The HFE Cys282Tyr mutation as a necessary but not sufficient cause of clinical hereditary hemochromatosis

Iron homeostasis in older adults: balancing nutritional requirements and health risks

Iron plays a crucial role in many physiological processes, including oxygen transport, bioenergetics, and immune function. Iron is assimilated from food and also recycled from senescent red blood cells. Iron exists in two dietary forms: heme (animal based) and non-heme (mostly plant based). The body uses iron for metabolic purposes, and stores the excess mainly in splenic and hepatic macrophages. Physiologically, iron excretion in humans is inefficient and not highly regulated, so regulation of intestinal absorption maintains iron homeostasis. Iron losses occur at a steady rate via turnover of the intestinal epithelium, blood loss, and exfoliation of dead skin cells, but overall iron homeostasis is tightly controlled at cellular and systemic levels. Aging can have a profound impact on iron homeostasis and induce a dyshomeostasis where iron deficiency or overload (sometimes both simultaneously) can occur, potentially leading to several disorders and pathologies. To maintain physiologically balanced iron levels, reduce risk of disease, and promote healthy aging, it is advisable for older adults to follow recommended daily intake guidelines and periodically assess iron levels. Clinicians can evaluate body iron status using different techniques but selecting an assessment method primarily depends on the condition being examined. This review provides a comprehensive overview of the forms, sources, and metabolism of dietary iron, associated disorders of iron dyshomeostasis, assessment of iron levels in older adults, and nutritional guidelines and strategies to maintain iron balance in older adults.

EASL Clinical Practice Guidelines on haemochromatosis

Haemochromatosis is characterised by elevated transferrin saturation (TSAT) and progressive iron loading that mainly affects the liver. Early diagnosis and treatment by phlebotomy can prevent cirrhosis, hepatocellular carcinoma, diabetes, arthropathy and other complications. In patients homozygous for p.Cys282Tyr in HFE, provisional iron overload based on serum iron parameters (TSAT >45% and ferritin >200 μg/L in females and TSAT >50% and ferritin >300 μg/L in males and postmenopausal women) is sufficient to diagnose haemochromatosis. In patients with high TSAT and elevated ferritin but other HFE genotypes, diagnosis requires the presence of hepatic iron overload on MRI or liver biopsy. The stage of liver fibrosis and other end-organ damage should be carefully assessed at diagnosis because they determine disease management. Patients with advanced fibrosis should be included in a screening programme for hepatocellular carcinoma. Treatment targets for phlebotomy are ferritin <50 μg/L during the induction phase and <100 μg/L during the maintenance phase.

PLXNA2 as a candidate gene in patients with intellectual disability

Intellectual disability (ID) is one of the most common disabilities in humans. In an effort to contribute to the expanding genetic landscape of ID, we describe a novel autosomal recessive ID candidate gene. Combined autozygome/exome analysis was performed in two unrelated consanguineous families with ID. Each of the two families had a novel homozygous likely deleterious variant in PLXNA2 and displayed the core phenotype of ID. PLXNA2 belongs to a family of transmembrane proteins that function as semaphorin receptors. Sema5A-PlexinA2 is known to regulate brain development in mouse, and Plxna2-/- mice display defective associative learning, sociability, and sensorimotor gating. We note the existence of variability in the phenotype among the three patients, including the existence of variable degree of ID, ranging from borderline intellectual functioning to moderate-severe ID, and the presence of cardiac anomalies in only one of the patients. We propose incomplete penetrance as a possible explanation of the observed difference in phenotypes. Future cases will be needed to support the proposed link between PLXNA2 and ID in humans.

Chelating Polymers for Hereditary Hemochromatosis Treatment

Hemochromatosis (iron overload) encompasses a group of diseases that are characterized by a toxic hyperaccumulation of iron in parenchymal organs. Currently, only few treatments for this disease have been approved; however, all these treatments possess severe side effects. In this study, a paradigm for hemochromatosis maintenance/preventive therapy is investigated: polymers with negligible systemic biological availability form stable complexes with iron ions in the gastrointestinal tract, which reduces the biological availability of iron. Macroporous polymer beads are synthesized with three different iron-chelating moieties (benzene-1,2-diol, benzene-1,2,3-triol, and 1,10-phenanthroline). The polymers rapidly chelate iron ions from aqueous solutions in vitro in the course of minutes, and are noncytotoxic and nonprooxidant. Moreover, the in vivo biodistribution and pharmacokinetics show a negligible uptake from the gastrointestinal tract (using ¹²⁵ I-labeled polymer and single photon emission computed tomography/computed tomography), which generally prevents them from having systemic side effects. The therapeutic efficacy of the prepared polymers is successfully tested in vivo, and exhibits a significant inhibition of iron uptake from the gastrointestinal tract without any noticeable signs of toxicity. Furthermore, an in silico method is developed for the prediction of chelator selectivity. Therefore, this paradigm can be applied to the next-generation maintenance/preventive treatment for hemochromatosis and/or other diseases of similar pathophysiology.

Early Onset Granulomatous Colitis Associated with a Mutation in NCF4 Resolved with Hematopoietic Stem Cell Transplantation

A 4-year-old boy presented with perianal abscess and granulomatous colitis, which led the diagnosis of Crohn's disease. He became refractory to all available therapies and required colectomy. Targeted sequencing revealed a deleterious variant in NCF4, causing severe neutrophil dysfunction. He underwent hematopoietic stem cell transplantation (HSCT) with an excellent outcome.

