Hemochromatosis at the intersection of classical medicine and molecular biology

Hemochromatosis is a genetic disease of iron overload due to intestinal hyperabsorption of iron. It is one of the most prevalent autosomal recessive diseases in Caucasian populations. Hemochromatosis causes severe visceral and metabolic complications at adulthood, which include cirrhosis, diabetes, arthropathy and cardiac failure. A major breakthrough has been the discovery, in 1996, of the HFE gene which is strongly associated with the phenotypic expression of the disease. This discovery has, very quickly, provided a powerful genetic blood test which permits, in most cases, to establish the diagnosis in a non invasive way (i.e. without a liver biopsy). Hemochromatosis can be cured by repeated venesections provided the diagnosis has been detected sufficiently early. Moreover, an efficient preventive strategy can be applied to family members and should now be proposed to the general population. Finally, the identification of the HFE gene has paved the way for the identification of new iron overload entities.

Stearoyl coenzyme A desaturase 1 expression and activity are increased in the liver during iron overload

In humans, hepatic iron overload can lead to hepatocellular carcinoma development. Iron related dysregulation of hepatic genes could play a role in this phenomenon. We previously found that the carbonyl-iron overloaded mouse was a useful model to study the mechanisms involved in the development of hepatic lesions related to iron excess. The aim of the present study was to identify hepatic genes overexpressed in conditions of iron overload by using this model. A suppressive subtractive hybridization was performed between hepatic mRNAs extracted from control and 3% carbonyl-iron overloaded mice during 8 months. This methodology allowed us to identify stearoyl coenzyme A desaturase 1 (SCD1) mRNA overexpression in the liver of iron loaded mice. The corresponding enzymatic activity was also found to be significantly increased. In addition, we demonstrated that both SCD1 mRNA expression and activity were increased in another iron overload model in mice obtained by a single iron-dextran subcutaneous injection. Moreover, we found, in both models, that SCD1 mRNA was not only influenced by the quantity of iron in the liver but also by the duration of iron overload since SCD1 mRNA upregulation was not detected in earlier stages of iron overload. In addition, we found that cellular repartition likely influenced SCD1 mRNA expression. In conclusion, we demonstrated that iron excess in the liver induced both the expression of SCD1 mRNA and its corresponding enzymatic activity. The level and duration of iron overload, as well as cellular repartition of iron excess in the liver likely play a role in this induction. The fact that the expression and activity of SCD1, an enzyme adding a double bound into saturated fatty acids, are induced in two models of iron overload in mice leads to the conclusion that iron excess in the liver may enhance the biosynthesis of unsaturated fatty acids.

A new mouse liver-specific gene, encoding a protein homologous to human antimicrobial peptide hepcidin, is overexpressed during iron overload

Considering that the development of hepatic lesions related to iron overload diseases might be a result of abnormally expressed hepatic genes, we searched for new genes up-regulated under the condition of iron excess. By suppressive subtractive hybridization performed between livers from carbonyl iron-overloaded and control mice, we isolated a 225-base pair cDNA. By Northern blot analysis, the corresponding mRNA was confirmed to be overexpressed in livers of experimentally (carbonyl iron and iron-dextran-treated mice) and spontaneously (beta(2)-microglobulin knockout mice) iron-overloaded mice. In addition, beta(2)-microglobulin knockout mice fed with a low iron content diet exhibited a decrease of hepatic mRNA expression. The murine full-length cDNA was isolated and was found to encode an 83-amino acid protein presenting a strong homology in its C-terminal region to the human antimicrobial peptide hepcidin. In addition, we cloned the corresponding rat and human orthologue cDNAs. Both mouse and human genes named HEPC are constituted of 3 exons and 2 introns and are located on chromosome 7 and 19, respectively, in close proximity to USF2 gene. In mouse and human, HEPC mRNA was predominantly expressed in the liver. During both in vivo and in vitro studies, HEPC mRNA expression was enhanced in mouse hepatocytes under the effect of lipopolysaccharide. Finally, to analyze the intracellular localization of the predicted protein, we used the green fluorescent protein chimera expression vectors. The murine green fluorescent protein-prohepcidin protein was exclusively localized in the nucleus. When the putative nuclear localization signal was deleted, the resulting protein was addressed to the cytoplasm. Taken together, our data strongly suggest that the product of the new liver-specific gene HEPC might play a specific role during iron overload and exhibit additional functions distinct from its antimicrobial activity.

