The evaluation of hyperferritinemia: an updated strategy based on advances in detecting genetic abnormalities

A newly identified ferritin L-subunit variant results in increased proteasomal subunit degradation, impaired complex assembly, and severe hypoferritinemia

Ferritin is a hetero-oligomeric nanocage, composed of 24 subunits of two types, FTH1 and FTL. It protects the cell from excess reactive iron, by storing iron in its cavity. FTH1 is essential for the recruitment of iron into the ferritin nanocage and for cellular ferritin trafficking, whereas FTL contributes to nanocage stability and iron nucleation inside the cavity. Here we describe a female patient with a medical history of severe hypoferritinemia without anemia. Following inadequate heavy IV iron supplementation, the patient developed severe iron overload and musculoskeletal manifestations. However, her serum ferritin levels rose only to normal range. Genetic analyses revealed an undescribed homozygous variant of FTL (c.92A > G), which resulted in a Tyr31Cys substitution (FTLY31C ). Analysis of the FTL structure predicted that the Y31C mutation will reduce the variant's stability. Expression of the FTLY31C variant resulted in significantly lower cellular ferritin levels compared with the expression of wild-type FTL (FTLWT ). Proteasomal inhibition significantly increased the initial levels of FTLY31C , but could not protect FTLY31C subunits from successive degradation. Further, variant subunits successfully incorporated into hetero-polymeric nanocages in the presence of sufficient levels of FTH1. However, FTLY31C subunits poorly assembled into nanocages when FTH1 subunit levels were low. These results indicate an increased susceptibility of unassembled monomeric FTLY31C subunits to proteasomal degradation. The decreased cellular assembly of FTLY31C -rich nanocages may explain the low serum ferritin levels in this patient and emphasize the importance of a broader diagnostic approach of hypoferritinemia without anemia, before IV iron supplementation.

A form of inherited hyperferritinemia associated with bi-allelic pathogenic variants of STAB1

Hyperferritinemia is a frequent finding in several conditions, both genetic and acquired. We previously studied eleven healthy subjects from eight different families presenting with unexplained hyperferritinemia. Their findings suggested the existence of an autosomal-recessive disorder. We carried out whole-exome sequencing to detect the genetic cause of hyperferritinemia. Immunohistochemistry and flow cytometry assays were performed on liver biopsies and monocyte-macrophages to confirm the pathogenic role of the identified candidate variants. Through a combined approach of whole-exome sequencing and homozygosity mapping, we found bi-allelic STAB1 variants in ten subjects from seven families. STAB1 encodes the multifunctional scavenger receptor stabilin-1. Immunohistochemistry and flow cytometry analyses showed absent or markedly reduced stabilin-1 in liver samples, monocytes, and monocyte-derived macrophages. Our findings show a strong association between otherwise unexplained hyperferritinemia and bi-allelic STAB1 mutations suggesting the existence of another genetic cause of hyperferritinemia without iron overload and an unexpected function of stabilin-1 in ferritin metabolism.

Hereditary Hyperferritinemia

Ferritin is a ubiquitous protein that is present in most tissues as a cytosolic protein. The major and common role of ferritin is to bind Fe²⁺, oxidize it and sequester it in a safe form in the cell, and to release iron according to cellular needs. Ferritin is also present at a considerably low proportion in normal mammalian sera and is relatively iron poor compared to tissues. Serum ferritin might provide a useful and convenient method of assessing the status of iron storage, and its measurement has become a routine laboratory test. However, many additional factors, including inflammation, infection, metabolic abnormalities, and malignancy-all of which may elevate serum ferritin-complicate interpretation of this value. Despite this long history of clinical use, fundamental aspects of the biology of serum ferritin are still unclear. According to the high number of factors involved in regulation of ferritin synthesis, secretion, and uptake, and in its central role in iron metabolism, hyperferritinemia is a relatively common finding in clinical practice and is found in a large spectrum of conditions, both genetic and acquired, associated or not with iron overload. The diagnostic strategy to reveal the cause of hyperferritinemia includes family and personal medical history, biochemical and genetic tests, and evaluation of liver iron by direct or indirect methods. This review is focused on the forms of inherited hyperferritinemia with or without iron overload presenting with normal transferrin saturation, as well as a step-by-step approach to distinguish these forms to the acquired forms, common and rare, of isolated hyperferritinemia.

Identification of Novel Mutations by Targeted NGS Panel in Patients with Hyperferritinemia

BACKGROUND

Several inherited diseases cause hyperferritinemia with or without iron overload. Differential diagnosis is complex and requires an extensive work-up. Currently, a clinical-guided approach to genetic tests is performed based on gene-by-gene sequencing. Although reasonable, this approach is expensive and time-consuming and Next Generation Sequencing (NGS) technology may provide cheaper and quicker large-scale DNA sequencing.

METHODS

We analysed 36 patients with non-HFE-related hyperferritinemia. Liver iron concentration was measured in 33 by magnetic resonance. A panel of 25 iron related genes was designed using SureDesign software. Custom libraries were generated and then sequenced using Ion Torrent PGM.

