Antiacetylcholine receptor antibody in neonatal myasthenia gravis.

Maternal titers to antiacetylcholine receptor antibody (anti-AChR Ab) were higher in two mothers with myasthenia gravis (MG) who had infants with neonatal MG than the nearly normal values in two mothers with MG who had unaffected infants. In one unaffected infant, another IgG antibody crossed the placenta, but an IgM antibody did not. In neonates there seems to be a correlation between the concentration of anti-AChR Ab and the presence and severity of the neonatal syndrome. The absence of fetal symptoms of MG and the delayed onset or worsening of some cases of neonatal MG may be due to high fetal levels of alpha-fetoprotein and its decline in concentration in infants after birth.