Characterization of genetic and lifestyle factors for determining variation in body mass index, fat mass, percentage of fat mass, and lean mass

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

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

Genetic Variant in ACVR2B Is Associated with Lean Mass

INTRODUCTION

Low lean mass (LM) is a risk factor for chronic disease, a major cause of disability and diminished quality of life, and is a heritable trait. However, relatively few specific genetic factors have been identified as potentially influencing this trait.

METHODS

In this study, we selected 1493 single-nucleotide polymorphisms (SNP) in 155 candidate genes involved in anabolic, catabolic, growth hormone, and other related pathways and examined their association with LM, assessed by dual-energy x-ray absorptiometry, in a sample of 2760 non-Hispanic and Hispanic white postmenopausal women from the Women's Health Initiative (WHI) Observational Study. We assessed the replication of our top findings in a meta-analysis of 20 genome-wide association studies (n = 38,292) conducted by the Cohorts for Heart and Aging Research in Genomic Epidemiology Consortium Musculoskeletal Working Group.

RESULTS

We identified 32 SNPs that had nominally significant associations with LM in the WHI cohort. In the replication stage, we find that SNP rs2276541 in the activin A receptor, type IIB (ACVR2B), was significantly associated with LM (β = 0.15, P = 2.17 × 10). ACVR2B codes for a receptor for a negative regulator of skeletal muscle, myostatin, and has previously been identified in a candidate gene study as a determinant of skeletal muscle mass.

CONCLUSIONS

Our findings support a previously proposed role of ACVR2B allelic variation as a determinant of muscle mass and extend prior findings in men and women. Additional large-scale studies will be needed to confirm our findings in different populations.

Meta-analysis of genome-wide association data identifies novel susceptibility loci for obesity

Obesity is a major public health problem with strong genetic determination. Multiple genetic variants have been implicated for obesity by conducting genome-wide association (GWA) studies, primarily focused on body mass index (BMI). Fat body mass (FBM) is phenotypically more homogeneous than BMI and is more appropriate for obesity research; however, relatively few studies have been conducted on FBM. Aiming to identify variants associated with obesity, we carried out meta-analyses of seven GWA studies for BMI-related traits including FBM, and followed these analyses by de novo replication. The discovery cohorts consisted of 21 969 individuals from diverse ethnic populations and a total of over 4 million genotyped or imputed SNPs. The de novo replication cohorts consisted of 6663 subjects from two independent samples. To complement individual SNP-based association analyses, we also carried out gene-based GWA analyses in which all variations within a gene were considered jointly. Individual SNP-based association analyses identified a novel locus 1q21 [rs2230061, CTSS (Cathepsin S)] that was associated with FBM after the adjustment of lean body mass (LBM) (P = 3.57 × 10(-8)) at the genome-wide significance level. Gene-based association analyses identified a novel gene NLK (nemo-like kinase) in 17q11 that was significantly associated with FBM adjusted by LBM. In addition, we confirmed three previously reported obesity susceptibility loci: 16q12 [rs62033400, P = 1.97 × 10(-14), FTO (fat mass and obesity associated)], 18q22 [rs6567160, P = 8.09 × 10(-19), MC4R (melanocortin 4 receptor)] and 2p25 [rs939583, P = 1.07 × 10(-7), TMEM18 (transmembrane protein 18)]. We also found that rs6567160 may exert pleiotropic effects to both FBM and LBM. Our results provide additional insights into the molecular genetic basis of obesity and may provide future targets for effective prevention and therapeutic intervention.

Genes, physical fitness and ageing

Persons aged 80 years and older are the fastest growing segment of the population. As more individuals live longer, we should try to understand the mechanisms involved in healthy ageing and preserving functional independence in later life. In elderly people, functional independence is directly dependent on physical fitness, and ageing is inevitably associated with the declining functions of systems and organs (heart, lungs, blood vessels, skeletal muscles) that determine physical fitness. Thus, age-related diminished physical fitness contributes to the development of sarcopenia, frailty or disability, all of which severely deteriorate independent living and thus quality of life. Ageing is a complex process involving many variables that interact with one another, including - besides lifestyle factors or chronic diseases - genetics. Thus, several studies have examined the contribution of genetic endowment to a decline in physical fitness and subsequent loss of independence in later life. In this review, we compile information, including data from heritability, candidate-gene association, linkage and genome-wide association studies, on genetic factors that could influence physical fitness in the elderly.

