-square tests and analyses of variance were performed to characterize the family clusters regarding their demographics and their perception of Family Health Climate.

Results: Three clusters of families with specific behavioral patterns were identified: “healthy behavior families” with levels of physical activity and consumption of healthful foods above average and levels of media use and consumption of sweets below average; “unhealthy behavior families” with low levels of consumption of healthful foods and high levels of screen time; “divergent behavior families” with unhealthier behavioral patterns in parents and healthier screen time and eating behaviors combined with low physical activity levels in children. Family Health Climate differed between family clusters with most positive ratings in “healthy behavior families” and least positive ratings in “unhealthy behavior families.” “Divergent behavior families” rated the nutrition climate nearly as high as “healthy behavior families” while they rated the physical activity climate nearly as low as the “unhealthy behavior families.”

Conclusions: The study shows that co-occurrence of multiple health behaviors occurs on the family level. Therefore, focusing the family as a whole instead of individuals and targeting aspects related to the Family Health Climate in interventions could result in benefits for both children and adults and enhance effectivity of intervention programs.

Inflammation mediates the association between visceral adiposity and obstructive sleep apnea in adolescents

Only a handful of studies, primarily in clinical samples, have reported an association between obesity, inflammation, and obstructive sleep apnea (OSA) in children and adolescents. No studies, however, have examined the pathogenetic link between visceral adiposity, systemic inflammation, and incident OSA in a large general population sample using objective measures of sleep and body fat. Adolescents (n = 392; mean age 17.0 ± 2.2 yr, 54.0% male) from the Penn State Child Cohort (PSCC) underwent 9-h overnight polysomnography; a DXA scan to assess body fat distribution; and a single fasting blood draw for the assessment of plasma interleukin-6 (IL-6), IL-6 soluble receptor (IL-6 sR), tumor necrosis factor alpha (TNFα), tumor necrosis factor receptor 1A (TNFR1), C-reactive protein (CRP), leptin, and adiponectin levels via ELISA. Visceral fat area was significantly elevated in moderate OSA (AHI ≥ 5), especially in boys. IL-6, CRP, and leptin were highest in adolescents with moderate OSA, even after adjusting for BMI percentile. Mediation analysis revealed that 42% of the association between visceral fat and OSA in adolescents was mediated by IL-6 (p = 0.03), while 82% of the association was mediated by CRP (p = 0.01). These data are consistent with the model of a feed-forward, vicious cycle, in which the release of proinflammatory cytokines by visceral adipocytes largely explains the association between central obesity and OSA; in turn, inflammation is also elevated in OSA independent of BMI. These findings, in a large, representative, non-clinical sample of young people, add to our understanding of the developmental pathogenesis of sleep apnea.

Genome-wide association studies suggest sex-specific loci associated with abdominal and visceral fat

BACKGROUND

To identify loci associated with abdominal fat and replicate prior findings, we performed genome-wide association (GWA) studies of abdominal fat traits: subcutaneous adipose tissue (SAT); visceral adipose tissue (VAT); total adipose tissue (TAT) and visceral to subcutaneous adipose tissue ratio (VSR).

SUBJECTS AND METHODS

Sex-combined and sex-stratified analyses were performed on each trait with (TRAIT-BMI) or without (TRAIT) adjustment for body mass index (BMI), and cohort-specific results were combined via a fixed effects meta-analysis. A total of 2513 subjects of European descent were available for the discovery phase. For replication, 2171 European Americans and 772 African Americans were available.

RESULTS

A total of 52 single-nucleotide polymorphisms (SNPs) encompassing 7 loci showed suggestive evidence of association (P<1.0 × 10(-6)) with abdominal fat in the sex-combined analyses. The strongest evidence was found on chromosome 7p14.3 between a SNP near BBS9 gene and VAT (rs12374818; P=1.10 × 10(-7)), an association that was replicated (P=0.02). For the BMI-adjusted trait, the strongest evidence of association was found between a SNP near CYCSP30 and VAT-BMI (rs10506943; P=2.42 × 10(-7)). Our sex-specific analyses identified one genome-wide significant (P<5.0 × 10(-8)) locus for SAT in women with 11 SNPs encompassing the MLLT10, DNAJC1 and EBLN1 genes on chromosome 10p12.31 (P=3.97 × 10(-8) to 1.13 × 10(-8)). The THNSL2 gene previously associated with VAT in women was also replicated (P=0.006). The six gene/loci showing the strongest evidence of association with VAT or VAT-BMI were interrogated for their functional links with obesity and inflammation using the Biograph knowledge-mining software. Genes showing the closest functional links with obesity and inflammation were ADCY8 and KCNK9, respectively.

CONCLUSIONS

Our results provide evidence for new loci influencing abdominal visceral (BBS9, ADCY8, KCNK9) and subcutaneous (MLLT10/DNAJC1/EBLN1) fat, and confirmed a locus (THNSL2) previously reported to be associated with abdominal fat in women.

Gender-assortative waist circumference in mother-daughter and father-son pairs, and its implications. An 11-year longitudinal study in children (EarlyBird 59)

BACKGROUND/OBJECTIVES

Body mass index (BMI) is reportedly gender assortative (mother-daughter, father-son) in contemporary children. We investigated the corresponding transmission of waist circumference (WC) and its implications.

METHODS

We measured parental WC at baseline and WC, height, weight and para-umbilical skin-fold (USF) annually in their offspring from 5 to 15 years (n = 223 trios). Parents were deemed normal metabolic risk (NR) or high risk (HR) according to World Health Organization (WHO) cut-points for WC (mothers 80 cm, fathers 94 cm). The residual from WC adjusted for BMI (WC|BMI ) was used as a surrogate for excess intra-abdominal fat, and its association with insulin resistance (HOMA2-IR) was sought.

RESULTS

WC and USF were both gender assortative, while WC|BMI was not. WC was greater by 1.62 cm (P < 0.05, confidence interval [CI]: 0.09-3.16) and USF by 0.37 cm (P < 0.01, CI: 0.19-0.56) among the daughters (but not the sons) of HR compared with those of NR mothers, and by 1.32 cm (P < 0.05, CI: 0.09-2.55) and 0.18 cm (P < 0.05, CI: 0.04-0.32), respectively in the corresponding father-son (but not father-daughter) pairings. No such differences could be demonstrated for WC|BMI . A standard deviation score 1(SDS) change in WC|BMI , independent of BMI, was associated with a 7.14% change in IR in girls (P < 0.01, CI: 1.76-12.80) and 8.02% in boys (P < 0.001, CI: 2.93-13.36), but there was no relationship between IR and USF.

CONCLUSION

The relationship of offspring WC to metabolic health and to parental size is complex. Subcutaneous abdominal fat is gender assortative but harmless, while intra-abdominal fat (its surrogate in this analysis) is unrelated to parental waist circumference, but metabolically harmful.

Use of anthropometry for the prediction of regional body tissue distribution in adults: benefits and limitations in clinical practice

Regional body composition changes with aging. Some of the changes in composition are considered major risk factors for developing obesity related chronic diseases which in turn may lead to increased mortality in adults. The role of anthropometry is well recognized in the screening, diagnosis and follow-up of adults for risk classification, regardless of age. Regional body composition is influenced by a number of intrinsic and extrinsic factors. Therapeutic measures recommended to lower cardiovascular disease risk include lifestyle changes. The aim of this review is to systematically summarize studies that assessed the relationships between anthropometry and regional body composition. The potential benefits and limitations of anthropometry for use in clinical practice are presented and suggestions for future research given.

