The lens in hereditary hyperferritinaemia cataract syndrome contains crystalline deposits of L-ferritin

Through the Cat-Map Gateway: A Brief History of Cataract Genetics

Clouding of the transparent eye lens, or cataract(s), is a leading cause of visual impairment that requires surgical replacement with a synthetic intraocular lens to effectively restore clear vision. Most frequently, cataract is acquired with aging as a multifactorial or complex trait. Cataract may also be inherited as a classic Mendelian trait-often with an early or pediatric onset-with or without other ocular and/or systemic features. Since the early 1990s, over 85 genes and loci have been genetically associated with inherited and/or age-related forms of cataract. While many of these underlying genes-including those for lens crystallins, connexins, and transcription factors-recapitulate signature features of lens development and differentiation, an increasing cohort of unpredicted genes, including those involved in cell-signaling, membrane remodeling, and autophagy, has emerged-providing new insights regarding lens homeostasis and aging. This review provides a brief history of gene discovery for inherited and age-related forms of cataract compiled in the Cat-Map database and highlights potential gene-based therapeutic approaches to delay, reverse, or even prevent cataract formation that may help to reduce the increasing demand for cataract surgery.

Genotypic-Phenotypic Correlations of Hereditary Hyperferritinemia-Cataract Syndrome: Case Series of Three Brazilian Families

Hereditary hyperferritinemia-cataract syndrome (HHCS) is a rare, frequently misdiagnosed, autosomal dominant disease caused by mutations in the FTL gene. It causes bilateral pediatric cataract and hyperferritinemia without iron overload. The objective of this case series, describing three Brazilian families, is to increase awareness of HHCS, as well as to discuss possible phenotypic interactions with concurrent mutations in HFE, the gene associated with autosomal recessive inheritance hereditary hemochromatosis. Whole-exome sequencing was performed in eight individuals with HHCS from three different families, as well as one unaffected member from each family for trio analysis-a total of eleven individuals. Ophthalmological and clinical genetic evaluations were conducted. The likely pathogenic variant c.-157G>A in FTL was found in all affected individuals. They presented slowly progressing bilateral cataract symptoms before the age of 14, with a phenotype of varied bilateral diffuse opacities. Hyperferritinemia was present in all affected members, varying from 971 ng/mL to 4899 ng/mL. There were two affected individuals with one concurrent pathogenic variant in HFE (c.187C>G, p.H63D), who were also the ones with the highest values of serum ferritin in our cohort. Few publications describe individuals with pathogenic mutations in both FTL and HFE genes, and further studies are needed to assess possible phenotypic interactions causing higher values of hyperferritinemia.

Ferritin L-subunit gene mutation and hereditary hyperferritinaemia cataract syndrome (HHCS): a case report and literature review

ABSTRACTObjectives: Hereditary hyperferritinaemia cataract syndrome (HHCS) is an autosomal dominant disease characterized by high serum ferritin levels and juvenile bilateral cataracts. It is often caused by mutations in the iron response element (IRE) of the ferritin L-subunit (FTL) gene. Here, we report a 73-year-old woman who presented to clinic with persistently elevated serum ferritin and family history of juvenile bilateral cataracts in four generations.Methods: Exome sequencing was used to identify the mutation of the FTL gene. Moreover, Sanger sequencing was performed to validate the mutation in the proband. We also reviewed the FLT gene mutations in published HHCS cases to provide experience for accurate diagnosis of similar patients.Results: A heterozygous mutation at position +33 (c.-167C > T, chr19:49468598) of the FTL gene was identified in the patient.Discussion: HHCS should be considered in the differential diagnosis of hyperferritinemia, especially in the presence of normal serum iron concentration and transferrin saturation.Conclusion: For patients with unexplained hyperferritinemia and bilateral cataracts who have experienced early vision loss, the establishment of genetic counseling is essential to diagnose other family members who are at risk in time.Abbreviations: FTL: ferritin L-subunit; HHCS: hereditary hyperferritinaemia cataract syndrome; IDT: integrated DNA technologies; IRE: iron response element; IRP: iron regulatory proteins; MRI: magnetic resonance imaging; SNV: single nucleotide variant; UTR: untranslated region.

Hereditary hyperferritinaemia-cataract syndrome (HHCS) – an underestimated condition: ferritin light chain variant spectrum in German families

Background

In hereditary hyperferritinaemia-cataract syndrome (HHCS), single nucleic acid alterations in the ferritin light chain (L-ferritin) iron response element (IRE) constitutively derepress ferritin synthesis, resulting in hyperferritinaemia, L-ferritin deposits in the lens of the eye and early bilateral cataract onset.

Methods

In this study, six German families with putative HHCS were analysed. Clinical diagnosis of HHCS was based on medical history, evaluation of ferritin serum levels, transferrin saturation and clinical ophthalmological examination. Diagnosis was confirmed by polymerase chain reaction (PCR)-based DNA sequencing of the L-ferritin IRE.

Results

Genetic analysis of the L-ferritin IRE revealed relevant single nucleic acid alterations in each of the affected families. Variants c.-168G > A, c.-168G > U and c.-167C > U were located in the C-bulge region; and variants c.-161C > U and c.-157G > A were located in the hexanucleotide loop of the L-ferritin IRE.

Conclusions

Family history of hyperferritinaemia and juvenile cataracts are strong indicators of HHCS. Genetic analysis of the L-ferritin IRE is a straightforward procedure to confirm the diagnosis. Accurate diagnosis of hyperferritinaemia can avoid unnecessary treatment by venesection, and focus attention on early cataract detection in offspring at risk.

