The sideroblastic anemias are a heterogeneous group of inherited and acquired disorders characterized by anemia of varying severity and the presence of ringed sideroblasts in the bone marrow.1 These latter are immature red cells with iron-loaded mitochondria visualized by Prussian blue staining as a perinuclear ring of blue granules. The most common of the inherited forms is X-linked sideroblastic anemia (XLSA, OMIM 301300), which is caused by mutations in the erythroid-specific ALA synthase gene (ALAS2). The most common acquired sideroblastic anemia is a myelodysplastic syndrome (MDS) defined as refractory anemia with ringed sideroblasts (RARS).2