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.     

Linkage to chromosome 1q in Greek families with juvenile hemochromatosis.

Hereditary hemochromatosis (HH) is a genetically heterogeneous disease. The HFE gene resides on chromosome 6 and its mutations account for the majority of HH cases in populations of northern European ancestry. Recently, two new types of hemochromatosis have been identified: Juvenile hemochromatosis (JH or HFE2), which maps to chromosome 1q21, and an adult form defined as HFE 3, which results from mutations of the TFR 2 gene, located at 7q22. We have performed a linkage study in five unrelated families of Greek origin with non-HFE hemochromatosis. Linkage at the chromosome 1q21 JH locus was detected in affected members with the use of polymorphic markers. Comparison of haplotypes between Greek and Italian JH patients revealed the presence of a common haplotype. However, the fact that many other haplotypes carrying the JH defect were observed in the two populations indicates that the respective mutations may have occurred in different genetic backgrounds. We suggest that hemochromatosis patients without HFE mutations should be evaluated for other possible types of hemochromatosis since hemochromatosis type 3 (HFE3) has a clinical appearance similar to HFE 1, and JH may have a late onset in some cases.     

Variable phenotypic presentation of iron overload in H63D homozygotes: are genetic modifiers the cause?

BACKGROUND: First considered as a polymorphism of the HFE gene, the H63D mutation is now widely recognised as a haemochromatosis associated allele. But few H63D homozygotes with clinical manifestations of hereditary haemochromatosis (HH) have been reported. Concurrently, an increasing number of genes have been shown to interact with HFE in iron metabolism. AIMS: To describe the clinical expression of iron overload (IO) associated with H63D homozygosity, and search for potential genetic modifiers (within the HFE or other genes) that could explain the variability of the phenotypes. PATIENTS AND METHODS: We retrospectively analysed the clinical phenotype of 56 H63D homozygotes referred for a personal or family history of IO. For each subject we examined intragenic HFE haplotypes and transferrin receptor (TfR) gene polymorphisms and searched for the Y250X mutation on the TFR2 gene. Additionally, we sequenced the HFE gene of H63D homozygotes with HH. RESULTS: Fifty of 56 subjects had biological and/or clinical abnormalities of iron metabolism. Up to two thirds of patients (n=34) had no acquired cause of IO. Among these, 12 had a phenotypic diagnosis of HH. In the iron loaded group there was a strong prevalence of male patients. No correlation was found between the potential genetic modifiers and phenotypes. No additional mutation of HFE was identified. CONCLUSION: The variable phenotypes associated with H63D homozygosity do not appear to be linked to other HFE mutations, to the TFR2 Y250X mutation, or to HFE or TfR gene intragenic polymorphisms. The exact role of H63D homozygosity in IO and HH needs to be further investigated in unselected populations.     

Transferrin receptor-2 gene and non-C282Y homozygous patients with hemochromatosis

More than 80% of the patients affected by hereditary hemochromatosis, a common inherited iron disorder, are homozygotes for the 845G --> A (C282Y) mutation of the HFE gene. However, depending on the population, 10-20% of hereditary hemochromatosis can be linked either to other HFE genotypes, particularly the compound heterozygous state for C282Y and the 187 C --> G (H63D) mutation, or to mutations of new other genes. Recently, Camaschella et al. (Nat. Genet. 25, 14-15, 2000) identified a stop mutation (exon 6 nt 750 C --> T, Y250X) on the transferrin receptor-2 (TFR2) gene in two unrelated Sicilian families with hereditary hemochromatosis. The TFR2 gene is a transferrin receptor gene homologue that seems to be involved in iron metabolism. Moreover, one of the patients described by Camaschella et al. was a H63D homozygote. H63D homozygosity can be associated with various phenotypes from asymptomatic subjects to patients with a typical form of hereditary hemochromatosis. Thus, the Y250X mutation could be the molecular defect responsible for hereditary hemochromatosis in subjects with atypical HFE genotypes. We have searched for the Y250X mutation in 63 unrelated French subjects. Forty-three had a diagnosis of hereditary hemochromatosis based on classical criteria. This group included 12 H63D homozygotes, 3 C282Y heterozygotes, and 3 patients with none of the two most prevalent HFE mutants. These 18 patients had no other HFE sequence change and were subsequently subjected to DNA sequencing of the 15 last exons and flanking sequences of the TFR2 gene. The 25 remaining hereditary hemochromatosis patients who were tested for the Y250X mutant were compound heterozygotes for the C282Y and H63D mutations. Finally, we also tested for this TFR2 mutation 20 H63D homozygotes with milder manifestations of iron overload and no acquired cause of iron overload. None of the 63 tested subjects had the Y250X mutation. Concurrently, none of the 18 hereditary hemochromatosis patients who had their TFR2 gene sequenced had any deleterious mutation. Thus, TFR2 mutations are not responsible for hemochromatosis in non-C282Y homozygous patients of our area.     

