The content of body iron is regulated primarily by absorption since humans have no physiological mechanism by which excess iron is excreted. This regulation, however, is not absolute. Many factors such as the content of diets, iron doses, life styles, etc. influence iron absorption. In the past, nutrition programs for iron fortification and the ingestion of iron preparations have been widely practiced because of the seriousness of worldwide iron deficiency. Also, we now know that a significant number of asymptomatic people carry the hemochromatosis gene, HFE, indicating that these people have the potential to accumulate excess body iron in their lifetime. Excess body iron can be highly toxic. This toxicity involves many organs leading to a variety of serious diseases such as liver disease, heart disease, diabetes mellitus, hormonal abnormalities, dysfunctional immune system, etc. The tissue damage associated with iron overload is believed to result primarily from free radical reactions mediated by iron. Iron is an effective catalyst in free radical reactions. The diseases associated with iron overload can be managed effectively or prevented. Therefore, early diagnosis of iron overload and appropriate therapy are critical. By providing the necessary laboratory data, clinical chemistry laboratories can play the pivotal role in the management of these health problems.

INDEX TERMS: clinical chemistry laboratories; diagnosis; free radical reactions; hemochromatosis; iron overload; iron toxicity.

Clin Lab Sci 2001; 14(3):209

LEARNING OBJECTIVES

1 . Describe the regulation of iron absorption.

2. List the three primary causes of iron overload.

3. Describe various chronic diseases associated with secondary iron overload and the mechanisms involved.

4. Contrast the absorption process for heme iron with that for non-heme iron.

5. List compounds in the diet that inhibit iron absorption and those that enhance iron absorption.

6. List the organs most frequently damaged by hemachromatosis.

7. Identify the clinical chemistry laboratory procedures that would detect damage to each of the organs most frequently damaged by hemachromatosis.

8. Discuss the biochemical theories most often proposed to explain the mechanisms that cause tissue damage due to excess iron.

Iron is an essential element in the body. It is required for growth, maintenance, and cell division. A normal 70 kg male adult contains about 4 g of iron. Of this amount, about 70% is present in hemoglobin; about 25% in ferritin and hemosiderin as iron stores; 5% in muscle myoglobin; and some in tissue enzymes and plasma transferrin.1,2 The average American daily diet contains 15 to 40 mg of iron. Less than 10% of this dietary iron is absorbed to balance the daily loss of approximately 1 mg. This loss is mainly via exfoliating dead cells from the skin, the intestine, and the urinary tract. Healthy females of reproductive age lose about 1.5 mg/day because of the additional loss of iron from menstruation and childbirth. Humans have no obvious physiological mechanism for iron excretion. Therefore, the homeostasis of body iron is dependent mainly on its absorption that appears to be regulated in the mucosa of the small intestine. Thus, more iron is absorbed in the face of iron deficiency and increased needs of erythropoiesis while the amount absorbed is reduced in the presence of iron overload.1,3 This regulation, however, is not absolute.

Various causes of chronic iron overload have been identified (Table 1).4 Iron overload is now being recognized as a health problem particularly in industrialized countries where red meat consumption is high and where cultural practices encourage iron intake, e.g., iron fortification of food and iron preparations.4,5 In the advanced state of iron overload, the iron content of the body can reach iron stores 20 to 30 times greater than the normal values. The iron store for normal men is about 1 g and for menstruating women about 0.3 g.6 Excessive amounts of iron in the body may cause a variety of serious medical problems. This review will focus on the primary causes of chronic iron overload, the pathophysiology associated with iron overload, the chemistry of iron toxicity, and the role of clinical laboratories in diagnosing and managing iron overload.

CAUSES OF CHRONIC IRON OVERLOAD

Chronic accumulation of excess body iron occurs for various reasons (Table I).4 In this review, the three primary ones will be discussed. First, individuals with hereditary hemochromatosis absorb more iron than the amount necessary to compensate for iron loss. This condition is associated with an autosomal recessive HLAlinked trait. The second situation is observed in patients with a number of pathological conditions that are linked to the elevation of body iron. In the third situation, iron overload results from the acquisition of excess iron from diets.

