Recent advances in understanding haemochromatosis: a transition state

Correlation of hepcidin and serum ferritin levels in thalassemia patients at Chiang Mai University Hospital

Hepcidin is a key iron-regulatory hormone, the production of which is controlled by iron stores, inflammation, hypoxia and erythropoiesis. The regulation of iron by hepcidin is of clinical importance in thalassemia patients in which anemia occurs along with iron overload. The present study aimed to evaluate the correlation between serum hepcidin and ferritin levels in thalassemia patients. This cross-sectional study investigated 64 patients with thalassemia; 16 β-thalassemia major (BTM), 31 β-thalassemia/hemoglobin (Hb) E (BE), and 17 Hb H + AE Bart’s disease (Hb H + AE Bart’s). The levels of serum hepcidin and ferritin, and Hb of the three groups were measured. The median values of serum ferritin and Hb were significantly different among the three groups, whereas serum hepcidin values were not observed to be significantly different. The correlation of the serum hepcidin and ferritin levels was not statistically significant in any of the three groups of thalassemia patients with BTM, BE, or Hb H + AE Bart’s (r = −0.141, 0.065 and −0.016, respectively). In conclusion, no statistically significant correlations were observed between serum hepcidin with any variables including serum ferritin, Hb, age, labile plasma iron (LPI), and number of blood transfusion units among the three groups of thalassemia patients. Likely, the regulation of hepcidin in thalassemia patients is affected more by erythropoietic activity than iron storage.

Juvenile Hemochromatosis, Genetic Study and Long-term Follow up after Therapy

BACKGROUND Hereditary hemochromatosis (HH) is a very rare disease in Iran and reported cases are all negative for HFE mutation. We report a family affected by severe juvenile hemochromatosis (JH) with a detailed molecular study of the family members. METHODS We studied a pedigree with siblings affected by juvenile HH and followed them for 3 years. Microsatellite and gene sequencing analysis was performed for all family members. RESULTS Two siblings (the proband and his sister, aged 26 and 30 years, respectively) were found to have clinical findings of JH. The proband's brother, who presented with hyperpigmentation, died of probable JH at the age of 24 years. Gene sequencing analysis showed that the proband has a homozygote c.265T>C (p.C89R) HJV mutation + a heterozygote c.884T>C (p.V295A) mutation of HFE. The affected proband's sister presented with the same HJV c.265T>C (p.C89R) homozygote mutation. In addition, we found the HJV c.98-6C>G polymorphic variant in both the sister and proband (homozygote). Sequencing of hepcidin (HAMP), TfR2, and FPN revealed no mutation. CONCLUSION We have shown that molecular analysis of the HH related gene is a powerful tool for reliable diagnosis of JH and, in conjunction with magnetic resonance imaging (MRI) and noninvasive liver stiffness measurement by elastography, is adequate tool for management and follow up of HH.

Molecular diagnosis of hemochromatosis

INTRODUCTION

The discovery of hemochromatosis genes and the availability of molecular-genetic tests considerably modified the knowledge of the disease relative to physiopathology, penetrance, and expression, and had major impact in the diagnostic settings.

AREAS COVERED

Hemochromatosis is a heterogenous disorder at both genetic and phenotypic level. The review discusses criteria to define patients' iron phenotype and to use molecular tests to diagnose HFE-related and non-HFE hemochromatosis. The material examined includes articles published in the journals covered by PubMed US National Library of Medicine. The author has been working in the field of iron overload diseases for several years and has contributed 18 of the papers cited in the references.

EXPERT OPINION

Hemochromatosis genotyping is inseparable from phenotype characterization. A full clinical assessment is needed and DNA test performed when data suggest a clear indication of suspicion of being at risk for HH. HFE testing for p.Cys282Tyr mutation and p.His63Asp variant is the first molecular diagnostic step. Genotyping for rare mutations can be offered to patients with negative first-level HFE testing who have iron overload with no other explanation and should be performed in referral centers for iron overload disorders that can provide genetic advice and in-house genotyping services.

Review article: the iron overload syndromes

BACKGROUND

Iron overload syndromes encompass a wide range of hereditary and acquired conditions. Major developments in the field of genetics and the discovery of hepcidin as a central regulator of iron homeostasis have greatly increased our understanding of the pathophysiology of iron overload syndromes.

AIM

To review advances in iron regulation and iron overload syndrome with special emphasis on hereditary haemochromatosis, the prototype iron overload syndrome.

METHODS

A PubMed search using words such as 'iron overload', 'hemochromatosis', 'HFE', 'Non-HFE', 'secondary iron overload' was undertaken.