The relationship between DXA-based and anthropometric measures of visceral fat and morbidity in women

Background

Excess accumulation of visceral fat is a prominent risk factor for cardiovascular and metabolic morbidity. While computed tomography (CT) is the gold standard to measure visceral adiposity, this is often not possible for large studies - thus valid, but less expensive and intrusive proxy measures of visceral fat are required such as dual-energy X-ray absorptiometry (DXA). Study aims were to a) identify a valid DXA-based measure of visceral adipose tissue (VAT), b) estimate VAT heritability and c) assess visceral fat association with morbidity in relation to body fat distribution.

Methods

A validation sample of 54 females measured for detailed body fat composition - assessed using CT, DXA and anthropometry – was used to evaluate previously published predictive models of CT-measured visceral fat. Based upon a validated model, we realised an out-of-sample estimate of abdominal VAT area for a study sample of 3457 female volunteer twins and estimated VAT area heritability using a classical twin study design. Regression and residuals analyses were used to assess the relationship between adiposity and morbidity.

Results

Published models applied to the validation sample explained >80% of the variance in CT-measured visceral fat. While CT visceral fat was best estimated using a linear regression for waist circumference, CT body cavity area and total abdominal fat (R² = 0.91), anthropometric measures alone predicted VAT almost equally well (CT body cavity area and waist circumference, R² = 0.86). Narrow sense VAT area heritability for the study sample was estimated to be 58% (95% CI: 51-66%) with a shared familial component of 24% (17-30%). VAT area is strongly associated with type 2 diabetes (T2D), hypertension (HT), subclinical atherosclerosis and liver function tests. In particular, VAT area is associated with T2D, HT and liver function (alanine transaminase) independent of DXA total abdominal fat and body mass index (BMI).

Conclusions

DXA and anthropometric measures can be utilised to derive estimates of visceral fat as a reliable alternative to CT. Visceral fat is heritable and appears to mediate the association between body adiposity and morbidity. This observation is consistent with hypotheses that suggest excess visceral adiposity is causally related to cardiovascular and metabolic disease.

Do genetic variations alter the effects of exercise training on cardiovascular disease and can we identify the candidate variants now or in the future?

Cardiovascular disease (CVD) and CVD risk factors are highly heritable, and numerous lines of evidence indicate they have a strong genetic basis. While there is nothing known about the interactive effects of genetics and exercise training on CVD itself, there is at least some literature addressing their interactive effect on CVD risk factors. There is some evidence indicating that CVD risk factor responses to exercise training are also heritable and, thus, may have a genetic basis. While roughly 100 studies have reported significant effects of genetic variants on CVD risk factor responses to exercise training, no definitive conclusions can be generated at the present time, because of the lack of consistent and replicated results and the small sample sizes evident in most studies. There is some evidence supporting “possible” candidate genes that may affect these responses to exercise training: APO E and CETP for plasma lipoprotein-lipid profiles; eNOS, ACE, EDN1, and GNB3 for blood pressure; PPARG for type 2 diabetes phenotypes; and FTO and BAR genes for obesity-related phenotypes. However, while genotyping technologies and statistical methods are advancing rapidly, the primary limitation in this field is the need to generate what in terms of exercise intervention studies would be almost incomprehensible sample sizes. Most recent diabetes, obesity, and blood pressure genetic studies have utilized populations of 10,000–250,000 subjects, which result in the necessary statistical power to detect the magnitude of effects that would probably be expected for the impact of an individual gene on CVD risk factor responses to exercise training. Thus at this time it is difficult to see how this field will advance in the future to the point where robust, consistent, and replicated data are available to address these issues. However, the results of recent large-scale genomewide association studies for baseline CVD risk factors may drive future hypothesis-driven exercise training intervention studies in smaller populations addressing the impact of specific genetic variants on well-defined physiological phenotypes.

The genetic epidemiology of obesity: a case study

Obesity (OMIM #601665) is a disease where excessive stores of body fat impact negatively on health. The first law of thermodynamics dictates that energy cannot be created or destroyed so if energy is taken into the body, but not transformed to ATP for metabolic work or dissipated as heat, it will be stored as fat. Therefore, the ultimate cause of obesity is a long-term positive energy imbalance [energy intake (EI) exceeds energy expenditure (EE)]. Despite this simple explanation, there is no single reason why EI may exceed EE meaning that the proximate causes of obesity are multi-factorial in origin involving a complex interplay of genetic, behavioural, and environmental influences on metabolism, diet, and activity.

Phenotypic and evolutionary plasticity of body composition in rats selectively bred for high endurance capacity

We investigated the effects of genetic selection and prolonged wheel access (8 wk) on food consumption and body composition in lines of rats selected for high and low intrinsic (untrained) endurance running capacity (HCR and LCR, respectively) to test the generality of phenotypic correlations between physical activity levels, aerobic capacity, and body composition. HCR rats ran more minutes per day on activity wheels than LCR rats, supporting the hypothesis that voluntary activity and physiological capacity are genetically correlated (self-induced adaptive plasticity). Both treatments (selection and wheel access) significantly affected food consumption. HCR rats consumed and digested more food than LCR rats. Access to running wheels did not result in changes in overall body mass, but lean body mass increased and percent body fat decreased in both lines. Selection for high endurance capacity resulted in hypertrophy of the heart and kidneys and decreased long intestine length. We found significant phenotypic flexibility in a number of organ masses after wheel running. Specifically, access to running wheels resulted in hypertrophy of the heart, liver, kidney, stomach, and small and large intestines in LCR and HCR rats. The selected line×wheel access interaction was significantly greater in HCR rats in relative mass for the heart and lung. Compared with LCR rats, HCR rats fortify wheel running with increased food consumption along with greater hypertrophy of key organs for O2 transport.

Family-based study of association between ENPP1 genetic variants and craniofacial morphology

BACKGROUND

Human craniofacial morphology is characterized by considerable diversity among individuals. The ENPP1 gene is essential for bone physiology. However, the potential effects of its genetic variants on head size phenotypes have not yet been studied.

AIM

The aim of this research was to investigate the association of polymorphisms in the ENPP1 locus with normal variability of craniofacial phenotypes.

SUBJECTS AND METHODS

Fourteen SNPs and 13 haplotypes in the ENPP1 locus were tested for association with six head size traits in 1042 Western Eurasian individuals.

RESULTS

The most significant and consistent association was observed between upper facial height and the polymorphisms located near the promoter region and upstream from ENPP1 gene (p = 0.00009), which remained significant after adjustment for multiple testing. Additionally, association signals were detected between head breadths and lower face height, and markers residing in or close to the promoter and 3' untranslated regions of the ENPP1 gene (p < 0.05).

CONCLUSIONS

The findings obtained in this study suggest that the upstream, promoter and 3' untranslated regions in the ENPP1 locus harbor genetic variants affecting different aspects of craniofacial morphology. Further research is required to validate the relevancy of the potentially functional ENPP1 regions to normal and pathologic craniofacial growth.