L-Ferritin: One Gene, Five Diseases; from Hereditary Hyperferritinemia to Hypoferritinemia-Report of New Cases

Ferritin is a multimeric protein composed of light (L-ferritin) and heavy (H-ferritin) subunits that binds and stores iron inside the cell. A variety of mutations have been reported in the L-ferritin subunit gene (FTL gene) that cause the following five diseases: (1) hereditary hyperferritinemia with cataract syndrome (HHCS), (2) neuroferritinopathy, a subtype of neurodegeneration with brain iron accumulation (NBIA), (3) benign hyperferritinemia, (4) L-ferritin deficiency with autosomal dominant inheritance, and (5) L-ferritin deficiency with autosomal recessive inheritance. Defects in the FTL gene lead to abnormally high levels of serum ferritin (hyperferritinemia) in HHCS and benign hyperferritinemia, while low levels (hypoferritinemia) are present in neuroferritinopathy and in autosomal dominant and recessive L-ferritin deficiency. Iron disturbances as well as neuromuscular and cognitive deficits are present in some, but not all, of these diseases. Here, we identified two novel FTL variants that cause dominant L-ferritin deficiency and HHCS (c.375+2T > A and 36_42delCAACAGT, respectively), and one previously reported variant (Met1Val) that causes dominant L-ferritin deficiency. Globally, genetic changes in the FTL gene are responsible for multiple phenotypes and an accurate diagnosis is useful for appropriate treatment. To help in this goal, we included a diagnostic algorithm for the detection of diseases caused by defects in FTL gene.

Hereditary Hyperferritinemia Cataract Syndrome: Ocular, Genetic, and Biochemical Findings

Purpose

To describe the cataract morphology and genetic and biochemical findings in a four-generation family with hereditary hyperferritinemia cataract syndrome (HHCS).

Methods

Family members of the proband with HHCS were investigated. DNA sequencing was carried out to identify the iron responsive element (IRE) of the L-ferritin gene in affected and non-affected family members. Molecular modeling allowed prediction of the structure of the mutant IRE in affected cases. Serum ferritin and transferrin saturation were determined using standard methods. All family members underwent slit lamp examination by an ophthalmologist to document presence of cataract or lens status. Cataract morphology was documented where present.

Results

This family with HHCS had the genetic heterozygous mutation G32C in the IRE of the L-ferritin mRNA. Lens opacities were detectable in young members of the family, and morphology of cataracts was consistent with previous reports. Biochemical testing demonstrated high serum ferritin levels in affected individuals.

Conclusions

The morphology of cataracts in HHCS seems to be similar in all cases. In the heterozygous G32C mutation, the age at onset of cataracts is very early. Greater awaeness of this condition among ophthalmologists will lead to effective family counseling of those affected, by genetic testing or simple biochemical tests. Serum ferritin levels can be effectively used to screen for this condition in suspected families.

Functional characterization of a novel non-coding mutation "Ghent +49A > G" in the iron-responsive element of L-ferritin causing hereditary hyperferritinaemia-cataract syndrome

Hereditary hyperferritinaemia-cataract syndrome (HHCS) is a rare disorder usually caused by heterozygous mutations in the iron-responsive element (IRE) in the 5′ untranslated region (5′UTR) of the L-ferritin gene (FTL), disturbing the binding of iron regulatory proteins (IRPs) and the post-transcriptional regulation of ferritin expression. Here, the proband of a consanguineous family displayed moderate bilateral cataracts and elevated serum ferritin in the absence of iron overload. The parents and siblings showed variable degrees of mild bilateral cataracts combined with elevated levels of circulating ferritin. Sequencing of FTL identified a novel 5′UTR mutation c.-151A > G, also named “Ghent +49A > G”. The zygosity of the mutation, occurring in homozygous and heterozygous state in the proband and other affected family members respectively, correlated well with severity of ophthalmological and hematological manifestations. The substitution is expected to impair the secondary structure of the upper IRE stem. Functional characterization of +49A > G by electrophoretic mobility shift assays demonstrated a reduced binding affinity for IRP1 compared to the wild-type IRE of FTL. Overall, we have expanded the repertoire of deleterious biallelic FTL IRE mutations in HHCS with this novel +49A > G mutation, the zygosity of which correlated well with the disease expression.

Ferritin light chain gene mutation in a large Australian family with hereditary hyperferritinemia-cataract syndrome

BACKGROUND

Hereditary hyperferritinemia-cataract syndrome (HHCS) is an autosomal dominant Mendelian disorder characterized by early onset cataracts and elevated levels of serum ferritin in the absence of iron overload. Numerous mutations associated with the development of HHCS have been reported in the 5' non-coding region of the ferritin light chain (FTL) gene in family studies. We present an FTL mutation in an Australian family with 10 HHCS-affected members spanning three generations.

MATERIALS AND METHODS

Blood and saliva samples were collected from affected and unaffected family members and DNA was extracted using commercially available kits (Qiagen). The complete sequencing of the iron-responsive element (IRE) of the FTL gene was analyzed using bi-directional genomic sequencing.

RESULTS

A heterozygous single nucleotide substitution (c.-167 C>T) was identified in the proband and five affected family members (logarithm of the odds score [Z] = 3.61, recombination distance [θ = 0]). All affected individuals had previously been found to have high ferritin levels and early onset cataracts.

