Mutation analysis in hereditary hemochromatosis

The hemochromatosis 845 G-->A and 187 C-->G mutations: prevalence in non-Caucasian populations

Hemochromatosis, the inherited disorder of iron metabolism, leads, if untreated, to progressive iron overload and premature death. The hemochromatosis gene, HFE, recently has been identified, and characterization of this gene has shown that it contains two mutations that result in amino acid substitutions-cDNA nucleotides 845 G-->A (C282Y) and 187 C-->G (H63D). Although hemochromatosis is common in Caucasians, affecting >=1/300 individuals of northern European origin, it has not been recognized in other populations. The present study used PCR and restriction-enzyme digestion to analyze the frequency of the 845 G-->A and 187 C-->G mutations in HLA-typed samples from non-Caucasian populations, comprising Australian Aboriginal, Chinese, and Pacific Islanders. Results showed that the 845 G-->A mutation was present in these populations (allele frequency 0.32%), and, furthermore, it was always seen in conjunction with HLA haplotypes common in Caucasians, suggesting that 845 G-->A may have been introduced into these populations by Caucasian admixture. 187 C-->G was present at an allele frequency of 2.68% in the two populations analyzed (Australian Aboriginal and Chinese). In the Australian Aboriginal samples, 187 C-->G was found to be associated with HLA haplotypes common in Caucasians, suggesting that it was introduced by recent admixture. In the Chinese samples analyzed, 187 C-->G was present in association with a wide variety of HLA haplotypes, showing this mutation to be widespread and likely to predate the more genetically restricted 845 G-->A mutation.

The effect of HFE mutations on serum ferritin and transferrin saturation in the Jersey population

High frequencies of the haemochromatosis-related HFE C282Y mutation have been reported in North European populations, in which a high proportion of patients with the disease are homozygotes. However, the degree of penetrance of this genotype is unknown. We determined the HFE C282Y and H63D genotypes of 411 consenting volunteer blood donors on Jersey, and the serum ferritin and transferrin saturation levels of 204 of these volunteers. The C282Y allele frequency was found to be 8.3% in 822 chromosomes, indicating a homozygote frequency of 1/145. Consistent with this, four C282Y homozygotes were detected in 411 volunteers. As there are only 18 patients presently receiving treatment for haemochromatosis on Jersey, out of a total population of about 85000, there is a large discrepancy between the number of haemochromatosis patients and the number of C282Y homozygotes in this population. In a preliminary study of 204 consenting volunteers we found a correlation between transferrin saturation and HFE H63D/ C282Y genotype (P=0.017) and between serum ferritin and genotype (P = 0.056). We also observed elevated values of transferrin saturation in the two C282Y homozygotes assayed. These results suggest that a large proportion of the many undetected C282Y homozygotes on Jersey and in similar populations could be in the preclinical stages of haemochromatosis, and warrant investigation. However, there may be a wide variation in the expression of the condition, and a more extensive study of the level of disease penetrance encompassing a large number of hitherto undetected C282Y homozygotes is therefore imperative.

HFE gene knockout produces mouse model of hereditary hemochromatosis

Hereditary hemochromatosis (HH) is a common autosomal recessive disease characterized by increased iron absorption and progressive iron storage that results in damage to major organs in the body. Recently, a candidate gene for HH called HFE encoding a major histocompatibility complex class I-like protein was identified by positional cloning. Nearly 90% of Caucasian HH patients have been found to be homozygous for the same mutation (C282Y) in the HFE gene. To test the hypothesis that the HFE gene is involved in regulation of iron homeostasis, we studied the effects of a targeted disruption of the murine homologue of the HFE gene. The HFE-deficient mice showed profound differences in parameters of iron homeostasis. Even on a standard diet, by 10 weeks of age, fasting transferrin saturation was significantly elevated compared with normal littermates (96 +/- 5% vs. 77 +/- 3%, P < 0.007), and hepatic iron concentration was 8-fold higher than that of wild-type littermates (2,071 +/- 450 vs. 255 +/- 23 microg/g dry wt, P < 0.002). Stainable hepatic iron in the HFE mutant mice was predominantly in hepatocytes in a periportal distribution. Iron concentrations in spleen, heart, and kidney were not significantly different. Erythroid parameters were normal, indicating that the anemia did not contribute to the increased iron storage. This study shows that the HFE protein is involved in the regulation of iron homeostasis and that mutations in this gene are responsible for HH. The knockout mouse model of HH will facilitate investigation into the pathogenesis of increased iron accumulation in HH and provide opportunities to evaluate therapeutic strategies for prevention or correction of iron overload.

