Comprehensive analysis of HFE gene in hereditary hemochromatosis and in diseases associated with acquired iron overload

BACKGROUND Patients with hepatitis C virus(HCV) and hepatocellular carcinoma(HCC) may or not develop iron overload(IO),which is associated with worst prognosis,because can cause serious damage to organs.HFE gene controls the iron uptake from gut,particularly in patients with hereditary hemochromatosis(HH).AIM To identify associations between HFE coding region in patients exhibiting hereditary hemochromatosis and in diseases associated with acquired IO.METHODS We sequenced exons 2 to 5 and boundary introns of HFE gene,evaluating all polymorphic sites in patients presenting hereditary(hemochromatosis) or acquired iron overload HCV and HCC) and in healthy controls,using Sanger sequencing.We also determined the ensemble of extended haplotype in healthy control individuals,including several major histocompatibility complex loci,using sequence specific probes.Haplotype reconstruction was performed using the Arlequin and Phase softwares,and linkage disequilibrium(LD) between histocompatibility loci and HFE gene was performed using the Haploview software.RESULTS The HFE*003 allele was overrepresented(f = 71%) and HFE*001 allele was underrepresented(f = 14%) in HH patients compared to all groups.A strong linkage disequilibrium was observed among the H63 D-G,IVS2(+4)-C and C282 YG gene variants,particularly in HH;however,the mutation IVS2(+4)TC was not directly associated with HH susceptibility.The HFE*001/HFE*002 genotype conferred susceptibility to HCC in HCV patients exhibiting IO(P = 0.02,OR =14.14).Although HFE is telomeric to other histocompatibility genes,the H63 DG/IVS2(+4)-C(P ≤ 0.00001/P ≤ 0.0057) combination was in LD with HLA-B*44 allele group in healthy controls.No LD was observed between HFE alleles and other major histocompatibility loci.CONCLUSION A differential HFE association was observed for HH and for diseases associated with acquired IO(HCV,HCC).Since HFE is very distant from other histocompatibility loci,only weak associations were observed with these alleles.     

Mutation analysis of the HFE gene associated with hereditary hemochromatosis in African Americans

Homozygosity for the mutation Cys282Tyr in the HFE gene has recently been identified as a cause of hereditary hemochromatosis, a disorder resulting in the inappropriate absorption of iron. Approximately 10% of Caucasians are heterozygous for this mutation; however, the gene frequency in African Americans is unknown. A study of a control population of African Americans was performed to determine the frequency of the Cys282Tyr and His63Asp alleles in this ethnic group. The carrier frequency for each mutant allele in our African American population was 3.0%. DNA studies of four African-American hemochromatosis patients did not identify any individuals with the Cys282Tyr allele. These findings suggest that if the Cys282Tyr mutation confers susceptibility to hemochromatosis in Caucasians (as suggested by recent studies) there is an alternative mechanism for hemochromatosis in the American black population. Am. J. Hematol. 58:213–217, 1998. © 1998 Wiley-Liss, Inc.     

Mutation analysis of the HFE gene associated with hereditary hemochromatosis in a Venezuelan sample

The frequency of the C282Y, H63D and S65C alleles of the HFE gene was determined in a sample of the Venezuelan population. Two new sets of primers were tested for amplifying the regions mapping these mutations, and genotyping was performed by restriction fragment length polymorphism (RFLP). DNA sequencing was used to validate the RFLP analysis. Serum ferritin levels were also determined. Two hundred and fourteen individuals were tested, extracting DNA from whole blood cells (n=177) or from serum (n=37). The frequency of heterozygous subjects was 3.7, 18.2 and 1.7% for the C282Y, H63D and S65C mutations, respectively, and the allele frequencies were 0.019±0.01 for C282Y, 0.119±0.016 for H63D and 0.009±0.005 for S65C. The results suggest that the admixture of native populations with subjects of South European origin might have had an important role in the diffusion of HFE alleles in Venezuela. C282Y homozygous subjects were not found in this study. No HFE genotype studied here was associated with a significant elevation of serum ferritin concentrations, except for C282Y/H63D compound heterozygote found in one asymptomatic male. This finding supports the theory that the H63D mutation could be involved in alterations of iron parameters when inherited together with C282Y. Our results indicate that C282Y homozygotes will be rarely detected. Performance of HFE mutation analysis in individuals with high iron determinations would be recommended.     

