Familial resemblance in fatness and fat distribution

Sex Differences in Adiposity and Cardiovascular Diseases

Body fat distribution is a well-established predictor of adverse medical outcomes, independent of overall adiposity. Studying body fat distribution sheds insights into the causes of obesity and provides valuable information about the development of various comorbidities. Compared to total adiposity, body fat distribution is more closely associated with risks of cardiovascular diseases. The present review specifically focuses on the sexual dimorphism in body fat distribution, the biological clues, as well as the genetic traits that are distinct from overall obesity. Understanding the sex determinations on body fat distribution and adiposity will aid in the improvement of the prevention and treatment of cardiovascular diseases (CVD).

Sibling Resemblances in Physical Fitness in Three Distinct Regions in Peru: The Peruvian Sibling Study on Growth and Health

We estimated sibling resemblance in health-related physical fitness (PF) and examined how individual characteristics and shared natural environment accounted for sibling similarities. The sample comprised 656 sibling pairs and 102 triplets (6-15 years of age), from three geographical areas of Peru. PF components included morphological (waist circumference, sum of skinfolds), muscular (handgrip strength, standing long jump), and motor (shuttle-run). Body mass index (BMI) and somatic maturation were also assessed. In general, sibling intraclass correlations differed significantly across sib-ship types for waist circumference and handgrip strength but were the same for sum of skinfolds, standing long jump, and shuttle-run. Further, in general, both individual characteristics and geographical area of residence significantly influenced the magnitude of sibling resemblance as well as the mean levels of PF. In conclusion, individual characteristics and shared natural environment jointly influenced the expression of PF in Peruvian siblings, revealing the importance of these features when designing individualized programs promoting fitness.

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.

Sibling Similarity in Metabolic Syndrome: The Portuguese Sibling Study on Growth, Fitness, Lifestyle and Health

This study aims to estimate sibling resemblance in metabolic syndrome (MS) markers, and to investigate the associations of biological and behavioral characteristics with MS. The sample comprises 679 biological siblings (363 females; 316 males) aged 9-20 years. MS markers included waist circumference (WC), high-density lipoprotein cholesterol (HDL-C), triglycerides (TRI), fasting glucose (GLU) and systolic blood pressure (SBP). Body mass index (BMI), biological maturation, muscular, and cardiorespiratory fitness were also assessed. Behavioral characteristics, including dietary intake and physical activity, were self-reported by questionnaire. Multilevel models were used, and sibling resemblance was estimated using the intraclass correlation (ρ). In general, same-sex siblings showed higher resemblance in MS markers than opposite-sex siblings. However, variability in sibling resemblance in MS markers was evident with the inclusion of covariates. Biological characteristics including age, BMI and maturity offset influenced all MS markers except for TRI. Importantly, behavioral characteristics diversely influenced MS markers: fruit and vegetables only influenced SBP, whereas physical activity affected HDL-C. Additionally, muscular fitness impacted significantly on MS Z-score, WC, SBP and GLU, whilst cardiorespiratory fitness only affected WC. In conclusion, biological and behavioral characteristics influenced the expression of MS markers. These results confirmed the importance of considering individual characteristics when designing individualized programs for diminishing the adverse effects of specific MS markers.

Change and Stability in Sibling Resemblance in Obesity Markers: The Portuguese Sibling Study on Growth, Fitness, Lifestyle, and Health

BACKGROUND/OBJECTIVES

Obesity markers evolve over time and these changes are shared within the family orbit and governed by individual and environmental characteristics. Available reports often lack an integrated approach, in contrast to a multilevel framework that considers their concurrent influence. Hence, this study aims to (1) describe mean changes in obesity markers (body fat (%BF), body mass index (BMI), and waist circumference (WC)) across sib-ships; (2) analyze tracking of individuals within their sib-ship in these markers during 2 years of follow-up; (3) probe consistency in sibling resemblance in these markers; and (4) analyze the joint influence of individual and familial characteristics in these markers.

SUBJECTS/METHODS

The sample comprises 168 biological Portuguese siblings (brother-brother (BB), sister-sister (SS), and brother-sister (BS)) aged 9-17 years. %BF, BMI, and WC were measured using standardized protocols, and biological maturation was assessed. Physical activity, diet, screen time, and familial characteristics were obtained by questionnaires. Multilevel models were used to analyze the clustered longitudinal data. Sibling resemblance was estimated with the intraclass correlation.

RESULTS

On average, all sib types increased in BMI and WC over 2 years of follow-up, and SS pairs increased in %BF. Individuals within sib-ships track high in all obesity markers across time. Consistency in siblings' resemblance was also noted, except for BB pairs in %BF which decreased at follow-up. More maturing siblings tend to have higher values in all markers. Greater screen time was associated with higher %BF, whereas those consuming more sugary drinks had lower %BF and BMI values. Siblings whose mothers had less qualified occupations tended to have lower BMI values.

