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Hemochromatosis: 1980 update
GASTROENTEROLOGY
CLINICAL
TRENDS
1980
AND TOPICS
Hemochromatosis:
1980Update
LAWRIE W. POWELL, and JUNE
78374-381,
MARK W. HALLIDAY
L. BASSETT,
Department of Medicine, University of Queensland. Royal Brisbane Hospital, Brisbane, Australia
During the past decade there have been major advances in the knowledge of the biology of iron and of clinical disorders resulting from abnormalities in body iron metabolism. These advances include: (a) structural and functional aspects of the major proteins of iron storage and transport, ferritin, and transferrin; (b) new concepts of the possible mechanisms of iron toxicity; (c) the early detection and management of iron deficiency and iron overload; and (d) clarification of the genetic nature of idiopathic hemochromatosis (IHC). This review is devoted primarily to the role of the liver in iron metabolism and iron-storage diseases, and to the major recent advances in the knowledge of hemochromatosis.
Iron Storage and the Liver The liver is the major storage organ for iron in normal subjects and in patients with iron overload. The total body iron in normal, iron-replete subjects amounts to approximately five grams, of which about 35% is present as storage iron. Approximately one-third of the storage iron is found in the liver, primarily as ferritin. This provides an internal reserve that can be mobilized when needed and also protects against iron toxicity. It is known that hepatocytes as well as Kupffer cells participate in iron storage.’ In the normal liver, most of the nonheme iron is found in hepatocytes, in the form of ferritin.’ When iron is given parenterally, both hepatocytes and Kupffer cells accumulate large amounts of additional ferritin, although Kupffer cells tend to store relatively more of the excess nonheme iron in forms other than ferritin, e.g., hemosiderin.” Ascorbic acid appears to be involved in the incorporation and release of iron from ferritin, at least in iron-storage disorders (e.g., thalassemia), and also in Received June 12, 1979. Accepted September 13.1979. Address requests for reprints to: Professor L. W. Powell, Department of Medicine, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, Queensland, Australia 4029. 0 1980 by the American Gastroenterological Association 00185085/80/020374-08$02.25
the removal of iron from hemosiderin.“,’ In ascorbic acid deficiency, serum iron levels are inappropriately low, and there is an increased cellular content of hemosiderin, which can be readily reversed by the administration of ascorbic acid.” A fall in the serum ferritin level has also been observed in ascorbic acid deficiency in guinea pigs.” However, further work is required to determine the precise role of ascorbic acid in normal iron and ferritin metabolism. The liver forms a major component of the reticuloendothelial (RE) system. At the end of their life span, erythrocytes are phagocytosed by macrophages of the RE system, and the released iron is either stored within the macrophages (including Kupffer cells), or returned to transferrin in the plasma. Surplus iron is stored within parenchymal cells of the liver, muscle, and other organs, as well as in macrophages of the spleen, liver, and bone marrow.
Structure
and Metabolism
of Ferritin
The existence of a high-molecular-weight iron-storage protein, ferritin, in the liver and many other tissues has been recognized for many years. It is now known that electrophoretically pure ferritins may be resolved into multiple isoferritins by isoelectric focusing. The ferritin molecule consists of 24 subunits. The existence of subunits of two types, designated H & L, which differ in molecular weight, immunologic reactivity, and amino acid composition, has been postulated as a mechanism for the observed microheterogeneity of the ferritin molecule.” Each tissue has a characteristic isoferritin profile that can be shown to change in different physiologic and pathologic states, particularly iron overload,7.R during phlebotomy’ and in malignancy.“,” However, the functional significance of isoferritins is still unclear. The synthesis of ferritin within the hepatocyte is stimulated by iron and occurs primarily on free polysomes.” However, ferritin synthesis also occurs on bound po1ysomes.‘3 The origin of circulating ferritin is a subject of considerable interest and specu-
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lation at present. It seems probable that serum ferritin is actively secreted, perhaps arising from the bound polysomes, and its presence in serum is not merely the result of tissue necrosis.14 There is some evidence that serum ferritin originates from RE cells.‘4,‘5 However, its exact origin and biologic function are far from clear. Injected ferritin derived from serum and various tissues has been shown to be taken up and metabolized rapidly by the liver.‘” The precise pathways are unknown. Whatever the source and biologic function of serum ferritin, its concentration reflects total body iron stores’4~‘” and its place as an important screening test for iron deficiency and iron overload is now firmly established.“,‘“,” Thus, as a noninvasive test it is particularly applicable to population surveys to detect iron deficiency. In contrast to the serum iron concentration and transferrin saturation, there are fewer false positives and false negatives, and there appears to be little or no diurnal variation. A serum ferritin concentration below 10 pg/liter is indicative of low iron stores. However, some other disease states may elevate serum ferritin concentration. Such states include hepatocellular necrosis,lH malignant neoplasms,1y~21 leukemia and related disorders of the RE system,22.23 The precise place of serum ferand inflammation.14~” ritin measurements in the detection of iron deficiency in these conditions has not yet been clearly defined.
Pathogenesis Overload
of Tissue Injury in Iron
The role of excess iron in producing the pathologic changes of acute iron toxicity is not disputed; however the pathogenesis of the tissue damage that accompanies chronic iron overload has been a matter of some debate. The pathologic changes seen in idiopathic hemochromatosis, for instance, were thought at one time to be due to excess alcohol ingestion, the iron deposition occurring coincidenThe inability to provide an experimental tally.“” model for hemochromatosis has in the past raised serious questions about the role of iron in the pathogenesis of chronic liver damage. However, despite this, it is now generally accepted that deposition of excess iron in hepatocytes and other parenchymal cells is responsible for tissue damage. Evidence for chronic iron toxicity is based on a number of observations: (a) Similar clinical and pathologic changes are seen following longstanding parenchymal iron overload, regardless of the etiology (idiopathic hemochromatosis, hemochromatosis secondary to ineffective erythropoiesis, dietary iron overload, etc).25.2” (b) In idiopathic hemochromatosis and “dietary” he-
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mochromatosis as seen in South African blacks, the presence of large amounts of iron in the liver and pancreas is frequently associated anatomically with fibrosis, and the severity of fibrosis is roughly proportional to the tissue iron concentration.‘” (c) Although there have been no controlled studies of phlebotomy therapy in idiopathic hemochromatosis, at least two studies have been published that show convincing evidence of clinical and pathologic improvement together with an increased survival rate following such therapy,Z7,“H and few clinicians would dispute the value of phlebotomy treatment in hemochromatosis. (d) In a prospective trial of chelation therapy in children with thalassemia major, subjects treated with deferoxamine showed a significant reduction in hepatic iron accumulation and a retardation in the progression of hepatic fibrosis when compared with patients not receiving chelation therapy.“’ (e) While earlier animal models have failed to demonstrate tissue damage resulting from chronic iron overload, several recent experiments in animals have produced some evidence for chronic iron toxor iron sorbitol in icity. Lisboa,“” using iron dextran parenteral doses ranging from 3.5 to 5.8 g iron/kg body weight over several months, produced a lesion histologically similar to human hemochromatosis in five of seven dogs. In rats fed a choline-deficient, high-fat diet with dietary iron supplementation for over 1 yr, cirrhosis with hepatic iron deposition developed”‘; however rats on a choline-deficient diet without iron also developed cirrhosis. More recently, Awai”” has observed deposition of iron in hepatocytes and pancreatic islet cells following daily intraperitoneal administration for 140 days, of an iron chelate complex, ferric nitrolotriacetate. The animals developed glycosuria, hyperglycemia, and ketonemia. These abnormalities returned to normal when the animals were subjected to weekly phlebotomy. There was no microscopic evidence of fibrosis, either hepatic or pancreatic: however, a longer period of iron administration may be required before these changes are observed. McLaren et al.“” have observed increased hepatic parenchymal iron stores in a male beagle dog treated with thiouracil and fed an atherogenic diet high in cholesterol and cholic acid. The dog was severely anemic (hematocrit 8%). On a normal diet without thiouracil there was a shift of storage iron from hepatocytes to Kupffer cells. Although of considerable interest, this cannot be considered as an animal model for human hereditary hemochromatosis. While no satisfactory animal model for hemochromatosis has yet been produced, this does not disprove a potential etiologic role for iron in human hemochromatosis. Animal models for hemochromatosis may have failed to produce tissue dam-
