Hereditary hemochromatosis: the clinical significance of the S65C mutation

Hereditary hemochromatosis (HH) is a common genetic disease with iron overload in certain organs, especially the liver. Most cases are homozygous for the C282Y mutation in the HFE gene; a few are C282Y heterozygous, compound C282Y/H63D heterozygous, or have no known mutation. A third mutation, S65C, has been associated with HH, but this finding is disputed. We have studied the clinical significance of various genotypes with the S65C mutation. In a population-based screening for HH in 65,238 persons, 613 had high serum transferrin saturation in two blood samples and were invited for HFE genotyping. In 556 persons with complete data sets, we studied the serum ferritin concentration and the risk of being diagnosed with phenotypic HH in the various genotypic groups. The phenotypic diagnosis was given without knowing the genotypic result. Except for the C282Y homozygotes, no differences in median serum ferritin concentrations were found between the various genotypic groups. However, the C282Y/S65C compound heterozygous group had a higher risk of being diagnosed with phenotypic HH than the wild-type group, as did the C282Y homozygous and the C282Y/H63D compound heterozygous groups. When combined with the C282Y mutation, the S65C mutation is associated with an increased risk of being diagnosed with phenotypic HH.     

Celtic origin of the C282Y mutation of hemochromatosis

The main hereditary hemochromatosis mutation C282Y in the HFE gene was recently described, and the C282Y frequencies were reported for various European populations. The aim of this synthesis is to compile the Y allele frequencies of the C282Y mutation for 40 European populations. The most elevated values are observed in residual Celtic populations in Ireland, the United Kingdom, and France, in accordance with the hypothesis of Simon et al. (1980) concerning a Celtic origin of the hereditary hemochromatosis mutation.     

A pilot C282Y hemochromatosis screening in Italian newborns by TaqMan technology

Hereditary hemochromatosis (HH) is a disorder of iron metabolism that leads to iron overload in middle age and can be caused by homozygosity for the C282Y mutation in the HFE gene. Preliminary studies have estimated the frequency of this mutation at 0.5-1% in Italy, but this has not been verified on a large sample. We analyzed 1,331 Italian newborns for the C282Y mutation in the HFE gene using dried blood spots (DBS) from the Neonatal Screening Center in Turin, Italy. The mutation was assessed using a semi-automatable 5'-nuclease assay (TaqMan technology). We detected 55 heterozygotes and no homozygotes in our sampling, resulting in an overall frequency of 2.1% +/- 0.6 for the C282Y allele. Differences in allele frequency were observed, and ranged from 2.7% +/- 1.3 in samples from Northern Italy, to 1.7% +/- 0.9 in samples from Central-Southern Italy. The low frequency of the at-risk genotype for iron overload suggests that genetic screening for HFE in Italy would not be cost effective. The present study, in addition to defining C282Y frequency, documents detection of the major HFE mutation on routine DBS samples from neonatal screening programs using a semi-automatable, rapid, reliable, and relatively inexpensive approach.     

Pitfalls in the genetic diagnosis of hereditary hemochromatosis

The widespread use of the genotype assay that identifies the common C282Y mutation in the HFE gene has allowed an earlier diagnosis to be made in many subjects. A significant number of these patients may have no evidence of phenotypic disease and have a normal serum ferritin level. This phenomenon is more common when the genotype assay is used to screen populations rather than higher-risk groups such as family members of a proband with hereditary hemochromatosis. Moreover, patients with significant iron overload may be wild type for the C282Y mutation and have no other demonstrable mutation of the HFE gene. The HFE genotype assay has recently been found to give a false-positive C282Y homozygous result in half of the subjects in one population screening study due to the presence of a single nucleotide polymorphism (SNP) that interfered with primer binding in the PCR assay. The problem may be overcome by using alternate primers. A number of other groups have confirmed the finding but in a much smaller number of subjects, whereas others found that their assays were not affected by the SNP. The use of the HFE genotype assay as the sole diagnostic criterion for hereditary hemochromatosis is not recommended. The genotype assay should be used as an adjunct to the established methods of demonstrating iron overload and be viewed as a predictor of either the presence of iron overload or the subsequent development of iron overload during an individual's lifetime.     

