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Tagliani S, Malaventura C, Ceccato C, Parmeggiani F, Suppiej A. Leber Mitochondrial Optic Neuropathy in Pediatric Females With Focus on Very Early Onset Cases. J Child Neurol 2023; 38:5-15. [PMID: 36659874 DOI: 10.1177/08830738221149962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The aim of this study was to describe the phenotype of Leber hereditary optic neuropathy occurring in pediatric females. This disease generally affects young adult males, but it can occur also in females, and research data in this population is lacking. The very early onset can challenge the diagnosis and delay treatment. We searched PubMed through February 2021 and identified 226 pediatric females with genetically confirmed Leber hereditary optic neuropathy and added a new case of a 3-year-old female. The male-female ratio was 1.8:1; the mean onset age in females was 11 years with the onset at 3 years of age occurring in 3 females only. Acute onset with mild visual impairment was the most common presentation, associated with optic disc edema in 16%. Differential diagnoses are pseudotumor cerebri, optic nerve drusen and optic neuritis. The outcome is poor with partial recovery in 50%, despite some receiving Idebenone therapy.
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Affiliation(s)
- Sara Tagliani
- Department of Medical Sciences, Pediatric Section, University Hospital of Ferrara, Ferrara, Italy
| | - Cristina Malaventura
- Department of Medical Sciences, Pediatric Section, University Hospital of Ferrara, Ferrara, Italy
| | | | - Francesco Parmeggiani
- Department of Translational Medicine and for Romagna, 9299University of Ferrara, Ferrara, Italy.,ERN-EYE Network - Center for Retinitis Pigmentosa of Veneto Region, 196013Camposampiero Hospital, Padova, Italy
| | - Agnese Suppiej
- Department of Medical Sciences, Pediatric Section, University Hospital of Ferrara, Ferrara, Italy.,87812Robert Hollman Foundation, Padova, Italy.,ERN-EYE Network - Center for Retinitis Pigmentosa of Veneto Region, 196013Camposampiero Hospital, Padova, Italy
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Sundaramurthy S, SelvaKumar A, Ching J, Dharani V, Sarangapani S, Yu-Wai-Man P. Leber hereditary optic neuropathy-new insights and old challenges. Graefes Arch Clin Exp Ophthalmol 2021; 259:2461-2472. [PMID: 33185731 DOI: 10.1007/s00417-020-04993-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 09/16/2020] [Accepted: 10/23/2020] [Indexed: 12/20/2022] Open
Abstract
Leber hereditary optic neuropathy (LHON) is the most common primary mitochondrial DNA (mtDNA) disorder with the majority of patients harboring one of three primary mtDNA point mutations, namely, m.3460G>A (MTND1), m.11778G>A (MTND4), and m.14484T>C (MTND6). LHON is characterized by bilateral subacute loss of vision due to the preferential loss of retinal ganglion cells (RGCs) within the inner retina, resulting in optic nerve degeneration. This review describes the clinical features associated with mtDNA LHON mutations and recent insights gained into the disease mechanisms contributing to RGC loss in this mitochondrial disorder. Although treatment options remain limited, LHON research has now entered an active translational phase with ongoing clinical trials, including gene therapy to correct the underlying pathogenic mtDNA mutation.
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Affiliation(s)
- Srilekha Sundaramurthy
- 1SN Oil and Natural Gas Corporation (ONGC) Department of Genetics & Molecular Biology, Vision Research Foundation, Chennai, India.