RESULTS

Iron overload is associated with significant morbidity and mortality. Sensitive diagnostic tests and effective therapy are widely available and can prevent complications associated with iron accumulation in end- organs. Therapeutic phlebotomy remains the cornerstone of therapy for removal of excess body iron, but novel therapeutic agents including oral iron chelators have been developed for iron overload associated with anaemia.

CONCLUSIONS

Iron overload disorders are common. Inexpensive screening tests as well as confirmatory diagnostic tests are widely available. Increased awareness of the causes and importance of early diagnosis and knowledge of the appropriate use of genetic testing are encouraged. The availability of novel treatments should increase therapeutic options for patients with iron overload disorders.

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer's and Parkinson's disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.

Iron overload in HFE C282Y heterozygotes at first genetic testing: a strategy for identifying rare HFE variants

BACKGROUND

Heterozygotes for the p.Cys282Tyr (C282Y) mutation of the HFE gene do not usually express a hemochromatosis phenotype. Apart from the compound heterozygous state for C282Y and the widespread p.His63Asp (H63D) variant allele, other rare HFE mutations can be found in trans on chromosome 6.

DESIGN AND METHODS

We performed molecular investigation of the genes implicated in hereditary hemochromatosis in six patients who presented with iron overload but were simple heterozygotes for the HFE C282Y mutation at first genetic testing. Functional impairment of new variants was deduced from computational methods including molecular modeling studies.

RESULTS

We identified four rare HFE mutant alleles, three of which have not been previously described. One mutation is a 13-nucleotide deletion in exon 6 (c.1022_1034del13, p.His341_Ala345 > LeufsX119), which is predicted to lead to an elongated and unstable protein. The second one is a substitution of the last nucleotide of exon 2 (c.340G > A, p.Glu114Lys) which modifies the relative solvent accessibility in a loop interface. The third mutation, p.Arg67Cys, also lies in exon 2 and introduces a destabilization of the secondary structure within a loop of the α1 domain. We also found the previously reported c.548T > C (p.Leu183Pro) missense mutation in exon 3. No other known iron genes were mutated. We present an algorithm at the clinical and genetic levels for identifying patients deserving further investigation. Conclusions Our results suggest that additional mutations in HFE may have a clinical impact in C282Y carriers. In conjunction with results from previously described cases we conclude that an elevated transferrin saturation level and elevated hepatic iron index should indicate the utility of searching for further HFE mutations in C282Y heterozygotes prior to other iron gene studies.

HFE gene mutations in patients with primary iron overload: is there a significant improvement in molecular diagnosis yield with HFE sequencing?

Rare HFE variants have been shown to be associated with hereditary hemochromatosis (HH), an iron overload disease. The low frequency of the HFE p.C282Y mutation in HH-affected Brazilian patients may suggest that other HFE-related mutations may also be implicated in the pathogenesis of HH in this population. The main aim was to screen for new HFE mutations in Brazilian individuals with primary iron overload and to investigate their relationship with HH. Fifty Brazilian patients with primary iron overload (transferrin saturation>50% in females and 60% in males) were selected. Subsequent bidirectional sequencing for each HFE exon was performed. The effect of HFE mutations on protein structure were analyzed by molecular dynamics simulation and free binding energy calculations. p.C282Y in homozygosis or in heterozygosis with p.H63D were the most frequent genotypic combinations associated with HH in our sample population (present in 17 individuals, 34%). Thirty-six (72.0%) out of the 50 individuals presented at least one HFE mutation. The most frequent genotype associated with HH was the homozygous p.C282Y mutation (n=11, 22.0%). One novel mutation (p.V256I) was indentified in heterozygosis with the p.H63D mutation. In silico modeling analysis of protein behavior indicated that the p.V256I mutation does not reduce the binding affinity between HFE and β2-microglobulin (β2M) in the same way the p.C282Y mutation does compared with the native HFE protein. In conclusion, screening of HFE through direct sequencing, as compared to p.C282Y/p.H63D genotyping, was not able to increase the molecular diagnosis yield of HH. The novel p.V256I mutation could not be implicated in the molecular basis of the HH phenotype, although its role cannot be completely excluded in HH-phenotype development. Our molecular modeling analysis can help in the analysis of novel, previously undescribed, HFE mutations.

