Identification of a mechanism by which lens epithelial cells limit accumulation of overexpressed ferritin H-chain

Fecal Proteome Profile in Dogs Suffering from Different Hepatobiliary Disorders and Comparison with Controls

In the present study, the fecal proteomes of clinically healthy dogs (HD = n. 10), of dogs showing clinical, ultrasonographic, and/or laboratory evidence of different hepatobiliary dysfunction (DHD = n. 10), and of dogs suffering from chronic hepatitis (CHD = n. 10) were investigated with an Ultimate 3000 nanoUPLC system, coupled to an Orbitrap Fusion Lumos Tribrid mass spectrometer. Fifty-two different proteins of canine origin were identified qualitatively in the three study groups, and quantitative differences were found in 55 proteins when comparing groups. Quantitatively, a total of 41 and 36 proteins were found differentially abundant in the DHD and CHD groups compared to the control HD, and 38 proteins resulted dysregulated in the CHD group as compared to the DHD group. Among the various proteins, differently abundant fecal fibronectin and haptoglobin were more present in the feces of healthy and DHD dogs than in chronic ones, leading us to hypothesize its possible diagnostic/monitoring role in canine chronic hepatitis. On the other hand, the trefoil factor 2 was increased in DHD dogs. Our results show that the analysis of the fecal proteome is a very promising field of study, and in the case of dogs suffering from different hepatobiliary disorders, it was able to highlight both qualitative and quantitative differences among the three groups included. Results need to be confirmed with western blotting and in further studies.

Vitreous Humor Changes Expression of Iron-Handling Proteins in Lens Epithelial Cells

Purpose

In humans, vitrectomy is associated with development of nuclear cataracts. Iron catalyzes free radical formation causing oxidative damage, which is implicated in cataract formation. This study was designed to determine if vitreous humor, which can initiate differentiation of lens epithelial cells, would have an effect on iron-handling proteins.

Methods

Cultured canine lens epithelial cells were treated with collected canine vitreous humor. Lysates of treated and control cells were separated by SDS-PAGE. Ferritin H- and L-chains, transferrin receptor 1, and aquaporin 0 were immunodetected and quantitated with specific antibodies. Morphologic changes in treated cells were assessed.

Results

Treatment of lens epithelial cells with a 33% (vol/vol) solution of vitreous humor changed the morphology of lens cells and induced expression of aquaporin 0, a marker of fiber cell differentiation that was undetectable in control cells. Treatment did not modify the size of iron-handling proteins but significantly increased content of ferritin from 2.9- to 8.8-fold over control and decreased levels of transferrin receptor by 37% to 59%.

Conclusions

Vitreous humor may significantly limit iron uptake by transferrin/transferrin receptor pathway, and by increasing ferritin levels could profoundly increase the iron-storage capacity of ferritin in lens cells. Vitreous humor may play a significant protective role against iron-catalyzed oxidative damage of lens epithelial cells and therefore in the formation of cataracts.

Hypoxia induced changes in expression of proteins involved in iron uptake and storage in cultured lens epithelial cells

Hypoxia inducible factor (HIF) regulates expression of over 60 genes by binding to hypoxia response elements (HRE) located upstream of the transcriptional start sites. Many genes encoding proteins involved in iron transport and homeostasis are regulated by HIF. Expression of iron handling proteins can also be translationally regulated by binding of iron regulatory protein (IRP) to iron responsive elements (IREs) on the mRNA of ferritin chains and transferrin receptor (TfR). Lens epithelial cells (LEC) function in a low oxygen environment. This increases the risk of iron catalyzed formation of reactive oxygen species (ROS) and oxidative cell damage. We examined changes in expression of ferritin (iron storage protein) and Tf/TfR1 (iron uptake proteins) in LEC cultured under hypoxic conditions. Ferritin consists of 24 subunits of two types, heavy (H-chain) and light (L-chain) assembled in a cell specific ratio. Real-time PCR showed that 24 h exposure to hypoxia lowered transcription of both ferritin chains by over 50% when compared with normoxic LEC. However it increased the level of ferritin chain proteins (20% average). We previously found that 6 h exposure of LEC to hypoxia increased the concentration of cytosolic iron which would stimulate translation of ferritin chains. This elevated ferritin concentration increased the iron storage capacity of LEC. Hypoxic LEC labeled with 59FeTf incorporated 70% more iron into ferritin after 6 h as compared to normoxic LEC. Exposure of LEC to hypoxia for 24 h reduced the concentration of TfR1 in cell lysates. As a result, hypoxic LEC internalized less Tf at this later time point. Incorporation of 59Fe into ferritin of hypoxic LEC after 24 h did not differ from that of normoxic LEC due to lower 59FeTf uptake. This study showed that hypoxia acutely increased iron storage capacity and lowered iron uptake due to changes in expression of iron handling proteins. These changes may better protect LEC against oxidative stress by limiting iron-catalyzed ROS formation in the low oxygen environment in which the lens resides.

