INTRODUCTION: In the newborn, myasthenia can present either as transient neonatal myasthenia or as a congenital syndrome. At present at least 8 syndromes involving neonatal neuromuscular junction (NMJ) malfunction have been described; one caused by the passage of transplacental antibodies from mother to child, while all but one of the rest are inherited. Inheritance in all but two syndromes is autosomal recessive. One is an autosomal dominantly inherited illness; in another the mode of inheritance is not clear. The deficit in function of the NMJ is presynaptic in 3 instances, at the junctional gap in 1, and postsynaptic in at least 3 other syndromes. DEVELOPMENT: We will review the clinical symptoms, as well as neurophysiologic and genetic testing available for diagnosis. We explain how, at least, in some of the syndromes, one can begin appropriate therapy based on clinical, neurophysiological and simple pharmacological testing. CONCLUSION: However, in many cases, it becomes necessary to refer the patient or a tissue sample, usually an intercostal nerve muscle preparation, to one of the very few centers in the world where in vitro neurophysiologic, microstructural and genetic procedures leading to a more precise diagnosis can be performed.
