ACTN3 polymorphism affects thigh muscle area

ACTN3 XX Genotype Negatively Affects Running Performance and Increases Muscle Injury Incidence in LaLiga Football Players

The aim of this study was to investigate the association of the ACTN3 rs1815739 polymorphism with match running performance and injury incidence in top-level professional football players. A total of 315 top-level professional football players from the first division of Spanish football (i.e., LaLiga) participated in this prospective and descriptive study. The ACTN3 rs1815739 genotype was identified for each player using genomic DNA samples. During LaLiga 2021-2022, players' performance was obtained through a validated camera system in all official matches. Additionally, the incidence of non-contact injuries was obtained by each team's medical staff according to the International Olympic Committee (IOC) statement. From the study sample, 116 (36.8%) players had the RR genotype, 156 (49.5%) had the RX genotype, and 43 (13.7%) had the XX genotype. The anthropometric characteristics of the players were similar across genotypes. However, the total running distance (p = 0.046), the distance at 21.0-23.9 km/h (p = 0.042), and the number of sprints (p = 0.042) were associated with the ACTN3 genotype. In all these variables, XX players had lower match performance values than RR players. Additionally, total and match injury incidences were higher in XX players than in RR players (p = 0.026 and 0.009, respectively). The rate of muscle injuries was also higher in XX players (p = 0.016). LaLiga football players with the ACTN3 XX genotype had lower match running performance and a higher incidence of non-contact injuries over the season.

Progressive strength training can reverse sarcopenia stage in middle-aged and older adults regardless of their genetic profile

The aim of this study was to verify the association of the ACTN3-R577X polymorphism with sarcopenia stage, according to the Revised European Consensus on the Definition and Diagnosis of Sarcopenia, in middle-aged and older adults, pre- and post- ST. In the 12-week longitudinal study, 71 middle-aged and older adults were evaluated; the participants were assigned to either control or intervention group. The intervention group underwent progressive ST three times a week. All participants underwent blood collection, DNA extraction, genotyping of the ACTN3-R577X polymorphism, anthropometric evaluations, and diagnostic tests for sarcopenia. The last two tests were repeated after 12 weeks. No association of the ACTN3-R577X polymorphism with sarcopenia stage was observed before and after 12 weeks. However, the intervention group remained non-sarcopenic (n = 25, p <0.05) or achieved changes in sarcopenia stage (from sarcopenic to non-sarcopenic) (n = 13, p <0.05). Our study demonstrates that progressive ST performed regularly can reverse or prevent sarcopenia regardless of genotype for the ACTN3-R577X polymorphism.

Association between ACTN3 R577X genotype and risk of non-contact injury in trained athletes: A systematic review

PURPOSE

The aim of this study was to review, systematically, evidence concerning the link between the ACTN3 R577X polymorphism and the rates and severity of non-contact injuries and exercise-induced muscle damage in athletes and individuals enrolled in exercise training programs.

METHODS

A computerized literature search was performed in the electronic databases PubMed, Web of Science, and SPORTDiscus, from inception until November 2020. All included studies compared the epidemiological characteristics of non-contact injury between the different genotypes of the ACTN3 R577X polymorphism.

RESULTS

Our search identified 492 records. After the screening of titles, abstracts, and full texts, 13 studies examining the association between the ACTN3 genotypes and the rate and severity of non-contact injury were included in the analysis. These studies were performed in 6 different countries (Spain, Japan, Brazil, China, the Republic of Korea, and Italy) and involved a total participant pool of 1093 participants. Of the studies, 2 studies involved only women, 5 studies involved only men, and 6 studies involved both men and women. All the studies included were classified as high-quality studies (≥6 points in the Physiotherapy Evidence Database (PEDro) scale score). Overall, evidence suggests there is an association between the ACTN3 R577X genotype and non-contact injury in 12 investigations. Six studies observed a significant association between ACTN3 R577X polymorphism and exercise induced muscle damage: 2 with non-contact ankle injury, 3 with non-contact muscle injury, and 1 with overall non-contact injury.

CONCLUSION

The present findings support the premise that possessing the ACTN3 XX genotype may predispose athletes to a higher probability of some non-contact injuries, such as muscle injury, ankle sprains, and higher levels of exercise-induced muscle damage.

Association of Alpha-Actinin-3 Polymorphism With Sarcopenia in Kidney Transplant Recipients

BACKGROUND

Sarcopenia is defined as the loss of skeletal muscle mass and function and is associated with increased mortality. Certain genetic polymorphisms represent risk factors used to assess the incidence of sarcopenia; however, few studies have evaluated the association between genetic polymorphisms and sarcopenia after kidney transplantation (KTx). We examined single-nucleotide polymorphisms (SNPs) in the genes involved in sarcopenia after KTx.

METHODS

Sixty-five patients who underwent KTx were enrolled in this study. We used the psoas mass index (PMI; the cross-sectional area of the bilateral psoas muscle/height) as a surrogate marker for assessing the extent of sarcopenia. We determined the PMI before KTx and 1 year after KTx, and we identified 5 SNPs in 5 genes associated with sarcopenia in the general population. Finally, the link between the changes in PMI 1 year after KTx and each SNP was examined.

RESULTS

The median PMI before KTx and 1 year after KTx was 7.4 (4.6-13.2) and 7.0 (3.6-13.6), respectively. The PMI decreased in 43 patients (66.2%). The alpha-actinin-3 rs1815739 genotype was associated with changes in PMI; the distribution of CT+TT genotypes in the PMI decrease group was significantly higher than that of the CC genotype (odds ratio, 4.23; 95% CI 0.05-0.97; P = 0.025). Moreover, the T allele frequency was significantly higher in the PMI decrease group than in the PMI increase group (odds ratio, 2.34; 95% CI 0.18-0.950; P = 0.025).

CONCLUSION

The alpha-actinin-3 rs1815739 genotype may represent a genetic risk factor for sarcopenia after KTx.