HFE codon 63/282 (H63D/C282Y) dimorphism in German patients with genetic hemochromatosis

Genetic hemochromatosis (GH) is closely associated with genes of the major histocompatibility complex (MHC) on chromosome 6. Recently, a candidate gene for GH, with structural similarities to MHC class I genes, designated HLA-H and presently named HFE, has been cloned. The HFE gene is localized telomeric to the MHC and several reports have indicated that the HFE gene is mutated in GH patients. In the present study we have analyzed the relationship of HFE gene variants and disease manifestation in GH patients and family members. Fifty-seven patients with GH, 73 family members and 153 healthy blood donors were studied for the amino acid dimorphism at codon 63 (His63Asp=H63D) and codon 282 (Cys282Tyr= C282Y) of the HFE gene. The codon 63 and 282 dimorphism were defined by PCR amplification of genomic DNA samples and restriction enzyme digestion using RsaI/SnaBI for C282Y and BclI/MboI for H63D. Ferritin, transferrin serum levels and total iron-binding capacity were determined prior to therapeutic intervention. The Tyr-282 substitution occurred in 53 (93%) of patients compared with 8 (5.2%) of controls (OR=169, P<0.0001). Fifty-one (90%) patients were Tyr-282 homozygous. In contrast, the Asp-63 substitution was present in 5 (8.8%) of the patients compared with 34 (22%) of controls (OR=0.39, P=NS) with none of the patients being homozygous. In Tyr-282 homozygous GH patients serum ferritin levels, transferrin saturation, liver iron and liver iron index were elevated significantly compared to Tyr-282-negative patients, whereas no difference was observed between Tyr/Cys-282 heterozygous and Tyr-282-negative patients.

Distribution of transferrin saturation in an Australian population: relevance to the early diagnosis of hemochromatosis

BACKGROUND & AIMS

An elevated transferrin saturation is the earliest phenotypic abnormality in hereditary hemochromatosis. Determination of transferrin saturation remains the most useful noninvasive screening test for affected individuals, but there is debate as to the appropriate screening level. The aims of this study were to estimate the mean transferrin saturation in hemochromatosis heterozygotes and normal individuals and to evaluate potential transferrin saturation screening levels.

METHODS

Statistical mixture modeling was applied to data from a survey of asymptomatic Australians to estimate the mean transferrin saturation in hemochromatosis heterozygotes and normal individuals. To evaluate potential transferrin saturation screening levels, modeling results were compared with data from identified hemochromatosis heterozygotes and homozygotes.

RESULTS

After removal of hemochromatosis homozygotes, two populations of transferrin saturation were identified in asymptomatic Australians (P < 0.01). In men, 88.2% of the truncated sample had a lower mean transferrin saturation of 24.1%, whereas 11.8% had an increased mean transferrin saturation of 37.3%. Similar results were found in women. A transferrin saturation threshold of 45% identified 98% of homozygotes without misidentifying any normal individuals.

CONCLUSIONS

The results confirm that hemochromatosis heterozygotes form a distinct transferrin saturation subpopulation and support the use of transferrin saturation as an inexpensive screening test for hemochromatosis. In practice, a fasting transferrin saturation of > or = 45% identifies virtually all affected homozygous subjects without necessitating further investigation of unaffected normal individuals.

HFE mutations in patients with hereditary haemochromatosis in Sweden

OBJECTIVE

To determine the frequency of mutations (C282Y and H63D) in a newly identified gene HFE in patients with hereditary haemochromatosis (HH) in Sweden.

DESIGN

Molecular genetic analyses of the HFE gene (polymerase chain reaction (PCR) followed by enzyme restriction) were performed in genomic DNA from unrelated patients with a clinical diagnosis of HH and in healthy subjects.

SETTINGS

Patients with HH treated with phlebotomies at Karolinska Hospital and Huddinge Hospital were analyzed.

SUBJECTS

Eighty-seven unrelated patients with HH and 117 healthy controls.

RESULTS

It was found that the HFE C282Y mutation occurs in 94.2% of chromosomes from patients with HH. Eighty patients (92.0%) were homozygous for the C282Y mutation and one was heterozygous. Three patients were heterozygous for both C282Y and H63D mutations. One patient was homozygous and one was heterozygous for the H63D mutation. One patient carried normal alleles. In healthy controls, the C282Y mutation occurred in nine subjects (7.7%), all of which were heterozygous. The H63D mutation was found in 28 control subjects, one of which was homozygous.

CONCLUSIONS

We found that the majority of patients with HH have the C282Y mutation in the HFE gene. The frequency of the H63D mutation was higher in controls than in patients with HH, although in chromosomes at risk the frequency of the H63D mutation was higher in patients.

