Genetic influences on muscle strength, lean body mass, and bone mineral density: a twin study

Pleiotropic effects on Sarcopenia subphenotypes point to potential molecular markers for the disease

Sarcopenia is a progressive age-related muscle disease characterized by low muscle strength, quantity and quality, and low physical performance. The clinical overlap between these subphenotypes (reduction in muscle strength, quantity and quality, and physical performance) was evidenced, but the genetic overlap is still poorly investigated. Herein, we investigated whether there is a genetic overlap amongst sarcopenia subphenotypes in the search for more effective molecular markers for this disease. For that, a Bioinformatics approach was used to identify and characterize pleiotropic effects at the genome, loci and gene levels using Genome-wide association study results. As a result, a high genetic correlation was identified between gait speed and muscle strength (rG=0.5358, p=3.39 × 10-8). Using a Pleiotropy-informed conditional and conjunctional false discovery rate method we identified two pleiotropic loci for muscle strength and gait speed, one of them was nearby the gene PHACTR1. Moreover, 11 pleiotropic loci and 25 genes were identified for muscle mass and muscle strength. Lastly, using a gene-based GWAS approach three candidate genes were identified in the overlap of the three Sarcopenia subphenotypes: FTO, RPS10 and CALCR. The current study provides evidence of genetic overlap and pleiotropy among sarcopenia subphenotypes and highlights novel candidate genes and molecular markers associated with the risk of sarcopenia.

Genetic and environmental determinants of bone quality: a cross-sectional analysis of the Hungarian Twin Registry

There is abundant evidence that bone mineral content is highly heritable, while the heritability of bone quality (i.e. trabecular bone score [TBS] and quantitative ultrasound index [QUI]) is rarely investigated. We aimed to disentangle the role of genetic, shared and unique environmental factors on TBS and QUI among Hungarian twins. Our study includes 82 twin (48 monozygotic, 33 same-sex dizygotic) pairs from the Hungarian Twin Registry. TBS was determined by DXA, QUI by calcaneal bone ultrasound. To estimate the genetic and environmental effects, we utilized ACE-variance decomposition. For the unadjusted model of TBS, an AE model provided the best fit with > 80% additive genetic heritability. Adjustment for age, sex, BMI and smoking status improved model fit with 48.0% of total variance explained by independent variables. Furthermore, there was a strong dominant genetic effect (73.7%). In contrast, unadjusted and adjusted models for QUI showed an AE structure. Adjustments improved model fit and 25.7% of the total variance was explained by independent variables. Altogether 70-90% of the variance in QUI was related to additive genetic influences. We found a strong genetic heritability of bone quality in unadjusted models. Half of the variance of TBS was explained by age, sex and BMI. Furthermore, the adjusted model suggested that the genetic component of TBS could be dominant or an epistasis could be present. In contrast, independent variables explained only a quarter of the variance of QUI and the additive heritability explained more than half of all the variance.

A GWAS for grip strength in cohorts of children-Advantages of analysing young participants for this trait

Grip strength (GS) is a proxy measure for muscular strength and a predictor for bone fracture risk among other diseases. Previous genome-wide association studies (GWASs) have been conducted in large cohorts of adults focusing on scores collected for the dominant hand, therefore increasing the likelihood of confounding effects by environmental factors. Here, we perform the first GWAS meta-analyses on maximal GS with the dominant (GSD) and non-dominant (GSND) hand in two cohorts of children (ALSPAC, N = 5450; age range = 10.65-13.61; Raine Study, N = 1162, age range: 9.42-12.38 years). We identified a novel significant association for GSND (rs9546244, LINC02465, p = 3.43e-08) and replicated associations previously reported in adults including with a HOXB3 gene marker that shows an expression quantitative trait locus (eQTL) effect. Despite a much smaller sample (~3%) compared with the UK Biobank we replicated correlation analyses previously reported in this much larger adult cohort, such as a negative correlation with coronary artery disease. Although the results from the polygenic risk score (PRS) analyses did not survive multiple testing correction, we observed nominally significant associations between GS and risk of overall fracture, as previously reported, as well ADHD which will require further investigations. Finally, we observed a higher SNP-heritability (24%-41%) compared with previous studies (4%-24%) in adults. Overall, our results suggest that cohorts of children might be better suited for genetic studies of grip strength, possibly due to the shorter exposure to confounding environmental factors compared with adults.

Skeletal muscle dysfunction with advancing age

As a result of advances in medical treatments and associated policy over the last century, life expectancy has risen substantially and continues to increase globally. However, the disconnect between lifespan and 'health span' (the length of time spent in a healthy, disease-free state) has also increased, with skeletal muscle being a substantial contributor to this. Biological ageing is accompanied by declines in both skeletal muscle mass and function, termed sarcopenia. The mechanisms underpinning sarcopenia are multifactorial and are known to include marked alterations in muscle protein turnover and adaptations to the neural input to muscle. However, to date, the relative contribution of each factor remains largely unexplored. Specifically, muscle protein synthetic responses to key anabolic stimuli are blunted with advancing age, whilst alterations to neural components, spanning from the motor cortex and motoneuron excitability to the neuromuscular junction, may explain the greater magnitude of function losses when compared with mass. The consequences of these losses can be devastating for individuals, their support networks, and healthcare services; with clear detrimental impacts on both clinical (e.g., mortality, frailty, and post-treatment complications) and societal (e.g., independence maintenance) outcomes. Whether declines in muscle quantity and quality are an inevitable component of ageing remains to be completely understood. Nevertheless, strategies to mitigate these declines are of vital importance to improve the health span of older adults. This review aims to provide an overview of the declines in skeletal muscle mass and function with advancing age, describes the wide-ranging implications of these declines, and finally suggests strategies to mitigate them, including the merits of emerging pharmaceutical agents.

Anthropometric indicators may explain the high incidence of follicular lymphoma in Europeans: Results from a bidirectional two-sample two-step Mendelian randomisation

BACKGROUND

Non-Hodgkin's lymphoma incidence rates vary between European and Asian populations. The reasons remain unclear. This two-sample two-step Mendelian randomisation (MR) study aimed to investigate the causal relationship between anthropometric indicators (AIs) and diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) and the possible mediating role of basal metabolic rate (BMR) in Europe.

METHODS

We used the following AIs as exposures: body mass index (BMI), whole-body fat mass (WBFM), whole-body fat-free mass (WBFFM), waist circumference(WC), hip circumference(HC), standing height (SH), and weight(Wt). DLBCL and FL represented the outcomes, and BMR was a mediator. A two-sample MR analysis was performed to examine the association between AIs and DLBCL and FL onset. We performed reverse-MR analysis to determine whether DLBCL and FL interfered with the AIs. A two-step MR analysis was performed to determine whether BMR mediated the causality.

FINDINGS

WBFFM and SH had causal relationships with FL. A causal association between AIs and DLBCL was not observed. Reverse-MR analysis indicated the causal relationships were not bidirectional. Two-step MR suggested BMR may mediate the causal effect of WBFFM and SH on FL.

CONCLUSIONS

We observed a causal relationship between WBFFM and SH and the onset of FL in Europeans, Which may explain the high incidence of follicular lymphoma in Europeans.

Insufficient Bone Mineralization to Sustain Mechanical Load of Weight in Obese Boys: A Cross-Sectional Study

CONTEXT

The increase in bone mineral content (BMC) and density (BMD) measured by dual-energy x-ray absorptiometry (DXA) in obese children may not sustain the mechanical load associated with weight, and the factors influencing bone mineralization are not well known.

OBJECTIVE

We described bone mineralization in boys with overweight/obesity and leanness in relation to body composition.

METHODS

Cross-sectional study in the Pediatric Endocrinology Unit of Angers University Hospital with 249 overweight/obese boys aged 8-18 who underwent DXA and insulin, testosterone, and IGF-1 measurements. Bone mineralization was compared with data from 301 lean boys of similar age and height from NHANES 2011-2015, using the same DXA model. Path analyses were performed to evaluate factors associated with total body less head (TBLH) BMC.

RESULTS

The mean age- and height-adjusted difference in TBLH BMC between obese and lean boys was 241 ± 20 g/cm2. Each 1 kg/m2 increase in BMI was associated with +39 ± 6 g of TBLH BMC in lean subjects vs + 25 ± 3 g in obese subjects (P < .05). Each 1 kg/m2 increase in lean BMI (LBMI) was associated with +78 ± 5 g of TBLH BMC in lean and obese boys, and each 1 kg/m2 increase in fat mass index (FMI) was associated with a decrease of 9 ± 3 g of TBLH BMC. The TBLH BMC was directly positively influenced by LBMI and indirectly and positively influenced by IGF-1, testosterone, and insulin (mediated through height and LBMI). FMI indirectly influenced TBLH BMC, both positively through LBMI and negatively through its negative impact on IGF-1 and testosterone.

CONCLUSION

The increase in bone mineralization in obese children does not adapt to the increase in body mass.

Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase

The Warburg effect links growth and glycolysis in cancer. A key purpose of the Warburg effect is to generate glycolytic intermediates for anabolic reactions, such as nucleotides → RNA/DNA and amino acids → protein synthesis. The aim of this study was to investigate whether a similar 'glycolysis-for-anabolism' metabolic reprogramming also occurs in hypertrophying skeletal muscle. To interrogate this, we first induced C2C12 myotube hypertrophy with IGF-1. We then added 14C glucose to the differentiation medium and measured radioactivity in isolated protein and RNA to establish whether 14C had entered anabolism. We found that especially protein became radioactive, suggesting a glucose → glycolytic intermediates → non-essential amino acid(s) → protein series of reactions, the rate of which was increased by IGF-1. Next, to investigate the importance of glycolytic flux and non-essential amino acid synthesis for myotube hypertrophy, we exposed C2C12 and primary mouse myotubes to the glycolysis inhibitor 2-Deoxy-d-glucose (2DG). We found that inhibiting glycolysis lowered C2C12 and primary myotube size. Similarly, siRNA silencing of PHGDH, the key enzyme of the serine biosynthesis pathway, decreased C2C12 and primary myotube size; whereas retroviral PHGDH overexpression increased C2C12 myotube size. Together these results suggest that glycolysis is important for hypertrophying myotubes, which reprogram their metabolism to facilitate anabolism, similar to cancer cells.

Familial Correlation and Heritability of Hand Grip Strength in Korean Adults (Korea National Health and Nutrition Examination Survey 2014 to 2019)

BACKGRUOUND

The onset and progression of sarcopenia are highly variable among individuals owing to genetic and environmental factors. However, there are a limited number of studies measuring the heritability of muscle strength in large numbers of parent-adult offspring pairs. We aimed to investigate the familial correlation and heritability of hand grip strength (HGS) among Korean adults.

METHODS

This family-based cohort study on data from the Korea National Health and Nutrition Examination Survey (2014 to 2019) included 5,004 Koreans aged ≥19 years from 1,527 families. HGS was measured using a digital grip strength dynamometer. Familial correlations of HGS were calculated in different pairs of relatives. Variance component methods were used to estimate heritability.

RESULTS

The heritability estimate of HGS among Korean adults was 0.154 (standard error, 0.066). Correlation coefficient estimates for HGS between parent-offspring, sibling, and spouse pairs were significant at 0.07, 0.10, and 0.23 (P<0.001, P=0.041, and P<0.001, respectively). The total variance in the HGS phenotype was explained by additive genetic (15.4%), shared environmental (11.0%), and unique environmental (73.6%) influences. The odds of weak HGS significantly increased in the offspring of parents with weak HGS (odds ratio [OR], 1.69-3.10; P=0.027-0.038), especially in daughters (OR, 2.04-4.64; P=0.029-0.034).

CONCLUSION

HGS exhibits a familial correlation and significant heritable tendency in Korean adults. Therefore, Asian adults, especially women, who have parents with weak HGS, need to pay special attention to their muscle health with the help of healthy environmental stimuli.

The phenotypic and genotypic association of grip strength with frailty, physical performance and functional limitations over time in older adults

OBJECTIVES

To replicate the phenotypic associations of grip strength with frailty, physical performance and functional limitations in older adults for longer follow-up periods and to examine whether these associations are due to shared genetic factors.

METHODS

In total 2,262 participants 55 years and older with follow-up data up to 23 years (Nobservations = 8,262) from the Longitudinal Aging Study Amsterdam were included. Weighted polygenic risk scores for grip strength (PRS-GS) were built using the genome-wide meta-analysis results from UK Biobank as reference. Grip strength was measured two times on each hand using a dynamometer. Frailty index (FI) and frailty phenotype were operationalised following standard procedures. Performance tests included a timed walk test, a repeated chair stands test and put on-take off cardigan test. Functional limitations were assessed using a questionnaire with six items.

RESULTS

Higher grip strength was phenotypically associated with lower FI (b = -0.013, 95% CI (-0.016, -0.009)), better physical performance (b = 0.040, 95% CI (0.026, 0.054)) and less functional limitations (OR = 0.965, 95% CI (0.954, 0.977)) over time for follow-up periods up to 23 years. However, PRS-GS was not associated with any of the traits.

CONCLUSION

The phenotypic associations between grip strength, frailty, physical performance and functional limitations were replicated for follow-up periods up to 23 years. However, the associations between the traits could not be explained by shared genetics potentially indicating a more relevant involvement of non-genetic factors.

UBAP2 plays a role in bone homeostasis through the regulation of osteoblastogenesis and osteoclastogenesis

Osteoporosis is a condition characterized by decreased bone mineral density (BMD) and reduced bone strength, leading to an increased risk of fractures. Here, to identify novel risk variants for susceptibility to osteoporosis-related traits, an exome-wide association study is performed with 6,485 exonic single nucleotide polymorphisms (SNPs) in 2,666 women of two Korean study cohorts. The rs2781 SNP in UBAP2 gene is suggestively associated with osteoporosis and BMD with p-values of 6.1 × 10-7 (odds ratio = 1.72) and 1.1 × 10-7 in the case-control and quantitative analyzes, respectively. Knockdown of Ubap2 in mouse cells decreases osteoblastogenesis and increases osteoclastogenesis, and knockdown of ubap2 in zebrafish reveals abnormal bone formation. Ubap2 expression is associated with E-cadherin (Cdh1) and Fra1 (Fosl1) expression in the osteclastogenesis-induced monocytes. UBAP2 mRNA levels are significantly reduced in bone marrow, but increased in peripheral blood, from women with osteoporosis compared to controls. UBAP2 protein level is correlated with the blood plasma level of the representative osteoporosis biomarker osteocalcin. These results suggest that UBAP2 has a critical role in bone homeostasis through the regulation of bone remodeling.

Rare genetic variants impact muscle strength

Muscle strength is highly heritable and predictive for multiple adverse health outcomes including mortality. Here, we present a rare protein-coding variant association study in 340,319 individuals for hand grip strength, a proxy measure of muscle strength. We show that the exome-wide burden of rare protein-truncating and damaging missense variants is associated with a reduction in hand grip strength. We identify six significant hand grip strength genes, KDM5B, OBSCN, GIGYF1, TTN, RB1CC1, and EIF3J. In the example of the titin (TTN) locus we demonstrate a convergence of rare with common variant association signals and uncover genetic relationships between reduced hand grip strength and disease. Finally, we identify shared mechanisms between brain and muscle function and uncover additive effects between rare and common genetic variation on muscle strength.

Validation of a genome-wide polygenic score in improving fracture risk assessment beyond the FRAX tool in the Women's Health Initiative study

BACKGROUND

Previous study has established two polygenic scores (PGSs) related to femoral neck bone mineral density (BMD) (PGS_FNBMDldpred) and total body BMD (PGS_TBBMDldpred) that are associated with fracture risk. However, these findings have not yet been externally validated in an independent cohort.

OBJECTIVES

This study aimed to validate the predictive performance of the two established PGSs and to investigate whether adding PGSs to the Fracture Risk Assessment Tool (FRAX) improves the predictive ability of FRAX in identifying women at high risk of major osteoporotic fracture (MOF) and hip fractures (HF).

METHODS

The study used the Women's Health Initiative (WHI) cohort of 9,000 postmenopausal women of European ancestry. Cox Proportional Hazard Models were used to assess the association between each PGS and MOF/HF risk. Four models were formulated to investigate the effect of adding PGSs to the FRAX risk factors: (1) Base model: FRAX risk factors; (2) Base model + PGS_FNBMDldpred; (3) Base model + PGS_TBBMDldpred; (4) Base model + metaPGS. The reclassification ability of models with PGS was further assessed using the Net Reclassification Improvement (NRI) and the Integrated discrimination improvement (IDI).

RESULTS

The study found that the PGSs were not significantly associated with MOF or HF after adjusting for FRAX risk factors. The FRAX base model showed moderate discrimination of MOF and HF, with a C-index of 0.623 (95% CI, 0.609 to 0.641) and 0.702 (95% CI, 0.609 to 0.718), respectively. Adding PGSs to the base FRAX model did not improve the ability to discriminate MOF or HF. Reclassification analysis showed that compared to the model without PGS, the model with PGS_TBBMDldpred (1.2%, p = 0.04) and metaPGS (1.7%, p = 0.05) improve the reclassification of HF, but not MOF.

CONCLUSIONS

The findings suggested that incorporating genetic information into the FRAX tool has minimal improvement in predicting HF risk for elderly Caucasian women. These results highlight the need for further research to identify other factors that may contribute to fracture risk in elderly Caucasian women.

The clinical utility of the BMD-related comprehensive genome-wide polygenic score in identifying individuals with a high risk of osteoporotic fractures

The potential of bone mineral density (BMD)-related genome-wide polygenic score (PGS) in identifying individuals with a high risk of fractures remains unclear. This study suggests that an efficient PGS enables the identification of strata with up to a 1.5-fold difference in fracture incidence. Incorporating PGS into clinical diagnosis is anticipated to increase the population-level screening benefits.

