CLONAL HEMATOPOIESIS AS DEFINED BY POLYMORPHIC X-LINKED LOCI OCCURS INFREQUENTLY IN APLASTIC-ANEMIA

We evaluated the methylation status of the X-linked gene phosphoglycer ate kinase (PGK(1)) and the DXS 255 locus detected by probe M27 beta t o study clonality in acquired aplastic anemia (AA). A total of 30 fema les were suitable for clonal analysis of peripheral blood polymorphonu clear cells (PMN) and mononuclear cells using a polymerase chain react ion-based procedure in 24 patients and Southern blotting in 9. Overall , 10 of 30 patients exhibited an imbalanced X-inactivation pattern. Ho wever, in 4 patients, analysis of constitutional DNA suggested a skewe d methylation pattern and 2 further cases had to be excluded because o f the lack of an appropriate control. A truly clonal pattern was thus established in 4 of 30 (13%) patients, In 7 patients who later develop ed clonal disorders of hematopoiesis, X-inactivation analysis did not predict this event in any case. In patients with a paroxysmal nocturna l hemoglobinuria phenotype, there was no correlation between the propo rtion of phosphatidylinositol glycan anchored protein (PIG-AP)-deficie nt blood cells and the corresponding X-inactivation pattern. X-inactiv ation analysis detected clonal hematopoiesis in only 3 of 10 patients with a deficiency in PIG-AP in the cell population under study, but so rting of nucleated cells on the basis of PIG-AP expression showed the clonal nature of PIG-AP-deficient cells. We conclude that the majority of patients with AA show polyclonal hematopoiesis using X-linked clon al analysis, but that minor clonal populations, such as PIG-AP-deficie nt cells, may not be detected unless sorted cell populations are separ ately analyzed. (C) 1995 by The American Society of Hematology.