The hemochromatosis gene product complexes with the transferrin receptor and lowers its affinity for ligand binding

We recently reported the positional cloning of a candidate gene for hereditary hemochromatosis called HFE. The gene product, a member of the major histocompatibility complex class I-like family, was found to have a mutation, Cys-282 --> Tyr (C282Y), in 85% of patient chromosomes. This mutation eliminates the ability of HFE to associate with beta2-microglobulin (beta2m) and prevents cell-surface expression. A second mutation that has no effect on beta2m association, H63D, was found in eight out of nine patients heterozygous for the C282Y mutant. In this report, we demonstrate in cultured 293 cells overexpressing wild-type or mutant HFE proteins that both the wild-type and H63D HFE proteins form stable complexes with the transferrin receptor (TfR). The C282Y mutation nearly completely prevents the association of the mutant HFE protein with the TfR. Studies on cell-associated transferrin at 37 degrees C suggest that the overexpressed wild-type HFE protein decreases the affinity of the TfR for transferrin. The overexpressed H63D protein does not have this effect, providing the first direct evidence for a functional consequence of the H63D mutation. Addition of soluble wild-type HFE/beta2m heterodimers to cultured cells also decreased the apparent affinity of the TfR for its ligand under steady-state conditions, both in 293 cells and in HeLa cells. Furthermore, at 4 degrees C, the added soluble complex of HFE/beta2m inhibited binding of transferrin to HeLa cell TfR in a concentration-dependent manner. Scatchard plots of these data indicate that the added heterodimer substantially reduced the affinity of TfR for transferrin. These results establish a molecular link between HFE and a key protein involved in iron transport, the TfR, and raise the possibility that alterations in this regulatory mechanism may play a role in the pathogenesis of hereditary hemochromatosis.

Increased hepatic iron concentration in nonalcoholic steatohepatitis is associated with increased fibrosis

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH) is a chronic liver disease that occasionally progresses to cirrhosis but usually has a benign course. The aim of this study was to investigate the role of the hemochromatosis mutation Cys282Tyr in development of the mild hepatic iron overload found in some patients with NASH and its association with hepatic damage in these patients.

METHODS

Fifty-one patients with NASH were studied. The presence of the Cys282Tyr mutation was tested in all patients, and the data were analyzed with respect to the histological grade of steatosis, inflammation, Perls' staining, hepatic iron concentration (HIC), and serum iron indices.

RESULTS

Thirty-one percent of patients with NASH were either homozygous or heterozygous for the Cys282Tyr mutation. This mutation was significantly associated with Perls' stain grade (P < 0.005), HIC (P < 0.005), and transferrin saturation percentage (P < 0.005) but not with serum ferritin levels. Linear regression analysis showed that increased hepatic iron (Perls' stain or HIC) had the greatest association with the severity of fibrosis (P < 0.0001).

CONCLUSIONS

The Cys282Tyr mutation is responsible for most of the mild iron overload found in NASH and thus has a significant association with hepatic damage in these patients. Heterozygosity for the hemochromatosis gene mutation therefore cannot always be considered benign.

Iron overload states

Hereditary hemochromatosis is a common disorder of iron metabolism that increasingly is diagnosed and treated prior to the development of cirrhosis or diabetes. The discovery of a candidate gene for hereditary hemochromatosis undoubtedly will result in improved diagnosis of hereditary hemochromatosis and to a better understanding of certain aspects of iron absorption, hepatic iron uptake and release, and whole body iron metabolism. In turn, this enhanced understanding of iron biology can be applied to the observations seen in patients with other hepatic diseases such as chronic viral hepatitis.

Hemochromatosis and iron needs

Although iron is an essential dietary requirement, the amount absorbed by the body is well regulated and depends on body iron stores and on dietary iron availability. There is very little iron excreted under normal conditions. Iron deficiency is a worldwide problem but iron overload, as seen in the inherited disease, hemochromatosis, is a major cause of morbidity in some Caucasian populations. This is a problem particularly where there is an adequate dietary iron intake and especially in males. A mutation has recently been described in an MHC Class l-like gene (HFE) that encodes for a protein (HFE) of 343 amino acids. The molecule contains a signal sequence peptide-binding region, alpha, and alpha(2) domains, and an immunoglobulinlike alpha(3) domain, in addition to a transmembrane region and a small cytoplasmic tail. It is a candidate gene for hemochromatosis. Several possibilities as to the function of this gene and the corresponding protein have been suggested but none has yet been confirmed. The mutation has been detected by several different groups in 80%-100% of subjects with the disease. However, in one study, 18%-20% of patients with the mutation did not exhibit significant iron overload. The discovery of this gene has important implications for both clinical studies and the elucidation of the pathways of iron metabolism.

Genotypic/phenotypic correlations in genetic hemochromatosis: evolution of diagnostic criteria

BACKGROUND & AIMS

The identification of a candidate gene for hereditary hemochromatosis in 69%-100% of patients with hemochromatosis has resulted in a diagnostic genotypic test (C282Y). The aim of this study was to reassess the phenotypic diagnostic criteria for hemochromatosis in patients homozygous for the C282Y mutation of the HFE gene.

METHODS

Transferrin saturation, ferritin, hepatic iron index, and iron removed by venesection were studied in C282Y++ homozygotes and C282Y-- putative homozygotes.