Hemochromatosis in Italy in the last 30 years: role of genetic and acquired factors

The clinical presentation of hereditary hemochromatosis has changed markedly in recent years. The aim of this study was to analyze a large series of consecutive Italian patients with hemochromatosis diagnosed between 1976 and 2007 to determine whether the genetic background and the presence of acquired risk factors influenced the severity of iron overload and the natural history of the disease. A cohort of 452 Italian patients with iron overload-338 HFE-related (C282Y homozygotes or compound C82Y/H63D heterozygotes) and 114 non-HFE-related-were followed prospectively for a median of 112 months. Alcohol intake, smoking habits, and iron removed to depletion were similar in patients with and without HFE-related iron overload. Hepatitis B virus (4% and 9%; P = 0.04) and hepatitis C virus (6% and 19%; P = 0.002) infections were more frequent in patients with non-HFE-related iron overload. Seventy-three percent of patients with HFE and 61% of patients with non-HFE-related disease had no acquired risk factor. Cirrhosis was significantly more frequent in non-HFE patients independent of the presence of acquired risk factors (P = 0.02). Sex, alcohol intake, prevalence of smoking, hepatitis C virus infection, glucose, lipids, iron-related parameters, and prevalence of C282Y/H63D differed significantly over the years. At enrollment, cirrhosis was present in 145 cases and was significantly more frequent in the first decade (80%, 47%, and 13%; P = 0.001). Survival did not differ across the decades in cirrhotic patients; hepatocellular carcinoma occurred similarly in HFE and non-HFE patients.

CONCLUSION

Patients with HFE and non-HFE-related iron overload have comparable iron overload and similar clinical history. Patients who were diagnosed during the last 10 years and were not identified as cirrhotic at enrollment have less severe disease and lower prevalence of acquired risk factors, independent of genetic background.

Alpha-1 antitrypsin binds preprohepcidin intracellularly and prohepcidin in the serum

Recent discoveries have indicated that the hormone hepcidin plays a major role in the control of iron homeostasis. Hepcidin regulates the iron level in the blood through the interaction with ferroportin, an iron exporter molecule, causing its internalization and degradation. As a result, hepcidin increases cellular iron sequestration, and decreases the iron concentration in the plasma. Only mature hepcidin (result of the cleavage of prohepcidin by furin proteases) has biological activity; however, prohepcidin, the prohormone form, is also present in the plasma. In this study, we aimed to identify new protein-protein interactions of preprohepcidin, prohepcidin and hepcidin using the BacterioMatch two-hybrid system. Screening assays were carried out on a human liver cDNA library. Preprohepcidin screening gave the following results: alpha-1 antitrypsin, transthyretin and alpha-1-acid glycoprotein showed strong interactions with preprohepcidin. We further confirmed and examined the alpha-1 antitrypsin binding in vitro (glutathione S-transferase, pull down, coimmunoprecipitation, MALDI-TOF) and in vivo (ELISA, cross-linking assay). Our results demonstrated that the serine protease inhibitor alpha-1 antitrypsin binds preprohepcidin within the cell during maturation. Furthermore, alpha-1 antitrypsin binds prohepcidin significantly in the plasma. This observation may explain the presence of prohormone in the circulation, as well as the post-translational regulation of the mature hormone level in the blood. In addition, the lack of cleavage protection in patients with alpha-1 antitrypsin deficiency may be the reason for the disturbance in their iron homeostasis.

Investigation of the biophysical and cell biological properties of ferroportin, a multipass integral membrane protein iron exporter

Ferroportin is a multipass membrane protein that serves as an iron exporter in many vertebrate cell types. Ferroportin-mediated iron export is controlled by the hormone hepcidin, which binds ferroportin, causing its internalization and degradation. Mutations in ferroportin cause a form of the iron overload hereditary disease hemochromatosis. Relatively little is known about ferroportin's properties or the mechanism by which mutations cause disease. In this study, we expressed and purified human ferroportin to characterize its biochemical/biophysical properties in solution and conducted cell biological studies in mammalian cells. We found that purified detergent-solubilized ferroportin is a well-folded monomer that binds hepcidin. In cell membranes, the N- and C-termini were both cytosolic, implying an even number of transmembrane regions, and ferroportin was mainly localized to the plasma membrane. Hepcidin addition resulted in a redistribution of ferroportin to intracellular compartments that labeled with early endosomal and lysosomal, but not Golgi, markers and that trafficked along microtubules. An analysis of 16 disease-related ferroportin mutants revealed that all were expressed and trafficked to the plasma membrane but that some were resistant to hepcidin-induced internalization. The characterizations reported here form a basis upon which models for ferroportin's role in regulating iron homeostasis in health and disease can be interpreted.