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age because of the relatively short duration of iron loading, or because the iron has been administered in a parenteral form that has been deposited primarily in cells of the RE system. This is analogous to iron overload in humans produced by repeated transfusions, such as may occur in aplastic anemia. In transfusional iron overload, tissue concentrations of iron may be as high as those seen in advanced idiopathic hemochromatosis (IHC); however, iron accumulates predominantly in RE cells and tissue damage is rarely seen except in the later stages when some redistribution of iron to parenchymal cells occurs. In contrast, in IHC and erythropoietic hemochromatosis (EHC) (e.g., iron overload secondary to anemias with a hyperplastic bone marrow, and ineffective erythropoiesis, such as thalassemia major) iron is deposited predominantly in parenchymal cells. Reticuloendothelial iron overload appears to be relatively innocuous, whereas parenchymal iron overload eventually results in cellular dysfunction. The distribution of tissue iron in ironoverload states is thus related to the source of excess iron; IHC and EHC are characterized by an inappropriate increase in iron absorption with a subsequent deposition of iron primarily in parenchymal cells, whereas in transfusional siderosis the excess iron arises from parenteral sources and iron is deposited primarily in RE cells. Although the mechanism of iron toxicity is unknown, a number of recent studies have demonstrated possible ways in which iron may produce cellular damage and fibrosis. It has been known for some time that excess iron is deposited in lysosomes, probably as hemosiderin.“” In patients with IHC or tranfusional iron overload, and in experimental iron overload, enzymic analyses have shown increased activities of acid hydrolases and enhanced lysosomal fragility in liver homogenates.35 Following phlebotomy therapy, these abnormalities were no longer detected. The mechanism of lysosomal disruption by iron is uncertain. It is possible that the excessive accumulation of ferritin or hemosiderin in lysosomes physically disrupts the organelle with intracellular release of its enzymes. An alternative explanation is that the normal mechanisms for handling excess iron, such as the storage of iron as ferritin, are exceeded, releasing free iron that induces membrane lipid peroxidation.36.37 This may occur through a number of possible mechanisms. One hypothesis is that iron promotes the production of free-radicals such as superoxide, hydrogen peroxide, and the hydroxyl radical. Since the Fe”+/Fe*+ reaction entails a one-electron transfer, iron catalyzes many redox reactions in which free-radicals are formed. Free-radicals, because of their unstable electronic configurations, have been implicated in tissue
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damage in a wide variety of disorders.38 It is possible that iron promotes free-radical mediated lipid peroxidation with consequent damage to lysosomal membranes and the release of lysosomal enzymes, which in turn cause cellular damage. The relationship of lysosomal fragility to hepatic fibrosis and cirrhosis is unclear. A puzzling feature of IHC is that hepatic fibrosis is often seen in the absence of marked hepatic necrosis and inflammatory infiltrate. In thalassemia major, an electron-microscopic study has demonstrated that collagen deposition precedes any morphologic evidence of cellular injury.3Y There is some evidence to suggest that excess iron stimulates the synthesis of collagen39 and that iron chelators inhibit the hydroxylation of proline and lysine residues.4” However, a greater understanding of the effect of iron-excess on fibrous tissue formation must await further research.
Changing Concepts of Hemochromatosis: Its Definition and Diagnostic Criteria Troisier41 first described the syndrome of diabetes mellitus, hyperpigmentation, and cirrhosis with iron overload. The term “hemochromatosis” was coined by von Recklinghausen” because he believed that the excess pigment came from the blood. Sheldon in his classic review of the literature to 1935,4” proposed that the various clinical and pathologic features of the syndrome had a common pathogenesis resulting from an inborn error of iron metabolism, and he concluded that the term “hemochromatosis” was, “in spite of its implicit and unproved assumptions,” the most suitable name for the disease. The widespread use of percutaneous needle biopsy of the liver led to definitions based primarily on pathologic features,24.25.44 essentially hepatic fibrosis or cirrhosis and excess iron in parenchymal cells of the liver and other organs. In recent years, the definition has come to be based on pathophysiologic criteria, and the term “hemochromatosis” has been broadened to include other disorders now known to lead to a very similar clinicopathologic picture (Table 1). All of these disorders result in a progressive increase in total body iron with deposition of iron in parenchymal cells. Hence the term “hemochromatosis” now refers to a group of disorders in which there is a progressive increase in total body iron stores with deposition of iron in the parenchymal cells of the liver, heart, pancreas, and other organs. The increase in total body iron results from iron absorption inappropriate to the level of body iron stores, either alone or in combination with parenteral iron loading. Parenchymal deposition of iron eventually results in cellular damage and functional insufficiency of the organs in-
February
Table
HEMOCHROMATOSIS:
1980
1.
Causes of Hemochromatosis
IDIOPATHIC (primary, SECONDARY
hereditary)
hemochromatosis
(IHC)
hemochromatosis
Secondary to anemia and ineffective Thalassemia major Sideroblastic anemia
erythropoiesis
Secondary to liver disease Alcoholic cirrhosis Following portacaval anastomosis Secondary to high oral iron intake Prolonged ingestion of medicinal iron Intake of iron with alcoholic beverages
(‘Bantu
siderosis’)
volved. In contrast, increased RE deposition of iron is relatively innocuous, and disorders associated with predominantly RE iron deposition, such as transfusional iron overload, are not included in the definition. The terms “hemosiderosis” and “siderosis” are best avoided; although they are used by some to indicate the deposition of stainable iron in tissues, they are not helpful in defining the site or the extent of the increased iron deposition. The most common causes of hemochromatosis are idiopathic hemochromatosis (IHC) and hemochromatosis secondary to iron-loading anemias, also known as erythropoietic hemochromatosis (EHC). The other causes are rare. The metabolic fault leading to inappropriate iron absorption in IHC remains an enigma, and it is still uncertain whether the site of the defect lies in the intestine or elsewhere in the body. Recent interest has centered on defects in the intestinal mucosal control of iron absorption,45 an abnormal affinity of the liver for transferrin iron,“’ and abnormalities in the reticuloendothelial handling of iron.47 The clinical and pathologic features of IHC have been described in detail elsewhere.25+4 In most cases of secondary hemochromatosis, the cause of the increased iron absorption and parenchymal deposition is obvious, e.g., in the anemias associated with ineffective erythropoiesis and erythropoictic hyperplasia. However, situations that lead to confusion as to the cause of the hemochromatosis include: (a) iron overload occurring in alcoholics (discussed below), and (b) hemochromatosis in subjects who have ingested large amounts of iron over extended periods. The question of whether hemochromatosis can result from prolonged ingestion of oral iron in normal subjects is an unresolved and important issue, especially since in some countries bread and other foodstuffs are fortified with iron. Hemochromatosis has been described in South African blacks (“Bantu hemochromatosis”) resulting from excessive oral iron
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combined with alcohol intake,” but this is an exceptional situation. There have been occasional reports of hemochromatosis occurring in Caucasian subjects following prolonged ingestion of medicinal iron, but the possibility that such subjects possessed a gene for IHC cannot be excluded. Recent family studies that included the determination of histocompatiblity antigens have suggested that IHC is inherited as an autosomal recessive trait and that the gene frequency is high, possibly of the order of 1~20.~” Clearly, until the basic genetic abnormality has been elucidated and the gene frequency of hemochromatosis is known, it would be unwise to fortify flour with iron, at least in developed countries. In addition, caution should be exercised in prescribing iron preparations except in pregnancy or established iron deficiency. This is especially important in patients with hepatic cirrhosis and in relatives of patients with IHC. It is noteworthy that fortification of food with iron has been associated with increased serum iron levels in some subjects48; these subjects may be carrying the gene for IHC. The minimum criteria acceptable for the diagnosis of IHC will continue to be conjectural until the basic metabolic defect is known. Ideally, it is desirable to have all of the following features: (a) increased total body iron stores with primarily parenchymal cell distribution: (b) absence of other known cause of iron overload; and (c) a family history of iron-storage disease. Subjects fulfilling these criteria usually demonstrate an inappropriate increase in iron absorption when this is measured. In practice, one often has to make a presumptive diagnosis of IHC on the basis of grossly increased parenchymal iron stores in the absence of other causes. In such cases, detailed family investigations, including HLA studies, may be of assistance (p 379). Thus, if one suspects the diagnosis of hemochromatosis on clinical grounds, one should proceed as follows: 1. Determine the serum concentrations of iron and ferritin and the percentage saturation of transferrin. If the results of all three tests are normal, the probability of the patient having IHC approaches zero.“” If one or more of these three tests is abnormal, liver biopsy should be performed with histochemica1 staining for iron and measurement of iron concentration. Known causes of iron overload, e.g., hemopoietic disorders, should be excluded. All first-degree relatives over the age of 10 yr should then be screened for excessive iron stores. Such screening should be repeated at appropriate intervals (see p 379).
