Iron homeostasis: fitting the puzzle pieces together

Increased serum hepcidin levels during treatment with deferasirox in iron-overloaded patients with myelodysplastic syndrome

Hepcidin is a major regulator of iron metabolism. We evaluated changes in serum hepcidin during 3 months of therapy with the iron-chelator deferasirox in patients with low-risk myelodysplastic syndrome and iron overload. Serum hepcidin was found to be high in these patients, correlated with their iron and oxidative status, and further increased by treatment with deferasirox. These findings support the concept that the hepcidin level represents a balance between the stimulating effect of iron overload and the inhibitory effects of erythropoietic activity and oxidative stress. These preliminary findings favour the rationale for iron chelation therapy in such patients.

Erythropoiesis-stimulating agents

Erythropoiesis is the process whereby erythroid progenitor cells differentiate and divide, resulting in increased numbers of red blood cells (RBCs). RBCs contain hemoglobin, the main oxygen carrying component in blood. The large number of RBCs found in blood is required to support the prodigious consumption of oxygen by tissues as they undergo oxygen-dependent processes. Erythropoietin is a hormone that when it binds and activates Epo receptors resident on the surface of cells results in stimulation of erythropoiesis. Successful cloning of the EPO gene allowed for the first time production of recombinant human erythropoietin and other erythropoiesis stimulating agents (ESAs), which are used to treat anemia in patients. In this chapter, the control of Epo levels and erythropoiesis, the various forms of ESAs used commercially, and their physical and biological properties are discussed.

Hepcidin in trauma: linking injury, inflammation, and anemia

BACKGROUND

Anemia is almost universal in trauma patients admitted to the intensive care unit (ICU). Hepcidin is a liver-derived peptide that is a negative regulator of iron stores. Hepcidin synthesis is suppressed by erythropoiesis and iron deficiency and upregulated by iron overload and inflammation. Hepcidin has been shown to have an important role in the anemia of chronic inflammatory diseases but has not been previously studied in the setting of trauma. We sought to define the link between traumatic injury, hepcidin, and inflammation.

METHODS

One hundred fifty trauma patients admitted to the ICU were prospectively enrolled in the study. Urine was collected at regular time points for hepcidin measurement. Serum for iron studies and measurement of those cytokines associated with acute inflammation was also collected.

RESULTS

The study population comprised 73% men. Mean age was 46 years, with a median Injury Severity Score (ISS) of 27. The mean lactate level was 2.9 mmol/L, and mean hemoglobin was 12.4 g/dL. More than 50% of patients were anemic on ICU admission, and nearly all were anemic by postinjury day 10. Urinary hepcidin levels were among the highest reported to date and had a rightward skew. Iron studies confirmed functional iron deficiency. Log hepcidin values were positively correlated with ISS and negatively correlated with admission Pao₂/FiO₂. Every increase in ISS by 10 was associated with a 40% increase in hepcidin. Initial hepcidin levels were positively correlated with duration of anemia.

CONCLUSIONS

Hepcidin levels rise to extremely high but variable levels after trauma and are positively correlated with injury severity measured by ISS and duration of anemia and negatively correlated with hypoxia. Hepcidin is likely a key factor in the impaired erythropoiesis seen in critically injured trauma patients.

Low iron stores are related to higher blood concentrations of manganese, cobalt and cadmium in non-smoking, Norwegian women in the HUNT 2 study