Association between ACTN3 R577x and the physical performance of Chinese 13 to 15-year-old elite and sub-elite football players at different positions

The purpose of this study was to investigate the prevalence of ACTN3 polymorphisms in Chinese elite and sub-elite football players aged 13–15 years at different positions. Specifically we explored whether ACTN3 genotypes were linked with athletic performance of elite and sub-elite players at different positions. The RR genotype frequency of elite defenders (p = 0.018) and midfielders (p = 0.008) was significantly higher than that of sub-elite XX genotype in elite players. Furthermore, the R allele frequency of elite defenders (p = 0.003) and midfielders (p = 0.008) was significantly higher than that of sub-elite players. In all subjects, RR players performed faster and exhibited more explosive power than RX or XX players. RR, RX and XX elite players’ 20 m/30 m sprint, 5 × 25-m repeated sprint ability (5 × 25 m RSA), and standing long jump were stronger than sub-elite players, but there was no significant different in aerobic endurance between elite and sub-elite players at different positions. In conclusion, there were significant differences in ACTN3 genotypes and alleles between elite and sub-elite players at different positions, and the RR genotype was significantly associated with power-related athletic performance in Chinese youth football players.

Association of the ACTN3 rs1815739 Polymorphism with Physical Performance and Injury Incidence in Professional Women Football Players

The p.R577X polymorphism (rs1815739) in the ACTN3 gene causes individuals with the XX genotype to be deficient in functional α-actinin-3. Previous investigations have found that XX athletes are more prone to suffer non-contact muscle injuries, in comparison with RR and RX athletes who produce a functional α-actinin-3 in their fast-twitch fibers. This investigation aimed to determine the influence of the ACTN3 R577X polymorphism on physical performance and injury incidence of players competing in the women’s Spanish first division of football (soccer). Using a cross-sectional experiment, football-specific performance and epidemiology of non-contact football-related injuries were recorded in a group of 191 professional football players. ACTN3 R577X genotype was obtained for each player using genomic DNA samples obtained through buccal swabs. A battery of physical tests, including a countermovement jump, a 20 m sprint test, the sit-and-reach test and ankle dorsiflexion, were performed during the preseason. Injury incidence and characteristics of non-contact injuries were obtained according to the International Olympic Committee (IOC) statement for one season. From the study sample, 28.3% of players had the RR genotype, 52.9% had the RX genotype, and 18.8% had the XX genotype. Differences among genotypes were identified with one-way analysis of variance (numerical variables) or chi-square tests (categorical variables). Jump height (p = 0.087), sprint time (p = 0.210), sit-and-reach distance (p = 0.361), and dorsiflexion in the right (p = 0.550) and left ankle (p = 0.992) were similar in RR, RX, and XX football players. A total of 356 non-contact injuries were recorded in 144 football players while the remaining 47 did not sustain any non-contact injuries during the season. Injury incidence was 10.4 ± 8.6, 8.2 ± 5.7, and 8.9 ± 5.3 injuries per/1000 h of football exposure, without differences among genotypes (p = 0.222). Injury rates during training (from 3.6 ± 3.7 to 4.8 ± 2.1 injuries per/1000 h of training exposure, p = 0.100) and match (from 47.8 ± 9.5 to 54.1 ± 6.3 injuries per/1000 h of match exposure, p = 0.209) were also similar in RR, RX, and XX football players. The ACTN3 genotype did not affect the mode of onset, the time needed to return to play, the type of injury, or the distribution of body locations of the injuries. In summary, women football players with different genotypes of the p.R577X ACTN3 polymorphism had similar values of football-specific performance and injury incidence. From a practical perspective, the ACTN3 genotyping may not be useful to predict performance or injury incidence in professional women football players.

Effect of the ACTN-3 gene polymorphism on functional fitness and executive function of elderly

During aging, physical integrity and cognitive abilities, especially executive function, become compromised, directly influencing the quality of life of the elderly. One good strategy to ensure healthy aging is the practice of physical exercise. Activities to improve aerobic capacity and muscle strength are extremely important in old age. However, some genetic factors can interfere both positively and negatively with these gains. In this context, the polymorphism rs1815739 (R577X) of the α-actinin 3 gene (ACTN-3) is commonly studied and related to muscle phenotype. Thus, the present study aimed to investigate the effect of the ACTN-3 gene polymorphism on the functional fitness (measured by the Senior Fit test) and cognitive capacity (evaluated by the Stroop test) of the elderly (n = 347), both men and women. We did not find the effect of genotype on functional fitness, but we did observed a positive effect of the ACTN-3 gene polymorphism on executive function. The presence of the X allele of the ACTN3 gene in the elderly was related to a better performance in the Stroop test (shorter answer time). Our results showed that ACTN-3 gene polymorphism affects the executive function of the elderly but not their functional fitness.

Polygenic Models Partially Predict Muscle Size and Strength but Not Low Muscle Mass in Older Women

Background: Heritability explains 45-82% of muscle mass and strength variation, yet polygenic models for muscle phenotypes in older women are scarce. Therefore, the objective of the present study was to (1) assess if total genotype predisposition score (GPSTOTAL) for a set of polymorphisms differed between older women with low and high muscle mass, and (2) utilise a data-driven GPS (GPSDD) to predict the variance in muscle size and strength-related phenotypes. Methods: In three-hundred 60- to 91-year-old Caucasian women (70.7 ± 5.7 years), skeletal muscle mass, biceps brachii thickness, vastus lateralis anatomical cross-sectional area (VLACSA), hand grip strength (HGS), and elbow flexion (MVCEF) and knee extension (MVCKE) maximum voluntary contraction were measured. Participants were classified as having low muscle mass if the skeletal muscle index (SMI) < 6.76 kg/m2 or relative skeletal muscle mass (%SMMr) < 22.1%. Genotyping was completed for 24 single-nucleotide polymorphisms (SNPs). GPSTOTAL was calculated from 23 SNPs and compared between the low and high muscle mass groups. A GPSDD was performed to identify the association of SNPs with other skeletal muscle phenotypes. Results: There was no significant difference in GPSTOTAL between low and high muscle mass groups, irrespective of classification based on SMI or %SMMr. The GPSDD model, using 23 selected SNPs, revealed that 13 SNPs were associated with at least one skeletal muscle phenotype: HIF1A rs11549465 was associated with four phenotypes and, in descending number of phenotype associations, ACE rs4341 with three; PTK2 rs7460 and CNTFR rs2070802 with two; and MTHFR rs17421511, ACVR1B rs10783485, CNTF rs1800169, MTHFR rs1801131, MTHFR rs1537516, TRHR rs7832552, MSTN rs1805086, COL1A1 rs1800012, and FTO rs9939609 with one phenotype. The GPSDD with age included as a predictor variable explained 1.7% variance of biceps brachii thickness, 12.5% of VLACSA, 19.0% of HGS, 8.2% of MVCEF, and 9.6% of MVCKE. Conclusions: In older women, GPSTOTAL did not differ between low and high muscle mass groups. However, GPSDD was associated with muscle size and strength phenotypes. Further advancement of polygenic models to understand skeletal muscle function during ageing might become useful in targeting interventions towards older adults most likely to lose physical independence.

