Genome-wide linkage scan for physical activity levels in the Quebec Family study

Genomic profile in association with sport-type, sex, ethnicity, psychological traits and sport injuries of elite athletes: review and future perspectives

In the last few years, some inherited determinants have been associated with elite athletic performance, but its polygenic trait character has limited the correct definition of elite athlete's genomic profile. This qualitative descriptive study aims to summarise the current understanding about genetic and epigenetic factors in elite athletes, as well as their genomic profile in association with sport-type, sex, ethnicity, psychological traits and sport injuries. A narrative review of the literature across a broad cross-section of the elite athletes' genomic profile was undertaken. Elite performance relies on rare gene variants within a great interface between molecular, cellular and behavioural sport-related phenotypes and the environment, which is still poorly understood. ACTN3 rs1815739 and ACE I/D polymorphisms appear to be associated to specific sprint phenotypes and influence the athletic status, i.e., the rs1815739 variant is more influential to 200-m performance and the ACE ID polymorphism is more involved in the longer, 400-m sprint performance. Generally, athletes show endurance-based sports characteristics or power-based sports characteristics, but some studies have reported some genes associations to both sports-based characteristics. Furthermore, genetic studies with larger cohorts of single-sport athletes might be preferable than studies combining athletes of different sports, given the existence of distinct athlete profiles and sport demands. Athletic performance may be influenced by the serotonergic pathway and the potential injury risk (namely stress fracture) might be associated to a genetic predisposition associated to the mechanical loading from the intense physical exercise. The study of gene variants associated to sex and ethnicity-related to athletic performance needs further investigation. The combination of genome-wide association studies addressing the genetic architecture of athletes and the subsequent replication and validation studies might for additional genetic data is mandatory.

Genetic test for the prescription of diets in support of physical activity

Owing to the fields of nutrigenetics and nutrigenomics today we can think of devising approaches to optimize health, delay onset of diseases and reduce its severity according to our genetic blue print. However this requires a deep understanding of nutritional impact on expression of genes that may result in a specific phenotype. The extensive research and observational studies during last two decades reporting interactions between genes, diet and physical activity suggest a cross talk between various genetic and environmental factors and lifestyle interventions. Although considerable efforts have been made in unraveling the mechanisms of gene-diet interactions the scientific evidences behind developing commercial genetic tests for providing personalized nutrition recommendations are still scarce. In this scenario the current mini-review aims to provide useful insights into salient feature of nutrition based genetic research and its commercial application and the ethical issue and concerns related to its outcome.

Genomewide Association Study of Leisure-Time Exercise Behavior in Japanese Adults

Supplemental digital content is available in the text.

Purpose

Although several genetic factors may play a role in leisure-time exercise behavior, there is currently no evidence of a significant genomewide association, and candidate gene replication studies have produced inconsistent results.

Methods

We conducted a two-stage genomewide association study and candidate single-nucleotide polymorphisms (SNP) association study on leisure-time exercise behavior using 13,980 discovery samples from the Japan Multi-Institutional Collaborative Cohort (J-MICC) study, and 2036 replication samples from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center-2 study. Leisure-time physical activity was measured using a self-administered questionnaire that inquired about the type, frequency and duration of exercise. Participants with ≥4 MET·h·wk⁻¹ of leisure-time physical activity were defined as exhibiting leisure-time exercise behavior. Association testing using mixed linear regression models was performed on the discovery and replication samples, after which the results were combined in a meta-analysis. In addition, we tested six candidate genetic variants derived from previous genomewide association study.

Results

We found that one novel SNP (rs10252228) located in the intergenic region between NPSR1 and DPY19L1 was significantly associated with leisure-time exercise behavior in discovery samples. This association was also significant in replication samples (combined P value by meta-analysis = 2.2 × 10⁻⁹). Several SNP linked with rs10252228 were significantly associated with gene expression of DPY19L1 and DP19L2P1 in skeletal muscle, heart, whole blood, and the nervous system. Among the candidate SNP, rs12612420 in DNAPTP6 demonstrated nominal significance in discovery samples but not in replication samples.

Conclusions

We identified a novel genetic variant associated with regular leisure-time exercise behavior. Further functional studies are required to validate the role of these variants in exercise behavior.

Identification of genetic association between cardiorespiratory fitness and the trainability genes in childhood acute lymphoblastic leukemia survivors

BACKGROUND

The progress of treatments of childhood acute lymphoblastic leukemia (ALL) has made it possible to reach a survival rate superior to 80%. However, the treatments lead to several long-term adverse effects, including cardiac toxicity. Although studies have reported associations between genetic variants and cardiorespiratory fitness, none has been performed on childhood ALL survivors.

METHODS

We performed whole-exome sequencing in 239 childhood ALL survivors from the PETALE cohort. Germline variants (both common and rare) in selected set of genes (N = 238) were analyzed for an association with cardiorespiratory fitness.

RESULTS

Our results showed that the common variant in the TTN gene was significantly associated with a low cardiorespiratory fitness level (p = 0.0005) and that the LEPR, IGFBPI and ENO3 genes were significantly associated with a low cardiorespiratory fitness level in female survivors (p ≤ 0.002). Also, we detected an association between the low cardiorespiratory fitness level in participants that were stratified to the "high risk" prognostic group and functionally predicted rare variants in the SLC22A16 gene (p = 0.001). Positive associations between cardiorespiratory fitness level and trainability genes were mainly observed in females.

CONCLUSIONS

For the first time, we observed that low cardiorespiratory fitness in childhood ALL survivors can be associated with variants in genes related to subjects' trainability. These findings could allow better childhood ALL patient follow-up tailored to their genetic profile and cardiorespiratory fitness, which could help reduce at least some of the burden of long-term adverse effects of treatments.

Genetic Factors Associated With Human Physical Activity: Are Your Genes Too Tight To Prevent You Exercising?

The benefits of physical activity (PA) on health and fitness are well known. It has become apparent from studies of heritability that there is a considerable genetic component to PA. However, PA is such a complex phenotype that the measurement and quantification of it provide a challenge to a clearer understanding of its genetic basis. In this review, we assessed available evidence from family and twin studies that have estimated the heritability of PA. Heritability is greater when evaluated by accelerometry compared with questionnaires, and for questionnaires higher in twin than family studies. Accelerometry studies suggest heritability of PA is 51% to 56%. There have been many genome-wide linkage studies, candidate gene studies, and four genome-wide association studies that have highlighted specific genetic factors linked to different PA levels. These studies have generally failed to replicate identified loci, with the exception of the melanocortin 4 receptor, and this may be because of the variability in the measurement techniques used to characterize the behavior. Future work should aim to standardize the procedures used to measure PA in the context of trying to identify genetic causes. The link of genetics to physical exercise is not so tight that it prevents voluntary interventions.

Genetic Determinants for Leisure-Time Physical Activity

PURPOSE

Leisure-time physical activity (LTPA) is a well-established modifiable lifestyle determinant for multiple cardiometabolic outcomes. However, current understanding of the genetic architecture that may determine LTPA remains very limited. Therefore, we aimed to examine the role of genetic factors in affecting LTPA, which has yet to be investigated comprehensively and in-depth.