RESULTS

Patients were homozygous for the C282Y mutation in 122 of 128 cases (95%). In C282Y homozygotes, the results were as follows: hepatic iron index, >1.9 in 91.3%; transferrin saturation, >55% in 90%; serum ferritin, >300 microg/L in 96% of men and >200 microg/L in 97% of women; and iron removed, >5 g in 70% of men and 73% of women. There were four homozygotes for C282Y with no biochemical evidence of iron overload.

CONCLUSIONS

The sensitivity of the phenotypic tests in decreasing order was as follows: serum ferritin, hepatic iron index, transferrin saturation, and iron removed by venesection. Although the genetic test is useful in the diagnostic algorithm, this study has shown both iron-loaded patients without the mutation and homozygous patients without iron overload.

Development of a multiplex ARMS test for mutations in the HFE gene associated with hereditary haemochromatosis

Genetic testing for hereditary haemochromatosis is likely to be a significant workload for diagnostic laboratories. The C282Y and H63D mutations in the HFE gene associated with hereditary haemochromatosis have previously been detected using a number of methods including alterations in the restriction digest pattern of polymerase chain reaction (PCR) amplified products. An amplification refractory mutation system (ARMS) has been developed that will simultaneously detect both hereditary haemochromatosis mutations. Comparison of the results obtained from the analysis of 46 samples referred for hereditary haemochromatosis testing showed no discrepancies between ARMS and restriction enzyme digestion. Furthermore, consistent results were obtained by ARMS from both blood and buccal mouthwash samples. The ARMS test is quicker and less expensive in terms of consumables and scientist time than restriction enzyme analysis, and is therefore suited to the routine diagnostic analysis of hereditary haemochromatosis.

High prevalence of the His63Asp HFE mutation in Italian patients with porphyria cutanea tarda

Sporadic porphyria cutanea tarda (PCT) is caused by a reduced activity of uroporphyrinogen decarboxylase (URO-D) in the liver. Mild to moderate iron overload is common in PCT, as iron is one of the factors which trigger the clinical manifestations of the disease through the inactivation of URO-D. A role for genetic hemochromatosis in the development of iron overload in sporadic PCT has been hypothesized in the past. The aim of this work was to investigate whether mutations of HFE, which is a candidate gene for hemochromatosis, play the role of genetic susceptibility factors for PCT in Italian patients, who have a high prevalence of acquired triggering factors, such as hepatitis C virus (HCV) chronic infection and alcohol. We determined HFE genotypes of 68 male patients with PCT. Our data do not confirm an association of PCT with the Cys282Tyr HFE mutation, strongly associated with hemochromatosis in Northern European countries. A second mutation of HFE, His63Asp, however, had a significantly increased frequency as it was present in half of the patients. Surprisingly, the presence of the His63Asp mutation was not related to the iron status of patients, suggesting that a subtle abnormality of iron metabolism induced by this mutation could escape detection by the standard parameters of iron status. In PCT patients with liver disease, the presence of the mutation could contribute to the inactivation of URO-D, either directly or through a synergistic action with other factors that cause liver damage.

Association of the transferrin receptor in human placenta with HFE, the protein defective in hereditary hemochromatosis

Hereditary hemochromatosis (HH) is a common autosomal recessive disease associated with loss of regulation of dietary iron absorption and excessive iron deposition in major organs of the body. Recently, a candidate gene for HH (also called HFE) was identified that encodes a novel MHC class I-like protein. Most patients with HH are homozygous for the same mutation in the HFE gene, resulting in a C282Y change in the HFE protein. Studies in cultured cells show that the C282Y mutation abrogates the binding of the recombinant HFE protein to beta2-microglobulin (beta2M) and disrupts its transport to the cell surface. The HFE protein was shown by immunohistochemistry to be expressed in certain epithelial cells throughout the human alimentary tract and to have a unique localization in the cryptal cells of small intestine, where signals to regulate iron absorption are received from the body. In the studies presented here, we demonstrate by immunohistochemistry that the HFE protein is expressed in human placenta in the apical plasma membrane of the syncytiotrophoblasts, where the transferrin-bound iron is normally transported to the fetus via receptor-mediated endocytosis. Western blot analyses show that the HFE protein is associated with beta2M in placental membranes. Unexpectedly, the transferrin receptor was also found to be associated with the HFE protein/beta2M complex. These studies place the normal HFE protein at the site of contact with the maternal circulation where its association with transferrin receptor raises the possibility that the HFE protein plays some role in determining maternal/fetal iron homeostasis. These findings also raise the question of whether mutations in the HFE gene can disrupt this association and thereby contribute to some forms of neonatal iron overload.

