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Gilea AI, Magistrati M, Notaroberto I, Tiso N, Dallabona C, Baruffini E. The Saccharomyces cerevisiae mitochondrial DNA polymerase and its contribution to the knowledge about human POLG-related disorders. IUBMB Life 2023; 75:983-1002. [PMID: 37470284 DOI: 10.1002/iub.2770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 07/05/2023] [Indexed: 07/21/2023]
Abstract
Most eukaryotes possess a mitochondrial genome, called mtDNA. In animals and fungi, the replication of mtDNA is entrusted by the DNA polymerase γ, or Pol γ. The yeast Pol γ is composed only of a catalytic subunit encoded by MIP1. In humans, Pol γ is a heterotrimer composed of a catalytic subunit homolog to Mip1, encoded by POLG, and two accessory subunits. In the last 25 years, more than 300 pathological mutations in POLG have been identified as the cause of several mitochondrial diseases, called POLG-related disorders, which are characterized by multiple mtDNA deletions and/or depletion in affected tissues. In this review, at first, we summarize the biochemical properties of yeast Mip1, and how mutations, especially those introduced recently in the N-terminal and C-terminal regions of the enzyme, affect the in vitro activity of the enzyme and the in vivo phenotype connected to the mtDNA stability and to the mtDNA extended and point mutability. Then, we focus on the use of yeast harboring Mip1 mutations equivalent to the human ones to confirm their pathogenicity, identify the phenotypic defects caused by these mutations, and find both mechanisms and molecular compounds able to rescue the detrimental phenotype. A closing chapter will be dedicated to other polymerases found in yeast mitochondria, namely Pol ζ, Rev1 and Pol η, and to their genetic interactions with Mip1 necessary to maintain mtDNA stability and to avoid the accumulation of spontaneous or induced point mutations.
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Affiliation(s)
- Alexandru Ionut Gilea
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
| | - Martina Magistrati
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
| | - Ilenia Notaroberto
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
| | - Natascia Tiso
- Department of Biology, University of Padova, Padova, Italy
| | - Cristina Dallabona
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
| | - Enrico Baruffini
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
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Lopes-Marques M, Silva R, Serrano C, Gomes V, Cardoso A, Prata MJ, Amorim A, Azevedo L. Complex interactions between p.His558Arg and linked variants in the sodium voltage-gated channel alpha subunit 5 (Na V 1.5). PeerJ 2022; 10:e13913. [PMID: 35996667 PMCID: PMC9392453 DOI: 10.7717/peerj.13913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 07/27/2022] [Indexed: 01/19/2023] Open
Abstract
Common genetic polymorphisms may modify the phenotypic outcome when co-occurring with a disease-causing variant, and therefore understanding their modulating role in health and disease is of great importance. The polymorphic p.His558Arg variant of the sodium voltage-gated channel alpha subunit 5 (Na V 1.5) encoded by the SCN5A gene is a case in point, as several studies have shown it can modify the clinical phenotype in a number of cardiac diseases. To evaluate the genetic backgrounds associated with this modulating effect, we reanalysed previous electrophysiological findings regarding the p.His558Arg variant and further assessed its patterns of genetic diversity in human populations. The Na V 1.5 p.His558Arg variant was found to be in linkage disequilibrium with six other polymorphic variants that previously were also associated with cardiac traits in GWAS analyses. On account of this, incongruent reports that Arg558 allele can compensate, aggravate or have no effect on Na V 1.5, likely might have arose due to a role of p.His558Arg depending on the additional linked variants. Altogether, these results indicate a major influence of the epistatic interactions between SCN5A variants, revealing also that phenotypic severity may depend on the polymorphic background associated to each individual genome.
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Affiliation(s)
- Monica Lopes-Marques
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Raquel Silva
- Center for Interdisciplinary Research in Health (CIIS), Universidade Católica Portuguesa, Faculdade de Medicina Dentária, Viseu, Portugal
| | - Catarina Serrano
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Verónica Gomes
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Ana Cardoso
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Maria João Prata
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Antonio Amorim
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
| | - Luisa Azevedo
- IPATIMUP-Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,Faculty of Sciences, University of Porto, Porto, Portugal,Population Genetics and Evolution, Institute of Innovation and Investigation in Health (i3S), Porto, Portugal
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Jha R, Patel H, Dubey R, Goswami JN, Bhagwat C, Saini L, K Manokaran R, John BM, Kovilapu UB, Mohimen A, Saxena A, Sondhi V. Clinical and molecular spectrum associated with Polymerase-γ related disorders. J Child Neurol 2022; 37:246-255. [PMID: 34986040 DOI: 10.1177/08830738211067065] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND POLG pathogenic variants are the commonest single-gene cause of inherited mitochondrial disease. However, the data on clinicogenetic associations in POLG-related disorders are sparse. This study maps the clinicogenetic spectrum of POLG-related disorders in the pediatric population. METHODS Individuals were recruited across 6 centers in India. Children diagnosed between January 2015 and August 2020 with pathogenic or likely pathogenic POLG variants and age of onset <15 years were eligible. Phenotypically, patients were categorized into Alpers-Huttenlocher syndrome; myocerebrohepatopathy syndrome; myoclonic epilepsy, myopathy, and sensory ataxia; ataxia-neuropathy spectrum; Leigh disease; and autosomal dominant / recessive progressive external ophthalmoplegia. RESULTS A total of 3729 genetic reports and 4256 hospital records were screened. Twenty-two patients with pathogenic variants were included. Phenotypically, patients were classifiable into Alpers-Huttenlocher syndrome (8/22; 36.4%), progressive external ophthalmoplegia (8/22; 36.4%), Leigh disease (2/22; 9.1%), ataxia-neuropathy spectrum (2/22; 9.1%), and unclassified (2/22; 9.1%). The prominent clinical manifestations included developmental delay (n = 14; 63.7%), neuroregression (n = 14; 63.7%), encephalopathy (n = 11; 50%), epilepsy (n = 11; 50%), ophthalmoplegia (n = 8; 36.4%), and liver dysfunction (n = 8; 36.4%). Forty-four pathogenic variants were identified at 13 loci, and these were clustered at exonuclease (18/44; 40.9%), linker (13/44; 29.5%), polymerase (10/44; 22.7%), and N-terminal domains (3/44; 6.8%). Genotype-phenotype analysis suggested that serious outcomes including neuroregression (odds ratio [OR] 11, 95% CI 2.5, 41), epilepsy (OR 9, 95% CI 2.4, 39), encephalopathy (OR 5.7, 95% CI 1.4, 19), and hepatic dysfunction (OR 4.6, 95% CI 21.3, 15) were associated with at least 1 variant involving linker or polymerase domain. CONCLUSIONS We describe the clinical subgroups and their associations with different POLG domains. These can aid in the development of follow-up and management strategies of presymptomatic individuals.
