From birth, she had generalized muscle weakness and delayed motor development, but later eventually acquired ambulation. However, after growing up, easy fatigability, mild muscle weakness in the proximal muscles of the extremities, dysphagia, and respiratory dysfunction reappeared upon infection and menstruation. Electrophysiological examination displayed waning in the repetitive stimulation test and repetitive compound muscle action potential in the nerve conduction velocity test. Genetic analysis revealed a novel heterozygous mutation in the COLQ gene (c.1216G>A p.G406R:c.600+2T>C), resulted in a definitive diagnosis of endplate AChE deficiency. When ephedrine (1.7 mg/kg/day) was administered, the patient promptly ceased to have easy fatigability and rescued from muscle weakness that appeared during menstruation and infection. She had settled in over the course of two years with no exacerbation of her symptoms.

We demonstrated that endplate AChE deficiency which causes muscle weakness exacerbated by infection and menstruation should be added as a new category in the differential diagnosis. We also demonstrated quick and long-lasting responsiveness by ephedrine even in an adult-onset case with CMS with this novel mutation.