PURPOSE

This study sought to construct genome-wide polygenic scores for femoral neck and total body BMD and to estimate their potential in identifying individuals with a high risk of osteoporotic fractures.

METHODS

Genome-wide polygenic scores were developed and validated for femoral neck and total body BMD. We externally tested the PGSs, both by themselves and in combination with available clinical risk factors, in 455,663 European ancestry individuals from the UK Biobank. The predictive accuracy of the developed genome-wide PGS was also compared with previously published restricted PGS employed in fracture risk assessment.

RESULTS

For each unit decrease in PGSs, the genome-wide PGSs were associated with up to 1.17-fold increased fracture risk. Out of four studied PGSs, [Formula: see text] (HR: 1.03; 95%CI 1.01-1.05, p = 0.001) had the weakest and the [Formula: see text] (HR: 1.17; 95%CI 1.15-1.19, p < 0.0001) had the strongest association with an incident fracture. In the reclassification analysis, compared to the FRAX base model, the models with [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] improved the reclassification of fracture by 1.2% (95% CI, 1.0 to 1.3%), 0.2% (95% CI, 0.1 to 0.3%), 1.4% (95% CI, 1.3 to 1.5%), and 2.2% (95% CI, 2.1 to 2.4%), respectively.

CONCLUSIONS

Our findings suggested that an efficient PGS estimate enables the identification of strata with up to a 1.7-fold difference in fracture incidence. Incorporating PGS information into clinical diagnosis is anticipated to increase the benefits of screening programs at the population level.

The association of dietary acid load (DAL) with estimated skeletal muscle mass and bone mineral content: a cross-sectional study

BACKGROUND & AIMS

Dietary patterns that promote mild metabolic acidosis may have a negative effect on bone and muscle, and a high dietary acid load (DAL) may be detrimental to skeletal muscle mass and bone mineral content. However, the association between skeletal muscle mass and bone mineral content with dietary acid load has not been consistently reported in previous studies. The objective of the study was to evaluate the association of potential renal net acid load (PRAL) and net endogenous acid production (NEAP) with bone mineral content and skeletal muscle mass in pre-menopause women with overweight or obesity in Iran.

METHOD

Three hundred and ninety women with a body mass index (BMI) of 25 were included in this cross-sectional study. We used a validated 147-item semi-quantitative food frequency questionnaire (FFQ) for evaluating the dietary intake. Based on the dietary data, potential renal net acid load (PRAL) and net endogenous acid production (NEAP) were calculated. Muscle mass and bone mineral content were estimated by a bioelectrical impedance analyzer (BIA).

RESULTS

After controlling for potential confounders, we discovered a significant linear relationship between PRAL (β = -0.027, 95%CI = -0.049 to -0.004, P = 0.02) and NEAP (β = -0.05, 95%CI = -0.097 to -0.003, P = 0.03) and skeletal muscle mass index. However, there was no significant difference between SMM and BMC across PRAL and NEAP tertiles.

CONCLUSION

PRAL and NEAP were found to be inversely related to skeletal muscle mass index among overweight/obese women. Further research is required to establish whether this relationship is important for musculoskeletal health in these populations.

Transcriptome-wide association study identifies novel genes associated with bone mineral density and lean body mass in children

OBJECTIVE

To identify novel candidate genes whose expression is associated with bone mineral density (BMD) and body lean mass (LM) in children.

METHODS

A tissue-specific transcriptome-wide association study (TWAS) was conducted utilizing a large-scale genome-wide association study (GWAS) dataset associated with BMD and LM and involving 10,414 participants. The measurement of BMD and LM phenotypes was made based on total-body dual-energy X-ray absorptiometry (TB-DXA) scans. TWAS was conducted by using FUSION software. Reference panels for muscle skeleton (MS), peripheral blood (NBL) and whole blood (YBL) were used for TWAS analysis. Functional enrichment and protein-protein interaction (PPI) analyses of the genes identified by TWAS were performed by using the online tool Metascape ( http://metascape.org ).

RESULTS

For BMD, we identified 174 genes with P < 0.05, such as IKZF1 (P = 1.46 × 10^-9) and CHKB (P = 8.31 × 10^-7). For LM, we identified 208 genes with P < 0.05, such as COPS5 (P = 3.03 × 10^-12) and MRPS33 (P = 5.45 × 10^-10). Gene ontology (GO) enrichment analysis of the BMD-associated genes revealed 200 GO terms, such as protein catabolic process (Log P = -5.09) and steroid hormone-mediated signaling pathway (Log P = -3.13). GO enrichment analysis of the LM-associated genes detected 287 GO terms, such as the apoptotic signaling pathway (Log P = -8.08) and lipid storage (Log P = -3.55).

CONCLUSION

This study identified several candidate genes for BMD and LM in children, providing novel clues to the genetic mechanisms underlying the development of childhood BMD and LM.

PUNTO ÓPTIMO CARDIORRESPIRATORIO, COMPOSICION CORPORAL Y MEDIDAS BIOQUÍMICAS: UN ESTUDIO CON GEMELOS

El propósito de este estudio fue investigar la relación de la composición corporal y las variables bioquímicas con el POC, así como observar la tendencia de la heredabilidad. Estudio transversal con gemelos monocigóticos y dicigóticos adultos. Para obtener los valores del POC, la prueba de ejercicio cardiopulmonar fue realizada se realizó un protocolo con sobre cinta rodante. Para la composición corporal, se utilizaron laabsorciometríade energía dual y la antropometría. Para las inferencias, se realizaron la concordancia de Spearman y la prueba de hipótesisMann-Whitney.Los resultados mostraron que lasvariables de composición corporal no se correlacionaron significativamente con el punto óptimo cardiorrespiratorio. El Punto Óptimo Cardiorrespiratorio y las variables bioquímicas en general demostraron una mayor tendencia a ser influenciados por factores ambientales. El comportamiento de las variables de composición corporal demostró una mayor influencia de la heredabilidad.

Lifetime serum concentration of 25-hydroxyvitamin D 25(OH) is associated with hand grip strengths: insight from a Mendelian randomisation

Clinical trials have suggested that increased 25-hydroxyvitamin D (25(OH)D) has positive effect on hand grip strength. This Mendelian randomisation (MR) was implemented using summary-level data from the largest genome-wide association studies on vitamin D (n = 73,699) and hand grip strength. Inverse variance weighted method (IVW) was used to estimate the causal estimates. Weighted median (WM)-based method, MR-Egger and leave-one-out were applied as sensitivity analysis. Results showed that genetically higher-serum 25(OH)D levels had a positive effect on both right hand grip (IVW = Beta: 0.038, P = 0.030) and left hand grip (IVW = Beta: 0.034, P = 0.036). There was a low likelihood (statistically insignificant) of heterogeneity and pleiotropy, and the observed associations were not driven by single single-nucleotide polymorphisms. Furthermore, MR pleiotropy residual sum and outlier did not highlight any outliers. In conclusion, our results highlighted the causal and beneficial effect of serum 25(OH) D on right- and left-hand grip strengths.

Sarcopenia: An Age-Related Multifactorial Disorder

Sarcopenia is an emerging clinical entity characterized by a gradual decline in skeletal muscle mass and strength that accompanies the normal aging process. It has been noted that sarcopenia is associated with various adverse health outcomes in the geriatric population like prolonged hospital admission, disability, poor quality of life, frailty, and mortality. Factors involved in the development of age-related sarcopenia include anorexia, alteration in the hormone levels, decreased neural innervation, low blood flow to the muscles, cytokine dysregulation, altered mitochondrial activity, genomic instability, intracellular proteolysis, and insulin resistance. Understanding the mechanism may help develop efficient preventive and therapeutic strategies which can improve the quality of life in elderly individuals. Thus, the objective of the present article is to review the literature regarding the mechanism involved in the development of sarcopenia in aged individuals.

Unveiling genetic variants for age-related sarcopenia by conducting a genome-wide association study on Korean cohorts

Sarcopenia is an age-related disorder characterised by a progressive decrease in skeletal muscle mass. As the genetic biomarkers for sarcopenia are not yet well characterised, this study aimed to investigate the genetic variations related to sarcopenia in a relatively aged cohort, using genome-wide association study (GWAS) meta-analyses of lean body mass (LBM) in 6961 subjects. Two Korean cohorts were analysed, and subgroup GWAS was conducted for appendicular skeletal muscle mass (ASM) and skeletal muscle index. The effects of significant single nucleotide polymorphisms (SNPs) on gene expression were also investigated using multiple expression quantitative trait loci datasets, differentially expressed gene analysis, and gene ontology analyses. Novel genetic biomarkers were identified for LBM (rs1187118; rs3768582) and ASM (rs6772958). Their related genes, including RPS10, NUDT3, NCF2, SMG7, and ARPC5, were differently expressed in skeletal muscle tissue, while GPD1L was not. Furthermore, the 'mRNA destabilisation' biological process was enriched for sarcopenia. Our study identified RPS10, NUDT3, and GPD1L as significant genetic biomarkers for sarcopenia. These genetic loci were related to lipid and energy metabolism, suggesting that genes involved in metabolic dysregulation may lead to the pathogenesis of age-related sarcopenia.

