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Yin X, Dong Q, Fan S, Yang L, Li H, Jin Y, Laurentinah MR, Chen X, Sysa A, Fang H, Lyu J, Yu Y, Wang Y. A novel pathogenic mitochondrial DNA variant m.4344T>C in tRNA Gln causes developmental delay. J Hum Genet 2024; 69:381-389. [PMID: 38730005 DOI: 10.1038/s10038-024-01254-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Revised: 03/26/2024] [Accepted: 04/17/2024] [Indexed: 05/12/2024]
Abstract
Mitochondrial diseases are a group of genetic diseases caused by mutations in mitochondrial DNA and nuclear DNA. However, the genetic spectrum of this disease is not yet complete. In this study, we identified a novel variant m.4344T>C in mitochondrial tRNAGln from a patient with developmental delay. The mutant loads of m.4344T>C were 95% and 89% in the patient's blood and oral epithelial cells, respectively. Multialignment analysis showed high evolutionary conservation of this nucleotide. TrRosettaRNA predicted that m.4344T>C variant would introduce an additional hydrogen bond and alter the conformation of the T-loop. The transmitochondrial cybrid-based study demonstrated that m.4344T>C variant impaired the steady-state level of mitochondrial tRNAGln and decreased the contents of mitochondrial OXPHOS complexes I, III, and IV, resulting in defective mitochondrial respiration, elevated mitochondrial ROS production, reduced mitochondrial membrane potential and decreased mitochondrial ATP levels. Altogether, this is the first report in patient carrying the m.4344T>C variant. Our data uncover the pathogenesis of the m.4344T>C variant and expand the genetic mutation spectrum of mitochondrial diseases, thus contributing to the clinical diagnosis of mitochondrial tRNAGln gene variants-associated mitochondrial diseases.
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Affiliation(s)
- Xiaojie Yin
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Qiyu Dong
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Shuanglong Fan
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Lina Yang
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Hao Li
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Yijun Jin
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Mahlatsi Refiloe Laurentinah
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Xiandan Chen
- International Sakharov Environmental Institute of Belarusian State University, Minsk, 220070, Republic of Belarus
| | - Aliaksei Sysa
- International Sakharov Environmental Institute of Belarusian State University, Minsk, 220070, Republic of Belarus
| | - Hezhi Fang
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China
| | - Jianxin Lyu
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China.
- Laboratory Medicine Center, Department of Clinical Laboratory, Zhejiang Provincial People's Hospital, Affiliated People's Hospital, Hangzhou Medical College, Hangzhou, 310053, Zhejiang, China.
| | - Yongguo Yu
- Department of Pediatric Endocrinology and Genetics, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Institute for Pediatric Research, Shanghai, 200092, China.
- Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Shanghai, 200092, China.
| | - Ya Wang
- Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, School of Laboratory Medicine and Life sciences, Wenzhou Medical University, Wenzhou, 325035, Zhejiang, China.
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Meldau S, Ackermann S, Riordan G, van der Watt GF, Spencer C, Raga S, Khan K, Blackhurst DM, van der Westhuizen FH. A novel mitochondrial DNA variant in MT-ND6: m.14430A>C p.(Trp82Gly) identified in a patient with Leigh syndrome and complex I deficiency. Mol Genet Metab Rep 2024; 39:101078. [PMID: 38571879 PMCID: PMC10987324 DOI: 10.1016/j.ymgmr.2024.101078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/23/2024] [Accepted: 03/25/2024] [Indexed: 04/05/2024] Open
Abstract
Leigh syndrome is a severe progressive mitochondrial disorder mainly affecting children under the age of 5 years. It is caused by pathogenic variants in any one of more than 75 known genes in the nuclear or mitochondrial genomes. A 19-week-old male infant presented with lactic acidosis and encephalopathy following a 2-week history of irritability, neuroregression and poor weight gain. He was hypotonic with pathological reflexes, impaired vision, and nystagmus. Brain MRI showed extensive bilateral symmetrical T2 hyperintense lesions in basal ganglia, thalami, and brainstem. Metabolic workup showed elevated serum alanine, and heavy lactic aciduria with increased ketones, fumarate, malate, and alpha-ketoglutarate as well as reduced succinate on urine organic acid analysis. Lactic acidemia persisted, with only a marginally elevated lactate:pyruvate ratio (16.46, ref. 0-10). He demised at age 7 months due to respiratory failure. Exome sequencing followed by virtual gene panel analysis for pyruvate metabolism and mitochondrial defects could not identify any nuclear cause for Leigh syndrome. Mitochondrial DNA (mtDNA) genome sequencing revealed 88% heteroplasmy for a novel variant, NC_012920.1(MT-ND6):m.14430A>C p.(Trp82Gly), in blood DNA. This variant was absent from the unaffected mother's blood, fibroblast, and urine DNA, and detected at a level of 5% in her muscle DNA. Mitochondrial respiratory chain analysis revealed markedly reduced mitochondrial complex I activity in patient fibroblasts (34% of parent and control cells), and reduced NADH-linked respirometry (less than half of parental and control cells), while complex II driven respirometry remained intact. The combined clinical, genetic, and biochemical findings suggest that the novel MT-ND6 variant is the likely cause of Leigh syndrome in this patient. The mitochondrial ND6 protein is a subunit of complex I. An interesting finding was the absence of a significantly elevated lactate:pyruvate ratio in the presence of severe lactatemia, which directed initial diagnostic efforts towards excluding a pyruvate metabolism defect. This case highlights the value of a multidisciplinary approach and complete genetic workup to diagnosing mitochondrial disorders in South African patients.
