What is myostatin-related muscle hypertrophy?

Myostatin-related muscle hypertrophy, also known as muscle hypertrophy syndrome, is a rare genetic disorder that causes a significant increase in muscle size and a decrease in body fat.

Up to double the amount of muscle mass can develop in people with the disease. Their strength can be normal or above average.

This article discusses myostatin-related muscle hypertrophy, including its symptoms, causes, diagnosis, and treatment.

Symptoms of Myostatin Related Muscle Hypertrophy

The main symptom of myostatin-related muscle hypertrophy is the presence of enlarged muscles, especially in the thighs, calves, and upper arms.

Oversized muscles are usually identified at birth or during infancy. Infants and children with the disease often measure above average on weight charts.

Myostatin-related muscle hypertrophy causes no other symptoms and has no known medical or health problems. For some people with the disease, bone strength also improves with increased muscle mass.

Causes of myostatin-related hypertrophy

Myostatin is a protein found in skeletal muscles that move the body. The role of myostatin is to ensure that the muscles do not grow too large. Instructions for the production of the protein are provided by the MSTN gene.

Mutations in the MSTN gene cause myostatin-related muscle hypertrophy.

How is myostatin-related hypertrophy diagnosed?

Myostatin-related hypertrophy is first recognized during a physical examination by seeing significantly large muscles throughout the body and very little body fat. Many people diagnosed later in life also report having above average strength.

Myostatin-related hypertrophy is also diagnosed by imaging. Ultrasound can be done to measure the size of an affected person’s muscles and the thickness of specific fat pads to compare them to what is considered normal. The technique uses sound waves to produce an image of the area being tested.

In some cases, magnetic resonance imaging (MRI) can be used to measure a person’s muscle mass. Images are produced using radio waves and strong magnetic forces.

Dual-energy X-ray absorptiometry (DEXA) can be done to assess the amount of muscle mass and body fat a person has.

The procedure is most often used to assess bone density, but it also provides images of soft tissue, such as muscle and fat.

Body fat can also be tested using calipers. The device gently pinches the skin on several parts of the body to measure the amount of fat directly under it. The measurements are used to estimate the amount of total body fat. However, it is not as accurate as using imaging to measure body fat.

Genetic testing can be done to look for mutations in the MSTN gene.

Genetics and testing

Myostatin-related hypertrophy is inherited in an incomplete autosomal dominant pattern. If a person inherits a mutated MSTN gene from both parents, they will have significantly more muscle mass and strength than normal.

If a mutated MSTN gene is inherited, they will still have bigger muscles than normal, but it won’t be as significant. Genetic testing for myostatin-related hypertrophy can be done using a blood or saliva sample or a swab from inside the cheek.

Summary

Myostatin-related muscle hypertrophy is a rare genetic condition that causes a person to build significantly more muscle mass than is considered normal. It also causes lower amounts of body fat. People with myostatin-related muscle hypertrophy may have normal strength or be stronger than average.

The condition is usually recognized at birth or during infancy. It is diagnosed by physical examination, imaging to measure muscle mass and body fat, and genetic testing to confirm an MSTN gene mutation.

No treatment is needed for myostatin-related hypertrophy. The condition is not painful and does not cause any other health or medical issues.

A word from Verywell

You might be concerned about the onset of myostatin-related muscle hypertrophy in your child, but keep in mind that the condition does not cause developmental delays and is not painful.

If you think your child might have myostatin-related muscle hypertrophy or another muscle condition, talk to your healthcare provider. They can do the tests to make sure you get an accurate diagnosis.