Prevalence of C282Y and H63D mutations in the haemochromatosis (HFE) gene in Tunisian population

The studies of the HFE mutations: H63D and C282Y in North African populations have revealed the extreme rarity or even the absence of the C282Y mutation. We have examined 1140 chromosomes (570 Tunisian people) for the presence of the two HFE mutations by PCR-RFLP analysis. We have found that the allele frequencies are, respectively, 15.17% (+/-2.1%) for the H63D and 0.09% (+/-0.17%) for the C282Y. These results are consistent with the worldwide spread of the H63D mutation and the north European restriction of the C282Y. This study will be completed by determining whether homozygote trait for H63D and associated risk factors (beta thalassémia) can lead to iron overload in Tunisia.     

Hereditary haemochromatosis: only 1% of adult HFEC282Y homozygotes in South Wales have a clinical diagnosis of iron overload

In northern Europe, about 90% of patients with hereditary haemochromatosis (HH) are homozygous for a single mutation (C282Y) of the HFEgene and approximately 1 in 150 people in the general population carries this genotype. However, the clinical significance of HFE mutations remains uncertain, as is the proportion of people homozygous for C282Y who will develop clinical symptoms leading to a diagnosis of HH. A systematic review of patients with HH over a 2-year period within a defined UK region has revealed that only 1.2% of adult C282Y homozygotes have been diagnosed with iron overload and received treatment. In those in whom body iron load could be estimated, only 51% has more than 4 g iron (the diagnostic threshold for iron overload).     

Frequency of HFE H63D, S65C, and C282Y mutations in patients with iron overload and controls from Toledo, Spain

Hereditary hemochromatosis (HH) is an autosomal recessive disease caused by a defective iron absorption. C282Y is the most frequent HFE gene mutation causing HH in Northern European populations and their descendants. However, two other mutations, H63D and S65C, have been described as pathogenic changes. In this study, we have tried to evaluate the frequency of these three mutations in our community. Eighty-three patients with clinical and/or biochemical features of hemochromatosis and 150 controls were screened for H63D, S65C, and C282Y mutations using a PCR-restriction fragment length polymorphism (RFLP)-based strategy. In contrast to previous studies, 7% of the patients were homozygous for C282Y mutation. The remaining patients were 20% H63D homozygous, 10% H63D/C282Y compound heterozygous, 1% H63D/S65C compound heterozygous, 22% H63D heterozygous, 2% C282Y heterozygous, 2% S65C heterozygous, and 36% of patients lacked any of the three mutations studied, despite the fact that they showed clinical/biochemical features of hemochromatosis. We observed a high frequency of the H63D mutation in both the control group and patients, whereas the main genotypes implicated in HH in our series were H63D homozygous and H63D/C282Y compound heterozygous. We propose that the H63D mutation be analyzed in HH patients from our geographic area. Moreover, further studies are needed to elucidate the role of this mutation in the development of HH and the genetic, environmental or other factors that affect the genotype-phenotype correlation between H63D and hemochromatosis.     

Hemochromatosis: As a conformational disorder

Hereditary hemochroamtosis (HH) refers to a unique clinicopathologic subset of iron overload syndromes that includes the disorder related to C282Y homozygous mutation of the hemochromatosis protein (HFE), the most common form of hereditary hemochromatosis. Recent reports have highlighted analogies with the class of disorders, known as the conformational diseases whereby HFE C282Y mutant protein forms aggregates and is subsequently retained in the endoplasmic reticulum (ER). In conformational disorders, accumulation of unfolded or misfolded proteins in the ER can activate a complex cascade linked to the regulation of diverse physiologic processes, disease onset and progression. To-date, reviews on HFE C282Y HH have largely dealt with the end-stage consequence of this disorder (iron overload). However, our review focuses on upstream molecular events resulting from the mislocalization of the aggregation-prone HFE C282Y protein leading to potential advances in treatment and diagnosis.     

Geography of HFE C282Y and H63D mutations

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder causing inappropriate dietary iron absorption that affects North Europeans. HH is associated with the C282Y mutation of the HFE gene, and the H63D mutation to a lesser degree. Both mutations are abundant in Europe, with H63D also appearing in North Africa, the Middle East, and Asia. Emigration from Europe over the past 500 years has introduced C282Y and H63D to America, Australia, New Zealand, and South Africa in an essentially predictable fashion. The distinctive characteristics of the population genetics of HH are the confined racial distribution and high frequency in North European peoples. C282Y frequencies in North Europeans are typically between 5% and 10%, with homozygotes accounting for between 1/100 and 1/400 of these populations. The scarcity of the C282Y mutation in other populations accounts for the lack of HH in non-Europeans.     