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Affiliation(s)
- Surita Meldau
- National Health Laboratory Service, Groote Schuur Hospital, Cape Town, South Africa
- Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa
| | - Sally Ackermann
- Private Practice, Constantiaberg Mediclinic, Cape Town, South Africa
| | - Gillian Riordan
- Division of Paediatric Neurology, Dept of Paediatrics and Child Health, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa
| | - George F. van der Watt
- National Health Laboratory Service, Groote Schuur Hospital, Cape Town, South Africa
- Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa
| | - Careni Spencer
- Department of Medicine, Groote Schuur Hospital and Division of Human Genetics, University of Cape Town, Cape Town, South Africa
| | - Sharika Raga
- Division of Paediatric Neurology, Dept of Paediatrics and Child Health, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa
- Neuroscience Institute, University of Cape Town, South Africa
- International Centre for Genomic Medicine in Neuromuscular Diseases Study, University College London, London, United Kingdom
| | - Kashief Khan
- National Health Laboratory Service, Groote Schuur Hospital, Cape Town, South Africa
- Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa
| | - Dee M. Blackhurst
- Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa
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Maruo Y, Ueda Y, Murayama K, Takeda A. A case report of Leigh syndrome diagnosed by endomyocardial biopsy. Eur Heart J Case Rep 2021; 5:ytaa582. [PMID: 33644659 PMCID: PMC7898571 DOI: 10.1093/ehjcr/ytaa582] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 10/07/2020] [Accepted: 12/24/2020] [Indexed: 01/20/2023]
Abstract
BACKGROUND Leigh syndrome is a neurodegenerative disorder caused by mitochondrial dysfunction with both phenotypic and genetic heterogeneity. Mitochondrial impairments are usually demonstrated by skeletal muscle biopsy. We report a case of Leigh syndrome diagnosed by endomyocardial biopsy (EMB), not by skeletal muscle biopsy. CASE SUMMARY At aged 7 months, the patient had delayed motor development. He developed metabolic acidosis triggered by an infection with elevated lactate and pyruvate values in serum and cerebrospinal fluid when he was 1 year old. T2-weighted imaging on magnetic resonance imaging of the brain revealed bilateral hyperintensity in midbrain and dorsal pons. Biopsied skeletal muscle did not show evidence of mitochondrial disease. Left ventricular hypertrophy, bilateral putamen hyperintensity in T2-weighted imaging and a lactate peak in the right basal ganglia in single voxel spectroscopy, and a convulsive seizure appeared at the age of 12, 15, and 16, respectively. When he was 17 years old, biopsied myocardium showed cytoplasmic vacuolization and a marked proliferation of mitochondria within myofibrils pathologically. Respiratory chain enzyme activity of the biopsied myocardium showed decreased activity of complex I. Genetic testing revealed an m.14453 A>G mutation on the MT-ND6 gene. He was finally diagnosed with Leigh syndrome. Administration of oral 5-aminolevulinic acid reduced the frequency of seizures. DISCUSSION EMB led to the diagnosis of Leigh syndrome. Efforts to find and conduct the biopsy of affected organs are important to diagnose mitochondrial disease. EMB is a useful diagnostic method when there is a difficulty in diagnosing mitochondrial disease by skeletal muscle biopsy.
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Affiliation(s)
- Yuji Maruo
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo 060-8638, Japan.,Department of Pediatrics, Japanese Red Cross Kitami Hospital, North 6 East 2, Kitami 090-8666, Japan
| | - Yuki Ueda
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo 060-8638, Japan
| | - Kei Murayama
- Department of Metabolism, Center for Medical Genetics, Chiba Children's Hospital, 579-1 Heta-cho, Midori-ku, Chiba 266-0007, Japan
| | - Atsuhito Takeda
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo 060-8638, Japan
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