Low penetrant hemochromatosis phenotype in eight families: no evidence of modifiers in the MHC region

The gene responsible for hemochromatosis (HFE) has been identified on the short arm of chromosome 6, 4.5 Mb telomeric to HLA-A. A major mutation C282Y is closely correlated with the disease, as it accounts for 68 to 100\% of the cases of hemochromatosis. Nevertheless, some C282Y homozygotes subjects have no clinical or biological expression of the disease. Moreover, in Northern European populations a large discrepancy is observed between the number of C282Y homozygotes and the number of diagnosed hemochromatosis patients, suggesting incomplete penetrance of the mutation. To localize and identify the modifying genes, we investigated eight families including C282Y homozygous relatives showing no clinical signs of the disease, in addition to the hemochromatosis patients. Genomic DNA from 20 C282Y homozygotes (10 patients and 10 siblings presenting no or minor biological abnormalities) were studied. Five polymorphisms from the HFE gene were determined by PCR restriction. Extended haplotypes of the 6p21.3 region were constructed with 10 microsatellite markers. All the C282Y homozygotes shared the same HFE polymorphism. The haplotypes presented no significant difference between the probands and their unaffected relatives. These studies suggest that neither HFE polymorphism nor genes surrounding HFE are able to modulate HFE expression.

Inhibition of hepatitis B virus production associated with high levels of intracellular viral DNA intermediates in iron-depleted HepG2.2.15 cells

BACKGROUNDS/AIMS

The effects of iron-depletion on hepatitis B virus (HBV) replication were examined in HepG2.2.15 cells.

METHODS

Proliferating cells were iron-depleted with desferrioxamine (DFO), at 20 or 100 microM for 48 h. Levels of viral mRNAs, cytoplasmic DNA replicative intermediates and virion production were examined. A comparative study was performed with hydroxyurea, a specific inhibitor of ribonucleotide reductase.

RESULTS

In desferrioxamine treated cells, virion production is dramatically decreased, while viral replicative intermediates accumulate in the cytoplasm. DFO, like hydroxyurea, blocks cell cycle progression in the G1/S transition or S phase with a corresponding 2-fold increase of viral mRNAs. As expected, hydroxyurea leads to a strong reduction of virion production associated with low levels of intracellular replicative intermediates.

CONCLUSIONS

These results strongly suggest that iron depletion affects the HBV life cycle indirectly through the cell cycle arrest and directly through the inhibition of the viral DNA secretion. They also indicate the need to re-evaluate with caution the iron depletion protocols on HBV infected patients since a decrease of viral markers in the serum following iron-depletion may not reflect a decrease of viral replicative forms, but on the contrary, could be associated with active viral DNA synthesis.

Clinical aspects of hemochromatosis

Hemochromatosis is one of the most frequent genetic diseases among the white populations, affecting one in three hundred persons. Its diagnosis has been radically transformed by the discovery of the HFE gene. In a given individual, the diagnosis can, from now on, be ascertained on the sole association of a plasma transferrin saturation (TS) over 45% and homozygosity for the C282Y mutation. Liver biopsy is only required to search for cirrhosis whenever there is hepatomegaly and/or serum ferritin >1000 ng/ml and/or elevated serum AST. Family screening is mandatory, primarily centered on the siblings. The treatment remains based on venesection therapy which improves many features of the disease (one of the most refractory, however, being the joint signs) and permits normal life expectancy provided the diagnosis is established prior to the development of cirrhosis or of insulin-dependent diabetes. In view of the prevalence, the non-invasive diagnosis, the spontaneous severity and the efficacy of a very simple therapy, hemochromatosis should benefit from population screening. This screening could be based, first, on the assessment of transferrin saturation, followed - when elevated - by the search for the C282Y mutation. The discovery of the HFE gene has also paved the road for the individualization of other types of iron overload syndromes which are not HFE-related.