HFE genotype frequencies in consecutive reference laboratory specimens: comparisons among referral sources and association with initial diagnosis

We quantified HFE genotype frequencies in specimens submitted by physicians grouped by specialty and determined associations of genotypes with initial diagnosis based on phenotyping in patients evaluated at an iron disorders center. Of 526 specimens (519 from Alabama), these "typical" hemochromatosis-associated genotypes were detected: 85 C282Y/C282Y, 50 C282Y/H63D, and 27 H63D/H63D. Respective frequencies of C282Y/C282Y in specimens from an iron disorders center (n = 156), gastroenterologists (n = 147), hematologists/medical oncologists (n = 85), liver transplant surgeons (n = 11), endocrinologists and rheumatologists (n = 9), and "other sources" (n = 7) were greater (p < 0.05) than in population controls. In 44 patients from an iron disorders center initially diagnosed as "presumed hemochromatosis," 27 (61.4%) had C282Y/C282Y, 10 (22.7%) had C282Y/H63D, and 3 (6.8%) had H63D/H63D. C282Y/C282Y was not detected in 48 patients with "abnormality probably not an iron overload disorder." A total of 20.5% of 44 family members of patients had "typical" hemochromatosis-associated HFE genotypes (7.0% controls; p = 0.02). We conclude that most physicians who submitted specimens identify patients by phenotyping who have greater frequencies of "typical" hemochromatosis-associated HFE genotypes than controls, and that HFE mutation testing is useful in detecting hemochromatosis in family members of persons with hemochromatosis or iron overload.     

Evidence from a Ghanaian population of known African descent to support the proposition that hemochromatosis is a Caucasian disorder

Mutations in the HFE gene on chromosome 6 are believed to cause the iron overload disorder hemochromatosis, the most common single gene disorder in northern Europeans. Two mutations have been described previously: C282Y, with an allele frequency of between 3% and 10% in the caucasian population, and H63D, which has an allele frequency of 16%. Published data shows that C282Y appears to be causative in the homozygous state, while the frequency of H63D/C282Y compound heterozygotes is much greater than expected in patient groups. There also appears to be a slightly elevated risk for H63D homozygotes. Hemochromatosis has been thought to be primarily a caucasian disorder. We have studied 97 healthy, black Ghanaian subjects, whose parents and grandparents were also African, to find the frequency of the two mutations. C282Y was absent, while H63D occurred in 2 individuals. These differences are significant at the 0.05 and 0.001 levels, respectively. The prevalence of H63D homozygotes in this population at 1 in 10,000 is clearly of no use in studying the effect of this genotype on phenotype. However, this study suggests an absence of the C282Y mutation in African populations, and the possibility that other populations might provide different genotypes and hence an analysis of H63D risk. A possible heterozygote advantage for the mutation is discussed.     

Multicentric origin of hemochromatosis gene (HFE) mutations

Genetic hemochromatosis (GH) is believed to be a disease restricted to those of European ancestry. In northwestern Europe, >80% of GH patients are homozygous for one mutation, the substitution of tyrosine for cysteine at position 282 (C282Y) in the unprocessed protein. In a proportion of GH patients, two mutations are present, C282Y and H63D. The clinical significance of this second mutation is such that it appears to predispose 1%-2% of compound heterozygotes to expression of the disease. The distribution of the two mutations differ, C282Y being limited to those of northwestern European ancestry and H63D being found at allele frequencies>5%, in Europe, in countries bordering the Mediterranean, in the Middle East, and in the Indian subcontinent. The C282Y mutation occurs on a haplotype that extends 相似文献   

Sequence variation and haplotype structure at the human HFE locus

The HFE locus encodes an HLA class-I-type protein important in iron regulation and segregates replacement mutations that give rise to the most common form of genetic hemochromatosis. The high frequency of one disease-associated mutation, C282Y, and the nature of this disease have led some to suggest a selective advantage for this mutation. To investigate the context in which this mutation arose and gain a better understanding of HFE genetic variation, we surveyed nucleotide variability in 11.2 kb encompassing the HFE locus and experimentally determined haplotypes. We fully resequenced 60 chromosomes of African, Asian, or European ancestry as well as one chimpanzee, revealing 41 variable sites and a nucleotide diversity of 0.08%. This indicates that linkage to the HLA region has not substantially increased the level of HFE variation. Although several haplotypes are shared between populations, one haplotype predominates in Asia but is nearly absent elsewhere, causing higher than average genetic differentiation among the three major populations. Our samples show evidence of intragenic recombination, so the scarcity of recombination events within the C282Y allele class is consistent with selection increasing the frequency of a young allele. Otherwise, the pattern of variability in this region does not clearly indicate the action of positive selection at this or linked loci.     