Coupling heme and iron metabolism via ferritin H chain

SIGNIFICANCE

Inflammation and immunity can be associated with varying degrees of heme release from hemoproteins, eventually leading to cellular and tissue iron (Fe) overload, oxidative stress, and tissue damage. Presumably, these deleterious effects contribute to the pathogenesis of systemic infections.

RECENT ADVANCES

Heme release from hemoglobin sensitizes parenchyma cells to undergo programmed cell death in response to proinflammatory cytokines, such as tumor necrosis factor. This cytotoxic effect is driven by a mechanism involving intracellular accumulation of free radicals, which sustain the activation of the c-Jun N-terminal kinase (JNK) signaling transduction pathway. While heme catabolism by heme oxygenase-1 (HO-1) prevents programmed cell death, this cytoprotective effect requires the co-expression of ferritin H (heart/heavy) chain (FTH), which controls the pro-oxidant effect of labile Fe released from the protoporphyrin IX ring of heme. This antioxidant effect of FTH restrains JNK activation, whereas JNK activation inhibits FTH expression, a cross talk that controls metabolic adaptation to cellular Fe overload associated with systemic infections.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Identification and characterization of the mechanisms via which FTH provides metabolic adaptation to tissue Fe overload should provide valuable information to our current understanding of the pathogenesis of systemic infections as well as other immune-mediated inflammatory diseases.

The hereditary hyperferritinemia-cataract syndrome in 2 italian families

Two 8- and 9-year-old brothers were referred to the Pediatric Oncology Unit, Perugia General Hospital, because of hyperferritinemia. Both had a history of bilateral cataract and epilepsy. Genetic investigation revealed two distinct mutations in iron haemostasis genes; homozygosity for the HFE gene H63D mutation in the younger and heterozygosity in the elder. Both displayed heterozygosity for C33T mutation in the ferritin light chain iron response element. A 7-year-old boy from another family was referred to our unit because of hyperferritinemia. Genetic analyses did not reveal HFE gene mutations. Family history showed that his mother was also affected by hyperferritinemia without HFE gene mutations. Magnetic resonance imaging in the mother was positive for iron overload in the spleen. Cataract was diagnosed in mother and child. Further genetic investigation revealed the C29G mutation of the ferritin light chain iron response element. C33T and C29G mutations in the ferritin light chain iron response element underlie the Hereditary Hyperferritinemia-Cataract Syndrome (HHCS). The HFE gene H63D mutation underlies Hereditary Haemochromatosis (HH), which needs treatment to prevent organ damages by iron overload. HHCS was definitively diagnosed in all three children. HHCS is an autosomal dominant disease characterized by increased L-ferritin production. L-Ferritin aggregates accumulate preferentially in the lens, provoking bilateral cataract since childhood, as unique known organ damage. Epilepsy in one case and the spleen iron overload in another could suggest the misleading diagnosis of HH. Consequently, the differential diagnosis between alterations of iron storage system was essential, particularly in children, and required further genetic investigation.

