IRON DEFICIENCY ANEMIA ASSOCIATED WITH AN ERROR OF IRON METABOLISM IN TWO SIBLINGS

Iron Deficiency Anemia Associated with an Error of Iron Metabolism in Two Siblings: A Thirty Year Follow Up

For thirty years we have followed two siblings with apparent iron deficiency anemia in the setting of systemic iron overload. This report details their clinical courses, which have been surprisingly disparate. The female sibling has been more severely affected, requiring multiple transfusions. In contrast, the male sibling demonstrated apparent improvement at puberty. Although both have shown evidence of systemic iron overload for many years, neither has had significant end organ toxicity. We discuss the probable pathophysiology of their disorder, drawing from animal models with similar defects in iron uptake and utilization.

Emergency do not consume/do not use concentrations for ferric chloride in drinking water

The U.S. Congress [PL 107-188] amended the Safe Drinking Water Act and required each community water system serving more than 3,000 people to conduct vulnerability assessments. These assessments address potential circumstances that could compromise the safety and reliability of municipal water. Ferric chloride is used in coagulation and flocculation, and it is used to treat raw water with high viral loads, elevated dissolved solids or high bromide. Iron is an essential nutrient, but elevated concentrations of FeCl3 are corrosive as a result of hydrolysis to HCl. Based on a no-observed-adverse effect level (NOAEL) of 0.5% FeCl3 • 6H2O administered in drinking water to male and female F344 rats for up to 2 years, a do not consume concentration of 200 mg FeCl3 /L can be derived. Since instillation of 0.3 M (48.7 g/L) FeCl3 in saline to rodent vagina failed to elicit damage, a topical do not use concentration of 2000 mg FeCl3/L (600 mg Fe/L) can be assigned. The only FeCl3 data available to quantify ocular toxicity involved a pH 1 solution in rabbit eyes, but HCl instillation (pH 2.5) to rabbit eyes found permanent corneal ulceration after 10 min. The pH of FeCl3 in water at the do not use limit (2.4–2.6) is near the pH (2.0) considered corrosive by regulatory agencies. As direct eye contact with water at pH 4.5 or below increases complaints of ocular discomfort, emergency response plans that address FeCl3 in drinking water must account for Fe levels and the pH of the affected water.

Mammalian iron metabolism and its control by iron regulatory proteins

Cellular iron homeostasis is maintained by iron regulatory proteins 1 and 2 (IRP1 and IRP2). IRPs bind to iron-responsive elements (IREs) located in the untranslated regions of mRNAs encoding protein involved in iron uptake, storage, utilization and export. Over the past decade, significant progress has been made in understanding how IRPs are regulated by iron-dependent and iron-independent mechanisms and the pathological consequences of IRP2 deficiency in mice. The identification of novel IREs involved in diverse cellular pathways has revealed that the IRP-IRE network extends to processes other than iron homeostasis. A mechanistic understanding of IRP regulation will likely yield important insights into the basis of disorders of iron metabolism. This article is part of a Special Issue entitled: Cell Biology of Metals.

Ferrokinetics in the syndrome of familial hypoferremic microcytic anemia with iron malabsorption

PURPOSE

In 1981, Buchanan and Sheehan described a previously unreported syndrome in three siblings who had iron malabsorption, hypoferremia, and microcytic anemia that did not respond to oral iron and responded only partly to parenteral iron dextran. Ferrokinetic studies were not done in these or subsequently reported patients with this syndrome. It has been postulated that this syndrome of abnormal iron metabolism is analogous to that observed in the mk/mk mouse, which has similar hematologic findings but also has abnormal ferrokinetics. Ferrokinetic studies were performed in one patient to determine whether the abnormality of iron metabolism in the human syndrome is analogous to the mk/mk mouse.

PATIENTS AND METHODS

Two sisters with severe microcytic anemia and iron malabsorption who have had only partial response to parenteral iron have been followed up for 15 years. Ferrokinetic studies with 59Fe were performed in one sister.

RESULTS

Ferrokinetic studies with radio iron were characteristic of iron deficient erythropoiesis (rapid 59Fe T1/2; rapid, complete incorporation of 59Fe into erythrocyte hemoglobin). These ferrokinetics differ from those of the mk/mk mouse, which has a missense mutation in Nramp2, a putative iron transporter protein. In these children, once iron enters the plasma its subsequent metabolism (including binding to transferrin), transfer into erythroid bone marrow cells, and subsequent incorporation into erythrocyte hemoglobin are all normal. The defect in these patients appears to be an undefined, novel abnormality that governs mobilization of iron into the plasma from both the intestinal mucosal and reticuloendothelial cells. Despite lifelong severe hypoferremia, the growth, development and intellectual performance of these children, who are teen-agers, are normal.

Microcytic anemia with iron malabsorption: an inherited disorder of iron metabolism

Two siblings were identified with severe hypoproliferative microcytic anemia and iron malabsorption, in the absence of any gastrointestinal disorder or blood loss. These children had severe microcytosis (MCV 48 fl, hemoglobin 7.5 g/dl) with decreased serum iron, elevated serum TIBC, and decreased serum ferritin, despite prolonged treatment with oral iron. An iron challenge study with an oral dose of 2 mg/kg elemental iron as ferrous sulfate documented iron malabsorption. After treatment with intravenous iron dextran, there was an absence of the expected reticulocytosis and only a partial correction of the hemoglobin, hematocrit, and microcytosis. The bone marrow was hypocellular with abnormal iron incorporation into erythroid precursor cells. This appears to be a rare form of inherited anemia characterized by iron malabsorption and disordered iron metabolism that only partially corrects after the administration of parenteral iron. These features resemble those found in the microcytic mouse (mk/mk), which also has severe microcytic anemia and iron malabsorption that partially responds to parenteral iron.

