Motor neuron syndrome and monoclonal IgM with antibody activity against gangliosides GM1 and GD1b

We demonstrated that an IgM M‐protein from a patient with motor neuron syndrome had antibody activity against gangliosides GM1, GD1b, and asialo GM1. Studies with a sugar‐binding lectin suggested that the epitope in the patient's M‐IgM involved the Gal(β1‐3) GalNAc moiety. Immunohistological techniques demonstrated staining of axons in the lumbar roots, granular cells, and white matter in the cerebellum by the patient's M‐IgM. We propose that, in this case, an autoimmune mechanism of motor neuron syndrome associated with a monoclonal protein is most likely.