Extracting Complementary Insights from Molecular Phenotypes for Prioritization of Disease-Associated Mutations

Rapid advances in next-generation sequencing technology have resulted in an explosion of whole-exome/genome sequencing data, providing an unprecedented opportunity to identify disease- and trait-associated variants in humans on a large scale. To date, the long-standing paradigm has leveraged fitness-based approximations to translate this ever-expanding sequencing data into causal insights in disease. However, while this approach robustly identifies variants under evolutionary constraint, it fails to provide molecular insights. Moreover, complex disease phenomena often violate standard assumptions of a direct organismal phenotype to overall fitness effect relationship. Here we discuss the potential of a molecular phenotype-oriented paradigm to uniquely identify candidate disease-causing mutations from the human genetic background. By providing a direct connection between single nucleotide mutations and observable organismal and cellular phenotypes associated with disease, we suggest that molecular phenotypes can readily incorporate alongside established fitness-based methodologies to provide complementary insights to the functional impact of human mutations. Lastly, we discuss how integrated approaches between molecular phenotypes and fitness-based perspectives facilitate new insights into the molecular mechanisms underlying disease-associated mutations while also providing a platform for improved interpretation of epistasis in human disease.

Hemochromatosis: pathophysiology, evaluation, and management of hepatic iron overload with a focus on MRI

Hereditary hemochromatosis (HH) is an autosomal recessive disorder that occurs in approximately 1 in 200-250 individuals. Mutations in the HFE gene lead to excess iron absorption. Excess iron in the form of non-transferrin-bound iron (NTBI) causes injury and is readily uptaken by cardiomyocytes, pancreatic islet cells, and hepatocytes. Symptoms greatly vary among patients and include fatigue, abdominal pain, arthralgias, impotence, decreased libido, diabetes, and heart failure. Untreated hemochromatosis can lead to chronic liver disease, fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Many invasive and noninvasive diagnostic tests are available to aid in diagnosis and treatment. MRI has emerged as the reference standard imaging modality for the detection and quantification of hepatic iron deposition, as ultrasound (US) is unable to detect iron overload and computed tomography (CT) findings are nonspecific and influenced by multiple confounding variables. If caught and treated early, HH disease progression can significantly be altered. Area covered: The data on Hemochromatosis, iron overload, and MRI were gathered by searching PubMed. Expert commentary: MRI is a great tool for diagnosis and management of iron overload. It is safe, effective, and a standard protocol should be included in diagnostic algorithms of future treatment guidelines.

An Ultrasensitive Magnetoelectric Sensor System For the Quantitative Detection of Liver Iron

Ultrasensitive magnetoelectric (ME) sensors have been developed using magnetostrictive/piezoelectric laminate heterostructures. This paper discusses a highly interdisciplinary design of a room temperature biomagnetic liver susceptometry system (BLS) based on the ME sensors. The ME-sensor based BLS maintains the ultrahigh sensitivity to detect the weak AC biomagnetic signals and introduces a low equivalent magnetic noise. The results reveal a "turning point" and successfully indicate the output signals to be linearly responsive to iron concentrations from normal iron level (0.05 mg_Fe/g_{liver phantom}) to 5 mg_Fe/g_{liver phantom} iron overload level (100X overdose). Further, the introduction of the water-bag technique shows the promise on the automatic deduction of the background (tissue) signal, enabling an even higher sensitivity and better signal-to-noise (SNR). With these improvements, it becomes feasible to get improved characterization flexibility and the field distribution mapping potential via signal processing from the correlations of multiple sensors in the system. Considering the wide presence of biomagnetic signals in human organs, the potential impact of such biomagnetic devices on medicine and health care could be enormous and far-reaching.

A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection

Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron.

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.

Phlebotomy-mobilized iron as a surrogate for liver iron content in hemochromatosis patients

We sought to establish the relationship of quantitative hepatic iron measurements and phlebotomy-mobilized iron in a large sample of HFE C282Y homozygotes with a hemochromatosis phenotype. Thus, we analyzed data from 79 unrelated C282Y homozygotes from treatment centers in Rochester, NY and Birmingham, AL who had undergone liver biopsy with measurement of hepatic iron content and who had achieved iron depletion (serum ferritin <25 ng/l) with quantitative phlebotomy. The sample consisted of 57 men and 22 women; their median age at diagnosis was 47 years (range 23-76 years). Sixty-three of 79 (79.7%) had hepatic iron index (HII; μmol/g dry weight of liver divided by age in years) ≥1.9, a conventional phenotypic definition of hemochromatosis. The mean quantity of phlebotomy-mobilized iron (± 1 sd) was 6.4 g (±4.0 g) in men (range 2.0-18.0 g) and 6.2 g (±5.8) in women (range 0.7-22.5 g). There was a significant positive correlation of liver iron levels with phlebotomy-mobilized iron in this patient sample (Pearson coefficient 0.75; R<PRE>2</PRE>=55.5%). This relationship was also demonstrable when data from males and females were analyzed separately. We calculated a phlebotomy-mobilized iron index (MII: phlebotomy-mobilized iron in mg divided by age in years) using the corresponding regression equations and evaluated its use as a surrogate for HII. Thus, a phlebotomy-mobilized iron of 3.5 g corresponds to liver iron levels of 80 μmol/g dry weight, and a MII of 80 corresponds to HII of 1.9. Forty-six of 79 subjects met all four phenotypic criteria for hemochromatosis (liver iron levels ≥80 μmol/g, HII≥1.9, phlebotomy-mobilized iron ≥3.5 g and MII≥80). Of the 20 subjects with MII<80, 9 had a HII≥1.9. Conversely, 5 of 16 subjects with HII<1.9 had MII≥80 and 8 had phlebotomy-mobilized iron ≥3.5 g. Most patients with a hemochromatosis phenotype and evidence of moderate or severe iron overload (>80%) are homozygous for the common HFE missense mutation C282Y. Thus, clinicians rely increasingly on HFE mutation analysis to diagnose hemochromatosis and on quantitative phlebotomy to estimate the severity of iron overload in many cases. Liver biopsy is now employed in selected patients to visualize fibrosis or cirrhosis and to identify coincidental hepatic disease. We conclude that the use of the MII permits a retrospective estimation of the age-adjusted severity of iron overload that has a diagnostic value similar to that of the HII in hemochromatosis patients with C282Y homozygosity.