CONCLUSIONS

Longitudinal individual tracking and sibling resemblance for obesity markers were found. Yet, different trajectories were also identified depending on the marker and sib type. Individual and familial characteristics exert different influences on each obesity marker.

Profile Resemblance in Health-Related Markers: The Portuguese Sibling Study on Growth, Fitness, Lifestyle, and Health

The co-occurrence of health-related markers and their associations with individual, family, and environmental characteristics have not yet been widely explored in siblings. We aimed to identify multivariate profiles of health-related markers, analyze their associations with biological, sociodemographic, and built environment characteristics, and estimate sibling resemblance in these profiles. The sample includes 736 biological siblings aged 9–20 years. Body fat was measured with a portable bioelectrical impedance scale; biological maturation was assessed with the maturity offset; handgrip strength, standing long jump, one-mile run, and shuttle run were used to mark physical fitness. Health behaviors, sociodemographic, and built environmental characteristics were recorded by questionnaire. Latent profile analysis and multilevel logistic regression models were used; sibling resemblance was estimated with the intraclass correlation (ρ). Two multivariate profiles emerged: “P1 = fit, lower fat and poorer diet” (86.7%) and “P2 = higher fat and lower fit, but better diet” (13.3%). Siblings whose fathers were less qualified in their occupation were more likely to belong to P2 (OR = 1.24, p = 0.04); those whose fathers with Grade 12 and university level education were more likely to fit in P2 compared to peers living with fathers having an educational level below Grade 12 (OR = 3.18, p = 0.03, and OR = 6.40, p = 0.02, Grade 12 and university level, respectively). A moderate sibling profile resemblance was found (0.46 ≤ ρ ≤ 0.55). In conclusion, youth health-related markers present substantial differences linked with their body composition, physical fitness and unhealthy diet. Furthermore, only father socio-demographic characteristics were associated with profile membership. Sibling´s profile resemblance mirrors the effects of genetics and shared characteristics.

Genetic Fine-Mapping and Identification of Candidate Genes and Variants for Adiposity Traits in Outbred Rats

OBJECTIVE

Obesity is a major risk factor for multiple diseases and is in part heritable, yet the majority of causative genetic variants that drive excessive adiposity remain unknown. Here, outbred heterogeneous stock (HS) rats were used in controlled environmental conditions to fine-map novel genetic modifiers of adiposity.

METHODS

Body weight and visceral fat pad weights were measured in male HS rats that were also genotyped genome-wide. Quantitative trait loci (QTL) were identified by genome-wide association of imputed single-nucleotide polymorphism (SNP) genotypes using a linear mixed effect model that accounts for unequal relatedness between the HS rats. Candidate genes were assessed by protein modeling and mediation analysis of expression for coding and noncoding variants, respectively.

RESULTS

HS rats exhibited large variation in adiposity traits, which were highly heritable and correlated with metabolic health. Fine-mapping of fat pad weight and body weight revealed three QTL and prioritized five candidate genes. Fat pad weight was associated with missense SNPs in Adcy3 and Prlhr and altered expression of Krtcap3 and Slc30a3, whereas Grid2 was identified as a candidate within the body weight locus.

CONCLUSIONS

These data demonstrate the power of HS rats for identification of known and novel heritable mediators of obesity traits.

A multilevel analysis of health-related physical fitness. The Portuguese sibling study on growth, fitness, lifestyle and health

This study investigates biological, behavioural and sociodemographic correlates of intra-pair similarities, and estimates sibling resemblance in health-related physical fitness (PF). The sample comprises 1101 biological siblings (525 females) aged 9–20 years. PF components and markers were: morphological [waist circumference (WC) and %body fat (%BF)], muscular [handgrip strength (GS) and standing long jump (SLJ)], motor [50-yard dash (50YD) and shuttle run (SR)], and cardiorespiratory (1-mile run). Biological maturation was assessed; physical activity (PA), TV viewing and socioeconomic status (SES) information was obtained. On average, older and more mature subjects are better performers in all PF components; PA was negatively associated with SR, while SES was negatively associated with SLJ and SR. A pattern was observed in the intraclass correlations (ρ) wherein same sex siblings demonstrate greater resemblance for most PF components (sister-sister: 0.35≤ ρ≤0.55; brother-brother: (0.25≤ρ≤0.60) than brother-sister pairs (BS) (0≤ρ≤0.15), except for %BF (ρBB>ρSS>ρBS), and the 1-mile run (ρSS>ρBS>ρBB). In conclusion, behavioural and sociodemographic correlates play different roles in siblings PF expression. Further, a significant familial PF resemblance was observed with different trends in different sibling types, probably due to variations in shared genetic factors and sociodemographic conditions.

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.

