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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 (ALA) synthase. Inherited autosomal and mitochondrial forms are also occasionally seen. Acquired sideroblastic anemias can occur as a result of the ingestion of drugs, alcohol, or toxins such as lead or zinc. A separate entity of an acquired sideroblastic anemia is being recognized in growing number of patients with sideroblastic macrocytic anemia and variable degrees thrombocytopenia and leukopenia caused by copper deficiency; the hematologic abnormalities typically resolve after copper replacement. Ring sideroblasts are also a feature of myelodysplastic states, which are discussed in Chap. 88. 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 (see Chap. 42) when it is more severe.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: ALA, 5-aminolevulinic acid; ALAS2, gene encoding ALA synthase 2; ATP, adenosine triphosphate; Fe-S, iron-sulfur cluster; GLRX5, glutaredoxin 5; MLASA, mitochondrial myopathy and sideroblastic anemia; PUS1, pseudouridine synthase 1 gene; STEAP 3, six-transmembrane epithelial antigen of prostate 3-ferric reductase; tRNA, mitochondrial transfer RNA; XLSA/A, X-linked sideroblastic anemia associated with ataxia.

Sideroblastic anemias are a heterogeneous group of disorders that have as common features the presence of large numbers of ringed sideroblasts in the marrow, ineffective erythropoiesis, increased levels of tissue iron, and varying proportions of hypochromic erythrocytes in the blood. They may be acquired or hereditary (Table 58–1).

Table 58–1. Classification of Sideroblastic Anemias

Acquired sideroblastic anemia may be a neoplastic disease, that is, a clonal disorder that can progress to acute leukemia. This subject is considered in Chap. 88, in which clonal preleukemic disorders are ...

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