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Turbo Gene: Getting a speed boost from DNA

Sorcha McDonagh

Whether you're better suited to run a marathon or a 100-meter sprint correlates with a gene called ACTN3, researchers find.

The gene encodes the protein a-actinin-3, which functions in the so-called fast-twitch muscles. These muscles give the extra power needed for brief and vigorous bursts of activity, such as sprinting and speed skating.

Previous studies revealed that about one out of five white people in Australia has a variant of the ACTN3 gene that cannot yield a-actinin-3. Because people with the deficiency seem healthy, the protein appears to be unimportant for day-to-day activities. Most likely, it's significant only "in the extremes of performance," says Kathryn North of the Children's Hospital at Westmead in Sydney, Australia.

That's where the athletic connection comes in. North and her colleagues theorized that because the protein affects fast-muscle fibers, a deficiency of a-actinin-3 might be detrimental to speedy running and thus less likely to occur in elite sprinters.

To test their theory, the researchers genetically screened a group of world-class athletes, including Australian Olympic competitors, and a control group of nonathletes. All the participants were white. The scientists divided the athletes into two groups: sprinters, which included speed skaters, and endurance athletes, such as marathon runners and rowers.

Of the sprinters, 6 percent had the gene variant leading to a-actinin-3 deficiency. That's one-third the rate for nonathletes, 18 percent of whom carried the variant. With a rate of 24 percent, endurance runners were similar to the nonathletes. The findings will appear in the September American Journal of Human Genetics.

"The unique finding of this study is that the sprint athletes are different," comments Tuomo Rankinen of the Pennington Biomedical Research Center at Louisiana State University in Baton Rouge. "The endurance athletes do not really differ from the nonathletes in terms of this genetic marker."

There is, however, a gender difference. None of the female sprinters was a-actinin-3 deficient. North thinks that in male sprinters lacking the protein, hormones such as testosterone may compensate for the protein deficiency.

Previous studies have shown ethnic differences. Some 25 percent of Asians are a-actinin-3 deficient, compared with only 1 percent of Bantu-speaking people in Africa. North says that the importance of a-actinin-3 protein for athletic performance may vary in different human populations. "We know that at the moment, the best sprinters in the world are black," Rankinen says. "The next question is to compare the frequency of these ACTN3 genotypes in black sprinters with [that of] the general African-American population, for example."

But North's first task is to establish how the gene's protein product, a-actinin-3, works in fast-twitch muscles. After knocking out mouse ACTN3 genes, "we're going to be putting mice through little sprinting tests" and looking for structural changes in the muscles, she says.

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Letters:

As a plodder without the turbo gene I can appreciate those fortunate enough to have it. I would direct the researchers to two other groups of track and field participants: discus throwers and shot putters. I was a thrower in the 1960s, and through the 1970s and 1980s, I was a meet official for these events. I observed that fast twitch with moderate technique, or even poor technique, usually wins over strength and good technique. World champions in these events have amazing speed.

Tom Herbert
Tallahassee, FL

References:

MacArthur, D.G. 2002. A common polymorphism in the skeletal muscle gene ACTN3 influences athletic performance. 3rd College of Health Sciences and Medical Foundation Research Conference. Sept. 18. Sydney, Australia.

Yang, N., et al. 2003. ACTN3 genotype is associated with human elite athletic performance. American Journal of Human Genetics 73(September):627–631. Abstract.

Further Readings:

North, K., et al. 1999. A common nonsense mutation results in a-actinin-3 deficiency in the general population. Nature Genetics 21(April):353–354. Abstract.

Sources:

Kathryn North
Institute for Neuromuscular Research
Children's Hospital at Westmead
Locked Bag 4001
Westmead, NSW 2145
Australia

Tuomo Rankinen
Pennington Biomedical Research Center
Louisiana State University
6400 Perkins Road
Baton Rouge, LA 70808


From Science News, Volume 164, No. 5, August 2, 2003, p. 70.