CLONALITY IN MYELODYSPLASTIC SYNDROMES - DEMONSTRATION OF PLURIPOTENT STEM-CELL ORIGIN USING X-LINKED RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS

Restriction fragment length polymorphisms (RFLP) of the X-chromosome genes phosphoglycerate kinase (PGK) and hypoxanthine phorphoribosyltransferase (HPRT) were used to determine the clonal nature of myelodysplastic syndromes (MDS) in 22 patients. These included eight with refractory anaemia (RA), four with RA with ring sideroblasts (RARS), six with RA with an excess of blasts (RAEB), three with RAEB in transformation (RAEB-T), and one with chronic myelomonocytic leukaemia (CMML). Monoclonal X-inactivation patterns were observed in 19/22 patients. The remaining three cases, one each with RA, RARS and RAEB, were of polyclonal composition. Separated T-lymphocyte and granulocyte fraction analyses in six patients of the former cases revealed that T-lymphocyte as well as granulocyte fractions showed a monoclonal pattern of X-inactivation. These results support the view that the majority of MDS arise from a pluripotent stem cell capable of myeloid and lymphoid differentiation.