Super Strong Kids May Hold Genetic Secrets

April 2, 2009— -- Every new child has a few surprises, but imagine bringing home an adopted baby to find he was born with a super strength beyond the biological limits of most humans.

At 5 months old, Liam Hoekstra of Grand Rapids, Mich., started doing an expert gymnast move called the iron cross. By 8 months old, Liam could do a pull-up and by 9 months, he could climb up and down stairs.

"I would hold him up by his hands and he would lift himself into an iron cross. That's when we were like, 'whoa, this is weird,'" Liam's mother, Dana Hoekstra told The Associated Press.

Soon, the family thought to take him to specialists, who diagnosed Liam with a rare condition loosely called myostatin-related muscle hypertrophy, according to reporting by the AP.

The condition is so rare, only a few similar cases have been documented in medical literature. Hoekstra declined to do more interviews with ABCNews.com, saying she hoped to get her son out of the limelight for a while.

Indeed, the handful of cases like Hoekstra's have caught the eye of scientists, doctors, and body builders, as a way to manipulate our natural strength.

Many substances in the body can control muscle growth, but in 1997, Johns Hopkins University researchers discovered a gene and a protein called myostatin, first in mice, then in a breed of muscular cattle called the Belgian Blue.

"It's one of the reasons why I don't look like Arnold Schwarzenegger," said Dominic Wells, a professor who studies myostatin at Imperial College London.

Wells explained that virtually every animal on Earth has a gene that produces a muscle growth-inhibiting protein called myostatin. High levels of myostatin make it hard for the body to build muscle, and low levels of myostatin allow muscle to grow.

After the mice and cattle discovery, scientists found natural mutations in some dogs and sheep, but never in a human until 2004.

"In 2004 we reported on this German child, and to my knowledge, that is the only clear-cut documented case of a mutation in a human," said Dr. Se-Jin Lee, professor of molecular biology and genetics at Johns Hopkins University School of Medicine in Baltimore.