Hereditary hemochromatosis

A significant portion of the general populations of Western countries is now known to have the potential to accumulate excess iron during their lifetime because of the inheritance of the mutant gene for hemochromatosis. Hereditary hemochromatosis is characterized by excess absorption of iron from the gastrointestinal tract and its progressive accumulation in the body. Edwards discovered that approximately 10% of the population carry the hemochromatic gene rather than the previous estimate of 0.01% to 0.2%.7 These authors, who made this observation from a large-scale screening of healthy blood donors in the United States, also found that as many as 0.8% of men and 0.3% of women are homozygous. Numerous subsequent studies have established that hereditary hemochromatosis is a common genetic disorder among the populations of northern European origin; it is very rare among other populations.

In 1996, Feder identified the gene on chromosome 6 whose mutation is highly correlated with hereditary hemochromatosis.8 From a group of 178 unrelated patients with hereditary hemochromatosis, it was found that 148 patients (83%) were homozygous for a guanine-to-adenine mutation occurring at nucleotide 845 of the HLA-H, a gene related to the major histocompatibility complex (MHQ. This mutation results in a substitution of tyrosine for cysteine at amino acid position 282 (C282Y). The second mutation was in a change in histidine at position 63 to aspartate (H63D). Eight patients (4%) were compound heterozygotes, with one allele containing the C282Y mutation and the other allele containing the H63D mutation (C282Y/H63D). One patient (0.5%) was homozygous for the H63D mutation. The rest of the patients were C282Y/wild type, H63D/wild type, or lacking mutations in this gene. More recently, a new variant, which is a serine-to-cysteine substitution (S65C), has been reported.98 Whether the S65C mutation contributes to iron overload is controversial. The hereditary hemochromatosis gene is now referred to as HFE.9 HFE encodes a cell transmembrane protein (HFE protein) which may play a role in iron transport across cell membranes by binding to the transferrin receptor.10

Subjects with hereditary hemochromatosis absorb about three to five mg of iron from the average American diet daily in comparison to a normal rate of about one mg.3 This relatively small positive balance can lead to 20 to 40 g iron accumulation during adulthood, compared to a normal value of about four g. Clinical manifestations associated with iron overload usually appear between 40 and 60 years of age. Full expression of the disease in women occurs less frequently and at a later age than men because of iron losses from menstruation and childbirth.6

In heterozygotes, body iron increases gradually. Adams compared the results of iron study from heterozygotes to those of controls.11 Heterozygotes showed moderately increased results: serum transferrin saturation-38% vs 29%; serum ferritin-140 vs 87 (mu)g/L. The differences between the heterozygotes and the controls were significant, p

Other diseases

A number of clinical conditions are associated with secondary iron overload. Increased erythropoiesis accompanies elevated iron absorption. Such a situation is observed in some forms of hemolytic anemia, e.g., thalassemia and sideroblastic anemia, that are associated with ineffective erythropoiesis.14 Repeated intravenous administration of whole blood or erythrocytes can introduce excess iron into the body. Each 500 mL transfusion of whole blood contains approximately 200 mg of hemoglobin iron.15 Also, iron accumulation is observed in a defect in the heme synthesis pathway. For example, porphyria cutanea tarda results from a deficiency of uroporphyrinogen decarboxylase, an enzyme required in the heme synthetic pathway. This condition, characterized by photosensitivity, is associated with moderately elevated body iron.16 In addition, hepatic cirrhosis, alcoholism, and pancreatic insufficiency are often associated with iron overload.14

Acquisition of excess iron from diet

Absorption of iron by the small intestine appears to be regulated by the body's iron needs. However, the quantity of dietary iron and the composition of the diet significantly influence iron absorption. Prolonged intake of high doses of iron can lead to the accumulation of excess iron. This phenomenon has been shown in a number of animal experiments.17,18 In humans, the effect of such high iron doses was well demonstrated in the episode of siderosis among the Bantu tribe in Africa. Tribe members ingested excessive amounts of iron from their diet and beer. Their use of iron pots for cooking and brewing beer increased the iron content. Their traditional beer contained approximately 80 mg/L and alcohol itself enhances iron absorption. Therefore, the beer they consumed may have had a twofold effect on increasing body iron.3,19 Some acquired as much as 100 mg daily.4 Excess hemosiderin-like deposits were observed in 81 % of autopsied subjects over 30 years of age, both male and female.20