Targeted mutagenesis of the murine transferrin receptor-2 gene produces hemochromatosis

Hereditary hemochromatosis (HH) is a common genetic disorder characterized by excess absorption of dietary iron and progressive iron deposition in several tissues, particularly liver. The vast majority of individuals with HH are homozygous for mutations in the HFE gene. Recently a second transferrin receptor (TFR2) was discovered, and a previously uncharacterized type of hemochromatosis (HH type 3) was identified in humans carrying mutations in the TFR2 gene. To characterize the role for TFR2 in iron homeostasis, we generated mice in which a premature stop codon (Y245X) was introduced by targeted mutagenesis in the murine Tfr2 coding sequence. This mutation is orthologous to the Y250X mutation identified in some patients with HH type 3. The homozygous Tfr2(Y245X) mutant mice showed profound abnormalities in parameters of iron homeostasis. Even on a standard diet, hepatic iron concentration was several-fold higher in the homozygous Tfr2(Y245X) mutant mice than in wild-type littermates by 4 weeks of age. The iron deposition in the mutant mice was predominantly hepatocellular and periportal. The mean splenic iron concentration in the homozygous Tfr2(Y245X) mutant mice was significantly less than that observed in the wild-type mice. The homozygous Tfr2(Y245X) mutant mice also demonstrated elevated transferrin saturations. There were no significant differences in parameters of erythrocyte production including hemoglobin levels, hematocrits, erythrocyte indices, and reticulocyte counts. Heterozygous Tfr2(Y245X) mice did not differ in any measured parameter from wild-type mice. This study confirms the important role for TFR2 in iron homeostasis and provides a tool for investigating the excess iron absorption and abnormal iron distribution in iron-overload disorders.     

Hemochromatosis gene (HFE) mutations in South East Asia: a potential for iron overload

Hereditary hemochromatosis (HH) is an autosomal recessive disease caused by mutations in the HFE gene that mainly affects populations of European descent. Recently a novel mutation (IVS5+1 G-->A) has been described in a Vietnamese patient with HH that was not detected in a European control population. We have developed a novel method to screen for this mutation based on restriction enzyme digestion of a PCR product using a modified forward primer. We have screened 314 Vietnamese people from several ethnic groups and 154 people from Thailand for this mutation and have detected two heterozygotes in the Vietnamese subjects (allele frequency 0.003). Analysis of these heterozygotes indicates that the mutation is on the same haplotype as that found in the original proband. Screening for the widely distributed HFE mutation, H63D, gave an allele frequency of 0.049 in the Vietnamese subjects and 0.032 in the subjects from Thailand. This is the first report of H63D allele frequencies in these populations. We suggest that the presence of the IVS5+1 G-->A and H63D mutations should be considered when investigating iron overload in Vietnamese patients and those of mixed origin as co-inheritance of both mutations is likely to be a risk factor for iron overload.     

HFE and non-HFE hemochromatosis

Hereditary hemochromatosis (HH) is a disorder of iron metabolism in which enhanced absorption of dietary iron causes increased iron accumulation in the liver, heart, and pancreas. Most individuals with HH are homozygous for a point mutation in the HFE gene, leading to a C282Y substitution in the HFE protein. The function of HFE protein is unknown, but the available evidence suggests that it acts in association with beta2-microglobulin and transferrin receptor 1 to regulate iron uptake from plasma transferrin by the duodenum, the proposed mechanism by which body iron levels are sensed. The identification of HFE has established the foundation for a better understanding of the molecular and cellular biology of iron homeostasis and its altered regulation in HH. Additionally, the ability to accurately diagnose iron overload disorders has been strengthened, family screening has been improved, and evaluation of patients with other forms of liver disease complicated by moderate-to-severe iron overload is now possible. However, the role of HFE testing in generalized population screening for HH is still controversial. Recently, other forms of HH have been described that are not related to HFE but are due to mutations in genes coding iron transport proteins.     

