HLA as a marker of the hemochromatosis gene in Sweden

HFE gene: Structure, function, mutations, and associated iron abnormalities

The hemochromatosis gene HFE was discovered in 1996, more than a century after clinical and pathologic manifestations of hemochromatosis were reported. Linked to the major histocompatibility complex (MHC) on chromosome 6p, HFE encodes the MHC class I-like protein HFE that binds beta-2 microglobulin. HFE influences iron absorption by modulating the expression of hepcidin, the main controller of iron metabolism. Common HFE mutations account for ~90% of hemochromatosis phenotypes in whites of western European descent. We review HFE mapping and cloning, structure, promoters and controllers, and coding region mutations, HFE protein structure, cell and tissue expression and function, mouse Hfe knockouts and knockins, and HFE mutations in other mammals with iron overload. We describe the pertinence of HFE and HFE to mechanisms of iron homeostasis, the origin and fixation of HFE polymorphisms in European and other populations, and the genetic and biochemical basis of HFE hemochromatosis and iron overload.

Was the C282Y mutation an Irish Gaelic mutation that the Vikings helped disseminate? HLA haplotype observations of hemochromatosis from the west coast of Sweden

The HLA-related hemochromatosis mutation C282Y is thought to have originated in Ireland in a person with HLA-A3-B14 and was spread by Vikings. Irish people with two HLA-A3 alleles had a high risk of hemochromatosis. In this study, from west Sweden, we wanted to test these hypotheses.

METHODS

HFE mutations in controls, bone marrow donors with HLA-A3/A3 and patients with hemochromatosis. HLA haplotypes, extended haplotype analysis and pedigree studies.

RESULTS

The allelic C282Y frequency 0.04, (CI 0.01-0.07) was lower (P < 0.001) in Sweden than in Ireland 0.10 (CI 0.08-0.11), and Swedish bone marrow donors with HLA-A3/A3 (n = 77) had a low risk of hemochromatosis. HLA haplotypes available from 239/262 (91.5%) proband patients homozygous for C282Y showed a dominance of A3-B7 and A3-B14 both in linkage disequilibrium with controls (P < 0.001). Pedigree studies extended into the 17th century supported a local founder effect of A3-B14 in the county of Bohuslän. The A3-B14 haplotype may well be the original and A3-B7 the result of centromeric recombinations. The haplotype diversity and recombination events were not different from a Celtic series. These findings do not support the hypothesis of the C282Y mutation being of an Irish Celtic origin.

CONCLUSIONS

The C282Y frequency shows a west to east decline from Ireland through the north of Europe. Vikings may have been involved in the spread of C282Y, but the mutation is probably older and may have been spread in Europe by earlier seafarers.

HLA haplotype map of river valley populations with hemochromatosis traced through five centuries in Central Sweden

BACKGROUND

The hemochromatosis mutation, C282Y of the HFE gene, seems to have originated from a single event which once occurred in a person living in the north west of Europe carrying human leukocyte antigen (HLA)-A3-B7. In descendants of this ancestor also other haplotypes appear probably caused by local recombinations and founder effects. The background of these associations is unknown. Isolated river valley populations may be fruitful for the mapping of genetic disorders such as hemochromatosis. In this study, we try to test this hypothesis in a study from central Sweden where the haplotyope A1-B8 was common.

METHODS

HLA haplotypes and HFE mutations were studied in hemochromatosis patients with present or past parental origin in a sparsely populated (1/km(2)) rural district (n = 8366 in the year of 2005), in central Sweden. Pedigrees were constructed from the Swedish church book registry. Extended haplotypes were studied to evaluate origin of recombinations.

RESULTS

There were 87 original probands, 36 females and 51 males identified during 30 yr, of whom 86% carried C282Y/C282Y and 14% C282Y/H63D. Of 32 different HLA haplotypes A1-B8 was the most common (34%), followed by A3-B7 (16%), both in strong linkage disequilibrium with controls, (P < 0.001). Twenty-nine different families with A1-B8 had a common founder origin 15 generations ago in small bottleneck populations of the late 16th century. A second A1-B8 founder born 1655 was of Norwegian origin. Most of the A3 carriers (n = 26) had a common founder origin 16 generations ago in an even smaller nearby river valley. A fourth founder family carrying HLA-A2 seems to have originated from a recombination along the descendant lines from the A3 ancestor supported by extended haplotype studies. A1-haplotypes with alleles at the B locus different from B8 had a similar recombination origin as HLA-A2 alleles and a common founder origin 11 generations ago. The intergenerational time interval averaged 35.5 +/- 7.9 yr in men and 31.9 +/- 5.9 in females.