The longitudinal relation between smoking and muscle strength in healthy adults

AIM

To assess longitudinally whether smoking tobacco is related to muscle strength in healthy adults and to assess the influence of lifestyle covariates on this relation.

METHODS

Data were obtained from the observational Amsterdam Growth and Health Longitudinal Study, with four repeated measurements at the ages of 21 (n = 181), 27 (n = 144), 32 (n = 426) and 36 (n = 373) years. Knee muscle strength (KMS) was measured at an angle of 300° per second. Smoking and the covariates physical activity and dietary intake were assessed with a questionnaire. Other covariates included physical fitness and body fat percentage. Cardiopulmonary fitness was assessed with a maximal running test and body fatness with skinfold measurements. Sex-specific longitudinal analyses were carried out using generalized estimating equations.

RESULTS

In men and women, an inverse relationship between smoking tobacco and KMS was found. Smoking 100 g of tobacco a week resulted in a reduction of 2.9% in KMS in men and a reduction of 5.0% in women. This relation existed largely independently of lifestyle covariates.

CONCLUSION

This study indicates that smoking is inversely related to skeletal muscle strength in healthy adults.

Molecular genetic studies of gene identification for sarcopenia

Sarcopenia, which is characterized by a progressive decrease of skeletal muscle mass and function with aging, is closely related to several common diseases (such as cardiovascular and airway diseases) and functional impairment/disability. Strong genetic determination has been reported for muscle mass and muscle strength, two most commonly recognized and studied risk phenotypes for sarcopenia, with heritability ranging from 30 to 85% for muscle strength and 45-90% for muscle mass. Sarcopenia has been the subject of increasing genetic research over the past decade. This review is designed to comprehensively summarize the most important and representative molecular genetic studies designed to identify genetic factors associated with sarcopenia. We have methodically reviewed whole-genome linkage studies in humans, quantitative trait loci mapping in animal models, candidate gene association studies, newly reported genome-wide association studies, DNA microarrays and microRNA studies of sarcopenia or related skeletal muscle phenotypes. The major results of each study are tabulated for easy comparison and reference. The findings of representative studies are discussed with respect to their influence on our present understanding of the genetics of sarcopenia. This is a comprehensive review of molecular genetic studies of gene identification for sarcopenia, and an overarching theme for this review is that the currently accumulating results are tentative and occasionally inconsistent and should be interpreted with caution pending further investigation. Consequently, this overview should enhance recognition of the need to validate/replicate the genetic variants underlying sarcopenia in large human cohorts and animal. We believe that further progress in understanding the genetic etiology of sarcopenia will provide valuable insights into important fundamental biological mechanisms underlying muscle physiology that will ultimately lead to improved ability to recognize individuals at risk for developing sarcopenia and our ability to treat this debilitating condition.

Association analysis of genetic polymorphisms and potential interaction of the osteocalcin (BGP) and ER-alpha genes with body mass index (BMI) in premenopausal Chinese women

AIM

To investigate whether estrogen receptor alpha (ER-alpha) PvuII and osteocalcin (also known as bone Gla protein, or BGP) HindIII genetic polymorphisms and their potential interactions are associated with body mass index (BMI) variation.

METHODS

Data on BMI and ER-alpha PvuII and BGP HindIII genotypes were obtained from 328 healthy premenopausal Chinese women in east China. The study subjects were unrelated, at least 21 years old (mean age of 33.2+/-5.9 years), and had an average BMI of 21.58+/-2.59. All subjects were genotyped at the ER-alpha PvuII and BGP HindIII loci using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP).

RESULTS

The BGP HindIII genotypes were significantly associated with BMI (P=0.003). Carriers of the HH and Hh genotypes had approximately 2.73% and 1.27% higher BMI than those of the hh genotype, respectively. In contrast, the ER-alpha PvuII polymorphism was not significantly associated with BMI (P=0.454). In addition, there was no evidence of potential interactions between the ER-alpha and BGP genes in our subjects (P>or=0.013).

CONCLUSION

The HindIII polymorphism of the BGP gene, but not the PvuII polymorphism of the ER-alpha gene or their potential interaction, was associated with BMI in premenopausal Chinese women.