Genes and Weightlifting Performance

A recent case-control study identified 28 DNA polymorphisms associated with strength athlete status. However, studies of genotype-phenotype design are required to support those findings. The aim of the present study was to investigate both individually and in combination the association of 28 genetic markers with weightlifting performance in Russian athletes and to replicate the most significant findings in an independent cohort of Japanese athletes. Genomic DNA was collected from 53 elite Russian (31 men and 22 women, 23.3 ± 4.1 years) and 100 sub-elite Japanese (53 men and 47 women, 21.4 ± 4.2 years) weightlifters, and then genotyped using PCR or micro-array analysis. Out of 28 DNA polymorphisms, LRPPRC rs10186876 A, MMS22L rs9320823 T, MTHFR rs1801131 C, and PHACTR1 rs6905419 C alleles positively correlated (p < 0.05) with weightlifting performance (i.e., total lifts in snatch and clean and jerk in official competitions adjusted for sex and body mass) in Russian athletes. Next, using a polygenic approach, we found that carriers of a high (6-8) number of strength-related alleles had better competition results than carriers of a low (0-5) number of strength-related alleles (264.2 (14.7) vs. 239.1 (21.9) points; p = 0.009). These findings were replicated in the study of Japanese athletes. More specifically, Japanese carriers of a high number of strength-related alleles were stronger than carriers of a low number of strength-related alleles (212.9 (22.6) vs. 199.1 (17.2) points; p = 0.0016). In conclusion, we identified four common gene polymorphisms individually or in combination associated with weightlifting performance in athletes from East European and East Asian geographic ancestries.

Intra-uterine effects on adult muscle strength

BACKGROUND

Maternal behaviors and exposures affect fetal growth and development. Smoking, malnutrition, sedentary behavior, and stress can each lead to fetal programming and intra-uterine growth restriction. As a result, tissue development may be impaired. Problems with muscle formation can lead to reductions in muscle performance throughout life. The purpose of this study was to determine if in utero effects on muscle mass, muscle function, or both are responsible for the relationship between size at birth and adult muscle strength.

STUDY DESIGN

One hundred adults (ages 18-40), who were singletons born at term (37-42 weeks), participated. Birth weight was adjusted for gestational age using neonatal growth reference data. Maximal voluntary contractions (MVC) of dominant and non-dominant handgrip, and right and left leg extension were measured. Linear regression analysis was used to determine the association between adjusted birth weight and muscle strength. Sex and lean body mass were covariates.

RESULTS

Dominant handgrip MVC increased by 1.533 kg per 1 SD increase in adjusted birth weight (p = 0.004). Lean body mass had a significant indirect effect on this relationship. The relationship between handgrip strength and adjusted birth weight was strongest among female subjects. No other muscle strength measures were significantly associated with adjusted birth weight.

CONCLUSIONS

Birth size was a significant predictor of handgrip strength in adulthood. Including lean body mass attenuated, but did not remove, the association. Thus, among individuals born to term, having a smaller-than-predicted birth size likely causes both reductions in muscle mass formation and decreased muscle function, ultimately impacting muscle strength in adulthood.

A Genome-Wide Association Study Identifies Novel Risk Loci for Sarcopenia in a Taiwanese Population

Purpose

A genome-wide association study (GWAS) of sarcopenia unraveled the importance of genetic contribution to decline in muscle. The current study investigated sarcopenia-related single nucleotide polymorphisms (SNPs) in Asian older adults, and further constructed a genotype score that tests the combined effect of these SNPs on risk of sarcopenia.

Patients and Methods

Ninety-six subjects aged 60 or above were recruited from the database of annual geriatric health examination at Tri-Service General Hospital during 2020. Eligible criteria included: 1) not having severe comorbidities; 2) agreed to join the Taiwan Precision Medicine Initiative project; and 3) having sufficient information of required sarcopenic measurements. Genotype–phenotype association analysis was performed to find SNPs that were significantly associated with each of three sarcopenic indices (low muscle mass, muscle strength, and physical performance). Subsequently, these SNPs comprised a sarcopenia-related genotype score that summed up the number of SNPs carrying unfavorable allele(s).

Results

Twelve SNPs revealed suggestive genome-wide significance with the three sarcopenic indices, and eight of them revealed a relationship with more than one index. Low muscle strength was the item that had the most (eight) related SNPs. Among them, rs10282247 affects cholesterol binding and rs7022373 participates in cellular apoptosis. In addition, higher genotype score demonstrated higher risk of sarcopenia (≥4 points: OR=630.6; 2–3 points: OR=408, p-value<0.001).

Conclusion

Several newly discovered SNPs suggest that genetic contribution plays a part in the pathogenesis of sarcopenia. Further studies are warranted to verify the underlying mechanisms. Moreover, a genotype score provides an estimate of the combined effect of genetic association with sarcopenia, which may modestly improve clinical risk classification.

Associations between genetic loci related to lean mass and body composition in type 2 diabetes

Aim

Several genetic loci related to lean mass have been identified in healthy individuals by genome‐wide association studies; however, the contribution of these loci to body composition in type 2 diabetes remains to be investigated. Here, we aimed to clarify the genetic determinants of body composition in individuals with type 2 diabetes.

Methods

A total of 176 Japanese outpatients (70 women and 106 men) with type 2 diabetes were studied using a cross‐sectional design. Body composition was measured using bioimpedance analysis with a commercially available device (InBody770). Single‐nucleotide polymorphisms in IRS1 (rs2943656), HSD17B11 (rs9991501), VCAN (rs2287926), ADAMTSL3 (rs4842924) and FTO (rs9936385) were evaluated by genotyping. The contributions of single‐nucleotide polymorphisms to body composition were examined, considering known clinical determinants.

Results

Sex, body composition and age were identified as clinical predictors. IRS1 rs2934656 was identified as an independent predictor of skeletal muscle mass (β = 0.11, P = 0.026), and ADAMTSL3 rs4842924 was an independent predictor of body fat mass (β = 0.15, P = 0.0095) and appendicular lean mass (β = −0.13, P = 0.017).

Conclusions

The findings clarified the contribution of genetic factors – IRS1 and ADAMTSL3 – to interindividual variation in body composition, independent of clinical factors, in type 2 diabetes patients. These data will contribute to the establishment of effective methods for the prediction, prevention, and intervention of sarcopenia and frailty in diabetes patients. Geriatr Gerontol Int 2021; 21: 932–938.

Identification of novel and rare variants associated with handgrip strength using whole genome sequence data from the NHLBI Trans-Omics in Precision Medicine (TOPMed) Program

Handgrip strength is a widely used measure of muscle strength and a predictor of a range of morbidities including cardiovascular diseases and all-cause mortality. Previous genome-wide association studies of handgrip strength have focused on common variants primarily in persons of European descent. We aimed to identify rare and ancestry-specific genetic variants associated with handgrip strength by conducting whole-genome sequence association analyses using 13,552 participants from six studies representing diverse population groups from the Trans-Omics in Precision Medicine (TOPMed) Program. By leveraging multiple handgrip strength measures performed in study participants over time, we increased our effective sample size by 7-12%. Single-variant analyses identified ten handgrip strength loci among African-Americans: four rare variants, five low-frequency variants, and one common variant. One significant and four suggestive genes were identified associated with handgrip strength when aggregating rare and functional variants; all associations were ancestry-specific. We additionally leveraged the different ancestries available in the UK Biobank to further explore the ancestry-specific association signals from the single-variant association analyses. In conclusion, our study identified 11 new loci associated with handgrip strength with rare and/or ancestry-specific genetic variations, highlighting the added value of whole-genome sequencing in diverse samples. Several of the associations identified using single-variant or aggregate analyses lie in genes with a function relevant to the brain or muscle or were reported to be associated with muscle or age-related traits. Further studies in samples with sequence data and diverse ancestries are needed to confirm these findings.

