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

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.

Ancestral association between HLA and HFE H63D and C282Y gene mutations from northwest Colombia

A significant association between HFE gene mutations and the HLA-A*03-B*07 and HLA-A*29-B*44 haplotypes has been reported in the Spanish population. It has been proposed that these mutations are probably connected with Celtic and North African ancestry, respectively. We aimed to find the possible ancestral association between HLA alleles and haplotypes associated with the HFE gene (C282Y and H63D) mutations in 214 subjects from Antioquia, Colombia. These were 18 individuals with presumed hereditary hemochromatosis (“HH”) and 196 controls. The HLA-B*07 allele was in linkage disequilibrium (LD) with C282Y, while HLA-A*23, A*29, HLA-B*44, and B*49 were in LD with H63D. Altogether, our results show that, although the H63D mutation is more common in the Antioquia population, it is not associated with any particular HLA haplotype, whereas the C282Y mutation is associated with HLA-A*03-B*07, this supporting a northern Spaniard ancestry.

Genetic hemochromatosis in Italian patients with porphyria cutanea tarda: possible explanation for iron overload

BACKGROUND/AIMS

Mild to moderate iron overload is found in most patients with porphyria cutanea tarda. This study aimed to evaluate whether iron overload in patients with porphyria cutanea tarda is related to the presence of a coexistent genetic hemochromatosis gene.

METHODS

A cohort study of 94 Italian patients with porphyria cutanea tarda (90 men and 4 women) and 20 relatives of five patients with iron overload were studied. Diagnosis of iron overload was assessed by transferrin saturation, serum ferritin and iron removed by phlebotomy to reach depletion. HLA typing by microlymphocytotoxicity test and duodenal ferritin analysis by immunohistochemistry were performed in a smaller number of patients. The chi square test was used to compare means and prevalences.

RESULTS

Iron overload was present in 62% of the patients. HLA-A3 prevalence was significantly higher (p < 0.01) in subjects with iron overload than in those without. A lack of duodenal ferritin was observed in 14/18 patients with and in 6/12 without iron overload. Family studies showed the presence of iron overload but not of porphyria cutanea tarda in HLA identical or semi-identical relatives of the patients.

CONCLUSIONS

Italian patients with porphyria cutanea tarda and iron overload appear to have one or even two genes for genetic hemochromatosis.

Practice guideline development task force of the College of American Pathologists. Hereditary hemochromatosis

Hereditary hemochromatosis is an autosomal recessive disorder, the gene for which occurs in approximately 10% of Americans, most of whom are unaffected heterozygotes. Approximately 5/1000 white Americans are homozygous and at risk of developing severe and potentially lethal hemochromatosis. The disorder affects numerous organ systems, but the most common symptoms are fatigue, palpitations, joint pains, and impotence; the most common signs are those that relate to hypothalamic, cardiac, hepatic or pancreatic dysfunction, including poor cold tolerance, impotence in males, amenorrhea in females, cardiac arrhythmias, dyspnea, edema, hepatosplenomegaly, spider telangiectases, ascites, deformity, swelling or limitation of motion of joints, weight loss, hyperpigmentation. Characteristic abnormalities of laboratory tests include elevated serum iron concentration, high transferrin saturation, elevated serum ferritin concentration, elevated serum transaminases, hyperglycemia and low values for thyroid-stimulating hormone (TSH) and gonadotropins. Death may be the result of cardiac arrhythmia, congestive heart failure, liver failure or liver cancer. Since many of these complications cannot be reversed once they have developed, early diagnosis and treatment are essential. In view of the high prevalence in the American population (prevalence varies with ethnic background), the low cost of diagnosis and treatment, the efficacy of treatment if begun early, and, on the other hand, high costs and low success rate of late diagnosis and treatment, systematic screening for hemochromatosis is warranted for all persons over the age of 20 years. The initial screening should be by measurement of serum iron concentration and transferrin saturation. The practice guideline provides a diagnostic algorithm for cases in which the serum transferrin saturation is 60% or greater. It also provides guidelines for clinical management.

Genetics of haemochromatosis

This review is largely concerned with the frequency of genetic haemochromatosis (GH) and attempts to find the gene responsible. Studies of disease prevalence are reviewed along with the association of GH with other inherited disorders. The high prevalence of the disorder found in a number of surveys of populations of European origin along with the relatively few patients presenting with the clinical features of the advanced disease remains a paradox. The tight linkage between HLA-A and GH has been known since 1975 but it has not been possible to distinguish between a telomeric or centromeric location for the gene (HFE) relative to HLA-A. The recent explosion in detailed knowledge of the genetic map of the region telomeric of HLA-A on chromosome 6p has made it possible to examine new genetic markers. The very strong association between GH and D6S105-8 suggests a gene location telomeric to HLA-A. The lack of a precise location, and uncertainty about either the primary biochemical abnormality or the tissues involved has delayed the identification of the gene but expressed genes in the region around HLA-A are now being isolated and tested.

Alleles at D6S265 and D6S105 define a haemochromatosis-specific genotype

Hereditary haemochromatosis is an HLA-linked, recessive disorder with HLA-A3 a strong marker for the gene. We have identified molecular markers for two serologically indistinguishable subtypes of HLA-A3 and examined these in 42 patients with haemochromatosis. The common HLA-A3 subtype HLA-A*0301 (highly correlated with allele 1 of D6S265) was a slightly better marker for haemochromatosis (RR = 10.1, Chi2 = 30) than the serologically recognized A3 antigen (RR = 9.1; Chi2 = 27.3). Allele 8 of the more telomeric locus D6S105 was also strongly associated with haemochromatosis (RR = 13.0; Chi2 = 21.1) but alleles at this locus were not in strong linkage disequilibrium with HLA-A alleles in the control subjects. The co-occurrence of D6S265-1 and D6S105-8 alleles yielded a higher risk (RR = 16.9; Chi2 = 44). Homozygosity for the haplotype including these markers was specific for haemochromatosis, i.e. did not occur in 376 healthy subjects but was observed in 21.4% of patients. These results refine the HLA-A3 association with haemochromatosis, suggest that the haemochromatosis gene is located on the telomeric side of HLA-A and define a possible haplotype in which the first mutation may have occurred.

Anonymous markers located on chromosome 6 in the HLA-A class I region: allelic distribution in genetic haemochromatosis

Two yeast artificial chromosomes of the HLA class I region were subcloned. Four of the subclones studied displayed restriction polymorphisms that corresponded to six bi-allelic series. Allelic distribution of the anonymous markers was then studied by comparing a control population with a group of patients with familial haemochromatosis. Only one marker presents an unequivocal association with the haemochromatosis gene and is 100 kb centromeric to HLA-A. This association however is not as strong as with HLA-A3. The results suggest two possible locations for the haemochromatosis gene: less than 100 kb centromeric to the HLA-A locus, or on the telomeric side.

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.