METHODS

We conducted a genomewide analysis using 1000 Genomes Project imputed data from the Women's Health Initiative (n = 11,865), the Jackson Heart Study (n = 3015), and the Framingham Heart Study (n = 7339). A series of secondary analyses, including candidate gene analysis, sequence kernel association tests, pathway analysis, functional annotation, and expression quantitative trait loci analysis, were performed to follow-up on the primary findings.

RESULTS

Ethnicity-specific genetic signals were investigated, respectively, for African Americans and European Americans. Two variants, rs116550874 (meta-analysis: P = 1.63 × 10) and rs3792874 (meta-analysis: P = 8.33 × 10), were associated with LTPA in African Americans; rs28524846 (meta-analysis: P = 1.30 × 10) was identified for EA. We also replicated four previously reported loci (GABRG3, CYP19A1, PAPSS2, and CASR; P for lead single nucleotide polymorphisms < 0.005). Further fine-mapping and functional annotation suggested that several identified loci (novel and replicated) are involved in 1) the homeostatic drive coupled with the reward system and 2) the development and regulation of the capacity to perform LTPA.

CONCLUSIONS

To our knowledge, our analysis is the first to comprehensively investigate the genomewide signals for LTPA in multiple ethnicities. These findings support the notion that genetic predisposition plays a critical role in determining LTPA, of which the biological and clinical implications warrants further investigation.

Differential methylation of insulin-like growth factor 2 in offspring of physically active pregnant women

Several studies have suggested that maternal lifestyle during pregnancy may influence long-term health of offspring by altering the offspring epigenome. Whether maternal leisure-time physical activity (LTPA) during pregnancy might have this effect is unknown. The purpose of this study was to determine the relationship between maternal LTPA during pregnancy and offspring DNA methylation. Participants were recruited from the Archive for Research on Child Health study. At enrollment, participants' demographic information and self-reported LTPA during pregnancy were determined. High active participants (averaged 637.5 min per week of LTPA; n=14) were matched by age and race to low active participants (averaged 59.5 min per week LTPA; n=28). Blood spots were obtained at birth. Pyrosequencing was used to determine methylation levels of long interspersed nucleotide elements (LINE-1) (global methylation) and peroxisome proliferator-activated receptor-gamma (PPARγ), peroxisome proliferator-activated receptor-gamma coactivator (PGC1-α), insulin-like growth factor 2 (IGF2), pyruvate dehydrogenase kinase, isozyme 4 (PDK4) and transcription factor 7-like 2 (TCF7L2). We found no differences between offspring of high active and low active groups for LINE-1 methylation. The only differences in candidate gene methylation between groups were at two CpG sites in the P2 promoter of IGF2; the offspring of low active group had significantly higher DNA methylation (74.70±2.25% methylation for low active v. 72.83±2.85% methylation for high active; P=0.045). Our results suggest no effect of maternal LTPA on offspring global and candidate gene methylation, with the exception of IGF2. IGF2 has been previously associated with regulation of physical activity, suggesting a possible role of maternal LTPA on regulation of offspring physical activity.

The Genetics of Physical Activity

PURPOSE OF REVIEW

Physical activity (PA) is a well-established modifiable lifestyle determinant for multiple cardio-metabolic outcomes. While many psychosocial and environmental correlates of PA have been identified, current understanding of the genetic architecture that contributes to PA is still very limited, especially when compared to other phenotypes such as obesity and diabetes.

RECENT FINDINGS

This review systematically and comprehensively assesses available evidence from animal experiments, family studies, population-based candidate gene analyses, and genome-wide association studies (GWAS) studying the genetics of physical activity patterns. It discusses the scientific evolution in the field of PA genetics, including the recognition of increased sample sizes, the shift from early family-based approaches to association-based design, and the rapidly advancement of enabling genotyping and sequencing technologies. In addition, this review points to the gaps in the current knowledge base, including the general lack of GWAS and whole-genome sequence analyses particularly understudied populations, and the need for large-scale collaborative effort in both observational and experimental settings. In this review, we also call for research utilizing systems biology strategies for PA genetic research and accounting for complex gene-environment interactions that may vary by race/ethnicity. The epidemic of physical inactivity has been a public health nemesis, encompassing a large burden of diseases and high societal costs. A better understanding of the genetic basis of PA can inform public health policies for the prevention, control, and treatment of many chronic diseases related to physical inactivity.

Heterogeneity of Physical Function Responses to Exercise in Older Adults: Possible Contribution of Variation in the Angiotensin-1 Converting Enzyme (ACE) Gene?

Behavioral exercise interventions, aimed at improving either aerobic endurance or muscular strength, are currently the only therapy found, on average, to consistently retard loss of physical function in aging adults. However, not all individuals experience the same magnitude of benefit from a given exercise treatment, and certain persons may respond more favorably to a particular mode of exercise than another. Research now shows that genetic predisposition is one of the factors accounting for interindividual differences in responses to exercise as well as differences in the propensity to engage in exercise. This article discusses how a common variant in a single gene (the angiotensin-1 converting enzyme gene) could emerge as a prospective tool to identify older individuals more likely to benefit from and adhere to a specific type of exercise activity over another type.

Fuel homeostasis and locomotor behavior: role of leptin and melanocortin pathways

BACKGROUND

While it is now accepted that genes and their products affect food intake, the concept that locomotor behavior or the propensity for physical activity is controlled by neuro hum oral regulators is frequently underappreciated. In mammals, complex interactions have developed to allow the cross-talk between fuel homeostasis and physical activity.

AIM

The aim of this review is to provide a synopsis of the influence of the leptin-melanocortin pathway, a well-studied pivotal player in body weight regulation, on locomotor behaviors.

CONCLUSIONS

In rodents, reductions in leptin levels that physiologically occur following acute food deprivation or a reduction of the fat mass consequent to prolonged caloric restrictions are associated with a decrease in total locomotor activity and simultaneous increase in food-anticipatory activity, a locomotor behavior which reflects a foraging attitude. These actions can be prevented by leptin administration and are at least partially mediated by the neurons of the melanocortin pathway. In humans, twin studies have attributed to genetic factors approximately 50% of the variance of physical activity. An elevated number of the genes or loci which may affect physical activity are involved in body weight homeostasis. Polymorphisms of the melanocortin-4 and leptin receptors have repeatedly been associated with the level of physical activity. Unraveling the complexity of the regulation of locomotor behavior and the interconnections with the pathways involved in energy homeostasis may help explain the substantial individual variability in physical activities in humans and disentangle the harmful effects of sedentary lifestyle, which may be distinct from the detrimental effects of obesity.

Genetic factors in exercise adoption, adherence and obesity

Physical activity and exercise play critical roles in energy balance. While many interventions targeted at increasing physical activity have demonstrated efficacy in promoting weight loss or maintenance in the short term, long term adherence to such programmes is not frequently observed. Numerous factors have been examined for their ability to predict and/or influence physical activity and exercise adherence. Although physical activity has been demonstrated to have a strong genetic component in both animals and humans, few studies have examined the association between genetic variation and exercise adherence. In this review, we provide a detailed overview of the non-genetic and genetic predictors of physical activity and adherence to exercise. In addition, we report the results of analysis of 26 single nucleotide polymorphisms in six candidate genes examined for association to exercise adherence, duration, intensity and total exercise dose in young adults from the Training Interventions and Genetics of Exercise Response (TIGER) Study. Based on both animal and human research, neural signalling and pleasure/reward systems in the brain may drive in large part the propensity to be physically active and to adhere to an exercise programme. Adherence/compliance research in other fields may inform future investigation of the genetics of exercise adherence.