A high-fat diet modulates iron metabolism but does not promote liver fibrosis in hemochromatotic Hjv⁻/⁻ mice

Hemojuvelin (Hjv) is a membrane protein that controls body iron metabolism by enhancing signaling to hepcidin. Hjv mutations cause juvenile hemochromatosis, a disease of systemic iron overload. Excessive iron accumulation in the liver progressively leads to inflammation and disease, such as fibrosis, cirrhosis, or hepatocellular cancer. Fatty liver (steatosis) may also progress to inflammation (steatohepatitis) and liver disease, and iron is considered as pathogenic cofactor. The aim of this study was to investigate the pathological implications of parenchymal iron overload due to Hjv ablation in the fatty liver. Wild-type (WT) and Hjv(-/-) mice on C57BL/6 background were fed a standard chow, a high-fat diet (HFD), or a HFD supplemented with 2% carbonyl iron (HFD+Fe) for 12 wk. The animals were analyzed for iron and lipid metabolism. As expected, all Hjv(-/-) mice manifested higher serum and hepatic iron and diminished hepcidin levels compared with WT controls. The HFD reduced iron indexes and promoted liver steatosis in both WT and Hjv(-/-) mice. Notably, steatosis was attenuated in Hjv(-/-) mice on the HFD+Fe regimen. Hjv(-/-) animals gained less body weight and exhibited reduced serum glucose and cholesterol levels. Histological and ultrastructural analysis revealed absence of iron-induced inflammation or liver fibrosis despite early signs of liver injury (expression of α-smooth muscle actin). We conclude that parenchymal hepatic iron overload does not suffice to trigger progression of liver steatosis to steatohepatitis or fibrosis in C57BL/6 mice.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Diagnostic utility of HFE variants in Spanish patients: association with HLA alleles and role in susceptibility to acute lymphoblastic leukemia

Two single nucleotide polymorphisms (SNPs) in the Human Hemochromatosis (HFE) gene, C282Y and H63D, are the major variants associated to altered iron status and it is well known that these mutations are in linkage disequilibrium with certain Human Leukocyte Antigen (HLA)-A alleles. In addition, the C282Y SNP has been previously suggested to confer susceptibility to acute lymphoblastic leukemia (ALL). We have aimed to assess the diagnosis utility of these polymorphisms in a population of Spanish subjects with suspicion of hereditary iron overload and to evaluate the effect of their associations with HLA-A alleles on the susceptibility to ALL. Both the 63DD [OR=4.31 (1.7-11.2)] and 282YY (p for trend=0.02) genotypes were more frequently found among subjects with suspicion of iron overload than among controls. 282YY carriers displayed significantly higher transferrin saturation index (TSI) values (p<0.001) as well as serum iron (p=0.01) and ferritin (p=0.01) levels. In addition, transferrin levels were lower in these subjects (p=0.01). Likewise, patients who were carriers of the compound heterozygous diplotype (282CY/63HD) showed significantly higher TSI and serum iron and ferritin concentrations. The H63D SNP did not significantly affect the analytical parameters measured. All 282YY carriers and 69.2% of compound heterozygotes showed an altered biochemical index. The frequencies of the HFE SNPs in ALL pediatric patients were lower than those found in controls, whereas the HLA-A*24 allele was significantly overrepresented in the patients group [OR=3.76 (1.9-7.3)]. No HFE-HLA-A associations were found to modulate the ALL risk. These results suggest that it may be useful to test for both HFE H63D and C282Y polymorphisms in patients with iron overload, as opposed to just genotyping for the C282Y SNP, which is customary in some healthcare centers. These HFE variants and their associations with HLA-A alleles were not observed to be relevant for the susceptibility to ALL in our population.

Ernest Beutler: his life and contribution to medical science

Ernest Beutler was one of the preeminent haematologists of the last half of the 20th and the early 21st century. In a career that spanned six decades, his research interests included such diverse areas as red cell metabolism, blood preservation, glycolipid storage diseases, leukaemias and iron metabolism. Indeed, he was quite different from most of his contemporaries in that his knowledge encompassed not only haematology and not only the medical sciences, but the biological sciences as a whole. He was among the first to describe X chromosome inactivation, and he established the critical link between glucose-6-phosphate dehydrogenase deficiency and drug-induced haemolysis. He was a skilled and innovative clinician, and an early advocate of bone marrow transplantation for the treatment of acute leukaemia. He was a prolific author, with over 800 publications; a long time member of the Editorial Board of Blood; founder of the journal Blood Cells Molecules and Diseases; and an editor of Williams Haematology from the time of its inception. He bequeathed $1 million to the American Society of Haematology to recognise and reward outstanding basic research and its clinical application: a pursuit to which he had committed his life. Indeed, he became an extraordinary exemplar of the bench-to-bedside ethos, which holds that even today, an MD researcher, working with limited means and independent of pharmaceutical companies, can have a great impact on the practice of medicine.

