The US National Library of Medicine defines myostatin related muscle hypertrophy as a muscular disorder that affects the skeletal muscles. Patients have reduced body fat and increased muscle size, which can be up to twice the normal mass. The disorder is passed down genetically; it is a rare condition, though the prevalence of the condition is not known. The symptoms of myostatin related muscle hypertrophy can cause increased muscle strength, but does not cause other medical problems.
Myostatin related muscle hypertrophy is caused by a mutation to the MSTN gene, which the US National Library of Medicine states is involved in myostatin production. The MSTN gene is part of the transforming growth factor beta, or TGFβ, subfamily; this subfamily is responsible for the growth and development of tissues, with the MSTN gene specifically involved with skeletal muscles. The US National Library of Medicine adds that the normal MSTN gene restricts muscle growth; however, when mutated, muscle growth is uninhibited. The MSTN gene is cytogenetically located at 2q32.2, and myostatin related muscle hypertrophy is the only disorder associated with a mutated MSTN gene.
The amount of excess muscle growth from this form of muscle hypertrophy is dependent on whether the patient has one or two copies of the mutated gene. The US National Library of Medicine states that the inheritance pattern of the disorder is incomplete autosomal dominance. If the patient has homozygotes (two copies) of the mutation, the amount of muscle are significantly larger compared to the general population. Larger muscle mass is also found in patients with heterozygotes (one copy) of the mutation, but not as big as patients with homozygotes of the mutated MSTN gene.
The National Institutes of Health (NIH) states that testing is done on the patient’s skeletal muscle size and fat pad thickness. The muscles are measured with either an ultrasound examination, DEXA (dual energy x-ray absorptiometry), or MRI (magnetic resonance imaging). The subcutaneous fat pad thickness is measured with either an ultrasound or with a caliper (a device to measure the width).
Symptoms and Prognosis
The major symptoms of myostatin related muscle hypertrophy are reduced subcutaneous fat pad thickness and increased muscle size, according to the US National Library of Medicine. Patients may or may not have an increase in muscle strength. However, patients with the disorder have normal intellect and cardiac function. This disorder is not known to cause any other medical problems, and should not affect the patient’s quality of life.
Genetic Home Reference: Myostatin-Related Muscle Hypertrophy (https://ghr.nlm.nih.gov/condition=myostatinrelatedmusclehypertrophy)
Genetic Home Reference: MSTN (https://ghr.nlm.nih.gov/gene=mstn)
Gene Reviews: Myostatin-Related Muscle Hypertrophy (https://www.ncbi.nlm.nih.gov/bookshelf/picrender.fcgi?book=gene&&partid=1498&blobtype=pdf)