NINDS :
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All forms of myasthenia are due to problems in the communication between nerve cells and muscles. Most involve the activities of neurotransmitters. Neurotransmitters are chemicals that allow neurons to relay information from one cell to the next. For neurotransmitters to be effective, the nerve cell must release the neurotransmitter properly, and the muscle cell must be able to detect the neurotransmitter and respond to its signal properly.
The most common type of myasthenia, myasthenia gravis, is caused by an abnormal immune response in which antibodies block the ability of the muscle to detect the neurotransmitter. Congenital myasthenia, however, differs from myasthenia gravis because the disrupted communication isn't caused by antibodies, but by genetic defects.
There are several different subtypes of congenital myasthenia, each the result of a specific genetic mutation. Since all types of myasthenia are due to the inability of nerves to trigger muscle activity, they all involve weakness, although there is some variability in the specific muscles affected.
Symptoms of congenital myasthenia usually appear in the first few years of childhood, but may not be noticeable until much later, occasionally remaining unrecognized until adulthood. If the symptoms begin in infancy, they usually appear as "floppiness" and a failure to meet developmental milestones, such as rolling over or sitting up. Some infants may also have episodes of choking or pauses in breathing. If the symptoms begin in toddlers or preschool children, they appear as weakness during physical activities or an inability to perform age-appropriate actions, such as running or climbing. In addition, if eye muscles are involved, children may have droopy eyelids, "lazy eye," or double vision. If mouth or throat muscles are involved, children may have difficulty speaking or swallowing. An important characteristic of myasthenia is that the weakness worsens during continuous activity, with strength returning, at least partially, after resting.
Congenital myasthenia is an inherited (genetic) disorder. All but one known subtype are recessive disorders, which means that a child will have to have two copies of the abnormal gene (one from each parent) in order to develop the disease. To diagnose congenital myasthenia, a neurologist will test various muscles to determine if they grow weaker with repeated activity. The doctor will also test the electrical activity of nerves and muscles using electromyography (EMG) and nerve conduction tests (NCS). Blood tests are often used to determine if antibodies could be causing the symptoms. Genetic tests may be ordered.
MalaCards based summary :
Congenital Myasthenic Syndrome, also known as
congenital myasthenia, is related to
postsynaptic congenital myasthenic syndromes and
slow-channel congenital myasthenic syndrome, and has symptoms including
facial paresis An important gene associated with Congenital Myasthenic Syndrome is
CHRNE (Cholinergic Receptor Nicotinic Epsilon Subunit), and among its related pathways/superpathways are
Neuroactive ligand-receptor interaction and
Glycerophospholipid metabolism. The drugs
Ephedrine and
Pseudoephedrine have been mentioned in the context of this disorder. Affiliated tissues include
eye,
testes and
skeletal muscle, and related phenotypes are
dysphagia and
ptosis
Disease Ontology :
12
A neuromuscular junction disease that is characterized by weakness and easy fatiguability resulting from a genetic defect at the junction where the nerve stimulates muscle activity that result in muscle weakness and may affect nerve cells (presynaptic), muscle cells (postsynaptic) or the space between nerve and muscle cells (synaptic).
Genetics Home Reference :
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Congenital myasthenic syndrome is a group of conditions characterized by muscle weakness (myasthenia) that worsens with physical exertion. The muscle weakness typically begins in early childhood but can also appear in adolescence or adulthood. Facial muscles, including muscles that control the eyelids, muscles that move the eyes, and muscles used for chewing and swallowing, are most commonly affected. However, any of the muscles used for movement (skeletal muscles) can be affected in this condition. Due to muscle weakness, affected infants may have feeding difficulties. Development of motor skills such as crawling or walking may be delayed. The severity of the myasthenia varies greatly, with some people experiencing minor weakness and others having such severe weakness that they are unable to walk.
Some individuals have episodes of breathing problems that may be triggered by fevers or infection. Severely affected individuals may also experience short pauses in breathing (apnea) that can lead to a bluish appearance of the skin or lips (cyanosis).
NIH Rare Diseases :
52
Congenital myasthenic syndromes (CMS) are a group of genetic conditions that all include muscle weakness that gets worse with physical activity. There are many subtypes of CMS with different symptoms, severity, and treatments. Most people with CMS develop symptoms in infancy or by early childhood, but the age at which symptoms begin can vary. Symptoms range from mild to severe muscle weakness and may get worse over time or only occur periodically. The muscles of the face, neck, throat, eyes and limbs are most affected. There are at least 32 genes associated with CMS. Most are inherited in an autosomal recessive pattern. Genetic testing is necessary to tell the difference between subtypes. Treatment is based on managing the symptoms, and may differ depending on the subtype. The long-term outlook is not well understood and differs greatly from person to person.
KEGG :
36
Congenital myasthenic syndromes (CMS) are a heterogenous group of genetic disorders caused by mutations in several proteins that compose the neuromuscular junction (NMJ) apparatus on which synaptic formation and function depend. The majority are recessively inherited. The disorders of the NMJ cause weakness and fatigue.
Wikipedia :
74
Congenital myasthenic syndrome (CMS) is an inherited neuromuscular disorder caused by defects of several...
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Rare neurological diseases 