[Genetics and physiopathology of hemochromatosis]

Thanks to the discovery of the HFE gene and of its mutations, it is now established that the most frequent form of hemochromatosis is related to homozygosity for the mutation C282Y, and that other types of hemochromatosis, unrelated to HFE mutations, do exist such as the juvenile hemochromatosis. From a pathophysiological standpoint, the C282Y mutation impairs HFE protein expression at the surface of the membrane and disturbs the cellular entry of iron (carried by circulating transferrin) into the cryptic duodenal cell. This, in turn, is likely to lead to an aberrant programmation of the degree of iron influx from the digestive lumen into the apical duodenal cells. The resulting hyperabsorption, which forms the basis of iron overload in hemochromatosis, is likely to implicate an overexpression of the transmembrane iron carrier DMT1. It is remarkable to observe that these major improvements in the knowledge of hemochomatosis have been accompanied by similar improvements in the understanding of normal iron metabolism.

Determination of non-transferrin-bound iron in genetic hemochromatosis using a new HPLC-based method

BACKGROUND/AIMS

Non-transferrin-bound iron may play a major pathogenic role in iron overload diseases due to its high hepatic uptake and potential damaging effect. The aim of this study was to evaluate the relevance of measuring serum non-transferrin-bound iron levels in genetic hemochromatosis using a new high performance liquid chromatography-based method.

METHODS

This method includes a presaturation step of transferrin with cobalt(II) in order to avoid secondary deplacement of non-transferrin-bound iron toward transferrin during the assay. Six genetic hemochromatotic patients were followed serially during venesection treatment.

RESULTS/CONCLUSIONS

The results indicate: (i) that this new method permits detection of non-transferrin-bound iron when transferrin is not fully saturated, (ii) that non-transferrin-bound iron levels persist almost until the completion of treatment, (iii) that non-transferrin-bound iron levels are well correlated with transferrin saturation for a given patient, and (iv) that despite some individual variations, a transferrin saturation value lower than 35% usually corresponds to the disappearance of non-transferrin-bound iron.

Antiproliferative and apoptotic effects of O-Trensox, a new synthetic iron chelator, on differentiated human hepatoma cell lines

We investigated the effects of a new iron chelator, O-Trensox (TRX), compared with desferrioxamine (DFO), on proliferation and apoptosis in cultures of the human hepatoblastoma HepG2 and hepatocarcinoma HBG cell lines. Our results show that TRX decreased DNA synthesis in a time- and dose-dependent manner and with a higher efficiency than DFO. Mitotic index was also strongly decreased by TRX and, unexpectedly, DFO inhibited mitotic activity to the same extent as TRX, thus there is a discrepancy between the slight reduction in DNA synthesis and a large decrease in mitotic index after DFO treatment. In addition, we found that TRX induced accumulation of cells in the G(1) and G(2) phases of the cell cycle whereas DFO arrested cells in G(1) and during progression through S phase. These data suggest that the partial inhibition of DNA replication observed after exposure to DFO may be due to a lower efficiency of metal chelation and/or that it does not inhibit the G(1)/S transition but arrests cells in late S phase. The effects of both TRX and DFO on DNA synthesis and mitotic index were reversible after removing the chelators from the culture medium. An apoptotic effect of TRX was strongly suggested by analysis of DNA content by flow cytometry, nuclear fragmentation and DNA degradation in oligonucleosomes and confirmed by the induction of a high level of caspase 3-like activity. TRX induced apoptosis in a dose- and time-dependent manner in proliferating HepG2 cells. In HBG cells, TRX induced apoptosis in proliferating and confluent cells arrested in the G(1) phase of the cell cycle, demonstrating that inhibition of proliferation and induction of apoptosis occurred independently. DFO induced DNA alterations only at concentrations >100 microM and without induction of caspase 3-like activity, indicating that DFO is not a strong inducer of apoptosis. Addition of Fe or Zn to the culture medium during TRX treatment led to a complete restoration of proliferation rate and inhibition of apoptosis, demonstrating that Fe/Zn-saturated TRX was not toxic in the absence of metal depletion. These data show that TRX, at concentrations of 20-50 microM, strongly inhibits cell proliferation and induces apoptosis in proliferating and non-proliferating HepG2 and HBG cells, respectively.