Is there a relationship between ACTN3 R577X gene polymorphism and sarcopenia?

BACKGROUND AND AIMS

The alpha-actinin (ACTN) genes are important structural components of the sarcomere. Sarcopenia is a common geriatric syndrome characterized by morbidity and mortality. Our study aimed to examine the relationship between the ACTN3 R577X gene and sarcopenia in community-dwelling Turkish adults.

METHODS

We designed a cross-sectional study among the patients aged ≥ 65 years admitted to the geriatric outpatient clinic. We recorded the general characteristics of the patients. We used the Jamar hand dynamometer to evaluate handgrip strength. Body composition was estimated using bioimpedance analysis. Sarcopenia was diagnosed according to the European Working Group on Sarcopenia in Older People2 criteria with population-specific cutoffs. We performed analyses of low muscle mass (LMM) with skeletal muscle mass index adjusted for body mass index [SMMI(BMI)]. We further categorized the SMMI(BMI) cutoffs into tenths. The analyzes were performed according to the 90th percentile SMMI(BMI) cutoffs. Peripheral blood samples were collected to determine the ACTN3 genotypes.

RESULTS

197 participants were included [mean age: 76.3 ± 6.1 years, 151 (76.6%) women]. The proportions of the ACTN3 genotypes were as follows: RX (45.1%) > RR (31%) > XX (23.9%). The significant difference between genotypes was found only for low SMMI(BMI) according to the 90th percentile (p = 0.025). In multivariate analysis, only gender (female) was independently associated with LMM.

CONCLUSION

We did not find any association between ACTN3 R577X gene polymorphism and probable sarcopenia, confirmed sarcopenia and LMM. Besides, much more research is needed to reveal how ethnicity affects the muscles of older adults with ACTN3 R577X gene polymorphism.

Associations of alpha-actinin-3 genotype with thigh muscle volume and physical performance in older adults with sarcopenia or pre-sarcopenia

BACKGROUND

This cross-sectional study aimed to investigate the relationship of the ACTN3 genotype with thigh muscle volume and physical performance in older adults with sarcopenia or pre-sarcopenia.

METHODS

Data from 64 older Japanese adults (mean age 74.4 ± 6.9 years, women 71.9%) with sarcopenia or pre-sarcopenia were analyzed. Sarcopenia and pre-sarcopenia were defined using the Asian Working Group for Sarcopenia. We collected oral mucosa samples to determine the ACTN3 genotype. Thigh muscle volumes were measured using magnetic resonance imaging. Physical performance was assessed using the usual and maximum gait speed, timed up and go test, and five-repetition sit-to-stand test. Muscle strength was assessed using grip strength.

RESULT

The ACTN3 genotype proportions were 20.3% for RR, 51.6% for RX, and 28.1% for XX. Participants with the RR genotype showed greater thigh muscle volume/ht² compared to those with the RX and XX ACTN3 genotypes (p < 0.05). The multiple linear regression analysis revealed that RX (p < 0.01) and XX (p < 0.01) ACTN3 genotypes, compared to RR, were associated with lower thigh muscle volume/ht² and with age, sex (reference; men), weight and maximum walking speed. There was no significant difference between physical performance and muscle strength between the ACTN3 genotypes.

CONCLUSION

The ACTN3 genotype of the X allele was associated with decreased thigh muscle volume compared to the ACTN3 genotype of RR in older adults with sarcopenia or pre-sarcopenia.

ACTN3 Genotypes and Their Relationship with Muscle Mass and Function of Kosovan Adults

Maintaining muscle mass and function is important throughout the lifestyle. While environmental factors such as physical activity and healthy nutrition are well investigated, the contribution of genetic factors is still controversial. Therefore, we aimed to investigate the impact of a common ACTN3 polymorphism (rs1815739) on body composition, handgrip strength, knee extensor peak torque, and physical performance (gait speed, 30-s arm curl, 30-s chair stand) in Kosovan adults. In total, 308 participants (160 females and 148 males, age range from 40 to 91 years) took part in this cross-sectional study. Genomic DNA was extracted from saliva and assessed for ACTN3 genotype distribution (41.5% of RR, 53.9% of RX and 4.6% of XX). Genotype allocation did not account for differences in any of the variables. Interestingly, female XX carriers were taller (p = 0.025) and had a higher isokinetic knee extension peak torque (p = 0.024) than the RX+RR group. In males, XX carriers were also taller (p = 0.049) and had a lower BMI (p = 0.026), but did not differ in any of the strength and performance parameters. These results indicate that the ACTN3 R577X polymorphism might exert a sex-specific impact on knee extensor peak torque and BMI.

ACTN3 genotype influences skeletal muscle mass regulation and response to dexamethasone

Homozygosity for the common ACTN3 null polymorphism (ACTN3 577X) results in α-actinin-3 deficiency in ~20% of humans worldwide and is linked to reduced sprint and power performance in both elite athletes and the general population. α-Actinin-3 deficiency is also associated with reduced muscle mass, increased risk of sarcopenia, and altered muscle wasting response induced by denervation and immobilization. Here, we show that α-actinin-3 plays a key role in the regulation of protein synthesis and breakdown signaling in skeletal muscle and influences muscle mass from early postnatal development. We also show that α-actinin-3 deficiency reduces the atrophic and anti-inflammatory response to the glucocorticoid dexamethasone in muscle and protects against dexamethasone-induced muscle wasting in female but not male mice. The effects of α-actinin-3 deficiency on muscle mass regulation and response to muscle wasting provide an additional mechanistic explanation for the positive selection of the ACTN3 577X allele in recent human history.