RESULTS

We identified six novel mutations in SLC40A1, three novel and one known mutation in TFR2, one known mutation and a de-novo deletion in HJV, and a novel mutation in HAMP in ten patients. In silico analyses supported the pathogenic role of the mutations.

CONCLUSIONS

Our results support the use of an NGS-based panel in selected patients with hyperferritinemia in a tertiary center for iron metabolism disorders. However, 26 out of 36 patients did not show genetic variants that can individually explain hyperferritinemia and/or iron overload suggesting the existence of other genetic defects or gene-gene and gene-environment interactions needing further studies.

Inherited iron overload disorders

Hereditary iron overload includes several disorders characterized by iron accumulation in tissues, organs, or even single cells or subcellular compartments. They are determined by mutations in genes directly involved in hepcidin regulation, cellular iron uptake, management and export, iron transport and storage. Systemic forms are characterized by increased serum ferritin with or without high transferrin saturation, and with or without functional iron deficient anemia. Hemochromatosis includes five different genetic forms all characterized by high transferrin saturation and serum ferritin, but with different penetrance and expression. Mutations in HFE, HFE2, HAMP and TFR2 lead to inadequate or severely reduced hepcidin synthesis that, in turn, induces increased intestinal iron absorption and macrophage iron release leading to tissue iron overload. The severity of hepcidin down-regulation defines the severity of iron overload and clinical complications. Hemochromatosis type 4 is caused by dominant gain-of-function mutations of ferroportin preventing hepcidin-ferroportin binding and leading to hepcidin resistance. Ferroportin disease is due to loss-of-function mutation of SLC40A1 that impairs the iron export efficiency of ferroportin, causes iron retention in reticuloendothelial cell and hyperferritinemia with normal transferrin saturation. Aceruloplasminemia is caused by defective iron release from storage and lead to mild microcytic anemia, low serum iron, and iron retention in several organs including the brain, causing severe neurological manifestations. Atransferrinemia and DMT1 deficiency are characterized by iron deficient erythropoiesis, severe microcytic anemia with high transferrin saturation and parenchymal iron overload due to secondary hepcidin suppression. Diagnosis of the different forms of hereditary iron overload disorders involves a sequential strategy that combines clinical, imaging, biochemical, and genetic data. Management of iron overload relies on two main therapies: blood removal and iron chelators. Specific therapeutic options are indicated in patients with atransferrinemia, DMT1 deficiency and aceruloplasminemia.

Effect of atorvastatin on iron metabolism regulation in patients with chronic kidney disease - a randomized double blind crossover study

INTRODUCTION

To determine the effect of 6-month administration of atorvastatin on hepcidin and hemojuvelin levels, inflammatory parameters and iron metabolism in patients with chronic kidney disease (CKD) stages 3 and 4.

METHODS

Thirty six statin- and erythropoiesis-stimulating agent-naive patients with CKD stages 3 and 4 and LDL cholesterol ≥100 mg/dl received atorvastatin or placebo for two 6-month periods in a double blind, randomized crossover study. Hepcidin, hemojuvelin, hsCRP, IL-6, hemoglobin, red blood cell distribution width, iron, total iron binding capacity (TIBC), and unsaturated iron binding capacity (UIBC) were measured before and after each treatment period.

RESULTS

Hepcidin decreased (from 102 [307] to 63 [170] pg/ml (p > .001)) in the course of statin therapy but remained unchanged after placebo administration (173 [256] to 153 [204] pg/ml, respectively). Hemojuvelin did not change after either part of the study. Both IL-6 and hsCRP decreased following statin therapy (from 8.7 [12.0] to 8.1 [13.9] pg/ml; p = .04 and from 4.7 [4.0] to 4.0 [3.6] mg/l; p = .4, respectively), but did not change after placebo administration. Blood hemoglobin increased slightly but significantly after 6-month statin therapy (from 11.6 ± 1.6 to 11.9 ± 1.5 g/dl, p = .002), and was unchanged after placebo treatment. TIBC and UIBC increased significantly after 6-month statin therapy, and serum iron also tended to increase. The change of eGFR during the study did not differ between the two treatment periods.

CONCLUSIONS

Statin may have a small but potentially beneficial effect on serum hepcidin, which may lead to improvement of anemia control in CKD patients.

Quantitative analysis of hepatic iron in patients suspected of coexisting iron overload and steatosis using multi-echo single-voxel magnetic resonance spectroscopy: Comparison with fat-saturated multi-echo gradient echo sequence

BACKGROUND

The coexistence of hepatic iron and fat is common in patients with hyperferritinemia, which plays an interactive and aggressive role in the progression of diseases (fibrosis, cirrhosis, and hepatocellular carcinomas).

PURPOSE

To evaluate a modified high-speed T₂ -corrected multi-echo, single voxel spectroscopy sequence (HISTOV) for liver iron concentration (LIC) quantification in patients with hyperferritinemia, with simultaneous fat fraction (FF) estimation.

STUDY TYPE

Retrospective cohort study.

POPULATION

Thirty-eight patients with hyperferritinemia were enrolled.

FIELD STRENGTH/SEQUENCE

HISTOV, a fat-saturated multi-echo gradient echo (GRE) sequence, and a spin echo sequence (FerriScan) were performed at 1.5T.