CONCLUSION

This is the first Australian report of the c.-167 C>T mutation in a large family with multiple affected individuals. This finding raises the possibility that identification of HHCS mutations may be an effective means of disease detection and may aid in facilitating appropriate genetic counseling.

Brain iron homeostasis: from molecular mechanisms to clinical significance and therapeutic opportunities

Iron has emerged as a significant cause of neurotoxicity in several neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), sporadic Creutzfeldt-Jakob disease (sCJD), and others. In some cases, the underlying cause of iron mis-metabolism is known, while in others, our understanding is, at best, incomplete. Recent evidence implicating key proteins involved in the pathogenesis of AD, PD, and sCJD in cellular iron metabolism suggests that imbalance of brain iron homeostasis associated with these disorders is a direct consequence of disease pathogenesis. A complete understanding of the molecular events leading to this phenotype is lacking partly because of the complex regulation of iron homeostasis within the brain. Since systemic organs and the brain share several iron regulatory mechanisms and iron-modulating proteins, dysfunction of a specific pathway or selective absence of iron-modulating protein(s) in systemic organs has provided important insights into the maintenance of iron homeostasis within the brain. Here, we review recent information on the regulation of iron uptake and utilization in systemic organs and within the complex environment of the brain, with particular emphasis on the underlying mechanisms leading to brain iron mis-metabolism in specific neurodegenerative conditions. Mouse models that have been instrumental in understanding systemic and brain disorders associated with iron mis-metabolism are also described, followed by current therapeutic strategies which are aimed at restoring brain iron homeostasis in different neurodegenerative conditions. We conclude by highlighting important gaps in our understanding of brain iron metabolism and mis-metabolism, particularly in the context of neurodegenerative disorders.

Noncoding variation of the gene for ferritin light chain in hereditary and age-related cataract

PURPOSE

Cataract is a clinically and genetically heterogeneous disorder of the ocular lens and an important cause of visual impairment. The aim of this study was to map and identify the gene underlying autosomal dominant cataract segregating in a four-generation family, determine the lens expression profile of the identified gene, and test for its association with age-related cataract in a case-control cohort.

METHODS

Genomic DNA was prepared from blood leukocytes, and genotyping was performed by means of single-nucleotide polymorphism markers and microsatellite markers. Linkage analyses were performed using the GeneHunter and MLINK programs, and mutation detection was achieved by dideoxy cycle sequencing. Lens expression studies were performed using reverse-transcription polymerase chain reaction (RT-PCR) and in situ hybridization.

RESULTS

Genome-wide linkage analysis with single nucleotide polymorphism markers in the family identified a likely disease-haplotype interval on chromosome 19q (rs888861-[~17Mb]-rs8111640) that encompassed the microsatellite marker D19S879 (logarithm of the odds score [Z]=2.03, recombination distance [θ]=0). Mutation profiling of positional-candidate genes detected a heterozygous, noncoding G-to-T transversion (c.-168G>T) located in the iron response element (IRE) of the gene coding for ferritin light chain (FTL) that cosegregated with cataract in the family. Serum ferritin levels were found to be abnormally elevated (~fourfold), without evidence of iron overload, in an affected family member; this was consistent with a diagnosis of hereditary hyperferritinemia-cataract syndrome. No sequence variations located within the IRE were detected in a cohort of 197 cases with age-related cataract and 102 controls with clear lenses. Expression studies of human FTL, and its mouse counterpart FTL1, in the lens detected RT-PCR amplicons containing full-length protein-coding regions, and strong in situ localization of FTL1 transcripts to the lens equatorial epithelium and peripheral cortex.

CONCLUSIONS

The data are consistent with robust transcription of FTL in the lens, and suggest that whereas variations clustered in the IRE of the FTL gene are directly associated with hereditary hyperferritinemia-cataract syndrome, such IRE variations are unlikely to play a significant role in the genetic etiology of age-related cataract.

Crystalline cataract caused by a heterozygous missense mutation in γD-crystallin (CRYGD)

PURPOSE

To describe phenotypic characteristics of two pedigrees manifesting early onset crystalline cataract with mutations in the γD-crystallin gene (CRYGD).

METHODS

A detailed medical history was obtained from two Caucasian pedigrees manifesting autosomal dominant congenital cataracts. Genomic DNA was extracted from saliva (DNA Genotek). Single Nucleotide Polymorphism (SNP) based genome analysis of the larger pedigree revealed linkage to an 8.2 MB region on chromosome 2q33-q35 which encompassed the crystallin-gamma gene cluster (CRYG). Exons and flanking introns of CRYGA, CRYGB, CRYGC and CRYGD were amplified and sequenced to identify disease-causing mutations.

RESULTS

A morphologically unique cataract with extensive refractile "crystals" scattered throughout the nucleus and perinuclear cortex was found in the probands from both pedigrees. A heterozygous C→A mutation was identified at position 109 of the coding sequence (R36S of the processed protein) in exon 2 of CRYGD and this missense mutation was found to cosegregate with the disease in the larger family; this mutation was then identified in affected individuals of pedigree 2 as well.

CONCLUSIONS

The heterozygous 109C→A CRYGD missense mutation is associated with a distinct crystalline cataract in two US Caucasian pedigrees. This confirms crystalline cataract formation with this mutation, as previously reported in sporadic childhood case from the Czech Republic and in members of a Chinese family.

