Life-course analysis of a fat mass and obesity-associated (FTO) gene variant and body mass index in the Northern Finland Birth Cohort 1966 using structural equation modeling

Understanding the metabolome and metagenome as extended phenotypes: The next frontier in macroalgae domestication and improvement

"Omics" techniques (including genomics, transcriptomics, metabolomics, proteomics, and metagenomics) have been employed with huge success in the improvement of agricultural crops. As marine aquaculture of macroalgae expands globally, biologists are working to domesticate species of macroalgae by applying these techniques tested in agriculture to wild macroalgae species. Metabolomics has revealed metabolites and pathways that influence agriculturally relevant traits in crops, allowing for informed crop crossing schemes and genomic improvement strategies that would be pivotal to inform selection on macroalgae for domestication. Advances in metagenomics have improved understanding of host-symbiont interactions and the potential for microbial organisms to improve crop outcomes. There is much room in the field of macroalgal biology for further research toward improvement of macroalgae cultivars in aquaculture using metabolomic and metagenomic analyses. To this end, this review discusses the application and necessary expansion of the omics tool kit for macroalgae domestication as we move to enhance seaweed farming worldwide.

Leisure-time physical activity is associated with socio-economic status beyond income - Cross-sectional survey of the Northern Finland Birth Cohort 1966 study

We apply neoclassical economic modelling augmented with behavioral aspects to provide a detailed empirical investigation into indicators of socio-economic status (SES) as determinants of leisure-time physical activity. We utilize the data from the Northern Finland Birth Cohort 1966 obtained at the most recent time point during 2012-2014 (response rate 67 %), at which time the participants were approximately 46 years old. Our final study sample consists of 3,335 employed participants (1520 men, 1815 women; 32.3 % of the target population). We apply logistic regression methods for estimating how the probability of being physically active is related to various indicators of socio-economic status, taking into account physical activity at work and individual lifestyle, family- and health-related factors. Overall, our findings show that belonging to a higher socio-economic group, whether defined by income level, educational attainment, or occupational status, is associated with higher leisure-time physical activity. However, when we analyze different socio-economic groups, defined in terms of education, income and occupation, separately, we find that income is not a significant determinant of leisure-time physical activity within any of the particular SES groups. Further, we find that leisure-time physical activity is negatively associated with higher screen time (i.e., watching TV and sitting at a computer), and other aspects of unhealthy lifestyle, and positively associated with self-assessed health. In addition, we note that proxies for individual motivational factors and childhood physical activity, such as the grade point average and the grade achieved in physical education when leaving basic education, are strongly correlated with leisure-time physical activity in middle age among men, but not among women. Our results are in line with behavioral economics reasoning that social comparisons and environments affect behaviors. We emphasize the importance of considering behavioral economic factors when designing policies to promote physical activity.

Using synthetic datasets to bridge the gap between the promise and reality of basing health-related decisions on common single nucleotide polymorphisms

Background: While the academic genetic literature has clearly shown that common genetic single nucleotide polymorphisms (SNPs), and even large polygenic SNP risk scores, cannot reliably be used to determine risk of disease or to personalize interventions, a significant industry of companies providing SNP-based recommendations still exists. Healthcare practitioners must therefore be able to navigate between the promise and reality of these tools, including being able to interpret the literature that is associated with a given risk or suggested intervention. One significant hurdle to this process is the fact that most population studies of common SNPs only provide average (+/- error) phenotypic or risk descriptions for a given genotype, which hides the true heterogeneity of the population and reduces the ability of an individual to determine how they themselves or their patients might truly be affected. Methods: We generated synthetic datasets generated from descriptive phenotypic data published on common SNPs associated with obesity, elevated fasting blood glucose, and methylation status. Using simple statistical theory and full graphical representation of the generated data, we developed a method by which anybody can better understand phenotypic heterogeneity in a population, as well as the degree to which common SNPs truly drive disease risk. Results: Individual risk SNPs had a <10% likelihood of effecting the associated phenotype (bodyweight, fasting glucose, or homocysteine levels). Example polygenic risk scores including the SNPs most associated with obesity and type 2 diabetes only explained 2% and 5% of the final phenotype, respectively. Conclusions: The data suggest that most disease risk is dominated by the effect of the modern environment, providing further evidence to support the pursuit of lifestyle-based interventions that are likely to be beneficial regardless of genetics.