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Distinction Between Liver Disease
GASTROENTEROLOGY
ICH and Alcoholic
Much of the confusion regarding iron overload and cirrhosis stems from misinterpretation of the significance of stainable iron as a measure of tissue iron concentration. Until recently, minor degrees of stainable iron were thought to represent excess iron. It is now recognized that slight-to-moderate stainable iron is quite common in normal livers, and is not incompatible with normal levels of body iron stores. Increased stainable hepatic iron is also common in patients with cirrhosis, particularly alcoholic cirrhosis. Alcoholic patients with cirrhosis and increased stainable iron in the liver can be divided into two groups: (a) those patients who have a mild-tomoderate increase in stainable iron but relatively normal body iron stores, and (b) patients with gross iron deposition and increased total body iron stores of the magnitude seen in IHC (15-50 g iron stores). The majority of the patients in the first group have alcoholic liver disease (usually cirrhosis) with some increase in stainable hepatic iron, but little increase in total body iron. These patients do not have IHC. Simon et a1.5’ concluded from their study, which included determination of HLA antigens, that such subjects were not heterozygous for the disease. Liver iron concentration in patients with alcoholic cirrhosis is usually less than twice the upper limit of normal.” The reason for the increased stainable iron is unknown. It may be related in part to cell necrosis and uptake of released iron by adjacent Kupffer and parenchymal cells. The second group of alcoholic subjects have cirrhosis with gross iron overload probably and have IHC.““~“”A study of the hepatic pathology of alcoholic patients with a family history of IHC”” revealed that in approximately 75% of them the histologic changes were indistinguishable from those in nonalcoholic subjects with IHC. The remaining 25% showed very similar changes, but with features of alcoholic liver disease superimposed. It is noteworthy that the same proportion (approximately 25%) of heavy drinkers in the general population show changes of alcoholic liver disease.53 In rare instances, patients with alcoholic cirrhosis may show the sequence of change from alcoholic cirrhosis without demonstrable iron to the full clinicopathologic picture of hemochromatosis.“” In our experience, other factors, e.g. hemolysis or portalsystemic anastomosis, contributing to the iron overload can be identified in most of these subjects. A controlled study of phlebotomy therapy in patients with alcoholic cirrhosis and iron overload showed that there was no improvement in clinical, biochemical or pathologic markers.55 As phlebotomy
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appears to benefit patients with IHC,27,*” the distinction between IHC and alcoholic cirrhosis is of prime importance.
Mode of Inheritance
of IHC
In 1975, Simon described an association between IHC and certain HLA antigens, in particular HLA A3.“” Subsequent reports have now confirmed this association in many countries. Detailed analysis of families with IHC has confirmed that in most, if not all, families IHC is inherited as an autosomal recessive trait.57.58It now appears almost certain that at least one IHC susceptibility gene is located on chromosome 6 in close proximity to the A 10cus.~~-@’ Since homozygotes require two such alleles for full expression of the disease, it is possible in family studies to identify homozygote and heterozygote relatives by comparing their HLA antigens to those of the proband, who is presumed to be homozygote. Partial biochemical expression of the disease occurs in a small proportion of heterozygote relatives.58.5g Thus, HLA-typing has provided a useful new tool for understanding the inheritance of IHC and for identifying relatives at risk of developing iron overload.
Diagnosis and Management of Precirrhotic Hemochromatosis in Relatives In the past few years, this aspect of IHC has received more attention than any other, probably because of increasing interest in the mode of inheritance and also because of mounting evidence that early diagnosis and therapy can prevent or delay the fatal complications. Although the value of early diagnosis and treatment is not in doubt, there has not been general agreement about the most reliable and the simplest regimen for screening relatives of patients with IHC. The most reliable single test for the estimation of body iron stores is hepatic biopsy and chemical measurement of hepatic iron concentration. I-Iowever, it is not feasible to perform liver biopsy on all relatives and simpler, less invasive, tests are obviously desirable. The noninvasive tests that have attracted most attention are estimation of the serum iron level, percentage saturation of transferrin, and, more recently, the serum ferritin concentration. Each has its inherent advantages and limitations. The serum iron level and transferrin saturation are elevated early in the course of the disease, but their specificity is reduced by a relatively high frequency
February
1980
of false positives and negatives. In a study of 242 members of 43 families with IHC, the serum iron level was elevated in only 76% of relatives with increased iron stores and also in 10% of relatives with normal iron stores.” Although the percentage saturation of transferrin was elevated in all relatives with increased iron stores, it was also elevated in 33% of relatives with normal iron stores. Wands et al.‘l reported two families in which the serum ferritin levels were normal in several subjects despite increased hepatic and total body iron stores. However, subsequent studies of large numbers of families with IHC in the U.S.A.,“’ England,“3 Europe, 59 and Australia’” have confirmed that in untreated patients with clinically manifest hemochromatosis, the serum ferritin level is greatly increased (approximately 5-10 times normal) and the level correlates with the magnitude of body iron stores. In these studies, the serum ferritin level was also elevated in most precirrhotic asymptomatic relatives with an increase in body iron stores. Hence the estimation of serum ferritin is a useful, noninvasive screening test for early IHC since it is usually elevated before there is any morphologic evidence of liver damage, a point of considerable practical importance. Several commercial radioimmunoassay kits for the estimation of serum ferritin are now available, and the test has virtually replaced the more cumbersome screening tests involving measurement of urinary iron excretion. In clinical practice, the combined measurements of (1) serum iron concentration, (2) percent transferrin saturation, and (3) serum ferritin level provide the best screening regimen for IHC, including the precirrhotic phase of the disease. HLA typing may help in identifying relatives at risk of developing the cost and diffidisease,M however the comparative culty in performing this determination limits its usefulness. Thus, the following are practical guidelines for the routine screening of relatives of patients with IHC: 1. All first-degree relatives (males and females) over the age of about 10 yr should be screened using the tests recommended for diagnosis of the disease in probands, i.e., the combination of serum iron concentration, percentage saturation of transferrin, and serum ferritin concentration. 2. If any one of the above tests is abnormal, liver biopsy should be performed with estimation of stainable parenchymal iron and hepatic iron concentration. 3. Serial investigations at intervals over a number of years are recommended, particularly in women and young subjects, since the presence of normal iron and ferritin levels does not preclude the later
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development of iron overload and cirrhosis. If HLA-typing is available, it can help determine the appropriate frequency of such reassessment. For example, if a sibling shares two HLA haplotypes in common with the proband, the risk of developing iron overload is high, and iron and ferritin studies should be performed yearly or secondyearly.” If one of the offspring has unequivocal evidence of the disease, this may allow identification of all HLA haplotypes associated with the disease (including the haplotype from the unaffected spouse), and thus aid in diagnosis of IHC in other offspring.” In contrast, if no HLA haplotype is shared with the proband, the risk of developing iron overload is low. However, it should be emphasized that patients with IHC have been described with neither HLA haplotype in common with the proband.” While there is evidence that phlebotomy therapy prolongs life in established symptomatic patients with hemochromatosis,27~‘R there have been no controlled studies reported of such therapy in early, precirrhotic IHC. However, in our experience, early phlebotomy therapy with removal of excess iron arrests tissue damage and appears to prevent the overt manifestations of the disease. In young, precirrhotic patients, weekly phlebotomy should reduce iron stores to normal within less than 2 yr. Following this, phlebotomy will be required every 3-4 mo to prevent reaccumulation of iron. The patient can be reassured that the life expectancy is excellent, providing iron reaccumulation does not occur over the long period of follow-up. The clinician should stress to the patient the importance of maintaining iron stores within normal limits and of checking subsequent generations for iron overload. It is noteworthy that to date, there has been no published report of the development of hepatocellular carcinoma in IHC before the occurrence of cirrhosis. Thus, early diagnosis and phlebotomy therapy in the precirrhotic stage is of paramount importance. Since inexpensive yet reliable techniques are now available for early detection and effective therapy of iron overload, IHC, as a clinical disease, should be preventable in a large proportion of patients. References 1. Halliday
JW, Powell LW: Ferritin Metabolism. In: Metals and the Liver. Edited by LW Powell. New York, Marcel Dekker Inc., 1978, p 68 2. Linder MC. Munro HN: Metabolic and chemical features of ferritins, a series of iron-inducible tissue proteins. Am J Path01 72263-282, 1973 3. Lipschitz DA, Bothwell TH, Seftel HC. et al: The role of
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7.
