Congenital myasthenic syndromes

**Definition:** Congenital myasthenic syndrome (CMS) is a heterogeneous group of genetically determined diseases. There are four well-defined categories: Congenital myasthenic syndrome with presynaptic defect, Synaptic basal lamina-associated CMS, Congenital myasthenia with postsynaptic defect, CMS with glycosylation deficiency, and the remaining category is that of unidentified CMS.

**Long definition:** A heterogeneous group of disorders characterized by a congenital defect in neuromuscular transmission at the neuromuscular junction. This includes presynaptic, synaptic, and postsynaptic disorders (that are not of autoimmune origin). The majority of these diseases are caused by mutations of various subunits of the nicotinic acetylcholine receptor (receptors, nicotinic) on the postsynaptic surface of the junction. These are characterized by fatigable weakness involving ocular, bulbar, and limb muscles secondary to congenital abnormalities leading to disordered transmission at the neuromuscular junction.