Myeloperoxidase Deficiency: The Secret Under the Flag of Unstained Cell

Myeloperoxidase (MPO) defi ciency is one of the most common inherited phagocyte defects, but it is rarely associated with clinical symptoms [1]. MPO, which is abundant in azurophilic granules of neutrophils and in the lysosomes of monocytes, plays a key role in amplifying the toxicity of hydrogen peroxide generated by the respiratory burst [1,2]. The diagnosis of MPO defi ciency was rare before 1979; currently, the diagnosis is easily made due to the widespread use of automated fl ow cytochemical analysis in clinical hematology laboratories for enumerating peripheral blood neutrophils with peroxidase activity [2]. The MPO gene is encoded on chromosome 17q23 [3]. Primary defi ciency of MPO is inherited as an autosomal recessive disorder. A secondary form of MPO defi ciency has been described in various disorders, including lead poisoning, severe infections, neuronal lipofuscinosis, obstructive jaundice, diabetes mellitus, and such disseminated cancers as acute and chronic myeloid leukemia, myelodysplastic syndrome, and Hodgkin’s lymphoma [1,2,4]. MPOdefi cient neutrophils are markedly less effi cient at killing Candida albicans and Aspergillus hyphae [1]. Although MPO is involved in killing certain microorganisms, to date, no particular susceptibility to persistent or severe infections has been noted in the vast majority of MPO-defi cient patients [1,2]. Recurrent Candida infection has been observed predominantly in MPO-defi cient patients that also have diabetes mellitus. In addition to infectious manifestations, the relationship between congenital MPO defi ciency and the occurrence of malignancy remains controversial [1,2]. There is no specifi c treatment for MPO defi ciency; however, in symptomatic patients antifungal treatment is crucial. Herein we present a 17-year-old male that presented to our hematology department with neutropenia. Anamnesis showed that the patient did not have any recurrent or severe infection, but had been receiving benzathine penicillin prophylaxis due to acute rheumatic fever for years. Physical examination showed the following: weight: 58 kg (3-10p); height: 169 cm (10-25p); 1-2-degree/6 systolic murmur in the mesocardial region; the remainder of the examination was unremarkable. Complete blood count results were as follows: hemoglobin: 13.1 g/dL; leucocyte count: 6140/mm3; platelet count: 503,000/mm3. The formulation of the leucocytes was interesting, with an absolute neutrophil count of 20/ mm3 and a high absolute unstained cell count of 3020/mm3 (nearly 50%). Although the absolute neutrophil count was Myeloperoxidase Defi ciency: The Secret Under the Flag of Unstained Cell