Fine-mapping of 98 obesity loci in Mexican children

BACKGROUND/OBJECTIVES

Mexico has one of the highest prevalence of childhood obesity in the world. Genome-wide association studies (GWAS) for obesity have identified multiple single-nucleotide polymorphisms (SNPs) in populations of European, East Asian, and African descent. The contribution of these loci to obesity in Mexican children is unclear. We assessed the transferability of 98 obesity loci in Mexican children and fine-mapped the association signals.

SUBJECTS/METHODS

The study included 405 and 390 Mexican children with normal weight and obesity. Participants were genotyped with a genome-wide dense SNP array designed for Latino populations, allowing for the analysis of GWAS index SNPs as well as fine-mapping SNPs, totaling 750 SNPs covering 98 loci. Two genetic risk scores (GRS) were constructed: a "discovery GRS" and a "best-associated GRS", representing the number of effect alleles at the GWAS index SNPs and at the best-associated SNPs after fine-mapping for each subject.

RESULTS

Seventeen obesity loci were significantly associated with obesity, and five had fine-mapping SNPs significantly better associated with obesity than their corresponding GWAS index SNPs in Mexican children. Six obesity-associated SNPs significantly departed from additive to dominant (N = 5) or recessive (N = 1) models, and a significant interaction was found between rs274609 (TNNI3K) and rs1010553 (ITIH4) on childhood obesity risk. The best-associated GRS was significantly more associated with childhood obesity (OR = 1.21 per additional risk allele [95%CI:1.17-1.25], P = 4.8 × 10^-25) than the discovery GRS (OR = 1.05 per additional risk allele [95%CI:1.02-1.08], P = 8.0 × 10^-4), and was also associated with waist-to-hip ratio, fasting glucose, fasting insulin and triglyceride levels, the association being mediated by obesity. An overall depletion of obesity risk alleles was observed in Mexican children with normal weight when compared to GWAS discovery populations.

CONCLUSIONS

Our study indicates a partial transferability of GWAS obesity loci in Mexican children, and supports the pertinence of post-GWAS fine-mapping experiments in the admixed Mexican population.

Longitudinal Analysis of Genetic Susceptibility and BMI Throughout Adult Life

Little is known about the genetic influence on BMI trajectory throughout adulthood. We created a genetic risk score (GRS) comprising 97 adult BMI-associated variants among 9,971 women and 6,405 men of European ancestry. Serial measures of BMI were assessed from 18 (women) or 21 (men) years to 85 years of age. We also examined BMI change in early (from 18 or 21 to 45 years of age), middle (from 45 to 65 years of age), and late adulthood (from 65 to 80 years of age). GRS was positively associated with BMI across all ages, with stronger associations in women than in men. The associations increased from early to middle adulthood, peaked at 45 years of age in men and at 60 years of age in women (0.91 and 1.35 kg/m² per 10-allele increment, respectively) and subsequently declined in late adulthood. For women, each 10-allele increment in the GRS was associated with an average BMI gain of 0.54 kg/m² in early adulthood, whereas no statistically significant association was found for BMI change in middle or late adulthood or for BMI change in any life period in men. Our findings indicate that genetic predisposition exerts a persistent effect on adiposity throughout adult life and increases early adulthood weight gain in women.

The importance of gene-environment interactions in human obesity

The worldwide obesity epidemic has been mainly attributed to lifestyle changes. However, who becomes obese in an obesity-prone environment is largely determined by genetic factors. In the last 20 years, important progress has been made in the elucidation of the genetic architecture of obesity. In parallel with successful gene identifications, the number of gene-environment interaction (GEI) studies has grown rapidly. This paper reviews the growing body of evidence supporting gene-environment interactions in the field of obesity. Heritability, monogenic and polygenic obesity studies provide converging evidence that obesity-predisposing genes interact with a variety of environmental, lifestyle and treatment exposures. However, some skepticism remains regarding the validity of these studies based on several issues, which include statistical modelling, confounding, low replication rate, underpowered analyses, biological assumptions and measurement precision. What follows in this review includes (1) an introduction to the study of GEI, (2) the evidence of GEI in the field of obesity, (3) an outline of the biological mechanisms that may explain these interaction effects, (4) methodological challenges associated with GEI studies and potential solutions, and (5) future directions of GEI research. Thus far, this growing body of evidence has provided a deeper understanding of GEI influencing obesity and may have tremendous applications in the emerging field of personalized medicine and individualized lifestyle recommendations.