Association of ALPL and ENPP1 gene polymorphisms with bone strength related skeletal traits in a Chuvashian population

Mineralization of the extracellular matrix of bone is an essential element of bone development, maintenance and repair. ALPL and ENPP1 genes and their products are known to be central in local regulation of bone mineralization. The present study investigates potential associations of ENPP1 and ALPL polymorphisms with several phenotypes reflecting bone size and hand BMD. The study sample included 310 Caucasian nuclear families. Forty SNPs in ALPL and 14 SNPs in ENPP1 genetic loci as well as pairwise haplotypes were tested for association with bone strength related traits. Our findings suggest that the region corresponding to exons 7 through 9 of the ALPL gene harbors functional polymorphism affecting both bone size at various skeletal sites (p-value ranged from 0.01 to 0.0001) and hand bone mineral density (p-value=0.0007). The other important finding of consistent association between bone size phenotypes and the 3' untranslated region of ENPP1 gene (p-value ranged from 0.01 to 0.001) imply functional significance of this region to bone growth. The considered anthropometric and radiographic bone phenotypes are closely related to bone fragility thus suggesting a role for both genes in osteoporosis. Further research is required to validate the relevancy of the potentially functional regions identified by our and other studies to normal and pathologic bone development as well as to determine the relevancy of the polymorphisms in ALPL and ENPP1 gene loci to clinical practice.

Morphological and biochemical features of obesity are associated with mineralization genes' polymorphisms

BACKGROUND

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) was recently extensively studied as a candidate gene for obesity phenotypes. As the human homologue of the mouse progressive ankylosis (ANKH) and alkaline phosphatase (ALPL) are known functional partners of ENPP1 in bone mineralization, we hypothesized that these genes may also be jointly involved in determining obesity features.

AIM

To examine the effects of the three genes, possible gene-sex and gene-gene interactions on variability of four obesity phenotypes: the body mass index (BMI), the waist-hip ratio (WHR), the epidermal growth factor receptor (EGFR), and leptin.

SUBJECTS AND METHODS

In all, 962 healthy individuals from 230 families were genotyped for 45 single nucleotide polymorphisms (SNPs). The association analysis was performed using two family based association tests (family based association test and pedigree disequilibrium test). The combined P-values of the two tests were estimated by Monte-Carlo simulations. Relative magnitude of the genetic and familial effects, gene-sex and gene-gene interactions were assessed using variance component models.

RESULTS

Associations were observed between ENPP1 polymorphisms and BMI (P=0.0037) and leptin (P=0.0068). ALPL markers were associated with WHR (P=0.0026) and EGFR (P=0.0001). The ANKH gene was associated with all four studied obesity-related traits (P<0.0184), and its effects were modulated by sex. Gene-gene interactions were not detected.

CONCLUSION

The observed pattern of association signals indicates that ANKH may have a generalized effect on adipose tissue physiology, whereas ENPP1 and ALPL affect distinct obesity features. The joint analysis of related genes and integration of the results obtained by different methods used in this research should benefit other studies of similar design.

Gln27Glu variant of Beta2-adrenoceptor gene affects male type fat accumulation in women

Background

The β₂-adrenergic receptor (BAR2) is the main lipolytic receptor in white human adipose tissue. There is a functional glutamine 27 glutamic acid (Gln27Glu, rs 1042714) polymorphism in its gene, which has been variably associated with body mass index. This gene variant may be associated with male-type adiposity in women and thus increased cardiovascular risk. We investigated whether the BAR2 Gln27Glu polymorphism is associated with visceral fat and coronary intima thickness in women.

Methods

The amount of mesenteric and omental fat was directly measured and anthropometric measurements were done from 112 forensic autopsy cases of women aged 15 to 49 years. The thickness of the coronary intima, which reflects the severity of atherosclerosis, was measured by computerized image analysis. The BAR2 Gln27Glu polymorphism was determined by polymerase chain reaction.

Results

We found that the amount of visceral fat was significantly higher in women with the Glu allele (689 ± 555 g) compared to Gln/Gln homozygotes (481 ± 392 g, P = 0.023). The waist-hip ratio also tended to be higher in women with the Glu allele compared to Gln/Gln homozygotes (p = 0.050). There were no statistically significant differences between the genotype groups in BMI or the thickness of coronary intima.

Conclusion

The Glu allele of the BAR2 gene may be a risk factor for visceral fat accumulation in young to middle-aged women. However, this polymorphism was not associated with preclinical atherosclerosis.

Anthropometric and bone-related biochemical factors are associated with different haplotypes of ANKH locus

BACKGROUND

The human homologue of the mouse progressive ankylosis (ANKH) gene is one of the key genetic factors involved in bone mineralization. Previous studies have shown that plasma levels of osteoprotegerin (OPG) and parathyroid hormone (PTH) are associated with the distal region of the ANKH gene, whereas skeletal size measurements are associated with the promoter region.

AIM

The present study examines the possible phenotype-haplotype specificity of the associations in these two gene regions.

SUBJECTS AND METHODS

The total sample consists of 1249 healthy individuals (mean age = 47.7, SD = 16.8) from 404 nuclear families. Fifteen interrelated anthropometric measurements were transformed into two principal components, reflecting body size and mass. Those, plus circulating levels of PTH and OPG, were subjected to association analysis, using transmission disequilibrium tests (TDTs) with ANKH gene. From 805 to 1150 individuals per SNP were genotyped.

RESULTS

In the proximal region (rs3006069-rs835154-rs835141), associations were found between the A-A-C haplotype and the first principal component reflecting body size (p < or = 0.048), whereas another haplotype, G-G-C, was associated with the first principal component, reflecting the body mass (p < or = 0.008). In the distal region of ANKH (rs39968-rs696294-rs875525), the A-A-C haplotype was found to be associated with OPG plasma levels (p < or = 0.001), whereas the G-A-C haplotype was associated with PTH circulating concentrations (p < or = 0.025).

CONCLUSION

Taken together, the results show discrimination between the corresponding regions and haplotypes, suggesting trait-specific gene variants that influenced bone-related phenotypic variation in the studied population.

Heritability of blood concentrations of sex-steroids in relation to body composition in young adult male siblings

OBJECTIVE

Sex steroid concentrations in men are related to body composition and both are determined by genetic and environmental factors. This study investigates heritability estimates of sex steroid serum concentrations and body composition as well as the genetic and environmental components of their interrelation.

PATIENTS

Six hundred and seventy-four men (25-45 years) were included in this study with 274 independent pairs of brothers.

MEASUREMENTS

Body composition and regional fat mass estimates were determined using dual-energy X-ray absorptiometry. Serum testosterone (T), SHBG, oestradiol (E(2)) and LH levels were determined by immunoassay; free T and E(2) levels were calculated.

RESULTS

Both sex steroid hormone concentrations and indices of body composition exhibited significant heritability estimates. Among sex steroid hormones, T had the highest heritability (h(2) = 0.65), followed by free T (h(2) = 0.54). A heritability of 0.73 was observed for SHBG; a heritability estimate of 0.83 was obtained for body weight. Significant genetic correlations were found between whole body fat mass and serum T (rho(G) = -0.46), free T (rho(G) = -0.27) and SHBG (rho(G) = -0.48) concentrations. No genetic relationship was observed between total (F) E(2) or LH concentrations, respectively, and body composition.

CONCLUSION

Both sex steroid serum levels and body composition are under strong genetic control. Their interrelation is in part underlied by a genetic correlation, indicative of the action of shared genes.

