Clinical severity and thermodynamic effects of iron-responsive element mutations in hereditary hyperferritinemia-cataract syndrome. (1/114)

Hereditary hyperferritinemia-cataract syndrome (HHCS) is a novel genetic disorder characterized by elevated serum ferritin and early onset cataract formation. The excessive ferritin production in HHCS patients arises from aberrant regulation of L-ferritin translation caused by mutations within the iron-responsive element (IRE) of the L-ferritin transcript. IREs serve as binding sites for iron regulatory proteins (IRPs), iron-sensing proteins that regulate ferritin translation. Previous observations suggested that each unique HHCS mutation conferred a characteristic degree of hyperferritinemia and cataract severity in affected individuals. Here we have measured the in vitro affinity of the IRPs for the mutant IREs and correlated decreases in binding affinity with clinical severity. Thermodynamic analysis of these IREs has also revealed that although some HHCS mutations lead to changes in the stability and secondary structure of the IRE, others appear to disrupt IRP-IRE recognition with minimal effect on IRE stability. HHCS is a noteworthy example of a human genetic disorder that arises from mutations within a protein-binding site of an mRNA cis-acting element. Analysis of the effects of these mutations on the energetics of the RNA-protein interaction explains the phenotypic variabilities of the disease state.  (+info)

Inborn errors of metabolism: iron. (2/114)

The iron content of the body is normally closely regulated. Despite this, iron deficiency anaemia is common in women because iron losses due to menstruation and childbirth are not always compensated for by iron absorption from the diet. The role of transferrin in delivering iron to cells and of ferritin in storing iron within cells is well understood but the proteins involved in iron transport across membranes are only now being investigated. Relatively few genetic disorders affecting iron metabolism are known and most are rare. This paper briefly describes pyridoxine responsive sideroblastic anaemia, hyperferritinaemia-cataract syndrome, atransferrinaemia and genetic haemochromatosis. Rather than rare, the latter is one of the most common inherited disorders in northern European populations. Mutations in genes regulating membrane iron transport causing simple iron deficiency have not yet been described.  (+info)

Survey of human mitochondrial diseases using new genomic/proteomic tools. (3/114)

BACKGROUND: We have constructed Bayesian prior-based, amino-acid sequence profiles for the complete yeast mitochondrial proteome and used them to develop methods for identifying and characterizing the context of protein mutations that give rise to human mitochondrial diseases. (Bayesian priors are conditional probabilities that allow the estimation of the likelihood of an event - such as an amino-acid substitution - on the basis of prior occurrences of similar events.) Because these profiles can assemble sets of taxonomically very diverse homologs, they enable identification of the structurally and/or functionally most critical sites in the proteins on the basis of the degree of sequence conservation. These profiles can also find distant homologs with determined three-dimensional structures that aid in the interpretation of effects of missense mutations. RESULTS: This survey reports such an analysis for 15 missense mutations, one insertion and three deletions involved in Leber's hereditary optic neuropathy, Leigh syndrome, mitochondrial neurogastrointestinal encephalomyopathy, Mohr-Tranebjaerg syndrome, iron-storage disorders related to Friedreich's ataxia, and hereditary spastic paraplegia. We present structural correlations for seven of the mutations. CONCLUSIONS: Of the 19 mutations analyzed, 14 involved changes in very highly conserved parts of the affected proteins. Five out of seven structural correlations provided reasonable explanations for the malfunctions. As additional genetic and structural data become available, this methodology can be extended. It has the potential for assisting in identifying new disease-related genes. Furthermore, profiles with structural homologs can generate mechanistic hypotheses concerning the underlying biochemical processes - and why they break down as a result of the mutations.  (+info)

Recent advances in disorders of iron metabolism: mutations, mechanisms and modifiers. (4/114)

The spectrum of known disorders of iron metabolism has expanded dramatically over the past few years. Identification of HFE, the gene most commonly mutated in patients with hereditary hemochromatosis, has allowed molecular diagnosis and paved the way for identification of other genes, such as TFR2, that are important in non-HFE-associated iron overload. There are clearly several other, unidentified, iron overload disease genes yet to be found. In parallel, our understanding of iron transport has expanded through identification of Fpn1/Ireg1/MTP1, Sfxn1 and DCYTB: Ongoing studies of Friedreich's ataxia, sideroblastic anemia, aceruloplasminemia and neurodegeneration with brain-iron accumulation are clarifying the role for iron in the nervous system. Finally, as the number of known iron metabolic genes increases and their respective functions are ascertained, new opportunities have arisen to identify genetic modifiers of iron homeostasis.  (+info)

Impaired retinal iron homeostasis associated with defective phagocytosis in Royal College of Surgeons rats. (5/114)