8. 9.
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15. 16.
17.
18.
19.
20.
21.
22.
23.
24.
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ascorbic acid in the metabolism of storage iron. Br J Haematol 20:155-163, 1971 Schwartz E, Cohen A: Iron Chelation and the Role of Ascorbic Acid Proceedings of the Fourth International Symposium of Proteins of Iron Storage and Transport, April, 1979 Davos, Switzerland Roeser HP, Halliday JW, Nikles A, et al: The effect of ascorbic acid deficiency on serum ferritin levels in guinea pigs. Proceedings of the British Biophysical Society April, 1979 Sheffield, UK Drysdale JW: Ferritin phenotypes: Structure and metabolism. In: Iron Metabolism Ciba Foundation Symposium 51 (New Series). Amsterdam, Elsevier, 1977, p 41-67 Powell LW, Alpert E, Drysdale JW, Isselbacher K: Abnormality in tissue isoferritins in idiopathic hemochromatosis. Nature (Lond) 250:333-335, 1974 Powell LW, McKeering LV, Halliday JW: Alterations in tissue ferritins in iron storage disorders. Gut 16:909-912, 1975 Halliday JW, McKeering LV, Tweedale, R, et al: Serum ferritin in hemochromatosis: changes in the isoferritin composition during venesection therapy. Br J Haematol 36:395-404, 1977 Alpert E: Characterization and subunit analysis of ferritin isolated from normal and malignant human liver. Cancer Res 351505-1509, 1975 Halliday JW, McKeering LV, Powell LW: Isoferritin composition of tissues and serum in human malignancies. Cancer Res 36:4486-4490, 1976 Hicks SJ, Drysdale JW, Munroe HN: Preferential synthesis of ferritin and albumin by different populations of liver polysome.% Science 164:584-585, 1969 Shafritz DA, Drysdale JW: Studies on cell-free synthesis of ferritin under direction of endogenous and exogenous mRNA. In: Proteins of Iron Storage and Transport in Biochemistry and Medicine. Edited by R Crichton. Amsterdam, North Holland, 1975, p 327-334 Halliday JW, Powell LW: Serum ferritin and isoferritins in clinical medicine. In: Progress in Hematology. Volume 11. Edited by EB Brown. New York, Grune & Stratton, 1979 (in press) Jacob A, Worwood M: Ferritin in serum: clinical and biochemical implications. N Engl J Med 292:951-956, 1975 Halliday JW, Mack U, Powell LW: Kinetics of serum and tissue ferritins: relation to carbohydrate content. Br J Haematol 42:(4)535-546, 1979 Addison GM, Beamish MR, Hales CW, et al: An Immunoradiometric assay for ferritin in the serum of normal subjects and patients with iron deficiency and iron overload. J Clin Path01 25326-329, 1972 Reissman KR, Dietrich MR: On the presence of ferritin in the peripheral blood of patients with hepatocellular disease. J Clin Invest 35:588-595, 1956 Marcus DM, Zinberg N: Measurement of serum ferritin by radioimmunoassay: results in normal individuals and patients with breast cancer. J Nat1 Cancer Inst 55:791-795, 1975 Hazard JH, Drysdale JW: Ferritinaemia in cancer. Nature (Lond) 265:755-756, 1977 Siimes MA, Wang WC, Dallman PR: Elevated serum ferritin in children with malignancies. Stand J Haematol 19:153-158, 1977 Jones PAE, Miller FM, Worwood M, et al: Ferritinaemia in leukaemia and Hodgkin’s Disease. Br J Cancer 27:212-217, 1973 Parry DH, Worwood M, Jacobs A: Serum ferritin in acute leukaemia at presentation and during remission. Br Med J 1:245247, 1975 MacDonald RA: Hemochromatosis and hemosiderosis. Springfield, Ill., Charles C Thomas, Publishers, Inc., 1964
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25. Finch SC, Finch CA: Idiopathic hemochromatosis: an iron storage disease. Medicine (Baltimore) 34:381-430, 1955 26. Isaacson C, Seftel HC, Helley KJ, et al: Siderosis in the Bantu: the relationship between iron overload and cirrhosis. J Lab Clin Med 58:845-853, 1961 27. Bomford A, Williams R: Long term results of venesection therapy in idiopathic haemochromatosis. Q J Med 45:611-623, 1976 28. Powell LW: Changing concepts in haemochromatosis. Postgrad Med J 46:200-209, 1970 29. Barry M, Flynn DM, Letsky EA, et al: Long-term chelation therapy in thalassemia major: Effect on liver iron concentration, liver histology, and clinical progress. Br Med J 2:16-20, 1974 30. Lisboa PE: Experimental hepatic cirrhosis in dogs caused by chronic massive iron overload. Gut 12:363-368, 1971 31. MacDonald RA, Pechet GA: Experimental hemochromatosis in rats. Am J Path01 46:85-109, 1965 32. Awai M: Intraperitoneal injection of a chelate iron complex salt causes diabetes in rat and rabbits. Acta Haematol Jap 41:1293-1300, 1978 33. McLaren G, Muir A, Sachs S, et al: Animal model for hemochromatosis: hereditary susceptibility to hepatocellular iron overload. Proc. of the Fourth International Conference on Proteins of Iron Metabolism, Davos, Switzerland, May, 1979 34. Trump BF, Valigorsky JM, Arstila AU, et al: The relationship of intracellular pathways of iron metabolism to cellular iron overload and iron storage diseases. Am J Path01 72:295-336, 1973 35. Peters TJ, Seymour CA: Acid hydrolase activities and lysosomal integrity in liver biopsies from patients with iron overload. Clin Sci Mol Med 50:75-78, 1976 36. Hunter FE, Gebicki JM, Hoffstein PE, et al: Swelling and lysis of rat liver mitochondria induced by ferrous ions. J Biol Chem 238:828-835, 1963 37. Arstila AU, Smith MA, Trump BF: Microsomal lipid peroxidation: morphological characterization. Science 175:530533, 1972 38. Aisen P: Some physiochemical aspects of iron metabolism. In: Iron Metabolism. Ciba Foundation Symposium 51 (New Series). Amsterdam, Elsevier North-Holland, 1977, p 1-18 39. Iancu TC, Neustein HB, Landing BH: The liver in thalassemia major ultrastructural observations. In: Iron Metabolism Ciba Foundation Symposium 51 (New Series). Amsterdam, Elsevier North-Holland, 1977, p 293 40. Rojkind M, Dunn MA: Hepatic fibrosis. Gastroenterology 76:849-863, 1979 41. Troisier M: Diabete sucre. Bull Sot Anat Paris 16:231-235, 1871 42. von Recklinghausen FD: Tageblatt der (62) Versammlung Deutsch, Naturforscher und Arzte in Heidelberg. p 324, 1889 43. Sheldon JH: Haemochromatosis. London, Oxford University Press, Humphrey Milford, 1935 44. Grace ND, Powell LW: Iron storage disorders of the liver. Gastroenterology 64:1257-1283, 1974 45. Cox TM, Peters TJ: Uptake of iron by duodenal biopsy specimens from patients with iron-deficiency anaemia and primary haemochromatosis. Lancet 1:123-124, 1978 46. Batey RG, Pettit JE, Nicholas AW, Sherlock Sheila, Hoffbrand AV: Hepatic iron clearance from serum in treated hemochromatosis. Gastroenterology 75:856-859, 1978 47. Fillet G, Marsaglia G: Idiopathic haemochromatosis: abnormality in RBC transport of iron by the reticuloendothelial system. Blood 1007:46, 1976 48. Simon M, Alexandre J-L, Fauchet R, et al: The genetics of hemochromatosis. Prog Med Genet (in press), 1979 49. Olsson KS, Heedman PA, Stangard F: Preclinical hemochromatosis in a population on a high-iron-fortified diet.
