Red cell size distribution curves in congenital sideroblastic anemia

(Top panel) Size distribution curve from a 28-year-old man with autosomal recessive congenital sideroblastic anemia (Hb, 6.7 g/dL; MCV, 65 fL; RDW, 35). The pattern indicates a broad population of red cells, varying markedly in size, with the majority of the cells being microcytic.
(Bottom panel) Size distribution curve from a 60-year-old woman with X-linked sideroblastic anemia (Hb, 9.9 g/dL; MCV, 93 fL; RDW, 14). It indicates the presence of two populations of red cells: one is comprised of normocytic to macrocytic red cells (black arrow) derived from precursors expressing the normal ALAS2, while a lesser population contains only microcytic red cells (red arrow) derived from precursors expressing the mutant ALAS2.