Findings from the Quebec Family Study on the Etiology of Obesity: Genetics and Environmental Highlights

The Quebec Family Study (QFS) was an observational study with three cycles of data collection between 1979 and 2002 in Quebec City, Canada. The cohort is a mixture of random sampling and ascertainment through obese individuals. The study has significantly contributed to our understanding of the determinants of obesity and associated disease risk over the past 35 years. In particular, the QFS cohort was used to investigate the contribution of familial resemblance and genetic effects on body fatness and behaviors related to energy balance. Significant familial aggregation and genetic heritability were reported for total adiposity, fat-free mass, subcutaneous fat distribution, abdominal and visceral fat, resting metabolic rate, physical activity level and other behavioral traits. The resources of QFS were also used to study the contribution of several nontraditional (non-caloric) risk factors as predictors of excess body weight and gains in weight and adiposity over time, including low calcium and micronutrient intake, high disinhibition eating behavior trait, and short sleep duration. An important finding relates to the interactions between dietary macronutrient intake and exercise intensity on body mass and adiposity.

Genomics and genetics in the biology of adaptation to exercise

This article is devoted to the role of genetic variation and gene-exercise interactions in the biology of adaptation to exercise. There is evidence from genetic epidemiology research that DNA sequence differences contribute to human variation in physical activity level, cardiorespiratory fitness in the untrained state, cardiovascular and metabolic response to acute exercise, and responsiveness to regular exercise. Methodological and technological advances have made it possible to undertake the molecular dissection of the genetic component of complex, multifactorial traits, such as those of interest to exercise biology, in terms of tissue expression profile, genes, and allelic variants. The evidence from animal models and human studies is considered. Data on candidate genes, genome-wide linkage results, genome-wide association findings, expression arrays, and combinations of these approaches are reviewed. Combining transcriptomic and genomic technologies has been shown to be more powerful as evidenced by the development of a recent molecular predictor of the ability to increase VO2max with exercise training. For exercise as a behavior and physiological fitness as a state to be major players in public health policies will require that the role of human individuality and the influence of DNA sequence differences be understood. Likewise, progress in the use of exercise in therapeutic medicine will depend to a large extent on our ability to identify the favorable responders for given physiological properties to a given exercise regimen.

Heritability of objectively assessed daily physical activity and sedentary behavior

BACKGROUND

Twin and family studies that estimated the heritability of daily physical activity have been limited by poor measurement quality and a small sample size.

OBJECTIVE

We examined the heritability of daily physical activity and sedentary behavior assessed objectively by using combined heart rate and movement sensing in a large twin study.

DESIGN

Physical activity traits were assessed in daily life for a mean (± SD) 6.7 ± 1.1 d in 1654 twins from 420 monozygotic and 352 dizygotic same-sex twin pairs aged 56.3 ± 10.4 y with body mass index (in kg/m(2)) of 26.1 ± 4.8. We estimated the average daily movement, physical activity energy expenditure, and time spent in moderate-to-vigorous intensity physical activity and sedentary behavior from heart rate and acceleration data. We used structural equation modeling to examine the contribution of additive genetic, shared environmental, and unique environmental factors to between-individual variation in traits.

RESULTS

Additive genetic factors (ie, heritability) explained 47% of the variance in physical activity energy expenditure (95% CI: 23%, 53%) and time spent in moderate-to-vigorous intensity physical activity (95% CI: 29%, 54%), 35% of the variance in acceleration of the trunk (95% CI: 0%, 44%), and 31% of the variance in the time spent in sedentary behavior (95% CI: 9%, 51%). The remaining variance was predominantly explained by unique environmental factors and random error, whereas shared environmental factors played only a marginal role for all traits with a range of 0-15%.

CONCLUSIONS

The between-individual variation in daily physical activity and sedentary behavior is mainly a result of environmental influences. Nevertheless, genetic factors explain up to one-half of the variance, suggesting that innate biological processes may be driving some of our daily physical activity.

Pharmacological blockade and genetic absence of the dopamine D2 receptor specifically modulate voluntary locomotor activity in mice

Dopaminergic signaling influences physical activity. Notably impaired D2 receptor (D2R) function has been associated with decreased voluntary physical activity. Most animal models investigating effects of genetic or pharmacological dopaminergic modulation measure physical activity for a limited time of up to few hours. The aim of this study is to investigate the impact of chronic or acute D2R dysfunction on physical activity over several days. For this purpose, we used a highly automated running wheel system to continuously record physical activity in mice. We found that D2R-knockout status led to a permanent decrease of running wheel activity. In contrast, acute D2R blockade by raclopride (1.5-5mg/kg) resulted in an initial dose-dependent reduction of running wheel usage and a compensating increase of activity in later stages of the activity phase. This indicates that D2R dysfunction reduces physical activity. Our data indicate that this reduction to a large extent cannot be explained by motor deficits. The delayed increase of activity after D2R blockade might be due to a rebound effect.

Genomics of elite sporting performance: what little we know and necessary advances

Numerous reports of genetic associations with performance- and injury-related phenotypes have been published over the past three decades; these studies have employed primarily the candidate gene approach to identify genes that associate with elite performance or with variation in performance-and/or injury-related traits. Although generally with small effect sizes and heavily prone to type I statistic error, the number of candidate genetic variants that can potentially explain elite athletic status, injury predisposition, or indeed response to training will be much higher than that examined by numerous biotechnology companies. Priority should therefore be given to applying whole genome technology to sufficiently large study cohorts of world-class athletes with adequately measured phenotypes where it is possible to increase statistical power. Some of the elite athlete cohorts described in the literature might suffice, and collectively, these cohorts could be used for replication purposes. Genome-wide association studies are ongoing in some of these cohorts (i.e., Genathlete, Russian, Spanish, Japanese, United States, and Jamaican cohorts), and preliminary findings include the identification of one single nucleotide polymorphism (SNP; among more than a million SNPs analyzed) that associates with sprint performance in Japanese, American (i.e., African American), and Jamaican cohorts with a combined effect size of ~2.6 (P-value <5×10(-7)) and good concordance with endurance performance between select cohorts. Further replications of these signals in independent cohorts will be required, and any replicated SNPs will be taken forward for fine-mapping/targeted resequencing and functional studies to uncover the underlying biological mechanisms. Only after this lengthy and costly process will the true potential of genetic testing in sport be determined.

