12 - Iron Metabolism and Related Disorders

Abstract

Iron is an essential element for numerous fundamental biological processes, including erythropoiesis; however, in large quantities and when unbound, iron can be highly toxic to cells. Much of iron metabolism involves maintaining a delicate balance between sequestered and available iron by regulating iron movement between compartments where iron can be absorbed, recycled, and stored. A wide spectrum of clinical disorders result from mutations in gene products with key roles in cellular and systemic iron regulation. Mutations in the gene products that encode the master iron regulatory hormone hepcidin or its receptor ferroportin lead to several hereditary forms of hemochromatosis with juvenile or adult onset. Genetic defects that restrict iron availability to erythroid precursors underlie several clinically-distinct forms of microcytic anemia that are also characterized by dysregulated systemic iron balance, including iron-refractory iron deficiency anemia, DMT1 mutation-related hypochromic microcytic anemia, and congenital atransferrinemia. A variety of other inherited conditions, including hereditary hyperferritinemia-cataract syndrome, neuroferritinopathy, aceruloplasminemia, Friedreich ataxia, and X-linked sideroblastic anemia with ataxia, also result from genetic defects that disrupt iron homeostasis at the local or systemic level. Furthermore, several genetic forms of neurodegeneration with brain iron accumulation have been described for which the relationship of the underlying mutated gene product to iron metabolism remains to be elucidated. In this chapter, we review the clinical features, molecular genetics, pathophysiology, diagnosis, and management of the major genetic disorders of iron metabolism.