Linkage and association between CA repeat polymorphism of the TNFR2 gene and obesity phenotypes in two independent Caucasian populations

Previously, our group has reported a suggestive linkage evidence of 1p36 with body mass index (BMI) (LOD = 2.09). The tumor necrosis factor receptor 2 (TNFR2) at 1p36 is an excellent positional and functional candidate gene for obesity. In this study, we have investigated the linkage and association between the TNFR2 gene and obesity phenotypes in two large independent samples, using the quantitative transmission disequilibrium tests (QTDT). The first group was made up of 1,836 individuals from 79 multi-generation pedigrees. The second group was a randomly ascertained set of 636 individuals from 157 US Caucasian nuclear families. Obesity phenotypes tested include BMI, fat mass, and percentage fat mass (PFM). A significant result (P = 0.0056) was observed for linkage with BMI in the sample of the multigenerational pedigrees. Our data support the TNFR2 gene as a quantitative trait locus (QTL) underlying BMI variation in the Caucasian populations.

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

OBJECTIVE

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

RESEARCH METHODS AND PROCEDURE

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

RESULTS

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

DISCUSSION

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

A bivariate whole-genome linkage scan suggests several shared genomic regions for obesity and osteoporosis

CONTEXT

A genome-wide bivariate analysis was conducted for body fat mass (BFM) and bone mineral density (BMD) in a large Caucasian sample. We found some quantitative trait loci shared by BFM and BMD in the total sample and the gender-specific subgroups, and quantitative trait loci with potential pleiotropy were disclosed. BFM and BMD, as the respective measure for obesity and osteoporosis, are phenotypically and genetically correlated. However, specific genomic regions accounting for their genetic correlation are unknown.

OBJECTIVE

To identify systemically the shared genomic regions for BFM and BMD, we performed a bivariate whole-genome linkage scan in 4498 Caucasian individuals from 451 families for BFM and BMD at the hip, spine, and wrist, respectively. Linkage analyses were performed in the total sample and the male and female subgroups, respectively.

RESULTS

In the entire sample, suggestive linkages were detected at 7p22-p21 (LOD 2.69) for BFM and spine BMD, 6q27 (LOD 2.30) for BFM and hip BMD, and 11q13 (LOD 2.64) for BFM and wrist BMD. Male-specific suggestive linkages were found at 13q12 (LOD 3.23) for BFM and spine BMD and at 7q21 (LOD 2.59) for BFM and hip BMD. Female-specific suggestive LOD scores were 3.32 at 15q13 for BFM and spine BMD and 3.15 at 6p25-24 for BFM and wrist BMD.

CONCLUSIONS

Several shared genomic regions for BFM and BMD were identified here. Our data may benefit further positional and functional studies, aimed at eventually uncovering the complex mechanism underlying the shared genetic determination of obesity and osteoporosis.

Bivariate whole genome linkage analysis for femoral neck geometric parameters and total body lean mass

A genome-wide bivariate analysis was conducted for femoral neck GPs and TBLM in a large white sample. We found QTLs shared by GPs and TBLM in the total sample and the sex-specific samples. QTLs with potential pleiotropy were also disclosed.

INTRODUCTION

Previous studies have suggested that femoral neck cross-section geometric parameters (FNCS-GPs), including periosteal diameter (W), cross-sectional area (CSA), cortical thickness (CT), buckling ratio (BR), and section modulus (Z), are genetically correlated with total body lean mass (TBLM). However, the shared genetic factors between them are unknown.

MATERIALS AND METHODS

To identify the specific QTLs shared by FNCS-GPs and TBLM, we performed bivariate whole genome linkage analysis (WGLA) in a large sample of 451 white families made up of 4498 subjects.

RESULTS

Multipoint bivariate linkage analyses for 22 autosomes showed evidence of suggestive or significant linkages (thresholds of LOD = 2.3 and 3.7, respectively) to chromosomes 3q12 and 20q13 in the entire sample, 6p25 and 10q24 in women, and 4p15, 5q34-35 and 7q21 in men. Two-point linkage analyses for chromosome X showed strong linkage to Xp22.13, Xp11.4, Xq22.3, Xq23-24, and Xq25. Complete pleiotropy was identified on 10q24 and 5q35 for TBLM and BR in women and for TBLM and CT in men, respectively. Furthermore, chromosomes 5q34-35, 7q21, 10q24, 20q13, Xp22.13, Xp11.4, and Xq25 are also of importance because of their linkage to multiple trait pairs. For example, linkage to chromosome 10q24 was found for TBLM x W (LOD = 2.31), TBLM x CT (LOD = 2.51), TBLM x CSA (LOD = 2.51), TBLM x BR (LOD = 2.64), and TBLM x Z (LOD = 2.55) in women.

