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The Mitochondrial tRNA Ser(UCN) Gene: A Novel m.7484A>G Mutation Associated with Mitochondrial Encephalomyopathy and Literature Review. Life (Basel) 2023; 13:life13020554. [PMID: 36836911 PMCID: PMC9963529 DOI: 10.3390/life13020554] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Revised: 01/26/2023] [Accepted: 02/14/2023] [Indexed: 02/18/2023] Open
Abstract
Mitochondrial tRNASer(UCN) is considered a hot-spot for non-syndromic and aminoglycoside-induced hearing loss. However, many patients have been described with more extensive neurological diseases, mainly including epilepsy, myoclonus, ataxia, and myopathy. We describe a novel homoplasmic m.7484A>G mutation in the tRNASer(UCN) gene affecting the third base of the anticodon triplet in a girl with profound intellectual disability, spastic tetraplegia, sensorineural hearing loss, a clinical history of epilepsia partialis continua and vomiting, typical of MELAS syndrome, leading to a myoclonic epilepticus status, and myopathy with severe COX deficiency at muscle biopsy. The mutation was also found in the homoplasmic condition in the mother who presented with mild cognitive deficit, cerebellar ataxia, myoclonic epilepsy, sensorineural hearing loss and myopathy with COX deficient ragged-red fibers consistent with MERRF syndrome. This is the first anticodon mutation in the tRNASer(UCN) and the second homoplasmic mutation in the anticodon triplet reported to date.
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Abstract
Progressive external ophthalmoplegia (PEO), characterized by ptosis and impaired eye movements, is a clinical syndrome with an expanding number of etiologically distinct subtypes. Advances in molecular genetics have revealed numerous pathogenic causes of PEO, originally heralded in 1988 by the detection of single large-scale deletions of mitochondrial DNA (mtDNA) in skeletal muscle of people with PEO and Kearns-Sayre syndrome. Since then, multiple point variants of mtDNA and nuclear genes have been identified to cause mitochondrial PEO and PEO-plus syndromes, including mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and sensory ataxic neuropathy dysarthria ophthalmoplegia (SANDO). Intriguingly, many of those nuclear DNA pathogenic variants impair maintenance of the mitochondrial genome causing downstream mtDNA multiple deletions and depletion. In addition, numerous genetic causes of nonmitochondrial PEO have been identified.
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Affiliation(s)
- Michio Hirano
- H. Houston Merritt Neuromuscular Research Center, Neuromuscular Medicine Division, Department of Neurology, Columbia University Irving Medical Center, New York, NY, United States.
| | - Robert D S Pitceathly
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom; NHS Highly Specialised Service for Rare Mitochondrial Disorders, Queen Square Centre for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, London, United Kingdom
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A mitochondrial myopathy-associated tRNA Ser(UCN) 7453G>A mutation alters tRNA metabolism and mitochondrial function. Mitochondrion 2020; 57:1-8. [PMID: 33279600 DOI: 10.1016/j.mito.2020.11.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 10/09/2020] [Accepted: 11/23/2020] [Indexed: 12/25/2022]
Abstract
BACKGROUND Mitochondrial disorders are a group of heterogeneous diseases characterized by biochemical disturbances in oxidative phosphorylation (OXPHOS). Mutations in mitochondrial transfer RNA (mt-tRNA) genes are the most frequently in mitochondrial disease. However, few studies have detailed the molecular mechanisms behind these mutations. METHODS We performed clinical evaluation, genetic analysis, muscle histochemistry, and molecular and biochemical investigations in muscle tissue and proband-derived cybrid cell lines. RESULTS We found a mitochondrial tRNASer(UCN) mutation (m.7453G>A) in a 15-year-old patient with severe mitochondrial myopathy. We demonstrated that this mutation caused impairment of mitochondrial translation, respiratory deficiency, overproduction of reactive oxygen species (ROS), and decreased mitochondrial membrane potential (MMP), which ultimately led to severe mitochondrial myopathy. CONCLUSION Our findings offer valuable new insights into the tRNASer(UCN) m.7453G>A mutation for both the pathogenic mechanism and functional consequences.