Low iron (Fe) stores may influence absorption or transport of divalent metals in blood. To obtain more knowledge about such associations, the divalent metal ions cadmium (Cd), manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn) and lead (Pb) and parameters of Fe metabolism (serum ferritin, haemoglobin (Hb) and transferrin) were investigated in 448 healthy, menstruating non-smoking women, age 20-55 years (mean 38 years), participating in the Norwegian HUNT 2 study. The study population was stratified for serum ferritin: 257 were iron-depleted (serum ferritin < 12 microg/L) and 84 had iron deficiency anaemia (serum ferritin < 12 microg/L and Hb < 120 g/L). The low ferritin group had increased blood concentrations of Mn, Co and Cd but normal concentrations of Cu, Zn and Pb. In multiple regression models, ferritin emerged as the main determinant of Mn, Co and Cd (p < 0.001), while no significant associations with Cu, Zn and Pb were found. Adjusted r(2) for the models were 0.28, 0.48 and 0.34, respectively. Strong positive associations between blood concentrations of Mn, Co and Cd were observed, also when controlled for their common association with ferritin. Apart from these associations, the models showed no significant interactions between the six divalent metals studied. Very mild anaemia (110 < or = Hb < 120 g/L) did not seem to have any effect independent of low ferritin. Approximately 26% of the women with iron deficiency anaemia had high concentrations of all of Mn, Co and Cd as opposed to 2.3% of iron-replete subjects. The results confirm that low serum ferritin may have an impact on body kinetics of certain divalent metal ions, but not all. Only a fraction of women with low iron status exhibited an increased blood concentration of divalent metals, providing indication of complexities in the body's handling of these metals.

Human iron-sulfur cluster assembly, cellular iron homeostasis, and disease

Iron-sulfur (Fe-S) proteins contain prosthetic groups consisting of two or more iron atoms bridged by sulfur ligands, which facilitate multiple functions, including redox activity, enzymatic function, and maintenance of structural integrity. More than 20 proteins are involved in the biosynthesis of iron-sulfur clusters in eukaryotes. Defective Fe-S cluster synthesis not only affects activities of many iron-sulfur enzymes, such as aconitase and succinate dehydrogenase, but also alters the regulation of cellular iron homeostasis, causing both mitochondrial iron overload and cytosolic iron deficiency. In this work, we review human Fe-S cluster biogenesis and human diseases that are caused by defective Fe-S cluster biogenesis. Fe-S cluster biogenesis takes place essentially in every tissue of humans, and products of human disease genes, including frataxin, GLRX5, ISCU, and ABCB7, have important roles in the process. However, the human diseases, Friedreich ataxia, glutaredoxin 5-deficient sideroblastic anemia, ISCU myopathy, and ABCB7 sideroblastic anemia/ataxia syndrome, affect specific tissues, while sparing others. Here we discuss the phenotypes caused by mutations in these different disease genes, and we compare the underlying pathophysiology and discuss the possible explanations for tissue-specific pathology in these diseases caused by defective Fe-S cluster biogenesis.

Speaking from the heart: systemic copper signaling

Copper is a ubiquitously essential nutrient for cells. In this issue of Cell Metabolism, Kim et al. (2010) demonstrate that tissue copper status can be communicated across organ systems. In a mouse model for cardiac copper deficiency, a serum-carried signal mobilized liver and intestinal copper by inducing ATP7A, a copper-exporting ATPase.

The role of hepatocyte hemojuvelin in the regulation of bone morphogenic protein-6 and hepcidin expression in vivo

Both hemojuvelin (HJV) and bone morphogenic protein-6 (BMP6) are essential for hepcidin expression. Hepcidin is the key peptide hormone in iron homeostasis, and is secreted predominantly by hepatocytes. HJV expression is detected in hepatocytes, as well as in skeletal and heart muscle. HJV binds BMP6 and increases hepcidin expression presumably by acting as a BMP co-receptor. We characterized the role of hepatocyte HJV in the regulation of BMP6 and hepcidin expression. In HJV-null (Hjv(-/-)) mice that have severe iron overload and marked suppression of hepcidin expression, we detected 4-fold higher hepatic BMP6 mRNA than in wild-type counterparts. These results indicate that Hjv(-/-) mice do not lack BMP6. Furthermore, iron depletion in Hjv(-/-) mice decreased hepatic BMP6 mRNA. Expression of HJV in hepatocytes of Hjv(-/-) mice using an AAV2/8 vector, increased hepatic hepcidin mRNA by 65-fold and phosphorylated Smad1/5/8 in the liver by about 2.5-fold. However, no significant change in BMP6 mRNA was detected in either the liver or the small intestine of these animals. Our results revealed a close correlation of hepatic BMP6 mRNA expression with hepatic iron-loading. Together, our data indicate that the regulation of hepatic BMP6 expression by iron is independent of HJV, and that expression of HJV in hepatocytes plays an essential role in hepcidin expression by potentiating the BMP6-mediated signaling.

