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Conditions

Neuromuscular Disorders

 

What Is a Neuromuscular Disorder?

Neuromuscular disorders are a group of diseases that affect the nerves outside the brain and spinal cord (peripheral nerves) as well as skeletal muscles, such as those in the chest area, arms, and legs, and the space between the nerves and muscles (called the neuromuscular junction). These disorders can be stable and unchanging (static) or worsen over time (progressive). Some neuromuscular disorders are more severe and are present from birth (congenital), while others present during childhood, adolescence, or even adulthood. Common neuromuscular disorders include muscular dystrophy, myotonic dystrophy, spinal muscular atrophy, hereditary sensorimotor neuropathy (Charcot-Marie-Tooth (CMT) disease), myasthenia gravis, Guillan-Barré syndrome, and other muscle and nerve disorders (such as those caused by mitochondrial disease).

What causes a neuromuscular disorder?

Neuromuscular disorders in children are usually caused by genetic abnormalities, meaning that there are problematic changes (mutations) to the genetic code, which impairs normal protein production. 

Some genetic neuromuscular disorders are passed from generation-to-generation because only one mutation is required to cause disease (called autosomal dominant inheritance). As a result, we see families with an affected grandparent, parent, and child – all with the same disease. Two common examples of autosomal dominant neuromuscular diseases are Charcot-Marie-Tooth disease type 1A (CMT1A) and myotonic dystrophy type 1 (DM1).

Another way to inherit a genetic neuromuscular disease is called autosomal recessive inheritance, which requires two mutations – typically one from each parent. Because of the need for two mutations, it is very common for there to be no known family history of neuromuscular disease. Spinal muscular atrophy (SMA) is an example of autosomal recessive neuromuscular disease.

Yet another inheritance pattern is called X-linked (recessive). Mutations are passed along on the X-chromosome, which is a sex chromosome. Because females have two X chromosomes, they are rarely affected by X-linked recessive conditions. However, males only have one X chromosome (and one Y chromosome), so a mutation on their only X chromosome leads to disease. Becker and Duchenne muscular dystrophies and Charcot-Marie-Tooth disease X are all inherited in this fashion.

How are neuromuscular disorders diagnosed?

The vast majority of childhood neuromuscular disorders can be diagnosed with a blood or saliva genetic test alone. Sometimes, an EMG/NCS (electromyography/nerve conduction study) test is necessary. EMG/NCS is a test performed in the clinic where nerve and muscle functioning is assessed with a combination of small stimulations to the nerves and small needles placed within the muscle. Rarely is a muscle or nerve biopsy required. A biopsy involves making a small incision, removing a piece of tissue, and examining it in a laboratory. Clinical examinations can also lead to a diagnosis. 

Because some disorders respond best to early treatment, it’s essential to get an accurate diagnosis as soon as you suspect your child has a neuromuscular disorder. Early treatment can also help prevent some secondary effects of the conditions. 

Although most neuromuscular disorders can’t be cured, proper treatment can lower the severity and slow the progression of symptoms. At Gillette Children’s, we design treatments to maximize function, increase independence, and improve the quality of your child’s life. 

Sometimes, medicines can slow the loss of muscle function. Although this is rare, an accurate diagnosis paired with proper management can help lessen the effects of a neuromuscular disorder.

 

Signs and Symptoms of Neuromuscular Disorders

Most neuromuscular disorders cause obvious muscle weakness and/or sensory problems (such as numbness, tingling, or burning). As mentioned above, depending on the condition, some worsen over time (progress) while others remain stable over the lifetime. With some diseases, symptoms are apparent at birth.

Many children with neuromuscular disorders develop gross motor skills such as learning to roll, crawl, stand, and walk, though they might learn new skills more slowly than typically developing children. For example, most babies hold their heads up at 2 to 3 months and sit by themselves at 6 months. Babies who have a neuromuscular disorder might develop those skills later or not at all. 

As they grow older and larger, some babies and young children might lose certain skills or have more problems with them. For example, they might have trouble getting up from the floor or have unusual or labored walking patterns. Younger children might have difficulty swallowing, eating, drinking, and learning to talk. Infants with severe neuromuscular disorders move very little and cry weakly. 
 
The Gillette Infant and Toddler Development Clinic can help determine next steps if your baby is experiencing any of these difficulties.

Muscle weakness describes a lack of muscle strength to move a limb or joint. Weakness can be generalized (affecting all muscles) or affect only certain muscles – especially early in the course of disease. For example, in CMT, we expect initial weakness to present in the feet and ankles (distal) while in Duchenne muscular dystrophy, we expect the first signs of weakness to present in the large muscle groups around the hips and pelvis.

Muscle tone is different from muscle strength. Muscle tone refers to the degree of resistance or tension in a resting/relaxed muscle. Unlike strength, muscle tone is not expected to change over time.

Hypotonia (low muscle tone) in babies can be one sign of a neuromuscular disorder. Young children who display symptoms of hypotonia are often described as “floppy,” "loosey-goosey," having low tone, or being "double jointed." Low tone by itself doesn’t necessarily mean a child has a neuromuscular disease. However, a knowledgeable team should evaluate hypotonia as soon as possible to ensure appropriate care and treatment.

As neuromuscular disorders progress—especially if not well managed by a team of specialists—a child might experience secondary conditions, such as: 

  •  Muscle or joint stiffness (contractures) 
  •  Deformed bones (especially the spine) 
  •  Difficulty breathing and eating   

Because most neuromuscular disorders can’t be cured, treatment aims to avoid or lessen the severity of secondary issues. 

 

Neuromuscular Disorder Care at Gillette

Gillette’s patient-centered approach to care means that not only do we provide expert care throughout our patients’ entire childhoods, but we also care for medically complex adults with genetically confirmed neuromuscular disorders. 
 
