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Comprised mainly of monocytes and tissue macrophages, the reticuloendothelial system (RES) plays two major roles in iron metabolism: it recycles iron from senescent red blood cells and it serves as a large storage depot for excess iron. Although iron recycling by the RES represents the largest pathway of iron efflux in the body, the precise mechanisms involved have remained elusive. However, studies characterizing the function and regulation of Nramp1, DMT1, HFE, FPN1, CD163, and hepcidin are rapidly expanding our knowledge of the molecular aspects of RE iron handling. This review summarizes fundamental physiological and biochemical aspects of iron metabolism in the RES and focuses on how recent studies have advanced our understanding of these areas. Also discussed are novel insights into the molecular mechanisms contributing to the abnormal RE iron metabolism characteristic of hereditary hemochromatosis and the anemia of chronic disease.
Crit Rev Biochem Mol Biol 2003
PMID:Iron metabolism in the reticuloendothelial system. 1264 43

The HFE gene, a member of the class-I transplantation antigen gene family, is responsible for hereditary hemochromatosis, one of the most common inherited diseases in individuals of European descent. Patients exhibit predictable changes in iron homeostasis, including elevations in both transferrin saturation and serum ferritin levels. A subset of patients progress to overt clinical sequelae, resulting from iron overload. A hallmark of the disease is increased absorption of iron by the intestine. Although the HFE protein appears to modulate the function of the transferrin receptor in vitro, its precise role in vivo remains obscure. With multiple cell types involved in iron metabolism, the function of HFE is likely to be complex.
Trends Mol Med 2003 Mar
PMID:The enigmatic role of the hemochromatosis protein (HFE) in iron absorption. 1265 33

Iron overload was found to be the major cause of disability in Chinese HbH disease patients although they were not on regular blood transfusion. The transferrin receptor 2 (TFR2) and hereditary hemochromatosis (HFE) genes were examined to see if inheritance of these gene defects may be a possible cause of iron overload in 45 HbH patients. A novel intronic (IVS6 (+6) T-->A) mutation of the TFR2 gene was identified in one patient, and six others were found to carry a known missense mutation (exon 5, I238M) that was also present in one normal control subject. One HbH patient and one normal control carried the H63D mutation of the HFE gene. Since only eight out of 45 iron-overloaded HbH patients carry a defect in the TFR2 or HFE gene in the heterozygote state and their iron loading status was comparable to the matched controls without such defects, it would appear that the accumulation of excess iron in HbH disease is more likely a result of increase dietary absorption secondary to ineffective erythropoiesis.
Blood Cells Mol Dis
PMID:Can defects in transferrin receptor 2 and hereditary hemochromatosis genes account for iron overload in HbH disease? 1266 93

We undertook a three-year screening program for mutations of the HFE gene among 41,000 subjects attending the Kaiser Permanente Health Appraisal Center in San Diego, California. Our results show that the C282Y and H63D mutations of the HFE gene associated with hemochromatosis have measurable and consistent effects on iron indicators and are associated with liver disorders, but have no measurable effect on other iron overload-related symptoms and life-expectancy. The very low clinical penetrance of the HFE mutations must be taken into account in calculating cost/benefit and risk/benefit ratios in screening for hemochromatosis.
Blood Cells Mol Dis
PMID:Penetrance of hemochromatosis. 1267 56

A number of factors, including increased iron stores and alcohol consumption, are known to be associated with the development of porphyria cutanea tarda (PCT) in susceptible individuals. Recent reports have described a significant association between inheritance of the C282Y and H63D mutations in the HFE gene, associated with genetic hemochromatosis (GH) and PCT. A strong association between hepatitis C virus infection and PCT has also been demonstrated, while case reports record a link between human immunodeficiency virus (HIV) and PCT. We have investigated the frequency of these factors in a racially-mixed population of patients with PCT in Cape Town, South Africa. 57 patients with PCT drawn from three ethnic groups were screened for the presence of the C282Y and H63D mutations linked to GH, and the prevalences were compared with corresponding healthy control populations. The seroprevalence of markers for HCV, hepatitis B (HBV) and HIV infection were examined in 28 of these. In the control populations, we found that both the C282Y and H63D mutations are highly prevalent in South Africans of European origin. In a population of mixed or Asian origin, the C282Y mutation is very rare whereas the H63D mutation is common. Neither mutation was encountered in any African subject. Both mutations are associated with PCT, but the association is dependent on the ethnic origins of the population to which the patient belongs. In contrast to other studies, HCV infection is numerically unimportant in PCT in our patients. HIV infection is increasingly encountered in our patients with PCT, but the strength of the association cannot be determined in view of the high background prevalence of HIV infection in some sectors of the South African population. The contribution of specific risk factors may be heavily dependent on the population from which patients are drawn, and care should be taken in extrapolating from observations in one racial or geographic population to any other.
Cell Mol Biol (Noisy-le-grand) 2002 Dec
PMID:Porphyria cutanea tarda: the etiological importance of mutations in the HFE gene and viral infection is population-dependent. 1269 43