Mutations of the HFE gene among Turkish hereditary hemochromatosis patients

Since the discovery of the HFE gene, C282Y and H63D mutations have been reported as significantly correlated with clinically manifested hereditary hemochromatosis (HH). As the other genes involved in iron metabolism have been described, non-HFE cases of HH have been identified. Since in the general Turkish population, the C282Y mutation is not found and the H63D mutation is of high frequency, we aimed to determine mutations in the HFE genes in our patients with HH. The HFE gene of the five patients with HH were sequenced. C282Y mutation was absent, and all HH patients were heterozygote for H63D mutation. No other mutation was found in HFE gene by sequencing. Although the higher allele frequency of the H63D mutation in Turkish HH patients than in the general population implies a role of the H63D mutation in iron overload, there is a strong possibility that Turkish HH patients have non-HFE hemochromatosis.     

Increased duodenal DMT-1 expression and unchanged HFE mRNA levels in HFE-associated hereditary hemochromatosis and iron deficiency

HFE-associated hereditary hemochromatosis is characterized by imbalances of iron homeostasis and alterations in intestinal iron absorption. The identification of the HFE gene and the apical iron transporter divalent metal transporter-1, DMT-1, provide a direct method to address the mechanisms of iron overload in this disease. The aim of this study was to evaluate the regulation of duodenal HFE and DMT-1 gene expression in HFE-associated hereditary hemochromatosis. Small bowel biopsies and serum iron indices were obtained from a total of 33 patients. The study population comprised 13 patients with hereditary hemochromatosis (C282Y homozygous), 10 patients with iron deficiency anemia, and 10 apparently healthy controls, all of whom were genotyped for the two common mutations in the HFE gene (C282Y and H63D). Total RNA was isolated from tissue and amplified via RT-PCR for HFE, DMT-1, and the internal control GAPDH. DMT-1 protein expression was additionally assessed by immunohistochemistry. Levels of HFE mRNA did not differ significantly between patient groups (P = 0.09), specifically between C282Y homozygotes and iron deficiency anemic patients, when compared to controls (P = 0.09, P = 0.9, respectively). In contrast, DMT-1 mRNA levels were at least twofold greater in patients with hereditary hemochromatosis and iron deficiency anemia when compared to controls (P = 0.02, P = 0.01, respectively). Heightened DMT-1 protein expression correlated with mRNA levels in all patients. Loss of HFE function in hereditary hemochromatosis is not derived from inhibition of its gene expression. DMT-1 expression in C282Y homozygote subjects is consistent with the hypothesis of a "paradoxical" duodenal iron deficiency in hereditary hemochromatosis. The observed twofold upregulation of the DMT-1 is consistent with the slow but steady increase in body iron stores observed in those presenting with clinical features of hereditary hemochromatosis.     

Role of HFE gene mutations in liver diseases other than hereditary hemochromatosis

Heavy iron overload, as occurs in primary and secondary hemochromatosis, may cause fibrosis of parenchymal organs, including the heart, liver, and pancreas, and it is a risk factor for the development of hepatocellular carcinoma. Recent evidence indicates that lesser degrees of hepatic iron deposition are also risk factors for nonhemochromatotic liver disease. For example, several recent studies showed extraordinarily high prevalences (about 60% to 75%) of HFE mutations in patients with porphyria cutanea tarda and significantly increased prevalences of these mutations in patients with nonalcoholic steatohepatitis from Australia and the United States. It is less well established that the prevalence of the HFE mutations is increased in alcoholic liver disease and in chronic viral hepatitis, but in both conditions, patients harboring one of these mutations, especially C282Y, are more likely to have advanced hepatic fibrosis or cirrhosis. Thus, these mutations both incite and exacerbate nonhemochromatotic liver disease. In this review, we summarize current knowledge of these associations and emphasize important unresolved questions that require further study     

Congenital spherocytosis with hereditary hemochromatosis without pathogenic mutations in the HFE gene

We report a case of an 80-year-old woman with congenital spherocytosis who presented with massive iron overload. Iatrogenic iron overload could be ruled out. Familial history was suggestive of hereditary hemochromatosis; however, molecular genetic testing for the most common HFE mutations remained negative. The patient was treated successfully with phlebotomies. The hypothesis that this patient suffered from hereditary hemochromatosis is discussed on the basis of a brief review of the literature.     

Hepatic iron in hemochromatosis

Ninety-two families with familial hemochromatosis were reviewed and analyzed in regard to hepatic iron and the value of the hepatic iron index (hepatic iron/age). Hepatic iron was measured in 29 hemochromatosis homozygotes, in 10 hemochromatosis heterozygotes, and in 30 control patients with other liver diseases. Hepatic iron content increased with age in homozygotes. Hepatic iron index differentiated homozygotes from heterozygotes (P<0.05) and heterozygotes from controls (P<0.05). The hepatic iron index is a useful measurement in the diagnosis and management of patients with familial hemochromatosis.The author acknowledges grant support from the Ministry of Health of Ontario and the Medical Research Council of Canada.     