Increased susceptibility to Mycobacterium avium in hemochromatosis protein HFE-deficient mice

Mycobacterium avium is an opportunistic infectious agent in immunocompromised patients, living inside macrophage phagosomes. As for other mycobacterial species, iron availability is a critical factor for M. avium survival and multiplication. Indeed, an association between host secondary iron overload and increased susceptibility to these mycobacteria is generally acknowledged. However, studies on the impact of primary iron overload on M. avium infection have not been performed. In this work, we used animal models of primary iron overload that mimic the human disease hereditary hemochromatosis. This pathology is characterized by increased serum transferrin saturation with iron deposition in parenchymal cells, mainly in the liver, and is most often associated with mutations in the gene encoding the molecule HFE. In this paper, we demonstrate that mice of two genetically determined primary iron overload phenotypes, Hfe(-/-) and beta2m(-/-), show an increased susceptibility to experimental infection with M. avium and that during infection these animals accumulate iron inside granuloma macrophages. beta2m(-/-) mice were found to be more susceptible than Hfe(-/-) mice, but depleting Hfe(-/-) mice of CD8(+) cells had no effect on resistance to infection. Overall, our results suggest that serum iron, rather than total liver iron, levels have a considerable impact on susceptibility to M. avium infection.

Analysis of SLC40A1 gene at the mRNA level reveals rapidly the causative mutations in patients with hereditary hemochromatosis type IV

Mutations in the SLC40A1 gene result in a dominant genetic disorder [ferroportin disease; hereditary hemochromatosis type (HH) IV], characterized by iron overload with two different clinical manifestations, normal transferrin saturation with macrophage iron accumulation (the most prevalent type) or high transferrin saturation with hepatocyte iron accumulation (classical hemochromatosis phenotype). In previous studies, the mutational analysis of SLC40A1 gene has been performed at the genomic DNA level by PCR amplification and direct sequencing of all coding regions and flanking intron-exon boundaries (usually in 9 PCR reactions). In this study, we analyzed the SLC40A1 gene at the mRNA level, in two RT-PCR reactions, followed by direct sequencing and/or NIRCA (non-isotopic RNase cleavage assay). This protocol turned out to be rapid, sensitive and reliable, facilitating the detection of the SLC40A1 gene mutations in two patients with hyperferritinemia, normal transferrin saturation and iron accumulation predominantly in macrophages and Kupffer cells. The first one displayed the well-described alteration V162 Delta and the second a novel mutation (R178G) that was further detected in two relatives in a pedigree analysis. The proposed procedure would facilitate the wide-range molecular analysis of the SLC40A1 gene, contributing to better understanding the pathogenesis of the ferroportin disease.

Non-HFE haemochromatosis

Non-HFE hereditary haemochromatosis (HH) refers to a genetically heterogeneous group of iron overload disorders that are unlinked to mutations in the HFE gene. The four main types of non-HFE HH are caused by mutations in the hemojuvelin, hepcidin, transferrin receptor 2 and ferroportin genes. Juvenile haemochromatosis is an autosomal recessive disorder and can be caused by mutations in either hemojuvelin or hepcidin. An adult onset form of HH similar to HFE-HH is caused by homozygosity for mutations in transferrin receptor 2. The autosomal dominant iron overload disorder ferroportin disease is caused by mutations in the iron exporter ferroportin. The clinical characteristics and molecular basis of the various types of non-HFE haemochromatosis are reviewed. The study of these disorders and the molecules involved has been invaluable in improving our understanding of the mechanisms involved in the regulation of iron metabolism.

A novel mutation of transferrin receptor 2 in a Taiwanese woman with type 3 hemochromatosis

Hereditary hemochromatosis (HH) is very rare in Asia. Here, we describe a Taiwanese woman presenting with fully developed characteristics of HH including bronze skin, DM, decreased MRI T2 signal intensity over liver and pituitary gland. Biochemistry of iron profile indicated a severe status of iron overload by serum iron: 194 microg/dL, serum ferritin: 6640 microg/L, transferrin saturation: 92.8%. By measuring the hepatic iron index 8.48 (>1.9) of her liver biopsy tissue, the diagnosis of HH was established. Diagnosis of non-HFE HH was carried out since the whole HFE genome was sequenced but failed to localize any genetic alterations. The whole genome of transferrin receptor 2 (TfR2) was sequenced and a novel mutation of 13528 G-->A (Arg 481 His) in exon 11 was detected. Therefore, type 3 hemochromatosis was confirmed. The distinct clinical features, extremely high iron index and impressive iron staining in her liver biopsy tissue may represent an aggravated iron deposition in the liver caused by this novel mutation. Our finding implicates functional importance of histidine in exchange of arginine at amino acid 481 of transferrin receptor 2 in iron homeostasis. This case reminds physicians in Asia to keep in mind that hemochromatosis could be a rare cause of DM.

Association of hemochromatosis with infectious diseases: expanding spectrum

Withholding iron from potential pathogens is a host defense strategy. There is evidence that iron overload per se compromises the ability of phagocytes to kill microorganisms. Several hypotheses exist to explain the association of hemochromatosis with infection. A combination of mechanisms likely contributes to the increase in susceptibility to infection in these patients. A review of the current literature delineating various pathogens to which patients with hemochromatosis are potentially susceptible, and recent advances in the understanding of the association of hemochromatosis with infection, are discussed.

