When pediatric neurologist Markus Schuelke of University Medical Center Berlin first examined the boy just a few days after birth, he could hardly believe his eyes. The baby’s biceps were bulging, his thighs massive and well defined.

Courtesy of the National Academy of Sciences, U.S.A., copyright 2004

A mutation builds bulk in Belgian blue cattle.

Now almost 6 years old, the child dubbed Superboy by the German media can easily lift two seven-pound weights with his arms extended horizontally. And Schuelke has finally pinpointed the cause of his preternatural strength—two copies of a mutated gene for the growth factor myostatin, which normally tells muscles when to stop growing.


In 1997 Johns Hopkins molecular biologist Se-Jin Lee made headlines with the creation of mighty mice with defective versions of the myostatin gene. Other researchers have since proved that the same defective gene is frequently present in Belgian blues—heavily muscled cattle bred to be so beefy that calves have to be delivered by C-section. But Schuelke is the first to find a myostatin mutation in a human. Though he has nearly twice the muscle in his arms and legs as other children his age, the German boy is perfectly healthy.

Drugs targeting myostatin could prove a godsend for people with muscle-wasting diseases such as muscular dystrophy. According to James Tobin, a researcher at Wyeth Pharmaceuticals, “we do have a promising myostatin inhibitor in development, but there is at least a couple of years of safety tests before anything hits the market.” A myostatin inhibitor may also be hard to keep out of the hands of athletes looking for a steroid without side effects, says Schuelke. “I’ve had a lot of calls and 60 or 70 e-mails from people who want to dope themselves.”