Family-based association study of polymorphisms in the RUNX2 locus with hand bone length and hand BMD

Osteoporosis is characterized by reduced bone strength. Bone size and bone mineral density (BMD) are major bone strength determinants. Identification of genes affecting the variability of these traits should improve prognosis and management of osteoporosis. This research was aimed to test the hypothesis of association of radiographic hand bone length (BL) and BMD with polymorphisms in the RUNX2 locus. Four SNPs linked to the two RUNX2 promoters were genotyped in 212 nuclear Caucasian families. These SNPs and four pairwise haplotypes were tested for association with eight BL and BMD traits, adjusted for covariates. We observed significant associations between polymorphisms linked to the RUNX2 P1 promoter and BL mean values for three studied bone groups: all 18 bones, proximal and medial bones (p = 0.0118, 0.0085, and 0.0056, respectively). Mean BMD values for all 18 bones, proximal and medial bones were associated with polymorphisms linked to the RUNX2 P2 promoter (p = 0.0032, 0.0077, 0.0007, respectively). Associations with BL and BMD mean values for medial and proximal bones remained significant even after correction for multiple testing. This study provides evidence of the association between polymorphisms linked to the two RUNX2 promoters and variability of hand BL and BMD. The results suggest independent roles for the two RUNX2 promoters in the determination of the traits studied.

First-degree relatives of patients with type 2 diabetes mellitus and risk of non-alcoholic Fatty liver disease

AIMS

The aim of this study was to determine whether first-degree relatives (FDR) of patients with type 2 diabetes mellitus (T2DM) are at higher risk of non-alcoholic fatty liver disease (NAFLD) than healthy controls.

METHODS

A total of 222 FDR of consecutive patients with T2DM aged between 35 and 55 years and 202 healthy individuals with no family history of diabetes were investigated for NAFLD. Fatty liver was diagnosed by ultrasonography using standard criteria. Height, weight, fasting glucose, alanine aminotransferase (ALT), total cholesterol and triglyceride were determined by routine laboratory methods.

RESULTS

Compared to subjects with no family history of diabetes, the age and sex adjusted odds ratio (OR) of NAFLD was 1.83 (95% CI: 1.11-3.03) for FDR of patients with T2DM. After further adjusting for BMI, fasting glucose, ALT, asparate aminotransferase (AST), triglyceride and cholesterol, the multivariate OR of prevalent NAFLD in FDR of patients with T2DM compared with individuals with no family history of diabetes was 1.56 (95% CI: 0.85-2.86).

CONCLUSIONS

The present study suggests that the relation between FDR of patients with T2DM and NAFLD is affected by the other covariates, in particular obesity, which points to a more complex relationship between the diseases. It appears that obesity and diabetes may independently predispose to NAFLD.

Genes implicated in serotonergic and dopaminergic functioning predict BMI categories

OBJECTIVE

This study addressed the hypothesis that variation in genes associated with dopamine function (SLC6A3, DRD2, DRD4), serotonin function (SLC6A4, and regulation of monoamine levels (MAOA) may be predictive of BMI categories (obese and overweight + obese) in young adulthood and of changes in BMI as adolescents transition into young adulthood. Interactions with gender and race/ethnicity were also examined.

METHODS AND PROCEDURES

Participants were a subsample of individuals from the National Longitudinal Study of Adolescent Health (Add Health), a nationally representative sample of adolescents followed from 1995 to 2002. The sample analyzed included a subset of 1,584 unrelated individuals with genotype data. Multiple logistic regressions were conducted to evaluate the associations between genotypes and obesity (BMI > 29.9) or overweight + obese combined (BMI > or = 25) with normal weight (BMI = 18.5-24.9) as a referent. Linear regression models were used to examine change in BMI from adolescence to young adulthood.

RESULTS

Significant associations were found between SLC6A4 5HTTLPR and categories of BMI, and between MAOA promoter variable number tandem repeat (VNTR) among men and categories of BMI. Stratified analyses revealed that the association between these two genes and excess BMI was significant for men overall and for white and Hispanic men specifically. Linear regression models indicated a significant effect of SLC6A4 5HTTLPR on change in BMI from adolescence to young adulthood.

DISCUSSION

Our findings lend further support to the involvement of genes implicated in dopamine and serotonin regulation on energy balance.

Familial resemblance and heritability

Familial resemblance arises when family members are more similar than unrelated pairs of individuals, and may be estimated in terms of correlations or covariances among family members. Multifactorial heritability (or generalized heritability) quantifies the strength of the familial resemblance and represents the percentage of variance that is due to all additive familial effects including additive genetic and those of the familial environment. However, the traditional concept of heritability, which may be more appropriately called the genetic heritability, represents only the percentage of phenotypic variance due to additive genetic effects. Resolving the various sources of familial resemblance entails other issues. For example, there may be major gene effects that are largely or entirely nonadditive, temporal or developmental trends, and gene-gene (epistasis) and gene-environment interactions. The design of a family study determines which of these sources are resolvable. For example, in nuclear families consisting of parents and offspring, the genetic and familial environmental effects are not resolvable because these relatives share both genes and environments. However, extended pedigree and twin and adoption designs allow separation of the heritable effects and, possibly, more complex etiologies, including interactions. Various factors affect the estimation and interpretability of heritabilities, for example, assumptions regarding linearity and additivity, assortative mating, and the underlying distribution of the data. Nonnormality of the data can lead to errors in hypothesis testing, although it yields reasonably unbiased estimates. Fortunately, these and other complications can be directly modeled in many of the sophisticated software packages available today in genetic epidemiology.

Family-based association study of ROR2 polymorphisms with an array of radiographic hand bone strength phenotypes

For the first time the study provides evidence of association of radiographic hand bone length (BL) and bone mineral density (BMD) with polymorphisms in ROR2 gene that plays important role in skeletal development. This contributes to better understanding of bone physiology and may have application in clinical practice.

INTRODUCTION AND HYPOTHESIS

Bone size and bone mineral density (BMD) are major determinants of bone strength. Identification of genes affecting these traits' variability is important for better understanding of normal and pathological bone physiology and identification of the individuals at risk for bone fracture. This study tested the hypothesis of association of radiographic hand bone length (BL) and BMD with polymorphisms in ROR2 gene that is important in skeletal development.

METHODS

Nineteen ROR2 SNPs were genotyped in 705 individuals, belonging to 212 nuclear families. The four tagging SNPs (tSNPs) and the pairwise haplotypes between adjacent tSNPs were tested for association with series of hand BL and BMD measurements, adjusted for covariates, using family-based association tests.

RESULTS

We observed significant associations with BL and BMD mean values for all 18 studied hand bones (p = 0.0080, 0.0030), mean BL and BMD for proximal phalanges (p = 0.0218, 0.0060) and metacarpal bones (p = 0.0014, 0.0004). In the latter, the association remained significant after correction for multiple testing.

CONCLUSIONS

The region of the first through the second ROR2 introns is most likely to contain the functional polymorphism/s responsible for the observed associations. Further studies are required to identify the ROR2 functional polymorphism/s affecting bone size and BMD variation.

Evidence of linkage and association with body fatness and abdominal fat on chromosome 15q26

OBJECTIVE

In the present study, we undertook a two-step fine mapping of a 20-megabase region around a quantitative trait locus previously reported on chromosome 15q26 for abdominal subcutaneous fat (ASF) in an extended sample of 707 subjects from 202 families from the Quebec Family Study.

RESEARCH METHODS AND PROCEDURE

First, 19 microsatellites (in addition to the 7 markers initially available on 15q24-q26; total = 26) were genotyped and tested for linkage with abdominal total fat, abdominal visceral fat, and ASF assessed by computed tomography and with fat mass (FM) using variance component-based approach on age- and sex-adjusted phenotypes. Second, 16 single nucleotide polymorphisms (SNPs) were genotyped and tested for association using family-based association tests.