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1980
JAMA 239:1999-2000, 1978 50. Halliday JW, Cowlishaw JL, Russo AM, et al: Serum ferritin in diagnosis of haemochromatosis. Lancet 1621-624, 1977 51. Simon M, Bourel M, Genetet B, et al: Idiopathic hemochromatosis and iron overload in alcoholic liver disease: differentiation by HLA phenotype. Gastroenterology 73:655-658, 1977 52. Powell LW: The role of alcoholism in hepatic iron storage disease. Ann NY Acad Sci 252124-134, 1975 53. Powell LW, Kerr JFR: The pathology of the liver in hemochromatosis. In: Pathobiology Annual 1975. Edited by HL Ioachim. New York, Appleton-Century-Crofts, 1975, p 317-336 54. Sabesin SM, Thomas LB: Parenchymal siderosis in patients with preexisting portal cirrhosis: a pathologic entity simulating idiopathic and transfusional hemochromatosis. Gastroenterology 46:477-485, l-964 55. Grace ND, Greenberg MS: Phlebotomy in the treatment of iron overload. A controlled trial (a preliminary report). Gastrocnterology 60:744, 1971 56. Simon M, Pawlotsky Y, Bourel M, et al: Hemochromatose idiopathiqur:: maladie associee a l’antigene HLA-A3? Nouv Pressc Med 14324, 1975 57. Simon M, Bourel M, Gcnetet B, et al: Idiopathic hemo-
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chromatosis: demonstration of recessive transmission and early detection by family HLA typing. N Engl J Med 297:10171021, 1977 58. Cartwright GE, Edwards CQ, Kravitz K, et al: Hereditary hemochromatosis: phenotypic expression of the disease. N Engl J Med 301:175-179, 1979 59. Beaumont C, Simon M, Fauchet R, et al: Serum ferritin as a possible marker of the hemochromatosis allele. N Engl J Med 301:169-174. 1979 60. Kidd KK: Genetic linkage and hemochromatosis (editorial). N Engl J Med 301:209-210, 1979 61. Wands JR, Rowe JA, Mezey SE, et al: Normal serum ferritin concentrations in precirrhotic hemochromatosis. N Engl J Med 294:302-305, 1976 62. Edwards CQ, Carroll M, Bray P. et al: Hereditary hemochromatosis: diagnosis in siblings and children. N Engl J Med 297:7-13, 1977 63. Batey RG, Hussein S, Sherlock S, ct al: The role of serum ferritin in the management of idiopathic haemochromatosis. Stand J Castroenterol 13:953-957, 1978 64. Bassett ML, Halliday JW, Powell LW, et al: Early detection of idiopathic hemochromatosis: relative value of serum ferritin and HLA typing. Lancet 24-7, 1979
CLINICAL
TRENDS
1980
AND TOPICS
Hemochromatosis:
1980Update
LAWRIE W. POWELL, and JUNE
78374-381,
MARK W. HALLIDAY
L. BASSETT,
Department of Medicine, University of Queensland. Royal Brisbane Hospital, Brisbane, Australia
During the past decade there have been major advances in the knowledge of the biology of iron and of clinical disorders resulting from abnormalities in body iron metabolism. These advances include: (a) structural and functional aspects of the major proteins of iron storage and transport, ferritin, and transferrin; (b) new concepts of the possible mechanisms of iron toxicity; (c) the early detection and management of iron deficiency and iron overload; and (d) clarification of the genetic nature of idiopathic hemochromatosis (IHC). This review is devoted primarily to the role of the liver in iron metabolism and iron-storage diseases, and to the major recent advances in the knowledge of hemochromatosis.
Iron Storage and the Liver The liver is the major storage organ for iron in normal subjects and in patients with iron overload. The total body iron in normal, iron-replete subjects amounts to approximately five grams, of which about 35% is present as storage iron. Approximately one-third of the storage iron is found in the liver, primarily as ferritin. This provides an internal reserve that can be mobilized when needed and also protects against iron toxicity. It is known that hepatocytes as well as Kupffer cells participate in iron storage.’ In the normal liver, most of the nonheme iron is found in hepatocytes, in the form of ferritin.’ When iron is given parenterally, both hepatocytes and Kupffer cells accumulate large amounts of additional ferritin, although Kupffer cells tend to store relatively more of the excess nonheme iron in forms other than ferritin, e.g., hemosiderin.” Ascorbic acid appears to be involved in the incorporation and release of iron from ferritin, at least in iron-storage disorders (e.g., thalassemia), and also in Received June 12, 1979. Accepted September 13.1979. Address requests for reprints to: Professor L. W. Powell, Department of Medicine, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, Queensland, Australia 4029. 0 1980 by the American Gastroenterological Association 00185085/80/020374-08$02.25
the removal of iron from hemosiderin.“,’ In ascorbic acid deficiency, serum iron levels are inappropriately low, and there is an increased cellular content of hemosiderin, which can be readily reversed by the administration of ascorbic acid.” A fall in the serum ferritin level has also been observed in ascorbic acid deficiency in guinea pigs.” However, further work is required to determine the precise role of ascorbic acid in normal iron and ferritin metabolism. The liver forms a major component of the reticuloendothelial (RE) system. At the end of their life span, erythrocytes are phagocytosed by macrophages of the RE system, and the released iron is either stored within the macrophages (including Kupffer cells), or returned to transferrin in the plasma. Surplus iron is stored within parenchymal cells of the liver, muscle, and other organs, as well as in macrophages of the spleen, liver, and bone marrow.
