Though the ACTN3 gene does appear to influence sprinting ability, making a sports decision based on it is like deciding what a puzzle depicts when you’ve only seen one of the pieces. You need that piece to complete the puzzle, but you certainly can’t see a meaningful picture without more pieces.
David Epstein, The Sports Gene (2013)
Dedicated training has long been known to improve athletic performance. But why do some individuals consistently outperform others who have undertaken comparable training regimens? The degree to which an individual’s genetic makeup can predict their future performance, and even their ability to respond to athletic training, has excited much debate. Although often framed as a nature versus nurture debate, the interaction between an athlete’s genetic make-up (i.e. nature) and their environment (i.e. nurture—training, nutrition etc.) may also have a significant effect on their athletic performance, susceptibility to sports-related injury and speed of recovery.
While studies measuring genetic variation between athletes may appear to find specific genetic predictors of athletic performance,1 these associations may not always hold up when more stringent genome-wide significance levels are demanded.2 A detailed understanding of the ‘genetic architecture’ of sport performance and recovery requires identification of the full spectrum of genetic contributors (including not only common polymorphisms, but also rare DNA variants) that influence athletic parameters such as strength, endurance, recovery time and coordination.
In the study of rare diseases, pinpointing the causal relationship between DNA variants and disease phenotypes is assisted by the fact that an individual patient’s rare disease often has a single genetic determinant—such that comparisons between affected persons can find different rare variants in the same gene. This strategy for monogenic disease traits cannot be used with non-disease phenotypes like athletic performance, because these human phenotypes are polygenic. In other words, each athlete’s phenotype is influenced by multiple DNA variants, both rare and common.
In this chapter we will explore:
important concepts and terminology needed to interpret genetic studies on sport performance and related injuries
methods of testing the association between genetic variation and health outcomes
implications of genomics for exercise and sport.
INTRODUCTORY GENETICS: IMPORTANT CONCEPTS AND TERMINOLOGY
An individual’s genome is made up of strings of the chemical nucleotide bases adenine (A), thymine (T), cytosine (C) and guanine (G). Two complementary strands of these bases wind around each other in a double helix, which is then wrapped like a spool of thread around proteins called ‘histones’. The packaging of DNA with these proteins and other molecules, like RNA, is called ‘chromatin’. Within the cell’s nucleus, chromatin is further packaged into units called ‘chromosomes’ (Fig. 35.1), of which humans have 23 pairs (22 pairs of autosomes and 1 pair of sex chromosomes). In addition to the DNA found in the nuclear ...