Height, weight, body composition, and waist circumference references for 7- to 17-year-old children from rural Portugal

The purpose of this study was (1) to develop references of height, weight, body mass index (BMI), waist circumference and body fat for rural Portuguese children and adolescents and (2) to compare these results with other international references. The sample comprised 3094 children and adolescents aged 7-17 years from Vouzela, a central region in Portugal. Height, weight, BMI, waist circumference and body fat were measured. Centile curves were constructed using the LMS method. The Vouzela sample showed similar height median values compared to Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) percentile curves but greater values for weight and BMI. Percent body fat 50th percentile was greater in Vouzela children and adolescents compared to their international peers, except for boys aged 8-12 years. Boys' waist circumference median values were similar to those from the USA, whilst girls were similar until 12 years of age, after which the differences increased with age. The percentile curves constructed provide population specific references for growth and body composition of children and adolescents from rural Portugal. It is expected that they will be a useful tool for clinical and public health settings in rural Portugal.

Are there genetic paths common to obesity, cardiovascular disease outcomes, and cardiovascular risk factors?

Clustering of obesity, coronary artery disease, and cardiovascular disease risk factors is observed in epidemiological studies and clinical settings. Twin and family studies have provided some supporting evidence for the clustering hypothesis. Loci nearest a lead single nucleotide polymorphism (SNP) showing genome-wide significant associations with coronary artery disease, body mass index, C-reactive protein, blood pressure, lipids, and type 2 diabetes mellitus were selected for pathway and network analyses. Eighty-seven autosomal regions (181 SNPs), mapping to 56 genes, were found to be pleiotropic. Most pleiotropic regions contained genes associated with coronary artery disease and plasma lipids, whereas some exhibited coaggregation between obesity and cardiovascular disease risk factors. We observed enrichment for liver X receptor (LXR)/retinoid X receptor (RXR) and farnesoid X receptor/RXR nuclear receptor signaling among pleiotropic genes and for signatures of coronary artery disease and hepatic steatosis. In the search for functionally interacting networks, we found that 43 pleiotropic genes were interacting in a network with an additional 24 linker genes. ENCODE (Encyclopedia of DNA Elements) data were queried for distribution of pleiotropic SNPs among regulatory elements and coding sequence variations. Of the 181 SNPs, 136 were annotated to ≥ 1 regulatory feature. An enrichment analysis found over-representation of enhancers and DNAse hypersensitive regions when compared against all SNPs of the 1000 Genomes pilot project. In summary, there are genomic regions exerting pleiotropic effects on cardiovascular disease risk factors, although only a few included obesity. Further studies are needed to resolve the clustering in terms of DNA variants, genes, pathways, and actionable targets.

My sibling, my weight. How gender, sibling gender, sibling weight and sibling weight level perception influence weight perception accuracy

Objective:

The objective of this study was to examine the impact of sibling weight level perception and sibling weight on the accuracy of respondent weight level perception dependent on sibling-pair gender composition.

Design:

A cross-sectional study based on the survey data, which include the children of a nationally representative sample of Danes. Logit regression models were used.

Subjects:

Two thousand nine hundred and sixty-eight respondents comprising 397 female sibling pairs, 357 male sibling pairs and 730 opposite-sex sibling pairs. The inclusion of both same-sex siblings and opposite-sex siblings is novel for studies on weight perceptions.

Measurements:

Weight underestimation and weight overestimation were calculated on the basis of difference between actual weight level and self-perceived weight level. Respondent gender, sibling gender, sibling body mass index (BMI) and the siblings' self-perceived weight level were included as the main controls.

Results:

Women frequently overestimate their weight level, whereas men often underestimate theirs. Women are more likely to overestimate their weight if their sister does the same but less likely if their brother overestimates his weight. Likewise, women are more likely to underestimate their weight if their sister also underestimates her weight but less likely if their brother underestimates his weight. The higher the BMI of their brother and the lower the BMI of their sister, the more likely men are to underestimate their own weight level.

Conclusion:

Results underline the importance of social context when looking at body formation and weight perceptions. The weight and weight perceptions of siblings influence own weight perception. Gender is central to studies on weight-related issues, not only respondent gender - equally so the gender of interaction.

The design and conduct of a community-based registry and biorepository: a focus on cardiometabolic health in Latinos

BACKGROUND

Latinos are disproportionately impacted by obesity and type 2 diabetes but remain underrepresented in biomedical research. Therefore, the purpose of this project was to develop a research registry and biorepository to examine cardiometabolic disease risk in the Latino community of Phoenix, Arizona. The overarching goal was to establish the research infrastructure that would encourage transdisciplinary research regarding the biocultural mechanisms of obesity-related health disparities and facilitate access to this research for the Latino community.

METHODS

Prior to recruitment, key stakeholders from the local Latino community were engaged to develop a broad rapport within the community and seek advice regarding recruitment, enrollment, and follow-up. Self-identified community-dwelling Latinos underwent a comprehensive cardiometabolic health assessment that included anthropometrics, a fasting laboratory panel, and a 2-hour oral glucose tolerance test with measures of insulin and glucose to estimate insulin action and secretion. Separate consent was requested for future contact and banking of serum, DNA, and RNA. Research collaborations were sought out based on the cultural and metabolic profile of participants, faculty research agendas, and the potential for generating hypotheses.