| | - Ambika SelvaKumar
- Department of Neuro-Ophthalmology, Medical Research Foundation, Chennai, India
| | - Jared Ching
- Cambridge Eye Unit, Addenbrooke's Hospital, Cambridge University Hospitals, Cambridge, UK
- John Van Geest Centre for Brain Repair and MRC Mitochondrial Biology Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK
| | - Vidhya Dharani
- Department of Neuro-Ophthalmology, Medical Research Foundation, Chennai, India
| | - Sripriya Sarangapani
- 1SN Oil and Natural Gas Corporation (ONGC) Department of Genetics & Molecular Biology, Vision Research Foundation, Chennai, India
| | - Patrick Yu-Wai-Man
- Cambridge Eye Unit, Addenbrooke's Hospital, Cambridge University Hospitals, Cambridge, UK
- John Van Geest Centre for Brain Repair and MRC Mitochondrial Biology Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK
- NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, UK
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Mitochondrial Genetic Heterogeneity in Leber's Hereditary Optic Neuropathy: Original Study with Meta-Analysis. Genes (Basel) 2021; 12:genes12091300. [PMID: 34573281 PMCID: PMC8472268 DOI: 10.3390/genes12091300] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 08/06/2021] [Accepted: 08/08/2021] [Indexed: 11/17/2022] Open
Abstract
Leber’s hereditary optic neuropathy (LHON) is a mitochondrial disorder that causes loss of central vision. Three primary variants (m.3460G>A, m.11778G>A, and m.14484T>C) and about 16 secondary variants are responsible for LHON in the majority of the cases. We investigated the complete mitochondrial DNA (mtDNA) sequences of 189 LHON patients and found a total of 54 disease-linked pathogenic variants. The primary variants m.11778G>A and m.14484T>C were accountable for only 14.81% and 2.64% cases, respectively. Patients with these two variants also possessed additional disease-associated variants. Among 156 patients who lacked the three primary variants, 16.02% harboured other LHON-associated variants either alone or in combination with other disease-associated variants. Furthermore, we observed that none of the haplogroups were explicitly associated with LHON. We performed a meta-analysis of m.4216T>C and m.13708G>A and found a significant association of these two variants with the LHON phenotype. Based on this study, we recommend the use of complete mtDNA sequencing to diagnose LHON, as we found disease-associated variants throughout the mitochondrial genome.
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Alharbi MA, Al-Kafaji G, Khalaf NB, Messaoudi SA, Taha S, Daif A, Bakhiet M. Four novel mutations in the mitochondrial ND4 gene of complex I in patients with multiple sclerosis. Biomed Rep 2019; 11:257-268. [PMID: 31798871 PMCID: PMC6873451 DOI: 10.3892/br.2019.1250] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 10/16/2019] [Indexed: 12/11/2022] Open
Abstract
Multiple sclerosis (MS) is an immune-mediated neurological, inflammatory disease of the central nervous system. Recent studies have suggested that genetic variants in mitochondrial DNA (mtDNA)-encoded complexes of respiratory chain, particularly, complex I (NADH dehydrogenase), contribute to the pathogenicity of MS among different ethnicities, and targeting mitochondrial function may represent a novel approach for MS therapy. In this study, we sequenced ND genes (ND1, ND2, ND3, ND4, ND4L, ND5 and ND6) encoding subunits of complex I in 124 subjects, 60 patients with relapsing-remitting MS and 64 healthy individuals, in order to identify potential novel mutations in these patients. We found several variants in ND genes in both the patients and controls, and specific variants only in patients with MS. While the majority of these variants were synonymous, 4 variants in the ND4 gene were identified as missense mutations in patients with MS. Of these, m.11150G>A was observed in one patient, whereas m.11519A>C, m.11523A>C and m.11527C>T were observed in another patient. Functional analysis predicted the mutations, m.11519A>C, m.11523A>C and m.11150G>A, as deleterious with a direct impact on ND4 protein stability and complex I function, whereas m.11527C>T mutation had no effect on ND4 protein stability. However, the 3 mutations, m.11519A>C, m.11523A>C and m.11527C>T, which were observed in the same patient, were predicted to cause a cumulative destabilizing effect on ND4 protein, and could thus disrupt complex I function. On the whole, this study identified 4 novel mutations in the mtDNA-encoded ND4 gene in patients with MS, which could lead to complex I dysfunction, and further confirmed the implication of mtDNA mutations in the pathogenicity of MS. The identified novel mutations in patients with MS may be ethnic-related and may prove to be significant in personalized treatment.
