MYELODYSPLASIA IN A PATIENT WITH PREEXISTING PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA - A CLONAL DISEASE ORIGINATING FROM WITHIN A CLONAL DISEASE

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired haemolytic a naemia, clonal in nature, due to somatic mutation. PNH may evolve to a plastic anaemia; more rarely to a myelodysplastic syndrome (MDS) or to acute myeloid leukaemia (AML). We have studied a patient who suffered from PNH and later developed refractory anaemia with ringed siderobla sts (RARS) associated with trisomy 8. By testing peripheral blood cell s with appropriate antibodies we have shown that all of the red cells, neutrophils and monocytes, as well as 20% of the lymphocytes, belonge d to the PNH clone; in contrast, only 43% of neutrophils and 22% of mo nocytes belonged to the MDS clone. We infer that the MDS must have ari sen from within the PNS clone.