ASSESSMENT

R₂ of the water signal and FF were calculated with HISTOV, and R2* values were derived from the GRE sequence, with R₂ and LIC from FerriScan serving as the references.

STATISTICAL TESTS

Linear regression, correlation analyses, receiver operating characteristic analyses, and Bland-Altman analyses were conducted.

RESULTS

Abnormal hepatic iron load was detected in 32/38 patients, of whom 10/32 had coexisting steatosis. Strong correlation was found between R2* and FerriScan-LIC (R² = 0.861), and between HISTOV-R_{2_} water and FerriScan-R₂ (R²  = 0.889). Furthermore, HISTOV-R_{2_} water was not correlated with HISTOV-FF. The area under the curve (AUC) for HISTOV-R_{2_} water was 0.974, 0.971, and 1, corresponding to clinical FerriScan-LIC thresholds of 1.8, 3.2, and 7.0 mg/g dw, respectively. No significant difference in the AUC was found between HISTOV-R_{2_} water and R2* at any of the LIC thresholds, with P-values of 0.42, 0.37, and 1, respectively. HISTOV-LIC showed excellent agreement with FerriScan-LIC, with a mean bias of 0.00 ± 1.18 mg/g dw, whereas the mean bias between GRE-LIC and FerriScan-LIC was 0.53 ± 1.49 mg/g dw.

DATA CONCLUSION

HISTOV is useful for the quantification and grading of liver iron overload in patients with hyperferritinemia, particularly in cases with coexisting steatosis. HISTOV-LIC showed no systematic bias compared with FerriScan-LIC, making it a promising alternative for iron quantification.

LEVEL OF EVIDENCE

3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2018.

Iron regulatory protein (IRP)-iron responsive element (IRE) signaling pathway in human neurodegenerative diseases

The homeostasis of iron is vital to human health, and iron dyshomeostasis can lead to various disorders. Iron homeostasis is maintained by iron regulatory proteins (IRP1 and IRP2) and the iron-responsive element (IRE) signaling pathway. IRPs can bind to RNA stem-loops containing an IRE in the untranslated region (UTR) to manipulate translation of target mRNA. However, iron can bind to IRPs, leading to the dissociation of IRPs from the IRE and altered translation of target transcripts. Recently an IRE is found in the 5′-UTR of amyloid precursor protein (APP) and α-synuclein (α-Syn) transcripts. The levels of α-Syn, APP and amyloid β-peptide (Aβ) as well as protein aggregation can be down-regulated by IRPs but are up-regulated in the presence of iron accumulation. Therefore, inhibition of the IRE-modulated expression of APP and α-Syn or chelation of iron in patient’s brains has therapeutic significance to human neurodegenerative diseases. Currently, new pre-drug IRE inhibitors with therapeutic effects have been identified and are at different stages of clinical trials for human neurodegenerative diseases. Although some promising drug candidates of chemical IRE inhibitors and iron-chelating agents have been identified and are being validated in clinical trials for neurodegenerative diseases, future studies are expected to further establish the clinical efficacy and safety of IRE inhibitors and iron-chelating agents in patients with neurodegenerative diseases.

Unexplained isolated hyperferritinemia without iron overload

Although hyperferritinemia may be reflective of elevated total body iron stores, there are conditions in which ferritin levels are disproportionately elevated relative to iron status. Autosomal dominant forms of hyperferritinemia due to mutations in the L-ferritin IRE or in A helix of L-ferritin gene have been described, however cases of isolated hyperferritinemia still remain unsolved. We describe 12 Italian subjects with unexplained isolated hyperferritinemia (UIH). Four probands have affected siblings, but no affected parents or offspring. Sequencing analyses did not identify casual mutations in ferritin gene or IRE regions. These patients had normal levels of intracellular ferritin protein and mRNA in peripheral blood cells excluding pathological ferritin production at transcriptional and post-transcriptional level. In contrast with individuals with benign hyperferritinemia caused by mutations affecting the ferritin A helix, low rather than high glycosylation of serum ferritin was observed in our UIH subjects compared with controls. These findings suggest that subjects with UIH have a previously undescribed form of hyperferritinemia possibly attributable to increased cellular ferritin secretion and/or decreased serum ferritin clearance. The cause remains to be defined and we can only speculate the existence of mutations in gene/s not directly implicated in iron metabolism that could affect ferritin turnover including ferritin secretion.

Simultaneous liver iron and fat measures by magnetic resonance imaging in patients with hyperferritinemia

OBJECTIVE

Hyperferritinemia is frequent in chronic liver diseases of any cause, but the extent to which ferritin truly reflects iron stores is variable. In these patients, both liver iron and fat are found in variable amount and association. Liver biopsy is often required to quantify liver fat and iron, but sampling variability and invasiveness limit its use. We aimed to assess single breath-hold multiecho magnetic resonance imaging (MRI) for the simultaneous lipid and iron quantification in patients with hyperferritinemia.

MATERIAL AND METHODS

We compared MRI results for both iron and fat with their respective gold standards - liver iron concentration and computer-assisted image analysis for steatosis on biopsy. We prospectively studied 67 patients with hyperferritinemia and other 10 consecutive patients were used for validation. We estimated two linear calibration equations for the prediction of iron and fat based on MRI. The agreement between MRI and biopsy was evaluated.