RESULTS

A total of 667 participants (20.4% children, and 79.6% adults) were enrolled with 97% consenting to the registry and 94% to banking of samples. The prevalence of overweight/obesity was 50% in children and 81% in adults. Nearly 20% of children and more than 45% of the adults exhibited some degree of hyperglycemia. To date, more than 15 research projects have been supported through this infrastructure and have included projects on the molecular biology of insulin resistance to the sociocultural determinants of health behaviors and outcomes.

CONCLUSIONS

The high prevalence of obesity and cardiometabolic disease risk factors coupled with the overwhelming majority of participants consenting to be re-contacted, highlights the importance of supporting research infrastructure to generate hypotheses about obesity-related health in Latinos. Future studies that stem from the initial project will likely advance the limited understanding regarding the biocultural determinants of health disparities in the Latino community.

Pathophysiology of human visceral obesity: an update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Assortative marriages by body mass index have increased simultaneously with the obesity epidemic

BACKGROUND

The genetic predisposition to obesity may have contributed to the obesity epidemic through assortative mating. We investigated whether spouses were positively assorted by body mass index (BMI; = kg/m(2)) in late childhood, and whether changes in assorted marriage by upper BMI-percentiles occurred during the obesity epidemic.

METHODS

In the Copenhagen School Health Records Register (CSHRR) boys and girls with measures of BMI at age 13 years later became 37,792 spousal-pairs who married between 1945 and 2010. Trends in the spousal BMI correlations using sex-, age-, and birth cohort-specific BMI z-scores across time were investigated. Odds ratios (ORs) of marriage among spouses both with BMI z-scores >90th or >95th percentile compared with marriage among spouses ≤90th percentile were analyzed for marriages entered during the years prior to (1945-1970), and during the obesity epidemic (1971-2010).

FINDINGS

Spousal BMI correlations were around 0.05 and stayed similar across time. ORs of marriage among spouses with BMIs >90th percentile at age 13 were 1.21, 1.05-1.39, in 1945-1970, and increased to 1.63, 1.40-1.91, in 1971-2010 (p = 0.006). ORs of marriage among spouses both >95th BMI percentile were higher and increased more; from 1.39, 1.10-1.81, to 2.39, 1.85-3.09 (p = 0.004).

INTERPRETATION

Spousal correlations by pre-marital BMIs were small and stable during the past 65 years. Yet, there were assorted marriages between spouses with high BMI at age 13 years and the tendency increased alongside with the obesity epidemic which may increase the offsprings' predisposition to obesity.

Genome-wide association for abdominal subcutaneous and visceral adipose reveals a novel locus for visceral fat in women

Body fat distribution, particularly centralized obesity, is associated with metabolic risk above and beyond total adiposity. We performed genome-wide association of abdominal adipose depots quantified using computed tomography (CT) to uncover novel loci for body fat distribution among participants of European ancestry. Subcutaneous and visceral fat were quantified in 5,560 women and 4,997 men from 4 population-based studies. Genome-wide genotyping was performed using standard arrays and imputed to ~2.5 million Hapmap SNPs. Each study performed a genome-wide association analysis of subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), VAT adjusted for body mass index, and VAT/SAT ratio (a metric of the propensity to store fat viscerally as compared to subcutaneously) in the overall sample and in women and men separately. A weighted z-score meta-analysis was conducted. For the VAT/SAT ratio, our most significant p-value was rs11118316 at LYPLAL1 gene (p = 3.1 × 10E-09), previously identified in association with waist-hip ratio. For SAT, the most significant SNP was in the FTO gene (p = 5.9 × 10E-08). Given the known gender differences in body fat distribution, we performed sex-specific analyses. Our most significant finding was for VAT in women, rs1659258 near THNSL2 (p = 1.6 × 10-08), but not men (p = 0.75). Validation of this SNP in the GIANT consortium data demonstrated a similar sex-specific pattern, with observed significance in women (p = 0.006) but not men (p = 0.24) for BMI and waist circumference (p = 0.04 [women], p = 0.49 [men]). Finally, we interrogated our data for the 14 recently published loci for body fat distribution (measured by waist-hip ratio adjusted for BMI); associations were observed at 7 of these loci. In contrast, we observed associations at only 7/32 loci previously identified in association with BMI; the majority of overlap was observed with SAT. Genome-wide association for visceral and subcutaneous fat revealed a SNP for VAT in women. More refined phenotypes for body composition and fat distribution can detect new loci not previously uncovered in large-scale GWAS of anthropometric traits.