Sensation-seeking genes and physical activity in youth

Many studies examining genetic influences on physical activity (PA) have evaluated the impact of single nucleotide polymorphisms (SNPs) related to the development of lifestyle-related chronic diseases, under the hypothesis that they would be associated with PA. However, PA is a multidetermined behavior and associated with a multitude of health consequences. Thus, examining a broader range of candidate genes associated with a broader range of PA correlates may provide new insights into the genetic underpinnings of PA. In this study, we focus on one such correlate - sensation-seeking behavior. Participants (N = 1130 Mexican origin youth) provided a saliva sample and data on PA and sensation-seeking tendencies in 2008-2009. Participants were genotyped for 630 functional and tagging variants in the dopamine, serotonin and cannabinoid pathways. Overall 30% of participants (males - 37.6% and females - 22.0%) reported ≥60 min of PA on 5 of 7 days. After adjusting for gender, age and population stratification, and applying the Bayesian False Discovery Probability approach for assessing noteworthiness, four gene variants were significantly associated with PA. In a multivariable model, being male, having higher sensation-seeking tendencies and at least one copy of the minor allele for SNPs in angiotensin I-converting enzyme gene [ACE; rs8066276 odds ratio (OR) = 1.44; P = 0.012] and tryptophan hydroxylase 2 gene (TPH2; rs11615016 OR = 1.73; P = 0.021) were associated with increased likelihood of meeting PA recommendations. Participants with at least one copy of the minor allele for SNPs in synaptosomal-associated protein 25 gene (SNAP25; rs363035 OR = 0.53; P = 0.005) and cannabinoid receptor 1 gene (CNR1; rs6454672 OR = 0.62; P = 0.022) have decreased likelihood of meeting PA recommendations. Our findings extend current knowledge of the complex relationship between PA and possible genetic underpinnings.

Correlates of physical activity: why are some people physically active and others not?

Physical inactivity is an important contributor to non-communicable diseases in countries of high income, and increasingly so in those of low and middle income. Understanding why people are physically active or inactive contributes to evidence-based planning of public health interventions, because effective programmes will target factors known to cause inactivity. Research into correlates (factors associated with activity) or determinants (those with a causal relationship) has burgeoned in the past two decades, but has mostly focused on individual-level factors in high-income countries. It has shown that age, sex, health status, self-efficacy, and motivation are associated with physical activity. Ecological models take a broad view of health behaviour causation, with the social and physical environment included as contributors to physical inactivity, particularly those outside the health sector, such as urban planning, transportation systems, and parks and trails. New areas of determinants research have identified genetic factors contributing to the propensity to be physically active, and evolutionary factors and obesity that might predispose to inactivity, and have explored the longitudinal tracking of physical activity throughout life. An understanding of correlates and determinants, especially in countries of low and middle income, could reduce the eff ect of future epidemics of inactivity and contribute to effective global prevention of non-communicable diseases.

Heritability of physical activity traits in Brazilian families: the Baependi Heart Study

Background

It is commonly recognized that physical activity has familial aggregation; however, the genetic influences on physical activity phenotypes are not well characterized. This study aimed to (1) estimate the heritability of physical activity traits in Brazilian families; and (2) investigate whether genetic and environmental variance components contribute differently to the expression of these phenotypes in males and females.

Methods

The sample that constitutes the Baependi Heart Study is comprised of 1,693 individuals in 95 Brazilian families. The phenotypes were self-reported in a questionnaire based on the WHO-MONICA instrument. Variance component approaches, implemented in the SOLAR (Sequential Oligogenic Linkage Analysis Routines) computer package, were applied to estimate the heritability and to evaluate the heterogeneity of variance components by gender on the studied phenotypes.

Results

The heritability estimates were intermediate (35%) for weekly physical activity among non-sedentary subjects (weekly PA_NS), and low (9-14%) for sedentarism, weekly physical activity (weekly PA), and level of daily physical activity (daily PA). Significant evidence for heterogeneity in variance components by gender was observed for the sedentarism and weekly PA phenotypes. No significant gender differences in genetic or environmental variance components were observed for the weekly PA_NS trait. The daily PA phenotype was predominantly influenced by environmental factors, with larger effects in males than in females.

Conclusions

Heritability estimates for physical activity phenotypes in this sample of the Brazilian population were significant in both males and females, and varied from low to intermediate magnitude. Significant evidence for heterogeneity in variance components by gender was observed. These data add to the knowledge of the physical activity traits in the Brazilian study population, and are concordant with the notion of significant biological determination in active behavior.

Genome-wide association study of exercise behavior in Dutch and American adults

INTRODUCTION

The objective of this study was to identify genetic variants that are associated with adult leisure time exercise behavior using genome-wide association (GWA) in two independent samples.

METHODS

Exercise behavior was measured in 1644 unrelated Dutch and 978 unrelated American adults of European ancestry with detailed questions about type, frequency, and duration of exercise. Individuals were classified into regular exercisers or nonexercisers using a threshold of 4 MET·h (metabolic equivalents-hours per week). GWA analyses of ∼1.6 million observed and imputed Single Nucleotide Polymorphism (SNP) were conducted in both samples independently using logistic regression in SNPTEST, including sex, age, and body mass index as covariates. A meta-analysis of the results was performed using the weighted inverse variance method in METAL.

RESULTS

Thirty-seven novel SNPs in the PAPSS2 gene and in two intergenic regions on chromosomes 2q33.1 and 18p11.32 were associated with exercise participation (pooled P values <1.0 × 10(-5)). Previously reported associations (ACE, CASR, CYP19A1, DRD2, LEPR, and MC4R genes) or linkage findings (2p22.3, 4q28, 4q31.21 7p13, 9q31, 11p15, 13q22, 15q13, 18q12.2, 18q21.1, 19p13.3, and 20q12) were not replicated, although suggestive evidence was found for association to rs12405556 in the LEPR gene (pooled P value 9.7 × 10(-4); American sample, P value 9.8 × 10(-5)) and for association to rs8036270 in the GABRG3 gene (pooled P value 4.6 × 10(-5)) in the linkage region 15q12-13.

CONCLUSIONS

The heritability of leisure time exercise behavior is likely to be accounted for by many genetic variants with small effect size. These can be detected by GWA as was shown here for the PAPSS2 gene, but larger samples with genome-wide genotypes and high-quality exercise data are needed for further progress.

Sex hormone effects on physical activity levels: why doesn't Jane run as much as Dick?

The relationship between physical activity levels and disease rates has become an important health-related concern in the developed world. Heart disease, certain cancers and obesity persist at epidemic rates in the US and Western Europe. Increased physical activity levels have been shown to reduce the occurrence of many chronic diseases leading to reductions in the burden on the healthcare system. Activity levels in humans are affected by many cultural and environmental factors; nevertheless, current research points to a strong biological input with potential genetic, neurological and endocrinological origins. Of unique interest, the sex hormones appear to have a very strong influence on activity levels. The current animal literature suggests that females tend to be more active than males due to biological pathways of estrogenic origin. The majority of human epidemiological and anthropological data, on the contrary, suggest women are less active than men in spite of this inherent activity-increasing mechanism. The purpose of this study is to review the current literature regarding the control of physical activity levels by the sex hormones in humans. Using the natural transitional phases of the aging endocrine system, natural periodicity of the menstrual cycle and pharmacological/hormone replacement therapy as variable experimental stages, some authors have been able to provide some information regarding the existence of an inherent activity-increasing mechanism in humans. In brief, activity levels during life stages prior to and after menopause do not significantly differ, despite the vast changes in sex hormone levels and function. Sex hormone differences throughout a regular menstrual cycle do not appear to influence activity levels in humans either; an effect that is pronounced in the female rodent. The use of hormone replacement therapies provides researchers with more systematic controls over hormone modulation in human subjects; however, this benefit comes with additional confounding variables, mostly due to disease or other states of malfunction. Despite the addition of these confounding factors, minor changes to the activity pattern have been observed in women, especially during the initial administration of the therapy. Observations are yet to be made in male subjects during replacement therapy. In general, some evidence exists suggesting that a biological mechanism extending from the sex hormones influences activity in humans. Unfortunately, despite a small number of investigative reports, the paucity of human research investigating how the sex hormones affect activity levels in humans prevents conclusive delineation of the mechanisms involved. Future research in this unique sub-field of endocrinology and exercise science utilizing more appropriate research protocols and effective techniques will provide definitive evidence of such mechanisms.