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Affiliation(s)
- Maram Atallah Alharbi
- College of Forensic Sciences, Naif Arab University for Security Sciences, Riyadh 14812, Kingdom of Saudi Arabia
| | - Ghada Al-Kafaji
- Department of Molecular Medicine, Al-Jawhara Centre for Genetics and Inherited Disorders, College of Medicine and Medical Sciences, Arabian Gulf University, Block 329, Manama, Kingdom of Bahrain
| | - Noureddine Ben Khalaf
- Department of Life Sciences, College of Graduate Studies, Arabian Gulf University, Block 329, Manama, Kingdom of Bahrain
| | - Safia Abdulsalam Messaoudi
- College of Forensic Sciences, Naif Arab University for Security Sciences, Riyadh 14812, Kingdom of Saudi Arabia
| | - Safa Taha
- Department of Molecular Medicine, Al-Jawhara Centre for Genetics and Inherited Disorders, College of Medicine and Medical Sciences, Arabian Gulf University, Block 329, Manama, Kingdom of Bahrain
| | - Abdulqader Daif
- King Saud University Medical City, Riyadh 12372, Kingdom of Saudi Arabia
| | - Moiz Bakhiet
- Department of Molecular Medicine, Al-Jawhara Centre for Genetics and Inherited Disorders, College of Medicine and Medical Sciences, Arabian Gulf University, Block 329, Manama, Kingdom of Bahrain
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Jancic J, Rovcanin B, Djuric V, Pepic A, Samardzic J, Nikolic B, Novakovic I, Kostic VS. Analysis of secondary mtDNA mutations in families with Leber's hereditary optic neuropathy: Four novel variants and their association with clinical presentation. Mitochondrion 2019; 50:132-138. [PMID: 31743754 DOI: 10.1016/j.mito.2019.10.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 10/12/2019] [Accepted: 10/30/2019] [Indexed: 01/16/2023]
Abstract
Leber's hereditary optic neuropathy (LHON) is a mitochondrial disease characterized by subacute optic atrophy which results in severe visual impairment. The penetrance, clinical expression and disease onset are variable, and frequently associated with other extraocular symptoms. The disease phenotype remains to be an intriguing question which is dependent upon primary as well as secondary mtDNA mutations. In this study we analyzed the whole mtDNA sequence in six LHON families from Serbian population. The mtDNA sequencing was performed by Sanger's method and various bioinformatic tools were used for analysis of detected mutations. LHON patients carry all three (m.3460G > A, m.11778G > A and m.14484 T > C) primary mutations, together with numerous secondary mtDNA mutations. Four novel mutations (m.4516G > A, m.8779C > T, m.13138G > A and m.15986insG) in four different families were discovered. The m.8779C > T and m.13138G > A mutations could have a potential influence on LHON symptoms, but the issue of effect of secondary mtDNA mutations in LHON patients needs to be better clarified in future studies.
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Affiliation(s)
- Jasna Jancic
- Clinic of Neurology and Psychiatry for Children and Youth, Faculty of Medicine, University of Belgrade, Belgrade, Serbia.
| | - Branislav Rovcanin
- Center for Endocrine Surgery, Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Vesna Djuric
- Clinic of Neurology and Psychiatry for Children and Youth, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Ana Pepic
- Clinic of Neurology and Psychiatry for Children and Youth, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Janko Samardzic
- Institute of Pharmacology, Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Blazo Nikolic
- Clinic of Neurology and Psychiatry for Children and Youth, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Ivana Novakovic
- Institute for Human Genetics, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Vladimir S Kostic
- Clinic of Neurology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
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Abstract
We report the case of a novel mitochondrial DNA mutation in the MT-ATP8 gene in an infant with tetralogy of Fallot. Next-generation sequencing was applied to sequence whole mitochondrial DNA of the patient. A known Leber's hereditary optic neuropathy-associated mutation (G9804A), a heteroplasmic T7501C mutation (17%), and a novel C8481 T Pro > Leu missense mutation in the MT-ATP8 gene was identified.
