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

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.

Mammalian iron metabolism and its control by iron regulatory proteins

Cellular iron homeostasis is maintained by iron regulatory proteins 1 and 2 (IRP1 and IRP2). IRPs bind to iron-responsive elements (IREs) located in the untranslated regions of mRNAs encoding protein involved in iron uptake, storage, utilization and export. Over the past decade, significant progress has been made in understanding how IRPs are regulated by iron-dependent and iron-independent mechanisms and the pathological consequences of IRP2 deficiency in mice. The identification of novel IREs involved in diverse cellular pathways has revealed that the IRP-IRE network extends to processes other than iron homeostasis. A mechanistic understanding of IRP regulation will likely yield important insights into the basis of disorders of iron metabolism. This article is part of a Special Issue entitled: Cell Biology of Metals.

Hyperferritinaemia-cataract syndrome: worldwide mutations and phenotype of an increasingly diagnosed genetic disorder

The hereditary hyperferritinaemia-cataract syndrome (HHCS) is characterised by an autosomal dominant cataract and high levels of serum ferritin without iron overload. The cataract develops due to L-ferritin deposits in the lens and its pulverulent aspect is pathognomonic. The syndrome is caused by mutations within the iron-responsive element of L-ferritin. These mutations prevent efficient binding of iron regulatory proteins 1 and 2 to the IRE in L-ferritin mRNA, resulting in an unleashed ferritin translation. This paper reviews all 31 mutations (27 single nucleotide transitions and four deletions) that have been described since 1995. Laboratory test showing hyperferritinaemia, normal serum iron and normal transferrin saturation are indicative for HHCS after exclusion of other causes of increased ferritin levels (inflammation, malignancy, alcoholic liver disease) and should prompt an ophthalmological consultation for diagnostic confirmation. Invasive diagnostics such as liver biopsy are not indicated. HHCS is an important differential diagnosis of hyperferritinaemia. Haematologists, gastroenterologists and ophthalmologists should be aware of this syndrome to spare patients from further invasive diagnosis (liver biopsy), and also from a false diagnosis of hereditary haemochromatosis followed by venesections. Patients diagnosed with HHCS should be counselled regarding the relative harmlessness of this genetic disease, with early cataract surgery as the only clinical consequence.

Ferritin nanoparticles as magnetic resonance reporter gene

Dynamic imaging of gene expression in live animals is among the exciting challenges of molecular imaging. To achieve that, one of the approaches is to use reporter genes that encode for the synthesis of easily detectable products. Such reporter genes can be designed to be expressed under the control of the regulatory elements included in a promoter region of a gene of interest, thus allowing the use of the same reporter gene for the detection of multiple genes. The most commonly used reporter genes include the firefly light-generating enzyme luciferase and the green fluorescent protein detectable by bioluminescence and fluorescence optical imaging, respectively. Over the last years a number of studies demonstrated the ability to use the iron-binding protein ferritin as a reporter gene that allows the detection of gene expression by magnetic resonance imaging (MRI). MRI provides high spatial resolution and soft tissue contrast for deep tissues along with a large arsenal of functional and anatomical contrast mechanisms that can be correlated with gene expression, and can potentially be translated into clinical use.

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.

Microelectronic DNA chip for hereditary hyperferritinemia cataract syndrome, a model for large-scale analysis of disorders of iron metabolism

Hereditary hyperferritinemia cataract syndrome (HHCS) is caused by mutations in the regulatory iron responsive element (IRE) in the 5'UTR of the L-ferritin transcript that reduce binding affinity to the iron regulatory proteins (IRPs) and lead to a constitutive upregulation of the protein in tissue and serum. Twenty-nine mutations have been reported within the L-ferritin (FTL) IRE sequence, 21 of which were available to us. In addition, we included in this study three new mutations. Thus, we analyzed 24 mutations spanning over a DNA stretch of 48 nucleotides, including four deletions 2-29 nucleotides long and 20 substitutions, seven of which were conservative transversions. With this unique experimental model we developed a microchip diagnostic platform for identifying known molecular defects in the L-ferritin IRE structure with a microelectronic array approach, which we optimized after studying the effects of various parameters. The system enables electronic deposition of biotinylated amplicons to selected pads. Under optimized conditions, no cross-hybridization was found, even for mutations that affected the same or adjacent nucleotide positions. The same cartridge could be serially hybridized with all the 24 reporter probe sets, which allowed correct genotyping right up until the end of the analysis. Extensive validation on 200 samples in a blinded fashion gave total concordance of results. This pilot study represents a first step toward developing a diagnostic microchip for large-scale analyses for epidemiological studies and screening of mutations associated with iron disorders.