Decoupling ferritin synthesis from free cytosolic iron results in ferritin secretion

Ferritin is a multisubunit protein that is responsible for storing and detoxifying cytosolic iron. Ferritin can be found in serum but is relatively iron poor. Serum ferritin occurs in iron overload disorders, in inflammation, and in the genetic disorder hyperferritinemia with cataracts. We show that ferritin secretion results when cellular ferritin synthesis occurs in the relative absence of free cytosolic iron. In yeast and mammalian cells, newly synthesized ferritin monomers can be translocated into the endoplasmic reticulum and transits through the secretory apparatus. Ferritin chains can be translocated into the endoplasmic reticulum in an in vitro translation and membrane insertion system. The insertion of ferritin monomers into the ER occurs under low-free-iron conditions, as iron will induce the assembly of ferritin. Secretion of ferritin chains provides a mechanism that limits ferritin nanocage assembly and ferritin-mediated iron sequestration in the absence of the translational inhibition of ferritin synthesis.

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.

Altered ferritin subunit composition: change in iron metabolism in lens epithelial cells and downstream effects on glutathione levels and VEGF secretion

PURPOSE

The iron storage protein ferritin is necessary for the safe storage of iron and for protection against the production of iron-catalyzed oxidative damage. Ferritin is composed of 24 subunits of two types: heavy (H) and light (L). The ratio of these subunits is tissue specific, and alteration of this ratio can have profound effects on iron storage and availability. In the present study, siRNA for each of the chains was used to alter the ferritin H:L chain ratio and to determine the effect of these changes on ferritin synthesis, iron metabolism, and downstream effects on iron-responsive pathways in canine lens epithelial cells.

METHODS

Primary cultures of canine lens epithelial cells were used. The cells were transfected with custom-made siRNA for canine ferritin H- and L-chains. De novo ferritin synthesis was determined by labeling newly synthesized ferritin chains with 35S-methionine, immunoprecipitation, and separation by SDS-PAGE. Iron uptake into cells and incorporation into ferritin was measured by incubating the cells with 59Fe-labeled transferrin. Western blot analysis was used to determine the presence of transferrin receptor, and ELISA was used to determine total ferritin concentration. Ferritin localization in the cells was determined by immunofluorescence labeling. VEGF, glutathione secretion levels, and cystine uptake were measured.

RESULTS

FHsiRNA decreased ferritin H-chain synthesis, but doubled ferritin L-chain synthesis. FLsiRNA decreased both ferritin H- and L-chain synthesis. The degradation of ferritin H-chain was blocked by both siRNAs, whereas only FHsiRNA blocked the degradation of ferritin L-chain, which caused significant accumulation of ferritin L-chain in the cells. This excess ferritin L-chain was found in inclusion bodies, some of which were co-localized with lysosomes. Iron storage in ferritin was greatly reduced by FHsiRNA, resulting in increased iron availability, as noted by a decrease in transferrin receptor levels and iron uptake from transferrin. Increased iron availability also increased cystine uptake and glutathione concentration and decreased nuclear translocation of hypoxia-inducible factor 1-alpha and vascular endothelial growth factor (VEGF) accumulation in the cell-conditioned medium.

CONCLUSIONS

Most of the effects of altering the ferritin H:L ratio with the specific siRNAs were due to changes in the availability of iron in a labile pool. They caused significant changes in iron uptake and storage, the rate of ferritin synthesis and degradation, the secretion of VEGF, and the levels of glutathione in cultured lens epithelial cells. These profound effects clearly demonstrate that maintenance of a specific H:L ratio is part of a basic cellular homeostatic mechanism.

Iron metabolism in the eye: a review

This review article covers all aspects of iron metabolism, which include studies of iron levels within the eye and the processes used to maintain normal levels of iron in ocular tissues. In addition, the involvement of iron in ocular pathology is explored. In each section there is a short introduction to a specific metabolic process responsible for iron homeostasis, which for the most part has been studied in non-ocular tissues. This is followed by a summary of our current knowledge of the process in ocular tissues.

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.

Changes in ferritin H- and L-chains in canine lenses with age-related nuclear cataract

PURPOSE

To determine potential differences in the characteristics of the iron storage protein ferritin and its heavy (H) and light (L) subunits in fiber cells from cataractous and noncataractous lenses of older dogs.

METHODS

Lens fiber cell homogenates were analyzed by SDS-PAGE, and ferritin chains were immunodetected with ferritin chain-specific antibodies. Ferritin concentration was measured by ELISA. Immunohistochemistry was used to localize ferritin chains in lens sections.