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Jančić J, Dejanović I, Samardžić J, Radovanović S, Pepić A, Kosanović-Jaković N, Ćetković M, Kostić V. Leber hereditary optic neuropathy in the population of Serbia. Eur J Paediatr Neurol 2014; 18:354-9. [PMID: 24508359 DOI: 10.1016/j.ejpn.2014.01.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 01/13/2014] [Accepted: 01/19/2014] [Indexed: 11/29/2022]
Abstract
BACKGROUND Leber hereditary optic neuropathy (LHON) is the most common mitochondrial disorder. However, few countries have published their population-based findings related to this multisystemic disease. THE AIM In order to get a better insight into the epidemiological and clinical picture of this maternally inherited disorder, we performed the first population-based clinical and molecular-genetic study of LHON in the Serbian population. METHODS Prospective study included patients who were diagnosed with LHON after detailed medical examination and molecular-genetic confirmation. RESULTS We identified 41 individuals from 12 genealogically unrelated families, carrying one of the three "primary" mitochondrial (mt) DNA point mutations associated with LHON. Fourteen of them were clinically affected, giving a minimum point prevalence of 1.9 per 1,000,000. The minimum point prevalence for mtDNA LHON mutations was 5.2 per 1,000,000. Male to female ratio was 6:1. Only one affected patient harboured mutant mtDNA in heteroplasmic condition. All patients were presented with common clinical findings. CONCLUSION We observed significantly lower prevalence and higher gender ratio than expected. However, frequencies of primary mutations, incidence of heteroplasmy and clinical findings are in accordance with other studies in Caucasoid populations. Our results might be a consequence of poor recognition and misdiagnosis due to lack of diagnostic possibilities of the entity in different region of our country or less likely be in part due to specific haplotype background of Serbian population which should be further investigated.
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Affiliation(s)
- Jasna Jančić
- Clinic of Neurology and Psychiatry for Children and Youth, Medical Faculty, University of Belgrade, Serbia.
| | - Ivana Dejanović
- Clinic of Neurology and Psychiatry for Children and Youth, Medical Faculty, University of Belgrade, Serbia
| | - Janko Samardžić
- Institute of Pharmacology and Toxicology, Medical Faculty, University of Belgrade, Serbia
| | | | - Ana Pepić
- Clinic of Neurology and Psychiatry for Children and Youth, Medical Faculty, University of Belgrade, Serbia
| | | | - Mila Ćetković
- Institute of Histology and Embryology, Medical Faculty, University of Belgrade, Serbia
| | - Vladimir Kostić
- Clinic of Neurology, Medical Faculty, University of Belgrade, Serbia
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Rezvani Z, Didari E, Arastehkani A, Ghodsinejad V, Aryani O, Kamalidehghan B, Houshmand M. Fifteen novel mutations in the mitochondrial NADH dehydrogenase subunit 1, 2, 3, 4, 4L, 5 and 6 genes from Iranian patients with Leber's hereditary optic neuropathy (LHON). Mol Biol Rep 2013; 40:6837-41. [PMID: 24158608 DOI: 10.1007/s11033-013-2801-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2012] [Accepted: 09/26/2013] [Indexed: 01/11/2023]
Abstract
Leber's hereditary optic neuropathy (LHON) is an optic nerve dysfunction resulting from mutations in mitochondrial DNA (mtDNA), which is transmitted in a maternal pattern of inheritance. It is caused by three primary point mutations: G11778A, G3460A and T14484C; in the mitochondrial genome. These mutations are sufficient to induce the disease, accounting for the majority of LHON cases, and affect genes that encode for the different subunits of mitochondrial complexes I and III of the mitochondrial respiratory chain. Other mutations are secondary mutations associated with the primary mutations. The purpose of this study was to determine MT-ND variations in Iranian patients with LHON. In order to determine the prevalence and distribution of mitochondrial mutations in the LHON patients, their DNA was studied using PCR and DNA sequencing analysis. Sequencing of MT-ND genes from 35 LHON patients revealed a total of 44 nucleotide variations, in which fifteen novel variations-A14020G, A13663G, C10399T, C4932A, C3893G, C10557A, C12012A, C13934T, G4596A, T12851A, T4539A, T4941A, T13255A, T14353C and del A 4513-were observed in 27 LHON patients. However, eight patients showed no variation in the ND genes. These mutations contribute to the current database of mtDNA polymorphisms in LHON patients and may facilitate the definition of disease-related mutations in human mtDNA. This research may help to understand the disease mechanism and open up new diagnostic opportunities for LHON.
