Myostatin (formerly known as growth differentiation factor 8) is a growth factor that limits muscle tissue growth, i.e. higher concentrations of myostatin in the body may cause the individual to have less developed muscles. The myostatin protein is produced primarily in skeletal muscle cells, circulates in the blood and lymph and acts on muscle tissue, apparently by slowing down the development of muscle stem cells. The precise mechanism remains unknown.
Myostatin has been found in humans and several other mammals, as well as in birds and fish. Its functions in non-mammalian vertebrates appear to be somewhat conserved, as muscle-specific actions have been demonstrated in birds. However, it is produced in many different fish tissues, suggesting that it may regulate more than just muscle mass in these vertebrates.
In 2004, a German boy was diagnosed with a mutation in both copies of the myostatin-producing gene, making him considerably stronger than his peers. His mother, a former sprinter, has a mutation in one copy of the gene.[10][11][12][13][14][15]
An American boy born in 2005 was diagnosed with a clinically similar condition but with a somewhat different cause.[16] In contrast to the first case, this boy produces a functional myostatin, however he has a defect in his myostatin receptor so that his muscles do not respond to the myostatin signal.
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