CONCLUSIONS

River valley populations may contain HLA haplotypes reflecting their demographic history. This study has demonstrated that the resistance against recombinations between HLA-A and HFE make HLA haplotypes excellent markers for population movements. Founder effects and genetic drift from bottleneck populations (surviving the plague?) may explain the commonness of the mutation in central Scandinavia. The intergenerational time difference >30 yr was greater than expected and means that the age of the original mutation may be underestimated.

HLA haplotypes associated with hemochromatosis mutations in the Spanish population

BACKGROUND

The present study is an analysis of the frequencies of HLA-A and -B antigens and HLA haplotypes in two groups of individuals homozygous for the two main HFE mutations (C282Y and H63D) and a group heterozygous for the S65C mutation.

METHODS

The study population includes: 1123 healthy individuals, 100 homozygous for the C282Y mutation, 138 homozygous for the H63D mutation and 17 heterozygous for the S65C mutation. HFE and HLA alleles were detected using DNA-based and microlymphocytotoxicity techniques respectively.

RESULTS

An expected significant association between C282Y and the HLA-A3/B7 haplotype was found, but other HLA haplotypes carrying the -A3 antigen were found: HLA-A3/B62 and HLA-A3/B44. Also, a significant association between H63D mutation and HLA-A29/B44 haplotype was found, and again other HLA haplotypes carrying the HLA-A29 antigen were also found: HLA-A29/B14 and HLA-A29/B62. In addition, the S65C mutation seems to be associated with a HLA haplotype carrying the HLA-A26 antigen.

CONCLUSION

These findings clearly suggest that HLA-A3/B7 and HLA-A29/B44 are the ancestral haplotypes from which the C282Y and H63D mutations originated, respectively. The frequencies of these mutations in different populations, their geographical distribution, and the degree of the statistical association to the ancestral haplotypes, suggest that the H63D mutation must have occurred earlier than the C282Y mutation.

Frequency of HFE mutations among Turkish blood donors according to transferrin saturation: genotype screening for hereditary hemochromatosis among voluntary blood donors in Turkey

BACKGROUND AND GOALS

The C282Y and H63D mutations of HFE gene are associated with hereditary hemochromatosis (HH), the most common autosomal recessive disorder in European population. This is the first Turkish population study of, the prevalence of these mutations.

STUDY

2677 healthy volunteer blood donors were screened by means of transferrin saturation (TS) with the cutoff value of 45. As study group, 86 donors with a TS 45 or higher and as control group 57 donors with TS less than 45 were tested for these mutations, ferritin, and alanin aminotransferase (ALT) levels.

RESULTS

The mean age of donors were 33+/-9 and 94.1% of them were male. The number of donors with TS 45 or higher was 265 (9.9%). C282Y mutation was not detected. The frequency of H63D mutation in the study, control and general groups were 27.32%, 21.05%, and 24.83%, respectively. As a result, the H63D mutation was present in 60 out of 143 participants in whom 49 were heterozygote (frequency of heterozygote allele 49/286 = 17.13%), 11 were homozygote (frequency of homozygote allele 22/286 = 7.69%). Serum ALT and TS were not affected from the type of H63D mutation. There was no difference in ferritin levels according to type of H63D mutations among 143 blood donors.

CONCLUSION

This study revealed the absence of C282Y mutation in our population. Although the frequency of H63D heterozygosity seems to be higher than the other population, the genetic screening for the HFE gene mutation is inadequate and the phenotypic screening with TS and ferritin seems to be preferable in Turkish population.

HLA-A and -B alleles and haplotypes in hemochromatosis probands with HFE C282Y homozygosity in central Alabama

BACKGROUND

We wanted to quantify HLA-A and -B allele and haplotype frequencies in Alabama hemochromatosis probands with HFE C282Y homozygosity and controls, and to compare results to those in other populations.

METHODS

Alleles were detected using DNA-based typing (probands) and microlymphocytotoxicity (controls).

RESULTS

Alleles were determined in 139 probands (1,321 controls) and haplotypes in 118 probands (605 controls). In probands, A*03 positivity was 0.7482 (0.2739 controls; p = or < 0.0001; odds ratio (OR) 7.9); positivity for B*07, B*14, and B*56 was also increased. In probands, haplotypes A*03-B*07 and A*03-B*14 were more frequent (p < 0.0001, respectively; OR = 12.3 and 11.1, respectively). The haplotypes A*01-B*60, A*02-B*39, A*02-B*62, A*03-B*13, A*03-B*15, A*03-B*27, A*03-B*35, A*03-B*44, A*03-B*47, and A*03-B*57 were also significantly more frequent in probands. 37.3% of probands were HLA-haploidentical with other proband(s).