Another important factor in iron absorption relates to the form of iron present in a diet. Herne iron and nonheme iron are the two major sources of iron.3 Heme iron, that is found in meat, fish, and poultry, is more effectively absorbed because this iron is associated with the porphyrin ring. This association also allows iron to escape from most of the inhibitors of iron absorption present in a diet. Studies have shown that heme iron absorption is about five to ten times greater than for nonheme iron, and is less sensitive to the amounts of dietary iron and body iron stores.12,21 In addition, heme iron promotes the absorption of nonheme iron which is mainly found in vegetables and grains.22 A recent epidemiological study from Australia showed that normal volunteers have average iron storage of about 1.9 g. This level of iron store is about twice as much as the optimal iron store for normal adults. High meat consumption is believed to be the critical factor.12,23,24

The bioavailability of nonheme iron is significantly influenced by several factors: e.g., the amount of nonheme iron present in the diet, cooking, and manufacturing processes, and the presence of inhibitors and promoters of iron absorption. The inhibitors and promoters of nonheme iron absorption are ubiquitously present in diets. Therefore, the amount of nonheme iron absorbed is markedly dependent on the interplay of these substances. For example, phytates are powerful inhibitors. These are present in nuts, legumes, and many cereals.23 Hallberg reported the dose-dependent inhibitory effect of sodium phytate on iron absorption in humans. Various amounts of phytate, ranging from 2 to 250 mg/serving as phytate phosphorus, and radioactive iron (four mg) were added to phytate-free bread.21 Healthy adults were given the prepared bread on alternate days. Inhibition of iron absorption was dose-dependent, ranging from 18% by two mg to 82% by 250 mg. Ironbinding polyphenols, such as tannins and chlorogenic acid, have about the same inhibitory effect as phytates on iron absorption.12,23 Tea, coffee, vegetables, and legumes contain such polyphenols. Soybeans significantly inhibit nonheme iron absorption since they contain phytic acid and a protein-related moiety that also has an inhibitory effect.26,27 However, soybeans contain high levels of iron, therefore partially compensating for the inhibitory effect.23 A number of studies have shown that milk and cheese inhibit nonheme iron absorption due to the presence of calcium.28-30. Calcium affects the absorption of both nonheme iron and heme iron.

The most powerful promoter of iron absorption is ascorbate (vitamin C).31,32 Ascorbate increases the bioavailability of nonheme iron in two ways: 1) chelating iron to render it more soluble in the alkaline environment of the duodenum; and 2) reducing ferric iron (Fe^sup 3+^) to ferrous iron (Fe^sup 2+^) which is three times more efficiently absorbed than ferric iron. 33 Because of its reducing power, ascorbate is a very effective antioxidant. At high concentrations, it can inhibit free radical-mediated damages to biomolecules, However, it should be noted that the administration of vitamin C to individuals with high levels of body iron can cause serious medical problems such as heart failure.19,34 The reason, at least in part, is that body iron is stored as ferric iron in two major proteins: ferritin and hemosiderin. In iron overload, the major storage protein is hemosiderin since it can increase about 100-fold while ferritin increases 10-fold.35 Ascorbate can reduce the ferric iron stored in these proteins to ferrous iron that is released from the proteins. The ferrous iron released can engage in a series of free radical reactions.

Iron deficiency has long been a worldwide medical problem. It still affects one-third of the world's population, particularly in developing countries.23 For many years, efforts have focused on ameliorating this condition through programs to supplement and fortify iron. Also, the idea that iron is an invigorating nutrient has encouraged people to take oral iron preparations and iron-supplemented vitamin tablets. Such practices have occurred even in industrialized countries where red meat consumption is high, and a significant portion of the population carry the hemochromatosis gene.23 Krikker estimated that about 30 million people in the United States acquire excess iron for different reasons.36 In normal adults who consume Western-type diets, there is a steady rise in iron storage as a function of aging (Figure 1). Brothwell points out that it could be anticipated that more patients would be presenting to hospitals with fully developed hemochromatosis because of the widespread use of iron fortification that has occurred over the past decades, but hospital statistics do not support this expectation.23 The author suggests that many subclinical cases are still being missed, or that full expression of the disease does not occur in many affected homozygous individuals. In addition, it is possible that patients have sought medical attention with clinical conditions other than hemochromatosis since excess iron leads to secondary pathological conditions. Recent studies show that subjects with only modestly increased iron stores are at a greater risk of developing malignancy, heart disease, infection, etc.4,37-39