The effect of 5-hydroxytryptamine 3A and 3B receptor genes on nausea induced by paroxetine

We investigated the effect of 5-hydroxytryptamine 3A and 3B receptor (HTR3A and HTR3B) gene polymorphisms on nausea induced by paroxetine in Japanese psychiatric patients. Blood samples were collected from 78 individuals after at least 2 weeks treatment with the same daily dose of paroxetine. The patients visited every 2 weeks and the paroxetine dose was changed in response to their clinical symptoms. Nausea was assessed at each visit. The Tyr129Ser polymorphism of the HTR3B gene had a significant effect on the incidence of nausea (P=0.038). Logistic regression analysis also showed that patients with the Tyr/Tyr genotype had a 3.95-fold (P=0.048) higher risk of developing nausea than patients with the Ser allele. HTR3A gene polymorphisms and the CYP2D6 gene polymorphisms had no significant effect on the incidence of nausea. The mean score of nausea severity was corrected by the Bonferroni test. HTR3B gene polymorphisms are significant predictors of paroxetine-induced nausea.

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.

Investigation of the human serotonin receptor gene HTR3B in bipolar affective and schizophrenic patients

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) mediates a multitude of central nervous functions by activating 5-HT receptor subtypes. A dysfunction of serotonergic neurotransmission is considered to play a major role in the pathophysiology of complex neuropsychiatric disorders. In our study, a mutation screen of the serotonin receptor gene HTR3B was carried out to explore a putative contribution to the etiology of bipolar affective disorder (BPAD) and schizophrenia (SZ). Screening of 49 patients suffering from BPAD, 78 patients with SZ and 62 control individuals revealed eleven sequence variations including a 3 bp deletion within the 5'UTR (5' untranslated region), four exonic and five intronic SNPs as well as a point mutation in the 3'UTR of HTR3B. Four of these sequence variations have not been described previously. Statistical computation rated most variants as probably non-disease related polymorphisms. However, IVS6 + 31C > T, IVS6 + 40C > A, and 1386T > C were solely detected in bipolar affective patients and in none of the controls. Interestingly, we observed a significant underrepresentation of the 3 bp deletion -100_-102delAAG in an extended sample of 162 bipolar affected patients compared to controls (allele-wise: 8% vs. 15%, P = 0.006, OR = 0.49, 95% CI: 0.3-0.82; genotype-wise: 15,5% vs. 29,0%, P = 0.005, OR = 0.45, 95% CI: 0.26-0.77). We suggest that this deletion may influence translational efficiency, thereby possibly affecting the development of bipolar affective disease.

Denaturing HPLC analysis of DNA deletions and insertions

Denaturing HPLC (DHPLC) is a useful technique for the fast screening of known and unknown heterozygous gene mutations. Most DNA mutations causing genetic disorders consist of nucleotide substitutions, but insertions and deletions occur, albeit less frequently. The heteroduplexes with insertions/deletions have gaps that may affect molecular stability differently from the mismatches caused by substitutions. Therefore, gaps and mismatches may be distinguished by DHPLC analysis, which is based on the differential thermal stability of amplicons with different characteristics. To verify this hypothesis, we examined 12 DNA samples containing insertions and deletions of different sizes (one to 29 residues) from four different genes (ABCA4, CFTR, FTL, and SLC11A3). We found that all of them were detected by DHPLC runs at 50 degrees C, which is considered a non-denaturing temperature, as well as by runs at the temperature optimized for mismatch recognition. The finding confirms that gaps reduce heteroduplex stability more than mismatches, and indicates that DHPLC analysis at low temperature may be applied to distinguish DNA deletions/insertions from substitutions.

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.

Pathogenesis of hyperferritinemia cataract syndrome

Hereditary hyperferritinemia-cataract syndrome (HHCS) is an autosomal dominant disorder characterized by bilateral cataracts and increased serum L-ferritin, in the absence of iron overload. Under physiological conditions, ferritin synthesis is finely regulated at the translational level by iron availability. This regulation is achieved by the high-affinity interaction between cytoplasmic mRNA-binding proteins (iron regulatory proteins, IRPs), and mRNA stem-loop structures, known as iron responsive elements (IREs), located in the untranslated regions (UTRs) of the mRNAs. A single IRE is located on the 5' UTR of a series of genes involved in iron metabolism, like L-ferritin, and the binding IRE-IRPs represses these genes translation. The deregulation of ferritin production responsible of HHCS is caused by heterogeneous mutations in the iron regulatory element (IRE) of L-ferritin that interfere with the binding of iron regulatory proteins, disrupting the negative control of L-ferritin synthesis and causing the constitutive up-regulation of ferritin L-chains. The HHCS families originate from different countries of Europe and North America, suggesting that HHCS may be distributed widely throughout the world and not sporadic, whereas its prevalence remains to be established. The lens seems to be particularly sensitive to the increased amount of L-ferritin and the alteration of the proteic equilibrium in this tissue can be responsible of the cataract. In spite of the elucidation of the genetic basis, the genotype phenotype correlation is not clear. Recently, a study based on the thermo-denaturation profile and dissociation constant of the IRE-IRP complex performed for several mutated IREs has provided evidence for a possible correlation between heterogeneous IRE mutations and serum ferritin levels. On the other hand, the in vivo relevance of these conclusions has not been determined completely. A clinical variability among subjects sharing the same mutation, whether they belonged to the same family or not, has also been demonstrated. These findings suggest that, besides the L-ferritin IRE genotype, additional factors are likely to modulate the lens involvement and the rate of progression to severe cataract in HHCS patients.