Current understanding of the genetic basis for physical activity

Although it is well known that physical activity prevents and ameliorates a large number of conditions and chronic diseases, it is also incontrovertible that physical inactivity is becoming more prevalent. This paradox has led some to suggest that genetic/biological factors influence activity levels as opposed to the classical notion that voluntary activity is solely regulated by environmental factors. There is a plethora of recent data showing that there is considerable genetic influence on activity levels in both humans and animals and emerging evidence suggesting potential genomic locations for those genetic factors. Several independent lines of evidence suggest that dopamine receptor 1 (Drd1) and nescient helix loop helix (Nhlh2) are excellent candidate genes for the regulation of physical activity, with several other potential candidate genes only partially supported. This foundation provides the basis for continuing work to identify additional candidate genes, to identify other genetic factors that are involved in the regulation of physical activity, and to investigate the mechanisms by which these genes and genetic factors regulate activity.

The biological control of voluntary exercise, spontaneous physical activity and daily energy expenditure in relation to obesity: human and rodent perspectives

Mammals expend energy in many ways, including basic cellular maintenance and repair, digestion, thermoregulation, locomotion, growth and reproduction. These processes can vary tremendously among species and individuals, potentially leading to large variation in daily energy expenditure (DEE). Locomotor energy costs can be substantial for large-bodied species and those with high-activity lifestyles. For humans in industrialized societies, locomotion necessary for daily activities is often relatively low, so it has been presumed that activity energy expenditure and DEE are lower than in our ancestors. Whether this is true and has contributed to a rise in obesity is controversial. In humans, much attention has centered on spontaneous physical activity (SPA) or non-exercise activity thermogenesis (NEAT), the latter sometimes defined so broadly as to include all energy expended due to activity, exclusive of volitional exercise. Given that most people in Western societies engage in little voluntary exercise, increasing NEAT may be an effective way to maintain DEE and combat overweight and obesity. One way to promote NEAT is to decrease the amount of time spent on sedentary behaviours (e.g. watching television). The effects of voluntary exercise on other components of physical activity are highly variable in humans, partly as a function of age, and have rarely been studied in rodents. However, most rodent studies indicate that food consumption increases in the presence of wheels; therefore, other aspects of physical activity are not reduced enough to compensate for the energetic cost of wheel running. Most rodent studies also show negative effects of wheel access on body fat, especially in males. Sedentary behaviours per se have not been studied in rodents in relation to obesity. Several lines of evidence demonstrate the important role of dopamine, in addition to other neural signaling networks (e.g. the endocannabinoid system), in the control of voluntary exercise. A largely separate literature points to a key role for orexins in SPA and NEAT. Brain reward centers are involved in both types of physical activities and eating behaviours, likely leading to complex interactions. Moreover, voluntary exercise and, possibly, eating can be addictive. A growing body of research considers the relationships between personality traits and physical activity, appetite, obesity and other aspects of physical and mental health. Future studies should explore the neurobiology, endocrinology and genetics of physical activity and sedentary behaviour by examining key brain areas, neurotransmitters and hormones involved in motivation, reward and/or the regulation of energy balance.

Association study of POMC variants with body composition measures and nutrient choice

Genome linkage scans and candidate gene studies have implicated the pro-opiomelanocortin (POMC) locus in traits related to food intake, metabolic function, and body mass index. Here we investigate single nucleotide polymorphisms at the POMC locus in order to evaluate the influence of its genetic variance on body fat distribution and diet in a sample of middle-aged men from The Netherlands. 366 Dutch males from the Hamlet cohort were asked detailed questions about food choice, nutrient intake and exercise. Furthermore, their weight and body fat composition were measured. Each cohort member was genotyped for a set of single nucleotide polymorphisms (SNPs) at the POMC locus. Regression analysis, adjusted for several covariates, was used to test for the association between genetic variants and the phenotypes measured. POMC variation was associated with waist:hip ratio, visceral fat and abdominal fat (rs6713532, P=0.020, 0.019, and 0.021, respectively), and nutrient choice (rs1042571, P=0.034), but in light of limited power and multiple testing these results should be taken with caution. POMC is a strong candidate for involvement in appetite regulation as supported by animal, physiological, and genetic studies and variation at the POMC locus may affect an individual's energy intake which in turn leads to variation in body composition and body fat.

Strain screen and haplotype association mapping of wheel running in inbred mouse strains

Previous genetic association studies of physical activity, in both animal and human models, have been limited in number of subjects and genetically homozygous strains used as well as number of genomic markers available for analysis. Expansion of the available mouse physical activity strain screens and the recently published dense single-nucleotide polymorphism (SNP) map of the mouse genome (approximately 8.3 million SNPs) and associated statistical methods allowed us to construct a more generalizable map of the quantitative trait loci (QTL) associated with physical activity. Specifically, we measured wheel running activity in male and female mice (average age 9 wk) in 41 inbred strains and used activity data from 38 of these strains in a haplotype association mapping analysis to determine QTL associated with activity. As seen previously, there was a large range of activity patterns among the strains, with the highest and lowest strains differing significantly in daily distance run (27.4-fold), duration of activity (23.6-fold), and speed (2.9-fold). On a daily basis, female mice ran further (24%), longer (13%), and faster (11%). Twelve QTL were identified, with three (on Chr. 12, 18, and 19) in both male and female mice, five specific to males, and four specific to females. Eight of the 12 QTL, including the 3 general QTL found for both sexes, fell into intergenic areas. The results of this study further support the findings of a moderate to high heritability of physical activity and add general genomic areas applicable to a large number of mouse strains that can be further mined for candidate genes associated with regulation of physical activity. Additionally, results suggest that potential genetic mechanisms arising from traditional noncoding regions of the genome may be involved in regulation of physical activity.