RESULTS

MRI showed good performances in both the training and validation samples. MRI information was almost completely in line with that obtained from liver biopsy.

CONCLUSION

Single breath-hold multiecho MRI is an accurate method to obtain a valuable measure of both liver iron and steatosis in patients with hyperferritinemia.

Hereditary hyperferritinemia cataract syndrome as a cause of childhood hyperferritinemia

A 2-year-old female was presented with high levels of serum ferritin (890 ng/mL) in a routine blood test. Clinical and laboratory investigations excluded the presence of iron overload and secondary causes of hyperferritinemia. A detailed family history and laboratory examinations revealed the presence of early-onset cataract in her 33-year-old mother, who also displayed hyperferritinemia (633 ng/mL), similar to other family members. Genetic testing confirmed the diagnosis of hereditary hyperferritinemia cataract syndrome (HHCS), demonstrating a C39>G (c.-161C>G) mutation into FTL gene. HHCS should be considered in the differential diagnosis of childhood hyperferritinemia, especially in the presence of normal transferrin saturation.

A novel deletion in the iron-response element of the L-ferritin gene, causing hyperferritinaemia cataract syndrome

A 47-year-old woman, presenting to her family physician with fatigue, was incidentally found to have persistently elevated ferritin. There was clinically no suggestion of iron overload, and laboratory testing showed transferrin saturation at the low end of the reference range. After ruling out acquired causes of hyperferritinaemia, as well as laboratory interference, further questioning revealed a history of bilateral early-onset cataracts, allowing a diagnosis of hyperferritinaemia cataract syndrome to be made. DNA sequencing of the 5' untranslated region of the L-ferritin gene revealed a novel 4-base deletion in the iron response element, within a region known to be crucial for binding iron regulatory protein.

Extreme hyperferritinaemia; clinical causes

There are many causes of raised serum ferritin concentrations including iron overload, inflammation and liver disease to name but a few examples. Cases of extreme hyperferritinaemia (serum ferritin concentration equal to or greater than 10 000 ug/l) are being reported in laboratories but the causes of this are unclear. We conducted an audit study to explore this further. Extreme hyperferritinaemia was rare with only 0.08% of ferritin requests displaying this. The main causes of extreme hyperferritinaemia included multiple blood transfusions, malignant disease, hepatic disease and suspected Still's disease.

Molecular diagnosis of hemochromatosis

INTRODUCTION

The discovery of hemochromatosis genes and the availability of molecular-genetic tests considerably modified the knowledge of the disease relative to physiopathology, penetrance, and expression, and had major impact in the diagnostic settings.

AREAS COVERED

Hemochromatosis is a heterogenous disorder at both genetic and phenotypic level. The review discusses criteria to define patients' iron phenotype and to use molecular tests to diagnose HFE-related and non-HFE hemochromatosis. The material examined includes articles published in the journals covered by PubMed US National Library of Medicine. The author has been working in the field of iron overload diseases for several years and has contributed 18 of the papers cited in the references.

EXPERT OPINION

Hemochromatosis genotyping is inseparable from phenotype characterization. A full clinical assessment is needed and DNA test performed when data suggest a clear indication of suspicion of being at risk for HH. HFE testing for p.Cys282Tyr mutation and p.His63Asp variant is the first molecular diagnostic step. Genotyping for rare mutations can be offered to patients with negative first-level HFE testing who have iron overload with no other explanation and should be performed in referral centers for iron overload disorders that can provide genetic advice and in-house genotyping services.

Hemochromatosis and fatty liver disease: building evidence for insulin resistance in bottlenose dolphins (Tursiops truncatus)

Hemochromatosis in bottlenose dolphins (Tursiops truncatus) is associated with high postprandial plasma insulin levels, suggestive of insulin resistance. In humans, insulin resistance is associated with liver pathologies, including excessive iron deposition and nonalcoholic fatty liver disease. Dolphin liver tissues, in addition to excessive iron storage, were evaluated for other pathologies supportive of underlying insulin resistance. Archived liver tissues collected postmortem during 1985-2010 from 18 dolphins (median age 27.9 yr, range 0.7-51.4) that were part of the Navy Marine Mammal Program's managed collection were assessed for the presence and severity of hemosiderin deposition, fatty liver disease, and hepatitis. Demographics, clinical pathology values, and percentage weight loss were compared among dolphins with and without these changes. Twelve (66.7%) dolphins had mild to moderate hemosiderin deposition, 7 (38.9%) had mild to severe fatty liver disease, and 11 (61.1%) had mild to moderate hepatitis. Of the 12 dolphins with hemosiderosis, deposition occurred in the Kupffer cells among 11 (91.7%). Dolphins with fatty liver disease were more likely to have higher postprandial serum hyperglycemia (>140 mg/dl), leukocytosis (>11,000 cells/microl), and hyperglobulinemia (>3.5 g/dl). Unlike in many nonhuman terrestrial animals, fatty liver disease was not associated with rapid weight loss or hypoglycemia. Interestingly, there were no significant associations among dolphins with hemosiderosis, fatty liver disease, and hepatitis. This study supports that both hemochromatosis and fatty liver disease were present in the dolphin study population, and histopathology and clinical pathology among these animals suggest a nonhereditary, metabolic etiology.