Preliminary Investigation Into the Effect of ACTN3 and ACE Polymorphisms on Muscle and Performance Characteristics

ABSTRACT

Wagle, JP, Carroll, KM, Cunanan, AJ, Wetmore, A, Taber, CB, DeWeese, BH, Sato, K, Stuart, CA, and Stone, MH. Preliminary investigation into the effect of ACTN3 and ACE polymorphisms on muscle and performance characteristics. J Strength Cond Res 35(3): 688-694, 2021-The purpose of this investigation was to explore the phenotypic and performance outcomes associated with ACTN3 and ACE polymorphisms. Ten trained men (age = 25.8 ± 3.0 years, height = 183.3 ± 4.1 cm, body mass = 92.3 ± 9.3 kg, and back squat to body mass ratio = 1.8 ± 0.3) participated. Blood samples were analyzed to determine ACTN3 and ACE polymorphisms. Standing ultrasonography images of the vastus lateralis (VL) were collected to determine whole muscle cross-sectional area (CSA-M), and a percutaneous muscle biopsy of the VL was collected to determine type I-specific CSA (CSA-T1), type II-specific CSA (CSA-T2), and type II to type I CSA ratio (CSA-R). Isometric squats were performed on force platforms with data used to determine peak force (IPF), allometrically scaled peak force (IPFa), and rate of force development (RFD) at various timepoints. One repetition maximum back squats were performed, whereby allometrically scaled dynamic strength (DSa) was determined. Cohen's d effect sizes revealed ACTN3 RR and ACE DD tended to result in greater CSA-M but differ in how they contribute to performance. ACTN3 RR's influence seems to be in the type II fibers, altering maximal strength, and ACE DD may influence RFD capabilities through a favorable CSA-R. Although the findings of the current investigation are limited by the sample size, the findings demonstrate the potential influence of ACTN3 and ACE polymorphisms on isometric and dynamic strength testing. This study may serve as a framework to generate hypotheses regarding the effect of genetics on performance.

Pilot Study on Genetic Associations With Age-Related Sarcopenia

Despite strong evidence of an inheritable component of muscle phenotypes, little progress has been made in identifying the specific genetic factors involved in the development of sarcopenia. Even rarer are studies that focus on predicting the risk of sarcopenia based on a genetic risk score. In the present study, we tested the single and combined effect of seven candidate gene variants on the risk of sarcopenia. Single nucleotide polymorphisms in candidate genes were genotyped using the KASP assay. We examined 190 older adults that were classified as non-sarcopenic or sarcopenic according to the diagnostic criteria of the European Working Group on Sarcopenia in Older People. Sarcopenia was associated with Methylenetetrahydrofolate reductase, Alpha-actinin-3, and Nuclear respiratory factor 2 genotypes. The combined effect of all three polymorphisms explained 39% of the interindividual variation in sarcopenia risk. Our results suggest that the single and combined effect of Methylenetetrahydrofolate reductase, Alpha-actinin-3, and Nuclear respiratory factor 2 polymorphism is associated with sarcopenia risk in older adults. Nowadays, as the population is getting older and older, great efforts are being made to research the etiology, diagnosis and treatment of sarcopenia. At the same time, small progress has been made in understanding the genetic etiology of sarcopenia. Given the importance of research on this disease, further genetic studies are needed to better understand the genetic risk underlying sarcopenia. We believe that this small-scale study will help to demonstrate that there is still much to be discovered in this field.

Differential regulation of Actn2 and Actn3 expression during unfolded protein response in C2C12 myotubes

ACTN2 and ACTN3 encode sarcomeric α-actinin-2 and α-actinin-3 proteins, respectively, that constitute the Z-line in mammalian skeletal muscle fibers. In human ACTN3, a nonsense mutation at codon 577 that encodes arginine (R) produces the R577X polymorphism. Individuals having a homozygous 577XX genotype do not produce α-actinin-3 protein. The 577XX genotype reportedly occurs in sprint and power athletes in frequency lower than in the normal population, suggesting that α-actinin-3 deficiency diminishes fast-type muscle function. Among humans who carry 577R alleles, varying ACTN3 expression levels under certain conditions can have diverse effects on atheletic and muscle performance. However, the factors that regulate ACTN3 expression are unclear. Here we investigated whether the unfolded protein response (UPR) under endoplasmic reticulum (ER) stress regulates expression of Actn3 and its isoform Actn2 in mouse C2C12 myotubes. Among UPR-related transcription factors, XBP1 upregulated Actn2, whereas XBP1, ATF4 and ATF6 downregulated Actn3 promoter activity. Chemical induction of ER stress increased Actn2 mRNA levels, but decreased those for Actn3. ER stress also decreased α-actinin-3 protein levels, whereas levels of α-actinin-2 were unchanged. The intracellular composition of muscle contraction-related proteins was altered under ER stress, in that expression of parvalbumin (a fast-twitch muscle-specific protein) and troponin I type 1 (skeletal, slow) was suppressed. siRNA-induced suppression of Actn3 mimicked the inhibitory effect of ER stress on parvalbumin levels. Thus, endogenous expression levels of α-actinin-3 can be altered by ER stress, which may modulate muscle performance and athletic aptitudes, particularly in humans who carry ACTN3 577R alleles.

Genetic Associations with Aging Muscle: A Systematic Review

The age-related decline in skeletal muscle mass, strength and function known as 'sarcopenia' is associated with multiple adverse health outcomes, including cardiovascular disease, stroke, functional disability and mortality. While skeletal muscle properties are known to be highly heritable, evidence regarding the specific genes underpinning this heritability is currently inconclusive. This review aimed to identify genetic variants known to be associated with muscle phenotypes relevant to sarcopenia. PubMed, Embase and Web of Science were systematically searched (from January 2004 to March 2019) using pre-defined search terms such as "aging", "sarcopenia", "skeletal muscle", "muscle strength" and "genetic association". Candidate gene association studies and genome wide association studies that examined the genetic association with muscle phenotypes in non-institutionalised adults aged ≥50 years were included. Fifty-four studies were included in the final analysis. Twenty-six genes and 88 DNA polymorphisms were analysed across the 54 studies. The ACTN3, ACE and VDR genes were the most frequently studied, although the IGF1/IGFBP3, TNFα, APOE, CNTF/R and UCP2/3 genes were also shown to be significantly associated with muscle phenotypes in two or more studies. Ten DNA polymorphisms (rs154410, rs2228570, rs1800169, rs3093059, rs1800629, rs1815739, rs1799752, rs7412, rs429358 and 192 bp allele) were significantly associated with muscle phenotypes in two or more studies. Through the identification of key gene variants, this review furthers the elucidation of genetic associations with muscle phenotypes associated with sarcopenia.