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Affiliation(s)
- Ruchika Jha
- Department of Pediatrics, 29590Armed Forces Medical College, Pune, India
| | - Harshkumar Patel
- Department of Pediatric Neurology, 246889Zydus Hospital, Ahmedabad, India
| | - Rachana Dubey
- Department of Pediatric Neurology, Medanta Hospital, Indore, India
| | - Jyotindra N Goswami
- Department of Pediatrics, Army Hospital (Research & Referral), New Delhi, India
| | - Chandana Bhagwat
- Department of Pediatrics, Pediatric Neurology Unit, 29751Postgraduate Institute of Medical Education and Research, Chandigarh, India
| | - Lokesh Saini
- Department of Pediatrics, Pediatric Neurology Unit, 29751Postgraduate Institute of Medical Education and Research, Chandigarh, India
| | - Ranjith K Manokaran
- Division of Pediatric Neurology, Department of Neurology, 204733Sri Ramachandra Institute of Higher Education, Chennai, India
| | - Biju M John
- Department of Pediatrics, 29590Armed Forces Medical College, Pune, India
| | - Uday B Kovilapu
- Department of Radiodiagnosis, 29590Armed Forces Medical College, Pune, India
| | - Aneesh Mohimen
- Department of Radiodiagnosis, 462017Command Hospital (Central Command), Lucknow, India
| | - Apoorv Saxena
- Department of Pediatrics, 29590Armed Forces Medical College, Pune, India
| | - Vishal Sondhi
- Department of Pediatrics, 29590Armed Forces Medical College, Pune, India
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Lopes‐Marques M, Pacheco AR, Peixoto MJ, Cardoso AR, Serrano C, Amorim A, Prata MJ, Cooper DN, Azevedo L. Common polymorphic OTC variants can act as genetic modifiers of enzymatic activity. Hum Mutat 2021; 42:978-989. [PMID: 34015158 PMCID: PMC8362079 DOI: 10.1002/humu.24221] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Revised: 05/05/2021] [Accepted: 05/18/2021] [Indexed: 12/24/2022]
Abstract
Understanding the role of common polymorphisms in modulating the clinical phenotype when they co‐occur with a disease‐causing lesion is of critical importance in medical genetics. We explored the impact of apparently neutral common polymorphisms, using the gene encoding the urea cycle enzyme, ornithine transcarbamylase (OTC), as a model system. Distinct combinations of genetic backgrounds embracing two missense polymorphisms were created in cis with the pathogenic p.Arg40His replacement. In vitro enzymatic assays revealed that the polymorphic variants were able to modulate OTC activity both in the presence or absence of the pathogenic lesion. First, we found that the combination of the minor alleles of polymorphisms p.Lys46Arg and p.Gln270Arg significantly enhanced enzymatic activity in the wild‐type protein. Second, enzymatic assays revealed that the minor allele of the p.Gln270Arg polymorphism was capable of ameliorating OTC activity when combined in cis with the pathogenic p.Arg40His replacement. Structural analysis predicted that the minor allele of the p.Gln270Arg polymorphism would serve to stabilize the OTC wild‐type protein, thereby corroborating the results of the experimental assays. Our findings demonstrate the potential importance of cis‐interactions between common polymorphic variants and pathogenic missense mutations and illustrate how standing genetic variation can modulate protein function.
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Affiliation(s)
- Mónica Lopes‐Marques
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
| | - Ana Rita Pacheco
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
| | - Maria João Peixoto
- ICVS‐ Life and Health Sciences Research Institute, School of MedicineUniversity of MinhoBragaPortugal
- ICVS/3B's‐PT Government Associate LaboratoryBragaGuimarãesPortugal
| | - Ana Rita Cardoso
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
| | - Catarina Serrano
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
| | - António Amorim
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
| | - Maria João Prata
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
| | - David N. Cooper
- Institute of Medical Genetics; School of MedicineCardiff UniversityCardiffUK
| | - Luísa Azevedo
- i3S‐Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution GroupUniversidade do PortoPortoPortugal
- IPATIMUP‐Institute of Molecular Pathology and Immunology, Population Genetics and Evolution GroupUniversity of PortoPortoPortugal
- Faculty of Sciences, Department of BiologyUniversity of PortoPortoPortugal
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A case of drug-induced parkinsonism and tardive akathisia with e1143g polymerase γ mutation-innocent bystander or a culprit? J Clin Transl Res 2021; 7:297-301. [PMID: 34179544 PMCID: PMC8221753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/30/2021] [Accepted: 03/30/2021] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND AND AIM Polymerase γ (POLG) is a protein that plays a pivotal role in the replication of the mitochondrial genome. POLG-related disorders constitute a sequence of overlying phenotypes that can present from early infancy to late adulthood. Parkinsonism is the most common movement disorder associated with POLG mutation. We also summarize all reported cases of POLG-related Parkinsonism, along with a literature review. CASE DESCRIPTION We present the case of an 80-year-old male presented with complaints of episodic confusion, tremors, and restlessness. He has been on risperidone for psychosis. A normal DaT scan ruled out Parkinson's disease, and molecular analysis for POLG was positive (E1143G). He was diagnosed with drug-induced Parkinsonism and tardive akathisia with an incidental POLG mutation. CONCLUSIONS A literature search revealed 55 cases of "POLG-related Parkinsonism" that met our criteria. These mutations can clinically affect multiple organ systems. Parkinsonism is the most common movement disorder reported in association with POLG mutations. We conducted a molecular analysis in our patient due to his Parkinsonism and recurrent episodes of encephalopathy. E1143G mutation found in our case was coincidental and reported a non-pathogenic or benign variant in literature. RELEVANCE FOR PATIENTS E1143G is a non-pathogenic variant and multiple studies have shown that its co-occurrence with other POLG mutations can aggravate disease occurrence and severity. Literature findings and the experience from our own case indicate that the pathogenicity of E1143G is debatable, and future studies involving this particular variant may help understand its pathological consequences.