[Diagnosis and treatment of genetic hemochromatosis]

Genetic hemochromatosis is an autosomal recessive disease, characterized by an increased iron absorption, leading to progressive iron overload. The fully expressed phenotype comprises fatigue, skin pigmentation, liver disease with hepatomegaly, cirrhosis and hepatocellular carcinoma, and diabetes. Arthralgias are frequent, cardiopathy or impotence may occur. This presentation is now unfrequent with earlier diagnosis, and patients are often asymptomatic--with only biochemical expression--or pauci-symptomatic (mild fatigue, arthralgias or increased transaminases). Transferrin saturation is always increased. Serum ferritin is proportional to iron burden. Diagnosis is now easy, since most patients are homozygote for the C282Y mutation of the HFE gene. Liver biopsy can be useful to quantify iron overload and assess liver fibrosis. The disease can be lethal due to liver disease, carcinoma or heart disease, but life expectancy goes to normal if patients are treated before the occurrence of cirrhosis. Treatment relies on regular venesections. Familial screening is essential.

Respective value of alkaline phosphatase, gamma-glutamyl transpeptidase and 5' nucleotidase serum activity in the diagnosis of cholestasis: a prospective study of 80 patients

We studied the value of alkaline phosphatase (AP), gamma-glutamyl transpeptidase (GGT), and 5'-nucleotidase (5'-NU) activities in the diagnosis of intrahepatic (IHC) versus extra-hepatic cholestasis (EHC). Eighty patients were included prospectively. All presented with cholestasis as defined by a concomitant increase in at least two of three cholestatic enzymes (AP, GGT, 5'-NU), a low cytolytic ratio (alanine aminotransferase/AP [xN/xN] < or = 5), and no evidence for associated liver tumor. We compared 43 patients with IHC due to chronic liver disease to 37 patients with EHC due to main bile duct obstruction. Fasting blood samples for activity determination (AP, GGT, 5'-NU) were taken before performing liver biopsy in cases of IHC and before endoscopic or surgical management in cases of EHC. Enzyme activities were compared using univariate and multivariate analysis. AP (276 IU/L [35-3,140] vs. 123 IU/L [37-699]: p < 0.0001), GGT (595 IU/L [98-5,200] vs. 211 IU/L [38-925]; p < 0.0001), and 5'-NU (32 IU/L [10-142] vs. 16 IU/L [4-107]: p < 0.0003) were significantly higher in EHC when compared to IHC. Only in GGT and 5'-NU activities were independent variables significantly linked to the mechanism of cholestasis. In IHC, the ratio GGT/5'-NU (xN/xN) was significantly lower than in EHC (2.8 [0.7-7.2] vs. 3.7 [1.8-10.5]: p < 0.006). A threshold of GGT/5'-NU < 1.9 had a sensitivity of 40% and a specificity of 100% for the diagnosis of IHC. Although such hepatobiliary enzymes cannot be regarded as diagnostic, they can provide useful information to orientate the clinician in the diagnosis of cholestasis.

Interferon and ursodeoxycholic acid combined therapy in chronic viral C hepatitis: controlled randomized trial in 203 patients

AIMS

This prospective randomized trial was carried out in order to determine whether the long-term administration of ursodeoxycholic acid after discontinuation of interferon had any beneficial effect on the clinical course of hepatitis C virus infection.