Frequency of hemochromatosis C282Y and H63D mutations in Sardinia

Hereditary hemochromatosis (HH) is one of the most common autosomal recessive disorders of iron metabolism among Caucasians, and it is associated with C282Y mutation of the HFE gene in populations of Celtic origins. A second mutation, H63D, shows a very high widespread frequency, although its role in iron metabolism is still inconclusive. There are no data on the frequencies of these two mutations in Sardinia, an island in the Mediterranean sea that has not been invaded by Celtic peoples. We examined 836 chromosomes from Sardinian subjects and tested for the mutation by restriction enzyme digestion of PCR products. Among the 836 analyzed chromosomes, we found a C282Y allele frequency of 0.0036 and an H63D allele frequency of 0.173. These data could explain the observed rarity of HH in Sardinia. The high allele frequency of H63D and the rarity of HH in Sardinia is suggestive that this mutation is not a major contributor to this disease.     

Hereditary hemochromatosis in Spain

The C282Y mutation of the HFE gene has been reported as the main cause of hereditary hemochromatosis (HH). Another missense mutation (H63D) has also been detected at an increased frequency in a compound heterozygote state with the C282Y mutation in HH patients. However, these two mutations are not present in all of the HH patients, indicating that other mutations in the HFE gene, or in other loci, should exist. The present study reports the frequencies of the C282Y and H63D mutations in 74 Spanish HH patients and the results of the sequencing analysis of the HFE exons, intron-exon boundaries, and 588 bp of the 5' region in 5 patients negative for the C282Y mutation. We have detected a high frequency of the C282Y mutation (85.1%) in Spanish HH patients, indicating that this mutation is the most common defect associated with the disease in Spain. The screening of the HFE regions in our patients without the C282Y mutation has revealed the presence of five polymorphisms. However, no other pathological mutations have been found. Therefore, further efforts to characterize the unscreened part of the HFE gene or other loci should be taken to identify the potential genetic factors causing HH in the C282Y-negative patients.     

The overlapping of local iron overload and HFE mutation in venous leg ulcer pathogenesis

Chronic venous stasis determines red blood cell extravasation and either dermal hemosiderin deposits or iron-laden phagocytes. Several authors have suspected that iron could play a role in the pathogenesis of venous leg ulcers. They hypothesized that local iron overload could generate free radicals or activate a proteolytic hyperactivity on the part of metalloproteinases (MMPs) or else down-regulate tissue inhibitors of MMPs. However, they were unable to explain why iron deposits, visible in the legs of patients with chronic venous disease (CVD), cause lesions in only some individuals, whereas in others they do not. We hypothesized that such individual differences could be genetically determined and investigated the role of the C282Y and H63D mutations of the HFE gene. C282Y mutation significantly increases the risk of ulcer in primary CVD more than six times (OR = 6.69; 1.45-30.8; p = 0.01). Patients carrying the H63D variant have an earlier age of ulcer onset, by almost 10 years (p > 0.004). The increased risk of skin lesion and the early age of onset of the disease in HFE carriers confirm in a clinical setting that intracellular iron deposits of mutated macrophages have less stability than those of the wild type. We hypothesize that the physiologic iron protective mechanisms are affected by the HFE mutations and should be investigated in all diseases characterized by the combination of iron overload and inflammation.     

Genetic hemochromatosis, a Celtic disease: is it now time for population screening?