If your child has a neuromuscular disorder, you’ll work closely with our physicians and genetic counselors. Gillette’s internationally recognized experts will identify the condition, helping you understand its causes and the likelihood of other family members developing it. 

Your child's care team might include:

 

Neuromuscular disorders we treat

There are hundreds of neuromuscular disorders, many with subtypes related to specific genetic causes. Although some muscle disorders look similar and have similar treatments, most require unique treatment strategies. Gillette’s world-renowned specialists design a comprehensive, individualized treatment plan for every child. In caring for neuromuscular disorders, Gillette serves children and medically complex adults.

Duchenne muscular dystrophy (DMD): This common neuromuscular disorder affects males almost exclusively, but some ~20% of female carriers show mild disease characteristics. With DMD, an abnormal gene on the X chromosome prevents the production of a critical muscle protein called dystrophin. During childhood, muscle cells break down, resulting in muscle weakness, lost mobility, breathing difficulties, and heart problems. DMD does have several FDA-approved treatments available to help slow the progression of disease, so early diagnosis is crucial.

Becker muscular dystrophy (BMD): BMD is like DMD, but with this disorder, the abnormal gene does make some dystrophin. As a result, some males with this form experience milder symptoms than those with Duchenne muscular dystrophy, although the range of severity is wide.

Facioscapulohumeral muscular dystrophy: This disorder mainly affects the face, shoulders, and upper arms (the definition of “facioscapulohumeral”). Muscle weakness results from a defect on chromosome 4, found throughout the body. Over time, other muscles and body parts can show slow—but progressive—weakening. 

Congenital muscular dystrophy (CMD): This group of disorders leads to severe muscle weakness noticeable from birth. CMD affects both males and females. Most forms affect bone development, heart and lung function, brain function and mobility. Types of CMD include:

  • Merosin-deficient muscular dystrophy
  • Ullrich congenital muscular dystrophy
  • Integrin-deficient
  • Fukuyama muscular dystrophy
  • Muscle-eye-brain disease
  • Walker-Warburg syndrome
  • CMD with rigid spine syndrome

Myotonic muscular dystrophy: This type affects all or most muscles and several organs and systems. The term “myotonic” refers to an inability to relax a muscle normally.

Spinal muscular atrophy (SMA) affects the motor nerves that control voluntary muscle movement. SMA makes activities such as crawling, walking, breathing, and eating difficult for children. 

SMA is caused by a change (mutation) in the survival motor neuron 1 gene (SMN1 gene). The SMN1 gene makes Survival Motor Neuron protein, which helps motor neurons grow and function properly. Without enough SMN protein, the motor neurons don't survive, leading to muscle weakness.

In most cases, both parents of a child with SMA are carriers. In a small number of cases, SMA develops from a new change (mutation) in the formation of either the egg or the sperm. Roughly one in 50 people are SMA carriers.

There are currently 3 FDA-approved therapies for the treatment of 5q SMA (the most common form). Early diagnosis and initiation of treatment is crucial.

CMT disease (also known as hereditary sensorimotor neuropathy) affects the nerves between the spinal cord and limbs. These nerves are responsible for transmitting messages to the muscles and from the skin/sensory organs. As a result, muscle tissue begins to lose mass and weaken over time. CMT has many types, each linked to specific genetic mutations, which in turn determine the severity of the condition and its most appropriate treatment.

FA causes progressive damage to the spinal cord and the nerves that extend from the spinal cord to the muscles. FA also affects the part of the brain that helps coordinate movement (the cerebellum) and can affect the heart muscle and function. FA can cause muscle weakness and loss of balance and coordination. There is currently one FDA-approved medication for FA patients aged 16 and older.

Mitochondrial myopathies are characterized by malfunctioning mitochondria. Mitochondria are the parts of muscle cells known as organelles that create the energy needed for the cell to do its job – so in muscles, for the muscle to tighten (or contract). Myopathy is a term that refers to a disease of muscle tissue. Causes and results vary, and new forms are discovered frequently. Most types lead to some form of muscle weakness. Others affect specific parts of the body. The most common mitochondrial myopathies are:

  • Kearns-Sayre syndrome
  • Leigh syndrome and maternally inherited Leigh syndrome
  • Mitochondrial DNA depletion syndrome
  • Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes
  • Mitochondrial neurogastrointestinal encephalomyopathy
  • Myoclonic epilepsy with ragged red fibers
  • Neuropathy, ataxia, and retinitis pigmentosa
  • Pearson syndrome
  • Progressive external ophthalmoplegia

Metabolic myopathies disrupt the ability of muscles to turn nutrients (usually glucose or lipids/fats) into energy.

Normally, that conversion process happens thousands of times every second and involves many steps, each linked to a nutrient, protein, or other substance. Understanding the exact type of metabolic myopathy is important, because treatments exist for some specific deficiencies.

JDM is a common form of inflammatory myopathy. Unlike the other muscle problems discussed thus far, JDM is not inherited or genetic and often happens in previously completely healthy patients. It can involve the muscles or their blood supply. With JDM, a red or purplish rash can develop on the face, neck, shoulders, or upper arms and legs. The inflammatory process can lead to muscle deterioration, muscle weakness, and joint problems.

 

Integrated Care

If your child has a neuromuscular disorder, our specialists work closely with you to ensure accurate testing and develop a customized treatment plan. Because most neuromuscular conditions aren’t curable, regular checkups are necessary to slow the progression of symptoms and avoid secondary complications.

Your child will benefit from the supportive treatments of our program, which is supported by the Muscular Dystrophy Association. Treatments might include rehabilitation therapies, assistive technology or medicine—as well as services for family members.