Transferrin receptor mutation analysis in hereditary hemochromatosis patients

The Cys282-->Tyr mutation in the HFE gene is carried by the majority of hereditary hemochromatosis patient chromosomes, yet some patients do not seem to harbor any mutation in this gene. This suggests a possibility that these patients may have a mutation in other genes in the same pathway as HFE. We analyzed the cDNA sequences of transferrin receptor (TFR), which was recently shown to interact with HFE, in twenty-one hereditary hemochromatosis patients including sixteen individuals who did not carry a Cys282-->Tyr mutation. A nucleotide substitution (424A-->G), which resulted in the Ser142-->Gly amino acid substitution, was the only amino acid polymorphism detected in the open reading frame of the TFR gene in these patients. This amino acid substitution was a rather common polymorphism in the general population (49%) and its frequency did not significantly differ in the hereditary hemochromatosis (HH) patients regardless of the HFE genotype. Thus, amino acid changes in the TFR gene do not appear to play a role in HH even when the patients do not have a HFE mutation. However, this study does not rule out the possibility of the involvement of mutations in non-coding regions.     

Iron overload and prolonged ingestion of iron supplements: clinical features and mutation analysis of hemochromatosis-associated genes in four cases

We evaluated and treated four white adults (one man, three women) who had iron overload associated with daily ingestion of iron supplements for 7, 15, 35, and 61 years, respectively. We performed HFE mutation analysis to detect C282Y, H63D, and S65C in each patient; in two patients, HFE exons were sequenced. In two patients, direct sequencing was performed to detect coding region mutations of TFR2, HAMP, FPN1, HJV, and ALAS2. Patients 1-4 ingested 153, 547, 1,341, and 4,898 g of inorganic iron as supplements. Patient 1 had hemochromatosis, HFE C282Y homozygosity, and beta-thalassemia minor. Patient 2 had spherocytosis and no HFE coding region mutations. Patient 3 had no anemia, a normal HFE genotype, and no coding region mutations in HAMP, FPN1, HJV, or ALAS2; she was heterozygous for the TFR2 coding region mutation V583I (nt 1,747 G-->A, exon 15). Patient 4 had no anemia and no coding region mutations in HFE, TFR2, HAMP, FPN1, HJV, or ALAS2. Iron removed by phlebotomy was 32.4, 10.4, 15.2, and 4.0 g, respectively. There was a positive correlation of log(10) serum ferritin and the quantity of iron removed by phlebotomy (P = 0.0371). Estimated absorption of iron from supplements in patients 1-4 was 20.9%, 1.9%, 1.1%, and 0.08%. We conclude that the clinical phenotypes and hemochromatosis genotypes of adults who develop iron overload after ingesting iron supplements over long periods are heterogeneous. Therapeutic phlebotomy is feasible and effective, and would prevent complications of iron overload.     

Severe iron overload with a novel aminolevulinate synthase mutation and hepatitis C infection. A case report

A 55 year old man with a history of chronic hepatitis C infection was found to have severe hemochromatosis: hepatic cirrhosis, cardiomyopathy, arrhythmia, hypogonadism, diabetes and bronzed skin color. After 50 phlebotomies, he underwent a combined heart and liver transplant. Genetic analyses identified a novel mutation in the iron responsive element of the ALAS2 gene. No mutations were found in other genes associated with adult or juvenile hemochromatosis including HFE, transferrin receptor-2 (TFR2), ferroportin (SLC40A1), hepcidin (HAMP) and hemojuvelin (HJV). We suggest that the ALAS2 mutation together with chronic hepatitis C infection may have caused the severe iron overload phenotype.     