In populations of northern European ancestry, hereditary hemochromatosis (HH) is tightly linked to mutations within the hemochromatosis gene (HFE gene). Over 93% of Irish HH patients are homozygous for the HFE gene C282Y mutation, providing a reliable diagnostic marker of the disease in this population. However, the prevalence of the C282Y mutation and that of the second HFE gene mutation, H63D, have yet to be determined within the Irish population. The objective of this study was to identify the true prevalence of the genetic form of HH in the Irish population. DNA was extracted from 1002 randomly selected newborn screening cards and analyzed for the C282Y and H63D mutations within the HFE gene. Complete results were obtained from 800 cards. Mutations were identified in 364 (46%) neonates. Eight (1%) neonates were homozygous for C282Y and 8 (1%) were homozygous for H63D. One hundred and fifty-five (19%) neonates were C282Y heterozygous and 226 (28%) were H63D heterozygous. Of these, 33 (4%) carried one copy of both C282Y and H63D mutations, i.e., compound heterozygous. Allele frequencies for C282Y and H63D were 11% and 15%, respectively. The high C282Y allele frequency in the Irish population together with its close linkage to HH indicate that C282Y genotyping is the preferred screening strategy for this disease in Ireland.     

Small-molecule inhibition of siderophore biosynthesis in Mycobacterium tuberculosis and Yersinia pestis

Mycobacterium tuberculosis and Yersinia pestis, the causative agents of tuberculosis and plague, respectively, are pathogens with serious ongoing impact on global public health and potential use as agents of bioterrorism. Both pathogens have iron acquisition systems based on siderophores, secreted iron-chelating compounds with extremely high Fe3+ affinity. Several lines of evidence suggest that siderophores have a critical role in bacterial iron acquisition inside the human host, where the free iron concentration is well below that required for bacterial growth and virulence. Thus, siderophore biosynthesis is an attractive target in the development of new antibiotics to treat tuberculosis and plague. In particular, such drugs, alone or as part of combination therapies, could provide a valuable new line of defense against intractable multiple-drug-resistant infections. Here, we report the design, synthesis and biological evaluation of a mechanism-based inhibitor of domain salicylation enzymes required for siderophore biosynthesis in M. tuberculosis and Y. pestis. This new antibiotic inhibits siderophore biosynthesis and growth of M. tuberculosis and Y. pestis under iron-limiting conditions.     

HLA-H and associated proteins in patients with hemochromatosis.

BACKGROUND: The 845A(C282Y) mutation in the HLA-H gene accounts for most cases of hereditary hemochromatosis in patients who are of European origin. Some lack this mutation, however, and it is not present in Asian patients. Thus, other mutations either in HLA-H or associated proteins may be present in such patients. HLA-H associates with beta-2-microglobulin. Calreticulin associates with class 1 HLA proteins and appears to be identical with mobilferrin, a putative iron transport protein. These two proteins are therefore candidates for mutations in patients with hemochromatosis. MATERIALS AND METHODS: We have sequenced the coding region and parts of introns of the HLA-H gene, the beta-2-microglobulin gene, and the calreticulin (mobilferrin) gene of 10, 7, and 5 hemochromatosis patients, respectively, selecting those who were not homozygous for the 845A(C282Y) mutation. The number of chromosomes at risk studied were 18 for HLA-H, 14 for beta-2-microglobulin and 10 for calreticulin. RESULTS: We detected 3 new intronic polymorphisms in the HLA-H gene, each a point mutation. Some differences from published sequences of beta-2-microglobulin and calreticulin were documented, but these were uniformly present in all samples. CONCLUSIONS: The lack of additional mutations in the HLA-H gene is remarkable, and we speculate that the C282Y mutation may be a gain-of-function change.     

Hemochromatosis: a genetic defect in iron metabolism

Hemochromatosis (HC), the common inherited disorder in iron metabolism, affects at least 1 in 300 Caucasians. The disorder causes inappropriately high iron absorption and accumulation of excess iron in the parenchymal cells of the major organs of the body. The gene responsible for HC has recently been cloned and is termed HFE; two missense mutations have been reported in the gene, both cause amino acid substitutions (H63D and C282Y), but to date only the C282Y mutation has been found to clearly correlate with HC in all affected populations. HFE is highly homologous to genes in the major histocompatibility complex (MHC) class I family; all of these genes encode a heterodimeric protein which is complexed to β₂-microglobulin, a coupling essential for cell surface expression of a functional molecule. The first important step toward establishing the role of HFE in the pathogenesis of HC came with the recent observation that the C282Y mutation disrupts the binding of β₂-microglobulin to the HFE protein and as a result the mutant molecule is not expressed on the cell surface. BioEssays 20: 562–568, 1998. © 1998 John Wiley & Sons Inc.