ACTN3, Morbidity, and Healthy Aging

As human longevity increases, recent research has focused on the maintenance of optimal health during old age. One such area of focus is that of muscle function in the elderly, with a loss of muscle mass increasing the risk of negative outcomes such as sarcopenia and a decrease in bone mineral density. In this mini-review, we focus on the impact of a single nucleotide polymorphism in ACTN3, shown to impact muscle phenotype in elite athletes, on loss of muscle function, maintenance of bone mineral density, and metabolic disorder risk in an elderly population. From the surveyed research, this polymorphism has a clear and demonstrable impact on muscle phenotype and bone mineral density in this population, and acts as a potential modulator for metabolic disorders. As such, knowledge of an individual's ACTN3 genotype may better inform the management of risk factors in the elderly, as well as driving innovations in exercise program design. Subsequently, such insights may contribute to the prolonged maintenance of health and function long into old age.

ACTN3 Gene and Susceptibility to Sarcopenia and Osteoporotic Status in Older Korean Adults

BACKGROUND

Little information is available about molecular markers for sarcopenia and osteoporosis in Asian populations.

OBJECTIVE

This study investigated the association of the ACTN3 polymorphism with sarcopenia and osteoporotic status in older Korean adults.

METHODS

Older Korean 62 men and 270 women (mean age 73.7 ± 6.6 years) participated in this study. Body mass index, percent body fatness, appendicular skeletal muscle mass, and bone mineral density of the lumbar spine, femur, and total body were analyzed with dual-energy X-ray absorptiometry. ACTN3 R/X genotyping was determined using TaqMan probes.

RESULTS

Determination of odds ratios (ORs) and 95% confidence intervals (CIs) using binary logistic regression analyses showed that XX homozygotes were at a significantly higher risk of sarcopenia (OR = 2.056, 95%  CI = 1.024-4.127, p = 0.043) and osteoporosis (OR = 2.794, 95%  CI = 1.208-5.461, p = 0.016) than RR homozygotes (reference group, OR = 1). The OR of XX homozygotes for having sarcopenia remained significant (OR = 2.237, 95%  CI = 1.044-4.836, p = 0.038) after adjustments for age, gender, body fatness, and serum vitamin D. The OR of XX homozygotes for having osteoporosis was no longer significant (OR = 2.682, 95%  CI = 0.960-7.942, p = 0.075) after adjustments for the covariates.

CONCLUSION

Our findings suggest that the ACTN3 R577X genotype may influence decline in muscle and bone health phenotypes in older Korean adults.

The influence of α-actinin-3 deficiency on bone remodelling markers in young men

There is a large individual variation in the bone remodelling markers (BRMs) osteocalcin (OC), procollagen 1 N-terminal propeptide (P1NP) and β-isomerized C-terminal telopeptide (β-CTx), as well as undercarboxylated osteocalcin (ucOC), at rest and in response to exercise. α-actinin-3 (ACTN3), a sarcomeric protein, is expressed in skeletal muscle and osteoblasts and may influence BRM levels and the cross-talk between muscle and bone. We tested the levels of serum BRMs in α-actinin-3 deficient humans (ACTN3 XX) at baseline, and following a single bout of exercise. Forty-three healthy Caucasian individuals were divided into three groups (ACTN3 XX, n=13; ACTN3 RX, n=16; ACTN3 RR, n=14). Participants completed a single session of High Intensity Interval Exercise (HIIE) on a cycle ergometer (8×2-min intervals at 85% of maximal power). Blood samples were taken before, immediately after, and three hours post exercise to identify the peak changes in serum BRMs. There was a stepwise increase in resting serum BRMs across the ACTN3 genotypes (XX>RX>RR) with significantly higher levels of tOC ~26%, P1NP ~34%, and β-CTX (~33%) in those with ACTN3 XX compared to ACTN3 RR. Following exercise BRMs and ucOC were higher in all three ACTN3 genotypes, with no significant differences between groups. Serum levels of tOC, P1NP and β-CTX are higher in men with ACTN3 XX genotype (α-actinin-3 deficiency) compared to RR and RX. It appears that the response of BRMs and ucOC to exercise is not explained by the ACTN3 genotype.

Effects of Aerobic and Resistance Training Combined with Fortified Milk on Muscle Mass, Muscle Strength, and Physical Performance in Older Adults: A Randomized Controlled Trial

OBJECTIVES

Fortified milk and resistance training (RT) increase muscle mass, muscle strength, and physical performance in older adults, but it remains unclear whether RT combined with aerobic training (AT) would have stronger effects on these outcomes. The purpose of this study was to examine the effects of aerobic and resistance training (ART) combined with fortified milk consumption on muscle mass, muscle strength, and physical performance in older adults.

DESIGN

Open-labeled randomized controlled trial.

SETTING

University of Tsukuba.

PARTICIPANTS

Fifty-six older adults aged 65-79.

INTERVENTION

Participants were randomly allocated into resistance training (RT + fortified milk, n = 28) and aerobic and resistance training (ART + fortified milk, n = 28) groups. All participants attended supervised exercise programs twice a week at University of Tsukuba and ingested fortified milk every day for 12 weeks. Skeletal muscle index ([SMI]: appendicular lean mass/height2) was assessed using dual-energy X-ray absorptiometry as a muscle mass measure. One-repetition maximum strength was measured using four kinds of resistance training machines (chest press, leg extension, leg curl, and leg press) as muscle strength measures. Sit-to-stand and arm curl tests were also assessed as physical performance measures.

MEASUREMENTS

The primary measurements were muscle mass and strength. The secondary outcomes were physical performance, blood samples, habitual diet, habitual physical activity, and medication use.

RESULTS

Although the muscle strength and physical performance measures significantly improved in both groups, SMI significantly improved in only the RT group. There was no significant difference in the change in SMI and muscle strength measures between the two groups. However, the change in sit-to-stand and arm curl measures in the ART group were significantly higher than those in the RT group.