KEYWORDS

Bottlenose dolphin, fatty liver disease, hemochromatosis, hemosiderosis, hepatic lipidosis, hepatitis, Tursiops truncatus.

Non-HFE hemochromatosis

Hereditary hemochromatosis (HH) is an autosomal recessive disorder classically related to HFE mutations. However, since 1996, it is known that HFE mutations explain about 80% of HH cases, with the remaining around 20% denominated non-HFE hemochromatosis. Nowadays, four main genes are implicated in the pathophysiology of clinical syndromes classified as non-HFE hemochromatosis: hemojuvelin (HJV, type 2Ajuvenile HH), hepcidin (HAMP, type 2B juvenile HH), transferrin receptor 2 (TFR2, type 3 HH) and ferroportin (SLC40A1, type 4 HH). The aim of this review is to explore molecular, clinical and management aspects of non-HFE hemochromatosis.

Mammalian iron metabolism

ABSTRACT Iron is an essential transition metal for mammalian cellular and tissue viability. It is critical to supplying oxygen through heme, the mitochondrial respiratory chain, and enzymes such as ribonucleotide reductase. Mammalian organisms have evolved with the means of regulating the metabolism of iron, because if left unregulated, the resulting excess amounts of iron may induce chronic toxicities affecting multiple organ systems. Several homeostatic mechanisms exist to control the amount of intestinal dietary iron uptake, cellular iron uptake, distribution, and export. Within these processes, numerous molecular participants have been identified because of advancements in basic cell biology and efforts in disease-based research of iron storage abnormalities. For example, dietary iron uptake across the intestinal duodenal mucosa is mediated by an intramembrane divalent metal transporter 1 (DMT1), and cellular iron efflux involves ferroportin, the only known iron exporter. In addition to duodenal enterocytes, ferroportin is present in other cell types, and exports iron into plasma. Ferroportin was recently discovered to be regulated by the expression of the circulating hormone hepcidin, a small peptide synthesized in hepatocytes. These recent studies on the role of hepcidin in the regulation of dietary, cellular, and extracellular iron have led to a better understanding of the pathways by which iron balance in humans is influenced, especially its involvement in human genetic diseases of iron overload. Other important molecular pathways include iron binding to transferrin in the bloodstream for cellular delivery through the plasma membrane transferrin receptor (TfR1). In the cytosol, iron regulatory proteins 1 and 2 (IRP1 and IRP2) play a prominent role in sensing the presence of iron in order to posttranscriptionally regulate the expression of TfR1 and ferritin, two important participants in iron metabolism. From a toxicological standpoint, posttranscriptional regulation of these genes aids in the sequestration, control, and hence prevention of cytotoxic effects from free-floating nontransferrin-bound iron. Given the importance of dietary iron in normal physiology, its potential to induce chronic toxicity, and recent discoveries in the regulation of human iron metabolism by hepcidin, this review will address the regulatory mechanisms of normal iron metabolism in mammals with emphasis on dietary exposure. It is the goal of this review that this information may provide in a concise format our current understanding of major pathways and mechanisms involved in mammalian iron metabolism, which is a basis for control of iron toxicity. Such a discussion is intended to facilitate the identification of deficiencies so that future metabolic or toxicological studies may be appropriately focused. A better knowledge of iron metabolism from normal to pathophysiological conditions will ultimately broaden the spectrum of the usefulness of this information in biomedical and toxicological sciences for improving and protecting human health.

Molecular diagnostic and pathogenesis of hereditary hemochromatosis

Hereditary hemochromatosis (HH) is an autosomal recessive disorder characterized by enhanced intestinal absorption of dietary iron. Without therapeutic intervention, iron overload leads to multiple organ damage such as liver cirrhosis, cardiomyopathy, diabetes, arthritis, hypogonadism and skin pigmentation. Most HH patients carry HFE mutant genotypes: homozygosity for p.Cys282Tyr or p.Cys282Tyr/p.His63Asp compound heterozygosity. In addition to HFE gene, mutations in the genes that encode hemojuvelin (HJV), hepcidin (HAMP), transferrin receptor 2 (TFR2) and ferroportin (SLC40A1) have been associated with regulation of iron homeostasis and development of HH. The aim of this review was to identify the main gene mutations involved in the pathogenesis of type 1, 2, 3 and 4 HH and their genetic testing indication. HFE testing for the two main mutations (p.Cys282Tyr and p.His63Asp) should be performed in all patients with primary iron overload and unexplained increased transferrin saturation and/or serum ferritin values. The evaluation of the HJV p.Gly320Val mutation must be the molecular test of choice in suspected patients with juvenile hemochromatosis with less than 30 years and cardiac or endocrine manifestations. In conclusion, HH is an example that genetic testing can, in addition to performing the differential diagnostic with secondary iron overload, lead to more adequate and faster treatment.