Association of TGF-β1 and IL-10 Gene Polymorphisms with Osteoporosis in a Study of Taiwanese Osteoporotic Patients

Osteoporosis is a rising health threat in the increasingly aging world population. It is a common skeletal disease strongly linked to genetic predisposition. We aim to identify the effects of the anti-inflammatory TGF-β1- and IL-10-specific single-nucleotide polymorphism (SNP) combination on the risk for osteoporosis. We investigated and analyzed the relationships between three TGF-β1 SNPs (-509C/T, +869 T/C and +29T/C), one IL-10 SNP (+1927A/C) and the level of bone mineral density (BMD), as well as the risk of osteoporosis in Taiwanese osteoporotic patients. A total of 217 subjects were recruited, including 88 osteoporotic patients and 129 healthy controls, for SNPs, BMD and clinical characteristics statistical analyses. Females with TGF-β1 SNP (-509 C/C) and IL-10 SNP (+1927 C/C) genotypes showed a great benefit for femoral neck T-scores. However, the combination of TGF-β1 SNP (-509 T/T) and IL-10 SNP (+1927 A/A) genotypes in all subjects showed a significant decrease in total hip BMD T-scores. The TGF-β1 SNP (-509 C/T) genotype in all subjects and TGF-β1 SNP (-509 T/T) and IL-10 SNP (+1927 A/C) genotypes in males showed positive effects on body height. The combination of the many SNPs in the anti-inflammatory TGF-β1 and IL-10 genes may be cooperatively involved in the development of osteoporosis. Our data suggested that the specific SNP combination of TGF-β1 (-509) and IL-10 (+1927) may act as a predictive factor for postmenopausal osteoporosis in Taiwanese women.

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.

Enhanced Identification of Novel Potential Variants for Appendicular Lean Mass by Leveraging Pleiotropy With Bone Mineral Density

Strong relationships have been found between appendicular lean mass (ALM) and bone mineral density (BMD). It may be due to a shared genetic basis, termed pleiotropy. By leveraging the pleiotropy with BMD, the aim of this study was to detect more potential genetic variants for ALM. Using the conditional false discovery rate (cFDR) methodology, a combined analysis of the summary statistics of two large independent genome wide association studies (GWAS) of ALM (n = 73,420) and BMD (n = 10,414) was conducted. Strong pleiotropic enrichment and 26 novel potential pleiotropic SNPs were found for ALM and BMD. We identified 156 SNPs for ALM (cFDR <0.05), of which 74 were replicates of previous GWASs and 82 were novel SNPs potentially-associated with ALM. Eleven genes annotated by 31 novel SNPs (13 pleiotropic and 18 ALM specific) were partially validated in a gene expression assay. Functional enrichment analysis indicated that genes corresponding to the novel potential SNPs were enriched in GO terms and/or KEGG pathways that played important roles in muscle development and/or BMD metabolism (adjP <0.05). In protein–protein interaction analysis, rich interactions were demonstrated among the proteins produced by the corresponding genes. In conclusion, the present study, as in other recent studies we have conducted, demonstrated superior efficiency and reliability of the cFDR methodology for enhanced detection of trait-associated genetic variants. Our findings shed novel insight into the genetic variability of ALM in addition to the shared genetic basis underlying ALM and BMD.

Responses to Maximal Strength Training in Different Age and Gender Groups

Purpose

The present study aimed to investigate the potential impact of age, gender, baseline strength, and selected candidate polymorphisms on maximal strength training (MST) adaptations.

Methods

A total of 49 subjects (22 men and 27 women) aged 20–76 years, divided into five age groups, completed an 8 weeks MST intervention. Each MST session consisted of 4 sets with 4 repetitions at ∼85–90% of one-repetition maximum (1RM) intensity in leg-press, three times per week. 1RM was tested pre and post the intervention and blood samples were drawn to genotype candidate polymorphisms ACE I/D (rs1799752), ACTN3 R577X (rs1815739), and PPARGC1A Gly482Ser (rs8192678).

Results

All age groups increased leg-press 1RM (p < 0.01), with a mean improvement of 24.2 ± 14.0%. There were no differences in improvements between the five age groups or between male and female participants, and there were no non-responders. Baseline strength status did not correlate with 1RM improvements. PPARGC1A rs8192678 T allele carriers had a 15% higher age- and gender corrected baseline 1RM than the CC genotype (p < 0.05). C allele carriers improved 1RM (%) by 34.2% more than homozygotes for the T allele (p < 0.05).

Conclusion

To the best of our knowledge, this is the first study to report improvement in leg-press maximal strength regardless of gender, baseline strength status in all age groups. The present study is also first to demonstrate an association between the PPARGC1A rs8192678 and maximal strength and its trainability in a moderately trained cohort. MST may be beneficial for good health and performance of all healthy individuals.

Identification of pleiotropic loci underlying hip bone mineral density and trunk lean mass

Bone mineral density (BMD) and lean body mass (LBM) not only have a considerable heritability each, but also are genetically correlated. However, common genetic determinants shared by both traits are largely unknown. In the present study, we performed a bivariate genome-wide association study (GWAS) meta-analysis of hip BMD and trunk lean mass (TLM) in 11,335 subjects from 6 samples, and performed replication in estimated heel BMD and TLM in 215,234 UK Biobank (UKB) participants. We identified 2 loci that nearly attained the genome-wide significance (GWS, p < 5.0 × 10-8) level in the discovery GWAS meta-analysis and that were successfully replicated in the UKB sample: 11p15.2 (lead SNP rs12800228, discovery p = 2.88 × 10-7, replication p = 1.95 × 10-4) and 18q21.32 (rs489693, discovery p = 1.67 × 10-7, replication p = 1.17 × 10-3). The above 2 pleiotropic loci may play a pleiotropic role for hip BMD and TLM development. So our findings provide useful insights that further enhance our understanding of genetic interplay between BMD and LBM.

Studies of Twin Responses to Understand Exercise Therapy (STRUETH): Body Composition

PURPOSE

We studied individual variability in exercise responses in twins. We hypothesized that 1) endurance (END) training would reduce fat mass whereas resistance (RES) training would increase lean mass, 2) individuals who did not respond to one modality would respond to the other, and 3) cross-sectional heritability estimates would be higher than estimates based on training responses.

METHODS

DXA was undertaken in 84 same-sex untrained twins (30 monozygotic [MZ], 12 dizygotic [DZ]). Participants underwent 3 months of END and RES training, separated by 3 months washout. Twins trained in pairs.

RESULTS

RES (P < 0.001) and END (P = 0.002) increased lean mass, with a greater change in RES (P < 0.001). Similarly, RES (P = 0.04) and END (P = 0.006) decreased fat mass. Eighty-four percent of subjects responded positively to RES for lean mass and 58% to END (P < 0.001). For fat mass, RES and END induced 56% and 66% responder rates, respectively (P = 0.28). Cross-sectional intraclass correlations, used to assess the similarity in twin responses, were higher for MZ than DZ pairs for all variables. Following training, only MZ pairs were significantly correlated (P < 0.001) for change in lean mass to RES.

CONCLUSION

To our knowledge, this study is the first to report individual responsiveness in body composition to both RES and END in the same subjects. Although RES and END induced favorable changes in fat mass, RES was superior for lean mass. The frequency of lean mass responders to RES exceeded that for END, whereas response rates for fat mass were similar. Cross-sectional heritability estimates were higher than training response estimates, and shared environment had the largest influence on changes in body composition. This study suggests that exercise professionals should consider modality and environmental factors when optimizing exercise interventions.

Three pleiotropic loci associated with bone mineral density and lean body mass

Both bone mineral density (BMD) and lean body mass (LBM) are important physiological measures with strong genetic determination. Besides, BMD and LBM might have common genetic factors. Aiming to identify pleiotropic genomic loci underlying BMD and LBM, we performed bivariate genome-wide association study meta-analyses of femoral neck bone mineral density and LBM at arms and legs, and replicated in the large-scale UK Biobank cohort sample. Combining the results from discovery meta-analysis and replication sample, we identified three genomic loci at the genome-wide significance level (p < 5.0 × 10-8): 2p23.2 (lead SNP rs4477866, discovery p = 3.47 × 10-8, replication p = 1.03 × 10-4), 16q12.2 (rs1421085, discovery p = 2.04 × 10-9, replication p = 6.47 × 10-14) and 18q21.32 (rs11152213, discovery p = 3.47 × 10-8, replication p = 6.69 × 10-6). Our findings not only provide useful insights into lean mass and bone mass development, but also enhance our understanding of the potential genetic correlation between BMD and LBM.

Associations of combined genetic and epigenetic scores with muscle size and muscle strength: a pilot study in older women

BACKGROUND

Inter-individual variance in skeletal muscle is closely related to genetic architecture and epigenetic regulation. Studies have examined genetic and epigenetic relationships with characteristics of ageing muscle separately, while no study has combined both genetic and epigenetic profiles in ageing muscle research. The aim of this study was to evaluate the association between combined genetic and methylation scores and skeletal muscle phenotypes in older women.

