Myeloperoxidase Deficiency

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Abstract
Leukocyte differential counting by flow cytochemistry revealed 28 subjects with partial or complete neutrophil myeloperoxidase (MPO) deficiency in a population of about 60,000 patients screened at a general hospital. Partial (13 patients) or complete (13 patients) MPO deficiency was confirmed by examination of cytochemical stains in 26, biochemical measurement of total enzymatic activity in 8 and flow cytometry in 6 patients. None had apparent hematologic disorders. Only 4 patients had infections; of these, 2 had major systemic infections (1, candidiasis; 1, bacteremia). In assays of leukocyte function only minor defects in killing of Staphylococcus aureus by MPO-deficient cells were noted; killing of Candida albicans was much more impaired. Family studies in 8 patients revealed various degrees of partial or complete MPO deficiency in 1st-degree relatives of 6. The incidence of MPO deficiency is evidently much higher than previously suspected. Although MPO appears to be necessary for killing of Candida spp. by neutrophils, the importance of its role in normal antibacterial defense must be reevaluated.