Hereditary hemochromatosis: effects of C282Y and H63D mutations on association with beta2-microglobulin, intracellular processing, and cell surface expression of the HFE protein in COS-7 cells

Hereditary hemochromatosis (HH) is the most common autosomal recessive disorder known in humans. A candidate gene for HH called HFE has recently been cloned that encodes a novel member of the major histocompatibility complex class I family. Most HH patients are homozygous for a Cys-282-->Tyr (C282Y) mutation in HFE gene, which has been shown to disrupt interaction with beta2-microglobulin; a second mutation, His-63-->Asp (H63D), is enriched in HH patients who are heterozygous for C282Y mutation. The aims of this study were to determine the effects of the C282Y and H63D mutations on the cellular trafficking and degradation of the HFE protein in transfected COS-7 cells. The results indicate that, while the wild-type and H63D HFE proteins associate with beta2-microglobulin and are expressed on the cell surface of COS-7 cells, these capabilities are lost by the C282Y HFE protein. We present biochemical and immunofluorescence data that indicate that the C282Y mutant protein: (i) is retained in the endoplasmic reticulum and middle Golgi compartment, (ii) fails to undergo late Golgi processing, and (iii) is subject to accelerated degradation. The block in intracellular transport, accelerated turnover, and failure of the C282Y protein to be presented normally on the cell surface provide a possible basis for impaired function of this mutant protein in HH.

Predominance of the HLA-H Cys282Tyr mutation in Austrian patients with genetic haemochromatosis

BACKGROUND/AIMS

Genetic haemochromatosis is the most common autosomal recessive disorder in Northern European populations. A major histocompatibility complex class I-like gene, HLA-H, has been proposed to be responsible for genetic haemochromatosis. The prevalence of HLA-H gene mutations 282(TGC; Cys/TAC; Tyr) and 63(CAT; His/GAT; Asp) was determined in patients of Austrian origin.

METHODS

DNA extracted from the blood of 40 Austrian patients and 271 controls was used to amplify HLA-H gene fragments by the polymerase chain reaction method. The base changes responsible for mutations Cys282Tyr and His63Asp alter recognition sites for restriction enzymes SnaB I and Bcl I, respectively. Digestion products were separated by agarose gel electrophoresis and visualised by ethidium bromide staining.

RESULTS

Thirty-one (77.5%) genetic haemochromatosis patients were homozygous for mutation Cys282Tyr and three compound heterozygous for mutations Cys282Tyr and His63Asp. One patient was homozygous for mutation His63Asp but normal for mutation Cys282Tyr. Four patients were normal at both genetic loci and one patient was heterozygous for mutation His63Asp. One control subject homozygous for mutation Cys282Tyr was found on investigation to fulfill diagnostic criteria for haemochromatosis. Eight control subjects homozygous for mutation His63Asp showed no biochemical or clinical evidence of haemochromatosis indicating that this variant is not directly responsible for haemochromatosis. Absence of the Cys282Tyr mutation in six genetic haemochromatosis patients with distinct haplotypes indicates mutations within the HLA-H gene or at alternative genetic loci are the cause of genetic haemochromatosis in these patients.

CONCLUSIONS

The HLA-H Cys282Tyr defect is likely to play a key role in the pathogenesis of haemochromatosis in most patients. Predominance of a single HLA-H gene mutation in haemochromatosis allows presymptomatic screening by genotypic analysis.

Homozygosity for the predominant Cys282Tyr mutation and absence of disease expression in hereditary haemochromatosis

A candidate gene for hereditary haemochromatosis, HLA-H, has recently been presented. Two missense mutations in the HLA-H gene sequence are predicted to account for nearly 90% of all cases of the disease. The aim of this study was to correlate the presence of these missense mutations with the expressivity of the disease, as assessed by standard biochemical evaluation of serum iron parameters. Detection of the known mutations in haemochromatosis, Cys282Tyr and His63Asp, was undertaken in a large pedigree showing variable expression of the disease in successive generations. In three sibs with overt disease (one male, two female, aged 50 to 53 years), homozygosity for the predominant G to A transition (Cys282Tyr) in HLA-H was detected. However, homozygosity for this mutation was also detected in an asymptomatic male sib, aged 50, harbouring an identical genotype. The finding of an asymptomatic homozygous Cys282Tyr subject, haplo-identical to affected sibs, indicates that clinical expression of symptomatic disease is variable, even in middle aged Cys282Tyr homozygotes. This has profound implications for the future use of genetic screening for haemochromatosis.

Compound heterozygotes for hemochromatosis gene mutations: may they help to understand the pathophysiology of the disease?