Hyperferritinemia without iron overload in patients with bilateral cataracts: a case series

Introduction

Hepatologists and internists often encounter patients with unexplained high serum ferritin concentration. After exclusion of hereditary hemochromatosis and hemosiderosis, rare disorders like hereditary hyperferritinemia cataract syndrome should be considered in the differential diagnosis. This autosomal dominant syndrome, that typically presents with juvenile bilateral cataracts, was first described in 1995 and has an increasing number of recognized molecular defects within a regulatory region of the L-ferritin gene (FTL).

Case presentation

Two patients (32 and 49-year-old Caucasian men) from our ambulatory clinic were suspected as having this syndrome and a genetic analysis was performed. In both patients, sequencing of the FTL 5' region showed previously described mutations within the iron responsive element (FTL c.33 C > A and FTL c.32G > C).

Conclusion

Hereditary hyperferritinemia cataract syndrome should be considered in all patients with unexplained hyperferritinemia without signs of iron overload, particularly those with juvenile bilateral cataracts. Liver biopsy and phlebotomy should be avoided in this disorder.

Hereditary hyperferritinemia-cataract syndrome in two large multigenerational American families

PURPOSE

Hereditary hyperferritinemia cataract syndrome (HHCS), an autosomal-dominant disorder characterized by hyperferritinemia and bilateral cataracts, is caused by mutations in the iron-responsive element of the ferritin light chain (FTL) gene. The purpose of this study is to describe the genotypic and phenotypic manifestations of HHCS observed in 2 large sets of unrelated American families.

METHODS

Forty-five patients were recruited from 2 unrelated families. Each underwent ophthalmological and general physical evaluation as well as laboratory testing of serum ferritin, iron, transferrin saturation, and total iron binding capacity. Serum DNA was evaluated for mutations by DNA amplification and sequencing of the FTL gene.

RESULTS

Numerous cortical and nuclear white opacities in a stellate pattern occurred in 22 affected individuals and were the only clinical manifestation of HHCS. Of the 22, 16 (73%) demonstrated >1.00 D of astigmatism. Genetic analysis revealed mutation G32A in Pedigree 1 and mutation G32T in Pedigree 2, both heterozygous and located in the iron-responsive element of the ferritin light chain mRNA. Serum ferritin levels of affected subjects ranged from 555 to 2,453 μg/L (normal range, 24-336 μg/L male, 11-307 μg/L female), with greater ferritin levels and more severe cataracts associated with mutation G32A.

CONCLUSIONS

Most clinical and genetic findings from these families are consistent with previous reports of HHCS. Astigmatism, previously not associated with HHCS, was present in the majority. Ferritin levels and age of cataract surgery varied among subjects with both FTL gene mutations, suggesting that phenotypic variability is modulated by other genetic or environmental factors.

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.

Hepcidin levels in hereditary hyperferritinemia: Insights into the iron-sensing mechanism in hepatocytes

AIM: To study the role of hepcidin in hereditary hyperferritinemia cataract syndrome (HHCS).

METHODS: Six patients from two families with HHCS, confirmed by genetic analysis showing A to G mutation at position +40 in the L-ferritin gene, were recruited to undergo serum hepcidin and prohepcidin measurements using radioimmunoassay and enzyme linked immunoassay, respectively, and measurements were compared with levels in serum from 25 healthy volunteers (14 females), mean age 36 ± 11.9 years.

RESULTS: The serum hepcidin and prohepcidin levels in patients with HHCS were 19.1 ± 18.6 and 187 ± 120.9 ng/mL, respectively. Serum ferritin was 1716.3 ± 376 μg/L. Liver biopsy in one patient did not show any evidence of iron overload. Serum hepcidin and prohepcidin values in healthy controls (HCs) were 15.30 ± 15.71 and 236.88 ± 83.68 ng/mL, respectively, while serum ferritin was 110 ± 128.08 μg/L. There was no statistical difference in serum hepcidin level between the two cohorts (19.1 ± 18.6 ng/mL vs 15.30 ± 15.71 ng/mL, P = 0.612) using two-tailed t-test.

CONCLUSION: Serum hepcidin levels in HHCS patients is similar to that in HCs. Our study suggests that circulating ferritin is not a factor influencing hepcidin synthesis and does not have a role in the iron-sensing mechanism in hepatocytes.

Cytosolic and mitochondrial ferritins in the regulation of cellular iron homeostasis and oxidative damage

BACKGROUND

Ferritin structure is designed to maintain large amounts of iron in a compact and bioavailable form in solution. All ferritins induce fast Fe(II) oxidation in a reaction catalyzed by a ferroxidase center that consumes Fe(II) and peroxides, the reagents that produce toxic free radicals in the Fenton reaction, and thus have anti-oxidant effects. Cytosolic ferritins are composed of the H- and L-chains, whose expression are regulated by iron at a post-transcriptional level and by oxidative stress at a transcriptional level. The regulation of mitochondrial ferritin expression is presently unclear.

SCOPE OF REVIEW

The scope of the review is to update recent progress regarding the role of ferritins in the regulation of cellular iron and in the response to oxidative stress with particular attention paid to the new roles described for cytosolic ferritins, to genetic disorders caused by mutations of the ferritin L-chain, and new findings on mitochondrial ferritin.

MAJOR CONCLUSIONS

The new data on the adult conditional knockout (KO) mice for the H-chain and on the hereditary ferritinopathies with mutations that reduce ferritin functionality strongly indicate that the major role of ferritins is to protect from the oxidative damage caused by iron deregulation. In addition, the study of mitochondrial ferritin, which is not iron-regulated, indicates that it participates in the protection against oxidative damage, particularly in cells with high oxidative activity.