CONCLUSIONS

A*03 and A*03-B*07 frequencies are increased in Alabama probands, as in other hemochromatosis cohorts. Increased absolute frequencies of A*03-B*35 have been reported only in the present Alabama probands and in hemochromatosis patients in Italy. Increased absolute frequencies of A*01-B*60, A*02-B*39, A*02-B*62, A*03-B*13, A*03-B*15, A*03-B*27, A*03-B*44, A*03-B*47, and A*03-B*57 in hemochromatosis cohorts have not been reported previously.

Inheritance of two HFE mutations in African Americans: cases with hemochromatosis phenotypes and estimates of hemochromatosis phenotype frequency

PURPOSE

Two unrelated African Americans had hemochromatosis phenotypes and genotypes. We sought to identify origins of their HFE mutations and estimate frequencies of similar cases.

METHODS

HFE and HLA genotyping were performed in index cases and family members. HFE genotypes of 1,373 African American controls in five regions were tabulated.

RESULTS

Index cases had C282Y/C282Y and C282Y/H63D, respectively; each corresponding Ch6p was likely of Caucasian origin. In controls, frequencies of hemochromatosis-associated genotypes were as follows: C282Y/C282Y, 0.00011; C282Y/H63D, 0.00067; and H63D/H63D, 0.00101.

CONCLUSIONS

Penetrance-adjusted estimates indicate that approximately 9 African Americans per 100,000 have a hemochromatosis phenotype and two common HFE mutations. Hemochromatosis-associated genotype frequencies varied 11.7-fold across regions.

Haemochromatosis in the new millennium

Hereditary haemochromatosis (HHC) is a common inherited disorder of iron metabolism characterised by progressive iron loading of parenchymal cells of the liver, pancreas, heart and other organs ultimately leading to cirrhosis and organ failure. Despite HLA studies which localised the defective gene to the short arm of chromosome 6, the haemochromatosis gene remained elusive until 1996, when the gene was identified by a massive positional cloning effort. The haemochromatosis gene (HFE) encodes a novel nonclassical MHC class-1-like molecule. Two missense mutations have been identified in patients with HHC, a G to A at nucleotide 845, resulting in a substitution of tyrosine for cysteine at amino acid 282 (referred to as the C282Y mutation) and a C to G at nucleotide 187, resulting in a substitution of aspartate for histidine at amino acid 63 (H63D). An average of 85-90% of patients with typical clinical features of HHC are homozygous for the C282Y mutation. H63D is not associated with the same degree of iron loading as C282Y. Clinical expression is variable depending on environmental (dietary) iron, physiological and pathological blood loss and as yet unidentified modifying genetic factors. One recent Australian study indicates that only about 50% of homozygous subjects are fully expressing and symptomatic and that about 30% show no clinical or biochemical expression. Genetic tests for identifying mutations in the HFE gene provide precise means for diagnosis, family testing and population screening and have led to re-evaluation of the indications for liver biopsy in this disease. At the present time, however, the most practical and cost-effective method of screening is for phenotypic expression by transferrin saturation or unsaturated iron binding capacity measurement. In the future, population screening by genotype should be feasible once the relevant technical, legal and ethical issues are resolved.

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.

Primary iron overload in African Americans

PURPOSE

To report African Americans with primary iron overload diagnosed during life and to study iron stores in African Americans undergoing autopsy.

PATIENTS AND METHODS

We summarized information for 4 African-American patients diagnosed during life with iron overload not explainable by alcohol, blood transfusions, or ineffective erythropoiesis. We reviewed liver specimens and hospital records of 326 unselected adult African Americans who were autopsied, assessing Prussian blue-stained sections for hepatocellular iron and measuring iron quantitatively in specimens that stained positively. We calculated the hepatic iron index (the hepatic iron concentration in mumol/g dry weight divided by the age in years). In autopsy subjects we corrected the index to account for iron administered by blood transfusion (the adjusted hepatic iron index). The hepatic iron index is useful for distinguishing primary iron overload from the moderate siderosis that may accompany alcoholic liver disease. The normal index is < or = 1.0. An index > or = 1.7 cannot be explained by alcohol effects and an index > or = 1.9 indicates the magnitude of iron-loading found in Caucasian homozygous HLA-linked hemochromatosis.