Hemojuvelin: a new link between obesity and iron homeostasis

The adipose tissue may play an active role in systemic iron regulation and this role may be determinant in obese patients. Indeed, we reported previously that hepcidin, the iron-regulatory hormone, is expressed in adipose tissue and its messenger RNA (mRNA) expression is increased in adipose tissue of morbidly obese patients. The objectives of this study were to characterize the status of hemojuvelin (HJV), another iron-regulatory protein, within the adipose tissue of morbidly obese patients. Since cell-associated HJV acts as a coreceptor of bone morphogenetic protein (BMP) to enhance hepcidin expression in liver cells, we investigated the possible involvement of this pathway in adipose tissue in regulating hepcidin expression. HJV expression was studied in adipose tissue of morbidly obese patients. Soluble HJV blood concentrations were assessed. Hepcidin regulation through BMP pathway was investigated in cultured adipocytes. HJV was expressed both at mRNA and protein levels in adipose tissue. Moreover, its mRNA expression was highly increased in adipose tissue of obese patients and correlated with mRNA hepcidin expression levels. Interestingly, HJV expressed by adipose tissue may be effective since cultured adipocytes increased their hepcidin expression when challenged with BMP2 through Smad effectors. In addition, blood concentrations of soluble HJV were significantly increased. In conclusion, adipose tissue may influence iron homeostasis in obese patients by expressing major iron-regulatory proteins and the BMP signaling pathway could be involved in regulating hepcidin expression in this tissue.

A child with hyperferritinemia: case report

Hereditary hyperferritinemia cataract syndrome (HHCS) is a rare condition caused by mutations in the gene coding for the light chain of ferritin; it does not lead to iron overload, but it is associated with the risk of developing a bilateral nuclear cataract also in childhood. On the contrary, a raise of serum ferritin levels is a common finding in pediatrics. We describe here a case of HHCS that offers some interesting clues for the daily practice. Our patient is a 6 year old Italian boy who came to our attention after some time of diagnostic uncertainties because of persistently high levels of ferritin with no apparent cause. We were guided to the suspect of this syndrome by the family history (5 members with various degrees of cataract developed in first infancy). High levels of serum ferritin and specific genetic testing (mutation A37C) confirmed the diagnosis. This case underlines the need of considering rare genetic syndromes, including hereditary hyperferritinemia cataract syndrome, in the differential diagnosis of raised serum ferritin in children and the importance of paying attention to family history in considering a patient with isolated raised levels of serum ferritin.

The hereditary hyperferritinemia-cataract syndrome: a family study

Ferritin is an acute-phase reactant that is elevated in the course of infectious, inflammatory, autoimmune, and oncological diseases and the hemophagocytic syndrome. In asymptomatic patients, isolated hyperferritinemia may be due to different causes depending on whether or not it is accompanied by iron overload. Hyperferritinemia values above 300 ng/ml and an excess of body iron levels may be indicative of hemochromatosis. However, if such values develop in the absence of iron overload, they may be secondary to hemochromatosis type 4a (ferroportin disease) or more often to hereditary hyperferritinemia-cataract syndrome (HHCS; Aguilar-Martinez et al., Am J Gastroenterol 100:1185-1194, 2005; Ferrante et al., Eur J Gastroenterol Hepatol 17:1247-1253, 2005). HHCS results from different mutations in the L-ferritin gene (FTL) on chromosome 19 (19q13.1), causing autosomal dominant transmission (Bertola et al., Curr Drug Targets Immune Endocr Metabol Disord 4:93-105, 2004). We present a child with HHCS due to the allelic variant c.-167C>T (C33T) in the iron-responsive element region of the FTL gene. When pediatricians encounter an asymptomatic patient with isolated hyperferritinemia in the absence of iron overload, they should consider the possibility of HHCS, especially if other members of the family have developed cataracts from a young age.

Iron regulatory proteins: from molecular mechanisms to drug development

Eukaryotic cells require iron for survival but, as an excess of poorly liganded iron can lead to the catalytic production of toxic radicals that can damage cell structures, regulatory mechanisms have been developed to maintain appropriate cell and body iron levels. The interactions of iron responsive elements (IREs) with iron regulatory proteins (IRPs) coordinately regulate the expression of the genes involved in iron uptake, use, storage, and export at the post-transcriptional level, and represent the main regulatory network controlling cell iron homeostasis. IRP1 and IRP2 are similar (but not identical) proteins with partially overlapping and complementary functions, and control cell iron metabolism by binding to IREs (i.e., conserved RNA stem-loops located in the untranslated regions of a dozen mRNAs directly or indirectly related to iron metabolism). The discovery of the presence of IREs in a number of other mRNAs has extended our knowledge of the influence of the IRE/IRP regulatory network to new metabolic pathways, and it has been recently learned that an increasing number of agents and physiopathological conditions impinge on the IRE/IRP system. This review focuses on recent findings concerning the IRP-mediated regulation of iron homeostasis, its alterations in disease, and new research directions to be explored in the near future.

Hemojuvelin and hepcidin genes sequencing in Brazilian patients with primary iron overload

BACKGROUND

most hereditary hemochromatosis (HH) patients are homozygous for the p.C282Y mutation in the HFE gene. Some studies reported that HH phenotypic expression could be modulated by genetic factors such as HJV and HAMP gene mutations.