Two mutations have been described on the gene considered to be responsible for genetic hemochromatosis, the HLA-H or HFE gene. The C282Y mutation is a disease-causing mutation in most cases of genetic hemochromatosis, but involvment of the H63D substitution in the pathogenesis of the disease is unclear. Compound heterozygotes for both substitutions could help to determine whether or not the second mutation is a worsening factor when associate in trans with the C282Y mutant. We found twenty nine compound heterozygotes during DNA analysis of patients referred to our laboratory for the screening of those mutations. Clinical and biological data were obtainable for 23 of them. Compound heterozygotes could be divided into two groups: subjects with or without iron overload. Five (22%) individuals had normal ferritin levels, whereas 18 had elevated ferritin concentrations (78%). Among those 18 patients, 7 (30% of the total) had clinical and biological criteria of genetic hemochromatosis. Eleven had iron overload without all the criteria of genetic hemochromatosis. Such a high proportion of genetic hemochromatosis is not found in heterozygotes for the C282Y mutation alone neither in our series nor in the literature. Compound heterozygotes for the C282Y and the H63D mutations may have a higher risk of iron overload or genetic hemochromatosis than single heterozygotes for the C282Y mutation. We propose a schematic theoretical representation that could explain this fact at the protein level. Further fundamental studies on the protein, and clinical follow up of compound heterozygotes could help to ascertain this hypothesis.

New diallelic markers in the HLA region of chromosome 6

Diallelic polymorphisms have been identified in the HLA-H gene and the ZNF192 gene located about 2 megabases centromeric to HLA-H. The three polymorphic sites in HLA-H together with the two hemochromatosis mutations in this gene give rise to 8 different haplotypes. The three polymorphic sites in ZNF192 give rise to 4 different haplotypes. The haplotypes in HLA-H are in complete linkage disequilibrium with the two common mutations in that gene, 845A (C282Y) and 187G (H63D). The 845A mutation is in weak linkage disequilibrium with the ZNF192 polymorphisms and the 187G mutation appears to be in equilibrium with this polymorphism. The 187G mutation therefore appears to be the older of the two HLA-H mutations.

Impact of HLA-H mutations on iron stores in healthy elderly men and women

The DNA of 287 healthy white elderly volunteers in the New Mexico Aging Process Study, between 63 and 91 years of age, was examined for mutations of the HLA-H gene at nt 845 and nt 187. None were found to be homozygous for the 845A mutation and there were no gender differences in the percentage of the various mutations. The frequency of the 845A mutation was 0.061 resulting in a carrier frequency of 12.2%. The frequency of the 187G mutation was 0.136 resulting in a carrier frequency of 19.9% for a single mutation; 2.4% were compound heterozygous, 834A/187G and 2.4% were homozygous for the 187G mutation. After excluding 5 men and 4 women with microcytic or macrocytic anemia, mean percent transferrin saturation (PSAT) and iron stores, as estimated from serum ferritin concentrations, were calculated for each mutation. Estimated iron stores were normally distributed (range approximately 50 to 1,550 mg) with men (n=111) having significantly higher mean estimated iron stores than women (n=167), 826 +/- 318 and 753 +/- 287 mg, respectively. More men, 15 of 28, (54%) with estimated iron stores in the upper quartile, >/= 1,050 mg, had a HLA-H mutation compared to 25 of 83 (30%) who had a mutation and whose estimated iron stores were < ,050 mg, P<0.05. Seven were heterozygous for the 845A mutation with mean estimated iron stores of 1,300 +/- 127 mg, 7 were heterozygous for the 187G mutation with mean estimated iron stores of 1,439 mg. Similar differences were not noted in women. Even though the potential role of the 187G mutation in the phenotypic expression of HH is less certain than the 845A mutation, the increase in PSAT seen in men with the 187G mutation and the equal distribution of 845A and 187G mutations seen with iron stores >/= 1,050 mg lends support for the involvement of the 187G mutation, or a linked mutation, in iron metabolism. We concluded that men having either a single chromosomal 845A and/or 187G mutation results in higher PSAT's and estimated iron stores than if no HLA-H mutation were present.

Correlation between genotype and phenotype in hereditary hemochromatosis: analysis of 61 cases

This report assesses the degree of iron overload in a cohort of patients in relationship to the presence or absence of the recently described 845 G-->A (C282Y) and 187 C-->G (H63D) mutations in the HFE (HLA-H) gene. Sixty-one patients with hereditary hemochromatosis diagnosed either with liver biopsy or on clinical grounds were included in this analysis. Forty-one patients were homozygous for C282Y, the genotype considered to be characteristic of hereditary hemochromatosis. At the time of this analysis, 37 of these 41 patients had achieved a state of iron depletion and mobilizable iron was calculated: 19 had less than 4 grams. Twenty-five of these 41 patients had liver biopsies; 4 of these patients had a hepatic iron index less than 1.9. Of the 4 patients with a normal hepatic iron index, 3 had a quantitative hepatic iron of greater than 50 micromol/g dry weight, and one had an inadequate biopsy sample. These findings support our suspicion that individuals may have hereditary hemochromatosis and homozygous C282Y despite relatively low body iron stores. Five patients were compound heterozygotes for C282Y and H63D. Four of these patients underwent liver biopsy; two had a hepatic iron index greater than 1.9. a third patient had a hepatic iron index of 1.3 but a quantitative hepatic iron of 90.6 micromol/g dry weight. All patients were phlebotomized to a state of iron depletion and only one of these patients had a mobilizable iron greater than 4 grams. Three patients were homozygous for H63D; these patients had either a hepatic iron index >1.9 or greater than 4 grams of mobilizable iron. Patients with homozygous H63D and significant iron overload are not well described. Seven patients were heterozygous for either C282Y or H63D; 4 had significant iron overload but three did not. Five patients had no HFE mutations; one of these patients unequivocally has iron overload with a hepatic iron index of 4.4 We conclude that: (1) Identification of HFE mutations will be clinically useful in identifying patients with hereditary hemochromatosis, (2) Patient genotyping will help confirm a diagnosis of hereditary hemochromatosis in some patients with relatively low body iron stores, (3) Significant iron loading can occur in the absence of homozygous C282Y, adding to the evidence that genes other than HFE may be involved in iron loading, and (4) Homozygous H63D can be associated with significant iron overload.

