Myeloperoxidase (MPO) on chromosome 17q22 codes for a heme-containing protein produced following commitment and during myeloid differentiation. Ultimately, mature neutrophil azurophilic granules have MPO as their major component. Consistently, high MPO expression, suggestive of a more differentiated type, has been associated with favorable outcomes in acute myeloid leukemia (AML). MPO deficiency is an extremely rare autosomal recessive disorder caused by any of a number of known germline variants, though the propensity to develop myeloid malignancy has not been reported for affected individuals. Somatic MPO mutations have not be identified in myeloid neoplasia (MN).