Myostatin-related muscle hypertrophy is a rare condition characterized by reduced body fat and increased muscle size. Affected individuals have up to twice the usual amount of muscle mass in their bodies. They also tend to have increased muscle strength. Myostatin-related muscle hypertrophy is not known to cause any medical problems, and affected individuals are intellectually normal.

Variants (also known as mutations) in the MSTN gene cause myostatin-related muscle hypertrophy. The MSTN gene provides instructions for making a protein called myostatin, which is active in muscles used for movement (skeletal muscles) both before and after birth. This protein normally limits muscle growth, ensuring that muscles do not grow too large. Variants that reduce the production of functional myostatin lead to an overgrowth of muscle tissue.

Normal Function

The MSTN gene provides instructions for making a protein called myostatin. This protein is part of the transforming growth factor beta (TGFβ) superfamily, which is a group of proteins that help control the growth and development of tissues throughout the body. Myostatin is found almost exclusively in muscles used for movement (skeletal muscles), where it is active both before and after birth. This protein normally limits muscle growth, ensuring that muscles do not grow too large. Myostatin has been studied extensively in mice, cows, and other animals, and it appears to have a similar function in humans.

Researchers are studying myostatin as a potential treatment for various muscular dystrophies that cause muscle weakness and wasting (atrophy).

Health Conditions Related to Genetic Changes

Myostatin-related muscle hypertrophy

At least one variant (also known as a mutation) in the MSTN gene has been found to cause myostatin-related muscle hypertrophy, a rare condition characterized by increased muscle mass and strength. The variant, which is written as IVS1+5G>A, disrupts the way the gene's instructions are used to make myostatin. As a result, cells produce little or no functional myostatin. A loss of this protein in muscle cells leads to an overgrowth of muscle tissue. It does not appear to cause any other medical problems in affected individuals.

Other Names for This Gene

• GDF-8
• GDF8
• GDF8_HUMAN
• growth differentiation factor 8

Genomic Location

Myostatin-related muscle hypertrophy has a pattern of inheritance known as incomplete autosomal dominance. People with a variant in both copies of the MSTN gene in each cell (homozygotes) have significantly increased muscle mass and strength. People with a variant in one copy of the MSTN gene in each cell (heterozygotes) also have increased muscle bulk, but to a lesser degree.