RESULTS

After the fine mapping, the peak logarithm of odds ratio (LOD) score (marker D15S1004) increased from 2.79 to 3.26 for ASF and from 3.52 to 4.48 for FM, whereas for abdominal total fat, the peak linkage (marker D15S996) decreased from 2.22 to 1.53. No evidence of linkage was found for abdominal visceral fat. Overall, for genotyped SNPs, three variants located in the putative MCTP2 gene were significantly associated with FM and the three abdominal fat phenotypes (p <or= 0.05). The major allele and genotype of rs1424695 were associated with higher adiposity values (p < 0.004). The same trend was found for the two other polymorphisms (p < 0.05). None of the other SNPs was associated with adiposity phenotypes. The linkage for FM became non-significant (LOD = 0.84) after adjustment for the MCTP2 polymorphisms, whereas the one for ASF remained unchanged.

DISCUSSION

These results suggest that the MCTP2 gene, located on chromosome 15q26, influences adiposity. Other studies will be needed to investigate the function of the MCTP2 gene and its role in obesity.

Regional fat deposition as a factor in FFA metabolism

Humans have a large variability in body fat distribution, which has tremendous implications for metabolic health. Obese individuals with an upper-body-fat distribution have increased health complications such as dyslipidemia, hypertension, insulin resistance, and type 2 diabetes in comparison with lower-body-obese individuals. Additionally, females have more body fat, a greater proportion of fat in their lower body, and much less visceral fat than do lean males at the same body mass index. The reasons for these differences in body fat distribution have not been clearly identified but could be important. Herein we review what has been learned about regional differences in triglyceride storage capacity and lipolysis as they relate to the causes and consequences of regional fat accumulation. Both sex and site differences in regional fat storage have been described. In contrast, with the exception of variations between men and women in the contribution of visceral adipose tissue to hepatic FFA delivery, most studies have failed to show important sex differences in regional lipolysis in vivo.

Biologie des viszeralen Fetts

Visceral obesity is an independent risk factor for the development of cardiovascular diseases and type 2 diabetes. This is likely to be due to biological characteristics of visceral tissue, which are different from those of subcutaneous adipose tissue in terms of decreased insulin sensitivity and increased lipolytic activity. In addition, the anatomical site of visceral fat could be one potential reason for the increased cardio-metabolic risk associated with visceral obesity. Visceral adipose tissue drains into the portal vein and therefore the liver is exposed to the undiluted metabolites and adipokines released from visceral fat. There are profound differences between visceral and subcutaneous adipocytes in the metabolism, expression of specific receptors and secretion of a specific adipokine pattern, which could contribute to the adverse consequences of visceral obesity.

Familial aggregation of the metabolic syndrome in Korean families with adolescents

We investigated the familial aggregation of the metabolic syndrome in Korean families with adolescents. In a cross-sectional observational study, the body mass index, waist circumference, blood pressure, fasting glucose, serum triglyceride, HDL-cholesterol, total cholesterol and fasting insulin concentrations, and homeostasis model assessment (HOMA) score, were examined in each individual in 132 Korean nuclear families. Most variables of the metabolic syndrome in offspring were significantly correlated with those of parents. Compared with sons, daughters had more significant difference for the metabolic parameters according to clustering of risk factors of their parents. Especially, daughters showed higher correlations with their parents for waist circumference, with their mothers for fasting glucose and HDL-cholesterol, and with their fathers for fasting insulin than sons. Compared with children whose parents did not have the metabolic syndrome, the odds ratios in children with at least one parent with the metabolic syndrome were 4.1 (1.6-10.6) for overweight, 3.6 (1.3-10.2) for abdominal obesity, 5.0 (2.0-12.3) for high triglycerides, and 4.8 (1.1-21.0) for the metabolic syndrome. We also observed significant correlations in variables of the metabolic syndrome between siblings and between spouses. In Korean families with adolescents, there is a familial aggregation of the metabolic syndrome, with daughters resembling their parents more than sons. These findings may have significant implications for clinical interventions directed at adolescents at high risk for the metabolic syndrome.

Strong association between polymorphisms in ANKH locus and skeletal size traits

Loss of bone strength is the main determinant of bone fragility. Bone strength is directly dependent on bone size (BS). A substantial portion of BS variation is attributable to genetic effects. However, the list of genes and allelic variants involved in the determination of BS variation is far from being complete. Polymorphisms in the ANKH gene have been shown to be associated with radiographic hand BS-related phenotypes. The present study examined the possible association of the ANKH gene with skeletal size and shape in order to test the universality of the ANKH effect on BS traits. Our sample consisted of a total of 212 ethnically homogeneous nuclear families (743 individuals) of European origin. Each individual was measured for body height, weight, and several other anthropometrical measurements, and genotyped for nine polymorphic markers (the average heterozygosity level was 0.4). We observed significant associations with practically all the anthropometrical phenotypes studied. More specifically, we found associations with body weight and height, limb length (P</=0.001; promoter region). After adjustment for body height, we demonstrated the substantial association increase for biacromial breadth (P=0.0012; some 140 kb downstream from ANKH) and vertebral column length (P=0.0008; exons 2-7 region). The majority of the observed associations persisted even after correction for multiple testing. For the first time the reliable evidence in support of universality of ANKH gene polymorphisms effect on bone size was provided.

Is visceral fat involved in the pathogenesis of the metabolic syndrome? Human model

OBJECTIVE

To review the evidence for and against the role of visceral adipose tissue as a major contributor to the metabolic complications of obesity through abnormal regulation of lipolysis.

RESEARCH METHODS AND PROCEDURES

Data from investigators in the field who have studied visceral adiposity and metabolic health and/or regional and systemic free fatty acid (FFA) release were considered.

RESULTS

Although visceral fat mass was positively correlated with adverse health consequences and excess FFA availability, visceral fat was not the source of excess systemic FFA availability. Upper body non-visceral fat contributes the majority of FFAs in lean, obese, diabetic, and non-diabetic humans. Increasing amounts of visceral fat probably result in greater hepatic FFA delivery.

DISCUSSION

Systemic, as opposed to hepatic, insulin resistance is unlikely to be caused by high rates of visceral adipose tissue lipolysis.

Quantitative genetic study of head size related phenotypes in ethnically homogeneous Chuvasha pedigrees

BACKGROUND

It is well established that genetic factors contribute significantly to the determination of head size and shape traits variability. However, the controversies in views and findings with respect to the more specific aspects of this issue have not yet been resolved.

AIM

The primary objective of the study was to examine the patterns of the intergenerational familial transmission of 12 head size related traits in a large ethnically homogeneous sample of Chuvasha pedigrees.

SUBJECTS AND METHODS

The research was carried out on 1406 individuals belonging to 357 nuclear and more complex families. Univariate and bivariate family-based analyses were performed to establish the pattern of head traits inheritance.

RESULTS

Maximum heritability estimates ranged from 0.52 to 0.72 for traits adjusted for significant covariates. No significant sex differences were observed with respect to the genetic determination of the studied traits. Bivariate analysis of horizontal and vertical head size components suggested the existence of common genetic and environmental factors that explained 33.0% and 23.2% of the total variance of the adjusted traits, respectively.

