This chapter contains sections titled: Linkage Studies, Candidate Genes, Conclusions, References. Gene variants (polymorphisms) causing interindividual variation in maximal isometric, dynamic strength, and power have been studied through family studies (linkage analyses), candidate-gene studies, and, most recently, genome-wide single-nucleotide polymorphism (SNP) association studies (GWAS). To date, there has been relatively little concordance between these three types of studies, and lack of replication may be due to the relatively small effect sizes of individual gene polymorphisms, differences in the study populations (age, sex, and ethnicity), and/or differences in phenotyping (baseline vs. response to intervention, or method to measure strength). To define the generics of strength and response to strength training, longitudinal intervention studies are needed on large cohorts (>300 individuals). Genotyping of 1 million or more SNPs in such cohorts will likely define key gene polyrnorphisms contributing to baseline strength and response to training. Until such large studies are accomplished, the development and use of any potential gene profile for elite strength performance is highly specularive, if not misleading. Individual gene variants contribute only about 1-2% to the overall variation in strength phenotypes, with the possible exception of a variant in IGF2 explaining as much as 10% of the observed variance. Only a limited number of studies have investigated gene-gene interacrion effects. Low-allele frequencies often prevent the study of these interactions in smaller study samples. Great efforts have been made to review genetic linkage and association reports related to strength and power in a series of MSSE special reports "The Human Gene Map for Performance and Health-Related Fitness Phenotypes" (Brav et al., 2009; Perusse et al, 2003; Rankinen et al., 2001, 2002, 2004, 2006; Wolfarth et al., 2005). In this chapter, hypothesis-free linkage studies will be discussed separately from candidate-gene, hypothesis-driven studies. In this last approach, candidate genes will be grouped based on their hypothetical function in the muscle or broader system. Owing to space limitation, references to original studies will be limited to recent publications, and numbered references are cross-references to the reference number in Brav et al., 2009.
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