Hemochromatosis: genetics and pathophysiology

A number of genetic disorders can result in the accumulation of excess iron in the body. These causes of hereditary hemochromatosis include defects in genes encoding HFE, transferrin receptor 2, ferroportin, hepcidin, and hemojuvelin. Hepcidin, with its cognate receptor, ferroportin, has emerged as a central regulator of iron homeostasis; all of the known causes of hemochromatosis appear to prevent this system from functioning normally. The most common form of primary hemochromatosis is that caused by C282Y mutation of the HFE gene. This mutation is most prevalent among Northern Europeans. Although the frequency of the homozygous genotype is approximately 5 per 1000, the disease itself is quite rare because the clinical penetrance of the genotype is very low.

Hereditary iron overload: update on pathophysiology, diagnosis, and treatment

Hereditary hemochromatosis, a very common genetic defect in the Caucasian population, is characterized by progressive tissue iron overload which leads to irreversible organ damage if it is not treated timely. The elucidation of the molecular pathways of iron transport through cells and its control has led to the understanding of various genetic iron-loading conditions. Four types of inherited iron overload have been recognized: type 1, the most common form with an autosomal recessive inheritance, is associated with mutations in the HFE gene on chromosome 6; type 2 (juvenile hemochromatosis) is an autosomal recessive disorder with causative mutations identified in the HJV gene (subtype A) on chromosome 1 and the HAMP gene (subtype B) on chromosome 19; type 3 has also an autosomal recessive inheritance with mutations in the TfR2 gene on chromosome 3; type 4 is an autosomal dominant condition with heterozygous mutations in the ferroportin 1 gene on chromosome 2. In this review, the genetics, pathophysiology, diagnosis, clinical features, and management of these different types of hereditary hemochromatosis are briefly discussed.

Metabolic syndrome, insulin resistance and the inflammation markers C-reactive protein and ferritin

BACKGROUND

Patients with metabolic syndrome (MS) have above-average risk of developing atherosclerosis and cardiovascular disease. Inflammation plays a key role in the development of atherosclerosis. High levels of the acute phase reactants C-reactive protein (CRP) and ferritin have been reported to correlate with various components of MS.

PATIENTS AND METHODS

The serum CRP, ferritin, glucose, insulin, triglycerides, HDL-cholesterol and total cholesterol concentrations of 598 obese or overweight patients were determined, together with relevant anthropometric parameters. Insulin resistance was evaluated by the HOMA method. MS was diagnosed using the ATP III criteria.

RESULTS

CRP levels were higher among patients with central obesity than in those without (5.8 vs 3.9 mg/l; P=0.003), and higher among those with fasting plasma glucose concentrations >or=110 mg/dl than in those with lower concentrations (7.4 vs 4.1 mg/l; P=0.01). Serum ferritin levels were higher among patients with triglyceride concentrations >or=150 mg/dl than in those with lower levels (76.8 vs 40.1 ng/ml; P<0.001), and higher among those with fasting plasma glucose concentrations >or=110 mg/dl than in those with lower concentrations (75.7 vs 41.7 ng/ml; P=0.005). The number of MS criteria that were satisfied increased with CRP and ferritin levels. Patients with insulin resistance also had higher CRP and ferritin levels than those without, 7.3 vs 4.3 mg/l for CRP (P=0.032) and 124.5 vs 80.1 ng/ml for ferritin (P<0.001).

CONCLUSIONS

MS and insulin resistance are associated with elevated serum CRP and ferritin. Evaluation of subclinical chronic inflammation in patients with MS and/or insulin resistance by determination of these markers might aid in their evaluation as candidates for aggressive intervention against cardiovascular risk factors.

The molecular genetics of haemochromatosis

The molecular basis of haemochromatosis has proved more complex than expected. After the 1996 identification of the main causative gene HFE and confirmation that most patients were homozygous for the founder C282Y mutation, it became clear that some families were linked to rarer conditions, first named 'non-HFE haemochromatosis'. The genetics of these less common forms was intensively studied between 2000 and 2004, leading to the recognition of haemojuvelin (HJV), hepcidin (HAMP), transferrin receptor 2 (TFR2) and ferroportin-related haemochromatosis, and opening the way for novel hypotheses such as those related to digenic modes of inheritance or the involvement of modifier genes. Molecular studies of rare haemochromatosis disorders have contributed to our understanding of iron homeostasis. In turn, recent findings from studies of knockout mice and functional studies have confirmed that HAMP plays a central role in mobilization of iron, shown that HFE, TFR2 and HJV modulate HAMP production according to the body's iron status, and demonstrated that HAMP negatively regulates cellular iron efflux by affecting the ferroportin cell surface availability. These data shed new light on the pathophysiology of all types of haemochromatosis, and offer novel opportunities to comment on phenotypic differences and distinguish mutations.