Structure
and Metabolism
of Ferritin
The existence of a high-molecular-weight iron-storage protein, ferritin, in the liver and many other tissues has been recognized for many years. It is now known that electrophoretically pure ferritins may be resolved into multiple isoferritins by isoelectric focusing. The ferritin molecule consists of 24 subunits. The existence of subunits of two types, designated H & L, which differ in molecular weight, immunologic reactivity, and amino acid composition, has been postulated as a mechanism for the observed microheterogeneity of the ferritin molecule.” Each tissue has a characteristic isoferritin profile that can be shown to change in different physiologic and pathologic states, particularly iron overload,7.R during phlebotomy’ and in malignancy.“,” However, the functional significance of isoferritins is still unclear. The synthesis of ferritin within the hepatocyte is stimulated by iron and occurs primarily on free polysomes.” However, ferritin synthesis also occurs on bound po1ysomes.‘3 The origin of circulating ferritin is a subject of considerable interest and specu-
HEMOCHROMATOSIS:
February 1980
lation at present. It seems probable that serum ferritin is actively secreted, perhaps arising from the bound polysomes, and its presence in serum is not merely the result of tissue necrosis.14 There is some evidence that serum ferritin originates from RE cells.‘4,‘5 However, its exact origin and biologic function are far from clear. Injected ferritin derived from serum and various tissues has been shown to be taken up and metabolized rapidly by the liver.‘” The precise pathways are unknown. Whatever the source and biologic function of serum ferritin, its concentration reflects total body iron stores’4~‘” and its place as an important screening test for iron deficiency and iron overload is now firmly established.“,‘“,” Thus, as a noninvasive test it is particularly applicable to population surveys to detect iron deficiency. In contrast to the serum iron concentration and transferrin saturation, there are fewer false positives and false negatives, and there appears to be little or no diurnal variation. A serum ferritin concentration below 10 pg/liter is indicative of low iron stores. However, some other disease states may elevate serum ferritin concentration. Such states include hepatocellular necrosis,lH malignant neoplasms,1y~21 leukemia and related disorders of the RE system,22.23 The precise place of serum ferand inflammation.14~” ritin measurements in the detection of iron deficiency in these conditions has not yet been clearly defined.
Pathogenesis Overload
of Tissue Injury in Iron
The role of excess iron in producing the pathologic changes of acute iron toxicity is not disputed; however the pathogenesis of the tissue damage that accompanies chronic iron overload has been a matter of some debate. The pathologic changes seen in idiopathic hemochromatosis, for instance, were thought at one time to be due to excess alcohol ingestion, the iron deposition occurring coincidenThe inability to provide an experimental tally.“” model for hemochromatosis has in the past raised serious questions about the role of iron in the pathogenesis of chronic liver damage. However, despite this, it is now generally accepted that deposition of excess iron in hepatocytes and other parenchymal cells is responsible for tissue damage. Evidence for chronic iron toxicity is based on a number of observations: (a) Similar clinical and pathologic changes are seen following longstanding parenchymal iron overload, regardless of the etiology (idiopathic hemochromatosis, hemochromatosis secondary to ineffective erythropoiesis, dietary iron overload, etc).25.2” (b) In idiopathic hemochromatosis and “dietary” he-
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mochromatosis as seen in South African blacks, the presence of large amounts of iron in the liver and pancreas is frequently associated anatomically with fibrosis, and the severity of fibrosis is roughly proportional to the tissue iron concentration.‘” (c) Although there have been no controlled studies of phlebotomy therapy in idiopathic hemochromatosis, at least two studies have been published that show convincing evidence of clinical and pathologic improvement together with an increased survival rate following such therapy,Z7,“H and few clinicians would dispute the value of phlebotomy treatment in hemochromatosis. (d) In a prospective trial of chelation therapy in children with thalassemia major, subjects treated with deferoxamine showed a significant reduction in hepatic iron accumulation and a retardation in the progression of hepatic fibrosis when compared with patients not receiving chelation therapy.“’ (e) While earlier animal models have failed to demonstrate tissue damage resulting from chronic iron overload, several recent experiments in animals have produced some evidence for chronic iron toxor iron sorbitol in icity. Lisboa,“” using iron dextran parenteral doses ranging from 3.5 to 5.8 g iron/kg body weight over several months, produced a lesion histologically similar to human hemochromatosis in five of seven dogs. In rats fed a choline-deficient, high-fat diet with dietary iron supplementation for over 1 yr, cirrhosis with hepatic iron deposition developed”‘; however rats on a choline-deficient diet without iron also developed cirrhosis. More recently, Awai”” has observed deposition of iron in hepatocytes and pancreatic islet cells following daily intraperitoneal administration for 140 days, of an iron chelate complex, ferric nitrolotriacetate. The animals developed glycosuria, hyperglycemia, and ketonemia. These abnormalities returned to normal when the animals were subjected to weekly phlebotomy. There was no microscopic evidence of fibrosis, either hepatic or pancreatic: however, a longer period of iron administration may be required before these changes are observed. McLaren et al.“” have observed increased hepatic parenchymal iron stores in a male beagle dog treated with thiouracil and fed an atherogenic diet high in cholesterol and cholic acid. The dog was severely anemic (hematocrit 8%). On a normal diet without thiouracil there was a shift of storage iron from hepatocytes to Kupffer cells. Although of considerable interest, this cannot be considered as an animal model for human hereditary hemochromatosis. While no satisfactory animal model for hemochromatosis has yet been produced, this does not disprove a potential etiologic role for iron in human hemochromatosis. Animal models for hemochromatosis may have failed to produce tissue dam-
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age because of the relatively short duration of iron loading, or because the iron has been administered in a parenteral form that has been deposited primarily in cells of the RE system. This is analogous to iron overload in humans produced by repeated transfusions, such as may occur in aplastic anemia. In transfusional iron overload, tissue concentrations of iron may be as high as those seen in advanced idiopathic hemochromatosis (IHC); however, iron accumulates predominantly in RE cells and tissue damage is rarely seen except in the later stages when some redistribution of iron to parenchymal cells occurs. In contrast, in IHC and erythropoietic hemochromatosis (EHC) (e.g., iron overload secondary to anemias with a hyperplastic bone marrow, and ineffective erythropoiesis, such as thalassemia major) iron is deposited predominantly in parenchymal cells. Reticuloendothelial iron overload appears to be relatively innocuous, whereas parenchymal iron overload eventually results in cellular dysfunction. The distribution of tissue iron in ironoverload states is thus related to the source of excess iron; IHC and EHC are characterized by an inappropriate increase in iron absorption with a subsequent deposition of iron primarily in parenchymal cells, whereas in transfusional siderosis the excess iron arises from parenteral sources and iron is deposited primarily in RE cells. Although the mechanism of iron toxicity is unknown, a number of recent studies have demonstrated possible ways in which iron may produce cellular damage and fibrosis. It has been known for some time that excess iron is deposited in lysosomes, probably as hemosiderin.“” In patients with IHC or tranfusional iron overload, and in experimental iron overload, enzymic analyses have shown increased activities of acid hydrolases and enhanced lysosomal fragility in liver homogenates.35 Following phlebotomy therapy, these abnormalities were no longer detected. The mechanism of lysosomal disruption by iron is uncertain. It is possible that the excessive accumulation of ferritin or hemosiderin in lysosomes physically disrupts the organelle with intracellular release of its enzymes. An alternative explanation is that the normal mechanisms for handling excess iron, such as the storage of iron as ferritin, are exceeded, releasing free iron that induces membrane lipid peroxidation.36.37 This may occur through a number of possible mechanisms. One hypothesis is that iron promotes the production of free-radicals such as superoxide, hydrogen peroxide, and the hydroxyl radical. Since the Fe”+/Fe*+ reaction entails a one-electron transfer, iron catalyzes many redox reactions in which free-radicals are formed. Free-radicals, because of their unstable electronic configurations, have been implicated in tissue
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damage in a wide variety of disorders.38 It is possible that iron promotes free-radical mediated lipid peroxidation with consequent damage to lysosomal membranes and the release of lysosomal enzymes, which in turn cause cellular damage. The relationship of lysosomal fragility to hepatic fibrosis and cirrhosis is unclear. A puzzling feature of IHC is that hepatic fibrosis is often seen in the absence of marked hepatic necrosis and inflammatory infiltrate. In thalassemia major, an electron-microscopic study has demonstrated that collagen deposition precedes any morphologic evidence of cellular injury.3Y There is some evidence to suggest that excess iron stimulates the synthesis of collagen39 and that iron chelators inhibit the hydroxylation of proline and lysine residues.4” However, a greater understanding of the effect of iron-excess on fibrous tissue formation must await further research.