Molecular biological xxxmethods in diagnosis and treatment of liver diseases

Molecular biology is making a tremendous impact on the diagnosis and treatment of liver diseases. Methods such as the polymerase chain reaction are changing the way physicians diagnose and monitor patients with viral hepatitis. Assays based on recombinant protein antigens allow for detection of specific autoantibodies in diseases such as primary biliary cirrhosis. The diagnosis of inherited metabolic diseases, such as hemochromatosis and Wilson disease, is being revolutionized by discovery of the defective genes involved and the development of methods to rapidly sequence DNA and identify mutations. Treatments and preventive measures are now possible with use of drugs and vaccines produced by recombinant DNA technology. Gene therapy and nucleic acid-based therapeutics are also realistic future treatment options for individuals with liver diseases.

A high prevalence of HLA-H 845A mutations in hemochromatosis patients and the normal population in eastern England

We have examined normal individuals and all the patients currently being treated for hemochromatosis at the Norfolk and Norwich hospital for mutations in the HLA-H gene. We found a gene frequency in 200 normal subjects for teh 845A (C282Y) allele of 0.085, corresponding to a carrier frequency of 17% which is among the highest reported anywhere in the world. The frequency for the less penetrant 187G (H63D) allele was 0.16 among 58 of the normal subjects, which corresponds to a carrier frequency of 32%. All 18 hemochromatosis patients were homozygous for the 845A allele which is not significantly different from other reports in our subset of 12 unrelated patients. These findings present a snapshot of a relatively stable population containing a predicted 3,500 individuals homozygous for the 845A allele but not diagnosed with hemochromatosis. This population will be an excellent model for studies on the penetrance of the 845A homozygous genotype and population screening.

The hemochromatosis founder mutation in HLA-H disrupts beta2-microglobulin interaction and cell surface expression

We recently reported the positional cloning of a candidate gene for hereditary hemochromatosis (HH), called HLA-H, which is a novel member of the major histocompatibility complex class I family. A mutation in this gene, cysteine 282 --> tyrosine (C282Y), was found to be present in 83% of HH patient DNAs, while a second variant, histidine 63 --> aspartate (H63D), was enriched in patients heterozygous for C282Y. The functional relevance of either mutation has not been described. Co-immunoprecipitation studies of cell lysates from human embryonic kidney cells transfected with wild-type or mutant HLA-H cDNA demonstrate that wild-type HLA-H binds beta2-microglobulin and that the C282Y mutation, but not the H63D mutation, completely abrogates this interaction. Immunofluorescence labeling and subcellular fractionations demonstrate that while the wild-type and H63D HLA-H proteins are expressed on the cell surface, the C282Y mutant protein is localized exclusively intracellularly. This report describes the first functional significance of the C282Y mutation by suggesting that an abnormality in protein trafficking and/or cell-surface expression of HLA-H leads to HH disease.

Global prevalence of putative haemochromatosis mutations

Haemochromatosis is a genetic disease associated with progressive iron overload, and is common among populations of northern European origin. HLA-H is a recently reported candidate gene for this condition. Two mutations have been identified, a substitution of cysteine for tyrosine at amino acid 282 (C282Y, nucleotide 845) and of histidine for aspartate at amino acid 63 (H63D, nucleotide 187). Over 90% of UK haemochromatosis patients are homozygous for the C282Y mutation. We have examined 5956 chromosomes (2978 people) for the presence of HLA-H C282Y and H63D by PCR followed by restriction enzyme analysis. We have found world wide allele frequencies of 1.9% for C282Y and 8.1% for H63D. The highest frequencies were 10% for C282Y in 90 Irish chromosomes and 30.4% for H63D in 56 Basque chromosomes. C282Y was most frequent in northern European populations and absent from 1042 African chromosomes, 484 Asian chromosomes, and 644 Australasian chromosomes. The distribution of the C282Y mutation coincides with that of populations in which haemochromatosis has been reported and is consistent with the theory of a north European origin for the mutation. The H63D polymorphism is more widely distributed and its connection with haemochromatosis remains unclear.