Iron nutrition in childhood: the interplay of genes, development and environment

The state of a child's iron nutrition depends on his genetic endowment, the stage of development he has reached and the environment in which he lives. Genetic disorders lead more commonly to iron overload than to deficiency. Generally interplay between genes and environment is apparently of little importance when considering iron deficiency; are we missing something? The greatest demands for iron are at the time of most rapid growth, i.e. during infancy and puberty, but during early infancy body stores can meet the demand without a need for dietary iron. Oxygen, diet and microbes are the important environmental factors related to iron nutrition. The relationship of oxygen toxicity to iron nutrition in the newborn has received only fleeting study, the availability of iron from many foods is unclear; the clinical significance of iron overload and deficiency in the evolution of an infection is also unclear despite a wealth of in vitro observation. I am not convinced that the bottle fed baby should receive iron in his diet during the first 4-6 months of life. Thereafter, while the concept of universal unselective supplementation causes some uneasiness there are considerable epidemiological arguments for fortification of food with iron.

Ferrochelatase deficiency of the bone marrow in a syndrome of congenital microcytic anaemia with iron overload of the liver and hyperferraemia

Ferrochelatase deficiency of the bone marrow was found in 2 sisters with a syndrome of congenital hypochromic anaemia, hyperferraemia and heavy iron deposits in the liver.

Ferrochelatase deficiency in the bone marrow in a syndrome of congenital hypochromic microcytic anemia, hyperferremia, and iron overload of the liver

Two sisters had congenital hypochromic microcytic anemia with hyperferremia, heavy iron deposits in the liver, and reduced bone marrow iron. Liver ferrochelatase activity was within normal limits, but in the bone marrow ferrochelatase activity was only 20% of that in healthy controls. There were no findings suggestive of lead intoxication, sideroblastic anemia, or erythropoietic protoporphyria.

Acquired iron-deficiency anemia caused by an antibody against the transferrin receptor

We report a case of anemia due to autoantibodies to the transferrin receptor interfering with iron incorporation by erythroid progenitors. A previously healthy woman with severe acquired microcytic anemia had increased serum iron levels, electrophoretically normal transferrin concentrations, and very high levels of free protoporphyrin in red cells. The bone marrow had no stainable iron but had an excess of normal-appearing plasma cells. Erythroid precursors stained with fluorescent mouse antihuman IgM. The serum contained an antibody that reduced 59Fe incorporation by erythroleukemia K562 cells in vitro but did not inhibit iron transferrin binding. An IgM fraction of the patient's serum immunoprecipitated the human transferrin receptor obtained from solubilized [35S]methionine-labeled K562 membranes. Binding of [59Fe]transferrin or fluorescent iron transferrin was not diminished by the patient's serum at 4 degrees C, but at 37 degrees C uptake was markedly reduced, as was the binding of fluorescent monoclonal antibodies to either surface transferrin or the human transferrin receptor. A complete clinical and hematologic remission occurred with azathioprine and prednisone therapy. We conclude that the patient's autoreactive IgM down-regulated the number of transferrin receptors and diminished iron incorporation by erythroblasts, leading to an iron-deficiency anemia.

Acquired iron-deficiency anaemia due to impaired iron transport

A previously healthy 39-year-old woman presented with severe iron-deficiency anaemia, but she had lost no blood and her serum iron level was high. Her bone marrow was hypercellular with a predominance of erythroid elements and had no stainable iron deposits, but it also showed dyserythropoiesis and an excess of apparently normal plasma cells. IgM was demonstrated on her bone-marrow erythrocytes and their precursors. On azathioprine and prednisone therapy she had a complete clinical and haematological remission. The impaired iron transport and the associated dyserythropoiesis were probably due to an IgM-mediated autoimmune process. Diabetes mellitus, which first appeared during her anaemic illness, could also have been due to an autoimmune process. This is the first report of an iron-deficiency anaemia caused by a naturally acquired impairment of iron transport.

Stimulation of globin synthesis: relative responsiveness of reticulocytes and nucleated erythroid cells

The effects of iron, cobalt, hemin, and plasma on hemoglobin synthesis by suspensions of rabbit reticulocytes and nucleated bone marrow cells were studied. L-Leucine-(14)C and sodium pyruvate-3-(14)C were employed to measure globin and heme synthesis, respectively. Normal plasma (or serum) was found to stimulate the rate of globin synthesis in both systems. The stimulatory effects of iron and hemin were additive to those of plasma or serum only in the reticulocytes. Cobaltous ion, at concentrations less than 1.0 mmole/liter, was found to stimulate globin synthesis by reticulocytes as effectively as ferrous ion; cobalt was inhibitory only at concentrations greater than 3.0-5.0 mmoles/liter. Heme synthesis by reticulocytes was inhibited at all concentrations employed (0.2-5.0 mmoles/liter). In bone marrow nucleated erythroid cells, globin synthesis was markedly enhanced by exogenous hemin. In contrast to reticulocytes, however, bone marrow cells were unresponsive to either cobalt or transferrin-bound iron. Possible implications of these findings on regulation of the rate and mechanism of iron uptake and hemoglobin synthesis in vivo are discussed.