Changing Concepts of Hemochromatosis: Its Definition and Diagnostic Criteria Troisier41 first described the syndrome of diabetes mellitus, hyperpigmentation, and cirrhosis with iron overload. The term “hemochromatosis” was coined by von Recklinghausen” because he believed that the excess pigment came from the blood. Sheldon in his classic review of the literature to 1935,4” proposed that the various clinical and pathologic features of the syndrome had a common pathogenesis resulting from an inborn error of iron metabolism, and he concluded that the term “hemochromatosis” was, “in spite of its implicit and unproved assumptions,” the most suitable name for the disease. The widespread use of percutaneous needle biopsy of the liver led to definitions based primarily on pathologic features,24.25.44 essentially hepatic fibrosis or cirrhosis and excess iron in parenchymal cells of the liver and other organs. In recent years, the definition has come to be based on pathophysiologic criteria, and the term “hemochromatosis” has been broadened to include other disorders now known to lead to a very similar clinicopathologic picture (Table 1). All of these disorders result in a progressive increase in total body iron with deposition of iron in parenchymal cells. Hence the term “hemochromatosis” now refers to a group of disorders in which there is a progressive increase in total body iron stores with deposition of iron in the parenchymal cells of the liver, heart, pancreas, and other organs. The increase in total body iron results from iron absorption inappropriate to the level of body iron stores, either alone or in combination with parenteral iron loading. Parenchymal deposition of iron eventually results in cellular damage and functional insufficiency of the organs in-
February
Table
HEMOCHROMATOSIS:
1980
1.
Causes of Hemochromatosis
IDIOPATHIC (primary, SECONDARY
hereditary)
hemochromatosis
(IHC)
hemochromatosis
Secondary to anemia and ineffective Thalassemia major Sideroblastic anemia
erythropoiesis
Secondary to liver disease Alcoholic cirrhosis Following portacaval anastomosis Secondary to high oral iron intake Prolonged ingestion of medicinal iron Intake of iron with alcoholic beverages
(‘Bantu
siderosis’)
volved. In contrast, increased RE deposition of iron is relatively innocuous, and disorders associated with predominantly RE iron deposition, such as transfusional iron overload, are not included in the definition. The terms “hemosiderosis” and “siderosis” are best avoided; although they are used by some to indicate the deposition of stainable iron in tissues, they are not helpful in defining the site or the extent of the increased iron deposition. The most common causes of hemochromatosis are idiopathic hemochromatosis (IHC) and hemochromatosis secondary to iron-loading anemias, also known as erythropoietic hemochromatosis (EHC). The other causes are rare. The metabolic fault leading to inappropriate iron absorption in IHC remains an enigma, and it is still uncertain whether the site of the defect lies in the intestine or elsewhere in the body. Recent interest has centered on defects in the intestinal mucosal control of iron absorption,45 an abnormal affinity of the liver for transferrin iron,“’ and abnormalities in the reticuloendothelial handling of iron.47 The clinical and pathologic features of IHC have been described in detail elsewhere.25+4 In most cases of secondary hemochromatosis, the cause of the increased iron absorption and parenchymal deposition is obvious, e.g., in the anemias associated with ineffective erythropoiesis and erythropoictic hyperplasia. However, situations that lead to confusion as to the cause of the hemochromatosis include: (a) iron overload occurring in alcoholics (discussed below), and (b) hemochromatosis in subjects who have ingested large amounts of iron over extended periods. The question of whether hemochromatosis can result from prolonged ingestion of oral iron in normal subjects is an unresolved and important issue, especially since in some countries bread and other foodstuffs are fortified with iron. Hemochromatosis has been described in South African blacks (“Bantu hemochromatosis”) resulting from excessive oral iron
1980 UPDATE
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combined with alcohol intake,” but this is an exceptional situation. There have been occasional reports of hemochromatosis occurring in Caucasian subjects following prolonged ingestion of medicinal iron, but the possibility that such subjects possessed a gene for IHC cannot be excluded. Recent family studies that included the determination of histocompatiblity antigens have suggested that IHC is inherited as an autosomal recessive trait and that the gene frequency is high, possibly of the order of 1~20.~” Clearly, until the basic genetic abnormality has been elucidated and the gene frequency of hemochromatosis is known, it would be unwise to fortify flour with iron, at least in developed countries. In addition, caution should be exercised in prescribing iron preparations except in pregnancy or established iron deficiency. This is especially important in patients with hepatic cirrhosis and in relatives of patients with IHC. It is noteworthy that fortification of food with iron has been associated with increased serum iron levels in some subjects48; these subjects may be carrying the gene for IHC. The minimum criteria acceptable for the diagnosis of IHC will continue to be conjectural until the basic metabolic defect is known. Ideally, it is desirable to have all of the following features: (a) increased total body iron stores with primarily parenchymal cell distribution: (b) absence of other known cause of iron overload; and (c) a family history of iron-storage disease. Subjects fulfilling these criteria usually demonstrate an inappropriate increase in iron absorption when this is measured. In practice, one often has to make a presumptive diagnosis of IHC on the basis of grossly increased parenchymal iron stores in the absence of other causes. In such cases, detailed family investigations, including HLA studies, may be of assistance (p 379). Thus, if one suspects the diagnosis of hemochromatosis on clinical grounds, one should proceed as follows: 1. Determine the serum concentrations of iron and ferritin and the percentage saturation of transferrin. If the results of all three tests are normal, the probability of the patient having IHC approaches zero.“” If one or more of these three tests is abnormal, liver biopsy should be performed with histochemica1 staining for iron and measurement of iron concentration. Known causes of iron overload, e.g., hemopoietic disorders, should be excluded. All first-degree relatives over the age of 10 yr should then be screened for excessive iron stores. Such screening should be repeated at appropriate intervals (see p 379).
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Distinction Between Liver Disease
GASTROENTEROLOGY
ICH and Alcoholic
Much of the confusion regarding iron overload and cirrhosis stems from misinterpretation of the significance of stainable iron as a measure of tissue iron concentration. Until recently, minor degrees of stainable iron were thought to represent excess iron. It is now recognized that slight-to-moderate stainable iron is quite common in normal livers, and is not incompatible with normal levels of body iron stores. Increased stainable hepatic iron is also common in patients with cirrhosis, particularly alcoholic cirrhosis. Alcoholic patients with cirrhosis and increased stainable iron in the liver can be divided into two groups: (a) those patients who have a mild-tomoderate increase in stainable iron but relatively normal body iron stores, and (b) patients with gross iron deposition and increased total body iron stores of the magnitude seen in IHC (15-50 g iron stores). The majority of the patients in the first group have alcoholic liver disease (usually cirrhosis) with some increase in stainable hepatic iron, but little increase in total body iron. These patients do not have IHC. Simon et a1.5’ concluded from their study, which included determination of HLA antigens, that such subjects were not heterozygous for the disease. Liver iron concentration in patients with alcoholic cirrhosis is usually less than twice the upper limit of normal.” The reason for the increased stainable iron is unknown. It may be related in part to cell necrosis and uptake of released iron by adjacent Kupffer and parenchymal cells. The second group of alcoholic subjects have cirrhosis with gross iron overload probably and have IHC.““~“”A study of the hepatic pathology of alcoholic patients with a family history of IHC”” revealed that in approximately 75% of them the histologic changes were indistinguishable from those in nonalcoholic subjects with IHC. The remaining 25% showed very similar changes, but with features of alcoholic liver disease superimposed. It is noteworthy that the same proportion (approximately 25%) of heavy drinkers in the general population show changes of alcoholic liver disease.53 In rare instances, patients with alcoholic cirrhosis may show the sequence of change from alcoholic cirrhosis without demonstrable iron to the full clinicopathologic picture of hemochromatosis.“” In our experience, other factors, e.g. hemolysis or portalsystemic anastomosis, contributing to the iron overload can be identified in most of these subjects. A controlled study of phlebotomy therapy in patients with alcoholic cirrhosis and iron overload showed that there was no improvement in clinical, biochemical or pathologic markers.55 As phlebotomy
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appears to benefit patients with IHC,27,*” the distinction between IHC and alcoholic cirrhosis is of prime importance.
