Genetic Testing and Youth Sports

Genetic testing is becoming available to consumers for many applications such as ancestry exploration, future disease risk, and prenatal carrier testing. Now there is another option—sports performance from online genetic testing companies offering everything from single gene tests to multiplex testing of numerous purported sports performance genes. In the “winning is everything” sports culture, societal pressure to use these tests in children may increasingly present a challenge to unsuspecting physicians. The aim of this Commentary is to bring this issue to the attention of physicians, provide evidence regarding this testing, and encourage clinicians to advocate for young patients when necessary.

As understanding of the human genome increases, more genetic variants will likely be implicated in sports performance. Although a number of genes are being marketed for sports performance,¹ the α-actinin-3 (ACTN3 [GenBank accession number M86407.1]) gene has received the most attention. Named the “speed gene,” ACTN3 produces α-actinin-3, a structural protein that stabilizes sarcomeres during forceful contraction of fast-twitch muscle fibers used during athletic activities that require explosive bursts, such as sprinting. Two polymorphisms of the ACTN3 gene exist: 577R, the normal allele producing functional protein; and 577X, the null allele prohibiting protein production. More than half of individuals of European descent are heterozygotes (RX).² In 2003, a study by Yang et al³ was the first to suggest that R allele homozygosity may be advantageous for power/sprint activities; 50% (53/107) of elite white sprint athletes had the RR genotype, compared with 30% (130/436) and 31% (60/194) of healthy white control participants and elite endurance athletes, respectively.

Subsequent small cross-sectional studies have demonstrated variable overrepresentation of the RR genotype, ranging from 31% to 73% in elite power/sprint athletes to 26% to 45% in control participants.² Evidence that different ACTN3 genotypes are significantly associated with sports performance in nonelite athletes or nonathletes is inconsistent and inconclusive at best.^{2 ,4} Moreover, complete deficiency of ACTN3 does not appear to preclude elite performance, as demonstrated by a Spanish Olympic long jumper with the XX genotype.⁵ Larger studies and randomized controlled trials of muscular strength, fiber-type proportion, and metabolism have not been conducted in elite athletes or the general population.⁴ Given the state of the evidence, claims that ACTN3 can accurately and reliably identify future athletic stars are premature.

Nonetheless, in 2004, 1 year after publication of the study by Yang et al³ describing this gene's possible link to sports performance, an Australian company developed a test for the ACTN3 gene, which it now distributes in gyms and health clubs. In 2008, a US-based company began offering this ACTN3 test directly to coaches, parents, and athletes of all levels and ages, including children as young as 1 year old.⁶ The test reportedly costs $170, does not require a physician order, and is performed on cells collected by swabbing the cheek.⁶ Test results are sent directly to the consumer with a brief explanation of implications for physiological strengths and suitability for strength/power, mixed, or endurance sports. Exactly how many parents and coaches are using this testing is unknown because such data are proprietary.

Such testing promotes a reductionist view of athletic performance among parents and coaches. Athletic performance is a multifactorial trait of which genetics is but 1 factor. Although researchers continue to investigate hundreds of genes for potential effects on sports performance,⁴ it is estimated that the ACTN3 gene accounts for only 2% of the variance in muscle performance.⁵ Yet companies selling genetic tests make unsubstantiated claims such as “Olympic success might be in your future!”¹ Marketing of these genetic tests has outpaced understanding about the complex genetic underpinnings of athletic performance. Current understanding of the spectrum of genes involved and their interactions with the environment (eg, different training regimens) and other contributing factors such as psychological traits, training facilities, finances, nutrition, coaching, and just plain luck is limited. Further research is needed to better understand factors that influence sports performance.

While there are clear challenges to fully understanding the genetics of athletic performance, there are even greater challenges communicating information about genetics to the public. Parents struggle to correctly comprehend information received during extensive genetic counseling for relatively well-understood diseases such as cystic fibrosis.⁷ Physicians will face an even greater challenge in helping parents accurately understand and interpret genetic information about sports performance, on which even less is known.

Perhaps the real question is whether talent identification, genetic or otherwise, is appropriate in youth sports. The role of sports can be very different for many families. For some, sports participation aids in the development of life skills such as socialization and teamwork. For others, the role of sports is to aid children in their ascent to stardom, fame, and fortune. While genetic testing for athletic ability might help young athletes choose a successful athletic path and guide training regimens, there is lingering concern that such early specialization could lead to burnout, injury, or both.⁸ Despite the reality that fewer than 1 in 20 high school athletes will play college athletics and fewer than 1 in 1000 will play professional sports,⁹ some parents may hope testing will increase their child's chances of success. By focusing intently on success in the win, loss, and earning potential column, rather than on success in character development, social relationships, and general health and fitness, dehumanizing the youth sports experience is at risk. In addition, with much still unknown about the genetics of athletic performance, many children might be excluded without merit. Moreover, even if the role of sports could help determine the validity of genetic testing, the ethical and moral issues would still present challenges.

Rather than embrace a reductionist view of youth athletic participation and performance, physicians should promote the importance of physical activity, both organized recreation and free play for all children.¹⁰ Given the rates of childhood and adult obesity, actions that decrease interest or limit participation in physical activity may jeopardize the health of youth. In discussions with parents, clinicians can (1) communicate the limits of scientific understanding of athleticism; (2) promote athletics for health and disease prevention; (3) discuss the risks and benefits of genetic information in the context of the child's best interest; (4) convey the potential implications if genes such as ACTN3, initially identified for sports performance, are later associated with disease risk; (5) respect the child's developing autonomy to choose activities found to be enjoyable; and (6) assert that no child should be forced or coerced to be genetically tested. In short, the message for parents should be that no single test or even battery of tests can predict whether a child will become an elite athlete. Parents should be encouraged to nurture their child's interests in sports regardless of any genetic test that claims to predict athletic potential.