SPORTS PHENOM? Would a simple swab of the cheek reveal whether a tyke is destined for athletic greatness?
iStockphoto/Rosemarie Gearhart

What if sideline rage could be nipped in the bud with a quick genetic test that told Mom and Dad what sports – if any – Junior could master? The Boulder, Colo., company Atlas Sports Genetics today began selling just that sort of product: for $149, it says it will screen for variants of the gene ACTN3, which in elite-level athletes is associated with the presence of the muscle protein alpha-actinin-3. The protein helps muscles contract powerfully at high speeds, which may explain why the combination of ACTN3 variants that produce it has been found in Olympic sprinters.

The company's president, Kevin Reilly, tells ScientificAmerican.com that parents shouldn’t view the test as the final word on whether their child will excel at a particular sport. But, he says, it is more useful than physical tests in determining a child's athletic abilities before age 9.

At that age, "they don’t have the physical maturity and motor skills to do well," Reilly says. "That’s where the genetic test can come in [handy] for looking for early indicators of talent in performance areas.

"It’s a question of their motivation. This is a tool, not the tool," he says of consumers. "If they're relying on the genetic test as the only performance indicator to tell whether they will do good or bad in sports, they're going to be disappointed, because it's not for that purpose. If it’s a tool along with other components, you can use it to select what may be the best sport for you or for a child."

It takes about three weeks to get the results of the saliva test, which looks for three combinations of ACTN3 genes, with a child getting one variant from his mother and one from his father. (Reilly says that the Atlas Genetics screen is the only one commercially available in the  U.S. that tests for fitness-related genes.) Kids who have two copies of the X variant from both parents don’t make alpha-actinin-3, and might excel at endurance sports such as cross-country skiing, distance running or swimming, according to the company's Web site. Those with one copy of the X variant and one of the R variant will make some protein, Reilly says, and may excel at endurance or "power" sports such as soccer or cycling. And children with two copies of the R variant will make more alpha-actinin-3, setting them up for possible achievement in power or endurance sports including football, weight-lifting or sprinting.

We asked Stephen Roth, an assistant professor of exercise physiology, aging and genetics at the University of Maryland in College Park, to explain what is and isn’t known about the relationship between DNA and sports performance. Roth is a co-author of the Human Gene Map for Performance and Health-Related Fitness Phenotypes, a catalog of genes associated with sports-related fitness. The map was last published in 2006 in Medicine and Science in Sports and Exercise, a journal of the American College of Sports Medicine. The new edition will be available shortly.

This is an edited transcript.

To what extent do genes determine athletic ability?

Nobody knows the answer for sure and it depends on how specifically you define athletic ability. Most research suggests that genetics contribute significantly to sports performance, but it's very hard to put a number on. It's very hard to quantify football performance, for example. Most studies look at very specific endpoints: how much a gene contributes to muscle strength or maximal aerobic capacity, because those endpoints are very easy to measure from a research standpoint. If you try to parse it out, as much as 50 percent of muscle strength is determined by genetic factors.