The ethnospecific distribution of the HFE haplotypes for IVS2(+4)t/c, IVS4(-44)t/c, and IVS5(-47)g/a in populations of Russia and possible effects of these single-nucleotide polymorphisms in splicing

AIM

The aim of this work was a haplotype analysis of the major mutations (C282Y, H63D, S65C) and IVS2(+4)t/c, IVS4(-44)t/c, and IVS5(-47)a/g polymorphisms of the hemochromatosis HFE gene in populations inhabiting the territories of Russia (Russians, Finno-Ugrians, Central Asians, and Arctic Mongoloids).

METHOD

The hemochromatosis gene (HFE) alleles were detected using the polymerase chain reaction/restriction fragment length polymorphism method.

RESULTS

Of the eight possible intronic haplotype variants, the TTG, TTA, CTA, and CCA were identified. The HFE alleles with the different haplotype variants were distributed in an ethnospecific manner among the populations. Our finding was that every one of the C282Y, H63D, and S65C mutations was in linkage disequilibrium only with one of the intronic haplotype variants: TTG, CTA, and CCA, respectively. The data from context analysis of DNA regions where the examined single-nucleotide polymorphisms are located suggested their involvement in splicing.

CONCLUSIONS

Different genotypes of the HFE gene occur at different frequencies among populations of Russia. Carriers of the specific genotype variants may potentially express distinct sets of alternative HFE mRNAs.

Hemochromatosis genotypes and risk of iron overload--a meta-analysis

PURPOSE

The incomplete phenotypic penetrance of high iron Fe genotypes in relation to hemochromatosis poses a practical problem in the interpretation of the genotyping results by clinicians. We carried out meta-analyses of the associations between hemochromatosis genotypes C282Y/C282Y, C282Y/H63D, C282Y/wild-type, H63D/H63D, H63D/wild-type, versus wild-type/wild-type and iron overload, both provisional (elevated serum iron markers) and documented (elevated serum iron markers associated with evidence of iron excess based on liver biopsy and/or quantitative phlebotomy).

METHODS

After reviewing 3572 article titles and evaluating 92 articles in detail, odds ratios were pooled from 43 study populations (9986 cases and 25,492 controls) using a random-effects model.

RESULTS

Homozygosity for either variant or compound heterozygosity was associated with both provisional and documented iron overload. Single heterozygosity conferred no risk for elevated hepatic iron index and/or mobilizable iron by quantitative phlebotomy. In patients with clinical hereditary hemochromatosis, no evidence of provisional and documented iron overload with transferrin saturation (TS) values greater than 55% was evidenced for C282Y and H63D single heterozygotes whereas documented iron overload including TS of 45% to 50% was weakly associated with C282Y/wild-type genotype; H63D/H63D genotype was not associated with documented iron overload in patients with TS values of 45% to 50%.

CONCLUSIONS

The results, mainly from case-control studies, cannot necessarily be extrapolated to the general population.

The effect of dietary iron intake on the development of iron overload among homozygotes for haemochromatosis

Objective

To quantify the role of dietary Fe in total body Fe (TBI) accumulation among homozygotes for theHFEgene associated with haemochromatosis.

Design

A Monte Carlo model was built to simulate Fe accumulation based on findings from human feeding experiments and national dietary surveys. A hypothetical cohort of 1000 homozygotes with starting age 25 years was used in 39-year simulations. The impact of reducing dietary Fe intake on Fe accumulation was tested.

Results

In the baseline model without any dietary intervention, by age 64, the percentage of males with TBI > 10 g, >15 g and >20 g was 93·2 %, 49·6 % and 14·7 %, respectively. When the Fe intake of individuals in the cohort was reduced to ≤200 % of the recommended dietary allowance (RDA), the corresponding percentages were 92·0 %, 40·5 % and 10·2 %, respectively. The corresponding figures were 91·0 %, 40·0 % and 9·3 % for Fe defortification and 70·3 %, 21·3 % and 4·1 % when Fe intake was capped at 100 % RDA. Similar trends were seen with sexes combined, although the impact of interventions was less. Sensitivity analysis revealed that the rate of Fe accumulation and the impact of dietary interventions are highly dependent on assumptions concerning Fe absorption rates.

Conclusions

Variation in Fe intake as currently observed in the USA contributes to variation in Fe accumulation among homozygotes, when continued over an extended period. Lifelong dietary habits and national fortification policy can affect the rate of Fe accumulation, although the magnitude of the effect varies by gender, the TBI level of interest and factors affecting the Fe absorption rate.

HFE-associated hereditary hemochromatosis

In populations of northern European descent, the p.C282Y mutation in the HFE gene is highly prevalent, and HFE-associated hereditary hemochromatosis is the most common type of inherited iron overload disorder. Inappropriate low secretion of hepcidin, which negatively regulates iron absorption, is postulated to be the mechanism for iron overload in this condition. The characteristic biochemical abnormalities are elevated serum transferrin-iron saturation and serum ferritin. Typical clinical manifestations include cirrhosis, liver fibrosis, hepatocellular carcinoma, elevated serum aminotransferase levels, diabetes mellitus, restrictive cardiomyopathy and arthropathy of the second and third metacarpophalangeal joints. Most patients are now diagnosed before the development of these clinical features. Molecular genetic tests are currently available for genotypic diagnosis. In selected individuals, diagnosis might require liver biopsy or quantitative phlebotomy. Iron depletion by phlebotomy is the mainstay of treatment and is highly effective in preventing the complications of iron overload if instituted before the development of cirrhosis. Genetic testing is currently not recommended for population screening because of low yield as the majority of the healthy, asymptomatic p.C282Y homozygotes do not develop clinically significant iron overload. HFE gene testing remains an excellent tool for the screening of first-degree relatives of affected probands who are p.C282Y homozygotes.