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Golubickaite I, Ugenskiene R, Korobeinikova E, Gudaitiene J, Vaitiekus D, Poskiene L, Juozaityte E. The impact of mitochondria-related POLG and TFAM variants on breast cancer pathomorphological characteristics and patient outcomes. Biomarkers 2021; 26:343-353. [PMID: 33715547 DOI: 10.1080/1354750x.2021.1900397] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
PURPOSE Breast cancer is the most frequent female cancer, leading to relapse with distant metastasis of approximately one-third of patients. Cancer is usually considered a genetic disease involving mutations in nuclear DNA. However, genes, coding for mitochondrial proteins or regulatory molecules, are rarely under consideration. This study aimed to analyse 10 single nucleotide variants in POLG and TFAM genes and assess their association with tumour phenotype and disease outcome. MATERIALS AND METHODS A total of 234 breast cancer patients were included in this study. Variations were determined with Real-Time PCR using TaqMan® probes. RESULTS We found that patients with POLG rs2307441 TT and CT genotypes had a lower probability for vascular invasion than those with CC genotype (p = 0.001). Patients with POLG rs2072267 AG genotype were predisposed for progression compared with GG genotype (p = 0.015). TFAM rs3900887 TT genotype was associated with a higher probability for positive oestrogen receptors (p = 0.003) and lymphatic invasion (p = 0.001) in comparison to AA genotype, patients with TT (p = 0.000) were more likely to have positive lymph nodes. CONCLUSIONS Our data suggest that variations in POLG and TFAM genes are important determinacies of tumour phenotype and disease outcome in breast cancer patients.
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Affiliation(s)
- Ieva Golubickaite
- Institute of Biology Systems and Genetic Research, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Rasa Ugenskiene
- Institute of Biology Systems and Genetic Research, Lithuanian University of Health Sciences, Kaunas, Lithuania.,Institute of Oncology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Erika Korobeinikova
- Department of Oncology and Hematology, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Jurgita Gudaitiene
- Institute of Oncology, Lithuanian University of Health Sciences, Kaunas, Lithuania.,Department of Oncology and Hematology, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Domas Vaitiekus
- Department of Oncology and Hematology, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Lina Poskiene
- Department of Pathological Anatomy, Lithuanian University of Health Sciences, Kaunas, Lithuania.,Department of Pathology, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Elona Juozaityte
- Institute of Oncology, Lithuanian University of Health Sciences, Kaunas, Lithuania.,Department of Oncology and Hematology, Hospital of Lithuanian University of Health Sciences, Kaunas, Lithuania
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MITOL-dependent ubiquitylation negatively regulates the entry of PolγA into mitochondria. PLoS Biol 2021; 19:e3001139. [PMID: 33657094 PMCID: PMC7959396 DOI: 10.1371/journal.pbio.3001139] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 03/15/2021] [Accepted: 02/04/2021] [Indexed: 02/01/2023] Open
Abstract
Mutations in mitochondrial replicative polymerase PolγA lead to progressive external ophthalmoplegia (PEO). While PolγA is the known central player in mitochondrial DNA (mtDNA) replication, it is unknown whether a regulatory process exists on the mitochondrial outer membrane which controlled its entry into the mitochondria. We now demonstrate that PolγA is ubiquitylated by mitochondrial E3 ligase, MITOL (or MARCH5, RNF153). Ubiquitylation in wild-type (WT) PolγA occurs at Lysine 1060 residue via K6 linkage. Ubiquitylation of PolγA negatively regulates its binding to Tom20 and thereby its mitochondrial entry. While screening different PEO patients for mitochondrial entry, we found that a subset of the PolγA mutants is hyperubiquitylated by MITOL and interact less with Tom20. These PolγA variants cannot enter into mitochondria, instead becomes enriched in the insoluble fraction and undergo enhanced degradation. Hence, mtDNA replication, as observed via BrdU incorporation into the mtDNA, was compromised in these PEO mutants. However, by manipulating their ubiquitylation status by 2 independent techniques, these PEO mutants were reactivated, which allowed the incorporation of BrdU into mtDNA. Thus, regulated entry of non-ubiquitylated PolγA may have beneficial consequences for certain PEO patients. This study shows that mitochondrial entry of the replicative polymerase PolgA is regulated by ubiquitylation by the E3 ligase MITOL; however, by manipulating their ubiquitylation status, some progressive external ophthalmoplegia mutants whose PolgA is polyubiquitylated and cannot enter the mitochondrion can be reactivated and hence become functionally active.
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Clinico-pathological and Molecular Spectrum of Mitochondrial Polymerase γ Mutations in a Cohort from India. J Mol Neurosci 2021; 71:2219-2228. [PMID: 33469851 DOI: 10.1007/s12031-020-01765-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 11/23/2020] [Indexed: 01/03/2023]
Abstract
Polymerase γ catalytic subunit (POLG), a nuclear gene, encodes the enzyme responsible for mitochondrial DNA (mtDNA) replication. POLG mutations are a major cause of inherited mitochondrial diseases. They present with varied phenotypes, age of onset, and severity. Reports on POLG mutations from India are limited. Hence, this study aimed to describe the clinico-pathological and molecular observations of POLG mutations. A total of 446 patients with clinical diagnosis of mitochondrial disorders were sequenced for all exons and intron-exon boundaries of POLG. Of these, 19 (4.26%) patients (M:F: 10:9) had POLG mutations. The age of onset ranged from 5 to 55 years with an overlapping phenotypic spectrum. Ptosis, peripheral neuropathy, seizures, and ataxia were the common neurological features observed. The most common clinical phenotype was chronic progressive external ophthalmoplegia (CPEO) and CPEO plus (n = 14). Muscle biopsy showed characteristic features of mitochondrial myopathy in fourteen patients (14/19) and respiratory chain enzyme deficiency in eleven patients (11/19). Multiple mtDNA deletions were seen in 47.36% (9/19) patients. Eight pathogenic POLG variations including two novel variations (p.G132R and p.V1106A) were identified. The common pathogenic mutation identified was p.L304R, being present in eight patients (42.1%) predominantly in the younger age group followed by p.W748S in four patients (21%). To the best of our knowledge, this is the first extensive study from India, highlights the clinico-pathological and molecular spectrum of POLG mutations.
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Abstract
The POLG gene encodes the mitochondrial DNA polymerase that is responsible for replication of the mitochondrial genome. Mutations in POLG can cause early childhood mitochondrial DNA (mtDNA) depletion syndromes or later-onset syndromes arising from mtDNA deletions. POLG mutations are the most common cause of inherited mitochondrial disorders, with as many as 2% of the population carrying these mutations. POLG-related disorders comprise a continuum of overlapping phenotypes with onset from infancy to late adulthood. The six leading disorders caused by POLG mutations are Alpers-Huttenlocher syndrome, which is one of the most severe phenotypes; childhood myocerebrohepatopathy spectrum, which presents within the first 3 years of life; myoclonic epilepsy myopathy sensory ataxia; ataxia neuropathy spectrum; autosomal recessive progressive external ophthalmoplegia; and autosomal dominant progressive external ophthalmoplegia. This Review describes the clinical features, pathophysiology, natural history and treatment of POLG-related disorders, focusing particularly on the neurological manifestations of these conditions.