Binding and uptake of H-ferritin are mediated by human transferrin receptor-1

Ferritin is a spherical molecule composed of 24 subunits of two types, ferritin H chain (FHC) and ferritin L chain (FLC). Ferritin stores iron within cells, but it also circulates and binds specifically and saturably to a variety of cell types. For most cell types, this binding can be mediated by ferritin composed only of FHC (HFt) but not by ferritin composed only of FLC (LFt), indicating that binding of ferritin to cells is mediated by FHC but not FLC. By using expression cloning, we identified human transferrin receptor-1 (TfR1) as an important receptor for HFt with little or no binding to LFt. In vitro, HFt can be precipitated by soluble TfR1, showing that this interaction is not dependent on other proteins. Binding of HFt to TfR1 is partially inhibited by diferric transferrin, but it is hindered little, if at all, by HFE. After binding of HFt to TfR1 on the cell surface, HFt enters both endosomes and lysosomes. TfR1 accounts for most, if not all, of the binding of HFt to mitogen-activated T and B cells, circulating reticulocytes, and all cell lines that we have studied. The demonstration that TfR1 can bind HFt as well as Tf raises the possibility that this dual receptor function may coordinate the processing and use of iron by these iron-binding molecules.

Hemochromatosis

Hemochromatosis is an iron metabolism disorder in which the intestines absorb excessive amounts of iron, which is eventually deposited into soft tissues. Hereditary hemochromatosis is the most common single-gene disorder in the US white population. Typically, adults do not begin to exhibit manifestations of the disease until the age of 40, after years of iron accumulation. Neonatal hemochromatosis is a very rare and serious disorder with no known etiology. It is unrelated to the hereditary mutation of the HFE gene and is thought of as a variety of fulminant hepatic failure. Neonatal hemochromatosis is associated with extremely poor outcomes, and liver transplant is the only reliable treatment. This literature review aims to describe hereditary and neonatal hemochromatosis as well as the sonographic characteristics and treatment.

Hepcidin assay in serum by SELDI-TOF-MS and other approaches

Hepcidin, a liver peptide hormone, is the central regulator of iron homeostasis. Hepcidin synthesis is modulated by iron stores, so that iron repletion increases its levels to prevent pathological overload, while iron deficiency strongly inhibits hepcidin to allow an increase in iron absorption from duodenal cells. The emerging pivotal role of hepcidin in iron homeostasis, along with its important links with basic pathways like inflammation, makes the availability of an accurate hepcidin assay as a potentially powerful investigative tool to improve our understanding as well as our diagnostic/prognostic capabilities in many human diseases. There has been a great interest worldwide in developing a reliable and widely applicable assay of the hormone in biological fluids. Being optimal for low-molecular-weight biomarkers, SELDI-TOF-MS has emerged as a valid tool for hepcidin assay. Here we review recent results obtained with this technique, as well as with other Mass Spectrometry-based and immunological methods.

A novel association between a SNP in CYBRD1 and serum ferritin levels in a cohort study of HFE hereditary haemochromatosis

