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 the ingestion of drugs, alcohol, or toxins such as lead or zinc, or copper deficiency. Patients with acquired sideroblastic macrocytic anemia and variable degrees of thrombocytopenia and leukopenia from copper deficiency have been recognized more frequently; the hematologic abnormalities typically resolve after copper replacement. Ring sideroblasts are also a feature of myelodysplastic neoplasms, and are discussed in Chap. 87. 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. 43) when it is more severe.
Sideroblastic anemias are a heterogeneous group of disorders that have as a common feature the presence of: (1) large numbers of pathologic sideroblasts in the marrow, which characteristically display abnormal mitochondrial iron accumulation is in a circumnuclear position in erythroblasts; these are referred to as ringed 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 59–1).1,2
Table 59–1.Classification of Sideroblastic Anemias ||Download (.pdf) Table 59–1. Classification of Sideroblastic Anemias
Primary sideroblastic anemia (myelodysplastic syndromes) (Chap. 88)
Subunit 1 of the mitochondrial cytochrome oxidase54,55
Sideroblastic anemia secondary to:
Chronic neoplastic disease (Chap. 8)
Zinc-induced copper deficiency124,125
X chromosome linked
Defects in the erythroid specific mitochondrial carrier family protein SLC25A3847
Mitochondrial myopathy and sideroblastic anemia (PSU1 mutations)57,108,109
Pearson marrow-pancreas syndrome15,16,17,18,19
Acquired monoclonal sideroblastic anemia is a neoplastic disease; that is, a clonal cytopenia or oligoblastic myelogenous leukemia that can progress to acute leukemia. This subject is considered in Chap. 87, Myeloid Neoplasms, in which ringed sideroblasts are a common phenotypic feature. Acquired polyclonal sideroblastic anemia may also develop as a result of the administration of certain drugs, exposure to toxins, or coincident to neoplastic or inflammatory disease. Hereditary sideroblastic anemias include X-linked, autosomal, and mitochondrial entities. Occasionally, a patient with familial disease develops a myelodysplastic syndrome later,1,2 but with these rare exceptions, the ...