Increased frequency of the haemochromatosis Cys282Tyr mutation in sporadic porphyria cutanea tarda

BACKGROUND

Sporadic porphyria cutanea tarda is a skin disease associated with hepatic siderosis. Depletion of iron stores by phlebotomy is curative. The role of haemochromatosis genes in determining susceptibility to this disorder is controversial. We have examined the frequency in sporadic porphyria cutanea tarda of mutations (Cys282Tyr, His63Asp) in a novel MHC class-I-like gene, one of which (Cys282Tyr) is believed to cause haemochromatosis.

METHODS

41 patients with sporadic porphyria cutanea tarda, in whom the frequency of microsatellite alleles that define the ancestral haemochromatosis haplotype had previously been determined, and 101 healthy blood donors were studied for the presence of the Cys282Tyr and His63Asp mutations. We used restriction-enzyme digestion of PCR-amplified genomic DNA.

FINDINGS

The Cys282Tyr mutation occurred in 18 (44%) of patients compared with 11 (11%) of controls (relative risk 6.2, 95% CI 2.6-14.5, p = 0.00003). Seven (17%) patients, aged 48-79 years, were homozygotes. In 12 patients, the Cys282Tyr mutation was associated with markers of the HLA-A3-containing ancestral haemochromatosis haplotype. Ages at presentation were the same for those with or without the Cys282Tyr mutation. There was no difference in the frequency of the His63Asp mutation.

INTERPRETATION

Inheritance of one or more haemochromatosis genes is an important susceptibility factor for sporadic porphyria cutanea tarda. Some homozygotes for the Cys282Tyr mutation present late in life with porphyria cutanea tarda, indicating that not all homozygotes present clinically with haemochromatosis. The relation between this genotype and disease needs further investigation.

Genetic and clinical description of hemochromatosis probands and heterozygotes: evidence that multiple genes linked to the major histocompatibility complex are responsible for hemochromatosis

We evaluated Alabama hemochromatosis probands (n = 74) and normal control subjects (n = 142) for expression of the hemochromatosis-associated mutations nt 845G-->A (845A; Cys282Tyr) and nt 187C-->G (His63Asp) in a gene linked to the major histocompatibility complex (MHC). We also tabulated parameters of iron metabolism and iron overload in probands and in obligate heterozygote family members of homozygous Cys282Tyr probands. Among probands, 59.4% were Cys282Tyr homozygotes and 20.3% were heterozygotes; 20.3% did not express this mutation. In normal control subjects, 14.7% were heterozygous for the Cys282Tyr mutation; one normal control subject was homozygous for the Cys282Tyr mutation. None (0 of 44) of our Cys282Tyr-homozygous hemochromatosis probands had the His63Asp mutation. Of the Cys282Tyr-heterozygous and -negative probands, the His63Asp mutation occurred in 26.7% (4/15) and 53.3% (8/15), respectively. In normal control subjects, 23.2% were heterozygous for the His63Asp mutation; 2.8% were homozygous. Induction phlebotomy requirements and other manifestations of iron overload were significantly greater in Cys282Tyr homozygotes than among other probands. Cys282Tyr-heterozygous probands had significantly higher values of serum iron parameters than did obligate Cys282Tyr heterozygotes whose values were, on the average, normal. Co-expression of HLA-A3, HLA-B7, and D6S105(8) was significantly more frequent in all subgroups of probands stratified by Cys282Tyr expression than in normal control subjects. These results demonstrate that the severity of iron overload in hemochromatosis is affected significantly by genetic factors. Further, our findings support the hypothesis that one or more MHC-linked genes other than that corresponding to the Cys282Tyr and His63Asp mutations contributes to increased iron absorption and iron overload in hemochromatosis probands.

HLA-H mutations in the Ashkenazi Jewish population

Hereditary hemochromatosis is a common disorder in people of European origin. The HLA-H gene has been found to have two mutations that apparently cause hemochromatosis. The principal mutation, 845G-->A (C282Y), is believed to have arisen relatively recently in the Celtic population. To determine the incidence of this mutation and the other hemochromatosis-associated mutation, 187C-->G (H63D), among Ashkenazi Jews, a people who are believed to have arrived in Europe in about the 8th Century A.D., we have examined the DNA from 381 unrelated Jewish subjects and 206 non-Jewish white controls. The gene frequency for the 845G-->A mutation among Jewish subjects was only 0.013 compared with a frequency of 0.070 among controls, a difference that is significant at the 0.00001 level. The phenotypically milder nt 187C-->G mutation had a frequency of 0.155 in the non-Jewish population and 0.097 in the Jewish population, a difference that was also statistically significant at the <0.01 level.