Sleep disorders in morbid obesity

The increasing prevalence of obesity has lead to an increase in the prevalence of sleep disordered breathing in the general population. The disproportionate structural characteristics of the pharyngeal airway and the diminished neural regulation of the pharyngeal dilating muscles during sleep predispose the obese patients to pharyngeal airway collapsibility. A subgroup of obese apneic patients is unable to compensate for the added load of obesity on the respiratory system, with resultant daytime hypercapnia. Weight loss using dietary modification and life style changes is the safest approach to reducing the severity of sleep apnea, but its efficacy is limited on the long run. Although it has inherent risks, bariatric surgery provides the most immediate result in alleviating sleep apnea. Obesity has been linked also to narcolepsy. The loss of neuropeptides co-localized in hypocretin neurons is suggested as the potential mechanism. Poor sleep quality, which leads to overall sleep loss and excessive daytime sleepiness has also become a frequent complaint in this population. Identifying abnormal nocturnal eating is critically important for patient care. Both sleep related eating disorder and night eating syndrome are treatable and represent potentially reversible forms of obesity.

Common variants in FTO, MC4R, TMEM18, PRL, AIF1, and PCSK1 show evidence of association with adult obesity in the Greek population

Twenty-four single-nucleotide polymorphisms (SNPs) have been reproducibly associated with obesity. We performed a follow-up study for obesity in the Greek adult population. A total of 510 obese and 469 lean adults were genotyped for 24 SNPs. We tested the association with obesity status using logistic regression and we evaluated the combined genetic risk of 24 SNPs by calculating the area under the receiver-operating characteristic (ROC) curves. We nominally replicated the association with obesity (BMI ≥30 kg/m(2)) of six SNPs in or near the FTO, MC4R, TMEM18, PRL, AIF1, and PCSK1 loci (1.28 ≤ odds ratio (OR) ≤ 1.35; 0.004 ≤ P ≤ 0.043). The discrimination ability for obesity was slightly stronger (P = 9.59 × 10(-6)) when the genetic information of the 24 SNPs was added to nongenetic risk factors (area under the curve (AUC) = 0.722) in comparison with nongenetic factors analyzed alone (AUC = 0.685). Our data suggest that SNPs in or near the FTO, MC4R, TMEM18, PRL, AIF1, and PCSK1 loci contribute to obesity risk in the Greek population.

Genetic influences in childhood obesity: recent progress and recommendations for experimental designs

The increasing prevalence of pediatric obesity around the world has become an area of scientific interest because of public health concern. Although since early stages of the lifespan body weight might be heavily influenced by an individual's behavior, epidemiological research highlights the involvement of genetic influences contributing to variation in fat accumulation and thus body composition. Results from genome-wide association studies and candidate gene approaches have identified specific regions across the human genome influencing obesity-related phenotypes. Reviewing the scientific literature provides support to the belief that at the conceptual level scientists understand that genes and environments do not act independently, but rather synergistically, and that such interaction might be the responsible factor for differences within and among populations. However, there is still limited understanding of genetic and environmental factors influencing fat accumulation and deposition among different populations, which highlights the need for innovative experimental designs, improved body composition measures and appropriate statistical methodology.

Obstructive sleep apnea syndrome: from phenotype to genetic basis

Obstructive sleep apnea syndrome (OSAS) is a complex chronic clinical syndrome, characterized by snoring, periodic apnea, hypoxemia during sleep, and daytime hypersomnolence. It affects 4-5% of the general population. Racial studies and chromosomal mapping, familial studies and twin studies have provided evidence for the possible link between the OSAS and genetic factors and also most of the risk factors involved in the pathogenesis of OSAS are largely genetically determined. A percentage of 35-40% of its variance can be attributed to genetic factors. It is likely that genetic factors associated with craniofacial structure, body fat distribution and neural control of the upper airway muscles interact to produce the OSAS phenotype. Although the role of specific genes that influence the development of OSAS has not yet been identified, current researches, especially in animal model, suggest that several genetic systems may be important. In this chapter, we will first define the OSAS phenotype, the pathogenesis and the risk factors involved in the OSAS that may be inherited, then, we will review the current progress in the genetics of OSAS and suggest a few future perspectives in the development of therapeutic agents for this complex disease entity.

Measures of adiposity in two cohorts of Hawaiian school children

BACKGROUND

Native Hawaiians have high rates of obesity and obesity-related diseases compared with non-Hawaiians in Hawaii, and the relation between this ethnic disparity in adiposity and socioeconomic status (SES) in children is unclear.

AIM

The present study compared measures of adiposity in two cohorts of school children residing in the Hilo area of Hawaii and related these measures to parental reports of ethnicity, household income and parent educational attainment.

SUBJECTS AND METHODS

All children in either Kindergarten (mean age 5.6 years) or third grade (mean age 8.7 years) in eight elementary schools in the Hilo area were invited to participate. A total of 125 children had anthropometric, bioelectric impedance and air displacement plethysmography measurements taken and their parents answered questions about household income, parental educational attainment and genealogical background that included ethnicity of ancestors.