BMI loci and longitudinal BMI from adolescence to young adulthood in an ethnically diverse cohort

Objective

The association of obesity susceptibility variants with change in body mass index (BMI) across the life course is not well understood.

Subjects

In ancestry stratified models of 5,962 European American (EA), 2,080 African American (AA), and 1,582 Hispanic American (HA) individuals from the National Longitudinal Study of Adolescent to Adult Health (Add Health), we examined associations between 34 obesity SNPs with per year change in BMI, measured by the slope from a growth-curve analysis of two or more BMI measurements between adolescence and young adulthood. For SNPs nominally associated with BMI change (p<0.05), we interrogated age differences within data collection Wave and time differences between age categories that overlapped between Waves.

Results

We found SNPs in/near FTO, MC4R, MTCH2, TFAP2B, SEC16B, and TMEM18 were significantly associated (p<0.0015 ≈ 0.05/34) with BMI change in EA and the ancestry-combined meta-analysis. Rs9939609 in FTO met genome-wide significance at p<5e-08 in the EA and ancestry combined analysis, respectively [Beta(se)=0.025(0.004);Beta(se)=0.021(0.003)]. No SNPs were significant after Bonferroni correction in AA or HA, although 5 SNPs in AA and 4 SNPs in HA were nominally significant (p<0.05). In EA and the ancestry-combined meta-analysis, rs3817334 near MTCH2 showed larger effects in younger respondents, while rs987237 near TFAP2B, showed larger effects in older respondents across all Waves. Differences in effect estimates across time for MTCH2 and TFAP2B are suggestive of either era or cohort effects.

Conclusion

The observed association between variants in/near FTO, MC4R, MTCH2, TFAP2B, SEC16B, and TMEM18 with change in BMI from adolescence to young adulthood suggest that the genetic effect of BMI loci varies over time in a complex manner, highlighting the importance of investigating loci influencing obesity risk across the life course.

Genetic and Environmental Effects on Weight, Height, and BMI Under 18 Years in a Chinese Population-Based Twin Sample

This study examined the genetic and environmental effects on variances in weight, height, and body mass index (BMI) under 18 years in a population-based sample from China. We selected 6,644 monozygotic and 5,969 dizygotic twin pairs from the Chinese National Twin Registry (CNTR) aged under 18 years (n = 12,613). Classic twin analyses with sex limitation were used to estimate the genetic and environmental components of weight, height, and BMI in six age groups. Sex-limitation of genetic and shared environmental effects was observed, especially when puberty begins. Heritability for weight, height, and BMI was low at 0-2 years old (less than 20% for both sexes) but increased over time, accounting for half or more of the variance in the 15-17 year age group for boys. For girls, heritabilities for weight, height and BMI was maintained at approximately 30% after puberty. Common environmental effects on all body measures were high for girls (59-87%) and presented a small peak during puberty. Genetics appear to play an increasingly important role in explaining the variation in weight, height, and BMI from early childhood to late adolescence, particularly in boys. Common environmental factors exert their strongest and most independent influence specifically in the pre-adolescent period and more significantly in girls. These findings emphasize the need to target family and social environmental interventions in early childhood years, especially for females. Further studies about puberty-related genes and social environment are needed to clarify the mechanism of sex differences.

Perceived weight discrimination, childhood maltreatment, and weight gain in U.S. adults with overweight/obesity

OBJECTIVE

Perceived weight discrimination and childhood maltreatment have been independently associated with physical and mental health issues, as well as weight gain. It is not known, however, whether childhood maltreatment modifies the relationship between perceived weight discrimination and weight changes.

METHODS

This study examined the relationship between perceived weight discrimination, childhood maltreatment, and changes in body mass index (BMI) over 3 years in 21,357 men and women with overweight and obesity from Wave 1 and Wave 2 surveys of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC).

RESULTS

Reporting childhood maltreatment, regardless of the specific form of maltreatment, was associated with a significantly greater likelihood of perceived weight discrimination in women. Perceived weight discrimination was associated with a significantly greater increase in BMI in both genders. Among all women with perceived weight discrimination, those who also reported having experienced childhood maltreatment had significantly less BMI increase compared to those reporting not having experienced childhood maltreatment.