AIMS

the aims of this study were to identify HJV and HAMP mutations and to analyze their impact on HH phenotype in non-p.C282Y homozygous individuals.

METHODS

Twenty-four Brazilian patients with primary iron overload and non-p.C282Y homozygous genotype (transferrin saturation >50% in women and >60% in men and absence of secondary causes) were selected. Subsequent bidirectional sequencing of the HJV and HAMP exons was performed.

RESULTS

sequencing revealed a substitution in heterozygosis, c.929C > G, which corresponds to p.A310G polymorphism in HJV exon 4 (rs7540883). In the same gene, in another individual, an IVS1-36C > G intronic variant was detected in heterozygosis. In the HAMP gene, an IVS3 + 42G > A intronic variant was identified. There were six (25.0%) patients carrying a heterozygous genotype for the HFE p.C282Y and nine (37.5%) patients carrying a heterozygous genotype for the HFE p.H63D.

CONCLUSION

HJV p.A310G polymorphism and two intronic variants were found, but none of these alterations were associated with digenic inheritance with the HFE gene. Our data indicate that HJV and HAMP functional mutations are not frequent in these patients.

HFE gene mutations in patients with primary iron overload: is there a significant improvement in molecular diagnosis yield with HFE sequencing?

Rare HFE variants have been shown to be associated with hereditary hemochromatosis (HH), an iron overload disease. The low frequency of the HFE p.C282Y mutation in HH-affected Brazilian patients may suggest that other HFE-related mutations may also be implicated in the pathogenesis of HH in this population. The main aim was to screen for new HFE mutations in Brazilian individuals with primary iron overload and to investigate their relationship with HH. Fifty Brazilian patients with primary iron overload (transferrin saturation>50% in females and 60% in males) were selected. Subsequent bidirectional sequencing for each HFE exon was performed. The effect of HFE mutations on protein structure were analyzed by molecular dynamics simulation and free binding energy calculations. p.C282Y in homozygosis or in heterozygosis with p.H63D were the most frequent genotypic combinations associated with HH in our sample population (present in 17 individuals, 34%). Thirty-six (72.0%) out of the 50 individuals presented at least one HFE mutation. The most frequent genotype associated with HH was the homozygous p.C282Y mutation (n=11, 22.0%). One novel mutation (p.V256I) was indentified in heterozygosis with the p.H63D mutation. In silico modeling analysis of protein behavior indicated that the p.V256I mutation does not reduce the binding affinity between HFE and β2-microglobulin (β2M) in the same way the p.C282Y mutation does compared with the native HFE protein. In conclusion, screening of HFE through direct sequencing, as compared to p.C282Y/p.H63D genotyping, was not able to increase the molecular diagnosis yield of HH. The novel p.V256I mutation could not be implicated in the molecular basis of the HH phenotype, although its role cannot be completely excluded in HH-phenotype development. Our molecular modeling analysis can help in the analysis of novel, previously undescribed, HFE mutations.

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.

Serum ferritin: Past, present and future

BACKGROUND

Serum ferritin was discovered in the 1930s, and was developed as a clinical test in the 1970s. Many diseases are associated with iron overload or iron deficiency. Serum ferritin is widely used in diagnosing and monitoring these diseases.

SCOPE OF REVIEW

In this chapter, we discuss the role of serum ferritin in physiological and pathological processes and its use as a clinical tool.

MAJOR CONCLUSIONS

Although many aspects of the fundamental biology of serum ferritin remain surprisingly unclear, a growing number of roles have been attributed to extracellular ferritin, including newly described roles in iron delivery, angiogenesis, inflammation, immunity, signaling and cancer.

GENERAL SIGNIFICANCE

Serum ferritin remains a clinically useful tool. Further studies on the biology of this protein may provide new biological insights.

Serum ferritin is derived primarily from macrophages through a nonclassical secretory pathway

The serum ferritin concentration is a clinical parameter measured widely for the differential diagnosis of anemia. Its levels increase with elevations of tissue iron stores and with inflammation, but studies on cellular sources of serum ferritin as well as its subunit composition, degree of iron loading and glycosylation have given rise to conflicting results. To gain further understanding of serum ferritin, we have used traditional and modern methodologies to characterize mouse serum ferritin. We find that both splenic macrophages and proximal tubule cells of the kidney are possible cellular sources for serum ferritin and that serum ferritin is secreted by cells rather than being the product of a cytosolic leak from damaged cells. Mouse serum ferritin is composed mostly of L-subunits, whereas it contains few H-subunits and iron content is low. L-subunits of serum ferritin are frequently truncated at the C-terminus, giving rise to a characteristic 17-kD band that has been previously observed in lysosomal ferritin. Taken together with the fact that mouse serum ferritin is not detectably glycosylated, we propose that mouse serum ferritin is secreted through the nonclassical lysosomal secretory pathway.

A new missense mutation in the L ferritin coding sequence associated with elevated levels of glycosylated ferritin in serum and absence of iron overload

BACKGROUND

Elevated serum ferritin levels are frequently encountered in clinical situations and once iron overload or inflammation has been ruled out, many cases remain unexplained. Genetic causes of hyperferritinemia associated to early cataract include mutations in the iron responsive element in the 5' untranslated region of the L ferritin mRNA, responsible for the hereditary hyperferritinemia cataract syndrome.

