Simultaneous occurrence of myelodysplastic syndrome and monoclonal B lymphocytes with a different clonal origin.

Bone marrow and peripheral blood from a myelodysplastic syndrome patient with trisomy 13 and monoclonal B lymphocytes (without evidence of systemic lymphoma) were investigated for clonal lymphoid lineage involvement using interphase fluorescence in situ hybridization (FISH) and X-chromosome inactivation assay (HUMARA) on CD19+ and CD34+ sorted cells. Trisomy 13 was detected in 55% of CD34+ cells and in 5.5% of CD19+ cells, the latter being comparable to the negative control specimen. X-chromosome inactivation showed both CD34+ and CD19+ cells to be monoclonal, though their inactivated X-chromosome was different. The results strongly suggested that both populations of CD34+ and CD19+ cells have originated from a different progenitor stem cell.