CONCLUSIONS

In this study, we identified several genomic regions (e.g., 3q12 and 20q13) that seem to be linked to both FNCS-GPs and TBLM. These regions are of interesting because they may harbor genes that may contribute to variation in both FNCS-GPs and TBLM.

Genetic and environmental correlations between bone geometric parameters and body compositions

The purpose of this study was to determine the genetic and environmental correlations between weight, lean mass and bone geometric parameters (sub-periosteal diameter, W; cross-sectional area, CSA; cortical thickness, CT; section modulus, Z; and buckling ratio, BR) of femoral neck. The sample was composed of 512 Caucasian pedigrees, including 2667 females and 1822 males. Bivariate quantitative genetic analyses were performed to evaluate the genetic (rho(G)), environmental (rho(E)) and phenotypic (rho(P)) correlations between the study traits. Univariate genetic analyses showed that the heritabilities (h(2)) for bone geometric parameters were significant (P < 0.001) ranging from 0.50 to 0.60. The significant common household effects indicated the common environment shared by household members for W, CSA, CT, Z and BR (P < 0.05), but the magnitude was small compared with heritabilities. rho(E), rho(G) and rho(P) between bone geometric parameters and weight, lean mass were generally significant. Interestingly, lean mass showed both stronger genetic and environmental correlations with the bone geometric parameters than weight. In addition, according to the magnitude of correlation coefficients, the rho(G) between body compositions and bone geometric parameters were generally stronger than rho(E) (except for that between BR and body compositions). These data suggested that the geometric parameters of femoral neck are under strong genetic control. Furthermore, some common genetic and environmental factors are shared by bone geometric parameters and weight, lean mass. The results may help understand the intertwined relationships between bone metabolisms, mechanical loading and body compositions.

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

BACKGROUND

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

PARTICIPANTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Genetic and environmental correlations between obesity phenotypes and age at menarche

OBJECTIVE

To assess the extent that the genetic and environmental factors contribute to the phenotypic correlations between obesity traits and age at menarche (AAM), and also to examine the influence of AAM on obesity in both pre- and postmenopausal women.

METHODS

F ive hundred and twelve pedigrees with 2667 Caucasian female subjects from two to four generations were recruited. Fat mass and lean mass (both in kg) were measured by dual-energy X-ray absorptiometry scanner. Body mass index (BMI) (kg/m(2)) was calculated. We performed bivariate quantitative genetic analyses in the total sample containing 2667 Caucasian women. We also selected 206 unrelated premenopausal women and 140 unrelated postmenopausal women from the total sample, and computed the respective phenotypic correlation between obesity and AAM in these two subgroups.

RESULTS

For fat mass, lean mass and BMI, we detected their significant negative genetic correlations with AAM after adjustment for significant covariates, which were -0.3170 (P<0.001), -0.1721 (P<0.05) and -0.3665 (P<0.001), respectively. However, their environmental correlations with AAM were all nonsignificant (P>0.05), ranging from -0.0016 to 0.0192. In the premenopausal subgroup, significant associations were observed between fat mass and AAM (rho=-0.231, P<0.01) as well as between BMI and AAM (rho=-0.257, P<0.01). In the postmenopausal subgroup, no such associations were observed.

CONCLUSION

Our results for the first time suggested that significant phenotypic association between obesity phenotypes and AAM is mainly attributable to shared genetic rather than environmental factors, and AAM may have stronger effects on obesity phenotypes in pre- than in postmenopausal women.

Genetic determination and correlation of body weight and body mass index (BMI) and cross-sectional geometric parameters of the femoral neck

INTRODUCTION

This study aimed to examine the genetic determination of body weight, body mass index (BMI) and cross-sectional geometric parameters of the femoral neck including cross-sectional area (CSA), cortical thickness (CT), sectional modulus (Z), and buckling ratio (BR), and to test the genetic correlation between body weight/BMI and the femoral neck geometric parameters.

METHODS

A total of 929 healthy subjects from 292 Chinese nuclear families was included. Femoral neck geometric parameters were estimated from bone mineral density (BMD) and bone area which were measured by dual energy X-ray absorptiometry (DXA).

