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Key Features

  • Heterogeneous group of disorders in which reduced hemoglobin synthesis occurs because of reduced ability to synthesize heme or an impaired ability to incorporate heme into protoporphyrin IX

  • Iron accumulates, particularly in mitochondria

  • Most often it is a subtype of myelodysplastic syndrome

  • Other causes include chronic alcoholism, lead poisoning, copper deficiency (hypocupremia), drugs (isoniazid and chloramphenicol), and chronic infection or inflammation

  • Inherited forms are usually X-linked but rare recessive forms have been documented

Clinical Findings

  • Symptoms of anemia; no other specific clinical features

  • Hypocupremia

    • Normocytic anemia in two-thirds of cases; macrocytic in remainder

    • Zinc level usually elevated

    • Neutropenia or thrombocytopenia may be present

    • Myelopathy or demyelinating peripheral neuropathy in some patients

Diagnosis

  • Anemia usually moderate, hematocrit 20–30%

  • Mean corpuscular volume

    • Usually normal or slightly increased in sideroblastic subtype of myelodysplastic syndrome

    • Usually low in other subtypes (especially inherited forms), leading to confusion with iron deficiency

  • Peripheral blood smear characteristically shows dimorphic population of RBCs: 1 normal and 1 hypochromic

  • Coarse basophilic stippling of RBCs and serum lead level elevated in lead poisoning

  • Bone marrow iron stain shows generalized increase in iron stores and ringed sideroblasts (RBCs with iron deposits encircling the nucleus) and marked erythroid hyperplasia (resulting from ineffective erythropoiesis)

  • Serum iron and transferrin saturation high

  • Ringed sideroblasts in bone marrow

Treatment

  • Occasionally, transfusion required for severe anemia

  • Recombinant erythropoietin therapy not usually effective

  • Oral pyridoxine (50–200 mg/day) occasionally useful

  • Removal of offending toxins and drugs is needed in the secondary acquired forms

  • Hypocupremia: copper sulfate (2.5 mg orally twice daily)

    • Associated with high hematologic response rate but low neurologic response rate

    • Exogenous or endogenous zinc exposure needs to be eliminated

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