CONCLUSIONS

Perceived weight discrimination may foster weight gain rather than encouraging weight loss in individuals with overweight/obesity and should be addressed in prevention efforts and clinical settings. Childhood maltreatment may perhaps sensitize individuals to subsequent stressors and increase vulnerability to perceived weight discrimination, particularly in women.

Combined early and adult life risk factor associations for mid-life obesity in a prospective birth cohort: assessing potential public health impact

OBJECTIVE

The combined effect of life-course influences on obesity development and thus their potential public health impact is unclear. We evaluated combined associations and predicted probabilities for early and adult life risk factors with central and general obesity in mid-adulthood.

SETTING

1958 British birth cohort.

PARTICIPANTS

4629 males and 4670 females with data on waist circumference.

OUTCOME MEASURES

45 year obesity measured via waist circumference, waist-hip ratio (WHR) and BMI.

RESULTS

At 45 years, approximately a third of the population were centrally obese and a quarter were generally obese. Three factors (parental overweight, maternal smoking during pregnancy and adult inactivity) were consistently associated with central and general obesity. Predicted probabilities for waist obesity increased from those with none to all three risk factors (0.15-0.33 in men; 0.19-0.39 in women (ptrend<0.001)), with a similar trend for general obesity. Additional factors (adult smoking, low fibre and heavy alcohol consumption) were associated with WHR obesity, although varying by gender. Prevalence of risk factors was higher in manual than non-manual groups: for example, in men 38% versus 25%, respectively, had ≥2 risk factors for waist and general obesity.

CONCLUSIONS

Early-life and adult factors that are amenable to change are highly prevalent and accumulate in association with central and general obesity in mid-adulthood. The increase in probabilities for mid-adult obesity associated with cumulative levels of risk factors suggests the potential for public health impact.

Behavioral and Environmental Modification of the Genetic Influence on Body Mass Index: A Twin Study

Body mass index (BMI) has a strong genetic basis, with a heritability around 0.75, but is also influenced by numerous behavioral and environmental factors. Aspects of the built environment (e.g., environmental walkability) are hypothesized to influence obesity by directly affecting BMI, by facilitating or inhibiting behaviors such as physical activity that are related to BMI, or by suppressing genetic tendencies toward higher BMI. The present study investigated relative influences of physical activity and walkability on variance in BMI using 5079 same-sex adult twin pairs (70 % monozygotic, 65 % female). High activity and walkability levels independently suppressed genetic variance in BMI. Estimating their effects simultaneously, however, suggested that the walkability effect was mediated by activity. The suppressive effect of activity on variance in BMI was present even with a tendency for low-BMI individuals to select into environments that require higher activity levels. Overall, our results point to community- or macro-level interventions that facilitate individual-level behaviors as a plausible approach to addressing the obesity epidemic among US adults.

Variation in the fat mass and obesity-related (FTO) genotype is not associated with body fatness in infants, but possibly with their length

BACKGROUND

Data relating variation at the fat mass and obesity-related (FTO) locus (rs9939609) to fat mass in infancy are inconclusive.

OBJECTIVE

To study relationships between FTO genotype and infant size (at 1 and 12 weeks and at 1 year of age) and body composition (at 1 and 12 weeks).

METHODS

Body composition was assessed using air displacement plethysmography in 207 infants. FTO was genotyped using the TaqMan assay.

RESULTS

The number of risk alleles was related to length at 1 and 12 weeks (P = 0.007-0.033) but not to fat mass. The relationship to length was stronger in boys than in girls.

CONCLUSIONS

Our results suggest that the FTO genotype is not related during infancy to fat mass but is related to length in boys but not in girls.

Body mass index and overweight in relation to residence distance and population density: experience from the Northern Finland birth cohort 1966

Background

The effect of urban sprawl on body weight in Finland is not well known. To provide more information, we examined whether body mass index (BMI) and the prevalence of overweight are associated with an individual’s distance to the local community centre and population density in his/her resident area.

