IgM monoclonal gammopathy and neuropathy in two siblings.

A sister and a brother with a progressive mixed axonal and demyelinating polyneuropathy were found to have a monoclonal IgM gammopathy of kappa and lambda type, respectively. Sural nerve and cutaneous nerve specimens obtained by biopsy showed deposits of IgM on myelin sheets. Sera from both patients contained antibodies directed to bovine peripheral nerve myelin as determined by ELISA technique and to normal human peripheral nerve myelin as demonstrated by indirect immunofluorescence histochemistry. These siblings may have a genetic predisposition to the formation of autoantibodies with peripheral nerve myelin as the target for the immune attack.