Sideroblastic anemia.

When first defined 50 years ago, sideroblastic anemia (SA) was already recognized to occur in heterogeneous settings, including as familial or acquired disease. The spectrum of SA has since become considerably expanded with respect to distinct clinical phenotypes as well as discrete causes. The singular feature that typifies all forms of SA and is required for initial diagnosis is the presence of telltale ring sideroblasts in the bone marrow aspirate smear. These erythroblasts contain numerous coarse Prussian blue–positive granules, characteristically appearing in a perinuclear distribution (Fig. 1A), which represent pathologic deposits of iron in mitochondria (see Fig. 1B). The magnitude of the quantity of iron used by the erythron to make hemoglobin is well appreciated. Hemoglobin contains nearly 80% of the body heme and therein more than two-thirds of the body iron. Heme is assembled from iron andprotoporphyrin