Congenital Myasthenic Syndrome (CMS) is a group of rare disorders of the neuromuscular junction characterized by early onset progressive muscle weakness. CMS4A is a slow channel CMS caused by mutations in the CHRNE gene. CMS4A has an early onset and symptoms can vary in intensity from minor fatigue to complete loss of mobility. Ptosis, opthalmoparesis, dysphagia, feeding problems, hypotonia, bulbar muscle weakness and respiratory problems are commonly seen. 

Diagnosis of CMS based solely on clinical evaluation can be difficult and patients can sometimes be mistaken to have myasthenia gravis or other similar disorders. Genetic tests for underlying mutations can help confirm a CMS diagnosis. Identification of the exact form of CMS and the underlying mutation is also essential for administering treatment because unlike other forms of CMS, slow channel CMS is not treated with cholinesterase inhibitors but with quinidine and fluoxetine.

CMS4A has been found to follow an autosomal dominant pattern of inheritance with incomplete penetrance but autosomal recessive cases have also been reported. 

The disorder is caused by mutations in the CHRNE gene which encodes the epsilon subunit of the acetylcholine receptor. Mutations in CHRNE produce a prolonged opening of the acetylcholine receptor channel resulting in slowed decay of end plate currents, calcium overload of the synaptic region and ultimately myopathy of the endplate and postsynaptic membrane.