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Cardoso AR, Lopes-Marques M, Silva RM, Serrano C, Amorim A, Prata MJ, Azevedo L. Essential genetic findings in neurodevelopmental disorders. Hum Genomics 2019; 13:31. [PMID: 31288856 PMCID: PMC6617629 DOI: 10.1186/s40246-019-0216-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Accepted: 06/26/2019] [Indexed: 12/12/2022] Open
Abstract
Neurodevelopmental disorders (NDDs) represent a growing medical challenge in modern societies. Ever-increasing sophisticated diagnostic tools have been continuously revealing a remarkably complex architecture that embraces genetic mutations of distinct types (chromosomal rearrangements, copy number variants, small indels, and nucleotide substitutions) with distinct frequencies in the population (common, rare, de novo). Such a network of interacting players creates difficulties in establishing rigorous genotype-phenotype correlations. Furthermore, individual lifestyles may also contribute to the severity of the symptoms fueling a large spectrum of gene-environment interactions that have a key role on the relationships between genotypes and phenotypes.Herein, a review of the genetic discoveries related to NDDs is presented with the aim to provide useful general information for the medical community.
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Affiliation(s)
- Ana R Cardoso
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal.,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal
| | - Mónica Lopes-Marques
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal.,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal
| | - Raquel M Silva
- Department of Medical Sciences and iBiMED, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal.,Present Address: Center for Interdisciplinary Research in Health (CIIS), Institute of Health Sciences (ICS), Universidade Católica Portuguesa, 3504-505, Viseu, Portugal
| | - Catarina Serrano
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal.,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal
| | - António Amorim
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal.,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal
| | - Maria J Prata
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal.,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal
| | - Luísa Azevedo
- i3S - Instituto de Investigação e Inovação em Saúde, Population Genetics and Evolution Group, Universidade do Porto, Rua Alfredo Allen 208, 4200-135, Porto, Portugal. .,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Rua Júlio Amaral de Carvalho 45, 4200-135, Porto, Portugal. .,Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal.
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Piekutowska-Abramczuk D, Kaliszewska M, Sułek A, Jurkowska N, Ołtarzewski M, Jabłońska E, Trubicka J, Głowacka A, Ciara E, Kowalski P, Langiewicz-Wojciechowska K, Tesarova M, Zeman J, Kierdaszuk B, Kuczyński D, Chmielewski D, Szymańska E, Bakuła A, Łusakowska A, Lipowska M, Brodacki B, Pera J, Dorobek M, Rydzanicz M, Płoski R, Chrzanowska KH, Bartnik E, Placha G, Kamińska A, Kostera-Pruszczyk A, Krajewska-Walasek M, Tońska K, Pronicka E. The frequency of mitochondrial polymerase gamma related disorders in a large Polish population cohort. Mitochondrion 2019; 47:179-187. [DOI: 10.1016/j.mito.2018.11.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Revised: 10/02/2018] [Accepted: 11/02/2018] [Indexed: 02/06/2023]
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12
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Blázquez-Bermejo C, Carreño-Gago L, Molina-Granada D, Aguirre J, Ramón J, Torres-Torronteras J, Cabrera-Pérez R, Martín MÁ, Domínguez-González C, de la Cruz X, Lombès A, García-Arumí E, Martí R, Cámara Y. Increased dNTP pools rescue mtDNA depletion in human POLG-deficient fibroblasts. FASEB J 2019; 33:7168-7179. [PMID: 30848931 DOI: 10.1096/fj.201801591r] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Polymerase γ catalytic subunit (POLG) gene encodes the enzyme responsible for mitochondrial DNA (mtDNA) synthesis. Mutations affecting POLG are the most prevalent cause of mitochondrial disease because of defective mtDNA replication and lead to a wide spectrum of clinical phenotypes characterized by mtDNA deletions or depletion. Enhancing mitochondrial deoxyribonucleoside triphosphate (dNTP) synthesis effectively rescues mtDNA depletion in different models of defective mtDNA maintenance due to dNTP insufficiency. In this study, we studied mtDNA copy number recovery rates following ethidium bromide-forced depletion in quiescent fibroblasts from patients harboring mutations in different domains of POLG. Whereas control cells spontaneously recovered initial mtDNA levels, POLG-deficient cells experienced a more severe depletion and could not repopulate mtDNA. However, activation of deoxyribonucleoside (dN) salvage by supplementation with dNs plus erythro-9-(2-hydroxy-3-nonyl) adenine (inhibitor of deoxyadenosine degradation) led to increased mitochondrial dNTP pools and promoted mtDNA repopulation in all tested POLG-mutant cells independently of their specific genetic defect. The treatment did not compromise POLG fidelity because no increase in multiple deletions or point mutations was detected. Our study suggests that physiologic dNTP concentration limits the mtDNA replication rate. We thus propose that increasing mitochondrial dNTP availability could be of therapeutic interest for POLG deficiency and other conditions in which mtDNA maintenance is challenged.-Blázquez-Bermejo, C., Carreño-Gago, L., Molina-Granada, D., Aguirre, J., Ramón, J., Torres-Torronteras, J., Cabrera-Pérez, R., Martín, M. Á., Domínguez-González, C., de la Cruz, X., Lombès, A., García-Arumí, E., Martí, R., Cámara, Y. Increased dNTP pools rescue mtDNA depletion in human POLG-deficient fibroblasts.
