What Is Myostatin-Related Muscle Hypertrophy?

Myostatin-related muscle hypertrophy—also called muscle hypertrophy syndrome—is a rare genetic disorder that causes significantly increased muscle size and decreased body fat.

Up to double the amount of muscle mass can develop in people with the condition. 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, particularly in the thighs, calves, and upper arms.

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

Myostatin-related muscle hypertrophy does not cause any other symptoms or lead to any known medical or health problems. For some people with the condition, bone strength also improves with increased muscle mass.

Causes of Myostatin-Related Hypertrophy

Myostatin is a protein present in the skeletal muscles that move the body. The role of myostatin is to make sure that the muscles do not grow too big. 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 on physical exam by seeing significantly large muscles throughout the body and very little body fat. Many people who are diagnosed later in life report having above-average strength as well.

Myostatin-related hypertrophy is also diagnosed with imaging. Ultrasound can be performed 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 the amount of muscle mass a person has. The images are produced using radio waves and strong magnetic forces.

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

The procedure is most commonly 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 nearly 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 of their parents, they will have significantly more muscle mass and strength than normal.

If one mutated MSTN gene is inherited, they will still have larger than normal muscles, 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 on the inside of the cheek.

Summary

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

The condition is typically recognized at birth or during infancy. It is diagnosed with physical examination, imaging to measure muscle mass and body fat, and genetic testing to confirm a mutation in the MSTN gene.

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

A Word From Verywell

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

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