An 8-month-old boy was admitted because of paleness. Laboratory studies disclosed microcytic and
hypochromic anemia: red blood cell count 156 x 10(4)/microliter,
hemoglobin 3.5 g/dl, mean cell volume 66 fl, and reticulocytes 0.5/1000. Serum
iron was 433 micrograms/dl and exocrine pancreatic dysfunction was not observed. Examination of bone marrow revealed prominent erythroid
hyperplasia; 18% of the erythroblasts were distinct ringed sideroblasts. Electron microscopic studies found intramitochondrial
iron deposits in the erythroblasts. The patient was given a diagnosis of
sideroblastic anemia and responded to oral
pyridoxine (50 mg/day) with an immediate increase of reticulocytes to 97/1000, resulting in an improved
hemoglobin concentration. He has maintained remission for more than 1 year following discontinuation of
pyridoxine, which was administered for 2 months. Congenital
sideroblastic anemia is relatively rare and mostly occurs in males, suggesting an X-linked recessive mode of inheritance. Recently,
X-linked sideroblastic anemia has been shown to be caused by missense mutations in the
delta-aminolevulinic acid synthase (ALAS) gene. A point mutation in exon 5 of the ALAS gene was found in this patient.
Iron-deficiency anemia is the most common
hematologic disease of infancy and childhood, resulting from lack of sufficient
iron for synthesis of
hemoglobin. It is therefore mandatory to differentiate
sideroblastic anemia from
iron-deficiency anemia and other common
anemias.