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Affiliation(s)
- Cora Blázquez-Bermejo
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Lidia Carreño-Gago
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - David Molina-Granada
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Josu Aguirre
- Translational Bioinformatics Group, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain
| | - Javier Ramón
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Javier Torres-Torronteras
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Raquel Cabrera-Pérez
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Miguel Ángel Martín
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Laboratorio de Enfermedades Mitocondriales, Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
| | - Cristina Domínguez-González
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Unidad de Neuromuscular, Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
| | - Xavier de la Cruz
- Translational Bioinformatics Group, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, Spain; and
| | - Anne Lombès
- Institut Cochin, INSERM Unité 1016-Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 8104-Service de Biochimie Métabolique et Centre de Génétique Moléculaire et Chromosomique, Groupement Hospitalier Universitaire (GHU) Pitié-Salpétrière, Assistance Publique-Hôpitaux de Paris (AP-HP)-Université Paris Descartes, Paris, France
| | - Elena García-Arumí
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Ramon Martí
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Yolanda Cámara
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca-Universitat Autònoma de Barcelona, Barcelona, Spain.,Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
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13
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Saneto RP. An update on Alpers-Huttenlocher syndrome: pathophysiology of disease and rational treatment designs. Expert Opin Orphan Drugs 2018. [DOI: 10.1080/21678707.2018.1540979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Russell P. Saneto
- Department of Neurology, Division of Pediatric Neurology, University of Washington and Seattle Children’s Hospital, Seattle, WA, USA
- Neuroscience Institute, Center for Integrative Brain Research, Seattle Children’s Hospital, Seattle, WA, USA
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14
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Hynynen J, Pokka T, Komulainen-Ebrahim J, Myllynen P, Kärppä M, Pylvänen L, Kälviäinen R, Sokka A, Jyrkilä A, Lähdetie J, Haataja L, Mäkitalo A, Ylikotila P, Eriksson K, Haapala P, Ansakorpi H, Hinttala R, Vieira P, Majamaa K, Rantala H, Uusimaa J. Variants p.Q1236H and p.E1143G in mitochondrial DNA polymerase gamma POLG1 are not associated with increased risk for valproate-induced hepatotoxicity or pancreatic toxicity: A retrospective cohort study of patients with epilepsy. Epilepsia 2018; 59:2125-2136. [PMID: 30255931 DOI: 10.1111/epi.14568] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 08/28/2018] [Accepted: 08/28/2018] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Previous studies have suggested that heterozygous variants p.Q1236H and p.E1143G in mitochondrial DNA polymerase gamma (POLG1) increase the risk for liver injury for patients on valproate (VPA) therapy. We assessed the prevalence of these common variants and seven other pathogenic mutations in POLG1 and determined the occurrence of VPA-induced hepatotoxicity (VHT) or pancreatic toxicity in a cohort of patients with epilepsy. METHODS Patients with epilepsy (N = 367) were retrospectively identified from medical record files and screened for mutations in POLG1. Patients who had received VPA monotherapy and carried either of the two variants, p.Q1236H or p.E1143G, without other pathogenic mutations in POLG1 (n = 33, variant group) and patients without these variants (n = 28, nonvariant group) were included in the study. Clinical data on epilepsy, characteristics of VPA treatment, risk factors for VHT, laboratory data on liver and pancreas functions, and adverse effects were collected. RESULTS A total of 122 patients had either the POLG1 p.Q1236H (n = 99) or p.E1143G (n = 24) variant in the heterozygous or homozygous state. Transient liver dysfunction was identified in three (n = 33, 9.1%) variant group patients and in one (n = 28, 3.6%) nonvariant group patient (P = 0.62). Mild to moderate elevations in liver enzymes were encountered in both groups. Furthermore, two patients on VPA polytherapy developed acute pancreatitis, and two pediatric patients with heterozygous p.Q1236H variants and mutations in IQSEC2 and GLDC, respectively, had elevated levels of VPA metabolites in urine, elevated plasma glycine, and/or increased acylglycine excretion. SIGNIFICANCE POLG1 p.Q1236H and p.E1143G variants could not be identified as statistically significant risk factors for VHT or pancreatic toxicity. We suggest that VPA treatment could be suitable for patients who harbor these common variants in the absence of other pathogenic mutations in POLG1.
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Affiliation(s)
- Johanna Hynynen
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Biocenter Oulu, University of Oulu, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
| | - Tytti Pokka
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
| | - Jonna Komulainen-Ebrahim
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Biocenter Oulu, University of Oulu, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
| | | | - Mikko Kärppä
- Medical Research Center, Oulu University Hospital, Oulu, Finland.,Department of Neurology, Oulu University Hospital, Oulu, Finland.,Research Unit of Clinical Neuroscience, Neurology, University of Oulu, Oulu, Finland
| | - Laura Pylvänen
- Department of Neurology, Oulu University Hospital, Oulu, Finland
| | - Reetta Kälviäinen
- Department of Neurology, Kuopio University Hospital, Kuopio, Finland.,Institute of Clinical Medicine, School of Medicine, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland
| | - Arja Sokka
- Institute of Clinical Medicine, School of Medicine, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.,Department of Pediatric Neurology, Kuopio University Hospital, Kuopio, Finland
| | - Aino Jyrkilä
- Institute of Clinical Medicine, School of Medicine, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.,Department of Pediatric Neurology, Kuopio University Hospital, Kuopio, Finland
| | - Jaana Lähdetie
- Department of Child Neurology, University of Turku and Turku University Central Hospital, Turku, Finland
| | - Leena Haataja
- Department of Pediatric Neurology, Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Anna Mäkitalo
- Department of Child Neurology, University of Turku and Turku University Central Hospital, Turku, Finland.,Department of Geriatric Medicine, University of Turku, Turku, Finland
| | - Pauli Ylikotila
- Department of Neurology, Institute of Clinical Medicine, University of Turku, Turku, Finland.,Division of Clinical Neurosciences, Turku University Hospital, Turku, Finland
| | - Kai Eriksson
- Tampere Center for Child Health Research and Pediatric Neurology, Tampere University Hospital, Tampere, Finland
| | - Piia Haapala
- Outpatient Intellectual Disabilities Clinic, Tampere University Hospital, Tampere, Finland
| | - Hanna Ansakorpi
- Medical Research Center, Oulu University Hospital, Oulu, Finland.,Department of Neurology, Oulu University Hospital, Oulu, Finland.,Research Unit of Clinical Neuroscience, Neurology, University of Oulu, Oulu, Finland
| | - Reetta Hinttala
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Päivi Vieira
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
| | - Kari Majamaa
- Medical Research Center, Oulu University Hospital, Oulu, Finland.,Department of Neurology, Oulu University Hospital, Oulu, Finland.,Research Unit of Clinical Neuroscience, Neurology, University of Oulu, Oulu, Finland
| | - Heikki Rantala
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
| | - Johanna Uusimaa
- Research Unit for Pediatrics, Pediatric Neurology, Pediatric Surgery, Child Psychiatry, Dermatology, Clinical Genetics, Obstetrics and Gynecology, Otorhinolaryngology and Ophthalmology, University of Oulu, Oulu, Finland.,Medical Research Center, Oulu University Hospital, Oulu, Finland.,Biocenter Oulu, University of Oulu, Oulu, Finland.,Department of Children and Adolescents, Division of Pediatric Neurology, Oulu University Hospital, Oulu, Finland
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15
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Chan SSL. Inherited mitochondrial genomic instability and chemical exposures. Toxicology 2017; 391:75-83. [PMID: 28756246 DOI: 10.1016/j.tox.2017.07.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 06/12/2017] [Accepted: 07/24/2017] [Indexed: 12/21/2022]
Abstract
There are approximately 1500 proteins that are needed for mitochondrial structure and function, most of which are encoded in the nuclear genome (Calvo et al., 2006). Each mitochondrion has its own genome (mtDNA), which in humans encodes 13 polypeptides, 22 tRNAs and 2 rRNAs required for oxidative phosphorylation. The mitochondrial genome of humans and most vertebrates is approximately 16.5kbp, double-stranded, circular, with few non-coding bases. Thus, maintaining mtDNA stability, that is, the ability of the cell to maintain adequate levels of mtDNA template for oxidative phosphorylation is essential and can be impacted by the level of mtDNA mutation currently within the cell or mitochondrion, but also from errors made during normal mtDNA replication, defects in mitochondrial quality control mechanisms, and exacerbated by exposures to exogenous and/or endogenous genotoxic agents. In this review, we expand on the origins and consequences of mtDNA instability, the current state of research regarding the mechanisms by which mtDNA instability can be overcome by cellular and chemical interventions, and the future of research and treatments for mtDNA instability.