There is emerging evidence that there are genetic modifiers of iron indices for HFE gene mutation carriers at risk of hereditary hemochromatosis. A random sample, stratified by HFE genotype, of 863 from a cohort of 31 192 people of northern European descent provided blood samples for genotyping of 476 single nucleotide polymorphisms (SNPs) in 44 genes involved in iron metabolism. Single SNP association testing, using linear regression models adjusted for sex, menopause and HFE genotype, was conducted for four continuously distributed outcomes: serum ferritin (log transformed), transferrin saturation, serum transferrin, and serum iron. The SNP rs884409 in CYBRD1 is a novel modifier specific to HFE C282Y homozygotes. Median unadjusted serum ferritin concentration decreased from 1194 microg/l (N = 27) to 387 microg/l (N = 16) for male C282Y homozygotes and from 357 microg/l (N = 42) to 69 microg/l (N = 12) for females, comparing those with no copies to those with one copy of rs884409. Functional testing of this CYBRD1 promoter polymorphism using a heterologous expression assay resulted in a 30% decrease in basal promoter activity relative to the common genotype (P = 0.004). This putative genetic modifier of iron overload expression accounts for 11% (95% CI 0.4%, 22.6%) of the variance in serum ferritin levels of C282Y homozygotes.

Regulation of intestinal iron absorption: the mucosa takes control?

Two studies (Shah et al., 2009; Mastrogiannaki et al., 2009) show that the hypoxia inducible factor HIF-2alpha is a major player in regulating iron absorption by directly controlling the transcription of iron transporters in the intestine in response to changes in mucosal iron or oxygen levels. The HIF-2alpha mechanism has major effects on iron metabolism which can override the well-known hepcidin-ferroportin regulatory axis.

The global burden of iron overload

There have been major developments in the field of iron metabolism in the past decade following the identification of the HFE gene and the mutation responsible for the C282Y substitution in the HFE protein. While HFE-associated hemochromatosis occurs predominantly in people of northern European extraction, other less-common mutations can lead to the same clinical syndrome and these may occur in other populations in the Asian-Pacific region. The most common of these is the mutation that leads to changes in the ferroportin molecule, the protein responsible for the transport of iron across the basolateral membrane of the enterocyte and from macrophages. Recent research has unraveled the molecular processes of iron transport and regulation of how these are disturbed in hemochromatosis and other iron-loading disorders. At the same time, at least one new oral iron chelating agent has been developed that shows promise in the therapy of hemochromatosis as well as thalassemia and other secondary causes of iron overload. It is pertinent therefore to examine the developments in the global field of iron overload that have provided insights into the pathogenesis, disease penetrance, comorbid factors, and management.

Iron absorption in dysmetabolic iron overload syndrome is decreased and correlates with increased plasma hepcidin

BACKGROUND/AIMS

The dysmetabolic iron overload syndrome (DIOS) is a common disorder but its origin remains unclear.

METHODS

A case-control study was conducted to compare intestinal absorption of iron in 16 men with DIOS (age 53 +/- 11 years, serum ferritin 750 +/- 372 microg/l, hepatic iron 78 +/- 25 micromol/g) and in 32 age-matched controls with normal body iron stores (16 overweight subjects and 16 lean subjects). Intestinal absorption was calculated as the area under the curve (AUC) of 58Fe administered orally and correlated with plasma hepcidin and with insulin resistance parameters including HOMA.

RESULTS

Intestinal iron absorption was lower in DIOS (AUC = 22.4 +/- 15.9 microg/l/h) compared to both overweight controls (AUC = 40.5 +/- 29.4 microg/l/h, p=0.04) and to lean controls (AUC = 102.5 +/- 113.5 microg/l/h, p < 0.01). There was an inverse correlation between intestinal iron absorption and plasma hepcidin (r = -0.61, p < 0.001), HOMA (r = -0.35, p = 0.01) and C reactive protein (r = -0.52, p < 0.001).

CONCLUSIONS

In overweight subjects with normal iron stores, iron absorption is decreased through hepcidin upregulation. In patients with DIOS, this decrease is more pronounced due to an additional effect of iron excess on circulating hepcidin levels.

