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Muscular Baby Has Genetic Mutation

Finding might lead to new treatments for muscle-wasting diseases

WEDNESDAY, June 23, 2004 (HealthDayNews) -- A German child born with unusually well-developed muscles has prompted researchers to study the child's genes and follow his growth and development.

The hope is that the boy's genetic profile might provide clues that could help in developing treatments for muscle-wasting diseases, such as muscular dystrophy.

In fact, the German researchers have already found that the child has a mutation in the gene that produces myostatin.

"Myostatin is a growth factor that regulates muscle mass during embryonal development as well as after birth. Myostatin prevents the muscles from growing too big," said one of the researchers, Dr. Markus Schuelke, a professor of molecular genetics and a principal investigator in the department of neuropediatrics at the Charite University Medical Center in Berlin.

The scientists report their discovery in the June 24 issue of the New England Journal of Medicine.

What's potentially exciting about finding this mutation in humans is that this research might help develop treatments for muscle-wasting diseases. Other studies have shown that when mice have their myostatin genes knocked out, their muscles grow to twice the size of other mice, according to Schuelke. But, he cautioned, long-term safety data isn't yet known, so any possible therapies for humans may be years away from development.

"Careful, long-term animal studies and observation of humans with myostatin mutations over a long period of time have to be done before [any potential therapies] may safely enter a clinical trial," he said.

The good news is that Schuelke and his colleagues have been able to follow the boy for almost five years, and he appears to suffer no ill effects from the lack of myostatin.

Schuelke first examined the boy when he was a newborn, and noticed the large muscles on the baby's upper legs and upper arms. Ultrasound examination confirmed that the child's muscles were about twice as large as would be expected. The baby otherwise appeared normal.

Other members of the child's family are reportedly stronger than average, but only the mother was available for DNA testing. His mother had been a professional athlete prior to becoming pregnant.

The researchers tested for possible causes for the over-developed muscles in the boy, such as an excess of testosterone or insulin-like growth factor and found no abnormal levels.

Because the baby's increased muscle was similar to that found in mice and in cattle lacking the gene that produces myostatin, the researchers checked the mother's and child's genetic profile. They discovered the mother had a mutation in one copy of the myostatin gene and that both copies of the baby's myostatin gene were defective. Humans inherit one copy of each gene from each parent.

The boy was 4 1/2 years old when the current study was completed. The researchers are concerned about ill effects the mutation might have on his heart muscle, but so far his cardiovascular system seems normal.

But Dr. Elizabeth McNally, director of cardiovascular research at the University of Chicago, said the boy is still very young and that problems could occur later in his life.

"The hope is that he's going to be fine. In large animal models, they seem to be OK," she said.

In an accompanying editorial in the same issue of the journal, McNally said that "this study documents how effective this pathway [for muscle growth] can be in humans, and my hope for this pathway is that it will be helpful for treating people with degenerative disorders."

However, McNally also expressed concern that people may use any potential treatments for developing muscles for non-medical uses.

"We don't know the long-term medical consequences. If you have a disease like muscular dystrophy, then the benefits outweigh the potential risks," McNally said.

But, she added, that's not the case for athletes or others trying to develop large muscles. "You can see from the history of steroid use, people will do things to grow muscle even though there are negative consequences."

More information

For more information on muscular dystrophy, visit the National Institute of Neurological Disorders and Stroke.

SOURCES: Markus Schuelke, M.D., professor, Molecular Genetics, principal investigator, Neuropediatrics, Charite University Medical Center, Berlin, Germany; Elizabeth McNally, M.D., Ph.D., director of cardiovascular research, the University of Chicago; June 24, 2004, New England Journal of Medicine; photo courtesy of New England Journal of Medicine
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