PATHOPHYSIOLOGY

Chronic accumulation of excess amounts of body iron leads to an increase in iron deposits in various tissues resulting in tissue damage and functional impairment of the organs involved. The toxicity involves multi-organs, and its clinical expression is versatile. In patients with advanced hemochromatosis, the most predominant features include hepatomegaly, hepatic dysfunction, heart failure, skin pigmentation, testicular atrophy, diabetes mellitus, and arthropathy.6,14,40 The total iron content of the body is usually between 20 g and 40 g. Particularly in the liver and pancreas, the iron concentrations may be 50 to 100 times normal. Iron concentration is elevated from five to 24 times normal in other organs such as the heart, endocrine glands, and skin.14

Liver fibrosis and dysfunction are common in hereditary hemochromatosis and transfusional iron overload.20,41 Patients with iron overload are at a higher risk for hepatoma. Among the African natives with siderosis, 52% developed hepatocellular carcinoma.4,42 The majority of patients who have elevated iron caused by persistent hepatitis B virus infection develop hepatocellular carcinoma.43 Patients with hereditary hemochromatosis develop liver cancer more than 200 times more frequently than controls.44 A It has been suggested that excess iron can increase the risk of cancer in a number of ways, e.g., serving as a limiting nutrient to the growth and development of a transformed cell; catalyzing the production of carcinogenic reactive oxygen species; or suppressing the activity of antitumor leukocytes.4,45-47

Several animal experiments support this suggestion. For example, Benbassat reported that mice inoculated with a plasmacytoma and fed a high iron diet had, at seven weeks, a tumor size nearly twice that of mice given a low iron diet.48 In the latter group, the implanted tumors stopped growing after about three weeks and some began to decrease in size.

Endocrine abnormalities are commonly associated with iron overload. Type I diabetes mellitus is found in all cases of transfusional siderosis and hereditary hemochromatosis.44,49,50 Abnormalities are also found in pituitary, thyroid, and gonadal functions. LOSS of libido, testicular atrophy, impotence, and amenorrhea usually result from iron-induced damage to the pituitary gland and hypothalamUS.4,20

Cardiac complications are the most common cause of death in patients with hereditary hemochromatosis or other conditions associated with iron overload.40 Lauffer has reported that hepatic iron levels are better correlated with the mortality rates of coronary artery disease than are cholesterol levels.39 And, the best index is the liver iron-serum cholesterol product. As mentioned in Acquisition of Excess Iron from Diet, the administration of ascorbate to patients with high levels of iron would exacerbate the heart problems since ascorbate can release ferrous iron from the storage proteins.19,34

A number of disorders of the central nervous system have been linked to high levels of iron. Iron in the brain is relatively high when compared to the iron content of other organs, and is not uniformly distributed.51,52 Its concentration is highest in the basal ganglia, almost equal to that of liver iron.52,53 Increased iron in the basal ganglia is found in several neurodegenerative diseases. A well-known neurological disorder is Hallervorden-Spatz disease that is characterized by progressive dementia and other functional disturbances beginning in childhood. Massive iron deposits in the ganglia were first reported by Spatz in 1922.52 Taylor found that patients with this disease have normal serum iron concentrations, suggesting that hemochromatosis is not necessarily linked to this disease.53

More recent research interest has been focused on Parkinson's disease and Alzheimer disease. Increased iron in the basal ganglia is found in these diseases. In Parkinson's disease, which is characterized by senescence of dopamine neurons, iron is increased particularly in the substantia nigra. Jellinger reported that iron in the substantia nigra zona compacta of patients with Parkinson's disease was about two times the iron concentration of controls.54 The increase of iron would make the tissue very vulnerable to oxidative damage. Indeed, there is evidence that this disease is closely associated with oxidative damage: accumulation of lipid peroxidation products; increases in antioxidant enzymes; and loss of reducing equivalent.55,56 It is unclear, however, whether these biochemical changes are responsible for the pathogenesis of Parkinson's disease. Patients with Alzheimer disease have a variety of neurological deficits.57 This disease is characterized by the presence of plaque and neurofibrillary in the brain. These lesions contain significant amounts of iron and the substances produced from lipid peroxidation and oxidative damage to protein and other biomolecules. A recent study by Smith showed that the iron present in the plaque could actively catalyze the generation of reactive oxygen species.58 Christen has suggested that biochemical destruction by reactive oxygen species is the major factor in the pathogenesis of Alzheimer disease.57

CHEMISTRY OF IRON TOXICITY

Several mechanisms have been proposed to elucidate how excess iron causes the biochemical and physical changes observed in hemochromatosis. The underlying theme pertaining to most of these proposals concerns free radical reactions.20,40,41 Since free radical reactions in biological systems are very complicated, this review will focus on the theory that is most relevant to the toxicity of chronic iron overload.