RESULTS

The 4 living patients, all males and 27 to 50 years of age, had elevated body iron burdens and one or more of the following: hepatomegaly, cirrhosis, cardiomyopathy, diabetes mellitus, and impotence. Hepatic iron indices were 2.3, 11.5, and 20.2 in the 3 whose liver iron concentrations were measured. Among the autopsy subjects, 4 (1.2%), 2 men and 2 women aged 50 to 63 years, had adjusted hepatic iron indices > or = 1.9 (range 1.9 to 5.6).

CONCLUSIONS

Primary iron overload occurs in African Americans. Further studies are needed to define prevalence, pathophysiology and clinical consequences. Clinicians should look for this condition.

Iron deficiency and iron overload in Swedish male adolescents

OBJECTIVES

The present study was undertaken to confirm or reject recent findings indicating a high prevalence of iron deficiency in Swedish male adolescents; a second aim was to study the prevalence of genetic iron overload.

DESIGN

The diagnostic criteria were: anaemia: Hb < 130 g L-1 (a): iron deficiency: serum ferritin (SF) < 12 micrograms L-1 + transferrin saturation (TS) < 16% (b): iron deficiency anaemia a + b. Iron overload: SF (90th percentile) + TS (90th percentile) in repeat tests.

SETTING

Central Sweden.

SUBJECTS

A total 3975 men aged 18 years studied on enrollment into military service.

RESULTS

Serum ferritin averaged 36.8 micrograms L-1. Anaemia was present in 0.5%, iron deficiency anaemia in 0.17% and iron deficiency in 0.4%. If iron deficiency is defined as SF < 16 micrograms L-1, as was recently suggested, the prevalence would be 2.8%. Such a cut-off value would include 73% normal people (false positives). Iron overload had the same prevalence as iron deficiency, 0.4%.

CONCLUSIONS

Iron stores, as measured by serum ferritin, are small in young men studied at the end of their growth spurt. However, iron deficiency is rare. Therefore, the present study has not been able to confirm the high prevalence of iron deficiency recently reported. A prevalence of genetic haemochromatosis of 0.4%, confirms earlier findings and would mean that 12.6% of the population are heterozygotic carriers of the iron-loading genes. These findings give no support for a proposed, more effective iron-enrichment of food. It is not needed and can be harmful.

Etiologies, consequences, and treatment of iron overload

From a global perspective, severe systemic iron overload occurs predominantly in individuals affected by geographically specific genetic mutations that permit the daily absorption from the diet of more iron than is physiologically needed. Two main types of hereditary iron overload are well recognized: (1) HLA-linked hemochromatosis in populations derived from Europe and (2) iron overload complicating thalassaemia major and intermedia syndromes in Southeast Asia, the Middle East, and the Mediterranean. Another very common form of iron overload occurs in Africa and is clearly related to high dietary iron content; recent evidence suggests that a genetic predisposition may also contribute to the pathogenesis. Patients with iron overload may develop multiorgan system toxicity; aggressive therapy with phlebotomy or iron chelation to remove excess iron from the body prevents organ damage and prolongs life.

An HLA study in 74 Danish haemochromatosis patients and in 21 of their families

HLA-A and -B alleles in 74 Danish patients and 21 homozygous relatives with idiopathic haemochromatosis (IH) were compared with those in a sample of 1719 chromosomes from healthy Danish control subjects. The following alleles occurred with higher frequencies in IH compared to controls: A3: 53.6% vs. 15.1% (Pc less than 0.001); B7: 33.1% vs. 15.6% (Pc less than 0.001); B14: 6.9% vs. 3.0% (Pc greater than 0.05); B38: 5% vs. 0.9% (Pc greater than 0.05); B47: 4.0% vs. 0.4% (Pc greater than 0.05). Pedigree analyses disclosed 19 different haplotypes in IH subjects, compared to 286 haplotypes in controls. The following haplotypes occurred with higher frequency in IH compared to controls: A3,B5: 10.3% vs. 0.3% (Pc less than 0.001); A3,B7: 25.6% vs. 6.6% (Pc = 0.001); A3,B14: 3.4% vs. 0.6% (Pc greater than 0.05); A3,B47: 6.9% vs. 0.2% (Pc greater than 0.05). The major IH marker HLA-A3 was found in 56% of the haplotypes. The patterns of HLA-alleles associated with IH in Denmark show similarities to those in Central Europe, Australia, USA and Canada, being A3,B7 dominated and those in Central Sweden, England and Ireland, being A3,B14 dominated.

