Between 10% and 20% of neonates born to mothers with
myasthenia gravis (MG) develop neonatal MG due to the transfer of maternal
autoantibodies across the placenta. Neonatal MG can occur in infants born not only from mothers with
acetylcholine receptor (AChR) or muscle-specific
tyrosine kinase (
MuSK)
antibodies but also from mothers without detectable muscle
antibodies. The low incidence rate may be due to specific
autoantibody characteristics that differ among individuals, but a
genetic predisposition in some infants is possible. The majority of reported neonatal MG cases are anti-AChR antibody-positive (AChR-MG), and a high anti-fetal/anti-adult AChR titer ratio in the mother is predictive of its occurrence. However, patients with
anti-MuSK antibody-positive MG (
MuSK-MG) are more likely to experience exacerbations during pregnancy and have a higher probability of developing neonatal MG than AChR-MG patients. Moreover, maternal
MuSK-MG may be associated with early-onset and more severe manifestations of neonatal MG. Although
cholinesterase inhibitors have been effectively used for treating neonatal AChR-MG, neonatal
MuSK-MG may be more difficult to treat with this type of medication. Maternal
MuSK-MG usually greatly benefits from
intravenous immunoglobulin (
IVIG) and
plasma exchange. In neonatal MG,
IVIG is considered for severely affected infants with
MuSK-MG, but the efficacy of
IVIG remains unclear. Although exchange transfusion may be a management adjunct, its clinical benefits are controversial. As the
therapy-induced reduction of
autoantibodies may be advantageous for fetal outcomes, maternal MG should be effectively treated during pregnancy. However, caution of
drug contraindication during pregnancy and lactation must be exercised to avoid unwanted effects for the fetus and neonate. In the future, MG caused by anti-
lipoprotein receptor-related
protein 4 or other
antibodies might be also identified in pregnant women and neonates. Therefore, the determination of
autoantibody specificity is essential for successful management.