Ferroportin is a monomer in vivo in mice

Ferroportin (FPN) is the main iron export protein in mammals. The actual structure of FPN in vivo and the pathogenesis of ferroportin-related disease are unknown. We aimed at studying the structure and biochemical properties of FPN in mouse tissues that are key for iron homeostasis during various iron manipulations in vivo. We performed glycosylation and oligomerization studies in spleen and liver extracts from mice fed a standard, iron-deprived or iron-enriched diet for 5 months. Purification by affinity chromatography and sucrose gradient show that FPN is not part of a large multiprotein complex. Dietary manipulations did not affect the monomeric status of the native or denatured protein. The glycosylation studies showed that ferroportin is digested by peptide: N-glycosidase F but not by endoglycosidase H. The same results were obtained using protein extracts from iron-deficient or iron-loaded mice. In conclusion, our studies indicate that mouse FPN, regardless of the tissue iron status, is glycosylated but not enriched in mannose residues, and that exists mainly in monomeric form. The latter finding may have important implications for understanding the pathogenesis of the disease due to ferroportin mutations.

Understanding iron homeostasis through genetic analysis of hemochromatosis and related disorders

Genetic analysis of hemochromatosis has led to the discovery of a number of genes whose mutations disrupt iron homeostasis and lead to iron overload. The introduction of molecular tests into clinical practice has provided a tool for early diagnosis of these conditions. It has become clear that hemochromatosis includes a spectrum of disorders that range from simple biochemical abnormalities to chronic asymptomatic tissue damage in midlife to serious life-threatening diseases in young subjects. Molecular studies have identified the systemic loop that controls iron homeostasis and is centered on the hepcidin-ferroportin interaction. The complexity of this regulatory pathway accounts for the genetic heterogeneity of hemochromatosis and related disorders and raises the possibility that genes encoding components of the pathway may be modifiers of the main genotype. Molecular diagnosis has improved the classification of the genetic conditions leading to iron overload and identified novel entities, characterized by both iron loading and variable degrees of anemia. Despite the progress in the diagnosis, classification, and mechanisms of iron overload disorders, the treatment of affected patients continues to rely on regular phlebotomy. Understanding the molecular circuitry of iron control may lead to the identification of potential therapeutic targets for novel treatment strategies to be used in association with or as an alternative to phlebotomy.

HFE gene mutations in susceptibility to childhood leukemia: HuGE review

The hereditary hemochromatosis (HHC) gene, HFE on chromosome 6p21.3, encodes a protein involved in iron homeostasis. HFE mutations have low penetrance with a mild effect on serum iron levels. Animal, twin, and population studies have shown that carrier state for C282Y can increase iron levels. A proportion of heterozygotes show slightly elevated serum iron levels. Increased serum iron has been suggested to increase the risk for oxidative damage to DNA. Epidemiologic studies established a correlation between iron levels and cancer risk. Case-control studies have reported associations between HFE mutations C282Y/H63D and several cancers, some of which in interaction with the transferrin receptor gene TFRC or dietary iron intake. Increased cancer risk in C282Y carriers is likely due to higher iron levels in a multifactorial setting. In childhood acute lymphoblastic leukemia (ALL), there is an association of C282Y with a gender effect in two British populations. No association has been found in acute myeloblastic leukemia and Hodgkin disease in adults. The childhood leukemia association possibly results from elevated intracellular iron in lymphoid cells increasing the vulnerability to DNA damage at a critical time window during lymphoid cell development. Interactions of HFE with environmental and genetic factors, most of which are recognized, may play a role in modification of susceptibility to leukemia conferred by C282Y. Given the population frequency of C282Y and the connection between iron and cancer, clarification of the mechanism of HFE associations in leukemia and cancer will have strong implications in public health.

