Congenital myasthenic syndrome from a MUSK gene mutation.

Slowly progressive neuromuscular symptoms often have a genetic basis. We present the case of a woman in her 40s with gradually progressive symmetrical weakness and respiratory muscle involvement. Extensive investigation found no specific cause. 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.