METHODS

Enrolled in the study were 203 patients with chronic active hepatitis C. They were all given: interferon alpha-2a (3 MU subcutaneously thrice a week) and ursodeoxycholic acid (10 mg/kg/day) for 9 months. At month 9, biochemical responders only were randomized into ursodeoxycholic acid treatment or placebo for 12 additional months (double blind study).

RESULTS

At the end of interferon therapy, 71 patients (37%) were virological responders and 107 (56%) patients were biochemical responders and were randomized: 54 into the ursodeoxycholic acid group and 53 into the placebo group. Sustained response was evaluated 12 months after withdrawal of interferon. Sustained biochemical and virological responses were, respectively, 30% and 22% in the ursodeoxycholic acid group and 46% and 32% in the placebo group, which did not significantly differ. Histological evolution of fibrosis and necrotic inflammatory activity were similar in the two groups.

CONCLUSION

Continuation of ursodeoxycholic acid therapy after withdrawal of interferon in patients with end-of-treatment response did not result in any significant improvement either in the maintenance of response to interferon or in liver histology.

In patients with cirrhosis, serum albumin determination should be carried out by immunonephelometry rather than by protein electrophoresis

OBJECTIVE

Serum albumin is a key parameter for prognosis in cirrhosis. We compared levels of serum albumin determined by both protein electrophoresis and immunonephelometry, with special reference to the Child-Pugh classification.

DESIGN AND METHODS

One hundred and thirty-one patients, including 39 with cirrhosis, were included prospectively during 2 months. The aetiology of cirrhosis was mainly alcoholism (67%) and hepatitis C virus (HCV) (18%). Serum albumin was determined simultaneously by electrophoresis (Hydrasys SEBIA following protein determination by the biuret reaction) and by immunonephelometry (BECKMAN Nephelometer). Values were compared by non-parametric tests.

RESULTS

For the whole population, electrophoretic and immunonephelometric values correlated (p = 0.85; P < 0.0001), but electrophoresis significantly overestimated serum albumin by a median 1.6 g/l (P < 0.0001) with a large spread in values (range, -3.9 to 12.7). Median overestimation in cirrhosis was 2.6 g/l (P < 0.0001; range, -2.0 to 10.2) and 1.0 g/l (P < 0.0001; range, -3.9 to 12.7) in patients without cirrhosis (difference, P < 0.02). For 6/39 (15.4%) patients with cirrhosis, this overestimation led to an underestimation in the Child-Pugh classification.

CONCLUSION

In our experience, electrophoresis can lead to serum albumin values which are significantly different compared to those obtained by immunonephelometry. This discrepancy may lead to an incorrect Child-Pugh classification. Therefore, in the follow-up of cirrhotic patients, serum albumin should be determined by immunonephelometry.

Insulin resistance-associated hepatic iron overload

BACKGROUND & AIMS

Hepatic iron overload has been reported in various metabolic conditions, including the insulin-resistance syndrome (IRS) and nonalcoholic steatohepatitis (NASH). The aim of this study was to show that such hepatic iron overload is part of a unique and unrecognized entity.

METHODS

A total of 161 non-C282Y-homozygous patients with unexplained hepatic iron overload were included. We determined the age; sex; presence of IRS (1 or more of the following: body mass index of >25, diabetes, or hyperlipidemia); serum iron tests and liver iron concentration (LIC; reference value, <36 micromol/g); liver function test results; C282Y and H63D HFE mutations; and liver histological status.