CONCLUSIONS

These results suggest that AT before RT combined with fortified milk consumption has similar effects on skeletal muscle mass and strength compared with RT alone, but it may be a more useful strategy to improve physical performance in older adults. Although the mechanism of our intervention is uncertain, our program would be an effective prevention for sarcopenia in older adults.

Association of ACTN3 polymorphisms with BMD, and physical fitness of elderly women

[Purpose] Association of ACTN3 polymorphism with bone mineral density and the physical fitness of elderly women is still unclear. Therefore, this study investigated the association between ACTN3 genotype and bone mineral density, and the physical fitness of elderly women. [Subjects and Methods] Sixty-eight elderly women (67.38 ± 3.68 years) were recruited at a Seongbuk-Gu (Seoul, Korea) Medical Service Public Health Center. Measurements of physical fitness included muscle strength, muscle endurance, flexibility, agility, balance and VO₂max. Bone mineral density (BMD), upper limb muscle mass, lower limb muscle mass, percent body fat and body fat mass for the entire body were measured by dual-energy X-ray absorptiometry and an analyzer. Genotyping for the ACTN3 R577X (rs1815739) polymorphism was performed using the TaqMan approach. [Results] ACTN3 gene distribution of subjects were in the Hardy-Weinberg equilibrium (p=0.694). The relative bone mineral density trunk, pelvis and spine differed significantly among the ACTN3 genotypes. There were no significant differences among bone mineral densities of the head, arms, legs, ribs and total, but the RR genotype tended to be higher than other genotypes. Physical fitness was not significantly different among the ACTN3 genotypes. [Conclusion] These results suggest that ACTN3 gene polymorphisms could be used as one of the genetic determinants of bone mass in elderly women, and in particular, they indicate that individuals with the RR genotype have higher BMD and bone mineral composition.

Evidence for ACTN3 as a Speed Gene in Isolated Human Muscle Fibers

Purpose

To examine the effect of α-actinin-3 deficiency due to homozygosity for the ACTN3 577X-allele on contractile and morphological properties of fast muscle fibers in non-athletic young men.

Methods

A biopsy was taken from the vastus lateralis of 4 RR and 4 XX individuals to test for differences in morphologic and contractile properties of single muscle fibers. The cross-sectional area of the fiber and muscle fiber composition was determined using standard immunohistochemistry analyses. Skinned single muscle fibers were subjected to active tests to determine peak normalized force (P₀), maximal unloading velocity (V₀) and peak power. A passive stretch test was performed to calculate Young’s Modulus and hysteresis to assess fiber visco-elasticity.

Results

No differences were found in muscle fiber composition. The cross-sectional area of type II_a and II_x fibers was larger in RR compared to XX individuals (P<0.001). P₀ was similar in both groups over all fiber types. A higher V₀ was observed in type II_a fibers of RR genotypes (P<0.001) but not in type I fibers. The visco-elasticity as determined by Young’s Modulus and hysteresis was unaffected by fiber type or genotype.

Conclusion

The greater V₀ and the larger fast fiber CSA in RR compared to XX genotypes likely contribute to enhanced whole muscle performance during high velocity contractions.

Association of angiotensin-converting enzyme I/D and α-actinin-3 R577X genotypes with metabolic syndrome risk factors in Korean children

OBJECTIVE

This study analysed the risk factors associated with metabolic syndrome through the interaction between ACTN3 and ACE gene polymorphism in Korean children.

METHODS

The subjects of the study consisted of elementary school students (n=788, age 10.10±0.07 yr). The anthropometric parameters, blood lipid profiles, and metabolic markers were compared among groups of the ACE I/D or the ACTN3 R577X polymorphisms.

RESULTS

The subjects with the DD genotype showed significantly higher systolic blood pressure than the subjects with the II and ID genotype of the ACE gene polymorphism. XX genotype had significantly lower waist-hip ratio than those with RR genotype of the ACTN3 gene polymorphism. Also, the subjects with XX genotype exhibited significantly higher blood HDL cholesterol level than those with RR or RX genotype. The interaction of ACTN3 and ACE gene polymorphism in subjects having both ACE DD and ACTN3 RR genotypes demonstrated a significantly higher metabolic syndrome score than any other groups.

CONCLUSION

The children having both ACTN3 RR or RX genotype and ACE DD genotype showed high systolic blood pressure and low blood HDL cholesterol level, which may be considered a high-risk in metabolic syndrome.

Effective utilization of genetic information for athletes and coaches: focus on ACTN3 R577X polymorphism

Training variants (type, intensity, and duration of exercise) can be selected according to individual aims and fitness assessment. Recently, various methods of resistance and endurance training have been used for muscle hypertrophy and VO₂max improvement. Although several genetic variants are associated with elite athletic performance and muscle phenotypes, genetic background has not been used as variant for physical training. ACTN3 R577X is a well-studied genetic polymorphism. It is the only genotype associated with elite athletic performance in multiple cohorts. This association is strongly supported by mechanistic data from an Actn3-knockout mouse model. In this review, possible guidelines are discussed for effective utilization of ACTN3 R577X polymorphism for physical training.

The ACTN3 R577X genotype is associated with muscle function in a Japanese population

Homozygosity for the common nonsense polymorphism R577X in the α-actinin-3 gene (ACTN3) causes complete α-actinin-3 deficiency in fast-twitch skeletal muscle fibers. This study investigated whether the ACTN3 R577X polymorphism affects fitness status using a battery of tests in a large Japanese cohort. In the present study, 1227 subjects (age: 25-85 years) were genotyped for the ACTN3 R577X polymorphism (rs1815739) using a TaqMan SNP genotyping assay (Applied Biosystems). All subjects were divided into 2 groups based on their age (<55 years and ≥55 years). All subjects completed a questionnaire about exercise habits and were subjected to a battery of tests to assess their fitness status (including grip strength test, chair stand test, and 8-foot walking test). A significant association between the ACTN3 R577X genotype and chair stand test performance was observed in the group of men ≥55 using ANCOVA adjusted for age and exercise habits (p = 0.036). The ACTN3 R577X genotype accounted for 2.5% of the variability in the results of the chair stand test among men in the ≥55 age group. Moreover, for the ≥55 age group, performance in the chair stand test was lower among those with the XX genotype than among those with the RR genotype (p = 0.024) or RX genotype (p = 0.005), unlike results for the <55 age group. No significant difference was noted for hand grip strength or 8-foot walking time. Thus, our results suggest that the ACTN3 R577X genotype is associated with lower-extremity muscle function in the Japanese population.