RESULTS

The heritability (h(2)) estimate values were 0.643, 0.626, 0.626, 0.674, 0.405, and 0.615 for body weight, BMI, CSA, CT, Z, and BR, respectively. Body weight was significantly correlated with bone geometric parameters (p</=0.001) with genetic correlation (rho(G)) values of 0.551, 0.457, 0.571, and -0.385, and bivariate heritability (rho2G) values of 0.304, 0.209, 0.326, and 0.148 for CSA, CT, Z, and BR, respectively. Similar correlations (p</=0.001) were observed between BMI and bone geometric parameters, with rho(G) values of 0.446, 0.432, 0.334, and -0.362, and (rho2G) values of 0.199, 0.187, 0.112, and 0.131 for CSA, CT, Z, and BR, respectively.

CONCLUSION

In summary, our study suggested that body weight, BMI, and femoral neck geometry were under strong genetic determination. The strong genetic correlations suggested that the genetic factors of bone geometry may be overlapped with those of body weight and BMI.

Genetic determination and correlation of body mass index and bone mineral density at the spine and hip in Chinese Han ethnicity

The purpose of the present study was to evaluate the magnitude of genetic determination of spine and hip bone mineral density (BMD) and body mass index (BMI), and to explore the genetic, environmental, and phenotypic correlations among the above phenotypes in Chinese Han ethnicity. The sample was composed of at least 217 complete nuclear families in Chinese Han ethnicity. BMD at the spine and hip was measured using a dual-energy X-ray absorptiometry scanner. The heritability (h2) of BMI and BMD at the spine and hip, the genetic correlation (rhoG) and environmental correlation (rhoE) among the three phenotypes were evaluated via variance analysis, with age, sex, and age-by-sex interaction as covariates. The phenotypic correlation (rhoP) and the bivariate heritability rhoG2 were also calculated. The heritability for BMD and BMI was approximately 0.70 and approximately 0.50, respectively (p<0.0001). The common environment shared by household members (household effect) is significant for BMI variation (p=0.0004). Significant genetic, environmental, and phenotypic correlation was observed. The rhoG2 values were 0.13 for BMI/spine BMD, 0.18 for BMI/hip BMD, and 0.58 for the spine BMD/hip BMD. While BMD at the spine and hip have significant genetic determination, BMI is more likely to be affected by environmental factors than BMD. In addition, BMD at the spine and hip shares more genetic effect (pleiotropy) than BMI and BMD do in Chinese Han ethnicity, though the effects are significant for both.

Estrogen receptor alpha gene relationship with peak bone mass and body mass index in Chinese nuclear families

Estrogen receptor alpha (ER-alpha) plays an important role in mediating estrogen signaling. Studies in Caucasian populations have shown that it is involved in endocrine-related diseases such as osteoporosis and obesity. In the present study, we first used a quantitative transmission disequilibrium test (QTDT) to examine the relationship between this gene and both the osteoporosis-related phenotype bone mineral density (BMD), and the obesity-related phenotype body mass index (BMI), in 384 Chinese nuclear families. We genotyped a dinucleotide repeat marker (TA)n, and a long-range haplotype was reconstructed using this marker and two other restriction fragment length polymorphism (RFLP) markers at PvuII and XbaI loci. Although we found significant total association [allele (TA)21 with hip BMD (P=0.001), and haplotype Px(TA)21 with spine (P=0.0007) and hip (P=0.0006) BMD], the more reliable within-family associations were not significant between these phenotype pairs. No linkage signal was obtained for either spine BMD or hip BMD. We found no association or linkage between any of the three studied polymorphisms and the long-range haplotypes of the ER-alpha gene and BMI. Our study does not support an association of the ER-alpha gene with BMD and BMI in the Chinese population.

Genetic Polymorphisms and the Risk of Stroke After Cardiac Surgery

Background and Purpose— Stroke represents a significant cause of morbidity and mortality after cardiac surgery. Although the risk of stroke varies according to both patient and procedural factors, the impact of genetic variants on stroke risk is not well understood. Therefore, we tested the hypothesis that specific genetic polymorphisms are associated with an increased risk of stroke after cardiac surgery.

Methods— Patients undergoing cardiac surgery utilizing cardiopulmonary bypass surgery were studied. DNA was isolated from preoperative blood and analyzed for 26 different single-nucleotide polymorphisms. Multivariable logistic regression modeling was used to determine the association of clinical and genetic characteristics with stroke. Permutation analysis was used to adjust for multiple comparisons inherent in genetic association studies.