RESULTS

Boys and girls in both cohorts had stature approximately at the 50(th) percentile (Z-score = 0) of national samples (CDC data). Z-scores of BMI were elevated compared to the CDC reference curves, but were significantly higher in male Native Hawaiian children in the older cohort among whom nearly 50% had a BMI above the 95(th) percentile for age. In the younger cohort, there was no significant ethnic difference in adiposity measures. In the older cohort, Native Hawaiian boys had significantly higher adiposity measures than their classmates. Adiposity in third grade girls was significantly and inversely related to their father's educational attainment. Percentage of Hawaiian ancestry was not significantly related to adiposity measures.

CONCLUSIONS

Ethnic disparity in adiposity among Native Hawaiians compared with non-Hawaiian age mates occurs after the age of 6 years, and is confined to males in this sample. For older girls, father's, but not mother's, educational attainment was inversely related to adiposity.

Spousal concordance for major coronary risk factors: a systematic review and meta-analysis

Spousal pairs permit assessment of determinants of diseases related to environment, because they share the same lifestyle and environment. The authors reviewed spouses' concordance for the major coronary risk factors. A search of the MEDLINE, PubMed, and EMBASE databases was performed. Seventy-one papers were selected for a total of 207 cohorts of pairs and 424,613 correlations in more than 100,000 couples. The most strongly correlated within-pairs factors were smoking and body mass index, with overall correlations of 0.23 (95% confidence interval: 0.12, 0.36) and 0.15 (95% confidence interval: 0.05, 0.25), respectively. Statistically significant positive correlations were also found for diastolic blood pressure, triglycerides, total and low density lipoprotein cholesterol, weight, and the waist/hip ratio. The overall odds ratios for concordance in hypertension, smoking, diabetes, and obesity were all statistically significant, ranging from 1.16 to 3.25. Assortative mating influenced concordance for blood pressure, smoking, glucose, low density lipoprotein cholesterol, weight, body mass index, and waist circumference. This systematic review shows a statistically significant positive spousal concordance for the majority of main coronary risk factors. However, the strength of the concordance was markedly different among factors and appeared to be quite modest for all of them. Interventions to reduce cardiovascular risk factors should be addressed jointly to both members of a marital couple.

Is obesity our genetic legacy?

CONTEXT

To design rational management regimes and identify novel therapeutic targets, it is essential to understand the biological drivers of the current epidemic of obesity. This review describes our current knowledge of genetic factors in obesity, drawing functional parallels in the underlying neuroendocrine mechanisms and suggesting promising new directions for research.

EVIDENCE ACQUISITION

Published literature, addressing both the current knowledge of genetics of monogenic and syndromic forms of extreme obesity, and the emerging literature on genetic factors associated with more common forms of obesity are analyzed.

EVIDENCE SYNTHESIS

The current genetic evidence in obesity underlines the importance of neuroendocrine mechanisms of appetite regulation. Monogenic forms of disease explain 6% of children with extreme obesity, having hyperphagia associated with defects in the leptin-melanocortin pathway, as a central feature. Candidate gene association studies indicate that more subtle variations of the same genes also contribute to common forms of obesity. Well-powered genome-wide association studies recently identified FTO as a strong contributor to both childhood and adult obesity, demonstrating the power of such hypothesis-free analysis to provide new insights into the underlying pathogenic mechanisms of a common complex disease.

CONCLUSIONS

Although there has been some very heartening recent progress in elucidating genetic mechanisms underlying obesity, we are still a long way from explaining the high heritability of adiposity. Investigations of different forms of variation, such as copy number polymorphism, may extend our understanding of this condition.

Heritability of somatotype components: a multivariate analysis

OBJECTIVE

To study the genetic and environmental determination of variation in Heath-Carter somatotype (ST) components (endomorphy, mesomorphy and ectomorphy).

DESIGN

Multivariate path analysis on twin data.

SUBJECTS

Eight hundred and three members of 424 adult Flemish twin pairs (18-34 years of age).

RESULTS

The results indicate the significance of sex differences and the significance of the covariation between the three ST components. After age-regression, variation of the population in ST components and their covariation is explained by additive genetic sources of variance (A), shared (familial) environment (C) and unique environment (E). In men, additive genetic sources of variance explain 28.0% (CI 8.7-50.8%), 86.3% (71.6-90.2%) and 66.5% (37.4-85.1%) for endomorphy, mesomorphy and ectomorphy, respectively. For women, corresponding values are 32.3% (8.9-55.6%), 82.0% (67.7-87.7%) and 70.1% (48.9-81.8%). For all components in men and women, more than 70% of the total variation was explained by sources of variance shared between the three components, emphasising the importance of analysing the ST in a multivariate way.

CONCLUSIONS

The findings suggest that the high heritabilities for mesomorphy and ectomorphy reported in earlier twin studies in adolescence are maintained in adulthood. For endomorphy, which represents a relative measure of subcutaneous adipose tissue, however, the results suggest heritability may be considerably lower than most values reported in earlier studies on adolescent twins. The heritability is also lower than values reported for, for example, body mass index (BMI), which next to the weight of organs and adipose tissue also includes muscle and bone tissue. Considering the differences in heritability between musculoskeletal robustness (mesomorphy) and subcutaneous adipose tissue (endomorphy) it may be questioned whether studying the genetics of BMI will eventually lead to a better understanding of the genetics of fatness, obesity and overweight.