The Q283P amino-acid change in HFE leads to structural and functional consequences similar to those described for the mutated 282Y HFE protein

In Caucasians, 4-35% of hemochromatosis patients carry at least one chromosome without a common HFE mutation (i.e. C282Y, H63D and S65C). Several studies have now shown that iron overload phenotypes in such patients can be associated with uncommon HFE mutations. We previously supported implication of the C282Y/Q283P compound heterozygous genotype in hemochromatosis phenotypes and, based on molecular dynamics simulations, proposed that the Q283P substitution prevents normal folding of the HFE alpha3-domain. In the current work, we have used HeLa cells carrying wild-type or Q283P-mutant HFE cDNA under the control of a tetracycline-sensitive promoter to functionally characterise the Q283P mutation. Experiments using cells over-expressing wild-type HFE confirm the existence of beta2microglobulin(beta2m)/HFE and HFE/transferrin receptor 1 (TfR1) interactions, as well as the capacity of HFE to reduce transferrin-mediated iron uptake. In contrast, neither beta2m/HFE nor HFE/TfR1 complex formation was detected in cells over-expressing the mutated form of HFE. Moreover, the 283P HFE protein was found to have a very limited effect on the major cellular iron uptake pathway. Combined, our results indicate that the Q283P mutation leads to structural and functional consequences similar to those described for the main hereditary hemochromatosis mutation. As a consequence, our study has implications for the screening of hemochromatosis patients that have one or two copies of HFE which lack the main mutations. It also highlights that protein structure prediction methods could be more generally used to better interpret relationships between rare genotypes and molecular diagnosis of a human inherited disorder.

Hémochromatose HFE : approche pathogénique et diagnostique

HFE hemochromatosis is the most frequent genetic iron overload disease. It is linked to the C282Y mutation of the HFE protein, protein encoded by the HFE gene, which is located on chromosome 6. The mechanisms accounting for iron excess are not only digestive hyperabsorption of iron but also excessive recycling of macrophagic iron coming from erythrophagocytosis and secreted into the blood. Both mechanisms are linked to an HFE-related hepatic failure in producing hepcidin, a key hormone of body iron regulation. The marked phenotypic variability of C282Y homozygosity expression is likely related to both genetic and environmental factors. The HFE gene discovery has rendered non invasive the positive diagnostic of HFE hemochromatosis, which is now based first on an increased level of plasma transferrin saturation leading to the request of the HFE mutation. Then, hepatic MRI is a reliable method to quantify iron overload. The HFE gene discovery has also paved the road of an enlarged field of differential diagnoses corresponding to novel entities of non-HFE related genetic iron overload syndromes.

Hemojuvelin: a supposed role in iron metabolism one year after its discovery

The discovery of hemojuvelin and its association with juvenile hemochromatosis are important not only for the diagnostics of this rare severe disease but also for the understanding of the complex mechanism of iron metabolism regulation. Currently, the physiological role of hemojuvelin is obscure. Recent experimental and clinical studies indicate that hemojuvelin will probably be a regulator of hepcidin, similar to HFE and transferrin receptor 2. However, in contrast to transferrin receptor 2, which is relevant in the hepcidin response to changes in transferrin saturation, HFE and especially hemojuvelin seem to be involved in the inflammation-induced hepcidin expression. Hepcidin, generally accepted as a hormone targeting enterocytes and macrophages, decreases iron absorption from the intestinal lumen and iron release from phagocytes. This mechanism explains the central role of hepcidin and, indirectly, its regulator, hemojuvelin, in the pathogenesis of hemochromatosis but also in anemia of chronic disease. Further basic and clinical research is needed to uncover the details of hemojuvelin pathophysiology required for potential pharmacological interventions.

Prevalence of the H63D mutation of the HFE in north India: its presence does not cause iron overload in beta thalassemia trait

OBJECTIVES

To determine the allele frequency in the north Indian population of the two mutations in the HFE gene, the C282Y and H63D, which are responsible for causing hereditary haemochromatosis particularly in Caucasians of north European descent. We also wanted to correlate these mutations with the iron status in beta thalassemia traits.

PATIENTS AND METHODS

Sixty normal subjects and 215 individuals with beta thalassemia trait from north India were screened for the C282Y and H63D by polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP). We studied the iron status in these subjects and correlated the same with the HFE gene mutations.

RESULTS

On screening for the C282Y gene mutation, all individuals were detected to be of the wild-type. The overall allele frequency of H63D was 9.09% with three individuals being homozygous for 63D. No statistically significant difference in the iron status was detected between the individuals of the wild-type and mutant for H63D. Haplotyping of the homozygous 63D alleles revealed the pattern to be identical to the Europeans.

CONCLUSIONS

Our study shows that H63D is prevalent and C282Y is rare in north Indians and the presence of 63D mutation does not increase body iron as measured by serum ferritin in beta thalassemia traits. Haplotype of H63D gene mutation is of an European haplotype, indicating a common origin.

