A Case of Waldenstrom Macroglobulinemia with Temporary Appearance of 7S IgM Half Molecule.

Background: We encountered a rare case of Waldenstrom macroglobulinemia with temporary appearance of 7S IgM half molecule and with monoclonal proteins binding to agarose gel. Methods: The patient's serum and urine were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The N-terminal amino acid sequences of the IgM with abnormal mass (68 kDa) were determined and compared with those of known immunoglobulin. Results: The 68 kDa IgM consisted of a defective Et chain (36 kDa) and an intact kappa chain. N-terminal amino acid sequence analysis demonstrated that the defective It chain had the variable region of IgM. The agarose gel-binding ability of the IgM-w M-protein was lost after reduction or alkaline treatment of serum. Conclusions: The 7S half molecule IgM in the present case may miss a large part of the constant region of the mu chain.