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Affiliation(s)
- Sherine S L Chan
- Drug Discovery and Biomedical Sciences, College of Pharmacy, Medical University of South Carolina, Charleston, SC 29425, United States; Neuroene Therapeutics, Mt. Pleasant, SC 29464, United States.
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16
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Origins of mtDNA mutations in ageing. Essays Biochem 2017; 61:325-337. [PMID: 28698307 DOI: 10.1042/ebc20160090] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 05/24/2017] [Accepted: 05/26/2017] [Indexed: 12/21/2022]
Abstract
MtDNA mutations are one of the hallmarks of ageing and age-related diseases. It is well established that somatic point mutations accumulate in mtDNA of multiple organs and tissues with increasing age and heteroplasmy is universal in mammals. However, the origin of these mutations remains controversial. The long-lasting hypothesis stating that mtDNA mutations emanate from oxidative damage via a self-perpetuating mechanism has been extensively challenged in recent years. Contrary to this initial ascertainment, mtDNA appears to be well protected from action of reactive oxygen species (ROS) through robust protein coating and endomitochondrial microcompartmentalization. Extensive development of scrupulous high-throughput DNA sequencing methods suggests that an imperfect replication process, rather than oxidative lesions are the main sources of mtDNA point mutations, indicating that mtDNA polymerase γ (POLG) might be responsible for the majority of mtDNA mutagenic events. Here, we summarize the recent knowledge in prevention and defence of mtDNA oxidative lesions and discuss the plausible mechanisms of mtDNA point mutation generation and fixation.
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17
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Nurminen A, Farnum GA, Kaguni LS. Pathogenicity in POLG syndromes: DNA polymerase gamma pathogenicity prediction server and database. BBA CLINICAL 2017; 7:147-156. [PMID: 28480171 PMCID: PMC5413197 DOI: 10.1016/j.bbacli.2017.04.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 04/11/2017] [Accepted: 04/12/2017] [Indexed: 12/19/2022]
Abstract
DNA polymerase gamma (POLG) is the replicative polymerase responsible for maintaining mitochondrial DNA (mtDNA). Disorders related to its functionality are a major cause of mitochondrial disease. The clinical spectrum of POLG syndromes includes Alpers-Huttenlocher syndrome (AHS), childhood myocerebrohepatopathy spectrum (MCHS), myoclonic epilepsy myopathy sensory ataxia (MEMSA), the ataxia neuropathy spectrum (ANS) and progressive external ophthalmoplegia (PEO). We have collected all publicly available POLG-related patient data and analyzed it using our pathogenic clustering model to provide a new research and clinical tool in the form of an online server. The server evaluates the pathogenicity of both previously reported and novel mutations. There are currently 176 unique point mutations reported and found in mitochondrial patients in the gene encoding the catalytic subunit of POLG, POLG. The mutations are distributed nearly uniformly along the length of the primary amino acid sequence of the gene. Our analysis shows that most of the mutations are recessive, and that the reported dominant mutations cluster within the polymerase active site in the tertiary structure of the POLG enzyme. The POLG Pathogenicity Prediction Server (http://polg.bmb.msu.edu) is targeted at clinicians and scientists studying POLG disorders, and aims to provide the most current available information regarding the pathogenicity of POLG mutations. Multi-level access to crucial data supporting diagnosis/prognosis of POLG syndromes Clustering protocol enables identification of novel neutral polymorphisms Identical alleles displaying variable symptoms evidence unidentified components POLG enzymes with premature stop codons, insertions/deletions group biochemically Dominant POLG mutations all lie within a critical location in the structure
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Key Words
- AHS, Alpers-Huttenlocher syndrome
- ANS, Ataxia neuropathy spectrum
- DNA polymerase gamma
- IP, Intrinsic processivity subdomain of POLGA spacer-domain
- MCHS, Childhood myocerebrohepatopathy spectrum
- MEMSA, Myoclonic epilepsy myopathy sensory ataxia
- Mitochondrial disorder
- Mutation database
- PDB ID, Four-character identification code for a protein structure in the RSCB PDB database
- PEO, Progressive external ophthalmoplegia
- PNF, Putatively non-functional enzyme
- POLG syndrome
- POLG, DNA polymerase gamma
- POLGA, Catalytic subunit of DNA polymerase gamma
- POLGB, Accessory subunit of DNA polymerase gamma
- Pathogenicity prediction
- Patient database
- SNP, Single nucleotide polymorphism/non-pathogenic mutation
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Affiliation(s)
- Anssi Nurminen
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland
| | - Gregory A Farnum
- Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, USA
| | - Laurie S Kaguni
- Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland.,Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine, Michigan State University, East Lansing, MI, USA
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18
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DeBalsi KL, Longley MJ, Hoff KE, Copeland WC. Synergistic Effects of the in cis T251I and P587L Mitochondrial DNA Polymerase γ Disease Mutations. J Biol Chem 2017; 292:4198-4209. [PMID: 28154168 DOI: 10.1074/jbc.m116.773341] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/26/2017] [Indexed: 01/28/2023] Open
Abstract
Human mitochondrial DNA (mtDNA) polymerase γ (Pol γ) is the only polymerase known to replicate the mitochondrial genome. The Pol γ holoenzyme consists of the p140 catalytic subunit (POLG) and the p55 homodimeric accessory subunit (POLG2), which enhances binding of Pol γ to DNA and promotes processivity of the holoenzyme. Mutations within POLG impede maintenance of mtDNA and cause mitochondrial diseases. Two common POLG mutations usually found in cis in patients primarily with progressive external ophthalmoplegia generate T251I and P587L amino acid substitutions. To determine whether T251I or P587L is the primary pathogenic allele or whether both substitutions are required to cause disease, we overproduced and purified WT, T251I, P587L, and T251I + P587L double variant forms of recombinant Pol γ. Biochemical characterization of these variants revealed impaired DNA binding affinity, reduced thermostability, diminished exonuclease activity, defective catalytic activity, and compromised DNA processivity, even in the presence of the p55 accessory subunit. However, physical association with p55 was unperturbed, suggesting intersubunit affinities similar to WT. Notably, although the single mutants were similarly impaired, a dramatic synergistic effect was found for the double mutant across all parameters. In conclusion, our analyses suggest that individually both T251I and P587L substitutions functionally impair Pol γ, with greater pathogenicity predicted for the single P587L variant. Combining T251I and P587L induces extreme thermal lability and leads to synergistic nucleotide and DNA binding defects, which severely impair catalytic activity and correlate with presentation of disease in patients.