METHODS

Forty-eight older Caucasian women (aged 65-79 years) were included in this study. Biceps brachii thickness and vastus lateralis anatomical cross-sectional area (ACSA_VL ) were measured by ultrasonography. Maximum isometric elbow flexion (MVC_EF ) and knee extension (MVC_KE ) torques were measured by a customized dynamometer. The muscle-driven genetic predisposition score (GPS_SNP ) was calculated based on seven muscle-related single nucleotide polymorphisms (SNPs). DNA methylation levels of whole blood samples were analysed using Infinium MethylationEPIC BeadChip arrays. The DNA methylation score was calculated as a weighted sum of methylation levels of sarcopenia-driven CpG sites (MS_SAR ) or an overall gene-wise methylation score (MS_SNP , the mean methylation level of CpG sites located in muscle-related genes). Linear regression models were built to study genetic and epigenetic associations with muscle size and strength. Three models were built with both genetic and methylation scores: (1) MS_SAR  + GPS_SNP , (2) MS_SNP  + GPS_SNP , and (3) gene-wise combined scores which were calculated as the ratio of the SNP score to the mean methylation level of promoters in the corresponding gene. Additional models with only a genetic or methylation score were also built. All models were adjusted for age and BMI.

RESULTS

MS_SAR was negatively associated with ACSA_VL , MVC_EF , and MVC_KE and explained 10.1%, 35.5%, and 40.1% of the variance, respectively. MS_SAR explained more variance in these muscular phenotypes than GPS_SNP , MS_SNP , and models including both genetic and methylation scores. MS_SNP and GPS_SNP accounted for less than 8% and 5% of the variance in all muscular phenotypes, respectively. The genotype and methylation level of CNTF was positively related to MVC_KE (P = 0.03) and explained 12.2% of the variance. The adjusted R² and Akaike information criterion showed that models with only a MS_SAR performed the best in explaining inter-individual variance in muscular phenotypes.

CONCLUSIONS

Our results improve the understanding of inter-individual variance in muscular characteristics of older women and suggest a possible application of a sarcopenia-driven methylation score to muscle strength estimation in older women while the combination with a genetic score still needs to be further studied.

Genetic variation in lean body mass, changes of appetite and weight loss in response to diet interventions: The POUNDS Lost trial

AIM

To investigate whether the genetic risk score (GRS) for lean body mass (LBM) modified the effects of weight-loss diets on changes in appetite and adiposity among overweight and obese individuals.

PARTICIPANTS AND METHODS

In the 2-year Preventing Overweight Using Novel Dietary Strategies (POUNDS Lost) trial, we included 692 adults who were randomly assigned to one of four diets varying in macronutrient intake. A GRS was calculated using five single nucleotide polymorphisms associated with LBM.

RESULTS

The LBM-GRS was not associated with the baseline LBM measured by dual-energy x-ray absorptiometry in a subgroup (50%) of the study population. We found that the LBM-GRS had significantly different associations with changes in appetite from baseline to 6 months according to low- or high-fat diet group (P-interaction < 0.001, 0.021, 0.005 and 0.024 for total appetite score, hunger, fullness and prospective consumption, respectively). Lower LBM-GRS (indicating a greater genetic predisposition to LBM) was associated with greater decreases in the total appetite score (P < 0.001), hunger (P = 0.01), fullness (P = 0.001) and prospective consumption (P = 0.019) in participants in the low-fat diet group, whereas no significant associations with these appetite measures were observed in the high-fat diet group. In addition, lower LBM-GRS was associated with greater reduction in body weight (P = 0.003) and waist circumference (P = 0.011) among participants in the low-fat diet group, while no associations were observed in the high-fat diet group. The interactions attenuated, along with weight regain, from 6 months to 2 years.

CONCLUSIONS

Our findings suggest that genetic variation in LBM may be differentially associated with appetite changes, and may subsequently be related to changes in body weight and waist circumference, according to dietary fat intake.

Masticatory muscle function affects the pathological conditions of dentofacial deformities

The causes of dentofacial deformities include various known syndromes, genetics, environmental and neuromuscular factors, trauma, and tumors. Above all, the functional effects of muscles are important, and deformation of the mandible is often associated with a mechanical imbalance of the masticatory muscles. With the vertical position of the face, weakness of the sling of the masseter muscle and medial pterygoid muscle causes dilatation of the mandibular angle. In patients with a deep bite, excessive function of the masticatory muscles is reported. Myosin heavy chain　(MyHC) properties also affect jawbone morphology. In short-face patients, the proportion of type II fibers, which are fast muscles, is high. The proportions of muscle fiber types are genetically determined but can be altered by postnatal environmental factors. Orthognathic surgery may results in the transition of MyHC to type II (fast) fibers, but excessive stretching enhances the release of inflammatory mediators and causes a shift toward a greater proportion of slow muscle fibers. This feature can be related to postoperative relapse. Bones and muscles are in close crosstalk, and it may be possible to use biochemical approaches as well as biomechanical considerations for the treatment of jaw deformities.

Comparison of the associations between appendicular lean mass adjustment methods and cardiometabolic factors

BACKGROUND AND AIMS

To compare the cross-sectional and longitudinal associations between appendicular lean mass (ALM) and cardiometabolic risk factors according to body-size adjustment methods and the contributions of genetic and/or environmental factors to the correlations between those traits.

METHODS AND RESULTS

Regression coefficients per sex-specific 1 standard deviation in bodyweight (wt), body mass index (BMI), or height-squared (ht²) adjusted ALM (assessed using a dual-energy X-ray absorptiometer (DXA) and a bioelectrical impedance analyzer (BIA) at baseline)/changes in these indices (assessed using BIA) were compared in terms of their associations with blood pressure (BP), lipid profiles, and insulin resistance profiles in 2655 participants for cross-sectional analysis and 332 participants for longitudinal analysis (follow-up time, 32.2 ± 7.9 months). A bivariate genetic analysis of the genetic/environmental cross-trait correlations was conducted to determine their cross-sectional relationships. After adjusting for sociodemographic factors, health behaviors, and BMI in the analysis for ALM/ht², ALM/wt and ALM/BMI had favorable associations with all cardiometabolic risk factors, while ALM/ht² had favorable associations with some risk factors. In longitudinal associations, changes in ALM/wt and ALM/BMI had inverse associations with increments of lipid profiles, insulin, and homeostasis model assessment of insulin resistance (HOMA), while change in ALM/ht² did not have associations with increments of cardiometabolic risk factors. ALM/ht² had genetic correlations with seven of nine risk factors; ALM/wt and ALM/BMI had correlations with three and one risk factors, respectively.

CONCLUSION

ALM/wt and ALM/BMI are better indicators for cardiometabolic risk factors; genetic factors may contribute more to the correlations between ALM/ht² and those traits.

The genetic architecture of appendicular lean mass characterized by association analysis in the UK Biobank study

Appendicular lean mass (ALM) is a heritable trait associated with loss of lean muscle mass and strength, or sarcopenia, but its genetic determinants are largely unknown. Here we conducted a genome-wide association study (GWAS) with 450,243 UK Biobank participants to uncover its genetic architecture. A total of 1059 conditionally independent variants from 799 loci were identified at the genome-wide significance level (p < 5 × 10-9), all of which were also significant at p < 5 × 10-5 in both sexes. These variants explained ~15.5% of the phenotypic variance, accounting for more than one quarter of the total ~50% GWAS-attributable heritability. There was no difference in genetic effect between sexes or among different age strata. Heritability was enriched in certain functional categories, such as conserved and coding regions, and in tissues related to the musculoskeletal system. Polygenic risk score prediction well distinguished participants with high and low ALM. The findings are important not only for lean mass but also for other complex diseases, such as type 2 diabetes, as ALM is shown to be a protective factor for type 2 diabetes.

Are the Relationships of Lean Mass and Fat Mass With Bone Microarchitecture Causal or Due to Familial Confounders? A Novel Study of Adult Female Twin Pairs

It is not known whether the relationships of lean mass (LM) and fat mass (FM) with bone microarchitecture and geometry are causal and/or are because of confounders, including familial confounders arising from genetic and environment effects shared by relatives. We tested the hypotheses that: (i) LM is associated with cortical bone traits, (ii) FM is associated with trabecular bone traits, and (iii) these relationships of LM and FM with bone microarchitecture and geometry have a causal component. Total body composition was quantified for 98 monozygotic (MZ) and 54 dizygotic (DZ) white female twin pairs aged 31 to 77 years. Microarchitecture at the distal tibia and distal radius was quantified using HRpQCT and StrAx software. We applied the Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) method. Within‐individuals, distal tibia total bone area, cortical area, cortical thickness, and trabecular number were positively associated with LM (standardized regression coefficient (β) = 0.13 to 0.43; all p < 0.05); porosity of the inner transitional zone (ITZ) was negatively associated with LM (β = −0.22; p < 0.01). Trabecular number was positively associated with FM (β = 0.40; p < 0.001), and trabecular thickness was negatively associated with FM (β = −0.27; p < 0.001). For porosity of ITZ and trabecular number, the cross‐pair cross‐trait association with LM was significant before and after adjustment for the within‐individual association with LM (all ps < 0.05). For trabecular number, the cross‐pair cross‐trait association with FM was significant before and after adjustment for the within‐individual association with FM (p < 0.01). There were no significant changes in these cross‐pair cross‐trait associations after adjustment for the within‐individual association (p = 0.06 to 0.99). Similar results were found for distal radius measures. We conclude that there was no evidence that the relationships of LM and FM with bone microarchitecture and geometry are causal; they must in part due to by familial confounders affecting both bone architecture and body composition. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Four pleiotropic loci associated with fat mass and lean mass

BACKGROUND

Fat mass and lean mass are two biggest components of body mass. Both fat mass and lean mass are under strong genetic determinants and are correlated.