GENERAL SIGNIFICANCE

Ferritins have a central role in the protection against oxidative damage, but they are also involved in non-iron-dependent processes.

The case of a 1-year-old girl with hereditary hyperferritinemia cataract syndrome

Hereditary hyperferritinemia cataract syndrome (HHCS) is an autosomal dominant disorder characterized by high serum ferritin levels in the absence of iron overload accompanied by early onset of bilateral cataracts. The authors report the case of HHCS in a 1-year-old girl in a family of German origin. Routine blood examination revealed serum ferritin levels up to 2530 microg/L. Slit-lamp examination showed bilateral cataracts. HHCS should be considered in cases of high serum ferritin level and bilateral cataracts, which can even occur in pediatric patients. A liver biopsy and bone marrow aspiration are unnecessary diagnostic procedures in cases of HHCS and repeated phlebotomies are harmful.

Iron homeostasis and eye disease

BACKGROUND

Iron is necessary for life, but excess iron can be toxic to tissues. Iron is thought to damage tissues primarily by generating oxygen free radicals through the Fenton reaction.

METHODS

We present an overview of the evidence supporting iron's potential contribution to a broad range of eye disease using an anatomical approach.

RESULTS

Iron can be visualized in the cornea as iron lines in the normal aging cornea as well as in diseases like keratoconus and pterygium. In the lens, we present the evidence for the role of oxidative damage in cataractogenesis. Also, we review the evidence that iron may play a role in the pathogenesis of the retinal disease age-related macular degeneration. Although currently there is no direct link between excess iron and development of optic neuropathies, ferrous iron's ability to form highly reactive oxygen species may play a role in optic nerve pathology. Lastly, we discuss recent advances in prevention and therapeutics for eye disease with antioxidants and iron chelators.

GENERAL SIGNIFICANCE

Iron homeostasis is important for ocular health.

Hereditary hyperferritinemia cataract syndrome in three unrelated families of western Greek origin caused by the C39 > G mutation of L-ferritin IRE

Hereditary hyperferritinemia-cataract syndrome (HHCS) is a well-characterized autosomal dominant disease caused by mutations in the iron responsive element (IRE) of ferritin L-chain (FTL) mRNA. Mutations in the IRE result in reduced binding of the trans-acting iron regulatory proteins (IRPs) and hence in upregulation of ferritin L-chain synthesis. The disease is characterized by increased L-ferritin in serum and tissues and early onset of bilateral cataracts. Iron metabolism is normal, and there is no tissue iron overload. At least 25 nucleotide substitutions and deletions in the L-ferritin IRE have been described in families with HHCS, originating from diverse European, Australian and North American populations. We studied the molecular pathogenesis of HHCS in three unrelated kinderships of western Greek origin, with 19 affected members. We identified a relatively rare C39G mutation located in the hexanucleotide loop of L-ferritin IRE. Computational analysis of mRNA folding of mutant FTL IRE predicted that the C39 > G mutation leads to a rearrangement of base pairing in this critical region, which is likely to modify the IRP binding affinity. All subjects with HHCS were heterozygotes for the same C39G mutation. Clinical and laboratory phenotypes were described. Moreover, there was evidence of an association between this FTL IRE stem-loop mutation and very high ferritin levels. Our findings broaden the list of populations where HHCS has been described.

Hereditary hyperferritinaemia-cataract syndrome: a challenging diagnosis for the hepatogastroenterologist

Hereditary hyperferritinaemia-cataract syndrome (HHCS) is a relatively rare disorder with an autosomal dominant trait. It can be caused by various mutations within the iron responsive element (IRE) of the L-ferritin gene. These mutations result in an increased translation of L-ferritin mRNA and consequently the accumulation of L-ferritin in different fluids and tissues. HHCS patients present with an isolated hyperferritinaemia in the absence of any sign of iron overload. Early onset bilateral cataract, probably due to accumulation of ferritin crystals in the lens, is the only presenting clinical manifestation. Internists, especially gastrohepatologists, should be aware of this syndrome and differentiate it from haemochromatosis which is much more frequent, in order to avoid unnecessary imaging procedures, liver biopsies and an eventual venesection therapy, which will only lead to microcytic anaemia. In the present paper we report the first cases with HHCS diagnosed in Belgium. At diagnosis, the seven known affected members of three different families had ferritin levels between 603 and 3432 microg/l (normal < 150 microg/l), and this in combination with normal iron and transferrin values. All of them were known with early-onset bilateral cataract and our postulated diagnosis of HHCS was confirmed after genetic sequencing of the L-ferritin gene, which showed a C39U point mutation in the first family, and an A40G point mutation in the IRE loop segment in the two other families. The other investigated members of the three families had normal ferritin values, no history of early-onset cataract and genetic analyses could not reveal a mutation in the IRE of their L-ferritin gene. In current clinical practice, gastroenterologists should remember that elevated ferritin levels in the absence of documented iron overload is not haemochromatosis.

Identification of a novel mutation in theL-ferritin IRE leading to hereditary hyperferritinemia-cataract syndrome

The hereditary hyperferritinemia-cataract syndrome (HHCS) is a rare autosomal dominant disorder due to mutations affecting the iron responsive element (IRE) of the L-ferritin mRNA. We report on a new mutation, 43G > A, in the loop of the stem-loop structure of the L-ferritin IRE in the proband of a pedigree with early-onset bilateral cataracts.

