GSTM1 and Decreased total neutrophil count: Laboratory investigations revealed severe neutropenia (ANC: 140 cells/μL) with normal lymphocyte, monocyte and platelet counts, slight microcytic anemia (Hb 10,5 g/dl; MCV 65,4 fl), normal serum immunoglobulins, protective antibody response to tetanus toxoid, and normal distribution of lymphocyte subsets.