The child can lift 7-pound weights at arms length, a deed many adults find difficult, said Dr. Markus Schulke, a child neurologist who has been studying the boy since birth, the Deutsche Welle reported.
"He's a normal boy -- you don't see it, you wouldn't recognize him" out of a crowd, Schulke said. "He can just lift heavy things."
The child has a genetic mutation that blocks the production of a protein that limits muscle growth. It's the first known case of a human having such a mutation.
Schukle published his findings in the New England Journal of Medicine, saying the discovery might aid in the fight against muscle-wasting diseases such as muscular dystrophy.
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