Secondary iron overload disorders.

Diverse clinical disorders distinct from hereditary hemochromatosis are associated with accumulation of excess body iron in heterogeneous patterns and through various mechanisms. A deranged iron turnover somehow relates to the altered physiological barrier for iron absorption in several defined chronic anemias with ineffective erythropoiesis. Unexcretable excess iron acquired from transfusions provides a therapeutic challenge. Genetic defects of proteins essential for transport of iron into and out of cells (transferrin and ceruloplasmin) deprive the erythron of the metal and cause its accumulation in other vital organs. The hemochromatosis alleles predictably contribute to an iron burden from other causes, commonly facilitate the expression of porphyria cutanea tarda, and their clinical expression may be accelerated by hereditary hemolytic anemias. Even minimal iron excess in liver disease may contribute to the hepatocellular injury from factors such as alcohol and viruses. Uniquely localized siderosis occurs in the lung and kidney where iron cannot turn over and causes variable tissue damage. The most devastating iron overload disorder, neonatal hemochromatosis, is understood least of all.