Congenital Myasthenic Syndromes

Congenital myasthenic syndromes (CMS) are a heterogeneous group of neuromuscular disorders that share clinical features with other neuromuscular transmission disorders but differ from acquired syndromes and among each other by their underlying molecular, genetic, and cellular pathogenesis. CMS may present in infancy or may not be recognized until childhood or later. Thus, a CMS may resemble neonatal or adult-onset myasthenia gravis (MG) or Lambert-Eaton syndrome (LES). Although impairment of neuromuscular transmission gives rise to similar clinical presentations, the sophisticated analysis of biopsied intact, muscle ifbers from CMS patients using electrophysiologic, microscopic, and molecular techniques has identified several varieties of CMS in which impairment of neuromuscular transmission occurs through distinct molecular and cellular mechanisms. In many cases, recording of evoked or spontaneous miniature endplate potentials (MEPPs) or miniature endplate currents (MEPCs) or single channel currents has identified the presence and type of pre- or postsynaptic defect of neuromuscular transmission. Coupled with electron microscopic, biochemical, and genetic data, these studies have led to the identification of the affected protein, gene, and mutation in several patients. This detailed molecular information has provided insights into disease mechanisms that have begun to guide the development of therapeutic strategies.