Abnormal regulation of HFE mRNA expression does not contribute to primary iron overload.
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BACKGROUND AND OBJECTIVES: Hereditary hemochromatosis (HHC) is a common, recessively inherited, genetic disorder associated with an abnormality of the HFE gene. Subjects homozygous for a point mutation in the gene coding sequence, leading to the amino acid substitution C282Y, are usually affected by the disease. A second point mutation, causing the amino acid substitution H63D, has been described, and compound heterozygotes for the two mutations or homozygotes for the H63D mutation are at risk of developing a milder form of HHC. In populations of northern European origin the C282Y substitution accounts for more than 90% of cases of HHC. In Italy, however, fewer than 70% of patients with HHC are homozygous or compound heterozygous for HFE mutations. Even in the absence of mutations in its coding region, the HFE gene might be involved in the pathogenesis of HHC through inhibition of transcription of the gene or reduced stability of its mRNA. DESIGN AND METHODS: Since little is known about the regulation of HFE expression, we investigated 17 subjects heterozygous for one of the HFE mutations and with biochemical evidence of iron overload and compared the levels of wild type and mutated mRNAs in their peripheral blood cells. c-DNA regions flanking the mutated codons were amplified by reverse transcriptase polymerase chain reaction (PCR). PCR products derived from the two alleles were differentiated and quantified by digestion with restriction enzymes, electrophoresis in an agarose gel stained with ethidium bromide and densitometric scanning of the gel. RESULTS: In all cases wild type and mutated mRNAs were expressed at similar levels, suggesting that reduced expression of an HFE allele coding a normal protein is not involved in the pathogenesis of iron overload. However, we can not rule out that a tissue specific regulation of HFE expression in the cells directly involved in iron absorption is altered and contributes to the pathogenesis of the disease. E INTERPRETATION AND CONCLUSIONS: Our results suggest that primary iron overload is a multigenic syndrome; this hypothesis is strongly supported by the recent demonstration that the juvenile hemochromatosis locus maps to human chromosome 1q. (+info)
Juvenile hemochromatosis associated with B-thalassemia treated by phlebotomy and recombinant human erythropoietin.
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Juvenile hemochromatosis is a rare genetic disorder that causes iron overload. Clinical complications, which include liver cirrhosis, heart failure, hypogonadotropic hypogonadism and diabetes, appear earlier and are more severe than in HFE-related hemochromatosis. This disorder, therefore, requires an aggressive therapeutic approach to achieve iron depletion. We report here the case of a young Italian female with juvenile hemochromatosis who was unable to tolerate frequent phlebotomy because of coexistent ss-thalassemia trait. The patient was successfully iron-depleted by combining phlebotomy with recombinant human erythropoietin. (+info)
Serum antibodies in human pancreatic disease.
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An immunofluorescent study of sera from patients with various pancreatic diseases and from controls was carried out using human pancreas as substrate. A reproducible pattern of immunofluorscence, consisting of a coarse granular appearance in the cytoplasm of acinar cells of the pancreas and independent of the ABO blood group system was found. This occurred in 21 of 61 patients with acute pancreatitis; it was not found in other pancreatic diseases, and occurred in only four of 170 control subjects consisting of mixed hospital patients and healthy adults. Preliminary absorption experiments suggest that the antigen is located in the microsomal fraction of pancreatic homogenates and may be organ-specific. The relationship of positive antibody tests to aetiological factors is discussed. (+info)
HFE gene mutation (C282Y) and phenotypic expression among a hospitalised population in a high prevalence area of haemochromatosis.
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BACKGROUND: Previous studies have shown that up to 0.5% of the Caucasian population is homozygous for the HFE gene C282Y mutation. High prevalence values have been reported in Northern Europe. To what extent the presence of this mutation is associated with overt clinical haemochromatosis is unclear. AIM: To determine the prevalence of the C282Y allele in a hospitalised population of an acute medical department, and study the phenotypic expression in the homozygotes. METHODS: Blood samples were obtained from 2027 hospitalised patients; 1900 Caucasians and 127 non-Caucasians. Serum iron, transferrin, and ferritin were measured at admission. The presence of the HFE gene mutation was determined by polymerase chain reaction based analysis. Follow up fasting blood samples were obtained from patients homozygous for the mutation. RESULTS: Fourteen of the 1900 Caucasian subjects (0.74%) were homozygous and 224 (11.8%) were heterozygous for the C282Y mutation, including 32 subjects (1.7%) who were compound heterozygous for the C282Y and H63D mutations. Ten of 14 (71%) homozygous patients displayed mild to moderate biochemical expression of haemochromatosis with a serum ferritin level <550 microg/l, two (14%) patients were "non expressing", and two of five in whom liver biopsies were carried out had cirrhosis, including one with advanced hepatocellular carcinoma. CONCLUSIONS: The prevalence of C282Y homozygosity in a hospitalised population was 0.74%. However, the majority of homozygous patients displayed mild to moderate biochemical expression. C282Y mutation screening may detect individuals that do not develop haemochromatosis. Transferrin saturation and ferritin, which are used as first line screening in haemochromatosis, may be highly unreliable in the presence of an inflammatory process. (+info)
Haemochromatosis: novel gene discovery and the molecular pathophysiology of iron metabolism.