Wild-type HFE protein normalizes transferrin iron accumulation in macrophages from subjects with hereditary hemochromatosis

Hereditary hemochromatosis (HC) is one of the most common single-gene hereditary diseases. A phenotypic hallmark of HC is low iron in reticuloendothelial cells in spite of body iron overload. Most patients with HC have the same mutation, a change of cysteine at position 282 to tyrosine (C282Y) in the HFE protein. The role of HFE in iron metabolism and the basis for the phenotypic abnormalities of HC are not understood. To clarify the role of HFE in the phenotypic expression of HC, we studied monocytes-macrophages from subjects carrying the C282Y mutation in the HFE protein and clinically expressing HC and transfected them with wild-type HFE by using an attenuated Salmonella typhimurium strain as a gene carrier. The Salmonella system allowed us to deliver genes of interest specifically to monocytes-macrophages with high transduction efficiency. The accumulation of (55)Fe delivered by (55)Fe-Tf was significantly lower in macrophages from patients with HC than from controls expressing wild-type HFE. Transfection of HC macrophages with the HFE gene resulted in a high level of expression of HFE protein at the cell surface. The accumulation of (55)Fe delivered by (55)Fe-Tf was raised by 40% to 60%, and this was reflected by an increase in the (55)Fe-ferritin pool within the HFE-transfected cells. These results suggest that the iron-deficient phenotype of HC macrophages is a direct effect of the HFE mutation, and they demonstrate a role for HFE in the accumulation of iron in these cells.     

Regulation of transferrin-mediated iron uptake by HFE, the protein defective in hereditary hemochromatosis

The protein defective in hereditary hemochromatosis, called HFE, is similar to MHC class I-type proteins and associates with beta2-microglobulin (beta2M). Its association with beta2M was previously shown to be necessary for its stability, normal intracellular processing, and cell surface expression in transfected COS cells. Here we use stably transfected Chinese hamster ovary cell lines expressing both HFE and beta2M or HFE alone to study the effects of beta2M on the stability and maturation of the HFE protein and on the role of HFE in transferrin receptor 1 (TfR1)-mediated iron uptake. In agreement with prior studies on other cell lines, we found that overexpression of HFE, without overexpressing beta2M, resulted in a decrease in TfR1dependent iron uptake and in lower iron levels in the cells, as evidenced by ferritin and TfR1 levels measured at steady state. However, overexpression of both HFE and beta2M had the reverse effect and resulted in an increase in TfR1-dependent iron uptake and increased iron levels in the cells. The HFE-beta2M complex did not affect the affinity of TfR1 for transferrin or the internalization rate of transferrin-bound TfR1. Instead, HFE-beta2M enhanced the rate of recycling of TfR1 and resulted in an increase in the steady-state level of TfR1 at the cell surface of stably transfected cells. We propose that Chinese hamster ovary cells provide a model to explain the effect of the HFE-beta2M complex in duodenal crypt cells, where the HFE-beta2M complex appears to facilitate the uptake of transferrin-bound iron to sense the level of body iron stores. Impairment of this process in duodenal crypt cells leads them to be iron poor and to signal the differentiating enterocytes to take up iron excessively after they mature into villus cells in the duodenum of hereditary hemochromatosis patients.     

HFE gene mutations and iron metabolism in Wilson's disease

BACKGROUND: There is increasing evidence for an interaction between iron and copper metabolism. METHODS: Iron indices (ferritin, transferrin saturation [TS], serum iron), liver parameters, the prevalence and significance of C282Y and H63D HFE mutations were studied in 40 unrelated, Caucasian patients with Wilson's disease and 295 healthy controls. Due to specific treatment Wilson's disease was well controlled in all but one patient. RESULTS: The allele frequencies for the C282Y (11.3% vs. 6.2%) and the H63D (18.8% vs. 16.4%) mutation did not differ between patients with Wilson's disease and healthy controls. One patient with C282Y homozygous HH and Wilson's disease was identified showing progressive liver disease despite reasonable venesection and copper chelation therapy. No differences in iron indices and liver values were seen between HFE heterozygous and HFE wildtype patients with Wilson's disease. Higher serum ferritin levels were noticed in patients with Wilson's disease compared to healthy controls (149 +/- 26 microg/l vs. 87 +/- 8 microg/l; P < 0.03). CONCLUSIONS: It appears reasonable to assess iron indices in patients with Wilson's disease in order to detect iron overload. HFE mutations other than C282Y homozygosity seem to have no impact on iron indices and liver parameters as long as Wilson's disease is controlled.