Leber's hereditary optic neuropathy (LHON/11778) with myoclonus: report of two cases.
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The previously unrecognised association of myoclonus in two patients with LHON with the 11778/ND4 pathogenic mutation is described. EEG failed to disclose epileptic figures, and a back averaging study suggested that myoclonus was cortical in origin in both patients. (+info)
Organization of the human IMPG2 gene and its evaluation as a candidate gene in age-related macular degeneration and other retinal degenerative disorders.
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PURPOSE: To characterize the genomic organization of human IMPG2, the gene encoding the retinal interphotoreceptor matrix (IPM) proteoglycan IPM 200, to evaluate its relationship to IPM 150, and to evaluate its involvement in inherited retinopathies, such as age-related macular degeneration, retinitis pigmentosa, and Leber congenital amaurosis. METHODS: After isolation of human genomic clones, the structure of IMPG2 was determined by sequence analysis. Mutational analyses were conducted on genomic DNA isolated from 316 probands using single-strand conformation polymorphism analysis. RESULTS: The IMPG2 gene is organized into 19 exons, and the structure of the gene is highly similar to that of the IMPG1 gene, which encodes another retinal proteoglycan, IPM 150. Mutational analyses indicate that the observed sequence changes are present at approximately equal rates in donors with and without retinal disease. Additional data derived from RT-PCR and Northern blot analysis show that IMPG2 is processed in the human retina into multiple alternatively sized transcripts that may represent splicing isoforms. CONCLUSIONS: Analysis of the overall relationship of human IMPG2 (located on chromosome 3q12.2-12.3) to human IMPG1 (located on chromosome 6q14) suggests that these genes have evolved from a common ancestral gene. Although this is an excellent candidate gene for hereditary retinopathies, single-strand conformation polymorphism analyses provided no evidence that variations in IMPG2 coding region are responsible for the inherited retinopathies examined. (+info)
Cells bearing mutations causing Leber's hereditary optic neuropathy are sensitized to Fas-Induced apoptosis.
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Three prevalent mitochondrial DNA pathogenic mutations at positions 11778, 3460, and 14484, which affect different subunits of Complex I, cause retinal ganglion cell death and optic nerve atrophy in Leber's hereditary optic neuropathy (LHON). The cell death is painless and without inflammation, consistent with an apoptotic mechanism. We have investigated the possibility that the LHON mutation confers a pro-apoptotic stimulus and have tested the sensitivity of osteosarcoma-derived cybrid cells carrying the most common and severe mutations (11778 and 3460) to cell death induced by Fas. We observed that LHON cybrids were sensitized to Fas-dependent death. Control cells that bear the same mitochondrial genetic background (the J haplogroup) without the pathogenic 11778 mutation are no more sensitive than other controls, indicating that increased Fas-dependent death in LHON cybrids was induced by the LHON pathogenic mutations. The type of death was apoptotic by several criteria, including induction by Fas, inhibition by the caspase inhibitor zVAD-fmk (zVal-Ala-Asp-fluoro-methyl ketone), activation of DEVDase activity (Asp-Glu-Val-Asp protease), specific cleavage of caspase-3, DNA fragmentation, and increased Annexin-V labeling. These data indicate that the most common and severe LHON pathogenic mutations 11778 and 3460 predispose cells to apoptosis, which may be relevant for the pathophysiology of cell death in LHON, and potential therapy. (+info)
Identification of a gene locus for Senior-Loken syndrome in the region of the nephronophthisis type 3 gene.
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Senior-Loken syndrome is an autosomal recessive disease with the main features of nephronophthisis (NPH) and Leber congenital amaurosis. The gene for adolescent nephronophthisis (NPHP3) was recently localized to chromosome 3q21-q22. The hypothesis was tested that Senior-Loken syndrome (SLS) might localize to the same region by studying a kindred of German ancestry with extended consanguinity and typical findings of SLS. Twenty highly polymorphic markers located in the vicinity of the NPHP3 genetic region were tested. Haplotype analysis revealed homozygosity by descent in affected individuals, and linkage analysis yielded a parametric maximum multipoint logarithm of likelihood of odds (LOD) score of 3.14, thus identifying the first locus for SLS. The SLS1 locus is flanked by D3S1587 and D3S621 and contains a 14-cM interval that contains the whole critical NPHP3 region. Three additional families with SLS were studied, and evidence for genetic heterogeneity in one of them was found. Localization of a SLS locus to the region of NPHP3 opens the possibilities of both diseases arising by mutations within the same pleiotropic gene or two adjacent genes. (+info)
Differentiation-specific effects of LHON mutations introduced into neuronal NT2 cells.
