Absent or extremely low neutrophil alkaline phosphatase activity levels in patients with myelodysplastic syndromes.

Three patients with myelodysplastic syndrome (MDS) had absent or extremely low levels of neutrophil alkaline phosphatase (NAP) activity (arbitrarily defined as an NAP score <10). All patients showed varying degrees of hypogranulation in neutrophil morphology. The NAP activity levels transiently normalized following the administration of granulocyte colony-stimulating factor (G-CSF) in two cases. No patients experienced any severe infectious episodes. These results suggest that NAP activity is not central to the neutrophil function.