Lipid peroxidation - iron overload

The association of lipid peroxidation with iron overload has been demonstrated by in vitro and in vivo studies.40,41,62,70,71 For example, studies by Fletcher showed that when rats were given a diet containing 1% or 2.5% carbonyl iron for 42 days, the level of MDA in the hepatocytes increased 400% and 1400%, respectively.71 During the 42-day period, the extent of lipid peroxidation was time- and iron concentration-dependent. Lipid peroxidation can cause extensive damage to cell membranes and to membrane lipids of various organelles such as mitochondria, lysomes, and microsomes. Indeed, several studies have suggested that the biochemical changes seen in hemochromatosis may result from the damage to cell membranes and the disruption of the integrity of subcellular organelles.41,67,72,73 Lipid peroxidation-associated decreases in cellular viability have been detected in hepatocytes isolated from rats with chronic iron overload.74 number of suggestions, some of which are discussed below, have been made to elaborate on how excess iron influences the integrity of subcellular organelles.

The respiratory chain in mitochondria involves the sequential reactions of electron-transfer from NADH to oxygen, which is coupled with energy conversion into ATR Most of the enzymes and proteins involved in these electron-transfer and oxidative phosphorylation reactions are associated with the inner membrane of mitochondria. Therefore, it is conceivable that any damage to mitochondrial membrane could influence mitochondrial functions. A number of research groups have examined the relationship between iron overload and the integrity of the hepatic mitochondria.72,74-78 Iron overload is closely associated with the increased mitochondrial lipid peroxidation which accompanies swelling, decreased transmembrane potential, reductions in the mitochondrial respiratory control ratio (RCR), and oxidative phosphorylation.72,75-77 Bacon and Britten observed that chronic iron overload could lower the hepatic ATP concentrations by about 40%.74

Lysosomes contain many powerful enzymes, e.g., proteases, nucleases, glycosidases, lipases, phosphatases, and sulfatases.73 These enzymes participate in the degradative process of compounds taken up by lysosomes. From the study of rats with chronic dietary iron overload, LeSage observed that excess hepatic iron was progressively sequestered in lysosomes.19 That process was closely linked to the fragility of lysosomal membranes. Mak and Weglicki reported the association of iron overload with peroxidative damage to lysosomal membrane and the subsequent release of iron and the enzymes from the lysosomes.80 It has been suggested that the cell degeneration and fibrosis seen in hemochromatosis may be the result of peroxidative damage to lysosomal membranes and the leakage of the powerful lyric enzymes to the cytosol.73

Isolated microsomes generate superoxide radical and H^sub 2O^sub 2^ during NADPH-dependent electron transfer.68 Since OH- may be generated from these reactive oxygen species in the presence of iron (Equations 3 and 4), the interaction between microsomes and iron can initiate lipid peroxidation. Indeed, this appears to be the case. Microsomes undergo active peroxidation in the presence of iron, which may also damage membrane-bound enzymes.68 Bacon observed that when the hepatic iron concentration was greater than 4 mg/g liver in a study of rats fed a 2% carbonyl iron diet, microsomal lipid peroxidation increased over ten times the control values.81 Concomitantly, cytochrome P-450 was decreased by 56% and aminopyrine demethylase by 16%. It is interesting to note that patients with hemochromatosis usually show the manifestations of liver disease when hepatic iron concentrations reach approximately 5 mg/g to 6 mg/g liver.41,81

Iron overload - oxidative DNA damage

Cellular DNA damage occurs under pro-oxidant conditions mediated by iron. It is believed that iron exerts this effect via catalyzing the generation of reactive oxygen species, particularly OH^sup -82^. Damage to DNA may cause a serious problem to cellular integrity since DNA is the repository of genetic information and exists in single copies. Also, the development of cancer is one of the most common features found in hemochromatosis. Accordingly, a great deal of research effort has been focused on the relationship between iron overload and DNA damage.47,82