In Caucasians, from 4 to 35% of hereditary hemochromatosis (HH) patients carry a least one chromosome without a common assigned HFE mutation (i.e., C282Y, H63D, and S65C). We have undertaken a D-HPLC scanning of the HFE coding region in such patients in order to identify uncommon mutations liable to explain their high transferrin saturation level. Twenty HH patients from Brittany carrying at least one chromosome without an assigned mutation were selected on the basis of a transferrin saturation level with the following threshold: > or = 60% in men and > or = 50% in women, in the absence of other known causes of iron disorders. This strategy allowed us to detect a heterozygous sequence variant in exon 4 of the HFE gene from one individual who was also heterozygous for C282Y. Subsequent DNA sequencing analysis identified an adenine to cytosine transversion at position 848 which changes amino acid 283 from glutamine to proline (Q283P). Family study revealed a clear association between the C282Y/Q283P compound heterozygote genotype and the development of HH. Molecular modeling studies are in favor of a destabilizing effect of the Q283P mutation on the tertiary structure of the HFE protein. This is the first report of a natural protein variant describing the introduction of a proline in a central beta-strand position. Our approach may have practical implications in screening strategies for hereditary hemochromatosis, molecular diagnosis, and HFE structure-function relationships.
Blood Cells Mol Dis
PMID:Phenotypic expression of the C282Y/Q283P compound heterozygosity in HFE and molecular modeling of the Q283P mutation effect. 1297 20

Our understanding of how iron transverses the intestinal epithelium has improved greatly in recent years, although the mechanism by which body iron demands regulate this process remains poorly understood. By critically examining the earlier literature in this field and considering it in combination with recent advances we have formulated a model explaining how iron absorption could be regulated by body iron requirements. In particular, this analysis suggests that signals to alter absorption exert a direct effect on mature enterocytes rather than influencing the intestinal crypt cells. We propose that the liver plays a central role in the maintenance of iron homeostasis by regulating the expression of hepcidin in response to changes in the ratio of diferric transferrin in the circulation to the level of transferrin receptor 1. Such changes are detected by transferrin receptor 2 and the HFE/transferrin receptor 1 complex. Circulating hepcidin then directly influences the expression of Ireg1 in the mature villus enterocytes of the duodenum, thereby regulating iron absorption in response to body iron requirements. In this manner, the body can rapidly and appropriately respond to changes in iron demands by adjusting the release of iron from the duodenal enterocytes and, possibly, the macrophages of the reticuloendothelial system. This model can explain the regulation of iron absorption under normal conditions and also the inappropriate absorption seen in pathological states such as hemochromatosis and thalassemia.
Blood Cells Mol Dis
PMID:The orchestration of body iron intake: how and where do enterocytes receive their cues? 1273 47

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.
Blood Cells Mol Dis
PMID:Hemochromatosis gene (HFE) mutations in South East Asia: a potential for iron overload. 1273 49

Diabetes mellitus is a recognized consequence of hereditary haemochromatosis. Whether the common HFE mutations, that associate with this condition and pre-dispose to increases in serum iron indices, are over-represented in diabetic populations remains controversial. We present data from the largest case-control study of the C282Y and H63D HFE allele frequencies in typical type 2 diabetes mellitus, as defined by an age of onset greater than 30 years and no requirement for insulin in the first year post-diagnosis. We also present a meta-analysis of all similar studies to date. We see no evidence for over-representation of iron loading HFE alleles in type 2 diabetes mellitus, suggesting that screening for HFE mutations in this population is of no value.
Hum Mol Genet 2003 Jun 15
PMID:Typical type 2 diabetes mellitus and HFE gene mutations: a population-based case - control study. 1278 44

There is interest in the role of iron in age-related diseases such as atherosclerosis. Tissue iron deposition could be harmful, because Fe(2+) can react with H(2)O(2) to form OH(-) radicals and Fe(2+) can react with O(2) to form reactive oxygen species. Free radicals react with cell membranes and cell organelles and could lead to the development of atherosclerosis by initiating lipid peroxidation. Hereditary hemochromatosis provides an opportunity for studying the effects of iron on cardiovascular disease. Some studies have shown that individuals who carried HFE mutations may be at greater risk of developing coronary heart disease than those without the mutations. In contrast, a large number of studies have reported no association between HFE mutations and coronary heart disease. These studies have possible confounding factors, such as the homogeneity of the population in term of geographical origin among others. We studied the relation between HFE mutations and acute myocardial infarction in two case-control studies involving two sets of subjects representing different age groups from different geographic regions in Italy. The first one was composed of 172 older patients (139 males and 33 females; mean age 67) and 207 healthy controls (91 males and 116 females; mean age 46) from Emilia-Romagna. The second one was composed of younger 77 patients (75 males and 2 females; mean age 41) and 172 healthy controls (75 males and 97 females, mean age: 38) from Sicily. All patients were genotyped for ApoE alleles, since the ApoE- epsilon 4 allele is considered a risk factor for cardiovascular diseases and can interfere with other genetic and environmental factors by modifying susceptibility to this disease. DNA typing for C282Y and H63D HFE alleles was performed also. There were no significant differences in frequencies of the different HFE alleles between acute myocardial infarction patients and controls in cohorts of both old and young patients. Also taking into account the presence or absence of the ApoE- epsilon 4 allele, no significant differences in H63D allele frequencies were observed. Thus, our study, performed in two samples of genetically homogeneous patients and controls, does not support the suggestion that HFE mutations may be associated with acute myocardial infarction in susceptible individuals.
Blood Cells Mol Dis
PMID:Association between HFE mutations and acute myocardial infarction: a study in patients from Northern and Southern Italy. 1285 Apr 85


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