Hereditary haemochromatosis

Haemochromatosis should currently refer to hereditary iron overload disorders presenting with a definite and common phenotype characterised by normal erythropoiesis, increased transferrin saturation and ferritin and primarily parenchymal iron deposition related to innate low (but normally regulated) production of the hepatic peptide hormone hepcidin. Since the discovery of the haemochromatosis gene (HFE) in 1996, several novel gene defects have been detected, explaining the mechanism and diversity of iron overload diseases. Overall, at least four main types of hereditary haemochromatosis (HH) have been identified. This review describes the systematic diagnostic and therapeutic strategy and pitfalls for patients suspected for HH and their relatives.

Intestinal hypoxia-inducible transcription factors are essential for iron absorption following iron deficiency

Iron deficiency and iron overload are among the most prevalent nutritional disorders worldwide. Duodenal cytochrome b (DcytB) and divalent metal transporter 1 (DMT1) are regulators of iron absorption. Their expression is increased during high systemic requirements for iron, but the molecular mechanisms that regulate DcytB and DMT1 expression are undefined. Hypoxia-inducible factor (HIF) signaling was induced in the intestine following acute iron deficiency in the duodenum, resulting in activation of DcytB and DMT1 expression and an increase in iron uptake. DcytB and DMT1 were demonstrated as direct HIF-2alpha target genes. Genetic disruption of HIF signaling in the intestine abolished the adaptive induction of iron absorption following iron deficiency, resulting in low systemic iron and hematological defects. These results demonstrate that HIF signaling in the intestine is a critical regulator of systemic iron homeostasis.

Structure of the membrane proximal oxidoreductase domain of human Steap3, the dominant ferrireductase of the erythroid transferrin cycle

The daily production of 200 billion erythrocytes requires 20 mg of iron, accounting for nearly 80% of the iron demand in humans. Thus, erythroid precursor cells possess an efficient mechanism for iron uptake in which iron loaded transferrin (Tf) binds to the transferrin receptor (TfR) at the cell surface. The Tf:TfR complex then enters the endosome via receptor-mediated endocytosis. Upon endosomal acidification, iron is released from Tf, reduced to Fe(2+) by Steap3, and transported across the endosomal membrane by divalent metal iron transporter 1. Steap3, the major ferrireductase in erythrocyte endosomes, is a member of a unique family of reductases. Steap3 is comprised of an N-terminal cytosolic oxidoreductase domain and a C-terminal heme-containing transmembrane domain. Cytosolic NADPH and a flavin are predicted cofactors, but the NADPH/flavin binding domain differs significantly from those in other eukaryotic reductases. Instead, Steap3 shows remarkable, although limited homology to FNO, an archaeal oxidoreductase. We have determined the crystal structure of the human Steap3 oxidoreductase domain in the absence and presence of NADPH. The structure reveals an FNO-like domain with an unexpected dimer interface and substrate binding sites that are well positioned to direct electron transfer from the cytosol to a heme moiety predicted to be fixed within the transmembrane domain. Here, we discuss possible gating mechanisms for electron transfer across the endosomal membrane.

Regulation of iron acquisition and storage: consequences for iron-linked disorders

Mammalian iron homeostasis must be meticulously regulated so that this essential element is available for use, but at the same time prevented from promoting the formation of toxic radicals. Controlling the entry of iron into blood plasma is the main mechanism by which iron stores in the body are physiologically manipulated and regulated. Defects in iron acquisition at the cellular and systemic levels lead to human disorders, which involve either iron overload or iron deficiency. Discoveries of iron transporters and insights into their regulation have provided important information about iron metabolism and genetic iron disorders.

HFE genotypes in patients with chronic pancreatitis and pancreatic adenocarcinoma

PURPOSE

The homozygous p.C282Y variant of the HFE gene is a major risk factor for hereditary hemochromatosis, a disorder of iron metabolism resulting in progressive iron accumulation in a variety of organs including the pancreas. Heterozygosity of p.C282Y and p.H63D may increase susceptibility to chronic liver and pancreatic disease. This study determines the frequencies of p.C282Y and p.H63D alterations in patients with chronic pancreatitis and pancreatic adenocarcinoma.

METHODS

In total, 958 patients (349 with alcoholic pancreatitis, 343 with idiopathic pancreatitis, 64 with familial chronic pancreatitis, 34 with acute pancreatitis, and 168 with pancreatic adenocarcinoma) were enrolled and compared with 681 healthy and 100 alcoholic controls. Furthermore, 45 parent-offspring trios were included for segregation analysis. Genotyping of p.C282Y and p.H63D was performed by restriction fragment length polymorphism or melting curve analyses.

RESULTS

No significant differences were found in heterozygosity for p.C282Y and p.H63D when patients with alcoholic (8.0/21.5%), idiopathic (7.3/24.5%), or familial (9.8/23.0%) pancreatitis, or pancreatic adenocarcinoma (5.4/28.6%) were compared with healthy (6.2/24.8%) and alcoholic (7.0/25.0%) controls. Neither genotype was associated with the presence of secondary diabetes mellitus in patients with chronic pancreatitis.

CONCLUSION

Although hemochromatosis is associated with pancreatic pathology, the p.C282Y and p.H63D variants do not play a significant role in the pathogenesis of chronic pancreatitis or pancreatic adenocarcinoma.