Results— A total of 1635 patients experiencing 28 strokes (1.7%) were included in the final genetic model. The combination of the 2 minor alleles of C-reactive protein (CRP; 3′UTR 1846C/T) and interleukin-6 (IL-6; −174G/C) polymorphisms, occurring in 583 (35.7%) patients, was significantly associated with stroke (odds ratio, 3.3; 95% CI, 1.4 to 8.1; P =0.0023). In a multivariable logistic model adjusting for age, the CRP and IL-6 single-nucleotide polymorphism combination remained significantly associated with stroke ( P =0.0020).

Conclusions— We demonstrate that common genetic variants of CRP (3′UTR 1846C/T) and IL-6 (−174G/C) are significantly associated with the risk of stroke after cardiac surgery, suggesting a pivotal role of inflammation in post–cardiac surgery stroke.

A TA-repeat polymorphism in the gene for the estrogen receptor alpha does not correlate with muscle strength or body composition in young adult Swedish women

OBJECTIVES

There are conflicting data in the literature whether estrogens affect muscle strength. Prospective studies with hormone replacement therapy have not been able to convincingly demonstrate a muscular effect and the putative role of estrogen in the development of lean body mass is not established. Both lean mass and fat mass are known to be under strong genetic control and therefore we have investigated the relation between a TA-repeat in the gene for the estrogen receptor alpha (ERalpha) and muscle strength and body composition.

METHODS

175 healthy Swedish women, aged 20-39 were randomly selected from the population registry and included in the study. Body mass measurements (lean mass, fat mass, body weight and BMI) and muscle strength (quadriceps, hamstring and grip strength) were evaluated. The TA-repeat in the ERalpha gene was amplified by polymerase chain reaction.

RESULTS

Alleles with a TA-repeat length of 16 repeats or shorter were denoted short (e), and repeat length of 17 repeats or longer were denoted long (E). Women homozygous for the short and long genotype were denoted ee (31%) and EE (21%), respectively, while heterozygous individuals were denoted Ee (48%). The frequencies were in Hardy-Weinberg equilibrium. No associations were found between ERalpha genotypes and muscle strength or body composition.

CONCLUSION

The TA-repeat in the human ERalpha gene does not correlate with muscle strength or body mass measurements, indicating that body composition is not as sensitive to genetic variation in this receptor as other target organs for estrogen.

Low skeletal muscle mass is associated with poor structural parameters of bone and impaired balance in elderly men--the MINOS study

In 796 men, 50-85 years of age, decreased relative skeletal muscle mass index was associated with narrower bones, thinner cortices, and a consequent decreased bending strength (lower section modulus), as well as with impaired balance and an increased risk of falls.

INTRODUCTION

In men, appendicular skeletal muscle mass (ASM) is correlated positively with BMC and areal BMD (aBMD). In elderly men, low muscle mass and strength (sarcopenia) is associated with difficulties in daily living activities. The aim of this study was to evaluate if ASM is correlated with bone size, mechanical properties of bones, balance, and risk of falls in elderly men.

MATERIALS AND METHODS

This study used 796 men, 50-85 years of age, belonging to the MINOS cohort. Lifestyle factors were evaluated by standardized questionnaires. Estimates of mechanical bone properties were derived from aBMD measured by DXA. ASM was estimated by DXA. The relative skeletal muscle mass index (RASM) was calculated as ASM/(body height)(2.3).

RESULTS

After adjustment for age, body size, tobacco smoking, professional physical activity, and 17beta-estradiol concentration, RASM was correlated positively with BMC, aBMD, external diameter, and cortical thickness (r = 0.17-0.34, p < 0.0001) but not with volumetric BMD. Consequently, RASM was correlated with section modulus (r = 0.29-0.39, p < 0.0001). Men in the lowest quartile of RASM had section modulus of femoral neck and distal radius lower by 12-18% in comparison with men in the highest quartile of RASM. In contrast, bone width was not correlated with fat mass, reflecting the load of body weight (except for L(3)), which suggests that the muscular strain may exert a direct stimulatory effect on periosteal apposition. After adjustment for confounding variables, a decrease in RASM was associated with increased risk of falls and of inability to accomplish clinical tests of muscle strength, static balance, and dynamic balance (odds ratio per 1 SD decrease in RASM, 1.31-2.23; p < 0.05-0.001).

