Myasthenia Gravis Symptoms & Causes

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At Boston Children’s Hospital, we know how important it is for parents and families to understand their child’s medical concerns. We’ve provided answers to many commonly asked questions about JMG in the following pages, and when you meet with our team of doctors, they’ll be able to explain your child’s condition and treatment options fully.

What is JMG?

  • JMG is an autoimmune disease, a type of disorder in which the body's immune system reacts against itself and attacks its own healthy cells and tissue.
  • In the most common type of JMG, the immune system creates antibodies that attack receptor sites for acetylcholine, a neurotransmitter that activates muscle movement.
  • When these receptor sites are damaged or destroyed, the affected muscles do not receive enough acetylcholine.
  • Without acetylcholine to stimulate movement, the muscles become weak and tired after a period of activity.
  • A child with JMG will experience fluctuating muscle weakness that may last throughout their lives. The degree of muscle weakness and the muscles that are affected will vary from person to person.
  • With treatment, symptoms usually become more sporadic, and some children go into remission for long periods of time before needing another treatment intervention.
  • Some people with JMG experience a myasthenic crisis, a life threatening condition in which the muscles used for breathing become very weak and cause severe breathing problems.

What are the different types of MG?

There are two types of MG in children:

Transient neonatal MG

  • Between 10 and 25 percent of babies born to mothers with MG may have this temporary form of the condition, which occurs when antibodies common in MG cross the placenta to the developing fetus.
  • Neonatal MG usually lasts only a few weeks and babies are not at greater risk for developing MG later in life.

Juvenile MG (JMG)

  • This form of the autoimmune disorder develops in children and adolescents.
  • It is a life-long condition that may go in and out of remission (symptom-free periods).
  • This type of MG accounts for 10-15 percent of all cases of MG.
    • Congenital myasthenic syndrome (CMS) is a very genetic disease of the neuromuscular junction. Both males and females are equally affected and that two copies of the gene, one inherited from each parent, are necessary to have the condition.
    • Symptoms of CMS usually begin in infancy or early childhood; this is generally a lifelong condition.

How serious is JMG?

People who receive effective treatment for JMG can significantly improve their muscle strength, experience long periods of remission and lead normal lives. However, not receiving treatment for JMG can have serious consequences.  A child with significant muscle weakness may injure himself during activities such as walking down a flight of stairs or riding a bike.

The most serious complication of JMG is myasthenic crisis; this generally occurs when patients have symptoms throughout their body (generalized myasthenia) as opposed to patients who only have symptoms in their eyes (ocular myasthenia).

  • Myasthenic crisis is a life threatening complication in which the muscles used for breathing become weak and cause severe respiratory problems. Potential triggers for myasthenic crisis include stress, acute illnesses, surgery, or an overdose of certain medications.  Myasthenic crisis requires immediate medical attention.

Is JMG curable?

There is no cure for JMG yet. However, effective treatment can significantly improve a child’s muscle strength and may increase the duration of symptom-free periods. 


What causes JMG?

JMG occurs in the following way:

  • Neurotransmitters are chemicals in the brain, spinal cord, and neuromuscular junction that send electrical signals from one neuron to another, or from a neuron to a muscle fiber. Different neurotransmitters control and regulate various bodily functions and emotions. The neurotransmitter that connects neurons to muscle fibers is called acetylcholine.
  • Normally, acetylcholine is released from the end of a neuron and travels across the synapse before binding to special receptor sites on the muscle fiber.
  • In the case of JMG, the immune system creates antibodies that damage or destroy the acetylcholine receptors. When these antibodies bind to the receptors, they prevent the neuron from sending signals to initiate muscle contraction.  This causes the muscle weakness that is associated with JMG.


What are the symptoms of JMG?

JMG is characterized by muscle weakness that typically gets worse later in the day or after a period of activity.  However, symptoms of JMG may be difficult to detect because they usually fluctuate. They may also resemble those of other conditions, and may be overlooked. If you observe the following signs in your child, you may want consult your child’s doctor to get an accurate diagnosis:

  • drooping eyelids or double vision
  • dysarthria (difficulty speaking)
  • dysphasia (difficulty swallowing)
  • fatigue
  • muscles that become progressively weaker after periods of activity or as the day progresses
  • weak neck muscles
  • problems walking
  • lopsided facial expressions

The severity of symptoms and the pattern of muscles affected vary from person to person. Every person with JMG doesn’t experience all of these symptoms, and a person’s clinical picture can change over time.

Symptoms of JMG can worsen due to :

  • alcohol use
  • fatigue and sleep deprivation
  • taking certain medications, especially penicillamine or interferons
  • certain antibiotics or cardiovascular drugs (in certain cases, these drugs may be used in patients with JMG, but the prescribing physician must be aware of the JMG and monitor the patient closely.)

Questions to ask your doctor

You will probably have a lot of questions on your mind before meeting with your child’s doctor. At the appointment, it can be easy to be overwhelmed with information and forget the questions you wanted to ask.

A lot of parents find it helpful to jot down questions beforehand. That way, when you talk to your child’s clinician, you can be sure that all your concerns are addressed. Remember that physicians are open to learning from families too. Attend conferences, read up on updated materials and don’t be afraid to share what you have learned.

Some questions you might ask include:

  • How should I talk to my child about this condition and his health?
  • Do I need to restrict my child’s physical activity?
  • Do I need to make any other changes to my child’s home and school routines?
  • How will JMG affect my child’s vision?
  • What does his long-term treatment plan involve?
  • What resources can you point me to for more information?
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