Sunday, December 21, 2008

Genetic Testing of Young Athletes?

“If you want to be an elite athlete, you should choose your parents wisely!” This tongue in cheek statement, often made by sport scientists emphasizes the importance of genetics in determining athletic performance. In fact, research shows that genetics may determine anywhere from 20-80% of the variation sports performance. Genetics influences many factors such as cardiorespiratory function, muscle biochemistry, body size and motor skills. Until now, sports scientists haven’t been able to identify specific genes that might contribute to athletic performance. New research, however, has identified a potential link between sprint performance and the gene ATCN-3. Research studies report that elite sprint and power athletes possess this gene whereas elite endurance athletes do not. This has lead to a number of articles in the popular press discussing the potential of genetic testing in children. The goal is to determine if they are predisposed to certain types of activities. Unfortunately the science linking the ACTN-3 gene and performance is not quite as clear cut as some suggest.

There are actually two variants or versions of the ACTN-3 gene. The R version allows for the production of the muscle protein alpha-actinin 3 whereas the X variant does not. If an athlete has the ACTN-3 gene (the R version), he/she also has the alpha-actinin 3 protein. Athletes without the gene (or having the X variant) do not produce the protein. At this time, muscle physiologists are not completely sure how this protein affects muscle performance. Most theorize that it has some influence on the contraction characteristics of fast twitch muscle fibers. Having alpha-actinin 3 makes the muscle contract more rapidly and with more force and may improve sprint and power performance. Muscles without the protein may be more suited for endurance. However, this is just a theory at this time as recent studies on genetically modified animals show that alpha-actinin 3 may not be as influential as expected.

In 2003, a group from the University of Sydney published a study examining the presence of ACTN-3 in elite athletes. Using athletes from their university, the researchers found that many of the sprint / power athletes possessed the R version of the gene exclusively. Endurance athletes tended to have both the R and X variants. This suggests that elite sprint/power athletes are genetically endowed with the alpha-actinin 3 protein which might account for there ability to excel at their sports. Several later studies found similar results.

These studies lead to the development of commercial tests for the ACTN-3 gene. For $85 to $149, parents can swab the inside of their child’s cheek, send off the sample and find out if their child is genetically “gifted” for sprint or endurance sports. Having this information in hand will allow parents to steer their child to activities where they might be successful. The idea is that if a child possesses this gene, they should avoid activities like cross-country, cycling and swimming and focus on sports where speed and strength are important. So, a child’s athletic destiny can be determined very early on in life. Without delving into the ethical concerns with this approach to youth sports, there are several problems surrounding the issue of ACTN-3 and performance.

First, contrary to what has been reported in the press, not all studies show strong associations between performance and the ACTN-3 gene. While a majority of studies do show an association, many do not show a clear difference in gene expression between sprinters, endurance athletes and non-athletes. In fact, there is one report of an Olympic long jumper who has been highly successful despite the absence of the gene. Given this, some researchers estimate that having the ACTN-3 gene accounts for less than 3% of the variation in sprint performance. While a 3% difference in performance my be important at the Olympic level, it is exceedingly small at the youth level.

This emphasizes that, even at the elite level, performance is determined by a multitude of factors, both genetic and environmental. Sprinting and marathoning are often called “pure” sports. However, most sports are considered “hybrid” since they require combinations of strength and endurance, along with other skills. Soccer certainly falls in this category requiring speed, endurance, technical skill and vision. Being genetically gifted in one of these characteristics does not necessarily make a complete player. Thus, it is very unlikely that testing children for the ACTN-3 gene predict their soccer performance later in life.

Second, all of the studies performed to date merely show associations between the presence of a gene and some characteristic of performance. They do not show cause and effect. Many are quick to make the argument that an association between two variables means that one factor directly causes the other. One could probably show that a majority of elite soccer players wear either Adidias or Nike boots. But it is unlikely that anyone would argue that swapping his or her Puma cleats for a pair of Nikes would elevate him to the elite level. The same can be said for genetic testing and possessing the ACTN-3 gene. The science is not at all clear if possessing this gene or the alpha-actinin 3 protein does, in fact, influence performance, especially in soccer players. So, it is very unlikely that possessing the ACTN-3 gene will predict a young athletes potential.

There is little doubt that then link between the ACTN-3 gene and athletic performance is very interesting from a scientific point of view. This gene may have important implications for muscle performance in disease and aging. However, at this time, its role in determining athletic performance is questionable. Certainly the use genetic testing to determine a child’s gifts for certain types of sports is questionable. It is very unlikely that such a genetic test will give parents or coaches ANY useful information on a child’s athletic potential.

Further Reading:

Lite, J (2008) Can genes predeict athletic performance? Scientific American, Dec 1, 2008 (link).

MacArthur DG, North KN (2007) ACTN3: A genetic influence on muscle function and athletic performance. Exercise and Sport Sciences Reviews, 35:30-34.

Macur J (2008) Born to run: Little ones get test for sports gene. New York Times, Nov 29, 2008 (link).