After a novel neuromuscular gene panel became available, we identified a mutation in the MUSK gene (muscle-specific kinase), confirming a diagnosis of congenital myasthenic syndrome. This group of rare disorders are caused by mutations in genes encoding the neuromuscular junction.

The slow-channel CMS (SCCMS) is an autosomal dominant postsynaptic defect caused by mutations in genes encoding alpha, beta, delta, or epsilon subunits of the acetylcholine receptor resulting in a functional defect which is an increase of the opening time of the receptor.

The typical phenotype of DOK7 CMS is of a limb girdle weakness with associated nonspecific myopathic features. The presence of stridor in early onset cases and the observation of tongue wasting may be specific clues. Worsening in adulthood is common, particularly affecting bulbar and respiratory function.

Mutations in many genes can cause congenital myasthenic syndrome. Mutations in the CHRNE gene are responsible for more than half of all cases. A large number of cases are also caused by mutations in the RAPSN, CHAT, COLQ, and DOK7 genes.