Arthrogryposis multiplex congenita with maternal autoantibodies specific for a fetal antigen.

Fetal arthrogryposis multiplex congenita (AMC) is characterised by non-progressive multiple joint contractures, which may result in fetal death, and is heterogeneous in origin. It can associate with maternal myasthenia gravis and autoantibodies to muscle acetylcholine receptor (AChR). We found maternal antibodies that selectively inhibit the fetal form of the AChR in a mother who herself had no features of myasthenia gravis. Maternal autoantibodies specific for fetal antigens could be an unrecognised cause of other congenital disorders.