Cataract formation in a strain of rats selected for high oxidative stress

The primary purpose of this study was to define the clinical and morphological features of cataractogenesis in the OXYS strain of rats that generate excess reactive oxygen species. Rats were sequentially examined from birth to the development of mature cataracts with slit lamp biomicroscopy. Morphology of selected stages of cataract development was studied using light and transmission electron microscopy (TEM), immunohistochemical localization of the lipid peroxidation product 4-hydroxynonenal (HNE) and fluorescent antibody labeling for DNA oxidation products. Lenses from age-matched normal rats were used as controls. OXYS rats developed cataracts as young as two weeks of age with progression to maturity by 1 year. Clinically, cataracts appeared initially either as nuclear or sub-capsular cortical changes and progressed to pronounced nuclear cataracts within months. TEM confirmed the light microscopic impression of region-specific alterations in both fiber cell cytoplasmic protein matrix and membrane structure. The outer adult nuclear region showed extensive cellular damage similar to osmotic cataracts, which is consistent with the postulated high uptake of glucose in the OXYS strain. The adult and outer fetal nuclear cells displayed several types of focal damage. The inner fetal and embryonic nuclear cells demonstrated textured cytoplasm, suggesting protein degradation or redistribution. Staining for HNE was increased in epithelium, cortex and nucleus compared to control lenses. Fluorescent antibody probes demonstrated increased levels of DNA oxidation products in OXYS rat lenses compared to age-matched controls. Fourier analysis of nuclear cytoplasm revealed significant components with corresponding sizes greater than 100 nm and, using a new theoretical approach, the texturing of the cytoplasm was shown to be sufficient to cause opacification of the nucleus. The OXYS rat appears to be an ideal model for oxidative stress cataractogenesis. The potential oxidative damage observed is extensive and characteristic of the developmental region. The source of oxidative damage may in part be a response to elevated levels of glucose. Because oxidative stress is thought to be a major factor in cataract formation in both diabetic and non-diabetic aging humans, this animal model may be a useful tool in assessing efficacy of antioxidant treatments that may slow or prevent cataract formation.

Granulocyte function in patients with L-ferritin iron-responsive element (IRE) 39C-->T-positive hereditary hyperferritinaemia-cataract syndrome

BACKGROUND

Hereditary hyperferritinaemia-cataract syndrome (HHCS) is an autosomal dominant trait associated with mutations in the iron responsive element (IRE) of the ferritin light-chain (L-ferritin) gene. Patients typically show elevated serum ferritin concentrations without iron overload and a bilateral cataract. Hyperferritinaemia can be associated with granulocyte dysfunction in patients with thalassemia beta and in haemodialysis patients. The effect of increased L-ferritin levels on granulocyte function in patients with HHCS is unknown.

MATERIAL AND METHODS

We examined glucose uptake, oxidative burst, chemotaxis, phagocytosis, apoptosis and intracellular calcium concentrations in polymorphonuclear leucocytes (PMNLs) of five affected members of a family with HHCS and in five healthy individuals matched for age and gender.

RESULTS

Mutation testing revealed a 39C-->T transition in IRE in all five patients with HHCS. Serum ferritin levels of patients ranged between 907 and 2030 microg L(-1), respectively. In comparison with healthy individuals, PMNLs of patients with HHCS showed a significant increase in PMA-mediated stimulation of the oxidative burst, as well as a significantly higher stimulation of glucose uptake but no difference with respect to chemotaxis, phagocytosis, apoptosis and intracellular calcium concentrations.

CONCLUSION

In summary, our study suggests that hyperferritinaemia in patients with IRE 39C-->T-positive HHCS is associated with activation of PMNLs but not with disturbance of fundamental PMNL function.

Clinical features and molecular analysis of seven British kindreds with hereditary hyperferritinaemia cataract syndrome

Hereditary hyperferritinaemia cataract syndrome (HHCS) is an autosomal dominant disorder characterised by early onset cataracts and increased serum L-ferritin concentration. Affected individuals show nucleotide substitutions in the region of the L-ferritin gene (FTL) that encodes a regulatory sequence within the (mRNA)FTL termed the iron responsive element (IRE). We report the clinical features of seven HHCS kindreds containing 49 individuals with premature cataract. All the probands received diagnoses of HHCS after the incidental discovery of increased serum L-ferritin concentration (median 1420 microg/l; normal range 15-360 microg/l), in most cases during investigation or screening for anaemia. All the probands developed characteristic 'sunflower' morphology cataracts in childhood (median age at diagnosis 5 years), but had no other phenotypic features. All the affected kindreds showed nucleotide substitutions in FTL that were predicted to disrupt function of the (mRNA)FTL IRE. The severity of the clinical phenotype of HHCS was variable both within and between kindreds and showed no clear relationship to FTL genotype. HHCS should be included in the differential diagnosis of hyperferritinaemia and should be carefully distinguished from hereditary haemochromatosis. Measurement of the serum L-ferritin concentration should be included in the investigation of all individuals with early onset cataracts.

Analysis of the biologic functions of H- and L-ferritins in HeLa cells by transfection with siRNAs and cDNAs: evidence for a proliferative role of L-ferritin

We describe the use of small interfering RNAs (siRNAs) to down-regulate H- and L-ferritin levels in HeLa cells. siRNAs repressed H- and L-ferritin expression to about 20% to 25% of the background level in both stable and transient transfections. HeLa cells transfected with H- and L-ferritin cDNAs were analyzed in parallel to compare the effects of ferritin up- and down-regulation. We found that large modifications of L-ferritin levels did not affect iron availability in HeLa cells but positively affected cell proliferation rate in an iron-independent manner. The transient down-regulation of H-ferritin modified cellular iron availability and resistance to oxidative damage, as expected. In contrast, the stable suppression of H-ferritin in HeLa cell clones transfected with siRNAs did not increase cellular iron availability but made cells less resistant to iron supplementation and chelation. The results indicate that L-ferritin has no direct effects on cellular iron homeostasis in HeLa cells, while it has new, iron-unrelated functions. In addition, they suggest that H-ferritin function is to act as an iron buffer.

