What Is Congenital Muscular Dystrophy?

Congenital muscular dystrophy (CMD) is the name for a category of genetic muscle diseases that first appear near birth or within two years of life. It’s an umbrella term for more than 30 conditions, which can cause a range of symptoms. Generally, they are all associated with the progressive weakening or degeneration of muscles.

This article discusses the types of congenital muscular dystrophy, causes, symptoms, diagnosis, and treatment options.

Signs and Symptoms

Scientists have identified over 30 different types of congenital muscular dystrophy, so symptoms vary greatly. Almost all forms of congenital muscular dystrophy include muscular symptoms, whereas some subtypes may also include intellectual disabilities or breathing or heart problems.

Muscular dystrophies can lead to difficulty moving, lack of muscle tone, difficulty breathing, delays in achieving movement or motor-skills milestones, or, in some cases, intellectual disability. Rate of progression differs and depends on the individual and the type of congenital muscular dystrophy.

Muscular Symptoms

Common muscular symptoms include:

• Muscle weakness 
• Low muscle tone 
• Joints that are too loose or seem out of place (dislocated) 
• Trouble straightening limbs 
• Very stiff spines, or spines that can't completely straighten

Non-muscular Symptoms

Some non-muscular symptoms include:

• Trouble eating
• Issues with brain or eye formation 
• Trouble swallowing 
• Breathing problems 
• Heart problems 
• Intellectual disability or other learning problems 

Types of Congenital Muscular Dystrophy

While subtypes of congenital muscular dystrophy used to be categorized by the physical symptoms of the condition or the area of the body in which it was first discovered, they are now identified based on the underlying biology of the condition.

CMD can be classified according to which proteins are affected by the disease. The three main categories are:

• Merosinopathies (LAMA2-related congenital muscular dystrophy)
• Collagenopathies (collagen VI-related myopathies)
• Dystroglycanopathies (alpha-dystroglycanopathy-related muscular dystrophy)

Merosinopathies

Merosinopathies, such as LAMA2 congenital muscular dystrophy, affect the function of proteins within the extracellular matrix. This matrix surrounds muscle cells, provides structural support, and helps keep cells healthy.

When all is well, proteins within the extracellular matrix can repair muscles, translate signals between muscle cells, or even help muscles move. When a genetic mutation changes the function of one of those proteins, these functions break down.

This is the case in LAMA2 CMD. Mutations arise in a gene called LAMA2, which is responsible for making a protein called merosin. Merosin binds to the membrane on muscle cells and to the intracellular matrix, and helps keep muscle fibers stable.

When merosin is lacking or missing, it can lead to weakened or unstable muscle fibers. This results in the common muscular symptoms seen with LAMA2 congenital muscular dystrophy. These include a lack of muscle tone, or weak muscles in the chest that lead to breathing problems.

Collagenopathies

Collagen VI-related CMD occurs when proteins that make up the extracellular matrix itself are affected. 

Collagen VI is made up of three “strands.” Each strand is created from a specific gene. If one of those genes has a mutation, the strand can either become deficient or absent. That leads to an unstable extracellular matrix that can't support healthy muscle cells. In time, muscle weakness or tightening can develop.

Some forms of collagen VI-related congenital muscular dystrophy include:

• Bethlem Myopathy
• Ullrich congenital muscular dystrophy

Dystroglycanopathies

This category of CMD occurs when genetic mutations cause the malfunction of a protein called alpha-dystroglycan. This protein usually binds the extracellular matrix to a structural support system inside the cell called the cytoskeleton. This helps muscle cells maintain their structural integrity. 

Disruptions in alpha-dystroglycan can affect how long muscle cells survive before they break down and die. But this condition can also affect the brain, because alpha-dystroglycan plays a role in brain development.

Some forms of alpha-dystroglycanopathy include:

• Walker-Warburg Syndrome 
• Muscle-eye-brain disease
• Fukuyama CMD
  

Causes

Congenital muscular dystrophy is caused by genetic mutations that affect proteins related to muscle function. These changes can be passed from parents to children, though they may also arise on their own.

In general, the gene mutations related to congenital muscular dystrophy are recessive. This means that two copies of the gene (one from each parent) are needed for the condition to manifest. 

This also means two parents without the condition can give birth to a child with CMD. This is because those parents are carriers. They each have one copy of the gene, but they don’t show any symptoms of congenital muscular dystrophy. If the child inherits both copies, they will develop the condition. 

Generally speaking, this means if both parents are carriers, the child has a 25% chance of developing the disease, a 50% chance of being a carrier (with no symptoms), and a 25% chance of not carrying the gene at all.

There are some forms of congenital muscular dystrophy that can also be inherited in an autosomal dominant manner, which means that only one copy of the gene is needed. For example, Bethlem myopathy is usually inherited this way. In this case, there would be a 50% chance of a person with Bethlem myopathy passing the condition on to their child.

Diagnosis

Congenital muscular dystrophy can be diagnosed in several ways. The process would start with a healthcare provider taking a full medical and family history of the patient.

Electrodiagnostic tests can be performed, which measure electrical signals in muscles or nerves. This often rules out nerve disorders.

They can also order certain blood tests. One common blood test measures levels of creatine kinase (CK), a protein that circulates when muscles are damaged. If there are high levels of that protein present, it may be a sign that muscles are being damaged by a condition.

To determine exactly how muscles are being damaged, a healthcare provider could also perform a muscle biopsy. A small sample of a muscle is removed, which is then sent to a lab for analysis, assessing for damage under a microscope.

Finally, genetic testing can reveal whether there’s a gene responsible for the patterns of muscle damage.

Treatment

There’s no cure for congenital muscular dystrophy at present. There are also no approved medications to treat CMD, so the current options are all designed to help manage symptoms.

Guidelines suggest that regular checkups to evaluate potential heart and breathing problems are one way to monitor the condition.

Because there are so many types of congenital muscular dystrophy and severity differs widely, treatment plans tend to be highly individualized.

Some common treatment options include:

• Physical therapy to improve muscle strength, including gentle exercise
• Occupational therapy to improve fine motor skills
• Braces or other mobility aids 
• Surgery to correct scoliosis (curvature of the spine)
• Breathing assistance, including sleep apnea devices to prevent stopping and starting breathing throughout the night or, in some severe cases, ventilation

Summary

Congenital muscular dystrophy is a group of genetic muscle diseases appearing around birth. It involves the weakening and degeneration of muscles over time. CMD can cause a lack of mobility and muscle tone, as well as difficulty breathing and eating and possibly intellectual disability.

A Word From Verywell

Congenital muscular dystrophy can be an upsetting diagnosis, especially considering the limits it may place on your or your child's life. Work with your healthcare provider to determine the best treatment plan available. Though there are minimal treatment options at present, research is ongoing to develop new medications and therapies to treat CMD.