RESUMO
Neutropenia exists when the neutrophil counts is less than 1000/mm3 in infants between 2 weeks and 1 year of age and less than 1500/mm3 beyond 1 year of age (1). Severe infections occur when the absolute neutrophil count is below 500/mm3 with perirectal abscesses, pneumonia, and sepsis being common. Granulocyte Colony-Stimulating Factor (G-CSF) produces a sustained neutrophil recovery in patients with severe neutropenia, reduces the incidence and severity of infection, and improves the quality of life. Various cytopenias, including neutropenia, thrombocytopenia and pancytopenia, have been reported in association with inborn errors of branched aminoacid metabolism such as methylmalonic, propionic and isovaleric acidemia. We report an infant with methylmalonic acidemia who presented severe neutropenia