Congenital myasthenic syndrome is a group of genetic disorders characterized by fatigable weakness of skeletal muscle that worsens with physical exertion with onset at or shortly after birth or in early childhood.  Any of the skeletal muscles can be affected, most commonly facial and bulbar musculature, affecting sucking and swallowing, and leading to dysphonia.  Other clinical features may include hypotonia (due to the axial and limb muscle weakness), ptosis and ophthalmoplegia (due to ocular muscles weakness).  The diagnosis of CMS is based on clinical features and the treatment may be with AChE inhibitors and/or the potassium channel blocker 3,4-diaminopyridine (3,4-DAP)

CMS4C is transmitted as an autosomal recessive pattern, and is caused by mutations in the CHRNE gene encoding the epsilon (ε) component of the AChR subunits.  To date, 90 different mutations have been reported; these mutations alter the ε subunit, leading to an increase or a decrease in AChR protein signaling.  Altering the AChR protein signaling impairs cell-to-cell communication at the neuromuscular junction; as decreased signaling causes muscle weakness due to a decrease in muscle movement, while increased signaling can damage muscle cells and also cause weakness.