Iron overload disease: recent findings

Iron overload diseases are due to a progressive increase in total body iron stores that leads to deposition of iron in parenchymal organs and to subsequent damage to these organs. The commonest inherited form of iron overload is hereditary hemochromatosis (HH), an autosomal recessive disorder affecting the white population. Although in the western world and in northern Europe the majority of cases of HH are associated with an HFE gene mutation (C282Y and H63D), there are families with a familial iron overload disorder in whom neither the C282Y nor the H63D mutations were found. Recently, other forms of HH that are not related to HFE, but are due to mutations in genes coding iron transport proteins (ferroportin-1, TfR2, hepcidin) have been described. The clinical presentation of the disorder is highly variable, depending on the severity of iron overload. In fact, the inappropriate absorption and deposition of dietary iron may result in the development of hepatic and non-hepatic end-organ injury, leading to liver cirrhosis, hepatocellular carcinoma, diabetes, arthritis, skin pigmentation and cardiac diseases. HH and its sequelae are preventable with an early diagnosis and treatment. Patients with evidence of iron overload, a family history of HH or other risk factors should be screened by genotype testing for the HFE mutation. Nowadays, HH is recognized as being a complex genetic disease with probable significant environmental and genetic modifying factors, such as hepatitis C virus infection and alcohol abuse, and it has been shown that HFE mutations represent an independent risk factor for fibrosis and cirrhosis in chronic hepatitis C.     

Unique genetic profile of hereditary hemochromatosis in Russians: high frequency of C282Y mutation in population, but not in patients

Hereditary hemochromatosis (HH) is a common cause of primary iron overload induced by genetic impairment of iron metabolism. More than 80% of HH patients in populations of European origin are homozygotes for a single mutation C282Y, or compound heterozygotes for C282Y and H63D mutations in the HFE gene. However, in the majority of Asian, African, Australasian, and Amerindian populations, frequencies of C282Y are close to zero. Data on the prevalence of HFE mutations in Russian population and in Russian patients with HH are very limited. In this work, we determined frequencies of C282Y and H63D in ethnical Russians living in the Central European region of Russia. Furthermore, we tested whether homozygocity for C282Y is the major cause of HH in Russians. We found that, in the Russian population, the frequency of C282Y mutation in the HFE gene is relatively high and corresponds to mean European levels. However, in contrast to the majority of European populations, homozygocity for C282Y is found only in a small proportion (5%) of patients with biochemical and clinical signs of HH. These data suggest that either the penetrance of C282Y in Russia is lower than in Western countries, or that a more frequent non-HFE dependent mechanism of primary iron overload dominates in Russian population.     

3个携带HJV E3D变异的遗传性血色病家系临床表型分析

目的了解3个携带HJV E3D变异的遗传性血色病家系基因变异及临床表型特点。方法 3个遗传性血色病家系中的先证者均完成了病史采集、铁指标、肝功能、腹部核磁检查、肝活检,排除铁过载的继发性原因,临床考虑为遗传性血色病。先证者及其一级亲属分别检测目前已知的遗传性血色病相关的5个基因(HFE、HAMP、HJV、TFR2和SLC40A1)。结果 3个携带HJV E3D变异的遗传性血色病先证者均具有明确的铁过载表现,家系1和家系2中各有1个成员具有铁过载。2例携带HJV E3D变异的先证者还同时携带其他类型血色病基因变异。结论 HJV基因E3D变异可能为我国遗传性血色病的热点变异,可能需要同时伴随其他位点变异才会出现表型,且男性、年龄增加更容易出现血色病表型。     

Inherited HFE-unrelated hemochromatosis in Italian families

Hemochromatosis (HH) is usually caused by the homozygous state for C282Y mutation in the HFE gene. A minority of iron loaded patients have no mutations in this gene. An infrequent subset shows an early-onset aggressive disorder, denoted juvenile hemochromatosis (JH), which has no linkage to 6p. In this report we describe six patients from three unrelated Italian families, four men and two women, aged 21 to 44 with the typical hemochromatosis phenotype, who are homozygous for the wild type allele at the HFE gene. In two families the disorder is unlinked to 6p; in one family some features of the juvenile form are seen, but linkage to 6p is not excluded. Our results point to genetic forms of hemochromatosis not associated with HFE and raise the problem of whether non-HFE hemochromatosis in Italy is related to the "juvenile" form. They also emphasize the importance of phenotypic as well as genetic diagnosis of HH.     