Methods

The sample consisted of 5363 men and women, members of the Northern Finland Birth Cohort 1966 (NFBC), who filled in a postal questionnaire and attended a medical checkup in 1997, at the age of 31 years. Body mass index (BMI; kg/m²) and the prevalence of overweight (BMI ≥ 25.0 kg/m²) were regressed on each subject’s road distance to the resident commune’s centre and on population density in the 1 km² geographical grid in which he/she resided, using a generalized additive model. Adjustments were made for sex, marital status, occupational class, education, leisure-time and occupational physical activity, alcohol consumption and smoking.

Results

The mean BMI among the subjects was 24.7 kg/m², but it increased by increasing road distance (by 1.3 kg/m² from 5–10 to 20–184 km) and by decreasing population density (by 1.7 kg/m² from 1000–19,192 to 1–5 inhabitants/km²). The respective increases in overweight (overall prevalence 41%) were 13 per cent units for distance and 14 per cent units for population density. Adjusted regressions based on continuous explanatory variables showed an inverse L-shaped pattern with a mean BMI of 24.6 kg/m² at distances shorter than 5 km and a rise of 2.6 kg/m² at longer distances, and an increase of 2.5 kg/m² from highest to lowest population density. The associations with road distance were stronger for women than men, while the sex difference in association with population density remained indeterminate.

Conclusions

We conclude that young adults in Northern Finland who live far away from local centres or in the most sparsely populated areas are fatter than those who live close to local centres or in densely populated areas. The likely explanations include variations in everyday physical activity in different residential environments, although causality of the associations remains to be confirmed.

Prospective analysis of the association of a common variant of FTO (rs9939609) with adiposity in children: results of the IDEFICS study

Objectives

We investigated cross-sectionally and longitudinally the relationship between FTO rs9939609 and obesity-related characteristics in the European children of the IDEFICS project and the interaction of this variant with a lifestyle intervention.

Population and Methods

A cohort of 16224 children (2–9 years) was recruited into a population-based survey (T0) from eight European countries. A second survey (T1) reassessed the children two years later. A random sample of 4405 children was extracted for genetic studies. 3168 children were re-examined two years later. Half of them underwent a lifestyle intervention program. The FTO rs9939609 was genotyped. Weight, height, waist circumference, triceps and subscapular skinfolds were measured at T0 and T1.

Results

At T0, the risk A allele of rs9939609 was significantly associated with higher values of body mass index (BMI), waist circumference and skinfolds (age, sex, and country-adjusted p-values: all p<0.001) and with a statistically significant increased risk of overweight/obesity.

Over the two year follow-up, no interaction between genotype and intervention was observed. The A allele was associated to a significantly higher increase in all the anthropometric variables examined at T0 independently from the study group (intervention versus control) (p-values: all p<0.002, adjusted for age, sex, country, intervention/control study group, T0 values, and individual time interval between T0 and T1). Over the two-year follow–up, 210 new cases of overweight/obesity occurred. A statistically significant higher incidence of overweight/obesity was associated to the A allele [OR_A = 1.95, 95% CI = (1.29; 2.97)].

Conclusions

We confirmed the association between the FTO rs9939609 and body mass and overweight/obesity risk in European children. The main finding of the study is that the A allele carriers present higher increase of body mass and central adiposity over time and higher risk of developing overweight/obesity during growth, independently from intervention measures.

Beyond the fourth wave of genome-wide obesity association studies

Obesity and related complications are major health burdens. Almost 700 million adults are currently obese globally and the prevalence is predicted to rise towards 2030. The sudden change of lifestyle with physical inactivity and excessive calorie intake undoubtedly have a major part of the epidemic development; however, some individuals seem to be more prone to be affected by an unhealthy lifestyle than others. Hence, genetic predisposition also has an essential role in determining disease susceptibility and response to lifestyle factors. Since the introduction of genome-wide association studies (GWAS), the success of identifying obesity susceptibility variants have increased, and a total of 32 variants have been identified associating genome-wide significantly with body mass index (BMI) and 18 with measures of fat distribution during four overall obesity GWAS waves. However, the immediate success of the GWAS approach has eased off, but the proportion of explained variance for BMI by the identified obesity variants remains low. This review suggests and discusses new initiatives to take GWAS of obesity to the next level, including gene–environment interactions as modulating/masking factors, low-frequent or rare variants and ways to address such analyses, and finally reflections about the applicability of epigenetic modifications when elucidating the genetic background of obesity.