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Affiliation(s)
- Zahra Rezvani
- Department of Biotechnology, Faculty of Chemistry, University of Kashan, Kashan, Iran
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Gürkan H, Ozal SA, Esgin H. Results of Mitochondrial DNA Sequence Analysis in Patients with Clinically Diagnosed Leber's Hereditary Optic Neuropathy. Balkan Med J 2012; 29:306-9. [PMID: 25207020 DOI: 10.5152/balkanmedj.2012.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Accepted: 02/24/2012] [Indexed: 11/22/2022] Open
Abstract
OBJECTIVE To investigate possible mitochondrial DNA (mtDNA) mutations in patients with Leber's hereditary optic neuropathy (LHON) in order to provide a precise diagnosis and genetic counseling. MATERIAL AND METHODS Between 1982 and 2007, ten patients were clinically diagnosed with LHON and six of these patients agreed to be involved in this study. Six healthy individuals were also included as a control group. mtDNA was isolated from peripheral blood samples and polymerase chain reaction and mtDNA sequence analysis were performed. RESULTS In one of the six patients, a homoplasmic mutant m.11778G>A mutation was detected. All of the clinically diagnosed LHON patients and the control groups had the m.14212C>T and m.14580G>A single nucleotide polymorphisms (SNPs). The m.11719A>G SNP was detected in three of six patients and four of the controls. Two of the six patients had the m.3197T>C SNP and, in addition, the m.14258G>A SNP was found in one of these two patients, while neither of these mutations were present in the control group. CONCLUSION The clinical diagnosis of LHON could be supported by molecular genetics only in one patient by the detection of one mutation. The m.3197T>C and m.14258G>A SNPs should be considered as potential mtDNA mutations due to the fact that they were detected in the patient group. These mutations should be investigated further in large case groups for suspected gene loci that could lead to optic neuropathy.
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Affiliation(s)
- Hakan Gürkan
- Department of Medical Biology, İstanbul Faculty of Medicine, İstanbul University, İstanbul, Turkey
| | - Sadık Altan Ozal
- Department of Ophtalmology, Faculty of Medicine, Trakya University, Edirne, Turkey
| | - Haluk Esgin
- Department of Ophtalmology, Faculty of Medicine, Trakya University, Edirne, Turkey
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Bosley TM, Abu-Amero KK. Assessing mitochondrial DNA nucleotide changes in spontaneous optic neuropathies. Ophthalmic Genet 2010; 31:163-72. [DOI: 10.3109/13816810.2010.514015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Houshmand M, Sharifpanah F, Tabasi A, Sanati MH, Vakilian M, Lavasani SH, Joughehdoust S. Leber's hereditary optic neuropathy: the spectrum of mitochondrial DNA mutations in Iranian patients. Ann N Y Acad Sci 2004; 1011:345-9. [PMID: 15126312 DOI: 10.1007/978-3-662-41088-2_35] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/06/2023]
Abstract
We studied 14 patients with Leber's hereditary optic neuropathy (LHON) to investigate the mtDNA haplotypes associated with the primary mutation(s). Eleven patients carried the mitochondrial DNA (mtDNA) G11778A mutation, while one had the T14484C mutation; one patient had the G3460A mutation and one the G14459A mutation. The Iranian G11778A LHON mutation was not associated with two mtDNA haplogroups-M (0.0% compared with 3.2% in healthy controls) and J (7.7% compared with 10% in healthy controls). Our results showed a similarity in the pattern of LHON primary point mutations between Iranian families with LHON and those of Russian, European, and North American origin. Our results also do not support an association between mtDNA haplogroups J and M with LHON primary point mutations.
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Affiliation(s)
- M Houshmand
- National Research Center for Genetic Engineering and Biotechnology, Tehran, Iran.
