Classification of microcytic anemias. In the middle of the figure is a schematic representation of the prosthetic group of hemoglobin with a protoporphyrin ring (with iron) and the globin chains. In the top panel (light blue) is the classification of microcytic anemias caused by alterations of globin chain synthesis. In the right panel (gray) is the classification of microcytic anemias caused by impairment of heme synthesis. In the bottom panel (pink) is the classification of microcytic anemias caused by iron metabolism defects. AD, autosomal dominant inheritance; AR, autosomal recessive inheritance; XLR, X-linked recessive inheritance.