Strong Baby Is Called a Normal Kid By MATT SURMAN, Associated Press Writer BERLIN - A genetic mutation made a Berlin 5-year-old extra strong, but the German doctor who has been studying the boy since just after his birth says he's just a regular kid. The boy doesn't stand out among his peers on the playground, but when he puts his mind to it, he can perform feats of strength, said Dr. Markus Schuelke. "He's a normal boy — you don't see it, you wouldn't recognize him" out of a crowd, Schuelke said. "He can just lift heavy things." Schuelke started studying the super-strong boy after he was brought to Berlin's Charite hospital shortly after birth because he was twitching. That turned out to be nothing, but Schuelke, a pediatric neurologist, found that even though the boy was well within normal birth weight, he was particularly muscular. Schuelke began conducting tests and found over the course of five years that the boy had a genetic mutation that boosts muscle growth. It is the first human case where a mutant DNA segment was found to block production of a protein called myostatin that limits muscle growth, though researchers discovered in 1997 that they could create mega-mice by "turning off" the gene that directs cells to produce the protein. Schuelke, who worked with researchers from the United States, wrote about the case in Thursday's New England Journal of Medicine (news - web sites), where he said the discovery could possibly help in the fight against muscle diseases, like muscular dystrophy. The boy, whose name Schuelke has promised not to divulge, has muscles twice the size of other children his age and half their body fat. He was born to a muscular mother, a former sprinter. Her brother and three other relatives were also very strong — one a construction worker with a talent for hefting curbstones. Schuelke said scientists have no way to tell how common the boy's ability is, or if a legion of super-strong tykes will be discovered now that researchers have learned what to look for. "How should we know?" Schuelke said. "We have the first case so far."