RESULTS

The concentration of assembled ferritin was comparable in noncataractous and cataractous lenses of similarly aged dogs. The ferritin L-chain detected in both lens types was modified and was approximately 11 kDa larger (30 kDa) than standard L-chain (19 kDa) purified from canine liver. The H-chain identified in cataractous fiber cells (29 kDa) differed from the 21-kDa standard canine H-chain and from the 12-kDa modified H-chain present in fiber cells of noncataractous lenses. Histologic analysis revealed that the H-chain was distributed differently throughout cataractous lenses compared with noncataractous lenses. There was also a difference in subunit makeup of assembled ferritin between the two lens types. Ferritin from cataractous lenses contained more H-chain and bound 11-fold more iron than ferritin from noncataractous lenses.

CONCLUSIONS

There are significant differences in the characteristics of ferritin H-chain and its distribution in canine cataractous lenses compared with noncataractous lenses. The higher content of H-chain in assembled ferritin allows this molecule to sequester more iron. In addition, the accumulation of H-chain in deeper fiber layers of the lens may be part of a defense mechanism by which the cataractous lens limits iron-catalyzed oxidative damage.

Ferritin and ferritin isoforms II: protection against uncontrolled cellular proliferation, oxidative damage and inflammatory processes

Ferritin is a major iron storage protein involved in the regulation of iron availability. Each ferritin molecule comprises 24 subunits. Various combinations of H-subunits and L-subunits make up the 24-subunit protein structure and these ferritin isoforms differ in their H-subunit to L-subunit ratio, as well as in their metabolic properties. Ferritin is an acute-phase protein and its expression is up-regulated in conditions such as uncontrolled cellular proliferation, in any condition marked by excessive production of toxic oxygen radicals, and by infectious and inflammatory processes. Under such conditions ferritin up-regulation is predominantly stimulated by increased reactive oxygen radical production and by cytokines. The major function of ferritin in these conditions is to reduce the bio-availability of iron in order to stem uncontrolled cellular proliferation and excessive production of reactive oxygen radicals. Ferritin is not, however, indiscriminately up-regulated in these conditions as a marked shift towards a predominance in H-subunit rich ferritins occurs. Preliminary indications are that, while the L-subunit primarily fulfils the conventional iron storage role, the H-subunit functions primarily as rapid regulator of iron availability, and perhaps indirectly as regulator of other cellular processes. It is suggested that the optimum differential expression of the two subunits differ for different cells and under different conditions and that the expression of appropriate isoferritins offers protection against uncontrolled cellular proliferation, oxidative stress and against side effects of infectious and inflammatory conditions.

Desferrioxamine and zinc-desferrioxamine reduce lens oxidative damage

Our purpose was to investigate the quality and morphology of cultured bovine lenses after exposure to hyperbaric oxygen (HBO) in the presence or absence of desferrioxamine (DFO) or zinc-desferrioxamine (Zn-DFO). Intact bovine lenses were cultured and exposed to HBO of 100% oxygen at 2.5 ATA for 120 min. One hundred and fifty lenses were included in the present study. Lenses were divided into study groups of 25 lenses each: (1a) HBO-exposed lenses; (1b) control lenses extracted from the contralateral eyes of group 1a and exposed to normal room air. (2a) HBO-exposed lenses treated with DFO; (2b) control lenses extracted from the contralateral eyes of group 2a exposed to normal room air in the presence of DFO (3a) HBO-exposed lenses treated with Zn-DFO; (3b) control lenses extracted from the contralateral eyes of group 3a, exposed to normal room air in the presence of Zn-DFO. Lens optical quality and structural changes were assessed. Oxygen toxicity to lenses was demonstrated by decreased light transmission, increase in focal length variability and a decrease in morphological integrity. Light intensity measurements showed a distinct pattern in control lenses. A different pattern was noticed for hyperbaric oxygen-exposed lenses. Focal length variability values were stable in control lenses and increased significantly in oxygen-exposed lenses. Structural damage to lenses was demonstrated by the appearance of bubbles between lens' fibers possibly demonstrating failure of lens tissue to cope with oxygen load. All measured parameters showed that both Zn-DFO and DFO attenuated the oxidative damage. The effect of DFO was small whereas Zn-DFO demonstrated a significantly stronger effect. Treatment of hyperbaric oxygen-exposed lenses with DFO only marginally reduced the oxidative damage. Treatment with Zn-DFO was superior in reducing the oxidative damage to lenses. These results indicate a possible role for Zn-DFO in the prevention of cataracts.

