10 September 2007

Endurance gene discovered

Researchers have discovered a gene that plays a crucial role in athletic endurance.

If you were a prehistoric human, would you prefer to be able to sprint very fast for short distances or to jog comfortably for kilometres? That's one of the questions thrown up by the so-called "gene for speed," known as ACTN3.

One of the most intriguing genes discovered, ACTN3 encodes a protein that governs metabolism in "fast twitch" muscle fibres, which generate force at high speed.

Around 18 percent of the world's population has a truncated variant of the gene which blocks this protein. The stubby variant, called R577X, is common among successful endurance athletes, previous research has found.

On the other hand, elite sprinters, who need explosive speed, are likelier to have the reverse - a functioning variant of ACTN3.

How the study was conducted
Keen to find out more, researchers led by Kathryn North, a professor at the Children's Hospital at Westmead, in Sydney, Australia, created a batch of mice that had been engineered to lack ACTN3.

The "knockout" mice and ordinary mice with a functioning ACTN3 gene were put on a motorised treadmill, which spun ever faster until the luckless rodents were exhausted.

The easy winners in this endurance test were the knockout mice, which were able to run on average a third further than their counterparts.

The apparent reason for this: the loss of ACNT3's protein was compensated for by a different protein, called alpha-actinin-2, which shifted muscle metabolism towards a smoother, more efficient, aerobic pathway.

Contracted again and again
As a result, fast-twitch leg muscles could be contracted again and again, without tiring.

North's team also looked through genetic profiles from individuals of European and East Asian descent and found that there was remarkably little sign of mutation in the wider stretch of genetic code in the vicinity of R577X.

Such similarity is a tell-tale sign of what evolutionary experts call positive selection. Genes which help the fight for survival get lastingly incorporated in the human genome, whereas those that encumber it get weeded out.

In other words, the ability to run longer distances became a preferential trait that became incorporated into a wide swathe of Homo sapiens.

Happened recently
If so, the incorporation happened recently in human evolutionary history.

According to North's calculations, R577X took root among populations in central Europe around 15 000 years ago, and in East Asia around 33 000 years ago.

The variant has not been incorporated in all of us, either because so little time has elapsed for this to happen, or it is being countered by selective pressures in favour of other genes, they speculate. The study was published on Sunday in the specialist journal Nature Genetics. – (Sapa-AFP)

Read more:
Genetically altered athletes: fact or fiction?

September 2007




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