Congenital myasthenic syndrome (CMS)

Congenital myasthenic syndrome (CMS) is a group of hereditary conditions characterized by muscle weakness (myasthenia) and easy fatiguibility , ie, the muscle strength worsens with physical exertion or exercise.

There are many types of CMS, grouped into three main categories , including those that affected the :

• Neuromuscular junction ( the synapse or the junction between the nerve cell and the muscle cell)
• Pre-neuromuscular junction (nerve cell)
• Post-neuromuscular junction (muscle cell)

Common features

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 skeletal muscles used for movement can be affected in this condition, and the affected children could have difficulty in walking. Due to muscle weakness, affected infants may have feeding difficulties. Development of motor skills such as crawling or walking may be delayed. Depending on the different types, symptoms of CMS vary from mild to severe, but generally include muscle weakness, easy fatiguibility and ptosis (droopy eyelids). The earlier the onset of CMS, the more severe the symptoms are likely to be.

Causes

Mutations in many genes can cause congenital myasthenic syndrome.

Diagnosis

Comprehensive nerve conduction study and genetic testing are both useful to confirm the diagnosis.

Treatment

Medical treatment is available for some forms of congenital myasthenic syndrome to improve muscle strength and fatigue symptom.