CONCLUSIONS

A significant genetic component is involved in inter-individual variation and covariation of various studied craniofacial traits.

Familial resemblance in eating behaviors in men and women from the Quebec Family Study

OBJECTIVE

It is commonly recognized that genetic, environmental, behavioral, and social factors are involved in the development of obesity. The family environment may play a key role in shaping children's eating behaviors. The purpose of this study was to estimate the degree of familial resemblance in eating behavioral traits (cognitive dietary restraint, disinhibition, and susceptibility to hunger).

RESEARCH METHODS AND PROCEDURES

Eating behavioral traits were assessed with the Three-Factor Eating Questionnaire in 282 men and 402 women (202 families) from the Quebec Family Study. Familial resemblance for each trait (adjusted for age, sex, and BMI) was investigated using a familial correlation model.

RESULTS

The pattern of familial correlation showed significant spouse correlation for the three eating behavior phenotypes, as well as significant parent-offspring and sibling correlations for disinhibition and susceptibility to hunger. According to the most parsimonious model, generalized heritability estimates (including genetic and shared familial environmental effects) reached 6%, 18%, and 28% for cognitive dietary restraint, disinhibition, and susceptibility to hunger, respectively.

DISCUSSION

These results suggest that there is a significant familial component to eating behavioral traits but that the additive genetic component appears to be small, with generalized heritability estimates ranging from 6% to 28%. Thus, non-familial environmental factors and gene-gene and gene-environmental interactions seem to be the major determinants of the eating/behavioral traits.

Lack of evidence for a major gene in the Mendelian transmission of BMI in Chinese

OBJECTIVES

To determine the heritability of BMI and to examine the mode of inheritance of BMI variation in Chinese.

RESEARCH METHODS AND PROCEDURES

Familial correlation and complex segregation analyses for BMI were undertaken in a Chinese sample composed of 392 nuclear families, with 1190 total individuals.

RESULTS

A moderate heritability was found for BMI (h2 = 0.419-0.492). The obtained results do not support a major gene for BMI in our samples. BMI may be inherited in a complex and non-Mendelian manner in Chinese.

DISCUSSION

The findings of this study suggest that identification of specific genes for BMI in Chinese, at least within the same data set, is a serious challenge because of the lack of evidence of a major gene for BMI in our Chinese sample.

Quantitative trait loci for abdominal fat and BMI in Hispanic-Americans and African-Americans: the IRAS Family study

OBJECTIVE

To conduct linkage analysis for body mass index (BMI, kg/m2), waist-to-hip ratio (WHR), visceral adipose tissue mass (VAT, cm2) and subcutaneous adipose tissue mass (SAT, cm2) using a whole genome scan.

DESIGN

Cross-sectional family study.

STUDY SUBJECTS

African-American families from Los Angeles (AA, n=21 extended pedigrees) and Hispanic-American families (HA) from San Antonio, TX (HA-SA, n=33 extended pedigrees) and San Luis Valley, CO (HA-SLV, n=12 extended pedigrees), totaling 1049 individuals in the Insulin Resistance and Atherosclerosis (IRAS) Family Study.

MEASUREMENTS

VAT and SAT were measured using a computed tomography scan obtained at the fourth and fifth lumbar vertebrae. All phenotypes were adjusted for age, gender, and study center. VAT, SAT, and WHR were analyzed both unadjusted and adjusted for BMI.

RESULTS

Significant linkage to BMI was found at D3S2387 (LOD=3.67) in African-Americans, and at D17S1290 in Hispanic-Americans (LOD=2.76). BMI-adjusted WHR was linked to 12q13-21 (D12S297 (LOD=2.67) and D12S1052 (LOD=2.60)) in Hispanic-Americans. The peak LOD score for BMI-adjusted VAT was found at D11S2006 (2.36) in Hispanic families from San Antonio. BMI-adjusted SAT was linked to D5S820 in Hispanic families (LOD=2.64). Evidence supporting linkage of WHR at D11S2006, VAT at D17S1290, and SAT at D1S1609, D3S2387, and D6S1056 was dependent on BMI, such that the LOD scores became nonsignificant after adjustment of these phenotypes for BMI.

CONCLUSIONS

Our findings both replicate previous linkage regions and suggest novel regions in the genome that may harbor quantitative trait locis contributing to variation in measures of adiposity.

Association of adipose tissue deposition and beta-2 adrenergic receptor variants: the IRAS family study

OBJECTIVE

Adipose tissue distribution (visceral vs subcutaneous) has been shown to be an important predictor of insulin resistance, diabetes and cardiovascular disease, independent of body mass index. The beta-2 adrenergic receptor is a major lipolytic receptor in human fat cells and the gene that codes for this protein is an important candidate gene for measures of adiposity and fat deposition. We examined whether two common polymorphisms in codons 16 (Arg16Gly) and 27 (Gln27Glu) are associated with measures of fat distribution in participants of the IRAS Family Study.

METHODS

We recruited African-American (AA) and Hispanic-American (HA) families from Los Angeles, CA, USA (18 pedigrees, 272 AA individuals), San Antonio, TX, USA (33 pedigrees, 448 HA individuals) and San Luis Valley, CO, USA (12 pedigrees, 272 HA individuals). We estimated adipose tissue distribution via computed tomography. To test for an association between adiposity measures and these polymorphisms, we used generalized estimating equations, adjusting for age, gender, clinical site (ethnicity), body mass index, and familial correlation.

RESULTS

Of the 992 individuals genotyped for these polymorphisms, 57% were female and 15% had been diagnosed with type 2 diabetes mellitus. The mean age was 42.7+/-14.6 y. The Glu27 allele of the Gln27Glu polymorphism was positively associated with (P-value for recessive model): body mass index (0.025), visceral adipose tissue (<0.0001) and visceral-to-subcutaneous adipose ratio (0.009), but not with subcutaneous adipose tissue (0.952). The Arg16Gly polymorphism was not associated with any of the adiposity measures.

CONCLUSIONS

These findings suggest that genetic variation in the beta-2 adrenergic receptor gene influences fat deposition and body size in AAs and HAs. In particular, these results support a role for the gene in the distribution of visceral adipose tissue but not subcutaneous adipose tissue.

Human resistin gene polymorphism is associated with visceral obesity and fasting and oral glucose stimulated C-peptide in the Québec Family Study

Obesity and insulin resistance are common features of Type 2 Diabetes. A new protein called resistin has been shown to be secreted by adipocytes in mice and to influence insulin sensitivity. The goal of the present study was to investigate the associations between one polymorphism (g-420C>G) of the human resistin gene and phenotypes related to adiposity and glucose metabolism. We genotyped 725 (including 42 diabetics) adult subjects participating in the Quebec Family Study (QFS) by a minisequencing method. Forty-two were diabetic subjects. Phenotypes measured were: body mass index (BMI) and waist circumference (WC), % body fat (PFAT) and fat mass (FM) assessed by under water weighing, abdominal total, subcutaneous and visceral fat assessed by computed tomography and fasting plasma glucose, insulin and C-peptide and their responses to an oral glucose tolerance test (OGTT). Comparisons between genotypes were performed in non-diabetic men (no.=280) and women (no.=403) separately by analyses of covariance (ANCOVA). Among men, g-420 G homozygotes had less visceral fat (p < 0.05), lower levels of acute insulin responses to an OGTT and lower levels of C-peptide in a fasting state and in responses to an OGTT than carriers of the C allele (p < 0.01). These associations were independent of age and adiposity but were not observed in women. These results suggest that in men, the human resistin gene is associated with reduced amount of visceral obesity and lower insulin secretory responses to a glucose load.