Association of FTO gene variants with body composition in UK twins

The association of FTO gene variants with body mass index (BMI) and other obesity characteristics is well established. However, uncertainties remain whether the association is present only in young populations and whether it is attributable to body fat mass specifically. We aimed to clarify these two questions in a large sample (N= 4,523 individuals) of middle-aged and older (range 40–80 years) British female twins. The women were assessed for BMI, waist and hip circumference, total lean (LBM) and fat (FBM) body mass. Since the majority of FTO association signals have been reported in a haploblock bordering 52,355–52,408 kb (on chromosome 16q12.2), we examined five genotyped and 43 imputed SNPs mapped to this block. Canonical correlation and other association analyses showed significant and consistent association between the selected SNP and studied body composition phenotypes, with p-values reaching p= 0.000004. Of particular interest, in addition to the expected significant associations between FTO variants and FBM, we also identified significant associations with LBM. These results suggest that the association between FTO variants and body composition phenotypes is present across a wide range of ages, and that FTO appears primarily to affect the amount of body soft tissue, influencing both fat and lean mass.

Genetics of pediatric obesity

Onset of obesity has been anticipated at earlier ages, and prevalence has dramatically increased worldwide over the past decades. Epidemic obesity is mainly attributable to modern lifestyle, but family studies prove the significant role of genes in the individual's predisposition to obesity. Advances in genotyping technologies have raised great hope and expectations that genetic testing will pave the way to personalized medicine and that complex traits such as obesity will be prevented even before birth. In the presence of the pressing offer of direct-to-consumer genetic testing services from private companies to estimate the individual's risk for complex phenotypes including obesity, the present review offers pediatricians an update of the state of the art on genomics obesity in childhood. Discrepancies with respect to genomics of adult obesity are discussed. After an appraisal of findings from genome-wide association studies in pediatric populations, the rare variant-common disease hypothesis, the theoretical soil for next-generation sequencing techniques, is discussed as opposite to the common disease-common variant hypothesis. Next-generation sequencing techniques are expected to fill the gap of "missing heritability" of obesity, identifying rare variants associated with the trait and clarifying the role of epigenetics in its heritability. Pediatric obesity emerges as a complex phenotype, modulated by unique gene-environment interactions that occur in periods of life and are "permissive" for the programming of adult obesity. With the advent of next-generation sequencing techniques and advances in the field of exposomics, sensitive and specific tools to predict the obesity risk as early as possible are the challenge for the next decade.

FTO, abdominal adiposity, fasting hyperglycemia associated with elevated HbA1c in Japanese middle-aged women

AIM

FTO is the most important polygene for obesity and type 2 diabetes. Our aims were to investigate whether a variant in FTO affects glucose dysregulation through its effect on fat accumulation or distribution, and when and how FTO influences fat accumulation and distribution and glucose dysregulation from birth until midlife.

METHODS

A total of 454 Japanese female university students (mean age: 20 years) and 132 middle-aged women (mean age: 50 years) who were the biological mothers of the students underwent the following: genotyping for rs1558902 in the FTO gene, assessment of fat accumulation and distribution, obesity-related metabolic traits and serum adipokine measurement. A subsample of 364 students reported their weight history since birth.

RESULTS

The A allele in rs1558902 was substantially less common in young and middle-aged Japanese women (18 and 17%, respectively) than in the European population (45%). The strong effect of genotype AA on BMI was evident at age 12, 15, 20 and 50 years whereas there was no effect on birth weight. In young and middle-aged women, the variant was strongly associated with higher body weight and fat mass. The effects on abdominal girth, fasting glucose, homeostasis model assessment insulin resistance and HbA1c were evident in mothers but not in students. In addition, genotype AA was associated with increased white blood cell counts and hsCRP in mothers only. Associations with fasting glucose, insulin resistance, and white blood cell counts remained after correction for BMI, abdominal girth and fat mass. In multiple logistic regression analysis, AA homozygote in FTO was associated with higher odds of overweight (BMI ≥25 kg/m(2)) in young (OR 1.73 (95%CI 1.06-30.0)) and middle-aged women (OR 1.73 (95%CI 1.06-30.0)). It was also associated with higher odds of abdominal fat accumulation (abdominal girth ≥90 cm, OR 1.73 (95%CI 1.06-30.0)) and fasting hyperglycemia (≥100 mg/dL) (OR 1.87(95%CI 1.05-40.4)) in middle-aged mothers.

