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A genetic mutation has been found to double or even triple muscle mass of mammals and fish. One German boy with the mutation, before he was 5 years old, could hold 7-pound weights with arms extended, something many adults can't do.
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updated 6/21/2011 12:17:37 PM ET 2011-06-21T16:17:37

Genetic mutations that cause mammals — including humans — to develop super ripped muscles are now resulting in exceedingly buff fish, according to a paper in the latest issue of Animal Genetics.

The mutations can result in a doubling or even tripling of muscle mass in affected species. So far, at least two children have been documented as having such changes to their genes. One is a young, and very beefy, German boy.

"At birth, the boy appeared to be extraordinarily muscular, with protruding muscles in his thighs and upper arms," lead author Anneleen Stinckens, paraphrasing a report by pediatric neurologist Markus Schuelke, told Discovery News. "Before he was 5 years old, he could hold 7-pound weights with arms extended, something many adults cannot do. He has muscles twice the size of other kids his age and half their body fat."

Yet another boy, Liam Hoekstra, was diagnosed with a clinically similar condition. Stinckens said that, based on reports, Hoekstra was able to do pull-ups, inverted sit-ups, Olympic-style iron crosses and more just months after birth. He has even punched "holes into walls during tantrums," according to accounts, and once accidentally gave his mother a black eye.

Stinckens and her colleagues studied data on the phenomenon in known affected species that, in addition to humans, include cattle, mice, sheep and dogs. She explained that a certain protein, called the myostatin (MSTN) protein, has a negative effect on muscle growth. Mutations related to this protein can cause it to completely fail, or to exist in very low levels.

"Since the MSTN gene can no longer exhibit its proper function or the levels of MSTN are very low, the negative control that was exercised by the MSTN protein disappears and muscles can grow much larger than they are supposed to," Stinckens explained.

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It's unclear at present if there are any drawbacks related to a myostatin protein deficiency.

"Scientists fear that maybe the hearts of the boys will not be able to cope when they are growing; however, this has to be studied in due time," Stinckens shared, adding that double-muscled cattle can have "calving difficulties and a large, muscular tongue."

Since age-related muscle wasting, inherited disorders such as muscular dystrophy, and certain diseases affecting muscles are prevalent, medical experts hope future research may lead to better treatments and cures for problems affecting muscles. As a result, according to Stinckens and her team, scientists have induced myostatin-related changes in three types of fish so far: rainbow trout, medaka fish and zebrafish.

Perhaps the most successful of the three experiments was the work on rainbow trout. They became "extremely muscular," Stinckens said, acquiring what other researchers called "six pack" double muscles. The zebrafish also changed, becoming 45 percent heavier than their normal counterparts.

Se-Jin Lee is a professor in the Department of Molecular Biology and Genetics at Johns Hopkins University School of Medicine.

Lee told Discovery News that "there is considerable evidence that myostatin plays an important role in regulating muscle mass/growth in mammals and, as a result, there is an enormous amount of activity focused on attempting to target this pathway for various types of applications."

One may even lead to heftier fish on your dinner plate.

Lee concluded, "Whether this pathway is important in fish is not as well established, although there is significant interest in the possibility of exploiting this for aquaculture."

© 2012 Discovery Channel

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