Follow-up study of muscle function in children of mothers with myasthenia gravis during pregnancy.

Most infants whose mothers have myasthenia gravis are healthy at birth, but 10% to 15% have a transient neonatal form of myasthenia gravis. In this study, the muscular function and neuromuscular transmission were examined in 31 children, aged 3 months to 31 years (median, 10 years), of 15 myasthenic mothers. Eleven of these children had had the neonatal form of myasthenia gravis. The children were examined clinically and with neurophysiologic methods. Blood samples were taken for HLA typing, creatine kinase levels, and myoglobin and acetylcholine receptor antibody studies. Twenty-nine of the 31 children had no signs of neuromuscular disease. Two children (who had had neonatal myasthenia gravis) had a moderate stationary myopathy, probably unrelated to the myasthenia gravis of their mother. Creatine kinase levels were normal for all subjects. Acetylcholine receptor antibody levels were similar to those of a control population. The HLA type B8 antigen was not significantly more prevalent in the children who had had neonatal myasthenia gravis than in the healthy children. Neonatal myasthenia gravis in a previous sibling was the only factor in the material that predicted the occurrence of myasthenic symptoms in the neonatal period.