Pathogenesis of hereditary hemochromatosis: genetics and beyond

Hereditary hemochromatosis (HH) comprises several inherited disorders of iron homeostasis characterized by increased gastrointestinal iron absorption and secondary tissue iron deposition. The most common form of this disorder is called HFE-related HH and is caused by homozygosity for the C282Y mutation in the HFE gene. Recently, other less common hereditary forms of iron overload have been recognized and are designated as non-HFE-related HH. The identification and cloning of HFE and other genes involved in iron metabolism has greatly expanded our understanding of many aspects of HH. The introduction of a commercially available genetic test for the C282Y and H63D mutations of HFE allows presymptomatic diagnosis, and adds precision to studies of the population genetics of HFE-related HH. It is now recognized that a substantial proportion of C282Y homozygotes does not develop clinically significant iron overload, and modifier genes may be involved in this phenomenon. Mouse models of HH and cell culture studies have increased our understanding of the normal physiology and pathophysiology of iron homeostasis. Future investigations will refine our knowledge of the mechanisms of action of HFE protein, the phenotypic variability observed in persons homozygous for the C282Y mutation, and the mechanisms responsible for non-HFE-related HH.     

Frequency of the HFE gene mutations in five Italian populations

Genetic hemochromatosis is an autosomal recessive disorder characterized by iron overload and a variety of clinical manifestations such as liver cirrhosis and arthropathy. It is the most common genetic disease of northern European populations. The principal gene responsible for hereditary hemochromatosis, designated HFE, is located on chromosome 6 in the HLA region. The single point mutation 845A, changing cysteine at position 282 to tyrosine (C282Y), in this gene has been identified as the main genetic basis of hereditary hemochromatosis. Two other mutations, 187G, a histidine to aspartate at amino acid 63 (H63D), and 193T, a serine to cysteine at amino acid 65 (S65C), appear to be associated with milder forms of hereditary hemochromatosis. There is a high prevalence of the C282Y mutation in northern European populations, whereas in those of the Mediterranean basin the prevalence seems low and almost absent in Far East countries. This mutation seems usually to occur on the ancestral haplotype 7.1. Accordingly, a Celtic origin of this mutation has been suggested. The aim of this study was to determine the frequency of HFE gene mutations in five geographic regions in Italy. Samples were tested for C282Y, H63D, and S65C mutations of the HFE gene according to methods of each laboratory and the results were standardized with the exchange of typed samples between the different laboratories. In addition, C282Y-positive DNA samples were typed for D6S105 allele 8 and HLA-A3 by ARMS-PCR. We have found that the allele frequency of the C282Y mutation decreases from northeast Italy (Friuli, 6%) to northwest Italy (Piedmont, 4.8%) and to central Italy (Emilia-Romagna, 1.7%). However, this mutation is lacking in the two regions of the Mediterranean basin's center (Sicily and Sardinia). Accordingly, a significant difference in the frequency of the mutation was observed between these Italian regions (P = 0.07 x 10(-3)). In contrast, no difference was observed in allele frequency of H63D in the five Italian regions. Finally, as regards the S65C mutation a very low frequency was observed in Friuli, Emilia-Romagna, and Sardinia, whereas in Sicily and Piedmont we have not found this mutation. In conclusion, these data are consistent with the hypothesis that the C282Y mutation occurred in Caucasian populations of Celtic origin, whereas the H63D mutation is more ancient as demonstrated by the ubiquitous distribution.     

Hepcidin is decreased in TFR2 hemochromatosis

The hepatic peptide hepcidin is the key regulator of iron metabolism in mammals. Recent evidence indicates that certain forms of hereditary hemochromatosis are caused by hepcidin deficiency. Juvenile hemochromatosis is associated with hepcidin or hemojuvelin mutations, and these patients have low or absent urinary hepcidin. Patients with C282Y HFE hemochromatosis also have inappropriately low hepcidin levels for the degree of iron loading. The relationship between the hemochromatosis due to transferrin receptor 2 (TFR2) mutations and hepcidin was unknown. We measured urinary hepcidin levels in 10 patients homozygous for TFR2 mutations, all with increased transferrin saturation. Urinary hepcidin was low or undetectable in 8 of 10 cases irrespective of the previous phlebotomy treatments. The only 2 cases with normal hepcidin values had concomitant inflammatory conditions. Our data indicate that TFR2 is a modulator of hepcidin production in response to iron.