Seeking candidate mutations that affect iron homeostasis

Hereditary hemochromatosis is characterized by marked variation of expression of the defect: very few homozygotes with the C282Y/C282Y HFE genotype have full-blown clinical disease, a larger number show biochemical stigmata of iron overload, and some seem normal biochemically. The following candidate genes have been examined in detail to determine whether polymorphisms in them may be responsible for this variation: transferrin, transferrin receptor 1, transferrin receptor 2, ferritin-L, ferritin-H, IRP1, IRP2, HFE, beta(2) microglobulin, mobilferrin/calreticulin, ceruloplasmin, ferroportin, NRAMP1, NRAMP2 (DMT1), haptoglobin, heme oxygenase-1, heme oxygenase-2, hepcidin, USF2, ZIRTL, duodenal cytochrome b ferric reductase (DCYTB), TNFalpha, keratin 8, and keratin 18. The coding sequence, exon-intron junctions, and promoters of each of these genes was sequenced in DNA from 20 subjects: 5 HFE C282Y/C282Y with clinical disease, 5 HFE C282Y/C282Y with normal/low ferritin levels and no disease, 5 wt/wt with high ferritin and transferrin saturation, and 5 wt/wt normal controls. When coding or promoter polymorphisms were encountered, DNA from large numbers of ethnically defined subjects was examined for these polymorphisms and a relationship between their existence and abnormalities of iron homeostasis was sought. Only in the case of one transferrin mutation did we find a strong relationship between the polymorphism and iron deficiency anemia. The putative genes that affect the expression of HFE mutations remain elusive.

Genetic hyperferritinaemia and reticuloendothelial iron overload associated with a three base pair deletion in the coding region of the ferroportin gene (SLC11A3)

Iron overload may predominantly involve parenchymal or reticuloendothelial cells, the prototype of parenchymal iron overload being HFE-related genetic haemochromatosis. We studied a family with autosomal dominant hyperferritinaemia in whom the proband showed selective iron accumulation in the Kupffer cells on liver biopsy. Analysis of L and H ferritin genes excluded mutations responsible for hereditary hyperferritinaemia/cataract syndrome or similar translational disorders. Sequence analysis of the ferroportin gene (SLC11A3) in four individuals with hyperferritinaemia singled out a three base pair deletion in a region that contains four TTG repeats. This mutation removes a TTG unit from 780 to 791, and predicts the loss of one of three sequential valine residues 160-162. Denaturing high performance liquid chromatography can be used for its detection. SLC11A3 polymorphism analysis indicates that this probably represents a recurrent mutation due to slippage mispairing. Affected individuals may show marginally low serum iron and transferrin saturation, and young women may have marginally low haemoglobin concentration levels. Serum ferritin levels are directly related to age, but are 10-20 times higher than normal. Heterozygosity for the ferroportin Val 162 deletion represents the prototype of selective reticuloendothelial iron overload, and should be taken into account in the differential diagnosis of hereditary or congenital hyperferritinaemias.

Pushing the limits of the scanning mechanism for initiation of translation

Selection of the translational initiation site in most eukaryotic mRNAs appears to occur via a scanning mechanism which predicts that proximity to the 5' end plays a dominant role in identifying the start codon. This "position effect" is seen in cases where a mutation creates an AUG codon upstream from the normal start site and translation shifts to the upstream site. The position effect is evident also in cases where a silent internal AUG codon is activated upon being relocated closer to the 5' end. Two mechanisms for escaping the first-AUG rule--reinitiation and context-dependent leaky scanning--enable downstream AUG codons to be accessed in some mRNAs. Although these mechanisms are not new, many new examples of their use have emerged. Via these escape pathways, the scanning mechanism operates even in extreme cases, such as a plant virus mRNA in which translation initiates from three start sites over a distance of 900 nt. This depends on careful structural arrangements, however, which are rarely present in cellular mRNAs. Understanding the rules for initiation of translation enables understanding of human diseases in which the expression of a critical gene is reduced by mutations that add upstream AUG codons or change the context around the AUG(START) codon. The opposite problem occurs in the case of hereditary thrombocythemia: translational efficiency is increased by mutations that remove or restructure a small upstream open reading frame in thrombopoietin mRNA, and the resulting overproduction of the cytokine causes the disease. This and other examples support the idea that 5' leader sequences are sometimes structured deliberately in a way that constrains scanning in order to prevent harmful overproduction of potent regulatory proteins. The accumulated evidence reveals how the scanning mechanism dictates the pattern of transcription--forcing production of monocistronic mRNAs--and the pattern of translation of eukaryotic cellular and viral genes.

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.