Myostatin: the gene that regulates muscle growth

Myostatin is a protein that tells muscle cells when to stop growing — and a mutation in its gene can cause exceptionally powerful muscle development. In 1997, Johns Hopkins University researchers Mcpherron and Lee discovered the gene, which soon came to be called the “Schwarzenegger gene” informally. Since then, myostatin has been a firmly established topic in bodybuilding and sports medicine.

What myostatin is and how it works

GDF-8 belongs molecularly to the TGF-β (transforming growth factor beta) family. In scientific terms, it is called growth and differentiation factor-8, or GDF-8. Put simply, this protein works as a brake: if the body produces too much of it, muscle mass stays modest; if the gene is mutated and less myostatin is produced, muscles grow by leaps and bounds.

It was initially thought that myostatin was produced only by skeletal muscles. New Zealand researchers, however, found it in heart muscle as well. Researchers at Purdue University even identified the myostatin gene in the mammary glands of pigs. This points to a much broader role than first suspected.

Myostatin is believed to play its most important role in prenatal muscle development — during the fetal stage. Exactly how this gene affects muscle recovery after birth is still under investigation. What is known: in animal studies, neither changing nutrition nor administering exogenous growth hormone altered myostatin levels. The gene works largely independently.

Myostatin in animal studies: 30 to 300% more muscle

In cattle, the result was clear: animals with a mutated myostatin gene had 30% more muscle mass than individuals with a normal gene structure. That figure alone caused great excitement in the scientific community.

In rats, the results were even more dramatic. A mutation in the myostatin gene produced 200–300% greater muscle mass in rats. Numbers like these don’t leave you indifferent — especially when you consider what they could mean for humans.

Today, the myostatin gene has been found in many vertebrates: cattle, pigs, chickens, turkeys and humans too. Each new species adds a piece to the puzzle.

Myostatin in humans — what science knows

In 2004, an article titled “A ‘strongman’ gene found in a human” appeared on the website of the Estonian Genome Center (www.genomics.ee) — clear confirmation that the myostatin gene exists in humans and that its mutations cause unusually rapid and powerful muscle development.

A concrete example: a German boy whose mother is a professional sprinter was able, at four and a half years old, to hold a three-kilogram weight in each hand with his arms extended horizontally. An international group of researchers identified a mutation in his myostatin gene. The study was published in the New England Journal of Medicine (vol 350, p. 2682).

Johns Hopkins researcher Se-Jin Lee said the goal is to find a way to regulate myostatin function — primarily to slow the progression of degenerative muscle diseases and extend patients’ lifespans. So myostatin is not of interest to bodybuilders alone: it is a broader medical question.

Bodybuilding authority Mauro Dipasquale has suggested that solving the myostatin puzzle could prove revolutionary. Dan Duchaine and Bill Roberts have likewise argued that if the expression of the myostatin gene could be inhibited, today’s top physiques could grow to a completely new level.

An interesting side note: BALCO laboratories have studied bodybuilder Flex Wheeler extensively. An extremely rare mutation of the myostatin gene, “exon 2”, was identified in Flex — meaning he has more muscle fibers than ordinary people.

High myostatin levels have also been observed in HIV-positive people. That does not mean, however, that GDF-8 alone causes muscle wasting — the relationship is more complex and still needs further research.

FAQ: myostatin, training and genetics

Can training affect myostatin levels?
Animal studies show that neither nutrition nor growth hormone changes myostatin levels. Exactly how training affects this gene in humans is still under investigation.

What happens if the myostatin gene is mutated?
In animals, 30–300% greater muscle mass was observed, depending on the species. In humans, isolated cases of exceptionally rapid muscle development have been documented, but such mutations are very rare.

Could myostatin research benefit the treatment of diseases?
Researchers hope that inhibiting myostatin could help patients with muscle diseases such as muscular dystrophy. Studies are under way, but clear treatment options have yet to be found.

Summarized and translated by Janar Rückenberg. Sources: Mcpherron & Lee, 1997; New England Journal of Medicine vol 350, p. 2682; www.genomics.ee Estonian Genome Center.

Author: Janar Rückenberg

Source: WHO – physical activity.

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