Somewhere in Germany is a baby Superman, born in Berlin with bulging arm and leg muscles. Not yet 5, he can hold 3.2-kilogram weights with arms extended, something many adults cannot do.

　　DNA testing showed why: The boy has a genetic mutation that boosts muscle growth.

　　The discovery, reported in yesterday's New England Journal of Medicine, represents the first documented human case of such a mutation.

　　Scientists believe the find could eventually lead to drugs for treating people with muscular dystrophy and other muscle-destroying conditions. And athletes would almost surely want to get their hands on such a drug and use it like steroids to bulk up.

　　Researchers would not disclose the German boy's identity but said he was born to a muscular mother, a 24-year-old former professional sprinter. Her brother and three other close male relatives all were unusually strong.

　　In the mother, one copy of the gene is mutated and the other is normal; the boy has two mutated copies. One almost definitely came from his father, but no information about him has been disclosed.

　　The boy's mutant DNA segment was found to block production of a protein called myostatin that limits muscle growth. The news comes seven years after researchers at Johns Hopkins University in Baltimore created buff "mighty mice" by "turning off" the gene that directs cells to produce myostatin.

　　"Now we can say that myostatin acts the same way in humans as in animals," said the boy's physician, Dr Markus Schuelke, a professor in the child neurology department at Charite/University Medical Center Berlin. "We can apply that knowledge to humans, including trial therapies for muscular dystrophy."

　　Given the huge potential market for such drugs, researchers are already trying to find a way to limit the amount of myostatin in the body.

　　Dr Lou Kunkel, director of the genomics program at Boston Children's Hospital, said success is possible within several years.

　　"Just decreasing this protein by 20, 30, 50 percent can have a profound effect on muscle bulk," said Kunkel, who is among the doctors participating in the Wyeth research.

　　Muscular dystrophy is the world's most common genetic disease. There is no cure and the most common form usually kills before adulthood. The few treatments being tried to slow its progression have serious side effects.

　　Dr Eric Hoffman, director of Children's National Medical Center's Research Center for Genetic Medicine, said he believes a muscular dystrophy cure will be found, but he is unsure whether it will be a myostatin-blocking drug, another treatment or a combination, because about a dozen genes have some effect on muscles.

　　He said a mystotatin-blocking drug could help other groups of people, including astronauts and others who lose muscle mass during long stints in zero gravity or when immobilized by illness or a broken limb.

　　The super strong boy is healthy now, but doctors worry he could eventually suffer heart or other health problems.

　　(The Associated Press)