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SUMMARY

SUMMARY

Sideroblastic anemias are characterized by the presence of ring sideroblasts in the marrow. These cells are erythroid precursors that have accumulated abnormal amounts of mitochondrial iron. A variety of abnormalities of porphyrin metabolism in affected erythroid cells have been documented. Hereditary sideroblastic anemias are usually X-linked, as the result of mutations in the erythroid form of 5-aminolevulinic acid synthase. Inherited autosomal and mitochondrial forms are seen occasionally. Acquired sideroblastic anemias can occur as a result of copper deficiency or the ingestion of drugs, alcohol, or toxins such as lead or zinc. Patients with acquired sideroblastic macrocytic anemia and variable degrees of thrombocytopenia and leukopenia caused by copper deficiency have been recognized more frequently; the hematologic abnormalities typically resolve after copper replacement. Ring sideroblasts are also a feature of myelodysplastic neoplasms. Some patients with sideroblastic anemia may respond to pharmacologic doses of pyridoxine. Iron loading is common in the sideroblastic anemias and can be treated by phlebotomy when the anemia is mild or with iron chelators (Chap. 11) when it is more severe.

DEFINITION AND HISTORY

Sideroblastic anemias are a heterogeneous group of disorders that have as a common feature the presence of (1) large numbers of pathological sideroblasts in the marrow, which characteristically display abnormal mitochondrial iron accumulation in a circumnuclear position, the location of mitochondria in erythroblasts; these are referred to as ring sideroblasts; (2) ineffective erythropoiesis; (3) increased levels of tissue iron; and (4) varying proportions of hypochromic erythrocytes in the blood. They may be acquired or hereditary (Table 20-1).

TABLE 20–1.Classification of Sideroblastic Anemias

Acronyms and Abbreviations:

ABCB7, ATP-binding cassette; ALA; 5-aminolevulinic acid; ALAS; 5-aminolevulinic acid synthase; ALAS2, gene encoding erythroid-specific ALA synthase 2; ATP, adenosine triphosphate; CoA, coenzyme A; FC, ferrochelatase; GLRX5, glutaredoxin 5; Fe-S, iron sulfur cluster; Hb, hemoglobin; IRE, the iron-responsive element; HSP70, heat shock protein 70; IRP1, iron regulatory protein 1; MDS, myelodysplastic syndrome; MLASA, mitochondrial ...

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