Congenital myopathy

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at July 27, 2016
StartDiseasesCongenital myopathy

A wide range of various muscle disorders (myopathies) that can be evident as soon as a child is born are referred to as congenital myopathies. These disorders tend to affect 6 out of 100,000 children born each year. Depending on the type of disorder, a child may have many different types of symptoms.

Contents

Definition & Facts

Any sort of disorder that results in malfunctioning muscles and is present before or immediately after childbirth is called a congenital myopathy. It typically results in weakened muscles due to abnormalities of the muscle fibers on a cellular level.

There are six broad types of congenital myopathies that are categorized based on their distinct symptoms and causes. The most common type of congenital myopathy is a nemaline myopathy. Other congenital myopathies include multicore myopathy, congenital fiber type disproportion, and central core disease. Both cylindrical spirals myopathy and centronuclear myopathy (myotubular myopathy) are quite rare.

Symptoms & Complaints

Overall, the primary symptom of a congenital myopathy is muscular weakness that is present since birth. Infants with a congenital myopathy tend to be described as "floppy," and they do not move as normally as other infants do.

Some newborns with a severe congenital myopathy will have difficulty breathing or difficulty eating. As they grow, many infants will not meet average developmental milestones for their age group, including sitting or rolling.

These symptoms tend to be evident in most babies with a myopathy, but each type of congenital myopathies may have a few more unique symptoms. A nemaline myopathy often causes scoliosis or deformed skeletons later in life. People with a myotubular myopathy tend to feel pain whenever they move for an extended period of time, and it is also associated with intellectual disability. Only boys are affected by myotubular myopathy.

A multicore myopathy causes about half of all people with this type of congenital myopathy to become gradually weaker over time. In contrast, patients with a congenital fiber type disorder often improve over time, and they just have weakened stamina. Central core myopathy is not progressive, but it normally is not evident until early childhood.

Any muscle in the body can be affected by a congenital myopathy, so some people have trouble with eye movements or fine motor skills while others have difficulty walking. Depending on the severity, people may be almost entirely unable to move, or they may feel tired or clumsy after periods of movement.

Causes

The basic cause of all congenital myopathies is that muscle cells are not working the way that they should be. However, the underlying cause for these malfunctioning muscles will depend on the specific type of myopathy. Nemaline myopathy is caused by nine genetic mutations that affect the actin filaments needed for muscle contraction, and these mutations may be inherited or spontaneous.

Myotubular myopathy is also genetic and results from mutations in the DNM2 gene and the BIN1 gene. Central core myopathy is caused by a genetic mutation in the RYR1 gene that raises body temperatures to excessive levels and causes muscular breakdown.

Congenital fiber type disproportion happens when people have too many type 1 muscle fibers (slow-twitch muscles) and not enough type 2 muscle fibers (fast-twitch muscles). Multicore myopathy's cause is similar to central core myopathy, but in addition to the muscular breakdown, patients also have too many type 1 muscle fibers (slow-twitch) like those with fiber type disproportion. Cylindrical spirals is a very rare type of myopathy that happens when abnormal muscle membranes with a spiral pattern are merged into surrounding muscle fibers.

Diagnosis & Tests

A diagnosis for a congenital myopathy may occur soon after birth, if an infant is having trouble moving, breathing, or eating. However, it may take up to a few years to notice that a child is not hitting developmental milestones for movement. If a congenital myopathy is suspected, there are three ways that a doctor can confirm the diagnosis:

  • An electromyography test can be used to detect the electric signals generated by muscles and see if they are functioning on a normal level.
  • The most common diagnosis method is a muscle biopsy. Though this is slightly invasive, it is the most accurate diagnosis method, and examining the muscle cells can show the specific abnormality. This helps doctors to determine the specific type of congenital myopathy that a patient has.
  • Though genetic testing is not commonly done, new advancements make it possible to look for mutations known to cause muscular issues.

Treatment & Therapy

Unfortunately, there are not effective cures for most types of congenital myopathies. Survival outlooks tend to be best for people with nonprogressive forms of myopathy. Individuals with progressive types of congenital myopathy may eventually become unable to breathe.

Central core myopathy is currently the only type that can be effectively treated through the administration of salbutamol which is a bronchodilator that helps to prevent weakness and poor stamina. People born with very severe forms of congenital myopathy may need help eating or breathing from medical machines.

Other types of less severe myopathies generally rely on physical therapy to alleviate any symptoms. Certain exercises can be used to strengthen muscles even if they are weaker than average, and physical therapy may be successful enough to help patients move normally.

Patients with myotubular myopathy often need pain medications to deal with the muscle pain and nerve pain associated with their condition. Some people may need surgery to deal with skeleton deformities which are often caused by weak muscles not supporting bones properly. 

Prevention & Prophylaxis

There is no known way of preventing the spontaneous genetic mutations that may cause certain types of congenital myopathy. Genetic counseling and testing can help expecting parents learn whether they are carrying a rare, recessive gene that may result in a congenital myopathy. Prenatal diagnostic testing may also be advised in some situations.