Myeloperoxidase deficiency.

MPO activity is critical for optimal microbicidal activity of normal PMNs. In the absence of MPO, auxiliary mechanisms protect most MPO-deficient hosts from clinically significant sequelae, except for some persons with diabetes mellitus who suffer severe candidal disease. However, given our limited knowledge of the clinical impact of MPO deficiency, histochemical staining of peripheral blood smears or MPO activity of isolated leukocytes should be assessed in patients with unexplained fungal disease or with suspected impaired host defenses. Recently isolated cDNA probes provide important tools for dissecting the molecular and cell biology underlying hereditary MPO deficiency and the link between MPO gene expression and myeloid differentiation.