Hereditary hemochromatosis screening: effect of mutation penetrance and prevalence on cost-effectiveness of testing algorithms

Screening for hereditary hemochromatosis, although largely discussed, is not yet implemented in clinical practice. We evaluated the cost-effectiveness of 165 hemochromatosis population-screening algorithms involving two or three of several screening tests by developing a computer program that simulates all possible screening scenarios. Input data comprised government estimates of health services data and costs and a virtual population with user-defined demographic characteristics (including variable HFE mutation frequencies and penetrance values). We show that when C282Y homozygote prevalence is set at 3:1000, population screening appears cost-effective when penetrance of the biochemical phenotype is >0.70. When only hepatocellular carcinoma and cirrhosis are considered as the cost-driving complications, population-based screening is not significantly more cost-efficient than no screening, but life expectancy of individuals identified with hereditary hemochromatosis and treated is still improved by 7 years. Among the 165 screening algorithms tested in 91 different virtual populations of one million individuals, biochemical tests usually perform better as the initial test than genetic testing. Indeed, the genetic testing is most cost-effective as the final confirmatory test. Finally, for most combinations of prevalence and penetrance of HFE, one screening algorithm--unbound iron-binding capacity + transferrin saturation--appeared robust enough to be always within the top 5 most cost-effective strategies.

Iron overload in the liver diagnostic and quantification

Hereditary Hemochromatosis is the most frequent modality of iron overload. Since 1996 genetic tests have facilitated significantly the non-invasive diagnosis of the disease. There are however many cases of negative genetic tests that require confirmation by hepatic iron quantification which is traditionally performed by hepatic biopsy. There are many studies that have demonstrated the possibility of performing hepatic iron quantification with Magnetic Resonance. However, a consensus has not been reached yet regarding the technique or the possibility to reproduce the same method of calculus in different machines. This article reviews the state of the art of the question and delineates possible future lines to standardise this non-invasive method of hepatic iron quantification.

Hemochromatosis (HFE) gene splice site mutation IVS5+1 G/A in North American Vietnamese with and without phenotypic evidence of iron overload

Homozygosity for a novel hemochromatosis (HFE) gene splice site mutation (IVS5+1 G/A) was previously reported in a 48-year-old Vietnamese man residing in Germany who had an elevated serum ferritin (SF) and transferrin saturation (TS) and severe iron overload on liver biopsy. This mutation was not found in 222 controls of central European origin but has been found in Southeast Asians living in Vietnam without evidence of iron overload. Hemochromatosis and iron overload screening (HEIRS) Study is an ongoing, multiethnic, primary care-based study of 101,168 North American adults, including 12,772 Asians, a group that the HEIRS Study found has a significantly higher than expected prevalence of elevated serum TS and SF but very low prevalence of the common C282Y and H63D HFE alleles usually associated with hereditary hemochromatosis. It was hypothesized that the IVS5+1 G/A splice site mutation might explain some elevated biochemical iron measures in North American Asians. Overall, 200 Vietnamese subjects from the Los Angeles Field Center who had TS and SF values greater than the 75th percentile of all HEIRS Study participants after adjusting for covariates and 149 controls randomly selected to represent this Vietnamese population were genotyped. Among cases, 1 homozygous mutant and 7 heterozygotes were found; among controls, 1 homozygous mutant and 4 heterozygotes were found yielding an allele frequency of 2.32% for cases and 2.04% for controls (P>0.5). This finding suggests that the HFE IVS5+1 G/A splice site mutation is not the major explanation for unexpectedly high prevalence of TS and SF in North American Asians.

Helicobacter pylori infection and HFE hemochromatosis

Helicobacter pylori infections are associated with iron deficiency, even in the absence of bleeding. To determine whether H. pylori infection plays a role in modifying the phenotype of patients homozygous for the c.845 G > A (C282Y) mutation of the HFE gene we studied 79 homozygous women and 76 homozygous men, comparing the pretreatment hemoglobin, MCV, serum ferritin, transferrin saturation of those who were seropositive and seronegative for H. pylori. No difference between seropositive and seronegative homozytoes was found. There was also no difference between seropositive and seronegative control subjects. We also compared the total iron of 56 of the male and 32 of the female homozygotes as determined by serial phlebotomy. No significant difference was found.

Hereditary hemochromatosis

The advent of the genetics era has profoundly changed the way we look at iron related diseases, particularly hemochromatosis. New discoveries have challenged historical concepts about the disease, such as its monogenic nature, intestinal origin or complete phenotypic penetrance. This review presents a new concept of hemochromatosis which stems from the idea that, beyond their genetic diversities, all known hemochromatoses have in common the same metabolic abnormality: the genetically determined failure to prevent unneeded iron from entering the circulatory pool. Inappropriate levels of hepcidin, the iron hormone, appear now as the central pathogenic event in all forms of hemochromatosis: depending on the protein involved, and its effect on hepatic production of hepcidin, the phenotype varies, ranging from massive early-onset iron loading with severe organ disease (e.g., associated with homozygous mutations of hemojuvelin or hepcidin itself) to the milder late-onset phenotype characterizing the classic and highly prevalent HFE-related form or the rare transferrin receptor 2-related form. In vitro and in vivo studies will be needed to dissect the consequences of each hereditary hemochromatosis allele and increase our understanding of the precise contribution of each gene to the hereditary hemochromatosis phenotype.

Iron-related transcriptomic variations in CaCo-2 cells, an in vitro model of intestinal absorptive cells

Regulation of iron absorption by duodenal enterocytes is essential for the maintenance of homeostasis by preventing iron deficiency or overload. Despite the identification of a number of genes implicated in iron absorption and its regulation, it is likely that further factors remain to be identified. For that purpose, we used a global transcriptomic approach, using the CaCo-2 cell line as an in vitro model of intestinal absorptive cells. Pangenomic screening for variations in gene expression correlating with intracellular iron content allowed us to identify 171 genes. One hundred nine of these genes are clustered into five types of expression profile. This is the first time that most of these genes have been associated with iron metabolism. Functional annotation of these five clusters indicates potential links between the immune response, proteolysis processes, and iron depletion. In contrast, iron overload is associated with cellular metabolism, especially that of lipids and glutathione involving redox function and electron transfer.