Actn3 genotype is associated with testosterone levels of athletes

α-Actinin-3 (ACTN3) has been proposed to regulate skeletal muscle differentiation and hypertrophy through its interaction with the signalling protein calcineurin. Since the inhibition of calcineurin potentiates the production of testosterone, we hypothesized that α-actinin-3 deficiency (predicted from the ACTN3 XX genotype) may influence serum levels of testosterone of athletes.

OBJECTIVE

To investigate the association of ACTN3 gene R577X polymorphism with resting testosterone levels in athletes.

METHODS

A total of 209 elite Russian athletes from different sports (119 males, 90 females) were genotyped for ACTN3 gene R577X polymorphism by real-time PCR. Resting testosterone was examined in serum of athletes using enzyme immunoassay.

RESULTS

The mean testosterone levels were significantly higher in both males and females with the ACTN3 R allele than in XX homozygotes (males: RR: 24.9 (5.7), RX: 21.8 (5.5), XX: 18.6 (4.9) ng · mL(-1), P = 0.0071; females: RR: 1.43 (0.6), RX: 1.21 (0.71), XX: 0.79 (0.66) ng · mL(-1), P = 0.0167).

CONCLUSIONS

We found that the ACTN3 R allele was associated with high levels of testosterone in athletes, and this may explain, in part, the association between the ACTN3 RR genotype, skeletal muscle hypertrophy and power athlete status.

ACTN3 genotype and modulation of skeletal muscle response to exercise in human subjects

α-Actinin-3 is a Z-disc protein expressed only in type II muscle fibers. A polymorphism in the ACTN3 gene (R577X) results in lack of α-actinin-3 in XX genotype. The prevalence of the mutated X-allele is lower among power/sprint oriented athletes compared with controls, indicating that the lack of α-actinin-3 is detrimental in these sports, but a mechanistic link has not been established. Results from Actn3-knockout (KO) mouse model suggest that α-actinin-3 may affect muscle mass and muscle glycogen levels. In the present investigation we examined muscle fiber type composition, cross-sectional fiber area (CSA), and muscle glycogen levels at baseline in 143 human subjects with different ACTN3 genotypes. In addition, hypertrophy signaling and glycogen utilization in response to sprint exercise were studied in a subset of subjects. Glycogen utilization was analyzed in separate pools of type I and type II fibers. No differences in fiber type composition, CSA, or muscle glycogen levels were observed at baseline across the ACTN3 genotypes. However, the sprint exercise-induced increase in phosphorylation of mTOR and p70S6k was smaller in XX than in RR+RX (P = 0.03 and P = 0.01, respectively), indicating a less pronounced activation of hypertrophy signaling in XX. Glycogen utilization during sprint exercise varied across ACTN3 genotypes in type II fibers (P = 0.03) but not in type I fibers (P = 0.38). The present results are in accordance with findings from the KO mice and reinforce the hypothesis that ACTN3 genotype-associated differences in muscle mass and glycogen utilization provide a mechanistic explanation for the modulation of human performance by the ACTN3 genotype.

Genes and the ageing muscle: a review on genetic association studies

Western populations are living longer. Ageing decline in muscle mass and strength (i.e. sarcopenia) is becoming a growing public health problem, as it contributes to the decreased capacity for independent living. It is thus important to determine those genetic factors that interact with ageing and thus modulate functional capacity and skeletal muscle phenotypes in older people. It would be also clinically relevant to identify 'unfavourable' genotypes associated with accelerated sarcopenia. In this review, we summarized published information on the potential associations between some genetic polymorphisms and muscle phenotypes in older people. A special emphasis was placed on those candidate polymorphisms that have been more extensively studied, i.e. angiotensin-converting enzyme (ACE) gene I/D, α-actinin-3 (ACTN3) R577X, and myostatin (MSTN) K153R, among others. Although previous heritability studies have indicated that there is an important genetic contribution to individual variability in muscle phenotypes among old people, published data on specific gene variants are controversial. The ACTN3 R577X polymorphism could influence muscle function in old women, yet there is controversy with regards to which allele (R or X) might play a 'favourable' role. Though more research is needed, up-to-date MSTN genotype is possibly the strongest candidate to explain variance among muscle phenotypes in the elderly. Future studies should take into account the association between muscle phenotypes in this population and complex gene-gene and gene-environment interactions.

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 ACTN3 XX Genotype’s Underrepresentation in Japanese Elite Wrestlers

Purpose:

To examine the relationship between ACTN3 polymorphisms and level of athletic performance in Japanese wrestlers.

Methods:

The control group consisted of 243 healthy Japanese individuals. The authors divided 135 wrestlers into 3 groups based on their results in national or international competitions. They classified as elite 24 wrestlers who had placed in the top 8 in a world championship or participated in Olympic games, 28 wrestlers who had participated in world championships or become champions in Japan’s national championships were classified as subelite, and 83 wrestlers were classified as national (N-W, ie, national-level wrestler). In addition, the authors combined the elite and subelite to form the classification international-level wrestlers (I-W).

Results:

The frequency of the null X allele and the XX genotype were significantly lower in the I-W group than in the control group. However, there was no significant difference in ACTN3 genotype or allele frequency between the N-W and control groups. The frequency of the ACTN3 XX genotype in the elite groups was lower than that of all groups, and a linear tendency was observed between ACTN3 XX genotype and athletic status.

Conclusions:

In conclusion, the data indicated that ACTN3 polymorphisms were related to athletic performance in Japanese wrestlers.