Molecular analyses of patients with hyperferritinemia and normal serum iron values reveal both L ferritin IRE and 3 new ferroportin (slc11A3) mutations

Unexplained hyperferritinemia is a common clinical finding, even in asymptomatic persons. When early onset bilateral cataracts are also present, the hereditary hyperferritinemia-cataract syndrome (HHCS), because of heterozygous point mutation in the L ferritin iron-responsive element (IRE) sequence, can be suspected. We sequenced the L ferritin exon 1 in 52 DNA samples from patients referred to us for molecular diagnosis of HHCS. We identified 24 samples with a point mutation/deletion in the IRE. For the 28 samples in which no IRE mutation was present, we also genotyped HFE mutations and sequenced both H ferritin and ferroportin genes. We found an increased frequency of His63Asp heterozygotes (12 of 28) but no H ferritin mutations. We identified 3 new ferroportin mutations, producing, respectively, Asp157Gly, Gln182His, and Gly323Val amino acid replacements, suggesting that these patients have dominant type 4 hemochromatosis. This study demonstrates that both L ferritin IRE and ferroportin mutations can account for isolated hyperferritinemia. The presence of cataract does not permit the unambiguous identification of patients with HHCS, although the existence of a family history of cataract was only encountered in these patients. This raises the intriguing possibility that lens ferritin accumulation might be a factor contributing to age-related cataract in the general population. Additional causes of isolated hyperferritinemia remain to be identified.

Scanning mutations of the 5'UTR regulatory sequence of L-ferritin by denaturing high-performance liquid chromatography: identification of new mutations

Hereditary hyperferritinaemia cataract syndrome is an autosomal dominant disorder caused by heterogeneous mutations of the iron regulatory element (IRE) in the ferritin l-chain mRNA. The mutations are rare and fast DNA scanning would facilitate diagnosis. The aim of the study was to compare the analytical performances of two fast DNA scanning techniques: denaturing high-performance liquid chromatography (DHPLC) and double-gradient denaturing gradient gel electrophoresis (DG-DGGE). We analysed the sequence encoding the 5' untranslated flanking region of ferritin l-chain mRNA, which includes an IRE stem loop structure. The two systems unambiguously identified all the 12 accessible mutations in a single run, including the difficult C-G transversions. DHPLC and DG-DGGE identified seven abnormal patterns in DNA samples from 47 subjects with unexplained hyperferritinaemia; all had mutations in the IRE sequence, including two not reported before: C36G and A37G. The scanning of 250 DNA samples from subjects genotyped for HFE led to the identification of four new mutations, all outside the IRE structure: C10T, C16T, C90T and del-T156. We conclude that DHPLC, similar to DG-DGGE, detects all the mutations in the l-ferritin 5'UTR sequence in a single run, and that various mutations occur outside the IRE structure.

Recent advance in molecular iron metabolism: translational disorders of ferritin

Ferritin, composed of H-subunits and L-subunits, plays important roles in iron storage and in the control of intracellular iron distribution. Synthesis of both subunits is controlled by common cytoplasmic proteins, iron regulatory proteins (IRP-1 and IRP-2) that bind to the iron-responsive element (IRE) in the 5'-untranslated region of ferritin messenger RNA (mRNA). When intracellular iron is scarce, IRPs display IRE binding to suppress translation of mRNA. When cellular iron is abundant, IRPs become inactivated (IRP-1) or degraded (IRP-2). In the last few years, IRE mutations that cause disorders due to dysregulation of ferritin subunit synthesis have been identified. Hereditary hyperferritinemia-cataract syndrome is associated with point mutations or deletions in the IRE of L-subunit mRNA and is characterized by constitutively increased synthesis of L-subunits but is unrelated to iron overload. A single-point mutation in the IRE of H-subunit mRNA in members of a family affected with dominantly inherited iron overload has been reported. This review summarizes the current understanding of the translational disorders caused by IRE mutations in ferritin mRNA.

Ferritin, iron homeostasis, and oxidative damage

Ferritin is one of the major proteins of iron metabolism. It is almost ubiquitous and tightly regulated by the metal. Biochemical and structural properties of the ferritins are largely conserved from bacteria to man, although the role in the regulation of iron trafficking varies in the different organisms. Recent studies have clarified some of the major aspects of the reaction between iron and ferritin, which results in the formation of the iron core and production of hydrogen peroxide. The characterization of cellular models in which ferritin expression is modulated has shown that the ferroxidase catalytic site on the H-chain has a central role in regulating iron availability. In turn, this has secondary effects on a number of cellular activities, which include proliferation and resistance to oxidative damage. Moreover, the response to apoptotic stimuli is affected by H-ferritin expression. Altered ferritin L-chain expression has been found in at least two types of genetic disorders, although its role in the determination of the pathology has not been fully clarified. The recent discovery of a new ferritin specific for the mitochondria, which is functionally similar to the H-ferritin, opens new perspectives in the study of the relationships between iron, oxidative damage and free radicals.

