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Genetics of muscle mass and strength
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Stephen M. Roth, Henning Wackerhage
The actinins, abbreviated ACTNs, are actin-binding proteins located in the Z discs of sarcomeres within skeletal muscle. There are two ACTN isoforms of which ACTN2 is expressed in all muscle fibres, whereas ACTN3 is only expressed in fast type II muscle fibres. Initially, an ACTN3 deficiency was found in patients with muscular dystrophies but then a team led by Kathryn North demonstrated that the absence of ACTN3 is common in individuals with no muscle disease and caused by a so-called ACTN3 R577X polymorphism (29). Using PCR and DNA sequencing, they identified a common C→T single nucleotide polymorphism (SNP) in exon 16 of the ACTN3 gene. This one nucleotide difference in the DNA sequence greatly changes the ACTN3 protein because as a consequence, amino acid 577, which is normally an arginine (abbreviated as R), is changed to a stop codon, abbreviated as X. Hence, the polymorphism is abbreviated as ACTN3 R577X.
Nutrigenomics for Sport and Exercise Performance
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Nanci S. Guest, Marc Sicova, Ahmed El-Sohemy
The ACTN3 (rs1815739) gene encodes the alpha-actin 3 protein, which plays a key role in the contraction of fast-twitch or power-type muscle fibres during short bursts of intense activities, such as sprinting or lifting heavy objects (154). Genetic variation in ACTN3 affects the expression of the resulting protein in fast-twitch fibres, and individuals who carry at least one copy of the T variant produce a lower-functioning ACTN3 protein that has been linked to increased risk of muscle damage (52). For example, a recent study showed that experienced endurance athletes with the T variant had higher levels of markers of muscle damage after a competitive marathon (38) compared to individuals with the CC variant. A similar trend was observed in a study where healthy young men performed knee extension exercises, working the quadriceps, in a laboratory setting (39).
Genetic testing for talent identification and development
Published in Silvia Camporesi, Mike McNamee, Bioethics, Genetics and Sport, 2018
Silvia Camporesi, Mike McNamee
Caulfield (2011) argues that these tests are examples of the widespread phenomenon of the exploitation of science, or to use his neologism, ‘scienceploitation’, defined as the ‘exploitation of legitimate fields of science and, too often, patients and the general public, for profit and personal gain’ (ibid., 4). More recently, in 2017, Stephan Montgomery, a genetic scientist from Stanford, has launched a company which has quickly gone viral, called ‘Except yes or no genomics’. This company mocks the claims of companies that work on a deterministic and reductionist understanding of biology and on the premise of genetic exceptionalism.6 Let us consider whether the general public is being subjected to ‘scienceploitation’ in the case of the tests for ACTN3 variants. These tests claim to assess the predisposition to athletic ability and prowess, yet the ACTN3 gene accounts for only 2% of total variance in muscle performance (Eynon et al. 2011). Moreover, Lucia et al. (2007) report the single case study of a Spanish two-times Olympic world-class long-jumper whose achievements were especially significant because of the lack of ACTN3 gene expression in his sample. Thus it seems something of a leap to suggest that those who express the variant are better suited for sprints.
ACTN3 R577X polymorphism related to sarcopenia and physical fitness in active older women
Published in Climacteric, 2021
C. Romero-Blanco, M. J. Artiga González, A. Gómez-Cabello, S. Vila-Maldonado, J. A. Casajús, I. Ara, S. Aznar
As well as the health benefits of physical activity in the elderly, investigating whether genetics determine better physical fitness or muscle mass8,9 is also of great interest. One of the most studied genetic polymorphisms has been ACTN3 R577X at position 1747 in exon 16, where an arginine turns into a codon stop due to the replacement of a cytosine by a thymine10. Homozygous XX people cannot produce the ACTN3 protein in the muscle, something estimated to take place in approximately 18% of the population11. ACTN3 is a structural protein and the predominant component of the Z areas of the sarcomere; α-actinin-3 deficiency in the general population seems to be connected to an age-related decrease of muscle mass and physical strength12.
PPARD CC and ACTN3 RR genotype prevalence among elite soccer players
Published in Science and Medicine in Football, 2020
Yoav Meckel, Alon Eliakim, Dan Nemet, Nir Levin, Sigal Ben-Zaken
Genetic variants among aerobic- and anaerobic-type athletes were previously demonstrated. The ACTN3 RR genotype was found to be significantly more prevalent among sprinters and jumpers (S/J) compared to long distance runners (LDR) and control non-athletes (Eynon et al. 2013; Papadimitriou et al. 2016). ACTN3 encodes for the synthesis of α-actinin-3 in skeletal-muscle fibers. This sarcomeric protein is necessary for powerful ‘explosive’ muscle contractions, and is associated with speed and other anaerobic-type performance qualities (Egorova et al. 2014). The prevalence of this genotype was also examined in team-sport athletes. The distribution of RR genotype was found to be significantly higher among soccer players than controls and endurance athletes(Santiago et al. 2008) and it seems to protect players from muscle injuries (Massidda et al. 2019) and eccentric muscle damage (Pimenta et al. 2012). Moreover, it was found that young soccer players who had higher frequencies of ACTN3 RR/RX genotypes presented better performance during jump and sprint tests (Dionísio et al. 2017). In line with this, Pimenta et al. (2013) examined 200 Brazilian professional soccer players and found that ACTN3/RR carriers exhibited better anaerobic performance results than XX carriers. Furthermore, the former scored higher in jump tests compared to both 577RX and 577XX carriers. In contrast to these findings, Coelho et al. (2016) did not find differences in physical performance between α-actinin-3 R577X genotypes in adult, U-20 and U-17 professional Brazilian first-division soccer players. In another study, team sport athletes showed a non-significant lower frequency of the 577RR genotype compared to the 577XX genotype than sprint/power athletes. The authors concluded that the ACTN3 R577X polymorphism was not associated with team-sport athletic status compared to endurance athletes and non-athletic controls (Massidda et al. 2015). Similar results were also found among a cohort from Poland, Russia and Spain (Eynon et al. 2014).
Clinical application of molecular biomarkers in Duchenne muscular dystrophy: challenges and perspectives
Published in Expert Opinion on Orphan Drugs, 2021
Fernanda Fortunato, Alessandra Ferlini
A common nonsense polymorphism (R577X, rs1815739) in the ACTN3 gene (MIM *102574) appeared to be associated with significantly reduced muscle strength and poorer performance at the 10 m walk test in young, ambulant DMD patients [27].