HLA antigens in Hungarian patients with idiopathic haemochromatosis

Thirteen unrelated patients with idiopathic haemochromatosis (eight men, five women) were studied. The diagnosis was based on clinical, biological, and histochemical findings. HLA typing was performed in all 13 and in all of their available first degree relatives (n = 31). HLA A3 was present in nine of 13 probands (69.2% compared with 18.8% in the group of 53 healthy blood donors and 22.4% in a selected Hungarian population (n = 1910). HLA B7 was present in five of 13 probands (38.4% compared with 11.3% and 14.6%). An A3B7 antigen association was found in five of 13 patients. The A3B7 haplotype was found in three, A2B12 and A2B38 haplotypes were found twice in 10 genotyped probands. Pedigree studies showed that there was one unaffected homozygote, 24 heterozygotes, and six non-carriers. Extended family and population studies are necessary to establish the prevalence of the gene in Hungary and an association with haplotypes other than A3B7.

Hemochromatosis

This article discusses the pathophysiology and clinical manifestations of idiopathic and secondary hemochromatosis. Pedigree studies documenting the hereditary evidence for hemochromatosis are discussed. Current theories for the molecular mechanisms that result in iron overload are presented. Diagnostic strategies for assessing hemochromatosis and therapeutic modalities are reviewed.

HLA typing in 67 Italian patients with idiopathic hemochromatosis and their relatives

The frequency of HLA A3 and B7 antigens was significantly higher in 67 unrelated patients with idiopathic hemochromatosis (IH) than in 700 controls (62.7% vs 22.5%, p less than 10(-8) and 26.9% vs 9.3%, p less than 10(-3), respectively). A3 B7, A3 B35 and A3 B5 were significantly more frequent in 72 haplotypes linked to IH gene than in 278 control haplotypes. The prevalence of B35 and A3 B35 was significantly higher in IH patients from North-Eastern Italy than from other regions (60% vs 21%, p less than .05 and 54.5% vs 8.2%, p less than 0.0001, respectively). All 15 siblings HLA identical to the respective proband were homozygous for IH with variable expression of the disease, whereas minor abnormalities of iron-related indexes were present in 23% of heterozygous relatives. Homozygous-heterozygous mating probably occurred in three of 40 families, accounting for the overt disease in three offspring and in one HLA semi-identical sibling; however, in this last case the possibility of a recombination event cannot be excluded.

Is all genetic (hereditary) hemochromatosis HLA-associated

1. GH in Australia is significantly associated with the HLA-A3 antigen, which is the only independent marker for the disease (B7 in linkage disequilibrium with A3). 2. The haplotype A3, B7, DR2 is the only one with increased prevalence in this disease, presumably due to its being the predominant haplotype among early immigrants. 3. Exceptions to HLA association in GH are rare and can be explained by: (1) incorrect HLA serotyping, (2) chromosomal recombination, or (3) rare homozygous-homozygous mating. 4. These data are consistent with GH being due to a mutant gene or genes in close proximity to HLA-A. 5. Heavy alcohol ingestion does not lead to expression of hemochromatosis in heterozygous subjects.

HLA determinants in 70 Danish patients with idiopathic haemochromatosis

HLA-A, -B, -C and -DR antigens were determined in 70 unrelated Danish patients with idiopathic haemochromatosis. The frequencies of HLA-A and -B antigens compared to 1967 normal control subjects and the relative risk values (RR) were: A3, 80.0% vs. 26.9% (P less than 0.0001), RR = 10.9; B7, 60.0% vs. 26.8% (P less than 0.0001), RR = 4.1; B14, 10.0% vs. 4.5% (P = 0.03), RR = 2.4; B47, 4.3% vs. 0.5% (P less than 0.0001), RR = 9.7; A3, B7, 51.4% vs. 12.2% (P less than 0.0001), RR = 7.6; A3, B14, 10.0% vs. 1.4% (P less than 0.0001), RR = 7.7; A3, B47, 4.3% vs. 0.5% (P less than 0.0001), RR = 9.7. Six patients (8.6%) possessed none of these four typical antigens. There was no association between disease and the frequencies of HLA-C and HLA-DR antigens. The pattern of HLA-antigens associated with haemochromatosis in Denmark shows similarities to those reported both in Germany, being HLA-A3, B7 dominated, and in Brittany, Great Britain and Central Sweden, being HLA-A3, B14 dominated.