A novel deletion of the L-ferritin iron-responsive element responsible for severe hereditary hyperferritinaemia-cataract syndrome

In the last few years, mutations that cause disease through increased efficiency of mRNA translation have been discovered. Hereditary hyperferritinaemia-cataract syndrome (HHCS) arises from various point mutations or deletions within the iron-responsive element (IRE) in the 5'-UTR of the L-ferritin mRNA. Each unique mutation confers a characteristic degree of hyperferritinaemia and severity of cataract in affected individuals. We report a novel six-nucleotide deletion identified in an Italian family presenting with elevated serum ferritin and early onset bilateral cataract. This deletion involves a sequence with a TCT repetition and may have occurred through a mechanism of slippage mispairing. Because of the above repetition, the observed mutation can be interpreted as deletion 22-27, 23-28, 24-29 or 25-30. Structural modelling predicted an IRE stem modification that is expected to markedly reduce the binding to iron-regulatory proteins. A double-gradient denaturing gradient gel electrophoresis (DG-DGGE) method easily detected the above deletion.

Crystal cataracts: human genetic cataract caused by protein crystallization

Several human genetic cataracts have been linked recently to point mutations in the gammaD crystallin gene. Here we provide a molecular basis for lens opacity in two genetic cataracts and suggest that the opacity occurs because of the spontaneous crystallization of the mutant proteins. Such crystallization of endogenous proteins leading to pathology is an unusual event. Measurements of the solubility curves of crystals of the Arg-58 to His and Arg-36 to Ser mutants of gammaD crystallin show that the mutations dramatically lower the solubility of the protein. Furthermore, the crystal nucleation rate of the mutants is enhanced considerably relative to that of the wild-type protein. It should be noted that, although there is a marked difference in phase behavior, there is no significant difference in protein conformation among the three proteins.

Double-Gradient Denaturing Gradient Gel Electrophoresis Assay for Identification of L-Ferritin Iron-responsive Element Mutations Responsible for Hereditary Hyperferritinemia-Cataract Syndrome: Identification of the New Mutation C14G

Background: Hereditary hyperferritinemia-cataract syndrome is an autosomic dominant disorder caused by heterogeneous mutations on the iron-responsive element (IRE) of ferritin L-chain mRNA. The mutations described to date were identified by direct sequencing of DNA from probands with hyperferritinemia often associated to bilateral cataracts. A direct genetic approach on a large population is useful to recognize polymorphisms in the DNA region and the prevalence of mutations associated with minor increases in serum ferritin and subclinical cataracts. We developed a rapid DNA scanning technique to detect mutations in a single electrophoretic analysis.

Methods: The double-gradient denaturing gradient gel electrophoresis (DG-DGGE) method consisted of PCR amplification of the target genomic DNA with GC-clamped oligonucleotides. The sequence encoded the 5′ untranslated flanking region of ferritin L-chain mRNA, which includes an IRE stem-loop structure. The product was subjected to DG-DGGE (8.5–15% polyacrylamide and 50–95% denaturant) to separate the homo- and heteroduplexes.

Results: The method clearly identified all eight accessible mutations, including C-G transversions, which are the most difficult to detect. The method was applied to scan DNA samples from 50 healthy subjects and from 230 subjects with serum ferritin &gt;400 μg/L. The new mutation G14C was identified.

Conclusions: The DG-DGGE method detects all the mutations in the L-ferritin IRE sequence, is rapid and economical, and can be applied to scan large populations. The first population study indicated that the mutations are rare and may involve regions of the IRE structure not yet characterized.

Distribution of ferritin and redox-active transition metals in normal and cataractous human lenses

Previous studies have shown that lenticular levels of Fe and Cu are elevated in age-related cataract. However, it is not known if these metals are present in a state that is permissive for redox reactions that may lead to the formation of free radicals. In addition, there is little data available concerning the concentration and lenticular distribution of ferritin, the major intracellular Fe-sequestering protein, in the lens. The aim of the present work was therefore to determine the distribution of ferritin and the redox-availability of Fe and Cu in healthy and cataractous lenses. Lens ferritin distribution was assessed by ELISA and immunohistochemistry. A modified ELISA detected ferritin in an 'insoluble' lens protein fraction. Ferritin levels were not significantly different in the cortex vs nucleus of healthy lenses. In contrast, ferritin levels in the cataractous lens nuclei appeared to be 70% lower compared to the cortex. This was at least partially due to the presence of ferritin within an insoluble protein fraction of the homogenized lenses. In normal lenses, ferritin staining was most intense in the epithelium, with diffuse staining observed throughout the cortex and nucleus. The redox-availability of lenticular metals was determined using: (1) autometallography; (2) Ferene-S as a chromogenic Fe chelator; and (3) NO release from nitrosocysteine to probe for redox-active Cu. The autometallography studies showed that the cataractous lenses stained more heavily for redox-active metals in both the nucleus and cortex when compared to age-matched control lenses. Chelatable Fe was detected in homogenized control lenses after incubation with Ferene-S, with almost three-fold higher levels detected in the cataractous lenses on average. The Cu-catalysed liberation of NO from added nitrosocysteine was not demonstrated in any lens sample. When exogenous Cu (50 n M) was added to the lenses, it was rapidly chelated. The cataractous samples were approximately twice as effective at redox-inactivation of added Cu. These studies provide evidence that a chelatable pool of potentially redox-active Fe is present at increased concentrations in human cataractous lenses. In contrast, it seems that lenticular Cu may not be readily available for participation in redox reactions.