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

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

Gender differences in familial aggregation of obesity-related phenotypes and dietary intake patterns in Korean families

PURPOSE

To investigate familial influences on obesity-related phenotypes and dietary intake patterns, and to examine gender differences in Korean families with adolescent children.

METHODS

A cross-sectional observational study was conducted on 134 biologically related families composed of 260 parents and 231 adolescent children aged 11 to 19 years. Anthropometric measurements, including total fatness and fat distribution, were measured. Dietary intake was assessed by the semi-quantitative food frequency questionnaire (FFQ).

RESULTS

The odds ratio and 95% confidence intervals for overweight were 6.6 (range, 1.5-29.7) in the sons and 13.7 (range, 2.5-76.4) in the daughters of overweight parents. Obesity and fat distribution in the adolescents were more significantly correlated with mothers than fathers. Daughters had more significant familial aggregations with their parents than did sons. The dietary intake patterns of both sons and daughters correlated more strongly with their mothers than their fathers. We observed significant correlations in anthropometric variables and dietary intake patterns between spouses and between siblings.

CONCLUSIONS

In the contemporary Korean nuclear family, maternal anthropometry and dietary behavior have a greater impact on children than do paternal contributions, and daughters resemble their parents more than sons. Genetics and environmental factors within the family infrastructure may provide strategies for the prevention and treatment of adolescent obesity.

Insulin sensitivity, body fat distribution, and family diabetes history: the IRAS Family Study

OBJECTIVE

Markers of insulin resistance are often apparent in nondiabetic relatives of subjects with type 2 diabetes. Whether diabetes family history (FH) also predicts visceral fat accumulation and, if so, whether the increased insulin resistance in relatives of diabetic subjects occurs independently of visceral fat accumulation are not known.

RESEARCH METHODS AND PROCEDURES

To examine this issue, we studied the relationship of diabetes FH with insulin sensitivity and fat measures, measured by minimal model analysis and computed tomography, respectively, in families participating in the Insulin Resistance Atherosclerosis (IRAS) Family Study. FH scores were based on the diabetes status of the participants' parents and older siblings.

RESULTS

FH scores were significantly correlated with reduced insulin sensitivity (p < 0.05) and increased subcutaneous (p < 0.05) and visceral (p < 0.05, San Antonio only) fat in families from San Antonio and Los Angeles but not in the leaner Hispanic families from San Luis Valley. There was no evidence for a stronger association of FH score with visceral fat accumulation than with subcutaneous fat or insulin resistance.

DISCUSSION

The absence of an association between FH score and insulin resistance/fat accumulation in San Luis Valley is consistent with the idea that the expression of transmitted diabetes genes may be suppressed in leaner, more physically active populations.

A genomewide scan for early-onset coronary artery disease in 438 families: the GENECARD Study

A family history of coronary artery disease (CAD), especially when the disease occurs at a young age, is a potent risk factor for CAD. DNA collection in families in which two or more siblings are affected at an early age allows identification of genetic factors for CAD by linkage analysis. We performed a genomewide scan in 1,168 individuals from 438 families, including 493 affected sibling pairs with documented onset of CAD before 51 years of age in men and before 56 years of age in women. We prospectively defined three phenotypic subsets of families: (1) acute coronary syndrome in two or more siblings; (2) absence of type 2 diabetes in all affected siblings; and (3) atherogenic dyslipidemia in any one sibling. Genotypes were analyzed for 395 microsatellite markers. Regions were defined as providing evidence for linkage if they provided parametric two-point LOD scores >1.5, together with nonparametric multipoint LOD scores >1.0. Regions on chromosomes 3q13 (multipoint LOD = 3.3; empirical P value <.001) and 5q31 (multipoint LOD = 1.4; empirical P value <.081) met these criteria in the entire data set, and regions on chromosomes 1q25, 3q13, 7p14, and 19p13 met these criteria in one or more of the subsets. Two regions, 3q13 and 1q25, met the criteria for genomewide significance. We have identified a region on chromosome 3q13 that is linked to early-onset CAD, as well as additional regions of interest that will require further analysis. These data provide initial areas of the human genome where further investigation may reveal susceptibility genes for early-onset CAD.

Genetics of bone mineral density: evidence for a major pleiotropic effect from an intercontinental study

BMD is a primary predictor of osteoporotic fracture, and its genetic determination is still unclear. This study showed that the correlation between BMD at different skeletal sites is caused by an underlying genetic structure of common genetic effects. In addition to possible shared (pleiotropic) genetic and environmental effects, each of the BMD variables may also be determined by site-specific genetic factors.

INTRODUCTION

BMD is a primary predictor of osteoporotic fracture and a key phenotype for the genetic study of osteoporosis. The interindividual variation in BMD measured at a given skeletal site is largely regulated by genetic factors. A strong phenotypic covariation exists for BMD at different skeletal sites. This study tests the hypothesis that the covariation is in fact caused by an underlying genetic structure of common genetic effects and that, in addition to possible shared (pleiotropic) genetic effects, each of the BMD variables may also be determined by site-specific genetic factors

MATERIALS AND METHODS

A bivariate complex segregation analysis as implemented in statistical package PAP was conducted to explore various models of pleiotropic genetic and environmental transmission in lumbar spine and femoral neck BMD, as well as in compact and spongious segments of hand phalanges. The BMD was obtained in three ethnically, culturally, and socially heterogeneous samples of white pedigrees, with 2549 individuals between 18 and 100 years of age, from Australia, Europe, and North America.

RESULTS AND CONCLUSIONS

The genetic correlation between BMD measures ranged between 0.50 +/- 0.09 and 0.79 +/- 0.04 in the three samples. In each sample, the model incorporated a major locus pleiotropic effect, and residual correlation was found to be the most parsimonious model. Estimated parameters from the model indicated a significant pleiotropic major gene effect on both lumbar spine and femoral neck BMD, with the existence of a significant residual correlation (0.51 +/- 0.07 to 0.66 +/- 0.04). These results suggest that the covariation in BMD at different skeletal sites, and between mostly compact versus mostly trabecular bone, was largely determined by common genetic factors that are pleiotropic or in close linkage and linkage disequilibirum, while at the same time, exhibiting considerable evidence of shared environmental effects. The results, for the first time, suggest that the possibility of pleiotropic genetic effect may be controlled by a major genetic locus. Identification of the major locus could open new opportunity to understanding the liability and pathogenic processes in which they are involved in the determination of fracture risk.

Complex segregation analyses of bone mineral density in Chinese

China has the largest population in the world; approximately 7% of the total population suffers from primary osteoporosis. Osteoporosis is mainly characterized by low bone mineral density (BMD). In the present study, familial correlation and segregation analyses for spine and hip BMDs have been undertaken for the first time in a Chinese sample composed of 401 nuclear families with a total of 1260 individuals. The results indicate a major gene of additive inheritance for hip BMD, whereas there is no evidence of a major gene influencing spine BMD. Significant familial residual effects are found for both traits, and heritability estimates (+/-SE) for spine and hip BMDs are 0.807(0.099) and 0.897(0.101), respectively. Sex and age differences in genotype-specific average BMD are also observed. This study provides the first evidence quantifying the high degree of genetic determination of BMD variation in the Chinese.