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Inheritance of one of three primary mutations at positions 11778, 3460 or 14484 of the mitochondrial genome in subunits of Complex I causes Leber's Hereditary Optic Neuropathy (LHON), a specific degeneration of the optic nerve, resulting in bilateral blindness. It has been unclear why inheritance of a systemic mitochondrial mutation would result in a specific neurodegeneration. To address the neuron-specific degenerative phenotype of the LHON genotype, we have created cybrids using a neuronal precursor cell line, Ntera 2/D1 (NT2), containing mitochondria from patient lymphoblasts bearing the most common LHON mutation (11778) and the most severe LHON mutation (3460). The undifferentiated LHON-NT2 mutant cells were not significantly different from the parental cell control in terms of mtDNA/nDNA ratio, mitochondrial membrane potential, reactive oxygen species (ROS) production or the ability to reduce Alamar Blue. Differentiation of NT2s resulted in a neuronal morphology and neuron-specific pattern of gene expression, and a 3-fold reduction in mtDNA/nDNA ratio in both mutant and control cells; however, the differentiation protocol yielded significantly less LHON cells than controls, by 30%, indicating either a decreased proliferative potential or increased cell death of the LHON-NT2 cells. Differentiation of the cells to the neuronal form also resulted in significant increases in ROS production in the LHON-NT2 neurons versus controls, which is abolished by rotenone, a specific inhibitor of Complex I. We infer that the LHON genotype requires a differentiated neuronal environment in order to induce increased mitochondrial ROS, which may be the cause of the reduced NT2 yield; and suggest that the LHON degenerative phenotype may be the result of an increase in mitochondrial superoxide which is caused by the LHON mutations, possibly mediated through neuron-specific alterations in Complex I structure. (+info)
On the genetics of retinitis pigmentosa and on mutation-independent approaches to therapeutic intervention.
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Retinitis pigmentosa (RP), the group of hereditary conditions involving death of retinal photoreceptors, represents the most prevalent cause of visual handicap among working populations in developed countries. Here we provide an overview of the molecular pathologies associated with such disorders, from which it becomes clearly apparent that RP is one of the most genetically heterogeneous of hereditary conditions for which molecular pathologies have so far been elucidated. While heterogeneity of such magnitude would appear to represent a major impediment to the development of therapeutics, mutation-independent approaches to therapy are being developed to effectively by-pass such diversity in genetic aetiology. The implications of such technologies in terms of therapeutic intervention in RP, and indeed other genetically heterogeneous conditions, will be addressed. (+info)
Recovery of visual functions in a mouse model of Leber congenital amaurosis.
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The visual process is initiated by the photoisomerization of 11-cis-retinal to all-trans-retinal. For sustained vision the 11-cis-chromophore must be regenerated from all-trans-retinal. This requires RPE65, a dominant retinal pigment epithelium protein. Disruption of the RPE65 gene results in massive accumulation of all-trans-retinyl esters in the retinal pigment epithelium, lack of 11-cis-retinal and therefore rhodopsin, and ultimately blindness. We reported previously (Van Hooser, J. P., Aleman, T. S., He, Y. G., Cideciyan, A. V., Kuksa, V., Pittler, S. J., Stone, E. M., Jacobson, S. G., and Palczewski, K. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 8623-8628) that in Rpe65-/- mice, oral administration of 9-cis-retinal generated isorhodopsin, a rod photopigment, and restored light sensitivity to the electroretinogram. Here, we provide evidence that early intervention by 9-cis-retinal administration significantly attenuated retinal ester accumulation and supported rod retinal function for more than 6 months post-treatment. In single cell recordings rod light sensitivity was shown to be a function of the amount of regenerated isorhodopsin; high doses restored rod responses with normal sensitivity and kinetics. Highly attenuated residual rod function was observed in untreated Rpe65-/- mice. This rod function is likely a consequence of low efficiency production of 11-cis-retinal by photo-conversion of all-trans-retinal in the retina as demonstrated by retinoid analysis. These studies show that pharmacological intervention produces long lasting preservation of visual function in dark-reared Rpe65-/- mice and may be a useful therapeutic strategy in recovering vision in humans diagnosed with Leber congenital amaurosis caused by mutations in the RPE65 gene, an inherited group of early onset blinding and retinal degenerations. (+info)
Leber hereditary optic neuropathy.
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Leber hereditary optic neuropathy (LHON) is a mitochondrial genetic disease that preferentially causes blindness in young adult males, affecting about 1 in 25 000 of the British population. It is characterised by bilateral subacute loss of central vision owing to focal degeneration of the retinal ganglion cell layer and optic nerve. Over 95% of LHON cases are primarily the result of one of three mitochondrial DNA (mtDNA) point mutations, G3460A, G11778A, and T14484C, which all involve genes encoding complex I subunits of the respiratory chain. An intriguing feature of LHON is that only approximately 50% of males and approximately 10% of females who harbour a pathogenic mtDNA mutation actually develop the optic neuropathy. This marked incomplete penetrance and gender bias imply that additional mitochondrial and/or nuclear genetic factors must be modulating the phenotypic expression of LHON. It is also likely that environmental factors contribute to the onset of visual failure. However, these secondary precipitating factors remain poorly defined at present. In this review, we describe the natural history of this optic nerve disorder and highlight issues relating to clinical diagnosis, management, and genetic counselling. We also discuss the findings of recently published studies and the light they shed on the complex aetiology and pathophysiology of LHON. (+info)