METHODS

We performed a bivariate genome-wide association meta-analysis of (lean adjusted) leg fat mass and (fat adjusted) leg lean mass in 12,517 subjects from 6 samples, and followed by in silico replication in large-scale UK biobank cohort sample (N = 370 097).

RESULTS

We identified four loci that were significant at the genome-wide significance (GWS, α = 5.0 × 10-8) level at the discovery meta-analysis, and successfully replicated in the replication sample: 2q36.3 (rs1024137, pdiscovery = 3.32 × 10-8, preplication = 4.07 × 10-13), 5q13.1 (rs4976033, pdiscovery = 1.93 × 10-9, preplication = 6.35 × 10-7), 12q24.31 (rs4765528, pdiscovery = 7.19 × 10-12, preplication = 1.88 × 10-11) and 18q21.32 (rs371326986, pdiscovery = 9.04 × 10-9, preplication = 2.35 × 10-95). The above four pleiotropic loci may play a pleiotropic role for fat mass and lean mass development.

CONCLUSIONS

Our findings further enhance the understanding of the genetic association between fat mass and lean mass and provide a new theoretical basis for their understanding.

Changes in Physical Fitness Among Preschool Children From Kraków (Poland) From 2008 to 2018

BACKGROUND

The aim of this study was to analyze the secular changes of the physical fitness of preschool children from Kraków, Poland between 2008 and 2018.

METHODS

The study group consisted of 2143 children (3- to 7-y-olds; 2008 cohort included 1037 children and the 2018 cohort included 1106 children). The following physical fitness tests were carried out: overhead medicine ball throw, standing broad jump, sit-and-reach test, and handgrip strength. Statistical differences between the cohorts were obtained using 2-way analysis of variance and Tukey tests.

RESULTS

Negative changes were noted for the standing broad jump and its relative results among boys. A negative trend was also observed for flexibility and ball throw. Positive changes were noted for the standing broad jump among girls, as well as the absolute and normalized results of handgrip strength in both sexes. Besides the flexibility, observed discrepancies were practically significant between the age groups. Differences between the cohorts reached practical significance in the case of absolute and normalized handgrip strength.

CONCLUSIONS

There was at least partial progress in the children's fitness. Physical fitness, in turn, is one of the most important health markers. Moreover, its low level is a predictor of diseases, including metabolic and cardiovascular ones, lower academic performance, and psychosocial problems.

Whole-exome sequencing and genome-wide association studies identify novel sarcopenia risk genes in Han Chinese

Sarcopenia is a complex polygenic disease, and its molecular mechanism is still unclear. Whole lean body mass (WLBM) is a heritable trait predicting sarcopenia. To identify genomic loci underlying, we performed a whole-exome sequencing (WES) of WLBM variation with high sequencing depth (more than 40*) in 101 Chinese subjects. We then replicated in the major findings in the large-scale UK Biobank (UKB) cohort (N = 217,822) for WLBM. The results of four single-nucleotide polymorphisms (SNPs) were significant both in the discovery stage and replication stage: SNP rs740681 (discovery p = 1.66 × 10-6 , replication p = .05), rs2272303 (discovery p = 3.20 × 10-4 , replication p = 3.10 × 10-4 ), rs11170413 (discovery p = 3.99 × 10-4 , replication p = 2.90 × 10-4 ), and rs2272302 (discovery p = 9.13 × 10-4 , replication p = 3.10 × 10-4 ). We combined p values of the significant SNPs. Functional annotations highlighted two candidate genes, including FZR1 and SOAT2, that may exert pleiotropic effects to the development of body mass. Our findings provide useful insights that further enhance our understanding of genetic interplay in sarcopenia.

Targeted genotype analyses of GWAS-derived lean body mass and handgrip strength-associated single-nucleotide polymorphisms in elite master athletes

Recent large genome-wide association studies (GWAS) have independently identified a set of genetic loci associated with lean body mass (LBM) and handgrip strength (HGS). Evaluation of these candidate single-nucleotide polymorphisms (SNPs) may be useful to investigate genetic traits of populations at higher or lower risk of muscle dysfunction. As such, we investigated associations between six SNPs linked to LBM or HGS in a population of elite master athletes (MA) and age-matched controls as a representative population of older individuals with variable maintenance of muscle mass and function. Genomic DNA was isolated from buffy coat samples of 96 individuals [consisting of 48 MA (71 ± 6 yr, age-graded performance 83 ± 9%) and 48 older controls (75 ± 6 yr)]. SNP validation and sample genotyping were conducted using the tetra-primer amplification refractory mutation system (ARMS). For the three SNPs analyzed that were previously associated with LBM (FTO, IRS1, and ADAMTSL3), multinomial logistic regression revealed a significant association of the ADAMTSL3 genotype with %LBM (P < 0.01). For the three HGS-linked SNPs, neither GBF1 nor GLIS1 showed any association with HGS, but for TGFA, multinomial logistic regression revealed a significant association of genotype with HGS (P < 0.05). For ADAMTSL3, there was an enrichment of the effect allele in the MA (P < 0.05, Fisher's exact test). Collectively, of the six SNPs analyzed, ADAMTSL3 and TGFA showed significant associations with LBM and HGS, respectively. The functional relevance of the ADAMTSL3 SNP in body composition and of TGFA in strength may highlight a genetic component of the elite MA phenotype.

Relationship of vitamin D receptor gene polymorphism with sarcopenia and muscle traits based on propensity score matching

Background

Vitamin D receptor (VDR) gene polymorphism is reported to be associated with muscle mass and muscle strength. Loss of skeletal muscle mass and decreased muscle strength are the main characteristics of sarcopenia. In this study, the relationship of VDR gene polymorphism with muscle traits (muscle mass, muscle strength, and physical performance) and sarcopenia were studied in Xinjiang, China.

Methods

Totally, 205 sarcopenia patients were enrolled. Propensity score method was used to match control group. FokI and BsmI polymorphisms were genotyped using improved multiplex ligation detection reaction (iMLDR).

Results

Fok1, but not Bsm1, polymorphism was significantly associated with sarcopenia. Patients with Fok1 GG genotype were more likely to have sarcopenia. Both Bsm1 and Fok1 polymorphism were related to muscle traits. Patients with Bsm1 CT genotype had lower gait speed (GS) but higher skeletal mass index. Patients with Fok1 GG genotype had lower GS, and female subjects with the Fok1 GG genotype had lower handgrip strength (HS). GS was decreased in Bsm1 CT genotype than CC carriers. HS and GS were decreased in Fok1 GG genotype than AA carriers.

Conclusion

Fok1, but not Bsm1, polymorphism is associated with sarcopenia. Both Bsm1 and Fok1 polymorphism affect both HS and GS.

Association between a literature-based genetic risk score and bone mineral density of African American women in Women Health Initiative Study

Genetic risk of low BMD in African American women remains unclear. Based on SNPs discovered from a predominantly Caucasian sample, genetic profile was summarized and was found to be significantly associated with BMD variation in African American women.

INTRODUCTION

Osteoporosis is largely under-recognized and undertreated in African-American women, the post-fracture morbidity and mortality rates in this racial group is rather high. Since BMD was proved to be highly heritable, based on a comprehensive genome-wide meta-analysis that reported 63 BMD-related single nucleotide polymorphisms (SNPs), we aim to unravel the overall genetic risk for decreased BMD and osteoporosis in African-American women.

METHODS

Genotype data of 842 African American women in a Women's Health Initiative cohort were analyzed. Comprehensive genotype imputation was conducted at the Sanger Imputation Server. Multi-locus genetic risk scores (GRSs) based on 62 BMD-related single-nucleotide polymorphisms (SNPs) were calculated. The association between GRS and BMD was assessed by regression analysis. Longitudinal data was further analyzed using a generalized estimating equation, which helps achieve more efficient and unbiased regression parameters by accounting for the within-subject correlation of responses on dependent variables.

RESULTS

After adjusting for age, body weight, hormone use, and previous fracture, for every unit increase of GRS.FN and GRS.LS, BMD at hip and lumbar spine decreased 0.124 g/cm² and 0.086 g/cm², respectively. Collectively, the model accounted for 34.95% of the femoral neck BMD variation and 25.79% of lumbar spine BMD variation. Notably, GRS.FN and GRS.LS accounted for 2.03% and 2.39% of the total explained variance, respectively. The proportion of BMD variation can be explained by GRSs increasing as participants aged.

CONCLUSIONS

Genetic risk score was significantly associated with lower BMD in the current study, suggesting that SNPs discovered from prior meta-analysis based on primarily Caucasian population can also explain a considerable proportion of BMD variation in African Americans.