Hereditary hemochromatosis: genetic complexity and new diagnostic approaches

Since the discovery of the hemochromatosis gene (HFE) in 1996, several novel gene defects have been detected, explaining the mechanism and diversity of iron-overload diseases. At least 4 main types of hereditary hemochromatosis (HH) have been identified. Surprisingly, genes involved in HH encode for proteins that all affect pathways centered around liver hepcidin synthesis and its interaction with ferroportin, an iron exporter in enterocytes and macrophages. Hepcidin concentrations in urine negatively correlate with the severity of HH. Cytokine-mediated increases in hepcidin appear to be an important causative factor in anemia of inflammation, which is characterized by sequestration of iron in the macrophage system. For clinicians, the challenge is now to diagnose HH before irreversible damage develops and, at the same time, to distinguish progressive iron overload from increasingly common diseases with only moderately increased body iron stores, such as the metabolic syndrome. Understanding the molecular regulation of iron homeostasis may be helpful in designing innovative and reliable DNA and protein tests for diagnosis. Subsequently, evidence-based diagnostic strategies must be developed, using both conventional and innovative laboratory tests, to differentiate between the various causes of distortions of iron metabolism. This review describes new insights in mechanisms of iron overload, which are needed to understand new developments in diagnostic medicine.

Genetic profiling of newborns: ethical and social issues

Identifying genetic factors that could reliably predict health risks for individuals has the potential to bring great health benefits, both for the individuals concerned and for health-care providers. Genetic profiling at birth would allow a person's genome to be analysed at an early stage, and the data electronically stored for future use. However, although this might seem like an attractive proposition, it carries with it serious ethical and social concerns that would need to be addressed if the genetic profiling of newborns were ever to be considered on a population-wide basis.

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

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

Genotype-based screening for hereditary hemochromatosis: II. Attitudes toward genetic testing and psychosocial impact--a report from a German pilot study

In collaboration with the German Sickness Fund (Kaufmännische Krankenkasse-KKH), we conducted a pilot study on DNA-based population screening of hereditary hemochromatosis (HH) in Germany. The health insurance organization KKH briefly informed their members about the possibility to participate voluntarily in this pilot project. A total of 5882 KKH members contacted us and received detailed information on the aim of the project and clinical and genetic aspects of HH. Of these individuals, 3961 requested HFE genotyping. After genotype results had been communicated to the participants' general practitioner, we sent a self-administered questionnaire to all homozygous (n = 67) and heterozygous (n = 485) as well as 448 wild-type study participants (sigma = 1000) to assess the psychosocial impact of HFE genotyping. In addition, questionnaires were sent to 8000 randomly selected members of the KKH to investigate their attitude toward genetic testing. Six hundred thirty-one (63.1%) of the test participants and 2141 (26.8%) of the randomly chosen KKH members responded. A total of 59.1% of the members would generally accept predictive genetic testing and 3.7% objected to such tests in principle. Individuals with higher educational status accepted predictive testing significantly more often than individuals with less education. Of the tested individuals, 69.9% thought that participation in the pilot study was probably beneficial for them and 1% (5 heterozygotes and 1 wild-type) thought that it was probably harmful. Of the participants, 94.6% judged their decision to have participated in the pilot study as right and 0.3% (2 heterozygotes) as probably wrong. Only very few of the tested individuals underwent pretest (1 case) or posttest (11 cases) genetic counseling. We conclude that genotype- based screening for HH is generally accepted and was perceived as beneficial. Negative psychosocial consequences are rare and could presumably have been prevented by delivering appropriate pretest and posttest information.

The molecular genetics of haemochromatosis

The molecular basis of haemochromatosis has proved more complex than expected. After the 1996 identification of the main causative gene HFE and confirmation that most patients were homozygous for the founder C282Y mutation, it became clear that some families were linked to rarer conditions, first named 'non-HFE haemochromatosis'. The genetics of these less common forms was intensively studied between 2000 and 2004, leading to the recognition of haemojuvelin (HJV), hepcidin (HAMP), transferrin receptor 2 (TFR2) and ferroportin-related haemochromatosis, and opening the way for novel hypotheses such as those related to digenic modes of inheritance or the involvement of modifier genes. Molecular studies of rare haemochromatosis disorders have contributed to our understanding of iron homeostasis. In turn, recent findings from studies of knockout mice and functional studies have confirmed that HAMP plays a central role in mobilization of iron, shown that HFE, TFR2 and HJV modulate HAMP production according to the body's iron status, and demonstrated that HAMP negatively regulates cellular iron efflux by affecting the ferroportin cell surface availability. These data shed new light on the pathophysiology of all types of haemochromatosis, and offer novel opportunities to comment on phenotypic differences and distinguish mutations.

HFE genotypes and dietary heme iron: no evidence of strong gene-nutrient interaction on serum ferritin concentrations in middle-aged women

BACKGROUND AND AIM

Hereditary hemochromatosis (HH) is a disorder characterized by inappropriately high intestinal iron absorption. In populations of Northern European descent, HH is most commonly caused by mutations (C282Y/H63D) in the HFE gene.

METHODS AND RESULTS

We investigated the effects of dietary heme iron intake and HFE mutations on serum ferritin concentrations in a population-based random sample of 1611 women aged >50 years using analysis of covariance (ANCOVA). Higher heme iron intake was associated with significantly higher serum ferritin concentrations (P(trend) < 0.001). Also, women with the compound or C282Y homozygous genotype had significantly higher serum ferritin concentrations (geometric mean 115.2 microg/L (95% CI 81.4-162.9 microg/L) than women carrying normal alleles (geometric mean 76.6 microg/L (95% CI 72.5-80.9 microg/L). We observed the highest serum ferritin concentrations among postmenopausal women who are compound heterozygous or C282Y homozygous, and who consume relatively high amounts of heme iron (geometric mean 183.9 microg/L (95% CI 97.2-347.8 microg/L).