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Affiliation(s)
- Karen L DeBalsi
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Matthew J Longley
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - Kirsten E Hoff
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
| | - William C Copeland
- From the Genome Integrity and Structural Biology Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709
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19
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Souren NYP, Gerdes LA, Kümpfel T, Lutsik P, Klopstock T, Hohlfeld R, Walter J. Mitochondrial DNA Variation and Heteroplasmy in Monozygotic Twins Clinically Discordant for Multiple Sclerosis. Hum Mutat 2016; 37:765-75. [PMID: 27119776 DOI: 10.1002/humu.23003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Accepted: 04/10/2016] [Indexed: 12/22/2022]
Abstract
We examined the debated link between mitochondrial DNA (mtDNA) variation and multiple sclerosis (MS) using 49 monozygotic (MZ) twin pairs clinically discordant for MS, which enables to associate de novo mtDNA variants, skewed heteroplasmy, and mtDNA copy number with MS manifestation. Ultra-deep sequencing of blood-derived mtDNA revealed 25 heteroplasmic variants with potentially pathogenic features in 18 pairs. All variants were pair-specific and had low and/or similar heteroplasmy levels in both cotwins. In one pair, a confirmed pathogenic variant (m.11778G>A, heteroplasmy ∼50%) associated with Leber hereditary optic neuropathy was detected. Detailed diagnostic investigation revealed subclinical MS signs in the prior nondiseased cotwin. Moreover, neither mtDNA deletions nor copy-number variations were involved. Furthermore, the majority of heteroplasmic variants were shared among MZ twins and exhibited more similar heteroplasmy levels in the same tissue of MZ twins as compared with different tissues of the same individual. Heteroplasmy levels were also more similar within MZ twins compared with nonidentical siblings. Our analysis excludes mtDNA variation as a major driver of the discordant clinical manifestation of MS in MZ twins, and provides valuable insights into the occurrence and distribution of heteroplasmic variants within MZ twins and nonidentical siblings, and across different tissues.
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Affiliation(s)
- Nicole Y P Souren
- Department of Genetics/Epigenetics, Saarland University, Saarbrücken, Germany
| | - Lisa A Gerdes
- Institute of Clinical Neuroimmunology, Medical Campus Großhadern, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Tania Kümpfel
- Institute of Clinical Neuroimmunology, Medical Campus Großhadern, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Pavlo Lutsik
- Department of Genetics/Epigenetics, Saarland University, Saarbrücken, Germany
| | - Thomas Klopstock
- Department of Neurology, Friedrich-Baur-Institute, Ludwig-Maximilians-Universität München, Munich, Germany.,Munich Cluster for Systems Neurology (SyNergy), Munich, Germany.,DZNE - German Center for Neurodegenerative Diseases, Munich, Germany
| | - Reinhard Hohlfeld
- Institute of Clinical Neuroimmunology, Medical Campus Großhadern, Ludwig-Maximilians-Universität München, Munich, Germany.,Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
| | - Jörn Walter
- Department of Genetics/Epigenetics, Saarland University, Saarbrücken, Germany
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20
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Qu X, Yu H, Jia B, Yu X, Cui Q, Liu Z, Sun C, Chu Y. Association of downregulated HDAC 2 with the impaired mitochondrial function and cytokine secretion in the monocytes/macrophages from gestational diabetes mellitus patients. Cell Biol Int 2016; 40:642-51. [PMID: 26936353 DOI: 10.1002/cbin.10598] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 02/27/2016] [Indexed: 12/20/2022]
Abstract
Gestational diabetes mellitus (GDM) is associated with an increased risk of type 2 diabetes (T2DM) and cardiovascular diseases in later life, yet with underlying mechanisms unclear. The present study was to explore the association of upregulated histone deacetylase 2 (HDAC 2) with the impaired mitochondrial function and the cytokine secretion in the monocytes/macrophages from GDM patients. In this study, we examined the mitochondrial function, proinflamatory cytokine secretion and the HDAC 2 level in the serum or in the monocytes/macrophages from GDM patients, investigated the influence by HDAC 2 inhibitor, AR-42 (N-hydroxy-4-[[(2S)-3-methyl-2-phenylbutanoyl]amino]benzamide), on the mitochondrial function and cytokine secretion in the isolated GDM monocytes/macrophages. Results demonstrated an increased mitochondria size, mitochondrial superoxide and reactive oxygen species (ROS) production, and an undermined mitochondria membrane potential (MMP) in the GDM monocytes/macrophages. And the serum levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α and IL-6 were also markedly higher in the GDM pregnancies, while the expression and activity of HDAC 2 was downregulated. Moreover, AR-42-mediated HDAC 2 inhibition in vitro contributed to the impaired mitochondrial function and the proinflamatory cytokine secretion. In conclusion, this study suggests an association of the impaired mitochondrial function and the promoted proinflamatory cytokine secretion with the reduced HDAC 2 activity in GDM. These findings may present HDAC 2 as a target for GDM treatment.