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HOUSHMAND M, SHARIFPANAH F, TABASI A, SANATI MH, VAKILIAN M, LAVASANI SH, JOUGHEHDOUST S. Leber's Hereditary Optic Neuropathy: The Spectrum of Mitochondrial DNA Mutations in Iranian Patients. Ann N Y Acad Sci 2004. [DOI: 10.1196/annals.1293.035] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Acaroğlu G, Kansu T, Doğulu CF. Visual recovery patterns in children with Leber's hereditary optic neuropathy. Int Ophthalmol 2004; 24:349-55. [PMID: 14750573 DOI: 10.1023/b:inte.0000006855.48323.f1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Three patients with Leber's hereditary optic neuropathy (LHON) showed spontaneous improvement in visual acuities after months of legal blindness. Two male patients with bilateral subacute visual loss were 14 years of age at presentation. The first male patient had a mitochondrial DNA mutation at nucleotide position 11778. The second male patient was found to be negative for the designated primary mutations (11778, 14484, 3460) and two of the secondary mutations (15257, 9804). The third patient was a 20-year-old female who presented with bilateral optic atrophy. She had been diagnosed as LHON and was found positive for the 3460 mutation when she was 15. These patients' pattern of visual recovery by developing small islands of normal vision within a central scotoma is characteristic in such rare cases of LHON.
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Affiliation(s)
- G Acaroğlu
- Social Security Eye Hospital, Neuro-ophthalmology & Orbital Disease Unit, Ankara, Turkey.
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Abstract
Mitochondria are increasingly recognized as central players in the life and death of cells and especially of neurons. The energy-dependence of retinal ganglion cells (RGC) and their axons, which form the optic nerve, is singularly skewed. In fact, while mitochondria are very abundant in the initial, unmyelinated part of the axons anterior to the lamina cribrosa, their number suddenly decreases as the myelin sheath begins more posteriorly. The vascular system also presents different blood-brain barrier properties anterior and posterior to the lamina, possibly reflecting the different metabolic needs of the optic nerve head (unmyelinated) and of the retrobulbar optic nerve (myelinated). Mitochondrial biogenesis occurs within the cellular somata of RGC in the retina. It needs the coordinated interaction of nuclear and mitochondrial genomes. Mitochondria are then transported down the axons and distributed where they are needed. These locations are along the unmyelinated portion of the nerve, under the nodes of Ranvier in the retrobulbar nerve, and at the synaptic terminals. Efficient transportation of mitochondria depends on multiple factors, including their own energy production, the integrity of the cytoskeleton and its protein components (tubulin, etc.), and adequate myelination of the axons. Any dysfunction of these systems may be of pathological relevance for optic neuropathies with primary or secondary involvement of mitochondria. Leber's hereditary optic neuropathy (LHON) is the paradigm of mitochondrial optic neuropathies where a primary role for mitochondrial dysfunction is certified by maternal inheritance and association with specific mutations in the mitochondrial DNA (mtDNA). Clinical phenocopies of this pathology are represented by the wide array of optic neuropathies associated with vitamin depletion, toxic exposures, alcohol and tobacco abuse, and use of certain drugs. Moreover, the recent identification of mutations in the nuclear gene OPA1 as the causative factor in dominant optic atrophy (DOA, Kjer's type) brought the unexpected finding that this gene encodes for a mitochondrial protein, suggesting that DOA and LHON may be linked by similar pathogenesis. Polymorphisms in this very same gene may be associated with normal tension glaucoma (NTG), which might be considered a genetically determined optic neuropathy that again shows similarities with both LHON and DOA. Exciting new developments come from first examples of mitochondrial optic neuropathies in animal models that are genetically determined or are the result of ingenious engineering of mitochondrial gene expression, or from biochemical manipulations of the respiratory complexes. Even more exciting is the first successful attempt to correct the LHON-related complex I dysfunction by the allotopic nuclear expression of the recoded mitochondrial gene. There is hope that the genetic complexities, biochemical dysfunctions, and integrated anatomical-physiological cellular relationships will soon be precisely delineated and that promising therapeutic and prophylactic strategies will be proposed.
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Affiliation(s)
- Valerio Carelli
- Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, CA, USA.
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