Lens epithelial cells synthesize and secrete ceruloplasmin: effects of ceruloplasmin and transferrin on iron efflux and intracellular iron dynamics

Although an essential nutrient, iron can catalyze damaging free radical reactions. Therefore elaborate mechanisms have evolved to carefully regulate iron metabolism. Ceruloplasmin, a protein with ferroxidase activity, and transferrin, an iron binding protein have important roles in maintaining iron homeostasis in cells. Since oxidative damage is a hallmark of cataractogenesis, it is essential to determine iron's role in lenticular physiology and pathology. In the current study of lens epithelial cells, the effects of ceruloplasmin and transferrin on intracellular distribution and efflux of iron were determined. Both ceruloplasmin and transferrin increased iron efflux from these cells and their effects were additive. Ceruloplasmin had significant effects on extracellular iron distribution only in cases of iron overload. Surprisingly, both transferrin and ceruloplasmin had significant effects on intracellular iron distribution. Under physiological conditions, ceruloplasmin increased iron incorporation into the storage protein, ferritin. Under conditions of iron overload, it decreased iron incorporation into ferritin, which is consistent with increased efflux of iron. Measurements of an intracellular chelatable iron pool indicated that both transferrin and ceruloplasmin increased the size of this pool at 24 h, but these increases had different downstream effects. Finally, lens epithelial cells made and secreted transferrin and ceruloplasmin. These results indicate an important role for these proteins in iron metabolism in the lens.

Hiperferritinemia familiar y cataratas congénitas asociadas a mutación del gen HFE. Dos nuevas familias españolas y una nueva mutación (A37T: «Zaragoza»)

BACKGROUND AND OBJECTIVE

Nuclear congenital cataracts associated with hyperferritinemia--hereditary hyperferritinemia cataract syndrome (HHCS)--without clinical or biochemical signs of iron overload have been recently described in several Spanish families. This HHCS is associated with mutations in the gene of ferritin subunit L, located in chromosome 19. We describe 2 new families with HHCS, one of them presenting a new L-ferritin mutation (A37T: -Zaragoza-).

PATIENTS AND METHOD

Patients and probands were studied according to the Anemia Unit protocol: complete blood count, biochemical profile (diabetes, hepatic and renal), hepatic serologies, iron metabolism (iron, transferrin, ferritin, transferrin saturation, reactive C protein) and mutation HFE gene studies (C282Y, H63D). All of them were sent to the Ophthalmology Service for cataract study. L-ferritin mutational scanning was performed by denaturing high performance liquid chromatography (DHPLC). Samples displaying an altered elution profile, as compared to a wild type control, were directly sequenced for the precise characterization of the L-ferritin mutation.

RESULTS

Family A proband was a 54 year-old-female, with cataracts, ferritin level: 942 pg/I, transferrin saturation: 14%, HFE gen study: H63D/H63D; L-ferritin gene study: C33T mutation/-. Her two sons had cataracts, hyperferritinemia (1607, and 1188 pg/I, respectively), normal transferrin saturation (40% and 9%), HFE gene study: H63D/N; and L-ferritin gen study: C33T/-. Family B proband was a 39 year-old-female, with cataract, ferritin level: 636 pg/I, transferrin saturation: 25%, HFE gene study: H63D/N; and L-ferritin gene study: A37T/-. Her two sons, sister, brother and nephew, who were affected with A37T mutation, showed hyperferritinemia (883, 747, 835, 613 and 1396 pg/I) with normal transferrin saturation levels (17%, 34%, 25%, 18% and 24%); but the ferritin levels of those non-affected were normal (35 and 50 pg/I).

CONCLUSIONS

HHCS is a dominant autosomic condition, with a possible world-wide distribution,which should be included in the differential diagnosis of hyperferritinemia studies. It is important to suspect it in order to avoid wrong treatment.

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.

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.