• biclonal gammopathy;
  • multiple myeloma;
  • Waldenström's macroglobulinaemia;
  • clonality;
  • isotypic variants.

We describe a case of Waldenström's macroglobulinaemia with two M-components (IgM and IgG) with the same λ light chain. Southern blot analysis of bone marrow cells showed rearrangements of immunoglobulin heavy and λ light chain genes.

Sequencing of the complementarity determining region 3 of the two γ and μ transcripts showed 100% homology. Immunofluorescence study showed that most cells stained for both IgG and IgM. These findings indicated that a single population of cells was expressing two isotypic variants of IgG and IgM, as the genes responsible for production of both components had the same origin.