DESIGN AND METHODS

We studied 91 probands with hyperferritinemia comprising 25 family cases belonging to families with at least two cases of unexplained hyperferritinemia, and 66 isolated cases. In the families, we also analyzed 30 relatives. Hyperferritinemia was considered as unexplained when transferrin saturation was below 45% and/or serum iron below 25 mumol/L and/or no tissue iron excess was detected, when inflammation had been ruled out and when iron responsive element mutation was absent. We carried out sequencing analysis of the FTL gene coding the L ferritin.

RESULTS

A novel heterozygous p.Thr30Ile mutation in the NH2 terminus of L ferritin subunit was identified in 17 probands out of the cohort. The mutation was shown to cosegregate with hyperferritinemia in all the 10 families studied. No obvious clinical symptom was found associated with the presence of the mutation. This unique mutation is associated with an unusually high percentage of ferritin glycosylation.

CONCLUSIONS

This missense mutation of FTL represents a new cause of genetic hyperferritinemia without iron overload. We hypothesized that the mutation increases the efficacy of L ferritin secretion by increasing the hydrophobicity of the N terminal "A" alpha helix.

Iron-regulatory proteins: molecular biology and pathophysiological implications

Iron is required for key cellular functions, and there is a strong link between iron metabolism and important metabolic processes, such as cell growth, apoptosis and inflammation. Diseases that are directly or indirectly related to iron metabolism represent major health problems. Iron-regulatory proteins (IRPs) 1 and 2 are key controllers of vertebrate iron metabolism and post-transcriptionally regulate expression of the major iron homeostasis genes. Here we discuss how dysregulation of the IRP system can result from both iron-related and unrelated effectors and explain how this can have important pathological consequences in several human disorders.

Iron overload syndromes and the liver

Iron can accumulate in the liver in a variety of conditions, including congenital, systemic iron-loading conditions (hereditary hemochromatosis), conditions associated with systemic macrophage iron accumulation (transfusions, hemolytic conditions, anemia of chronic disease, etc), in some hepatitidies (hepatitis C, alcoholic liver disease, porphyria cutanea tarda), and liver-specific iron accumulation of uncertain pathogenesis in cirrhosis. The anatomic pathologist will be faced with the task of determining whether iron accumulation in the liver is significant and, if so, the nature of the disease that lead to the accumulation (ie diagnosis). The tools available to the pathologist include (most importantly) histologic examination with iron stain, quantitative iron analysis, clinical history, laboratory iron tests (serum iron and iron-binding capacity, serum ferritin) and germline genetic analysis for mutations in genes known to be associated with hemochromatosis (HFE, ferroportin, hepcidin, hemojuvelin, transferrin receptor-2). This article provides an overview of the above.

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 and clinical heterogeneity of ferroportin disease

Ferroportin is encoded by the SLC40A1 gene and mediates iron export from cells by interacting with hepcidin. SLC40A1 gene mutations are associated with an autosomal type of genetic iron overload described as haemochromatosis type 4, or HFE4 (Online Mendelian Inheritance in Man number 606069), or ferroportin disease. We report three families with this condition caused by novel SLC40A1 mutations. Denaturing high-performance liquid chromatography was employed to scan for the SLC40A1 gene. A D181V (A846T) mutation in exon 6 of the ferroportin gene was detected in the affected members of an Italian family and shown to have a de novo origin in a maternal germinal line. This mutation was associated with both parenchymal and reticuloendothelial iron overload in the liver, and with reduced urinary hepcidin excretion. A G80V (G543T) mutation in exon 3 was found in the affected members of an Italian family with autosomal hyperferritinaemia,. Finally, a G267D (G1104A) mutation was identified in exon 7 in a family of Chinese descent whose members presented with isolated hyperferritinaemia. Ferroportin disease represents a protean genetic condition in which the different SLC40A1 mutations appear to be responsible for phenotypic variability. This condition should be considered not only in families with autosomal iron overload or hyperferritinaemia, but also in cases of unexplained hyperferritinaemia.

Hémochromatose HFE : approche pathogénique et diagnostique

HFE hemochromatosis is the most frequent genetic iron overload disease. It is linked to the C282Y mutation of the HFE protein, protein encoded by the HFE gene, which is located on chromosome 6. The mechanisms accounting for iron excess are not only digestive hyperabsorption of iron but also excessive recycling of macrophagic iron coming from erythrophagocytosis and secreted into the blood. Both mechanisms are linked to an HFE-related hepatic failure in producing hepcidin, a key hormone of body iron regulation. The marked phenotypic variability of C282Y homozygosity expression is likely related to both genetic and environmental factors. The HFE gene discovery has rendered non invasive the positive diagnostic of HFE hemochromatosis, which is now based first on an increased level of plasma transferrin saturation leading to the request of the HFE mutation. Then, hepatic MRI is a reliable method to quantify iron overload. The HFE gene discovery has also paved the road of an enlarged field of differential diagnoses corresponding to novel entities of non-HFE related genetic iron overload syndromes.