Cross-Sectional Associations Between Dietary Antioxidant Vitamins C, E and Carotenoid Intakes and Sarcopenic Indices in Women Aged 18-79 Years

The prevalence of sarcopenia is increasing in aging populations, so prevention is critical. Vitamins (A, C, E and carotenoids) modify skeletal muscle via protein and collagen synthesis and anti-inflammatory activities. Previous studies have not investigated intake of these vitamins in relation to sarcopenic indices in both younger and older-aged women. Indices of skeletal muscle mass (as fat-free mass (FFM) relative to body size) were measured using DXA and leg explosive power (LEP) using the Nottingham Power Rig in 2570 women aged 18-79 years. Adjusted measures of skeletal muscle were calculated according to quintiles of vitamin C, E, retinol and carotenoid intake, derived from Food Frequency Questionnaires, after stratification by age. Higher vitamin C intake was associated with significantly higher indices of FFM and LEP, (Q5-Q1 = 2.0-12.8%, P < 0.01-0.02). Intakes of total and individual carotenoids were significantly associated with indices of FFM and LEP (Q5-Q1 = 1.0-7.5%). Vitamin E was significantly associated with FFM% and FFM_BMI only. In mutually adjusted analysis with vitamin C, total carotene, vitamin E and protein in the model, the strongest associations were with vitamin C. These associations were stronger in younger women (< 65 years). For the first time, our research shows higher dietary intakes of antioxidant vitamins, particularly vitamin C, is associated with higher skeletal muscle mass and power in free-living women. These findings have relevance for the treatment and prevention of frailty and sarcopenia throughout adulthood.

Association of 3p27.1 Variants with Whole Body Lean Mass Identified by a Genome-wide Association Study

Whole body lean mass (WBLM) is a heritable trait predicting sarcopenia. To identify genomic locus underlying WBLM, we performed a genome-wide association study of fat-adjusted WBLM in the Framingham Heart Study (FHS, N = 6,004), and replicated in the Kansas City Osteoporosis Study (KCOS, N = 2,207). We identified a novel locus 3p27.1 that was associated with WBLM (lead SNP rs3732593 P = 7.19 × 10^-8) in the discovery FHS sample, and the lead SNP was successfully replicated in the KCOS sample (one-sided P = 0.04). Bioinformatics analysis found that this SNP and its adjacent SNPs had the function of regulating enhancer activity in skeletal muscle myoblasts cells, further confirming the regulation of WBLM by this locus. Our finding provides new insight into the genetics of WBLM and enhance our understanding of sarcopenia.

Associations of TNF-α -308 G>A and TNF-β 252 A>G with Physical Function and BNP-Rugao Longevity and Ageing Study

OBJECTIVES

To explore the associations of TNF-α -308 G>A (rs1800629) and TNF-β 252 A>G (rs909253) with physical function and plasma B-type natriuretic peptide (BNP).

METHODS

Data of 1747 community-dwelling elders from the ageing arm of the Rugao Longevity and Ageing Study was used. Physical function was measured by handgrip strength, Timed Up and Go (TUG) test and 5-meter walking test (5MWT).

RESULTS

AA genotype of the TNF-α -308 G>A was associated with higher mean time of TUG test and 5MWT (multivariable adjusted β=5.75 and 5.70, respectively, p<0.05), compared with GG genotype. For the TNF-β 252 A>G polymorphism, GG genotype was associated with higher mean time of TUG test and 5MWT (multivariable adjusted β=1.55 and 0.83, respectively, p<0.05) and lower handgrip strength (multivariable adjusted β=-0.69, p<0.05), compared with AA genotype. Further, GG was associated with greater odds of low handgrip strength (OR=1.47, 95% CI=1.06-2.04), low speed of TUG test (OR=1.87, 95% CI=1.20-2.01) and elevated BNP (OR=1.30, 95% CI=1.08-1.84). GG also interacted with elevated BNP to be associated with greater odds of low handgrip strength and 5MWT.

CONCLUSIONS

TNF-β 252 A>G was associated with physical function measurements, plasma BNP level, and odds of elevated BNP in an elderly population. TNF-β 252 A>G also interacted with elevated BNP to be associated with greater odds of physical function measurements.

Fat oxidation at rest and during exercise in male monozygotic twins

PURPOSE

We aimed to investigate if hereditary factors, leisure-time physical activity (LTPA) and metabolic health interact with resting fat oxidation (RFO) and peak fat oxidation (PFO) during ergometer cycling.

METHODS

We recruited 23 male monozygotic twin pairs (aged 32-37 years) and determined their RFO and PFO with indirect calorimetry for 21 and 19 twin pairs and for 43 and 41 twin individuals, respectively. Using physical activity interviews and the Baecke questionnaire, we identified 10 twin pairs as LTPA discordant for the past 3 years. Of the twin pairs, 8 pairs participated in both RFO and PFO measurements, and 2 pairs participated in either of the measurements. We quantified the participants' metabolic health with a 2-h oral glucose tolerance test.

RESULTS

Fat oxidation within co-twins was correlated at rest [intraclass correlation coefficient (ICC) = 0.54, 95% confidence interval (CI) 0.15-0.78] and during exercise (ICC = 0.67, 95% CI 0.33-0.86). The LTPA-discordant pairs had no pairwise differences in RFO or PFO. In the twin individual-based analysis, PFO was positively correlated with the past 12-month LTPA (r = 0.26, p = 0.034) and the Baecke score (r = 0.40, p = 0.022) and negatively correlated with the area under the curve of insulin (r = - 0.42, p = 0.015) and glucose (r = - 0.31, p = 0.050) during the oral glucose tolerance test.

CONCLUSIONS

Hereditary factors were more important than LTPA for determining fat oxidation at rest and during exercise. Additionally, PFO, but not RFO, was associated with better metabolic health.

Trends in grip strength: Age, period, and cohort effects on grip strength in older adults from Germany, Sweden, and Spain

Grip strength is seen as an objective indicator of morbidity and disability. However, empirical knowledge about trends in grip strength remains incomplete. As trends can occur due to effects of aging, time periods and birth cohorts, we used hierarchical age-period-cohort models to estimate and disentangle putative changes in grip strength. To do this, we used population-based data of older adults, aged 50 years and older, from Germany, Sweden, and Spain from the SHARE study (N = 22500) that encompassed multiple waves of first-time respondents. We found that there were contrasting changes for different age groups: Grip strength improved over time periods for the oldest old, whereas it stagnated or even decreased in younger older adults. Importantly, we found strong birth cohort effects on grip strength: In German older adults, birth cohorts in the wake of the Second World War exhibited increasingly reduced grip strength, and in Spanish older adults, the last birth cohort born after 1960 experienced a sharp drop in grip strength. Therefore, while grip strength increased in the oldest old aged 80 years and older, grip strength stagnated or decreased in comparatively younger cohorts, who might thus be at risk to experience more morbidity and disability in the future than previous generations. Future studies should investigate factors that contribute to this trend, the robustness of the observed birth cohort effects, and the generalizability of our results to other indicators of functional health.

Angiotensin-Converting Enzyme Insertion/Deletion Polymorphism, Lower Extremity Strength, and Physical Performance in Older Adults

BACKGROUND

Evidence for associations between the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene and physical performance is conflicting. Furthermore, investigations of relationships between lower extremity strength and physical performance have usually not considered the role of the ACE genotype, and it is unclear whether there are variations in relationships between lower extremity strength and physical performance among ACE genotypes in older adults.

OBJECTIVE

The objectives of this study were to investigate associations between the ACE I/D polymorphism and physical performance and to determine whether relationships between lower extremity strength and physical performance vary among ACE genotypes in older adults.

DESIGN

This was a cross-sectional observational study.

METHODS

Community-dwelling adults (N = 88) who were at least 60 years old completed physical performance and lower extremity strength tests. After DNA was extracted from saliva, ACE I/D polymorphism genotyping was done. The Spearman rank order correlation coefficient was used to examine associations between lower extremity strength and physical performance within ACE genotype subgroups. Analysis of covariance and linear regression were used to examine ACE genotype and ACE genotype × lower extremity strength interaction effects in relation to physical performance.

RESULTS

Genotype-specific correlation coefficients exhibited substantial variation among ACE genotype subgroups; however, differences did not attain statistical significance. Statistically significant genotype × lower extremity strength interaction effects in relation to physical performance were detected.

LIMITATIONS

The cross-sectional design precludes inferring causal relationships between strength and performance. The small sample size contributed to limited power to detect additional interaction effects and to detect statistically significant differences between correlation coefficients among ACE genotype subgroups.

CONCLUSIONS

The ACE I/D polymorphism is, interactively with lower extremity strength, associated with physical performance. Genotype-specific correlation coefficients and ACE genotype × lower extremity strength interaction effects on physical performance are consistent with variations in relationships between lower extremity strength and performance among ACE genotype subgroups.