ACTN3 and muscle function

Variants of the ACTN3 gene show pretty large population differences (also not present in chimps) and have been associated with ability in sprint sports vs. endurance. This is thought to be due to the function of ACTN3 in determining the slow twitch vs. fast twitch muscle fiber proportions. In this paper they look at some Greek people (not a self-selected group, because unlike previous studies, these are not professional or even amateur athletes and they are young) to see if they can reproduce that association and they only find an association for the 40 meter sprint in the predicted direction. They cite a paper that I had also missed that fails to support the hypothesized association among Kenyan marathon runners.

Association analysis of the ACTN3 R577X polymorphism and complex quantitative body composition and performance phenotypes in adolescent Greeks

European Journal of Human Genetics

advance online publication 11 October 2006

Colin N Mora, Nan Yang, Mark E S Bailey, Athanasios Tsiokanos, Athanasios Jamurtas, Daniel G MacArthur, Kathryn North, Yannis P Pitsiladis and Richard H Wilson

Abstract: The functional allele (577R) of ACTN3, which encodes human -actinin-3, has been reported to be associated with elite athletic status and with response to resistance training, while the nonfunctional allele (577X) has been proposed as a candidate metabolically thrifty allele. In a study of 992 adolescent Greeks, we show that there is a significant association (P=0.003) between the ACTN3 R577X polymorphism and 40 m sprint time in males that accounts for 2.3% of phenotypic variance, with the 577R allele contributing to faster times in an additive manner. The R577X polymorphism is not associated with other power phenotypes related to 40 m sprint, nor with an endurance phenotype. Furthermore, the polymorphism is not associated with obesity-related phenotypes in our population, suggesting that the 577X allele is not a thrifty allele, and thus the persistence of this null allele must be explained in other terms.