Genetic architecture of voluntary exercise in an advanced intercross line of mice

Exercise is essential for health, yet the amount, duration, and intensity that individuals engage in are strikingly variable, even under prescription. Our focus was to identify the locations and effects of quantitative trait loci (QTL) controlling genetic predisposition for exercise-related traits, utilizing a large advanced intercross line (AIL) of mice. This AIL (G(4)) population originated from a reciprocal cross between mice with genetic propensity for increased voluntary exercise [high-runner (HR) line, selectively bred for increased wheel running] and the inbred strain C57BL/6J. After adjusting for family structure, we detected 32 significant and 13 suggestive QTL representing both daily running traits (distance, duration, average speed, and maximum speed) and the mean of these traits on days 5 and 6 (the selection criteria for HR) of a 6-day test conducted at 8 wk of age, with many co-localizing to similar genomic regions. Additionally, seven significant and five suggestive QTL were observed for the slope and intercept of a linear regression across all 6 days of running, some representing a combination of the daily traits. We also observed two significant and two suggestive QTL for body mass before exercise. These results, from a well-defined animal model, reinforce a genetic basis for the predisposition to engage in voluntary exercise, dissect this predisposition into daily segments across a continuous time period, and present unique QTL that may provide insight into the initiation, continuation, and temporal pattern of voluntary activity in mammals.

QTL underlying voluntary exercise in mice: interactions with the "mini muscle" locus and sex

Exercise improves many aspects of human health, yet many people remain inactive even when exercise is prescribed. We previously created a backcross (BC) between mice selectively bred for high levels of voluntary wheel running (VWR) and fixed for "mini muscle" (MM), a recessive mutation causing approximately 50% reduction in triceps surae mass. We previously showed that BC mice having the MM trait ran faster and further than mice without MM and that MM maps to chromosome 11. Here, we genotyped the BC with genome-wide single nucleotide polymorphisms to identify quantitative trait loci (QTL) controlling voluntary exercise and tissue and body mass traits and to determine whether these QTL interact with the MM locus or with sex. We detected 3 VWR QTL, representing the first voluntary exercise QTL mapped using this high running selection line, and 5 tissue mass QTL. Several interactions between trait QTL and the MM locus as well as sex were also identified. These results begin to explain the genetic architecture of VWR and further support MM as a locus having major effects, including its main effects on the muscle phenotype, its pleiotropic effects on wheel running and tissue mass traits, and through its interactions with other QTL and with sex.

Driven to be inactive? The genetics of physical activity

The health implications of physical inactivity, including its integral role in promoting obesity, are well known and have been well documented. Physical activity is a multifactorial behavior with various factors playing a role in determining individual physical activity levels. Research using both human and animal models in the past several years has clearly indicated that genetics is associated with physical activity. Furthermore, researchers have identified several significant and suggestive genomic quantitative trait loci associated with physical activity. To date, the identities of the causal genes underlying physical activity regulation are unclear, with few strong candidate genes. The current research provides a foundation from which future confirmatory research can be launched as well as determination of the mechanisms through which the genetic factors act. The application of this knowledge could significantly augment the information available for physical activity behavior change interventions resulting in more efficient programs for those predisposed to be inactive.

Parent-of-origin effects on voluntary exercise levels and body composition in mice

Despite the health-related benefits of exercise, many people do not engage in enough activity to realize the rewards, and little is known regarding the genetic or environmental components that account for this individual variation. We created and phenotyped a large G(4) advanced intercross line originating from reciprocal crosses between mice with genetic propensity for increased voluntary exercise (HR line) and the inbred strain C57BL/6J. G(4) females (compared to males) ran significantly more when provided access to a running wheel and were smaller with a greater percentage of body fat pre- and postwheel access. Change in body composition resulting from a 6-day exposure to wheels varied between the sexes with females generally regulating energy balance more precisely in the presence of exercise. We observed parent-of-origin effects on most voluntary wheel running and body composition traits, which accounted for 3-13% of the total phenotypic variance pooled across sexes. G(4) individuals descended from progenitor (F(0)) crosses of HRfemale symbol and C57BL/6Jmale symbol ran greater distances, spent more time running, ran at higher maximum speeds/day, and had lower percent body fat and higher percent lean mass than mice descended from reciprocal progenitor crosses (C57BL/6Jfemale symbol x HRmale symbol). For some traits, significant interactions between parent of origin and sex were observed. We discuss these results in the context of sex dependent activity and weight loss patterns, the contribution of parent-of-origin effects to predisposition for voluntary exercise, and the genetic (i.e., X-linked or mtDNA variations), epigenetic (i.e., genomic imprinting), and environmental (i.e., in utero environment or maternal care) phenomena potentially modulating these effects.

The human gene map for performance and health-related fitness phenotypes: the 2006-2007 update

This update of the human gene map for physical performance and health-related fitness phenotypes covers the research advances reported in 2006 and 2007. The genes and markers with evidence of association or linkage with a performance or a fitness phenotype in sedentary or active people, in responses to acute exercise, or for training-induced adaptations are positioned on the map of all autosomes and sex chromosomes. Negative studies are reviewed, but a gene or a locus must be supported by at least one positive study before being inserted on the map. A brief discussion on the nature of the evidence and on what to look for in assessing human genetic studies of relevance to fitness and performance is offered in the introduction, followed by a review of all studies published in 2006 and 2007. The findings from these new studies are added to the appropriate tables that are designed to serve as the cumulative summary of all publications with positive genetic associations available to date for a given phenotype and study design. The fitness and performance map now includes 214 autosomal gene entries and quantitative trait loci plus seven others on the X chromosome. Moreover, there are 18 mitochondrial genes that have been shown to influence fitness and performance phenotypes. Thus,the map is growing in complexity. Although the map is exhaustive for currently published accounts of genes and exercise associations and linkages, there are undoubtedly many more gene-exercise interaction effects that have not even been considered thus far. Finally, it should be appreciated that most studies reported to date are based on small sample sizes and cannot therefore provide definitive evidence that DNA sequence variants in a given gene are reliably associated with human variation in fitness and performance traits.

Too Little Exercise and Too Much Sitting: Inactivity Physiology and the Need for New Recommendations on Sedentary Behavior

Moderate- to vigorous-intensity physical activity has an established preventive role in cardiovascular disease, type 2 diabetes, obesity, and some cancers. However, recent epidemiologic evidence suggests that sitting time has deleterious cardiovascular and metabolic effects that are independent of whether adults meet physical activity guidelines. Evidence from "inactivity physiology" laboratory studies has identified unique mechanisms that are distinct from the biologic bases of exercising. Opportunities for sedentary behaviors are ubiquitous and are likely to increase with further innovations in technologies. We present a compelling selection of emerging evidence on the deleterious effects of sedentary behavior, as it is underpinned by the unique physiology of inactivity. It is time to consider excessive sitting a serious health hazard, with the potential for ultimately giving consideration to the inclusion of too much sitting (or too few breaks from sitting) in physical activity and health guidelines.

Evolutionary origins of obesity

Although it appeared relatively suddenly, the current obesity epidemic - largely manifest in industrialized societies but now spreading to the rest of the world - is the result of interaction between human biology and human culture over the long period of human evolution. As mammals and primates, humans have the capacity to store body fat when opportunities to consume excess energy arise. But during the millions of years of human evolution such opportunities were rare and transient. More commonly ancestral hominins and modern humans were confronted with food scarcity and had to engage in high levels of physical activity. In tandem with encephalization, humans evolved elaborate and complex genetic and physiological systems to protect against starvation and defend stored body fat. They also devised technological aids for increasing energy consumption and reducing physical effort. In the last century, industrialization provided access to great quantities of mass-produced, high-calorie foods and many labour-saving and transportation devices, virtually abolishing starvation and heavy manual work. In the modern obesogenic environment, individuals possessing the appropriate combination of ancestral energy-conserving genes are at greater risk for overweight and obesity and associated chronic diseases.

