Arthrogryposis multiplex congenita (AMC) is a nonprogressive condition characterized by multiple joint contractures in two or more body regions. 1 Most cases are sporadic and result from lack of fetal movement in utero. AMC is often associated with hypotonia, micrognathia, lung hypoplasia, intrauterine growth retardation, and perinatal death. Some cases may have a genetic basis, but in many environmental factors may be involved.

AMC is sometimes associated with maternal myasthenia gravis (MG). 2 AMC-M1 is an asymptomatic woman who has one surviving firstborn son, but subsequently had a 35-week intrauterine death and five terminations for AMC. AMC-M2 has one surviving daughter (second child) and had a total of three stillborn babies before myasthenia was eventually diagnosed. 3, 4 She has since been treated for her MG and has had a fifth pregnancy with a successful outcome (unpublished observations). Both these women had high levels of serum anti-AChR antibodies, and their plasmas and IgG preparations were shown to inhibit the function of fetal AChR4, 5 with no effect on adult AChR. Thus, antibodies specific for a functional site on fetal AChR appear to be responsible for causing AMC in these women (see also Vincent et al. in this volume).