Neonatal myasthenia gravis in the infant of a myasthenic mother in remission.

A 26-year-old woman was in spontaneous clinical remission from myasthenia gravis (MG) for six months, yet gave birth to a full-term infant with typical neonatal MG. It is believed that transplacental transfer of anti-acetylcholine (ACh) receptor antibodies is responsible for neonatal MG; therefore, neonatal MG represents an in vivo assay of the pathogenic potential of anti-ACh receptor antibodies in 2 human individuals. Anti-ACh receptor antibodies were present in both mother and infant (titers 12.3 X 10(-9) and 4.4 X 10(-9) moles per liter, respectively) at the time of birth, and both mother's and infant's sera accelerated the degradation of ACh receptors in myotube cultures. This case suggests that "host factors" unique to the individual appear to modify or even determine whether the presence of anti-ACh receptor antibodies will result in clinical myasthenia.