 animals treated with substances such as follistatin that block the binding of myostatin to its receptor have significantly larger muscles. Thus, reduction of myostatin could potentially benefit the livestock industry, with even a 20 percent reduction in myostatin levels potentially having a large effect on the development of muscles.
However, the animal breeds developed as homozygous for myostatin deficiency have reproduction issues due to their unusually heavy and bulky offspring, and require special care and a more expensive diet to achieve a superior yield. This negatively affects economics of myostatin-deficient breeds to the point where they do not usually offer an obvious advantage. While hypertrophic meat (e.g. from Piedmontese beef) has a place on the specialist market due to its unusual properties, at least for purebred myostatin-deficient strains the expenses and (especially in cattle) necessity of veterinary supervision place them at a disadvantage in the bulk market.
Performance enhancement in dogs
A 2007 NIH study in PLOS Genetics found a significant relationship in whippets between a myostatin mutation and racing performance. Whippets that were heterozygous for a 2 base pair deletion in the myostatin gene were significantly over-represented in the top racing classes. The mutation resulted in a truncated myostatin protein, likely resulting in an inactive form of myostatin.
Whippets with a homozygous deletion were apparently less able runners although their overall appearance was significantly more muscular. Whippets with the homozygous deletion also had an unusual body shape, with a broader head, pronounced overbite, shorter legs, and thicker tails. These whippets have also been called "bully whippets" by the breeding community due to their size. Despite the name "bully", these dogs tend to have a friendly and positive demeanour towards people as usual for whippets.
This particular mutation was not found in other muscular dog breeds such as boxers and mastiffs, nor was it found in other sighthounds such as greyhounds, Italian greyhounds, or Afghan hounds. The authors of the study suggest that myostatin mutation may not be desirable in greyhounds, the whippets' nearest relative, because greyhound racing requires more significant endurance due to the longer races (900 meters for greyhounds vs. 300 meters for whippets).
Effect in humans
Myostatin is active in muscles used for movement (skeletal muscles) both before and after birth. It normally restrains muscle growth, ensuring that muscles do not grow too large. Mutations that reduce the production of functional myostatin lead to an overgrowth of muscle tissue. Myostatin-related muscle hypertrophy has a pattern of inheritance known as incomplete autosomal dominance. People with a mutation in both copies of the MSTN gene in each cell (homozygotes) have significantly increased muscle mass and strength. People with a mutation in one copy of the MSTN gene in each cell (heterozygotes) also have increased muscle bulk, but to a lesser degree.
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 has a mutation in one copy of the gene.
An American boy born in 2005, Liam Hoekstra, was diagnosed with a clinically similar condition but with a somewhat different cause: his body produces a normal level of functional myostatin; but, because he is stronger and more muscular than most others his age, his doctor believes that a defect in his myostatin receptors prevents his muscle cells from responding normally to myostatin. Liam appeared on the television show World's Strongest Toddler.
A technique for detecting mutations in myostatin variants has been developed.
Further research into myostatin and the myostatin gene may lead to therapies for muscular dystrophy. The idea is to introduce substances that block myostatin. A monoclonal antibody specific to myostatin increases muscle mass in mice. Similar results in monkeys were obtained.
A two-week treatment of normal mice wi