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Bacalhau M, Simões M, Rocha MC, Hardy SA, Vincent AE, Durães J, Macário MC, Santos MJ, Rebelo O, Lopes C, Pratas J, Mendes C, Zuzarte M, Rego AC, Girão H, Wong LJC, Taylor RW, Grazina M. Disclosing the functional changes of two genetic alterations in a patient with Chronic Progressive External Ophthalmoplegia: Report of the novel mtDNA m.7486G>A variant. Neuromuscul Disord 2018; 28:350-360. [PMID: 29398297 PMCID: PMC5952895 DOI: 10.1016/j.nmd.2017.11.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 11/14/2017] [Accepted: 11/15/2017] [Indexed: 01/06/2023]
Abstract
Chronic Progressive External Ophthalmoplegia (CPEO) is characterized by ptosis and ophthalmoplegia and is usually caused by mitochondrial DNA (mtDNA) deletions or mt-tRNA mutations. The aim of the present work was to clarify the genetic defect in a patient presenting with CPEO and elucidate the underlying pathogenic mechanism. This 62-year-old female first developed ptosis of the right eye at the age of 12 and subsequently the left eye at 45 years, and was found to have external ophthalmoplegia at the age of 55 years. Histopathological abnormalities were detected in the patient's muscle, including ragged-red fibres, a mosaic pattern of COX-deficient muscle fibres and combined deficiency of respiratory chain complexes I and IV. Genetic investigation revealed the "common deletion" in the patient's muscle and fibroblasts. Moreover, a novel, heteroplasmic mt-tRNASer(UCN) variant (m.7486G>A) in the anticodon loop was detected in muscle homogenate (50%), fibroblasts (11%) and blood (4%). Single-fibre analysis showed segregation with COX-deficient fibres for both genetic alterations. Assembly defects of mtDNA-encoded complexes were demonstrated in fibroblasts. Functional analyses showed significant bioenergetic dysfunction, reduction in respiration rate and ATP production and mitochondrial depolarization. Multilamellar bodies were detected by electron microscopy, suggesting disturbance in autophagy. In conclusion, we report a CPEO patient with two possible genetic origins, both segregating with biochemical and histochemical defect. The "common mtDNA deletion" is the most likely cause, yet the potential pathogenic effect of a novel mt-tRNASer(UCN) variant cannot be fully excluded.
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Affiliation(s)
- Mafalda Bacalhau
- FMUC - Faculty of Medicine, University of Coimbra, Coimbra, Portugal; CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal
| | - Marta Simões
- CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal
| | - Mariana C Rocha
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle Upon Tyne, UK
| | - Steven A Hardy
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle Upon Tyne, UK
| | - Amy E Vincent
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle Upon Tyne, UK
| | - João Durães
- CHUC - Neurology Department of Coimbra University Hospitals, Coimbra, Portugal
| | - Maria C Macário
- CHUC - Neurology Department of Coimbra University Hospitals, Coimbra, Portugal
| | - Maria João Santos
- FMUC - Faculty of Medicine, University of Coimbra, Coimbra, Portugal; CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal
| | - Olinda Rebelo
- CHUC - Neurology Department of Coimbra University Hospitals, Coimbra, Portugal
| | - Carla Lopes
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal
| | - João Pratas
- CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal
| | - Cândida Mendes
- CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal
| | - Mónica Zuzarte
- IBILI - Institute for Biomedical Imaging and Life Sciences, University of Coimbra, Coimbra, Portugal
| | - A Cristina Rego
- FMUC - Faculty of Medicine, University of Coimbra, Coimbra, Portugal; CNC - Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal
| | - Henrique Girão
- FMUC - Faculty of Medicine, University of Coimbra, Coimbra, Portugal; IBILI - Institute for Biomedical Imaging and Life Sciences, University of Coimbra, Coimbra, Portugal
| | - Lee-Jun C Wong
- Mitochondrial Diagnostic Laboratory, Baylor College of Medicine, Houston, USA
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle Upon Tyne, UK
| | - Manuela Grazina
- FMUC - Faculty of Medicine, University of Coimbra, Coimbra, Portugal; CNC - Center for Neuroscience and Cell Biology, Laboratory of Biochemical Genetics, University of Coimbra, Coimbra, Portugal.
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