CONCLUSION

Despite the small sample size, the low average BMI, and the low risk allele frequency, a genetic variation at the FTO locus was related to greater weight gain before age 12 in Japanese women. At age 20, it was related to general adiposity. In midlife, however, it was related to abdominal adiposity in addition to general adiposity, fasting hyperglycemia, higher HbA1c and subtle systemic inflammation. Fasting hyperglycemia associated with higher HbA1c in midlife was independent of its effects on general and abdominal adiposity.

Variation in sequence and expression of the avian FTO, and association with glucose metabolism, body weight, fatness and body composition in chickens

OBJECTIVE

The fat mass and obesity-associated gene (FTO), a crucial gene that affects human obesity and metabolism, has been widely studied in mammals but remains poorly characterized in birds. We aimed to identify variant FTO transcripts in domestic avian species, and to characterize the expression and biological functions of FTO in chickens.

METHODS

Variant FTO transcripts and their expression in birds were investigated using RACE and real-time quantitative reverse transcriptase-PCR technology. The effects of FTO on glucose metabolism, growth and body composition were determined by fasting and various diet treatments, as well as association analysis in a F₂ resource population. The function of cFTO1 was further studied by overexpression in chick embryo fibroblast (CEF) cells.

RESULTS

Variant FTO transcripts were identified in chicken (cFTO1 to cFTO4), duck (dFTO1, dFTO2 and dFTO4) and goose (gFTO1, gFTO2 and gFTO5). In the chicken, the complete transcript (cFTO1) was predominantly expressed in the leg muscle, pituitary, hypothalamus and cerebellum. Fasting increased both cFTO1 and PGC1α gene expression in the cerebrum, liver, breast muscle and subcutaneous fat, but decreased expression in the pituitary and anterior hypothalamus. In all tested tissues in chickens, a high-glucose diet markedly increased cFTO1 and PGC1α expression. Feeding a high-fat diet increased both cFTO1 and PGC1α expression, except in the pituitary. Overexpression of cFTO1 in CEF cells significantly increased the expression of PGC1α (2.5-fold), STAT3 (2.2-fold) and HL (1.5-fold), a cluster of genes related to energy metabolism. A total of 65 single nucleotide polymorphisms (SNPs) were identified in chicken FTO, and 18 tested SNPs were significantly associated with traits of body weight, body composition and fatness.

CONCLUSIONS

These data collectively indicate that FTO is related to glucose metabolism, body weight, fatness and body composition in birds, thus expanding knowledge of FTO function to non-mammalian species.

Genetics of Obesity: What have we Learned?

Candidate gene and genome-wide association studies have led to the discovery of nine loci involved in Mendelian forms of obesity and 58 loci contributing to polygenic obesity. These loci explain a small fraction of the heritability for obesity and many genes remain to be discovered. However, efforts in obesity gene identification greatly modified our understanding of this disorder. In this review, we propose an overlook of major lessons learned from 15 years of research in the field of genetics and obesity. We comment on the existence of the genetic continuum between monogenic and polygenic forms of obesity that pinpoints the role of genes involved in the central regulation of food intake and genetic predisposition to obesity. We explain how the identification of novel obesity predisposing genes has clarified unsuspected biological pathways involved in the control of energy balance that have helped to understand past human history and to explore causality in epidemiology. We provide evidence that obesity predisposing genes interact with the environment and influence the response to treatment relevant to disease prediction.

Physical activity attenuates the influence of FTO variants on obesity risk: a meta-analysis of 218,166 adults and 19,268 children

BACKGROUND

The FTO gene harbors the strongest known susceptibility locus for obesity. While many individual studies have suggested that physical activity (PA) may attenuate the effect of FTO on obesity risk, other studies have not been able to confirm this interaction. To confirm or refute unambiguously whether PA attenuates the association of FTO with obesity risk, we meta-analyzed data from 45 studies of adults (n = 218,166) and nine studies of children and adolescents (n = 19,268).