In vitro binding of HFE to the cation-independent mannose-6 phosphate receptor

Hereditary hemochromatosis is most frequently associated with mutations in HFE, which encodes a class Ib histocompatibility protein. HFE binds to the transferrin receptor-1 (TfR1) in competition with iron-loaded transferrin (Fe-Tf). HFE is released from TfR1 by increasing concentrations of Fe-Tf, and free HFE may then regulate iron homeostasis by binding other ligands. To search for new HFE ligands we expressed recombinant forms of HFE in the human cell line 293T. HFE protein was purified, biotinylated and made into fluorescently labelled tetramers. HFE tetramers bound to TfR1 in competition with Tf, but in addition we detected a binding activity on some cell types that was not blocked by Fe-Tf or by mutations in HFE that prevent binding to TfR1. We identified this second HFE ligand as the cation independent mannose-6-phosphate receptor (CI-MPR, also known as the insulin-like growth factor-2 receptor, IGF2R). HFE:CI-MPR binding was mediated through phosphorylated mannose residues on HFE. Recombinant murine Hfe also bound to CI-MPR. HFE bound to TfR1 was prevented from binding CI-MPR until released by increasing concentrations of Fe-Tf, a feature consistent with an iron sensing mechanism. However, it remains to be determined whether endogenous HFE in vivo also acquires the mannose-6 phosphate modification and binds to CI-MPR.

Expression of hsp22 and hsp70 transgenes is partially predictive of drosophila survival under normal and stress conditions

Drosophila Hsp70 is a highly conserved molecular chaperone with numerous cytoplasmic targets. Hsp22 is an alpha-crystallin-related chaperone (small hsp) that localizes to the mitochondrial matrix. The hsp70 and hsp22 genes are induced in response to acute heat and oxidative stress and are also upregulated during normal aging. Here the hsp22 promoter (-314 to +10) and the hsp70 promoter (-194 to +10) were used to drive expression of the fluorescent reporter proteins green fluorescent protein (GFP) and Discosoma sp. red fluorescent protein (DsRED) in transgenic flies. Multiple transgenic lines were analyzed under normal culture conditions and under oxidative stress and heat stress conditions that significantly shorten life span. Flies were individually housed, and GFP (or DsRED) was quantified at young-age time points using the fluorescence stereomicroscope and image analysis software. Expression of the hsp reporters in young flies was partially predictive of remaining life span: Young flies with high expression tended to die sooner under both control and stress conditions.

Plasma hepcidin levels are elevated but responsive to erythropoietin therapy in renal disease

Hepcidin is a critical inhibitor of iron export from macrophages, enterocytes, and hepatocytes. Given that it is filtered and degraded by the kidney, its elevated levels in renal failure have been suggested to play a role in the disordered iron metabolism of uremia, including erythropoietin resistance. Here, we used a novel radioimmunoassay for hepcidin-25, the active form of the hormone, to measure its levels in renal disease. There was a significant diurnal variation of hepcidin and a strong correlation to ferritin levels in normal volunteers. In 44 patients with mild to moderate kidney disease, hepcidin levels were significantly elevated, positively correlated with ferritin but inversely correlated with the estimated glomerular filtration rate. In 94 stable hemodialysis patients, hepcidin levels were also significantly elevated, but this did not correlate with interleukin-6 levels, suggesting that increased hepcidin was not due to a general inflammatory state. Elevated hepcidin was associated with anemia, but, intriguingly, the erythropoietin dose was negatively correlated with hepcidin, suggesting that erythropoietin suppresses hepcidin levels. This was confirmed in 7 patients when hepcidin levels significantly decreased after initiation of erythropoietin treatment. Our results show that hepcidin is elevated in renal disease and suggest that higher hepcidin levels do not predict increased erythropoietin requirements.

Expression of iron-related genes in human brain and brain tumors

BACKGROUND

Defective iron homeostasis may be involved in the development of some diseases within the central nervous system. Although the expression of genes involved in normal iron balance has been intensively studied in other tissues, little is known about their expression in the brain. We investigated the mRNA levels of hepcidin (HAMP), HFE, neogenin (NEO1), transferrin receptor 1 (TFRC), transferrin receptor 2 (TFR2), and hemojuvelin (HFE2) in normal human brain, brain tumors, and astrocytoma cell lines. The specimens included 5 normal brain tissue samples, 4 meningiomas, one medulloblastoma, 3 oligodendrocytic gliomas, 2 oligoastrocytic gliomas, 8 astrocytic gliomas, and 3 astrocytoma cell lines.

