Mr. Universe Jr.: child's gene mutation confirms protein's role in human-muscle growth.

Find the kid a sports agent. Researchers studying an unusually muscular tot have found that he has gene mutations similar to ones that produce abnormally brawny cattle and mice. Less-severe variations in the same gene may underlie the success of some athletes, the scientists speculate.

The boy's mutations disrupt both copies of the gene encoding a muscle protein called myostatin. Previous studies of the gene in animals had suggested that myostatin restrains muscle growth during development and adult life. But scientists didn't know whether the protein serves the same function in people.

The boy's powerhouse physique "says pretty definitively that myostatin plays the same role in humans that it does in mice and cattle," concludes Se-Jin Lee of Johns Hopkins Medical Institutions in Baltimore. If so, he adds, then drugs to block myostatin might have some benefits in people with muscle-wasting diseases.

Lee is a member of the international group of investigators who have studied the boy since 1999 and now report their results in the June 24 New England Journal of Medicine (NEJM).

In 1997, Lees team at Johns Hopkins and two other research groups independently reported that Belgian Blue cattle, an unusually muscular breed, have mutations in their myostatin genes. At that time, Lee and his colleagues also produced hulking mice by deactivating the rodent version of the gene (SN:11/22/97, p. 325).

Now about 5 years old, the child at the focus of the recent work was initially spotted by Markus Schuelke of Charite-University Medical Center in Berlin. Asked to look at a jittery newborn, the neurologist noticed the infant's bulging thigh and arm muscles. Schuelke and his colleagues had read about myostatin only a few weeks earlier. "It was pure chance we made the connection," he says.

After identifying the boy's mutation, the team found no myostatin in his blood. He still might make small amounts of the protein in his muscle tissue, says Lee. Other than showing increased muscle mass and strength compared to other boys his age, the child has developed normally. Because myostatin may have a role in heart muscle as well, physicians intend to monitor whether the boy's cardiac function remains normal.

"For any kid who looks a bit like an infant Hercules, this will be one of the genes to look at now," says Tejvir S. Khurana of the Pennsylvania Muscle Institute in Philadelphia. Khurana, as well as Lee and other researchers, are studying whether compounds that inhibit myostatin could preserve muscle in people with various muscular dystrophies or even stimulate new muscle to grow.

"Myostatin blockade will probably work its way into professional and amateur athletics, as well as into the ever-growing business of physical enhancement," adds Elizabeth M. McNally of the University of Chicago in a NEJM commentary.

In fact, nutritional supplements that claim to block myostatin are already being sold, primarily to bodybuilders. "That's all rubbish. We tested [one] and it doesn't work," warns Schuelke.

Natural variations in the myostatin gene may confer an athletic advantage on some people, McNally says. The boy's mother, who has a mutation in one of her myostatin genes, is a former professional sprinter. She reports that several of her family members are also stronger than normal; one is a construction worker who used to lift large curbstones unaided. DNA from the boy's father hasn't yet been analyzed.