Genetics of obesity and the prediction of risk for health

Obesity has always existed in human populations, but until very recently was comparatively rare. The availability of abundant, energy-rich processed foods in the last few decades has, however, resulted in a sharp rise in the prevalence of obesity in westernized countries. Although it is the obesogenic environment that has resulted in this major healthcare problem, it is acting by revealing a sub-population with a pre-existing genetic predisposition to excess adiposity. There is substantial evidence for the heritability of obesity, and research in both rare and common forms of obesity has identified genes with significant roles in its aetiology. Application of this understanding to patient care has been slower. Until very recently, the health risks of obesity were thought to be well understood, with a straightforward correlation between increasing obesity and increasing risk of health problems such as type 2 diabetes, coronary heart disease, hypertension, arthritis and cancer. It is becoming clear, however, that the location of fat deposition, variation in the secretion of adipokines and other factors govern whether a particular obese person develops such complications. Prediction of the health risks of obesity for individual patients is not straightforward, but continuing advances in understanding of genetic factors influencing obesity risk and improved diagnostic technologies mean that the future for such prediction is looking increasingly bright.

What makes a champion?

Variation in human athletic performance is determined by a complex interaction of socio-cultural, psychological, and proximate physiological factors. Human physiological trait variance has both an environmental and genetic basis, although the classic gene-environment dichotomy is clearly too simplistic to understand the full range of variation for most proximate determinants of athletic performance, e.g., body composition. In other words, gene and environment interact, not just over the short term, but also over the lifetime of an individual with permanent effects on the adult phenotype. To further complicate matters, gene and environment may also be correlated. That is, genetically gifted individuals may be identified as children and begin training pulmonary, cardiovascular, and muscle systems at an early critical age. This review covers evidence in support of a genetic basis to human athletic performance, with some emphasis on the recent explosion of candidate gene studies. In addition, the review covers environmental influences on athletic performance with an emphasis on irreversible environmental effects, i.e., developmental effects that may accrue during critical periods of development either before conception (epigenetic effects), during fetal life (fetal programming), or during childhood and adolescence. Throughout, we emphasize the importance of gene-environment interaction (G x E) as a means of understanding variation in human physiological performance and we promote studies that integrate genomics with developmental biology.

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.

Shared genetic risk factors for obstructive sleep apnea and obesity

Both obesity and obstructive sleep apnea (OSA) are complex disorders with multiple risk factors, which interact in a complicated fashion to determine the overall phenotype. In addition to environmental risk factors, each disorder has a strong genetic basis that is likely due to the summation of small to moderate effects from a large number of genetic loci. Obesity is a strong risk factor for sleep apnea, and there are some data to suggest sleep apnea may influence obesity. It is therefore not surprising that many susceptibility genes for obesity and OSA should be shared. Current research suggests that approximately half of the genetic variance in the apnea hypopnea index is shared with obesity phenotypes. Genetic polymorphisms that increase weight will also be risk factors for apnea. In addition, given the interrelated pathways regulating both weight and other intermediate phenotypes for sleep apnea such as ventilatory control, upper airway muscle function, and sleep characteristics, it is likely that there are genes with pleiotropic effects independently impacting obesity and OSA traits. Other genetic loci likely interact with obesity to influence development of OSA in a gene-by-environment type of effect. Conversely, environmental stressors such as intermittent hypoxia and sleep fragmentation produced by OSA may interact with obesity susceptibility genes to modulate the importance that these loci have on defining obesity-related traits.

Associations between physical activity and fat mass in adolescents: the Stockholm Weight Development Study

BACKGROUND

Obesity is multifactorial. However, the accumulation of fat mass (FM) is proposed to be due to a positive energy balance, which may be caused by reduced physical activity (PA).

OBJECTIVE

The objectives of the study were to describe the independent associations between PA and FM in adolescents and to describe the intergenerational association of FM between mothers and their offspring.

DESIGN

We conducted a cross-sectional study in 445 (190 M, 255 F) 17-y-old adolescents and their mothers. PA was assessed with a self-reported questionnaire and validated by comparison with accelerometric data in a subsample of the cohort. Body composition was measured by using air-displacement plethysmography.

RESULTS

Males were significantly more active than were females (P<0.01). PA was significantly and inversely associated with FM (beta=-3.63, P=0.005) and percentage FM (beta=-3.117, P=0.017) in males but not in females (beta=-0.576, P=0.54; beta=-0.532, P=0.59, respectively) after adjustment for birth weight and maternal FM and education level. However, FM and percentage FM in females were significantly associated with maternal FM (beta=0.159, P<0.0001; beta=0.145, P=0.002, respectively) and education level (beta=-1.048, P<0.005; beta=-1.085, P=0.006, respectively). No such associations were observed in males.