Genome-wide linkage scan for athlete status in 700 British female DZ twin pairs

Association studies, comparing elite athletes with sedentary controls, have reported a number of genes that may be related to athlete status. The present study reports the first genome wide linkage scan for athlete status. Subjects were 4488 adult female twins from the TwinsUK Adult Twin Registry (793 monozygotic [MZ] and 1000 dizygotic [DZ] complete twin pairs, and single twins). Athlete status was measured by asking the twins whether they had ever competed in sports and what was the highest level obtained. Twins who had competed at the county or national level were considered elite athletes. Using structural equation modeling in Mx, the heritability of athlete status was estimated at 66%. Seven hundred DZ twin pairs that were successfully genotyped for 1946 markers (736 microsatellites and 1210 SNPs) were included in the linkage analysis. Identical-by-descent probabilities were estimated in Merlin for a 1 cM grid, taking into account the linkage disequilibrium of correlated SNPs. The linkage scan was carried out in Mx using the [Formula: see text]-approach. Suggestive linkages were found on chromosomes 3q22-q24 and 4q31-q34. Both areas converge with findings from previous studies using exercise phenotypes. The peak on 3q22-q24 was found at the SLC9A9 gene. The region 4q31-q34 overlaps with the region for which suggestive linkages were found in two previous linkage studies for physical fitness (FABP2 gene; Bouchard et al., 2000) and physical activity (UCP1 gene; Simonen et al., 2003). Future association studies should further clarify the possible role of these genes in athlete status.

Genome-wide linkage scan for exercise participation in Dutch sibling pairs

This study was aimed at identifying the genomic loci linked to exercise participation in males and females. Cross-sectional exercise data of twins and siblings (18-50 years) were used from the Netherlands Twin Registry. The sample consisted of 1432 genotyped sibling pairs from 622 families (1120 sibling pairs were genotyped on all chromosomes). Exercise participation (no/yes, based on a cutoff criterion of four metabolic equivalents and 60 min weekly) was assessed by survey. Genotyping was based on 361 markers and an average marker density of 10.6 cM. Identical by descent status was estimated for a 1 cM grid. A variance components-based sex-limited linkage scan was carried out for exercise participation. The heritability of exercise participation in males was 68.5% and in females 46.3%. The genetic overlap was estimated at 0.32, indicating that partly different genes affect exercise in the two sexes. Suggestive linkage was found in all subjects on chromosome 19p13.3 (LOD=2.18). Although sex differences in linkage effect were not significant, mainly females contributed to the suggestive linkage. The 19p13.3-13.2 region harbors a number of genes related to muscle performance and muscle blood flow, which might affect exercise behavior through exercise ability. Most likely, a large number of genes with each small effects affect exercise participation in males and females. Large collaborative samples are needed to detect these effects.

The human gene map for performance and health-related fitness phenotypes: the 2005 update

The current review presents the 2005 update of the human gene map for physical performance and health-related fitness phenotypes. It is based on peer-reviewed papers published by the end of 2005. The genes and markers with evidence of association or linkage with a performance or fitness phenotype in sedentary or active people, in adaptation to acute exercise, or for training-induced changes are positioned on the genetic map of all autosomes and the X chromosome. Negative studies are reviewed, but a gene or locus must be supported by at least one positive study before being inserted on the map. By the end of 2000, in the early version of the gene map, 29 loci were depicted. In contrast, the 2005 human gene map for physical performance and health-related phenotypes includes 165 autosomal gene entries and QTL, plus five others on the X chromosome. Moreover, there are 17 mitochondrial genes in which sequence variants have been shown to influence relevant fitness and performance phenotypes. Thus, the map is growing in complexity. Unfortunately, progress is slow in the field of genetics of fitness and performance, primarily because the number of laboratories and scientists focused on the role of genes and sequence variations in exercise-related traits continues to be quite limited.

Resting metabolic rate and respiratory quotient: results from a genome-wide scan in the Quebec Family Study

BACKGROUND

Genes influencing resting metabolic rate (RMR) and respiratory quotient (RQ) represent candidate genes for obesity, type 2 diabetes, and the metabolic syndrome because of the involvement of these traits in energy balance and substrate oxidation.

OBJECTIVE

We conducted a genome-wide scan for quantitative trait loci (QTL) contributing to the variability in RMR and RQ.

DESIGN

Regression-based and variance components-based genome-wide autosomal scans on RMR and RQ phenotypes, obtained from indirect calorimetry, were performed in 169 families ascertained via an obese proband or from the general population.

RESULTS

We found evidence for linkage to RMR on chromosomes 3q26.1 (lod = 2.74), 1q21.2 (2.44), and 22q12.3 (1.33). QTL influencing RQ were found on chromosomes 12q13 (1.65) and 14q22 (1.83) when the analyses were performed in all families. Considerable locus heterogeneity within this population was suggested because most of the families were unlinked to any one quantitative trait locus. Significant associations between traits and linked microsatellites were detected within the linked, informative subsets.

CONCLUSIONS

We found several new QTL for energy metabolism, but the QTL on 1q may be a replication of the one reported in Pima Indians. All 3 RMR linkages overlapped regions previously linked to the metabolic syndrome or its components, and the significant association between RMR and the metabolic syndrome in the present cohort reinforces this relation. We conclude that considerable locus heterogeneity exists even within populations, which should be taken into account when considering candidate gene studies of energy metabolism phenotypes and other complex traits.

Heterozygosity for a POMC-null mutation and increased obesity risk in humans

Congenital deficiency of proopiomelanocortin (POMC) results in a syndrome of hypoadrenalism, severe obesity, and altered skin and hair pigmentation. The concept that subtle variation in POMC expression and/or function might contribute to common obesity is suggested by studies reporting linkage of obesity-related traits to a locus on chromosome 2p22 encompassing the POMC gene. We identified a novel homozygous frameshift (C6906del) mutation in POMC in a child of Turkish origin with severe obesity and hypoadrenalism. This mutation would be predicted to lead to the loss of all POMC-derived peptides. The availability of a large extended pedigree provided the opportunity to address whether loss of one copy of the POMC gene was sufficient to alter obesity risk. Twelve relatives were heterozygous for the mutation and 7 were wild type. Of the heterozygotes, 11 of 12 heterozygotes were obese or overweight compared with only 1 of 7 of the wild-type relatives. The mean BMI SD score was 1.7 +/- 0.5 in heterozygotes and 0.4 +/- 0.4 in the wild-type relatives. Parametric linkage analysis of the trait "overweight" provided statistically significant evidence of linkage with this locus, with a maximum "location score" (comparable with multipoint logarithm of odds scores) of 3.191. We conclude that loss of one copy of the POMC gene predisposes to obesity in humans. Thus, genetic variants having relatively subtle effects on POMC expression and function could influence susceptibility to obesity.

