Congenital myasthenic syndromes are a group of rare hereditary conditions caused by a gene change that results in muscle weakness, which worsens with physical activity. Any muscles used for movement can be affected, including muscles that control speaking, chewing and swallowing, seeing and blinking, breathing, and walking.
There are many types of congenital myasthenic syndromes, depending on which gene is affected. The changed gene also determines many of the signs and symptoms and severity of the condition.
Congenital myasthenic syndromes are usually identified at birth or early childhood and are lifelong conditions.
There is no cure for congenital myasthenic syndromes. Medications are generally an effective treatment for muscle weakness symptoms. Which medication works depends on which gene is identified as the cause of the congenital myasthenic syndrome. Rarely, some children may have a mild form that doesn't need treatment.
Congenital myasthenic syndromes are typically identified at birth. But if signs and symptoms are mild, the condition may not be identified until childhood, or rarely, early adulthood.
Depending on the type of congenital myasthenic syndrome, the severity of signs and symptoms vary greatly, from minor weakness to the inability to move. Some symptoms can be life-threatening.
Common to all congenital myasthenic syndromes is muscle weakness that worsens with physical activity. Any muscles used for movement can be affected, but the most commonly affected muscles are those that control movement of the eyelids and eyes and chewing and swallowing.
During infancy and early childhood, progressive loss of essential voluntary muscle activity occurs with muscle use. Impaired muscle weakness can result in:
Depending on the type of congenital myasthenic syndrome, other signs and symptoms can include:
Talk to your doctor if you observe any signs listed above in your child or if you have concerns about your own signs or symptoms.
Caused by any one of more than 30 identified genes, the type of congenital myasthenic syndrome depends on which gene is affected.
Congenital myasthenic syndromes are classified by which location is affected in the neuromuscular junction ― the area that provides signals (impulses) between the nerve cells and the muscle cells to trigger movement (synapses). Disrupted signals that cause loss of muscle function can occur in different locations:
Some types of congenital myasthenic syndromes are the result of congenital disorders of glycosylation. Glycosylation is a complex chemical process that plays a role in regulating communication between cells. Glycosylation defects can adversely affect the transmission of signals from nerve cells to muscles.
Congenital myasthenic syndromes are most commonly inherited in an autosomal recessive pattern. That means both parents must be carriers, but they do not typically show signs of the condition. The affected child inherits two copies of the abnormal gene — one from each parent. If children inherit only one copy, they won't develop the syndrome, but they'll be carriers and possibly pass the gene to their own children.
Rarely, congenital myasthenic syndromes can be inherited in an autosomal dominant pattern, meaning that only one parent passes on the affected gene. In some cases, the affected gene occurs randomly and is not inherited. In other cases, no gene can be identified.
A child is at risk of a congenital myasthenic syndrome if both parents are carriers of a gene known to cause the syndrome. The child then inherits two copies of the gene. Children who inherit only one copy of the gene from one parent typically won't develop the syndrome but will be carriers.
Your doctor will do a physical examination ― including a neurological exam ― and review symptoms and medical history to check for signs of a congenital myasthenic syndrome. Your doctor may also order tests to exclude other conditions with similar symptoms.
The following tests can help diagnose a congenital myasthenic syndrome and determine how severe the disorder is.
Genetic testing involves examining your DNA, the chemical database that carries instructions for your body's functions. Genetic testing can reveal changes, sometimes called mutations, in genes that cause congenital myasthenic syndromes. Genetic testing may also be recommended for family members.
Talking to your doctor, a medical geneticist or a genetic counselor about why the test is being done and how the results may affect you is an important step in the process of genetic testing.
Rarely, some children with mild congenital myasthenic syndromes may not need treatment.
Medications aren't a cure, but they can improve muscle contraction and muscle strength in people with congenital myasthenic syndromes. Which medications are effective depends on the type of affected gene. Medications that are effective for one type of syndrome may be ineffective for another type, so genetic testing is recommended before starting medications.
Medication treatment options may include:
Supportive treatments depend on the type and severity of the congenital myasthenic syndrome. Options may include:
Regular follow-up appointments with a team of medical professionals provides ongoing care and may help prevent certain complications. Your health care team can link you with appropriate support for home, school or work.
Pregnancy can worsen symptoms of congenital myasthenic syndromes, so close monitoring during and after pregnancy is required.
Caring for a child or family member with a congenital myasthenic syndrome can be stressful and exhausting. You may not know what to expect, and you may worry about your ability to provide the care needed.
Consider these steps to prepare yourself:
Make an appointment with your doctor if you notice signs or symptoms common to congenital myasthenic syndromes. After the initial evaluation, you may be referred to a doctor trained in evaluating and treating these conditions.
Here's some information to help you prepare for your appointment, as well as what to expect from your doctor.
You may want to prepare answers to these questions:
After getting detailed information about the symptoms and your family's medical history, your doctor may order tests to help with diagnosis and plan treatment.
