Neonatal myasthenia gravis and the role of agalactosyl IgG

Neonatal autoimmune diseases are thought to be due to the transfer of maternal autoantibodies. However, there is a puzzling lack of correlation between maternal autoantibody titres and disease in the neonate. So far, no factor reliably predictive of neonatal disease has been found. Agalactosyl IgG is a variable feature of normal IgG. Preliminary studies indicated that the percentage of agalactosyl IgG is lower in the serum of normal neonates, than in the serum of the mother at delivery. Since raised % agalactosyl IgG is often associated with autoimmune disease we sought to determine whether this relationship holds true in a neonatal autoimmune disease. We measured the % agalactosyl IgG in paired maternal-cord sera from patients with myasthenia gravis, some of whom had offspring with neonatal myasthenia gravis. We found that the percentage of agalactosyl IgG was significantly higher in affected than in unaffected neonates. Moreover % agalactosyl IgG was higher in sera of affected neonates than in serum from their mothers, while unaffected infants of mothers with myasthenia had %Gal(0) lower than their mothers, mimicking the normal situation. This suggests that in affected neonates a high proportion of the IgG is synthesised by the baby itself rather than derived from the mother. This agrees with previous evidence based on the presence of idiotypes not found in the mother which implied that the neonates with neonatal myasthenia gravis produce their own autoantibodies.