[Immunochemical study of serum in the diagnosis of mu-chain disease].

An abnormal protein revealed in the serum of a patient with an unknown lymphoproliferative disorder proved to be micron-paraprotein: micron-heavy chain complexes of various molecular weight totally lacking light chains. The results of immunochemical analysis of this case are compared with the published data on micron-chain disease. The following immunochemical features typical for micron-chain disease were observed in this patient: anodal mobility of paraprotein, failure to reveal it by serum electrophoresis, that is, absence of M-gradient, and presence of Bence Jones protein, type x in the urine and the serum. The peculiarity of the case consists in a high tendency of free x-chains to form complexes, and therefore in their marked electrophoretic heterogeneity giving a false impresssion of the ability of micron-paraprotein to react with the anti-x serum, thus complicating the diagnosis. Possible causes of a defect in the IgM assembly are discussed.