The DNA polymorphisms currently used in sports were identified in studies that test a small number of candidate genes using relatively small athlete populations (typically several hundred). There is a large and rich source of additional genetic information that could be used by athletes based on genome-wide association studies (GWAS) that examine health risks in the general population. Genomic-wide association studies can test over 1 million different polymorphisms and often include tens of thousands of subjects. Therefore, the statistical power of discovering significant genetic variants that contribute to complex phenotypes is very high.46 The results from these health studies in the general population can also provide key information to athletes about their risk for injury or nutritional needs. Low bone mineral density, for example, affects both older individuals (osteoporosis and skeletal fracture) and athletes (stress fracture).47–50 A large meta-analysis assessing bone mineral density integrated the results of 17 GWAS that screened approximately 1 million SNPs in a total of 32 961 elderly individuals.51 Sixty-three SNPs associated with bone mineral density at genome-wide significance were identified. The weighted contributions of each of these 63 SNPs were combined into 1 genetic score. Elderly individuals in the highest risk category have 1.56 increased odds for osteoporosis and 1.60 increased odds for fracture. Conversely, elderly individuals in the lowest category are protected against osteoporosis and fracture (0.62 and 0.46 decreased odds, respectively).51 Genetic variants related to osteoporosis in elderly women may very well have prognostic application regarding stress fractures in young athletes. First, bone mineral density is a major determinant for stress fractures, especially among endurance athletes.47–50 Second, higher rates of osteoporosis in older women and higher rates of stress fractures in young, active women tend to appear together in the same family.52–54 Thus, the genetic score developed for low bone mineral density in the elderly could also be a powerful tool for athletes, especially endurance athletes. The sports genetics program at Stanford University uses genetic variants associated with bone mineral density—as well as other pathological or predisposing states such as osteoporosis, asthma, vitamin and mineral levels, red blood cell phenotypes, caffeine metabolism, and disc degeneration—that can be used to reduce injury risk.45,55 By incorporating results from GWAS, the Stanford Sports Genetics Program has greatly expanded the set of DNA polymorphisms that can be used to reduce sports injury risk from approximately 13 previously known polymorphisms to 195 polymorphisms now currently in use.45
It is too early to measure the effect of genetic testing on reducing the incidence of injuries or inducing behavioral changes that will promote health and/or prevent injury. It is clear that there are many genetic polymorphisms that provide information about risk for sports-related injuries and performance-related conditions. Athletes, coaches, and medical practitioners can use this information to generate personalized training regimens for athletes. It is too early, however, to gauge the effectiveness of these personalized regimens at reducing injury incidence compared with standard training. Nevertheless, any additional information about performance might be useful to help reduce injuries and maximize performance among elite athletes, who are typically early adopters of many medical treatments designed to speed recovery from injury and/or reduce pain so that they can return to play as soon as possible.56–58 For recreational athletes, the benefits of genetic testing may be small when compared with the results of increased participation in standard approaches to training.59 Besides prompting athletes to include new modifications in their training or diet, genetic knowledge may also increase compliance with currently prescribed “prehabilitation” strategies.60
As genetic testing in sports gains momentum, it is important to develop best practices to protect the legal, ethical, and social rights of the athlete. The existing guidelines regarding genetic testing of athletes are currently unclear. The Genetic Information Nondiscrimination Act of 2008 places employees in a protected statutory class and prohibits employer discrimination based on genetic information and family medical history36; it is unclear whether this act protects collegiate athletes who do not qualify as employees of universities.33,36 However, collective bargaining agreements in major league sports may permit mandated genetic testing of athletes.36 Genetic testing has the potential to empower athletes with new information that might increase their competitive edge. As teams begin to adopt genetic programs, careful steps should be taken to ensure that players are not coerced into participating as part of a screening process that determines athletic eligibility or playing time.
Genetic information is growing at an exceptional rate, producing new information faster than Moore Law—which predicts that overall processing power doubles every 2 years. We anticipate that the power of genetic testing to predict the likelihood of sports-related injuries sustained by athletes will grow rapidly. This new field of study is exciting; it holds great potential for injury prevention for athletes at every level.
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