The DNA lesions produced by OH- can be grouped into strand breaks and base modifications. Hydroxyl radicals can induce strand breaks in the phosphodiester backbone of DNA or by a calciumdependent endonuclease. Crichton has indicated that the cellular repair mechanisms for mending these breaks have a lower fidelity than DNA polymerases.11 Therefore, the probability that the wrong base will be incorporated into the repaired DNA increases if the incidence of strand breaks is high. With regard to base modifications, more than 20 products have been detected from DNA subjected to oxidative damage. 12 Hydroxylation of constituent bases is the most prominent characteristics of the modification products. One of the most intensively studied products is 8-hydroxy2'-deoxyguanosine (8-OHdG) (or 8-oxo-2'-deoxyguanosine). 8OHdG is widely used as a marker of oxidative DNA damage.84 In 1987, Kuchino discovered that the formation of 8-OHdG leads to mutations by inducing G:C to T.A transversion at the time of DNA replication.85 Since then, using a variety of models for carcinogenesis induced by pro-oxidant conditions, numerous studies have demonstrated the mutagenic properties of 8-OHdG.

It should be noted that OH- must be generated in situ to attack DNA since it is so reactive that it cannot diffuse significant distances within a cell. This indicates that iron must be present within the nucleus to mediate the production of OH- in close proximity to the DNA. Indeed, a number of researchers have discovered iron accumulation in the hepatic and pulmonary nuclei when laboratory animals were treated with excess iron chronically or acutely.86,87 Thus, it appears that iron generates OH in situ by reacting with H^sub 2^O^sub 2^ which probably diffuses through membranes into the nucleus.82

Recently, a number of scientists have reported that cellular DNA undergoes oxidative damage as a result of acute or chronic iron overload in rats (Table 2). Kang reported that oxidative damage took place in the hepatic nuclear DNA when rats were given a diet containing 3.0% carbonyl iron for 8 weeks.18 These authors measured the production of 8-OHdG as a marker. The levels of 8-OHdG in the hepatic nuclear DNA of the experimental group were significantly increased, over 100 % higher than the control group. Lucesoli measured the production of 8-OHdG in the testes of rats injected with different doses of iron, ranging from 250 mg to 1000 mg/kg body weight.88 The production of 8-OHdG increased in a dosedependent manner. Wellejus studied the nuclear DNA in the testes and epididymal sperm cells after intraperitoneal injections with 200 mg iron/kg to rats.89 The levels of 8-OHdG were increased in the sperm nuclei, but not in the testicular nuclei.

ROLE OF CLINICAL CHEMISTRY LABORATORIES

The diagnosis of hemochromatosis is made on the basis of laboratory data, family history, and clinical features. Today, clinical chemistry laboratories can play the primary role since a screening test for the HFE gene is becoming available. This review will focus on the role of clinical chemistry laboratories in diagnosing iron overload (Table 3).

Determination of plasma nontransferrin-bound iron

Recently, Breuer developed an analytical method to assess nontransferrin-bound iron in the blood.93 It utilizes an iron-specific chelator deferoxamine that is immobilized on the plate. This methodology permits screening a large number of patients.

Liver function enzymes

A number of liver function enzymes have been studied in conjunction with hemochromatosis. The enzymes studied may not be specific for iron overload. However, once the disease has been diagnosed, changes in some enzymes may provide valuable information concerning the disease course and the effectiveness of treatment. Young studied several plasma enzymes in 15 patients with confirmed hereditary hemochromatosis and in controls.92 In this study, alkaline phosphatase, gammaglutamyl transferase, aspartate transaminase, and alanine transaminase were assessed. All of the enzymes increased noticeably in the patients' blood. However, only the increase in aspartate transaminase was statistically different from controls: 34 U/L for patients vs 21 U/L for controls (p = 0.014). The increases in other enzymes were not statistically different from the control values (p >0.05). Similar results, except for alkaline phosphatase, were obtained from animal experiments performed by Kang." A number of other researchers observed that alanine transaminase had statistically different activity in rats with iron overload and patients with hemochromatosis.79,94