Mode of Inheritance
of IHC
In 1975, Simon described an association between IHC and certain HLA antigens, in particular HLA A3.“” Subsequent reports have now confirmed this association in many countries. Detailed analysis of families with IHC has confirmed that in most, if not all, families IHC is inherited as an autosomal recessive trait.57.58It now appears almost certain that at least one IHC susceptibility gene is located on chromosome 6 in close proximity to the A 10cus.~~-@’ Since homozygotes require two such alleles for full expression of the disease, it is possible in family studies to identify homozygote and heterozygote relatives by comparing their HLA antigens to those of the proband, who is presumed to be homozygote. Partial biochemical expression of the disease occurs in a small proportion of heterozygote relatives.58.5g Thus, HLA-typing has provided a useful new tool for understanding the inheritance of IHC and for identifying relatives at risk of developing iron overload.
Diagnosis and Management of Precirrhotic Hemochromatosis in Relatives In the past few years, this aspect of IHC has received more attention than any other, probably because of increasing interest in the mode of inheritance and also because of mounting evidence that early diagnosis and therapy can prevent or delay the fatal complications. Although the value of early diagnosis and treatment is not in doubt, there has not been general agreement about the most reliable and the simplest regimen for screening relatives of patients with IHC. The most reliable single test for the estimation of body iron stores is hepatic biopsy and chemical measurement of hepatic iron concentration. I-Iowever, it is not feasible to perform liver biopsy on all relatives and simpler, less invasive, tests are obviously desirable. The noninvasive tests that have attracted most attention are estimation of the serum iron level, percentage saturation of transferrin, and, more recently, the serum ferritin concentration. Each has its inherent advantages and limitations. The serum iron level and transferrin saturation are elevated early in the course of the disease, but their specificity is reduced by a relatively high frequency
February
1980
of false positives and negatives. In a study of 242 members of 43 families with IHC, the serum iron level was elevated in only 76% of relatives with increased iron stores and also in 10% of relatives with normal iron stores.” Although the percentage saturation of transferrin was elevated in all relatives with increased iron stores, it was also elevated in 33% of relatives with normal iron stores. Wands et al.‘l reported two families in which the serum ferritin levels were normal in several subjects despite increased hepatic and total body iron stores. However, subsequent studies of large numbers of families with IHC in the U.S.A.,“’ England,“3 Europe, 59 and Australia’” have confirmed that in untreated patients with clinically manifest hemochromatosis, the serum ferritin level is greatly increased (approximately 5-10 times normal) and the level correlates with the magnitude of body iron stores. In these studies, the serum ferritin level was also elevated in most precirrhotic asymptomatic relatives with an increase in body iron stores. Hence the estimation of serum ferritin is a useful, noninvasive screening test for early IHC since it is usually elevated before there is any morphologic evidence of liver damage, a point of considerable practical importance. Several commercial radioimmunoassay kits for the estimation of serum ferritin are now available, and the test has virtually replaced the more cumbersome screening tests involving measurement of urinary iron excretion. In clinical practice, the combined measurements of (1) serum iron concentration, (2) percent transferrin saturation, and (3) serum ferritin level provide the best screening regimen for IHC, including the precirrhotic phase of the disease. HLA typing may help in identifying relatives at risk of developing the cost and diffidisease,M however the comparative culty in performing this determination limits its usefulness. Thus, the following are practical guidelines for the routine screening of relatives of patients with IHC: 1. All first-degree relatives (males and females) over the age of about 10 yr should be screened using the tests recommended for diagnosis of the disease in probands, i.e., the combination of serum iron concentration, percentage saturation of transferrin, and serum ferritin concentration. 2. If any one of the above tests is abnormal, liver biopsy should be performed with estimation of stainable parenchymal iron and hepatic iron concentration. 3. Serial investigations at intervals over a number of years are recommended, particularly in women and young subjects, since the presence of normal iron and ferritin levels does not preclude the later
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1980 UPDATE
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development of iron overload and cirrhosis. If HLA-typing is available, it can help determine the appropriate frequency of such reassessment. For example, if a sibling shares two HLA haplotypes in common with the proband, the risk of developing iron overload is high, and iron and ferritin studies should be performed yearly or secondyearly.” If one of the offspring has unequivocal evidence of the disease, this may allow identification of all HLA haplotypes associated with the disease (including the haplotype from the unaffected spouse), and thus aid in diagnosis of IHC in other offspring.” In contrast, if no HLA haplotype is shared with the proband, the risk of developing iron overload is low. However, it should be emphasized that patients with IHC have been described with neither HLA haplotype in common with the proband.” While there is evidence that phlebotomy therapy prolongs life in established symptomatic patients with hemochromatosis,27~‘R there have been no controlled studies reported of such therapy in early, precirrhotic IHC. However, in our experience, early phlebotomy therapy with removal of excess iron arrests tissue damage and appears to prevent the overt manifestations of the disease. In young, precirrhotic patients, weekly phlebotomy should reduce iron stores to normal within less than 2 yr. Following this, phlebotomy will be required every 3-4 mo to prevent reaccumulation of iron. The patient can be reassured that the life expectancy is excellent, providing iron reaccumulation does not occur over the long period of follow-up. The clinician should stress to the patient the importance of maintaining iron stores within normal limits and of checking subsequent generations for iron overload. It is noteworthy that to date, there has been no published report of the development of hepatocellular carcinoma in IHC before the occurrence of cirrhosis. Thus, early diagnosis and phlebotomy therapy in the precirrhotic stage is of paramount importance. Since inexpensive yet reliable techniques are now available for early detection and effective therapy of iron overload, IHC, as a clinical disease, should be preventable in a large proportion of patients. References 1. Halliday
JW, Powell LW: Ferritin Metabolism. In: Metals and the Liver. Edited by LW Powell. New York, Marcel Dekker Inc., 1978, p 68 2. Linder MC. Munro HN: Metabolic and chemical features of ferritins, a series of iron-inducible tissue proteins. Am J Path01 72263-282, 1973 3. Lipschitz DA, Bothwell TH, Seftel HC. et al: The role of
380
4.
5.
6.
7.
8. 9.
10.
11.
12.
13.
14.
15. 16.
17.
18.
19.
20.
21.
22.
23.
24.
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JAMA 239:1999-2000, 1978 50. Halliday JW, Cowlishaw JL, Russo AM, et al: Serum ferritin in diagnosis of haemochromatosis. Lancet 1621-624, 1977 51. Simon M, Bourel M, Genetet B, et al: Idiopathic hemochromatosis and iron overload in alcoholic liver disease: differentiation by HLA phenotype. Gastroenterology 73:655-658, 1977 52. Powell LW: The role of alcoholism in hepatic iron storage disease. Ann NY Acad Sci 252124-134, 1975 53. Powell LW, Kerr JFR: The pathology of the liver in hemochromatosis. In: Pathobiology Annual 1975. Edited by HL Ioachim. New York, Appleton-Century-Crofts, 1975, p 317-336 54. Sabesin SM, Thomas LB: Parenchymal siderosis in patients with preexisting portal cirrhosis: a pathologic entity simulating idiopathic and transfusional hemochromatosis. Gastroenterology 46:477-485, l-964 55. Grace ND, Greenberg MS: Phlebotomy in the treatment of iron overload. A controlled trial (a preliminary report). Gastrocnterology 60:744, 1971 56. Simon M, Pawlotsky Y, Bourel M, et al: Hemochromatose idiopathiqur:: maladie associee a l’antigene HLA-A3? Nouv Pressc Med 14324, 1975 57. Simon M, Bourel M, Gcnetet B, et al: Idiopathic hemo-
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