RESULTS

Patients were predominantly male and middle-aged. Most (94%) had IRS. Transferrin saturation was increased in 35% (median, 42%; range, 13%-94%). LIC ranged from 38 to 332 micromol/g (median, 90 micromol/g), and LIC/age ratio ranged from 0.5 to 4.8 (median, 1.8). Allelic frequencies of both HFE mutations were significantly increased compared with values in normal controls (C282Y, 20% vs. 9%; H63D, 30% vs. 17%), only because of a higher prevalence of compound heterozygotes. Patients with no HFE mutations had similar degrees of iron overload as those with other genotypes, except for compound heterozygotes, who had slightly more iron burden. Steatosis was present in 25% of patients and NASH in 27%. Portal fibrosis (grades 0-3) was present in 62% of patients (grade 2 or 3 in 12%) in association with steatosis, inflammation, and increased age. Sex ratio, IRS, transferrin saturation, and LIC did not vary with liver damage. Serum ferritin concentration, liver function test results, and fibrosis grade were more elevated in patients with steatosis and NASH than in others, but LIC and allelic frequencies of HFE mutations were similar.

CONCLUSIONS

This study shows that patients with unexplained hepatic iron overload are characterized by a mild to moderate iron burden and the nearly constant association of an IRS irrespective of liver damage.

[Iron in the era of molecular biology]

Identification of the HFE gene and its C282Y and H63D mutations has improved the classification of iron overload disorders. Inherited hemochromatosis is due mainly, or perhaps only, to C282Y homozygosity, whereas nonhemochromatosis forms of iron overload are due to other HFE mutations and are usually responsible for mild overload precipitated by another factor such as cirrhosis or insulin-resistance. In practice, the diagnosis of inherited hemochromatosis rests on demonstration of homozygosity for the C282Y mutation; in this setting, the role of liver biopsy is to evaluate the prognosis by looking for fibrosis. In patients who are not homozygous for the C282Y mutation but have severe iron overload, causes other than hemochromatosis should be looked for before the extremely remote possibility of nonC282Y-related hemochromatosis is considered; here, liver biopsy remains of considerable diagnostic usefulness.

Cytoprotection and iron mobilization in rat hepatocyte cultures by a new synthetic dihydroxamate chelator

The cytoprotection and iron mobilization effect of a new dihydroxamate chelator 1,1 bis [(11-N-hydroxy)-2,5,11-triaza-1,6,10-trioxo dodecanyl] ethane or KD was studied in primary rat hepatocyte cultures exposed to iron-citrate. Lactate dehydrogenase (LDH) release and malondialdehyde (MDA) production were measured as indexes of cytotoxicity. Cell viability was evaluated using the [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyl tetrazolium bromide] (MTT) reduction test. To demonstrate that this chelator was able to decrease iron uptake or increase iron release from the hepatocytes, labelled cells were obtained by maintaining the cultures in the presence of 0.02 microM 55Fe-citrate. The efficacy of KD was compared to desferrioxamine B (DFO) at stoechiometry concentrations. After 24 h of exposure to 50 microM of iron-citrate, a significant release of LDH and MDA was observed. Cell viability was also significantly decreased. When 100 microM of KD were added at the same time as iron, LDH and MDA release was decreased and cell viability was improved. In the presence of the same chelator concentration, a net decrease of iron uptake by the cells was observed as attested by the low intracellular 55Fe level. Moreover, in the 55Fe loaded hepatocytes, the chelator increased the iron extracellular level indicating its iron release effect from the cells. In all tested experimental conditions, the efficacy of 100 microM of the dihydroxamate chelator KD was close to that of 50 microM of the trihydroxamate chelator DFO. In conclusion, KD is effective at a level comparable to DFO in protecting rat hepatocytes against the toxic effect of iron-citrate by decreasing the uptake of the metal and increasing its release from the cells. This synthetic compound appears to have some potential therapeutical interest and the results obtained encourage the synthesis of new hydroxamate ligands.

Haemochromatosis and HFE gene

The discovery of the HFE gene has improved classification and diagnosis of iron overload. Most patients with a phenotypic diagnosis of haemochromatosis are homozygote for the C282Y mutation. Among those with other genotypes, only compound heterozygotes, who present the C282Y mutation on one chromosome and the H63D on the other, may present with haemochromatosis, but with a low penetrance and a mild expression. Other patients usually present with another cause of iron overload, such as insulin resistance, alcoholic liver disease or liver cirrhosis. The practical management of haemochromatosis has been greatly modified, since liver biopsy is no more necessary for diagnosis in C282Y homozygotes, and is only needed for exclusion of cirrhosis. Family screening has also greatly benefited from genotyping.

