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Neuromuscular junction disorders in newborns and infants

Olaf A Bodamer, MD, PhD, FAAP, FACMG
Geoffrey Miller, MD
Section Editors
Marc C Patterson, MD, FRACP
Richard Martin, MD
Deputy Editor
John F Dashe, MD, PhD


Weakness and hypotonia in newborns can be caused by disorders of the neuromuscular junction. These rare conditions include transient acquired neonatal myasthenia gravis, congenital myasthenia, elevated levels of magnesium or aminoglycosides, and infantile botulism (table 1). They are characterized by abnormal neuromuscular transmission leading to muscle fatigability and weakness. Most of these disorders are transient, but congenital forms are permanent.


Transient neonatal myasthenia gravis occurs in 10 to 20 percent of infants born to mothers with myasthenia gravis [1]. Most mothers of affected infants have active clinical disease, although some may have no evidence of myasthenia or may be in remission [2,3].

Myasthenia gravis is an autoimmune disorder caused by antibodies that usually are directed against the acetylcholine receptor (AChR), resulting in postsynaptic inhibition of neuromuscular transmission [4,5]. (See "Pathogenesis of myasthenia gravis".)

Maternal AChR antibodies transferred to the fetus are responsible for transient neonatal myasthenia gravis [1]. Higher ratios of antibodies directed against the fetal versus the adult type of AChR in mothers with myasthenia gravis are correlated with an increased likelihood of transmitting the disorder [6].

Rarely, there are persistent myopathic sequelae related to the fetal acetylcholine receptor inactivation syndrome (FARIS). Although the pathophysiologic mechanism is not established, this condition is probably related to elevated levels of maternal AChR antibodies directed against the fetal subunit of the AChR receptor, causing abnormal endplate development of the embryonic neuromuscular junction in a subset of infants [7-9]. The facial and bulbar musculature may be particularly susceptible to permanent injury caused by this process.


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Literature review current through: Sep 2016. | This topic last updated: Jul 20, 2016.
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