METHODS AND FINDINGS

All studies identified to have data on the FTO rs9939609 variant (or any proxy [r(2)>0.8]) and PA were invited to participate, regardless of ethnicity or age of the participants. PA was standardized by categorizing it into a dichotomous variable (physically inactive versus active) in each study. Overall, 25% of adults and 13% of children were categorized as inactive. Interaction analyses were performed within each study by including the FTO×PA interaction term in an additive model, adjusting for age and sex. Subsequently, random effects meta-analysis was used to pool the interaction terms. In adults, the minor (A-) allele of rs9939609 increased the odds of obesity by 1.23-fold/allele (95% CI 1.20-1.26), but PA attenuated this effect (p(interaction)  = 0.001). More specifically, the minor allele of rs9939609 increased the odds of obesity less in the physically active group (odds ratio  = 1.22/allele, 95% CI 1.19-1.25) than in the inactive group (odds ratio  = 1.30/allele, 95% CI 1.24-1.36). No such interaction was found in children and adolescents.

CONCLUSIONS

The association of the FTO risk allele with the odds of obesity is attenuated by 27% in physically active adults, highlighting the importance of PA in particular in those genetically predisposed to obesity.

Advances in exercise, fitness, and performance genomics in 2010

This review of the exercise genomics literature emphasizes the strongest articles published in 2010 as defined by sample size, quality of phenotype measurements, quality of the exercise program or physical activity exposure, study design, adjustment for multiple testing, quality of genotyping, and other related study characteristics. One study on voluntary running wheel behavior was performed in 448 mice from 41 inbred strains. Several quantitative trait loci for running distance, speed, and duration were identified. Several studies on the alpha-3 actinin (ACTN3) R577X nonsense polymorphism and the angiotensin-converting enzyme (ACE) I/D polymorphism were reported with no clear evidence for a joint effect, but the studies were generally underpowered. Skeletal muscle RNA abundance at baseline for 29 transcripts and 11 single nucleotide polymorphisms (SNPs) were both found to be predictive of the V˙O2max response to exercise training in one report from multiple laboratories. None of the 50 loci associated with adiposity traits are known to influence physical activity behavior. However, physical activity seems to reduce the obesity-promoting effects of at least 12 of these loci. Evidence continues to be strong for a role of gene-exercise interaction effects on the improvement in insulin sensitivity after exposure to regular exercise. SNPs in the cAMP-responsive element binding position 1 (CREB1) gene were associated with training-induced HR response, in the C-reactive protein (CRP) gene with training-induced changes in left ventricular mass, and in the methylenetetrahydrofolate reductase (MTHFR) gene with carotid stiffness in low-fit individuals. We conclude that progress is being made but that high-quality research designs and replication studies with large sample sizes are urgently needed.

FTO, type 2 diabetes, and weight gain throughout adult life: a meta-analysis of 41,504 subjects from the Scandinavian HUNT, MDC, and MPP studies

OBJECTIVE

FTO is the most important polygene identified for obesity. We aimed to investigate whether a variant in FTO affects type 2 diabetes risk entirely through its effect on BMI and how FTO influences BMI across adult life span.

RESEARCH DESIGN AND METHODS

Through regression models, we assessed the relationship between the FTO single nucleotide polymorphisms rs9939609, type 2 diabetes, and BMI across life span in subjects from the Norwegian population-based HUNT study using cross-sectional and longitudinal perspectives. For replication and meta-analysis, we used data from the Malmö Diet and Cancer (MDC) and Malmö Preventive Project (MPP) cohorts, comprising a total sample of 41,504 Scandinavians.

RESULTS

The meta-analysis revealed a highly significant association for rs9939609 with both type 2 diabetes (OR 1.13; P = 4.5 × 10(-8)) and the risk to develop incident type 2 diabetes (OR 1.16; P = 3.2 × 10(-8)). The associations remained also after correction for BMI and other anthropometric measures. Furthermore, we confirmed the strong effect on BMI (0.28 kg/m(2) per risk allele; P = 2.0 × 10(-26)), with no heterogeneity between different age-groups. We found no differences in change of BMI over time according to rs9939609 risk alleles, neither overall (ΔBMI = 0.0 [-0.05, 0.05]) nor in any individual age stratum, indicating no further weight gain attributable to FTO genotype in adults.

CONCLUSIONS

We have identified that a variant in FTO alters type 2 diabetes risk partly independent of its observed effect on BMI. The additional weight gain as a result of the FTO risk variant seems to occur before adulthood, and the BMI difference remains stable thereafter.