Resistance to hepcidin is conferred by hemochromatosis-associated mutations of ferroportin

Ferroportin (FPN) mediates iron export from cells; FPN mutations are associated with the iron overloading disorder hemochromatosis. Previously, we found that the A77D, V162del, and G490D mutations inhibited FPN activity, but that other disease-associated FPN variants retained full iron export capability. The peptide hormone hepcidin inhibits FPN as part of a homeostatic negative feedback loop. We measured surface expression and function of wild-type FPN and fully active FPN mutants in the presence of hepcidin. We found that the Y64N and C326Y mutants of FPN are completely resistant to hepcidin inhibition and that N144D and N144H are partially resistant. Hemochromatosis-associated FPN mutations, therefore, either reduce iron export ability or produce an FPN variant that is insensitive to hepcidin. The former mutation type is associated with Kupffer-cell iron deposition and normal transferrin saturation in vivo, whereas patients with the latter category of FPN mutation have high transferrin saturation and tend to deposit iron throughout the liver parenchyma. FPN-linked hemochromatosis may have a variable pathogenesis depending on the causative FPN mutant.

Recent advances in hereditary hemochromatosis

Hereditary hemochromatosis, a very common genetic defect in the Caucasian population, is characterized by progressive tissue iron overload which leads to irreversible organ damage if it is not treated in a timely manner. Recent developments in the field of molecular medicine have radically improved the understanding of the physiopathology and diagnosis of this disease. However, transferrin saturation and serum ferritin are still the most reliable tests for identifying subjects with hereditary hemochromatosis. Therapeutic phlebotomy is the mainstay of the treatment of this disease and the life expectancy of these patients is similar to that of the normal population if phlebotomy is started before the onset of irreversible organ damage. In this review we discuss the genetics, pathophysiology, diagnosis, clinical features, and management of hereditary hemochromatosis.

In vitro functional analysis of human ferroportin (FPN) and hemochromatosis-associated FPN mutations

Type IV hemochromatosis is associated with dominant mutations in the SLC40A1 gene encoding ferroportin (FPN). Known as the "ferroportin disease," this condition is typically characterized by high serum ferritin, reduced transferrin saturation, and macrophage iron loading. Previously FPN expression in vitro has been shown to cause iron deficiency in human cell lines and mediate iron export from Xenopus oocytes. We confirm these findings by showing that expression of human FPN in a human cell line results in an iron deficiency because of a 3-fold increased export of iron. We show that FPN mutations A77D, V162delta, and G490D that are associated with a typical pattern of disease in vivo cause a loss of iron export function in vitro but do not physically or functionally impede wild-type FPN. These mutants may, therefore, lead to disease by haploinsufficiency. By contrast the variants Y64N, N144D, N144H, Q248H, and C326Y, which can be associated with greater transferrin saturation and more prominent iron deposition in liver parenchyma in vivo, retained iron export function in vitro. Because FPN is a target for negative feedback in iron homeostasis, we postulate that the latter group of mutants may resist inhibition, resulting in a permanently "turned on" iron exporter.

Iron and microbial infection

The use of iron as a cofactor in basic metabolic pathways is essential to both pathogenic microorganisms and their hosts. It is also a pivotal component of the innate immune response through its role in the generation of toxic oxygen and nitrogen intermediates. During evolution, the shared requirement of micro- and macroorganisms for this important nutrient has shaped the pathogen-host relationship. Here, we discuss how pathogens compete with the host for iron, and also how the host uses iron to counteract this threat.

Allele frequencies of hemojuvelin gene (HJV) I222N and G320V missense mutations in white and African American subjects from the general Alabama population

Background

Homozygosity or compound heterozygosity for coding region mutations of the hemojuvelin gene (HJV) in whites is a cause of early age-of-onset iron overload (juvenile hemochromatosis), and of hemochromatosis phenotypes in some young or middle-aged adults. HJV coding region mutations have also been identified recently in African American primary iron overload and control subjects. Primary iron overload unexplained by typical hemochromatosis-associated HFE genotypes is common in white and black adults in Alabama, and HJV I222N and G320V were detected in a white Alabama juvenile hemochromatosis index patient. Thus, we estimated the frequency of the HJV missense mutations I222N and G320V in adult whites and African Americans from Alabama general population convenience samples.

Methods

We evaluated the genomic DNA of 241 Alabama white and 124 African American adults who reported no history of hemochromatosis or iron overload to detect HJV missense mutations I222N and G320V using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Analysis for HJV I222N was performed in 240 whites and 124 African Americans. Analysis for HJV G320V was performed in 241 whites and 118 African Americans.

Results

One of 240 white control subjects was heterozygous for HJV I222N; she was also heterozygous for HFE C282Y, but had normal serum iron measures and bone marrow iron stores. HJV I222N was not detected in 124 African American subjects. HJV G320V was not detected in 241 white or 118 African American subjects.

Conclusions

HJV I222N and G320V are probably uncommon causes or modifiers of primary iron overload in adult whites and African Americans in Alabama. Double heterozygosity for HJV I222N and HFE C282Y may not promote increased iron absorption.