A major gene model of adult height is suggested in Chinese

Adult height (stature), as a complex quantitative trait, has been studied in different populations. However, few genetic studies on height were performed on the Chinese, the largest population in the world. In this study, familial correlation and segregation analyses were carried out for adult height in a Chinese sample composed of 385 nuclear families with a total of 1,169 informative individuals. The results suggest that a major gene with a recessive effect accounts for about 17.2% of the total adult height variation in the Chinese. Significant familial residual effects are found. The heritability (+/-SE) of height is estimated to be 0.647 (+/-0.122). This study, for the first time, provides evidence for the high degree of genetic determination of adult height in the Chinese population and furnishes a valuable reference for further mapping and identification of adult height genes in the Chinese.

Heritability analysis of cytokines as intermediate phenotypes of tuberculosis

Numerous studies have provided support for genetic susceptibility to tuberculosis (TB); however, heterogeneity in disease expression has hampered previous genetic studies. The purpose of this work was to investigate possible intermediate phenotypes for TB. A set of cytokine profiles, including antigen-stimulated whole-blood assays for interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, and the ratio of IFN to TNF, were analyzed in 177 pedigrees from a community in Uganda with a high prevalence of TB. The heritability of these variables was estimated after adjustment for covariates, and TNF-alpha, in particular, had an estimated heritability of 68%. A principal component analysis of IFN-gamma, TNF-alpha, and TGF-beta reflected the immunologic model of TB. In this analysis, the first component explained >38% of the variation in the data. This analysis illustrates the value of such intermediate phenotypes in mapping susceptibility loci for TB and demonstrates that this area deserves further research.

Effects of beta2-adrenergic receptor gene variants on adiposity: the HERITAGE Family Study

We investigated whether the Arg16Gly and Gln27Glu polymorphisms of the beta2-adrenergic receptor gene were associated with body-fat and fat-distribution phenotypes measured before and in response to a 20-week endurance-training program. BMI, fat mass (FAT), percentage of body fat (%FAT), sum of eight skinfolds (SF8), and abdominal fat areas assessed by computed tomography were measured in adult sedentary white and black participants of the HERITAGE Family Study. Evidence of gene-by-obesity interaction was found in whites for several adiposity phenotypes measured before training. Analyses performed separately in nonobese and obese subjects revealed that obese men carrying the Glu27 allele have lower fat accumulation (BMI, FAT, and %FAT) than noncarriers. Among white obese women, Gly16Gly homozygotes had a lower fat accumulation (BMI, FAT, and SF8) than Arg16Gly and Arg16Arg carriers. In response to endurance training, white women with the Arg16Arg genotype exhibited a greater reduction in BMI, FAT, and %FAT. Results observed in blacks were mostly negative. These results suggest that polymorphisms in the beta2-adrenergic receptor gene influence the amount of body fat in white obese men (Gln27Glu) and women (Arg16Gly), as well as the changes in adiposity in response to endurance training in white women (Arg16Gly).

Interactions among the beta2- and beta3- adrenergic receptor genes and total body fat and abdominal fat level in the HERITAGE Family Study

OBJECTIVE AND SUBJECTS

Interactions between markers in the beta2- and beta3-adrenergic receptor (ADR) genes and total body fat and computerized tomography-measured abdominal fat phenotypes were studied in the HERITAGE Family Study cohort of Black (n=205; 81 males and 124 females) and White (n=415; 198 males and 217 females) subjects before and after an endurance training program.

RESULTS

In Black subjects, beta2- and beta3-ADR gene variants showed evidence of interactions on changes in total body fat mass and abdominal fat area (P<0.005 and =0.010, respectively). Black subjects who were carriers of both beta2-ADR Arg16 and beta3-ADR Arg64 alleles had a greater decrease in total fat mass as well as abdominal total and subcutaneous, but not visceral fat areas in response to endurance training than subjects with other genotype combinations (P from 0.011 to 0.047). After correction for multiple tests, the findings remained essentially unchanged for total body fat mass and abdominal fat area, but became nonsignificant for subcutaneous fat area. The changes in abdominal fat correlated positively with the changes in fat mass (P<0.0001). The interactions between beta2 and beta3-ADR gene markers accounted for a maximum of 3% of the variances in the response of total fat mass and abdominal fat area to endurance training in Black subjects but it was not significant in White subjects.

CONCLUSION

Interactions between sequence variants in the beta2-beta3-ADR gene contributed to the changes in fat mass and abdominal adiposity in response to endurance training in Black subjects.

Evidence for a major gene underlying bone size variation in the Chinese

Osteoporosis is a major public health problem defined as a loss of bone strength, of which bone size is an important determinant. In the present study, familial correlation and segregation analyses for the spine and hip bone sizes were performed for the first time in a Chinese sample composed of 393 nuclear families with a total of 1,193 individuals. The results indicate a major gene of codominant inheritance for spine bone size; however, there is no evidence of a major gene influencing hip bone size. Significant familial residual effects are found for both traits, suggesting their polygenic inheritance. Heritability estimates (+/-SE) for spine and hip bone size were 0.62 (0.13) and 0.59 (0.12), respectively. Sex and age differences in genotype-specific average bone size were observed. Compared with our previous study on bone mineral density (BMD) in the same population, this study suggests that genetic determination of bone size may be different from that of BMD, and thus studying bone size as one surrogate phenotype for osteoporotic fractures may be necessary.

Lack of pleiotropic genetic effects between adiposity and sex hormone-binding globulin concentrations before and after 20 weeks of exercise training: the HERITAGE family study

The relationship between sex hormone-binding globulin (SHBG) concentrations and body fat accumulation and distribution is governed by complex dynamic factors, which may involve common genetic and/or environmental factors. The current study investigated the genetic and environmental basis for the correlation between SHBG and body fat. Several measures of adiposity were investigated including body mass index (BMI) and a trunk to extremity skinfold thickness ratio (TER) assessed by anthropometry, body composition measured by hydrostatic weighing (total body fat mass [FM], fat-free mass [FFM], and percent body fat [%BF]), and abdominal fat measured by computerized tomography scanning (abdominal visceral fat [AVF]). The study comprised 501 white subjects from 99 families and 277 black subjects from 117 families participating in the HERITAGE Family Study. Familial correlations between traits and their cosegregation were investigated both at baseline and in response to endurance exercise training. Significant inverse phenotypic correlations were detected in both races between SHBG and adiposity measures at baseline and also in response to training. Significant cross-trait familial resemblance was found between SHBG and both BMI and FFM at baseline that accounted for 11% and 4% of maximal heritability, respectively, in white families. However, a joint segregation analysis of the traits failed to implicate shared genetic effects. Specifically, neither a pleiotropic major locus nor pleiotropic polygenic effects were detected between SHBG and BMI or FFM. A maximal cross-trait heritability of 45% was obtained for SHBG and TER at baseline in black families. However, no firm conclusions as to the etiology of this relationship could be drawn because of the limitations of small sample size. For the training response phenotypes, there was no significant cross-trait correlation between SHBG and any adiposity measures studied here, suggesting that their correlation may have an environmental basis. Therefore, this study fails to support the hypothesis of genetic pleiotropy between SHBG concentrations and body fat phenotypes, and suggests an environmental basis for the correlation, ie, SHBG concentrations are genetically independent of body composition and abdominal adiposity phenotypes.

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

OBJECTIVE

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

RESEARCH METHODS AND PROCEDURES

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

RESULTS

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

DISCUSSION

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