The fetal/adult acetylcholine receptor antibody ratio in mothers with myasthenia gravis as a marker for transfer of the disease to the newborn.

High anti-fetal/anti-adult muscle anti-acetylcholine receptor (AChR) antibody (Ab) titer ratio is predictive of the occurrence of neonatal myasthenia gravis in a first child. The aim of the present study was to determine whether the ratio between the levels of antibodies is an intrinsic property of the mother's sera or varies with physiologic status such as pregnancy. We performed a longitudinal study of the levels of Ab directed against both fetal and adult AChRs and the ratio between them in 11 mothers with myasthenia gravis (MG). Sera were taken during, before, and after pregnancy. Absolute levels of Ab varied considerably during the time of observation as indicated by analyzing the maximum change between any two sample times during the study (adult mean percentage change 45.9 +/- 26.4; fetal 42.51 +/- 22.05). In contrast to this, the anti-fetal/anti-adult muscle AChR Ab titer ratio was much less variable (mean percentage change 16.66 +/- 10.11; p < 0.0033). The levels of the two Ab types yielded a correlation of 0.918, consistent with the stability of the ratio between them. This stability of ratio has practical value in the management of pregnancy and infant care in mothers with MG because the ratio at any time, before or during pregnancy, will predict whether the child will contract neonatal MG. We determined this for the first child, but further studies are necessary to establish if this remains true for subsequent pregnancies.