Role of alpha-actinin-3 in contractile properties of human single muscle fibers: a case series study in paraplegics

A common nonsense polymorphism in the ACTN3 gene results in the absence of α-actinin-3 in XX individuals. The wild type allele has been associated with power athlete status and an increased force output in numeral studies, though the mechanisms by which these effects occur are unclear. Recent findings in the Actn3(-/-) (KO) mouse suggest a shift towards 'slow' metabolic and contractile characteristics of fast muscle fibers lacking α-actinin-3. Skinned single fibers from the quadriceps muscle of three men with spinal cord injury (SCI) were tested regarding peak force, unloaded shortening velocity, force-velocity relationship, passive tension and calcium sensitivity. The SCI condition induces an 'equal environment condition' what makes these subjects ideal to study the role of α-actinin-3 on fiber type expression and single muscle fiber contractile properties. Genotyping for ACTN3 revealed that the three subjects were XX, RX and RR carriers, respectively. The XX carrier's biopsy was the only one that presented type I fibers with a complete lack of type II(x) fibers. Properties of hybrid type II(a)/II(x) fibers were compared between the three subjects. Absence of α-actinin-3 resulted in less stiff type II(a)/II(x) fibers. The heterozygote (RX) exhibited the highest fiber diameter (0.121±0.005 mm) and CSA (0.012±0.001 mm(2)) and, as a consequence, the highest peak force (2.11±0.14 mN). Normalized peak force was similar in all three subjects (P = 0.75). Unloaded shortening velocity was highest in R-allele carriers (P<0.001). No difference was found in calcium sensitivity. The preservation of type I fibers and the absence of type II(x) fibers in the XX individual indicate a restricted transformation of the muscle fiber composition to type II fibers in response to long-term muscle disuse. Lack of α-actinin-3 may decrease unloaded shortening velocity and increase fiber elasticity.

Genetic aspects of skeletal muscle strength and mass with relevance to sarcopenia

Skeletal muscle is a highly heritable quantitative trait, with heritability estimates ranging 30-85% for muscle strength and 50-80% for lean mass. That strong genetic contribution indicates the possibility of using genetic information to individualize treatments for sarcopenia or even aid in prevention strategies through the use of genetic screening prior to the functional limitations. Though these possibilities provide the rationale for genetic studies of skeletal muscle traits, few genes have been identified that appear to contribute to variation in either skeletal muscle strength or mass phenotypes, and sarcopenia per se is remarkably understudied as a trait in this regard. This review examines the heritability of skeletal muscle traits, findings of linkage and genome-wide association analyses and impact of specific genes and gene-sequence variants on these traits as relevant to sarcopenia. Despite considerable work in the area, the genetic underpinnings of skeletal muscle traits remain largely unknown and the genetic aspects of sarcopenia are even less clear. Large-scale longitudinal clinical studies relying on advanced genome-wide association and other techniques are needed to provide further insights into the genes and gene variants that contribute to skeletal muscle strength and mass, and ultimately to susceptibility to sarcopenia.

α-Actinin-3 deficiency is associated with reduced bone mass in human and mouse

Bone mineral density (BMD) is a complex trait that is the single best predictor of the risk of osteoporotic fractures. Candidate gene and genome-wide association studies have identified genetic variations in approximately 30 genetic loci associated with BMD variation in humans. α-Actinin-3 (ACTN3) is highly expressed in fast skeletal muscle fibres. There is a common null-polymorphism R577X in human ACTN3 that results in complete deficiency of the α-actinin-3 protein in approximately 20% of Eurasians. Absence of α-actinin-3 does not cause any disease phenotypes in muscle because of compensation by α-actinin-2. However, α-actinin-3 deficiency has been shown to be detrimental to athletic sprint/power performance. In this report we reveal additional functions for α-actinin-3 in bone. α-Actinin-3 but not α-actinin-2 is expressed in osteoblasts. The Actn3(-/-) mouse displays significantly reduced bone mass, with reduced cortical bone volume (-14%) and trabecular number (-61%) seen by microCT. Dynamic histomorphometry indicated this was due to a reduction in bone formation. In a cohort of postmenopausal Australian women, ACTN3 577XX genotype was associated with lower BMD in an additive genetic model, with the R577X genotype contributing 1.1% of the variance in BMD. Microarray analysis of cultured osteoprogenitors from Actn3(-/-) mice showed alterations in expression of several genes regulating bone mass and osteoblast/osteoclast activity, including Enpp1, Opg and Wnt7b. Our studies suggest that ACTN3 likely contributes to the regulation of bone mass through alterations in bone turnover. Given the high frequency of R577X in the general population, the potential role of ACTN3 R577X as a factor influencing variations in BMD in elderly humans warrants further study.

Advances in exercise, fitness, and performance genomics in 2010

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

ACTN3 genotype, athletic status, and life course physical capability: meta-analysis of the published literature and findings from nine studies

The ACTN3 R577X (rs1815739) genotype has been associated with athletic status and muscle phenotypes, although not consistently. Our objective was to conduct a meta-analysis of the published literature on athletic status and investigate its associations with physical capability in several new population-based studies. Relevant data were extracted from studies in the literature, comparing genotype frequencies between controls and sprint/power and endurance athletes. For life course physical capability, data were used from two studies of adolescents and seven studies in the Healthy Ageing across the Life Course (HALCyon) collaborative research program, involving individuals aged between 53 and 90+ years. We found evidence from the published literature to support the hypothesis that in Europeans the RR genotype is more common among sprint/power athletes compared with their controls. There is currently no evidence that the X allele is advantageous to endurance athleticism. We found no association between R577X and grip strength (P = 0.09, n = 7,672 in males; P = 0.90, n = 7,839 in females), standing balance, timed get up and go, or chair rises in our studies of physical capability. The ACTN3 R577X genotype is associated with sprint/power athletic status in Europeans, but does not appear to be associated with objective measures of physical capability in the general population. Hum Mutat 32:1–11, 2011. © 2011 Wiley-Liss, Inc.

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.

A gene for speed: the emerging role of alpha-actinin-3 in muscle metabolism

A common polymorphism (R577X) in the ACTN3 gene results in complete deficiency of alpha-actinin-3 protein in approximately 16% of humans worldwide. The presence of alpha-actinin-3 protein is associated with improved sprint/power performance in athletes and the general population. Despite this, there is evidence that the null genotype XX has been acted on by recent positive selection, likely due to its emerging role in the regulation of muscle metabolism. alpha-Actinin-3 deficiency reduces the activity of glycogen phosphorylase and results in a fundamental shift toward more oxidative pathways of energy utilization.