PURPOSE: To determine whether iron homeostasis disorder accompanies retinal degeneration in Royal College of Surgeons (RCS) rats. METHODS: The presence of iron was revealed directly by proton-induced X-ray emission (PIXE) and indirectly by electron microscopy (EM). Ferritin, transferrin (Tf), and transferrin receptor (Tf-R) were localized by immunohistochemistry. Ferritin and Tf proteins were analyzed by Western blot analysis. Comparative study of Tf-R content was performed by slot-blot analysis and ferritin content was evaluated by enzyme-linked immunosorbent assay (ELISA). Ferritin and Tf-R expression was studied by reverse transcription-polymerase chain reaction (RT-PCR) and Tf expression by in situ hybridization (ISH). All studies were performed in RCS and control retinas from postnatal days (PN)20 to PN55. RESULTS: PIXE analysis showed iron accumulation in outer retina of RCS rats in a time-dependent manner. EM studies revealed irregular iron inclusions on partially degenerated outer segments (OS) of photoreceptors and lamellar whorls at PN35 and very large iron deposits on membranes from a debris layer at PN55. No such deposits were found in the inner retina. Ferritin and Tf-R expression and protein levels seemed to be unaffected in the inner part of the retina. Iron accumulation was preceded by Tf degradation, as revealed by immunohistochemistry and Western blot analysis. Tf mRNA was detected in RCS rat retinal pigment epithelium (RPE) at all stages studied. CONCLUSIONS: This study presents the first evidence for a correlation of iron homeostasis imbalance with the neurodegenerative state of the retina in RCS rats. The iron imbalance is not the underlying genetic defect but is the result of impaired RPE-photoreceptor interaction, which leads to debris accumulation and subsequent blockage of the outer retina's iron delivery pathway. The increase of iron in the photoreceptor area may enhance the vulnerability of cells to oxidative stress.  (+info)

Ferritin crystal cataracts in hereditary hyperferritinemia cataract syndrome. (6/114)

PURPOSE: Hereditary hyperferritinemia cataract syndrome (HHCS) is a genetic disease defined by cataracts, hyperferritinemia, and ferritin light-chain (L-ferritin) gene mutations. HHCS was diagnosed in this study in one of the first families known to be affected in the United States, and the basis of lens opacities in HHCS was determined. METHODS: DNA amplification and sequencing of the human L-ferritin gene was used for mutation detection. RNA electrophoretic mobility shift analysis was performed to demonstrate functional consequences of a new mutation. Opacities were characterized by immunohistochemical and electron microscopic analyses of human HHCS lens aspirate. RESULTS: HHCS was diagnosed in five members of one family who had all three hallmark features: hyperferritinemia, a prominent cataract or history, and the finding of a novel mutation in the L-ferritin gene (C33T). This mutation interferes with function of the L-ferritin transcript in an RNA gel shift assay. Light-diffracting crystalline deposits were present in cataractous lenses from two affected family members but not in control lenses. Immunohistochemical analysis showed strong anti-L-ferritin reactivity in the crystalline deposits. Analysis of these deposits by transmission electron microscopy with fast Fourier transformation demonstrated macromolecular crystalline structure of the deposits. The data were consistent with a face-centered cubic crystal having a unit crystal cell size of 17 nm, both findings characteristic of ferritin crystals grown in vitro. CONCLUSIONS: HHCS cataract is due to numerous small opacities, predominantly in the lens cortex, that are light-diffracting ferritin crystals. Patients with HHCS may be recognized by a family history of cataracts and hyperferritinemia without increased serum iron.  (+info)

Glucose and oxygen hypometabolism in aceruloplasminemia brains. (7/114)

OBJECTIVE: Aceruloplasminemia is an iron metabolic disorder caused by mutations in the ceruloplasmin gene. It is characterized by progressive neurodegeneration in association with iron accumulation. Excess iron functions as a potent catalyst of biologic oxidation. Previously we showed that an increased iron concentration is associated with the products of lipid peroxidation in the serum, cerebrospinal fluid, and brain tissues. To clarify the free radical-mediated tissue injury caused by intracellular iron accumulation through mitochondrial dysfunction. PATIENTS AND METHODS: We have measure brain oxygen and glucose metabolisms using positron emission tomography (PET) and examined brains at autopsy for iron contents and activities of the mitochondrial respiratory chain in two affected patients who had different truncation mutations of the ceruloplasmin gene. RESULTS: PET showed a marked decrease in glucose and oxygen consumption in the entire brain of aceruloplasminemia patients, with a preponderance of metabolic reduction in basal ganglia. Enzyme activities in the mitochondrial respiratory chain of the basal ganglia were reduced to approximately 45% and 42% respectively for complexes I and IV. An inverse relationship was shown between the amounts of iron accumulated and the levels of mitochondrial enzyme activities in all the brain regions examined. CONCLUSION: Iron-mediated free radicals may contribute to the impairment of mitochondrial energy metabolism in aceruloplasminemia.  (+info)

Genetic disorders affecting proteins of iron and copper metabolism: clinical implications. (8/114)

Iron and copper are essential transition metals that permit the facile transfer of electrons in a series of critical biochemical pathways. Recent work has identified the specific proteins involved in the absorption, transport, utilization, and storage of iron and copper. Remarkable progress is being made in understanding the molecular basis of disorders of human iron and copper metabolism. This review describes these proteins and examines the clinical consequences of new insights into the pathophysiology of genetic abnormalities affecting iron and copper metabolisms. Hereditary hemochromatosis is the most common genetic disorder of iron metabolism caused by mutations in the HFE gene. Aceruloplasminemia is a rare iron metabolic disorder that results from deficiency of ceruloplasmin ferroxidase activity as a consequence of mutations in the ceruloplasmin gene. Menkes disease and Wilson's disease are inherited disorders of copper metabolism resulting from the absence or dysfunction of homologous copper-transporting ATPases.  (+info)