Neuromuscular junction disorders in newborns and infants
- Olaf A Bodamer, MD, PhD, FAAP, FACMG
Olaf A Bodamer, MD, PhD, FAAP, FACMG
- Park Gerald Chair in Genetics and Genomics
- Associate Chief, Genetics and Genomics
- Boston Children’s Hospital/Harvard Medical School
- Geoffrey Miller, MD
Geoffrey Miller, MD
- Professor of Pediatrics and Neurology
- Yale University
- Section Editors
- Marc C Patterson, MD, FRACP
Marc C Patterson, MD, FRACP
- Section Editor — Pediatric Neurology
- Professor of Neurology, Pediatrics, and Medical Genetics
- Chair, Division of Child and Adolescent Neurology
- Mayo Clinic College of Medicine
- Richard Martin, MD
Richard Martin, MD
- Section Editor — Neonatology
- Professor, Pediatrics, Reproductive Biology, and Physiology & Biophysics
- Case Western Reserve University School of Medicine
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.
NEONATAL MYASTHENIA GRAVIS
Transient neonatal myasthenia gravis occurs in 10 to 20 percent of infants born to mothers with myasthenia gravis . 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 . 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 .
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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- NEONATAL MYASTHENIA GRAVIS
- Clinical features
- CONGENITAL MYASTHENIC SYNDROMES
- Clinical features
- ELEVATED MAGNESIUM OR AMINOGLYCOSIDE LEVELS
- Aminoglycoside toxicity
- INFANT BOTULISM
- Clinical features
- SUMMARY AND RECOMMENDATIONS