CONCLUSIONS

In elderly men, decreased RASM is associated with narrower bones and thinner cortices, which results in a lower bending strength. Low RASM is associated with impaired balance and with an increased risk of falls in elderly men. It remains to be studied whether low RASM is associated with decreased periosteal apposition and with increased fracture risk in elderly men, and whether the difference in skeletal muscle mass between men and women contributes to the between-sex difference in fracture incidence.

Hormonal and lifestyle determinants of appendicular skeletal muscle mass in men: the MINOS study

BACKGROUND

Aging-related sarcopenia is characterized by a loss of muscle mass and strength and increased fatigability. However, studies of its determinants in elderly men are scarce.

OBJECTIVE

We investigated risk factors for sarcopenia in a large cohort of men.

DESIGN

We analyzed 845 men aged 45-85 y who belonged to the MINOS cohort. Lifestyle factors (physical activity, tobacco smoking, alcohol intake, caffeine intake) were evaluated by using a standardized questionnaire. Appendicular skeletal muscle mass (ASM) was estimated by using dual-energy X-ray absorptiometry. The relative appendicular skeletal muscle mass index (RASM) was calculated as ASM/body height(2.3). Apparent free testosterone concentration (AFTC) and free testosterone index (FTI) were calculated on the basis of concentrations of total testosterone and sex hormone-binding globulin.

RESULTS

RASM decreased with age (r = -0.29, P < 0.0001). Current smokers had lower RASM than did subjects who never smoked (-3.2%; P < 0.003). RASM increased with the intensity of physical activity at work (P for trend < 0.001). Men who participated in regular exercise during leisure time had 2.2% higher RASM than did those who did not (P < 0.03). Men whose values for AFTC, FTI, or 25-hydroxycholecalciferol [25(OH)D] were >2 SDs below the mean for young men had significantly lower RASM than did men with higher values. Men with sarcopenia, defined as the lowest quartile of RASM in the studied cohort (<6.32 kg/m(2.3)), were significantly older than men with normal RASM, weighed significantly less, smoked more, and spent significantly less time on leisure-time activities. Sarcopenic men also had lower values for testosterone, AFTC, FTI, and 25(OH)D.

CONCLUSION

In elderly men, low physical activity, tobacco smoking, thinness, low testosterone (AFTC and FTI), and decreased 25(OH)D concentrations are risk factors for sarcopenia.

Prevention of postmenopausal bone loss by a low-magnitude, high-frequency mechanical stimuli: a clinical trial assessing compliance, efficacy, and safety

A 1-year prospective, randomized, double-blind, and placebo-controlled trial of 70 postmenopausal women demonstrated that brief periods (<20 minutes) of a low-level (0.2g, 30 Hz) vibration applied during quiet standing can effectively inhibit bone loss in the spine and femur, with efficacy increasing significantly with greater compliance, particularly in those subjects with lower body mass.

INTRODUCTION

Indicative of the anabolic potential of mechanical stimuli, animal models have demonstrated that short periods (<30 minutes) of low-magnitude vibration (<0.3g), applied at a relatively high frequency (20-90 Hz), will increase the number and width of trabeculae, as well as enhance stiffness and strength of cancellous bone. Here, a 1-year prospective, randomized, double-blind, and placebo-controlled clinical trial in 70 women, 3-8 years past the menopause, examined the ability of such high-frequency, low-magnitude mechanical signals to inhibit bone loss in the human.

MATERIALS AND METHODS

Each day, one-half of the subjects were exposed to short-duration (two 10-minute treatments/day), low-magnitude (2.0 m/s2 peak to peak), 30-Hz vertical accelerations (vibration), whereas the other half stood for the same duration on placebo devices. DXA was used to measure BMD at the spine, hip, and distal radius at baseline, and 3, 6, and 12 months. Fifty-six women completed the 1-year treatment.