RESULTS

Except for hemojuvelin, all genes studied had detectable levels of mRNA. In most tumor types, the pattern of gene expression was diverse. Notable findings include high expression of transferrin receptor 1 in the hippocampus and medulla oblongata compared to other brain regions, low expression of HFE in normal brain with elevated HFE expression in meningiomas, and absence of hepcidin mRNA in astrocytoma cell lines despite expression in normal brain and tumor specimens.

CONCLUSION

These results indicate that several iron-related genes are expressed in normal brain, and that their expression may be dysregulated in brain tumors.

Iron sensing as a partnership: HFE and transferrin receptor 2

The mechanism by which HFE participates in the regulation of iron homeostasis has remained enigmatic. Gao et al. (2009) make the key discovery that the regulation of hepcidin in response to holotransferrin requires the interaction between HFE and transferrin receptor 2 (TfR2).

Hepcidin modulation in human diseases: From research to clinic

By modulating hepcidin production, an organism controls intestinal iron absorption, iron uptake and mobilization from stores to meet body iron need. In recent years there has been important advancement in our knowledge of hepcidin regulation that also has implications for understanding the physiopathology of some human disorders. Since the discovery of hepcidin and the demonstration of its pivotal role in iron homeostasis, there has been a substantial interest in developing a reliable assay of the hormone in biological fluids. Measurement of hepcidin in biological fluids can improve our understanding of iron diseases and be a useful tool for diagnosis and clinical management of these disorders. We reviewed the literature and our own research on hepcidin to give an updated status of the situation in this rapidly evolving field.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Homozygous deletion of HFE produces a phenotype similar to the HFE p.C282Y/p.C282Y genotype

Hemochromatosis is predominantly associated with the HFE p.C282Y homozygous genotype, which is carried by approximately 1 person in 200 in Northern European populations. However, p.C282Y homozygosity is often characterized by incomplete penetrance. Here, we describe the case of a woman who had a major structural alteration in the HFE gene. Molecular characterization revealed an Alu-mediated recombination leading to the loss of the entire HFE gene sequence. Although homozygous for the HFE deleted allele, the woman had a phenotype similar to that seen in most women homozygous for the common p.C282Y mutation. Contrasting with previously reported results in Hfe knockout and Hfe knockin mice, our report gives further evidence that progression of the disease depends on modifying factors.

Hereditary hemochromatosis in the post-HFE era

Following the discovery of the HFE gene in 1996 and its linkage to the iron overload disorder hereditary hemochromatosis (HH) there have been profound developments in our understanding of the pathogenesis of the biochemical and clinical manifestations of a number of iron overload disorders. This article provides an update of recent developments and key issues relating to iron homeostasis and inherited disorders of iron overload, with emphasis on HFE-related HH, and is based on the content of the American Association for the Study of Liver Diseases Single-Topic Conference entitled "Hemochromatosis: What has Happened After HFE?" which was held at the Emory Convention Center in Atlanta, September 7-9, 2007.

Modifying factors of the HFE hemochromatosis phenotype

C282Y homozygosity is the only common HFE genotype able to produce a complete hemochromatosis phenotype. However, its biochemical penetrance is incomplete (75% in men and 50% in women) and its clinical penetrance is low, especially in women (1 vs 25% in men). Environmental (e.g., diet, alcohol, drugs and metabolic syndrome) and genetic (digenism, common polymorphisms in the bone morphogenetic protein pathway involved in the regulation of hepcidin synthesis) explain a part of the variability of the C282Y homozygous phenotype. All other common HFE genotypes--including C282Y-H63D compound heterozygosity--are not associated with significant biochemical and clinical expression in the absence of comorbid factors (e.g., alcohol, diabetes or steatohepatitis). Better identification of acquired and genetic modifiers of iron burden and iron-related organ damage is needed to improve the preventive, diagnostic and therapeutic management of HFE hemochromatosis.