Clonal studies in the myelodysplastic syndrome using X-linked restriction fragment length polymorphisms.

We used the X-linked restriction fragment length polymorphism (RFLP)-methylation strategy to study the clonal basis of the myelodysplastic syndrome (MDS) in seven patients. RFLP-methylation analysis was performed on cell populations from bone marrow (BM) aspirates and peripheral blood using probes specific for the hypoxanthine phosphoribosyltransferase (HPRT) or phosphoglycerate kinase (PGK) gene regions. Density gradient centrifugation methods were used to separate granulocytes and monocytes, and T lymphocytes were positively selected by CD2 (a pan-T marker) immunoconjugated magnetic beads. Cell populations from BM aspirates in 6 of the 7 patients with MDS showed a monoclonal pattern of X-inactivation. The neutrophilic and T-lymphocytic cell fractions were analyzed in 4 of the 6 patients, and the monocytic cell fraction in one of these, and all fractions analyzed showed a similar monoclonal pattern. In 2 of the latter 4 patients, both of whom had normal karyotypes, DNA from a skin biopsy showed a polyclonal pattern. Our data suggest that MDS is a clonal disorder, even in the absence of detectable cytogenetic abnormalities, and that the abnormal clone is capable of myeloid, monocytic, and lymphoid differentiation.