IgM monoclonal antibody against terminal moiety of GM2, GalNAc-GD1a and GalNAc-GM1b from a pure motor chronic demyelinating polyneuropathy patient: effects on neurotransmitter release.

We describe a patient with a pure motor chronic demyelinating polyneuropathy with an IgM monoclonal component showing anti-GM2, GalNAc-GD1a and GalNAc-GM1b reactivity whose common epitope appears to be -[GalNAcbeta1-4Gal(3-2alphaNeuAc)beta1]. We used intracellular recording to study how IgM from this patient affected neurotransmitter release in the mouse diaphragm in vitro. Adding serum (and specifically, the purified monoclonal IgM component) blocked the nerve-evoked response in both quantal content and evoked endplate potential (EPP) amplitude in a complement-independent and reversible manner. The IgM increased the frequency of spontaneous miniature endplate potentials (MEPPs) in a complement-dependent and reversible manner but had no effect on MEPP amplitude.