Quantification of non-transferrin-bound iron in the presence of unsaturated transferrin

Non-transferrin-bound iron (NTBI) has been reported to be associated with several clinical states such as thalassemia, hemochromatosis, and in patients receiving chemotherapy. We have investigated a number of ligands as potential alternatives to nitrilotriacetic acid (NTA) to capture NTBI without chelating transferrin- or ferritin-bound iron in plasma. We have established, however, that NTA is the optimal ligand to chelate the different forms of NTBI present in sera and can be adopted for utilization in the NTBI assay. NTA (80 mM) removes all forms of NTBI, while only mobilizing a small fraction of the iron bound to both transferrin and ferritin. We have compared three different detection systems for the quantification of NTA-chelated NTBI: the established HPLC-based method, a simple colorimetric method, and a method based on inductive conductiometric plasma spectroscopy. The sensitivity and reproductibility of the colorimetric method were acceptable compared with the other two methods and would be more convenient as a routine laboratory screening assay for NTBI. However, the limitations of this method are such that it can only be utilized in situations where desferrioxamine is not used and when transferrin saturation levels are close to 100%. Only the HPLC-based method is applicable for patients receiving (desferrioxamine) chelation therapy. In some diseases such as hemochromatosis, transferrin may be incompletely saturated. In such cases, to avoid in vitro donation of iron onto the vacant sites of transferrin, sodium-tris-carbonatocobaltate(III) can be added to block the free iron binding sites on transferrin. If this step is not taken, there may be an underestimation of NTBI values.

[Current data on iron metabolism]

Iron is required for cellular life. However, abnormalities of its metabolism may lead to iron deficiency or iron overload, both conditions which are deleterious. Therefore, stock and distribution of iron in the body must be very stable. Classically, four major proteins are involved in iron metabolism: (a) transferrin which is implicated in its plasmatic transport, (b) transferrin receptor which regulates iron-transferrin uptake, (c) ferritin, the major iron storage protein, and (d) IRP (Iron Regulatory Protein) which regulates both the entry and storage of iron by linking to the IRE (Iron Responsive Element), a nucleotidic sequence found on transferrin receptor and ferritin mRNA. Thus, IRP adapts gene expression to the iron cellular status. Recent data give informations about new proteins involved in iron metabolism: HFE whose gene is mutated in genetic hemochromatosis, ceruloplasmin which permits cellular iron egress and frataxin which is implicated in the exit of iron from mitochondria.

[The diagnosis of hemochromatosis in the era of the gene]

The discovery of the hemochromatosis gene has deeply changed and simplified the diagnosis of the disease. In a given individual, establishing the diagnosis relies, from now on, on a simple blood sample showing the couple: elevated transferrin saturation and homozygous C282Y mutation (= C282Y +/+). Liver biopsy should only be performed when iron overload is massive in order to detect cirrhosis (or bridging fibrosis), i.e. in a prognostic view. Practically, liver biopsy is confined to the following two situations: when the C282Y +/+ patient exhibits hepatomegaly and/or an increase in serum transaminases and/or a serum ferritin level above 1,000 micrograms/L; whenever, despite a strong bio-clinical suspicion of iron overload, genetic testing does not show the expected homozygosity for C282Y. At the family level, evaluating the risk for hemochromatosis is now "instantaneous" thanks to genetic testing. One must, however, keep in mind in interpreting the data of the family members that: clinical expression of the homozygous status is not constant; heterozygosity for C282Y does not per se lead to significant iron overload, but may constitute a co-factor exacerbating (or increasing the risk of) other hepatic or non hepatic diseases. Heterozygosity exposes also to the risk of homozygosity among the offspring; this knowledge of C282Y status must be balanced by the negative impact from the standpoint of possible societal genetic discrimination.