CONCLUSIONS

PA was independently associated with FM in males but not in females. The data also showed an intergenerational association of FM between mothers and their daughters but not between mothers and their sons.

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.

Genetic and environmental contributions to carotid intima-media thickness and obesity phenotypes in the Northern Manhattan Family Study

BACKGROUND AND PURPOSE

Both carotid intima-media thickness (IMT) and obesity are independent determinants of stroke and cardiovascular disease. The prevalence of obesity is higher in Hispanics. The genetic basis of IMT and obesity has not been well-characterized in Caribbean Hispanics. The purpose of this study was to examine the genetic and environmental contributions to IMT and obesity in this population.

METHODS

The data included 440 subjects from 77 Caribbean Hispanic families. Mean IMT and maximum IMT were measured in the internal carotid artery, common carotid artery, and carotid bifurcation. The total IMT was calculated as the mean value of IMT at all segments. Obesity phenotypes included body mass index (BMI), waist circumference, waist-to-hip ratio (WHR), and skin-fold thickness. Variance component methods were used to estimate age-adjusted and sex-adjusted heritability. Bivariate analyses were conducted to test for genetic and environmental correlations between IMT and obesity.

RESULTS

Heritabilities for IMT ranged from 9% to 40%, with the highest for total maximum IMT and lowest for internal carotid artery maximum IMT. Heritabilities for BMI, waist circumference, WHR, and skin-fold thickness were 44%, 47%, 5%, and 36%, respectively. There were significant genetic, but not environmental, correlations between IMT and BMI, waist circumference, and skin-fold thickness. There were no genetic or environmental correlations between IMT and WHR.

CONCLUSIONS

We found a substantial genetic contribution to IMT, BMI, waist circumference, and skin-fold thickness. Obesity and IMT may share common genetic factors. Future gene mapping studies are warranted to identify genes predisposing to IMT and obesity in this population.

BMI in the Trois-Rivières study: child-adult and child-parent relationships

This study evaluated intraindividual child-adult and interindividual child-parent relationships of body mass index (BMI) using data from the Trois-Rivières semilongitudinal study of growth and development. Intraindividual correlations between age 12 and 35 years were substantial (r(2) = 36% of variance in women, 30% of variance in men). Interindividual child-parent correlations for mothers and fathers age 36.6 +/- 0.4 and 39.5 +/- 0.4 years, respectively, were very low to low for daughters age 12 years (r = 0.09, NS and 0.34, P < 0.001 vs. father and mother, respectively) but all very low for sons age 12 years (r = 0.07, NS and 0.16, NS vs. father and mother, respectively). A multiple regression analysis predicted adult BMI from the individual's BMI at 10, 11, 12 years plus the maternal and paternal BMIs as calculated from self-reported heights and weights. The BMI at age 12 years was a better predictor of adult BMI than the parental BMI in both men and women (P < 0.001) and multivariate analysis revealed that this index at age 12 years was the sole significant predictor of adult BMI for both men and women. The results from our study do not support the hypothesis that parental BMI is a stronger predictor of adult BMI than childhood BMI. However, useful information for the prediction and prevention of adult overweight can be obtained from the BMI at age 12 years. Our results suggest that environmental influences may be the major factor in the present obesity epidemic.

Familial resemblance of 7-year changes in body mass and adiposity

OBJECTIVE

To investigate the familial resemblance of 7-year changes in body mass and adiposity among Canadian families.

RESEARCH METHODS AND PROCEDURES

The sample consisted of 655 women and 660 men from 521 families who participated in the Canada Fitness Survey in 1981 and the follow-up Campbell's Survey in 1988. Indicators of baseline and 7-year changes in body mass and adiposity included body mass (kilograms), body mass index (BMI; kilograms per square meter), sum of five skinfolds (SF5; millimeters), and waist circumference (WC; millimeters). The data were adjusted for the effects of age and sex, and the change scores were adjusted for baseline levels. A familial correlation model was used to determine the heritability of each phenotype using maximum likelihood techniques.

RESULTS

Significant familial resemblance was observed at baseline and for 7-year changes in all phenotypes. At baseline, moderate heritabilities were observed [body mass: heritability coefficient (h(2)) = 56%; BMI, h(2) = 39%; SF5, h(2) = 41%; and WC, h(2) = 39%], whereas values were attenuated for each change score except for WC (Deltabody mass, h(2) = 23%; DeltaBMI, h(2) = 14%; DeltaSF5, h(2) = 12%; and DeltaWC, h(2) = 45%).

DISCUSSION

Changes in body mass and adiposity significantly aggregate within families over 7 years. However, baseline values are characterized by higher heritability levels except WC. The significant heritabilities observed for change scores suggest that lifestyle, transient environmental factors, and possibly age-related gene effects are important determinants of changes in body mass and adiposity.

Human obesity: an evolutionary approach to understanding our bulging waistline

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