Myelodysplasia in a patient with pre-existing paroxysmal nocturnal haemoglobinuria: a clonal disease originating from within a clonal disease.

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired haemolytic anaemia, clonal in nature, due to somatic mutation. PNH may evolve to aplastic 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 sideroblasts (RARS) associated with trisomy 8. By testing peripheral blood cells with appropriate antibodies we have shown that all of the red cells, neutrophils and monocytes, as well as 20% of the lymphocytes, belonged to the PNH clone; in contrast, only 43% of neutrophils and 22% of monocytes belonged to the MDS clone. We infer that the MDS must have arisen from within the PNS clone.