CONCLUSIONS

Even when there are currently no clinical signs, women with the compound or C282Y homozygous genotype may still be at risk for developing iron overload sometime after menopause.

Intermediate phenotypes in schizophrenia: a selective review

Studies aiming to identify susceptibility genes for schizophrenia and other complex psychiatric disorders are faced with the confounds of subjective clinical criteria, commonly occurring phenocopies, significant between-subject variability of candidate traits, and the likelihood of allelic and locus heterogeneity that has been shown to define the genetics of other complex human brain and somatic disorders. Additionally, research aimed at identification of the molecular origins of schizophrenia must also deal with the confounding nature of the human brain. Unlike organs with a few common cellular phenotypes, transcriptomes, and proteomes, individual neurons are often distinct from one another in all of these respects. In this review, we present recent work testing the assumption that studies of genetic susceptibility in complex polygenic disorders such as schizophrenia might be enhanced by the identification of intermediate phenotypes related to more fundamental aspects of brain development and function. Progress in the identification of meaningful intermediate phenotypes in schizophrenia has been made possible by the advent of newer methods in cognitive neuroscience and neuroimaging, and the use of combined multimodal techniques.

Mutation analysis of the HFE gene associated with hereditary hemochromatosis in a Venezuelan sample

The frequency of the C282Y, H63D and S65C alleles of the HFE gene was determined in a sample of the Venezuelan population. Two new sets of primers were tested for amplifying the regions mapping these mutations, and genotyping was performed by restriction fragment length polymorphism (RFLP). DNA sequencing was used to validate the RFLP analysis. Serum ferritin levels were also determined. Two hundred and fourteen individuals were tested, extracting DNA from whole blood cells (n=177) or from serum (n=37). The frequency of heterozygous subjects was 3.7, 18.2 and 1.7% for the C282Y, H63D and S65C mutations, respectively, and the allele frequencies were 0.019+/-0.01 for C282Y, 0.119+/-0.016 for H63D and 0.009+/-0.005 for S65C. The results suggest that the admixture of native populations with subjects of South European origin might have had an important role in the diffusion of HFE alleles in Venezuela. C282Y homozygous subjects were not found in this study. No HFE genotype studied here was associated with a significant elevation of serum ferritin concentrations, except for C282Y/H63D compound heterozygote found in one asymptomatic male. This finding supports the theory that the H63D mutation could be involved in alterations of iron parameters when inherited together with C282Y. Our results indicate that C282Y homozygotes will be rarely detected. Performance of HFE mutation analysis in individuals with high iron determinations would be recommended.

Iron dysregulation combined with aging prevents sepsis-induced apoptosis

BACKGROUND

Sepsis, iron loading, and aging cause independent increases in gut epithelial and splenic apoptosis. It is unknown how their combination will affect apoptosis and systemic cytokine levels.

MATERIALS AND METHODS

Hfe-/- mice (a murine homologue of hemochromatosis) abnormally accumulate iron in their tissues. Aged (24-26 months) or mature (16-18 months) Hfe-/- mice and wild type (WT) littermates were subjected to cecal ligation and puncture (CLP) or sham laparotomy. Intestine, spleen, and blood were harvested 24 h later and assessed for apoptosis and cytokine levels.

RESULTS

Gut epithelial and splenic apoptosis were low in both aged septic and sham Hfe-/- mice, regardless of the amount of iron in their diet. Mature septic WT mice had increased apoptosis compared to age-matched sham WT mice. Mature septic Hfe-/- mice had similar levels of intestinal cell death to age-matched septic WT mice but higher levels of splenic apoptosis. Apoptosis was significantly lower in septic aged Hfe-/- mice than septic mature Hfe-/- animals. Interleukin-6 was elevated in septic aged Hfe-/- mice compared to sham mice.

CONCLUSIONS

Although sepsis, chronic iron dysregulation, and aging each increase gut and splenic apoptosis, their combination yields cell death levels similar to sham animals despite the fact that aged Hfe-/- mice are able to mount an inflammatory response following CLP and mature Hfe-/- mice have elevated sepsis-induced apoptosis. Combining sepsis with two risk factors that ordinarily increase cell death and increase mortality in CLP yields an apoptotic response that could not have been predicted based upon each element in isolation.

Prevalence of Three Hereditary Hemochromatosis Mutant Alleles in the Michigan Caucasian Population

OBJECTIVE

To investigate the prevalence in the Michigan non-Hispanic Caucasian population of the C282Y, H63D and S65C mutations in the HFE gene associated with hereditary hemochromatosis.

METHODS

Polymerase chain reaction and restriction fragment length polymorphism analysis were performed on 3,532 blood samples from newborn screening cards provided by the state of Michigan.

RESULTS

More than 30% of Michigan Caucasians carry one HFE mutation, while 6% have two mutations. The allele frequency of the C282Y mutation is 5.7%, significantly higher than expected (p < 0.05), while the frequency of the H63D mutation is 14%, significantly lower than expected (p < 0.01).

CONCLUSIONS

This is the first publication to examine HFE allele frequencies in an unbiased sample of the Caucasian population. Results indicate that the C282Y mutation may be more common in the non-Hispanic Caucasian population than previously reported, and medical problems related to iron overload may be a health concern for Michigan non-Hispanic Caucasians. Additional studies of penetrance for the C282Y allele are required to fully understand the impact of this information.