RESULTS AND CONCLUSIONS

The detection threshold of the study design failed to show any changes in bone density using an intention-to-treat analysis for either the placebo or treatment group. Regression analysis on the a priori study group demonstrated a significant effect of compliance on efficacy of the intervention, particularly at the lumbar spine (p = 0.004). Posthoc testing was used to assist in identifying various subgroups that may have benefited from this treatment modality. Evaluating those in the highest quartile of compliance (86% compliant), placebo subjects lost 2.13% in the femoral neck over 1 year, whereas treatment was associated with a gain of 0.04%, reflecting a 2.17% relative benefit of treatment (p = 0.06). In the spine, the 1.6% decrease observed over 1 year in the placebo group was reduced to a 0.10% loss in the active group, indicating a 1.5% relative benefit of treatment (p = 0.09). Considering the interdependence of weight, the spine of lighter women (<65 kg), who were in the highest quartile of compliance, exhibited a relative benefit of active treatment of 3.35% greater BMD over 1 year (p = 0.009); for the mean compliance group, a 2.73% relative benefit in BMD was found (p = 0.02). These preliminary results indicate the potential for a noninvasive, mechanically mediated intervention for osteoporosis. This non-pharmacologic approach represents a physiologically based means of inhibiting the decline in BMD that follows menopause, perhaps most effectively in the spine of lighter women who are in the greatest need of intervention.

Linkage and association of the CA repeat polymorphism of the IL6 gene, obesity-related phenotypes, and bone mineral density (BMD) in two independent Caucasian populations

Genetic factors play an important role in osteoporosis and obesity, two serious public health problems in the world. We investigated the relationships between obesity-related phenotypes, bone mineral density (BMD) and the CA repeat polymorphism of the IL6 gene in two large independent samples using the quantitative transmission disequilibrium test (QTDT). The first sample consisted of 1,816 individuals from 79 multigenerational pedigrees. Each pedigree was identified through a proband with BMD Z-scores </=-1.28 at the hip or spine. The second sample was a randomly ascertained set of 636 individuals from 157 nuclear families. Ten alleles containing 9-18 CA repeats were identified in our Caucasian populations. For body mass index (BMI), fat mass and percentage fat mass (PFM), highly significant (P<0.01) or significant (P<0.05) results were found for linkage in our sample of nuclear families and for association in the multigenerational pedigrees. We also observed weak evidence for linkage (P=0.069) with spine BMD and for association with hip BMD in the sample of multigenerational pedigrees. Our results suggest that genetic variation in or near the IL6 locus may be involved in the etiology of obesity and osteoporosis.

Can obesity be a risk factor in elderly people?

Obesity is increasing in middle-aged adults and in elderly subjects (over 65 years), owing to the concurrence of different factors: inactivity, wrong nutritional habits, and basal metabolism and nutritional need reduction. This condition is becoming a serious problem because of the increasing numbers of the aged population all over the world. In the past, obesity was considered as a 'secondary' pathology of no medical importance in old age; but nowadays, obesity is increasingly being studied in Geriatrics too, because it causes disability and because of its quality-of-life impairment consequences. The Euronut-Seneca study has confirmed the presence of obesity in both men and women in Europe. The definition of obesity, the reference values of body mass index and obesity as a mortality factor in elderly persons are still under discussion. Even when overweight does not represent a serious problem in old age, obese elderly people are certainly at risk of disability, morbidity and mortality. This review focuses on the potential risks of overweight and obesity in the aged population.

A genomewide linkage scan for quantitative-trait loci for obesity phenotypes

Obesity is an increasingly serious health problem in the world. Body mass index (BMI), percentage fat mass, and body fat mass are important indices of obesity. For a sample of pedigrees that contains >10,000 relative pairs (including 1,249 sib pairs) that are useful for linkage analyses, we performed a whole-genome linkage scan, using 380 microsatellite markers to identify genomic regions that may contain quantitative-trait loci (QTLs) for obesity. Each pedigree was ascertained through a proband who has extremely low bone mass, which translates into a low BMI. A major QTL for BMI was identified on 2q14 near the marker D2S347 with a LOD score of 4.04 in two-point analysis and a maximum LOD score (MLS) of 4.44 in multipoint analysis. The genomic region near 2q14 also achieved an MLS >2.0 for percentage of fat mass and body fat mass. For the putative QTL on 2q14, as much as 28.2% of BMI variation (after adjustment for age and sex) may be attributable to this locus. In addition, several other genomic regions that may contain obesity-related QTLs are suggested. For example, 1p36 near the marker D1S468 may contain a QTL for BMI variation, with a LOD score of 2.75 in two-point analysis and an MLS of 2.09 in multipoint analysis. The genomic regions identified in this and earlier reports are compared for further exploration in extension studies that use larger samples and/or denser markers for confirmation and fine-mapping studies, to eventually identify major functional genes involved in obesity.