It is interesting to note that Kang observed significant decreases in serum alkaline phosphatase in rats with chronic iron overload: 139 U/L for iron overload vs 230 U/L for controls (p

Screening for hemochromatosis gene (HFE)

In the past, liver biopsy has been performed to make the definite diagnosis of hereditary hemochromatosis.96 With the discovery of the HFE gene, Bacon stated that, if there are increases in iron saturation and/or ferritin or a family history of hemochromatosis, the diagnosis can be made confidently based on genetic testing for the C282Y mutation.96 These authors suggest that liver biopsy is no longer necessary to diagnose hemochromatosis. However, it is necessary to assess tissue damage. Recently, a blood test for the C282Y mutation in the HFE gene has been developed, and commercial test kits are available.97

CONCLUSION

Iron is the second most abundant metal on the earth's crust. Yet, one-third of the world population suffers from iron deficiency, particularly the populations of developing countries.23 In the past, widespread nutrition programs increasing the iron content of food have been conducted to alleviate this problem.4,23 Also, the intake of iron is encouraged in some societies because iron is considered to be an invigorating nutrient. Such practices, however, have taken place not only in the societies where iron-supplementation is necessary but also in industrialized societies where the general populations obtain sufficient iron from normal diets. It was realized only recently that a significant portion of the populations in many industrialized countries, including the United States, carry the gene for hemochromatosis, now defined as the HFE gene.7 Brothwell has pointed out that individuals with this gene may have participated in the past practice of over acquisition of iron just as noncarriers have.23 Hemochromatosis is considered to be a rare disease since relatively few patients seek medical treatment with the characteristic symptoms of fully developed hemochromatosis, e.g., hepatic dysfunction, heart failure, diabetes mellitus, arthropathy, etc.23 Growing evidence suggests that moderate levels of body iron may induce a variety of different pathological conditions such as cancer, infection, neurodegenerative diseases, inflammation, and heart disease.4,12 Free radical reactions mediated by excess body iron have been implicated in these diseases. At this time, it is not clear whether these reactions are directly involved in causing these medical problems. However, several lines of data obtained from well-controlled animal experiments strongly suggest that they play a critical role in the pathogenesis of at least some of the diseases.4,23,41,55,57,58

With early diagnosis and appropriate treatment, the toxicity of chronic iron overload can be effectively treated, and even prevented. For example, a study by Niederau showed that when phlebotomies were initiated before patients developed cirrhosis, hemochromatosis reverted to normal.44 Even among those with cirrhosis, the 10-year survival rate was over 75% which was a remarkable improvement over the 6% 10-year survival rate after diagnosis without the removal of excess iron. Clinical chemistry laboratories can play a vital role in diagnosing and monitoring iron overload, particularly since a non-invasive test for the HFE gene has been developed and commercial reagent kits are now available.97 Some scientists have suggested that screening for the HFE gene in the asymptomatic population be considered.96 Such a widespread screening program, if adopted, would expand the role of clinical laboratory scientists significantly. These professionals must be prepared to accept this important role.

ACKNOWLEDGEMENT

The author acknowledges the assistance of Claire A Archambault in the preparation of this manuscript.

The Focus section seeks to publish relevant and timely continuing education for clinical laboratory practitioners. Section editors, topics, and authors are selected in advance to cover current areas of interest in each discipline. Readers can obtain continuing education credit (CE) through P.A.C.E.(R) by completing the tearout form/examination questions included in each issue of CLS and mailing it with the appropriate fee to the address designated on the form. Suggestions for future Focus topics and authors, and manuscripts appropriate for CE credit are encouraged. Direct all inquiries to Carol McCoy PhD, CLS Continuing Education Editor Department of Clinical Sciences, 343 Cowley Hall, University of Wisconsin, La Crosse WI 54601; (608) 785-6968. cmccoy@mail.uwlax.edu

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Jae 0 Kang PhD CLS is in the Department ofMedical Laboratory Science, University ofNew Hampshire, Durham NH Address for correspondence.-Jae OK-ang PhD, Department ofMedical Laboratory Science, 202 Hewitt Hall, University ofNew Hampshire, Durham AIY03824. (603) 862-1631, (603) 862-3108 ax). JOK@christa.unh.edu

Rebecca Laudicina is the Focus: Iron Overload guest editor.

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