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The application of molecular genetics to haemochromatosis and experimental mutagenesis in animals has transformed our capacity to investigate the unique physiology of iron homeostasis-a key problem in biology and medicine. The identification of HFE, the principal determinant of adult haemochromatosis (HFE1; OMIM 235200) and TfR2, recently implicated in a rarer form of the inherited disorder (HFE3; OMIM 604250), and the promise of candidate genes for juvenile haemochromatosis (HFE2; OMIM 602390) and neonatal haemochromatosis (OMIM 231100) provide the foundation for important studies into the control mechanism of iron balance in humans. The rare conditions atransferrinaemia (OMIM 209300) and acaeruloplasminaemia (OMIM 604290), each associated with tissue iron overload, have already implicated the iron transport ligand transferrin and the copper transporter caeruloplasmin in the control of iron homeostasis. Gene mapping studies in animal mutants with anaemia due to defects in the uptake or tissue transfer of iron have yielded novel proteins involved in iron transport: DMT1 (brush border transporter of ferrous iron) in the mk/mk mouse, hephaestin (basolateral multi-copper ferroxidase) in the sex-linked anaemic mouse (sla) and ferroportin1 (basolateral iron exporter) in zebrafish weh mutants. The discovery of genes that determine heritable defects of iron absorption and regulation in animals and humans thus holds promise for a complete mechanistic understanding of the molecular pathophysiology of iron metabolism. (+info)
Rapid single-tube screening of the C282Y hemochromatosis mutation by real-time multiplex allele-specific PCR without fluorescent probes.
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BACKGROUND: An accurate determination of the major HFE mutation (C282Y), which is associated with hereditary hemochromatosis, is important in diagnosis and risk assessment for this disease. We report a single-tube high-throughput PCR method for the detection of C282Y. METHODS: We combined three previously described principles: allele-specific PCR, mutagenically separated PCR, and amplicon identification by specific dissociation curves. PCR amplification was performed with fluorescence detection or conventional thermocycler using the same primers, reactant constituents, and cycling protocol. Primer cross-reactions were prevented by deliberate primer:primer and primer:template mismatches. RESULTS: PCR products were identified by their characteristic melting temperatures based on SYBR Green I fluorescence. For each of the 256 random and 17 known HFE C282Y samples, mutant homozygous, wild-type, and heterozygous samples were unequivocally distinguished. CONCLUSIONS: This homogeneous assay is rapid, reproducible, does not require fluorescent oligonucleotide probes, and correctly identifies HFE genotypes. (+info)
A 3-dimensional model building by homology of the HFE protein: molecular consequences and application to antibody development.
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Genetic hemochromatosis (GH) is a common inherited disease of iron metabolism affecting 2-5 in 1000 individuals of European origin. A candidate gene for GH, namely HFE has been recently characterized. Structural studies of the protein product of the HFE gene are of major interest for a better understanding of the molecular physiopathology in iron overload. We have built a 3-dimensional model of the HFE protein based on congruent with40% homology of sequence identity with HLA-Aw68, another MHC class I molecule. This work presents the first 3-dimensional structure of HFE available in the public domain (http://swift.embl-heidelberg.de/service/francois). The 3-dimensional characteristics of the protein complexed with the beta2-microglobulin are presented. The model has been used to predict immunogenic loops and to develop an antibody able to recognize a protein exhibiting the same molecular weight as HFE. Structural consequences of two common mutations are debated and evolutionary hypotheses are considered in the discussion of the particular biological activity of HFE. This study shows that a strategy based on homology modeling is sufficient to undertake biological investigations. (+info)
Comparison of the interactions of transferrin receptor and transferrin receptor 2 with transferrin and the hereditary hemochromatosis protein HFE.
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The transferrin receptor (TfR) interacts with two proteins important for iron metabolism, transferrin (Tf) and HFE, the protein mutated in hereditary hemochromatosis. A second receptor for Tf, TfR2, was recently identified and found to be functional for iron uptake in transfected cells (Kawabata, H., Germain, R. S., Vuong, P. T., Nakamaki, T., Said, J. W., and Koeffler, H. P. (2000) J. Biol. Chem. 275, 16618-16625). TfR2 has a pattern of expression and regulation that is distinct from TfR, and mutations in TfR2 have been recognized as the cause of a non-HFE linked form of hemochromatosis (Camaschella, C., Roetto, A., Cali, A., De Gobbi, M., Garozzo, G., Carella, M., Majorano, N., Totaro, A., and Gasparini, P. (2000) Nat. Genet. 25, 14-15). To investigate the relationship between TfR, TfR2, Tf, and HFE, we performed a series of binding experiments using soluble forms of these proteins. We find no detectable binding between TfR2 and HFE by co-immunoprecipitation or using a surface plasmon resonance-based assay. The affinity of TfR2 for iron-loaded Tf was determined to be 27 nm, 25-fold lower than the affinity of TfR for Tf. These results imply that HFE regulates Tf-mediated iron uptake only from the classical TfR and that TfR2 does not compete for HFE binding in cells expressing both forms of TfR. (+info)