At the age of 8 years, during fever with a Parvovirus B19 infection, the child experienced severe anemia (Hb 5.3 g/dL) and reticulocytopenia (reticulocytes 0.4 × 109/L), which required red blood transfusions and concomitant reduction of leukocyte (2.0 × 109/L) and platelet (84 × 109/L) levels. The gene discussed is GSTM1; the disease is Reticulocytopenia.