It Takes Genes to Make Olympians
Athletes and coaches long have assumed that talented runners are gifted with exceptional genes. Now scientists have identified a specific gene that conceivably could push a runner over the line between good and great.
Of course it takes more than genes to develop an elite athlete, but scientists are learning more just how much genes do contribute to superior athletic ability.
Australian researchers studied athletes at Canberra's Australian Institute of Sport, a national Olympic athlete training center. The researchers found that a gene called alpha-actinin can make runners better at either sprinting or endurance, depending on which version of the gene they have.
"There is increasing evidence for strong genetic influences on athletic performance and for an evolutionary 'trade-off' between performance traits for speed and endurance activities," the researchers reported in a paper published in the July 23 issue of the American Journal of Human Genetics.
They found that sprinters tend to have one version of the gene, alpha-actinin-3 or ACTN3, while long-distance runners tend to have a different version, ACTN2.
Neurogeneticist Kathryn North and her colleagues at the University of Sydney in Australia also found that more elite sprinters had not one but two copies of the alpha-actinin-3 gene. ACTN3 creates the code for a protein produced exclusively in "fast-twitch" muscle fibers -- they're fueled by glucose and are essential for power and speed.
"This suggests that the presence of alpha-actinin-3 has a beneficial effect on the function of skeletal muscle in generating forceful contractions at high velocity, and provides an evolutionary advantage because of increased sprint performance," the authors wrote.
Endurance runners, on the other hand, often have two copies of ACTN2, which creates the code for a protein produced exclusively in "slow-twitch" muscle fibers. Long-distance runners typically have slow-twitch muscles. Instead of glucose, slow-twitch muscles are fueled by oxygen, and are responsible for sustained exercise.
But for coaches or parents who want to predict a child's future in sports, the answer is not as simple as a genetic test.
Correlations between genes and athletic ability, or any other physical outcome, do not necessarily indicate a cause-and-effect relationship, said R. Alta Charo, law and bioethics professor at University of Wisconsin's law and medical schools.
For example, she said that one day redheads may be known for younger-looking skin because they're more diligent about staying out of the sun and wearing sunscreen. But that doesn't mean their genes give them better skin -- it's due to their behavior.
"Here too, not only are the relative roles of genes, motivation, training and diet unknown, but the entire effect of the genes may be only indirectly related to the outcomes," Charo said. "A coach might well be more foolish than unethical to use such limited and preliminary information to make such important judgments."
Still, researchers and sports-medicine doctors can learn from genetic information that relates to athletics, according to Claude Bouchard, who annually updates his "fitness genome map," a database of genetic research on human athletic ability.
Instead of studying diseases, as does the Human Genome Project, Bouchard and his colleagues at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, gather information on fitness genes.
"This review brings in a single publication the findings that are dispersed in more than a hundred papers," Bouchard said. "It helps the scientists in other areas than genetics to get a rapid but yet comprehensive overview of where the field stands."
The information is useful for researchers who want to know how humans adapt to regular exercise and why athletic training is more effective for some individuals than others, Bouchard said.
The same genes that play key roles in sports performance also sometimes figure in common chronic problems such as cardiovascular diseases, diabetes, osteoporosis, obesity and others. Knowing more about these genes could lead to prevention and eventually treatment, Bouchard said.
Bouchard started with an obesity genome map 10 years ago, and three years ago branched out with the fitness map, which is published in the August issue of Medicine and Science in Sports and Exercise. Anyone with a journal subscription can access the map.
Twenty new genes were put on the map this year, including genes associated with "exercise intolerance," a condition that prevents people from enduring any amount of sustained physical activity. Various genes associated with muscle strength, muscle performance and cardiorespiratory endurance also were added.
Several studies focused on the angiotensin-converting enzyme (ACE) gene, which also seems to have alternate versions in sprinters and endurance runners. The I form of the gene is more common in sprinters while the D form of the gene is associated with long-distance runners.
This year, a researcher found that congestive heart failure patients with two copies of the I version of the ACE gene had a greater capacity for exercise than those with the D form, according to the Genome News Network, an online journal for genome researchers published by The Institute for Genomic Research.
Another study involving British military recruits found that soldiers with two copies of the I form of the ACE gene responded better to training.
The information likely will not lead to custom-made athletes, according to Bouchard, who said anyone dreaming of engineering his own Carl Lewis can dream on.
"This is not in the cards at this time. Some parents and coaches may be dreaming about such a capability," he said. "However, the fact of the matter is that this is still pure science fiction."