A quantitative trait locus on chromosome 18q for physical activity and dietary intake in Hispanic children

OBJECTIVE

Genetic components of energy homeostasis contributing to childhood obesity are poorly understood. Genome scans were performed to identify chromosomal regions contributing to physical activity and dietary intake traits in Hispanic children participating in the VIVA LA FAMILIA Study.

RESEARCH METHODS AND PROCEDURES

We report linkage findings on chromosome 18 for physical activity and dietary intake in 1030 siblings from 319 Hispanic families. Measurements entailed physical activity by accelerometry, dietary intake by two 24-hour recalls, and genetic linkage analyses using SOLAR software.

RESULTS

Significant heritabilities were seen for physical activity and dietary intake, ranging from 0.46 to 0.69, except for vigorous activity (h2 = 0.18). Percentage time in sedentary activity mapped to markers D18S1102-D18S64 on chromosome 18 [logarithm of the odds (LOD) score = 4.07], where melanocortin 4 receptor gene (MC4R) resides. Quantitative trait loci (QTLs) for total activity counts, percentage time in light or in moderate activity, and carbohydrate intake and percentage of energy intake from carbohydrates were detected in the same region (LOD = 2.28, 2.79, 2.2, 1.84, and 1.51, respectively). A novel loss of function mutation in MC4R (G55V) was detected in six obese relatives, but not in the rest of the cohort. Removal of these MC4R-deficient subjects from the analysis reduced the LOD score for sedentary activity to 3.94.

DISCUSSION

Given its role in the regulation of food intake and energy expenditure, MC4R is a strong positional candidate gene for the QTL on chromosome 18 detected for physical activity and dietary intake in Hispanic children.

Within- and between-individual variability in estimated energy expenditure and habitual physical activity among young adults

OBJECTIVE

To examine the within- and between-individual variability in the estimated total energy expenditure (TEE) and habitual physical activity (PA) in free-living young adults. We were specifically interested in the day-to-day variation.

DESIGN

Cross-sectional.

SETTING

University.

SUBJECTS

A total of 277 (125 males, 152 females) participants aged 18-24 years.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Subjects recorded their daily PA with the Bouchard 3-day diary. Descriptive statistics for TEE, moderate-to-vigorous physical activity (MVPA), inactivity (IA), and activity energy expenditure (AEE) were calculated and presented as a frequency distribution. Within- and between-individual variability were tested by RMANOVA and also presented as the coefficient of variation (CV).

RESULTS

Mean values for TEE, MVPA, AEE, and IA were comparable between males and females; however, considerable between-individual variability existed. Only MVPA showed a significant difference between sexes (P<0.05), due to slightly greater vigorous PA in males compared to females (8.0 and 6.8 kcal/kg/day, respectively; P=0.12). Results from the RMANOVA revealed no significant day-to-day variability in any TEE or PA variable and the CVs were not significantly different between males and females. TEE and IA displayed mean CVs of approximately 12% while mean CVs for AEE and MVPA approximated 32 and 84%, respectively.

CONCLUSIONS

Results from this study suggest (1) a limited day-to-day variability in TEE and (2) a large degree of between-individual variation for TEE and PA exist. This study highlights the importance of understanding the variability associated with TEE, which is important for PA measurement and proper PA and nutritional recommendations.

SPONSORSHIP

None.

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.

Genetic Factors in Physical Activity and the Equal Environment Assumption – the Swedish Young Male Twins Study

The aims of this study were to examine the genetic contribution on physical activity (PA) within a nationwide population of young adult male twin pairs from Sweden and to investigate the equal environment assumption (EEA) in relation to PA. Information on PA was collected by questionnaires in 1998 and 2002 and the impact of genetic factors was estimated by structural equation modeling (SEM). The study included 1,022 pairs of twins and the best fitting SEM-model gave a heritability of 49% (95% CI, 40-56%) for total PA and all PA dimensions showed genetic contributions between 40% and 65%. Non-shared environmental factors were also important, whereas shared environmental factors did not contribute to PA behaviors. The EEA was investigated with a linear regression model, examining if the twins contact frequency predicted within-pair differences in PA, and further by a simulation study. We found no support for violation of the EEA.

Linkage analysis of LDL cholesterol in American Indian populations: the Strong Heart Family Study

Previous studies have demonstrated that low density lipoprotein cholesterol (LDL-C) concentration is influenced by both genes and environment. Although rare genetic variants associated with Mendelian causes of increased LDL-C are known, only one common genetic variant has been identified, the apolipoprotein E gene (APOE). In an attempt to localize quantitative trait loci (QTLs) influencing LDL-C, we conducted a genome-wide linkage scan of LDL-C in participants of the Strong Heart Family Study (SHFS). Nine hundred eighty men and women, age 18 years or older, in 32 extended families at three centers (in Arizona, Oklahoma, and North and South Dakota) were phenotyped for LDL-C concentration and other risk factors. Using a variance component approach and the program SOLAR, and after accounting for the effects of covariates, we detected a QTL influencing LDL-C on chromosome 19, nearest marker D19S888 at 19q13.41 [logarithm of odds (LOD) = 4.3] in the sample from the Dakotas. This region on chromosome 19 includes many possible candidate genes, including the APOE/C1/C4/C2 gene cluster. In follow-up association analyses, no significant evidence for an association was detected with the APOE*2 and APOE*4 alleles (P = 0.76 and P = 0.53, respectively). Suggestive evidence of linkage to LDL-C was detected on chromosomes 3q, 4q, 7p, 9q, 10p, 14q, and 17q. These linkage signals overlap positive findings for lipid-related traits and harbor plausible candidate genes for LDL-C.

Quantitative trait locus determining dietary macronutrient intakes is located on human chromosome 2p22

BACKGROUND

Obesity is generally accompanied by increased food intake.

OBJECTIVE

We sought to identify the genes influencing variation in dietary macronutrient intakes in Mexican Americans.

DESIGN

We conducted a genome-wide scan by using data derived from food-frequency questionnaires in 816 participants from the San Antonio Family Heart Study. Household effect was simultaneously estimated in a variance component model with the use of SOLAR.

RESULTS

All dietary intake measures (total calories, proteins, fat, saturated fat, monounsaturated fat, polyunsaturated fat, carbohydrates, and sucrose) were moderately heritable. Household effect was insignificant except on total calories and sucrose. Suggestive evidence of linkage with saturated fat intake was found on chromosome 2p22 near marker D2S1346 [logarithm of odds (LOD) = 2.62]. Intakes of total calories, fat, protein, and monounsaturated fat were also suggestively linked to the same marker. A significant linkage signal on chromosome 2p22 for leptin concentrations and fat mass was localized in this population, so we used leptin or fat mass as a covariate. Multipoint LOD scores for saturated fat dropped to 1.27 and 1.90, respectively, which suggested that this region on chromosome 2p contributes to both saturated fat intake and body adiposity. This chromosomal region contains the proopiomelanocortin gene (POMC). However, 2 polymorphisms in exon 3 of the POMC gene showed no association with saturated fat intake.

CONCLUSIONS

The results strengthen the hypothesis that chromosome 2p22 harbors genes that influence a variety of obesity-related phenotypes, including macronutrient intakes.