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Affiliation(s)
- Xin Qu
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Hongna Yu
- Department of Ultrasonography, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Bei Jia
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Xiaoyan Yu
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Qing Cui
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Zhifen Liu
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Chengming Sun
- Clinical laboratory, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
| | - Yongli Chu
- Department of Obstetrics and Gynecology, the Affiliated Yantai Yuhuangding Hospital of Medical College, Qingdao University, Yantai 264000, Shandong, China
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Janssen W, Quaegebeur A, Van Goethem G, Ann L, Smets K, Vandenberghe R, Van Paesschen W. The spectrum of epilepsy caused by POLG mutations. Acta Neurol Belg 2016; 116:17-25. [PMID: 26104464 DOI: 10.1007/s13760-015-0499-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 06/08/2015] [Indexed: 12/21/2022]
Abstract
Mutations in POLG are increasingly recognized as a cause of refractory occipital lobe epilepsy (OLE) and status epilepticus (SE). Our aim was to describe the epilepsy syndrome in seven patients with POLG mutations. We retrospectively reviewed the medical records of seven patients with POLG mutations and epilepsy. Mutation analysis was performed by direct sequencing of the coding exons of the POLG gene. Disease onset was at a median age of 18 years (range 12-26). Epilepsy was the presenting problem in six patients. All had focal seizures, with motor (n = 6) and visual (n = 6) phenomena. Six patients had secondarily generalized seizures and two patients had myoclonic seizures. Six patients had one or more episodes of refractory SE, including focal (n = 5), subtle (n = 4), myoclonic (n = 2) and convulsive (n = 3) SE. During or after SE, brain MRI showed lesions affecting the occipital lobe in all patients, probably due to continuous epileptic activity. Five of the six patients with SE died during treatment of SE, one due to valproate-induced hepatotoxicity. Associated clinical symptoms were ataxia (n = 6), polyneuropathy (n = 6), progressive external ophthalmoplegia (PEO) (n = 3) and migraine (n = 3). Epilepsy may be the first and dominant neurological problem caused by POLG mutations. The epilepsy may be severe and the condition of the patient may end in fatal SE. Refractory OLE and SE in a patient with polyneuropathy, ataxia, PEO or migraine warrant screening for POLG mutations. In this clinical setting, valproate should not be given in view of the risk of fatal hepatotoxicity.
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Affiliation(s)
- Wouter Janssen
- Department of Neurology, University Hospitals Leuven, Herestraat 49, 3000, Louvain, Belgium.
| | - Annelies Quaegebeur
- Department of Neurology, University Hospitals Leuven, Herestraat 49, 3000, Louvain, Belgium
| | - Gert Van Goethem
- Neurogenetics Group, Department of Molecular Genetics, VIB, Antwerp, Belgium
- Laboratory of Neurogenetics, Institute Born-Bunge, Antwerp, Belgium
- University of Antwerpen, Antwerp, Belgium
- Department of Neurology, University Hospital Antwerpen, Antwerp, Belgium
| | - Löfgren Ann
- Laboratory of Neurogenetics, Institute Born-Bunge, Antwerp, Belgium
- University of Antwerpen, Antwerp, Belgium
| | - Katrien Smets
- Neurogenetics Group, Department of Molecular Genetics, VIB, Antwerp, Belgium
- Laboratory of Neurogenetics, Institute Born-Bunge, Antwerp, Belgium
- University of Antwerpen, Antwerp, Belgium
- Department of Neurology, University Hospital Antwerpen, Antwerp, Belgium
| | - Rik Vandenberghe
- Department of Neurology, University Hospitals Leuven, Herestraat 49, 3000, Louvain, Belgium
| | - Wim Van Paesschen
- Department of Neurology, University Hospitals Leuven, Herestraat 49, 3000, Louvain, Belgium.
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Akhmedov AT, Marín-García J. Mitochondrial DNA maintenance: an appraisal. Mol Cell Biochem 2015; 409:283-305. [DOI: 10.1007/s11010-015-2532-x] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 08/06/2015] [Indexed: 12/13/2022]
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Polymorphisms in DNA polymerase γ affect the mtDNA stability and the NRTI-induced mitochondrial toxicity in Saccharomyces cerevisiae. Mitochondrion 2014; 20:52-63. [PMID: 25462018 PMCID: PMC4309887 DOI: 10.1016/j.mito.2014.11.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Revised: 11/10/2014] [Accepted: 11/11/2014] [Indexed: 12/23/2022]
Abstract
Several pathological mutations have been identified in human POLG gene, encoding for the catalytic subunit of Pol γ, the solely mitochondrial replicase in animals and fungi. However, little is known regarding non-pathological polymorphisms found in this gene. Here we studied, in the yeast model Saccharomyces cerevisiae, eight human polymorphisms. We found that most of them are not neutral but enhanced both mtDNA extended mutability and the accumulation of mtDNA point mutations, either alone or in combination with a pathological mutation. In addition, we found that the presence of some SNPs increased the stavudine and/or zalcitabine-induced mtDNA mutability and instability. We studied the effects of 8 human polymorphisms in Pol γ in the model system yeast. Most polymorphisms increase mtDNA extended and point mutability. Treatment with NRTIs determines mtDNA instability in wt and mutant strains. Some polymorphisms make Mip1 more sensitive to NRTIs-induced mtDNA toxicity.
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Hynynen J, Komulainen T, Tukiainen E, Nordin A, Arola J, Kälviäinen R, Jutila L, Röyttä M, Hinttala R, Majamaa K, Mäkisalo H, Uusimaa J. Acute liver failure after valproate exposure in patients with POLG1 mutations and the prognosis after liver transplantation. Liver Transpl 2014; 20:1402-12. [PMID: 25065347 DOI: 10.1002/lt.23965] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Revised: 07/21/2014] [Accepted: 07/21/2014] [Indexed: 01/12/2023]
Abstract
Patients with mutations in the POLG1 gene encoding mitochondrial DNA polymerase gamma have an increased risk of valproate-induced liver failure. POLG1 mutations are common, and these patients often suffer from intractable seizures. The role of liver transplantation in the treatment of patients with mitochondrial diseases has been controversial. We studied valproate-induced liver failure associated with POLG1 mutations and the prognosis for these patients after liver transplantation. POLG1 was analyzed in blood DNA, mitochondrial DNA (mtDNA) was quantified in liver samples, and clinical data were collected. Five patients with valproate-induced liver failure associated with POLG1 mutations were retrospectively identified. Three patients were previously suspected to have Wilson's disease. Four patients with homozygous p.W748S and p.E1143G mutations had mtDNA depletion in the liver. One of these patients died before anticipated transplantation; the other 3 patients with liver transplantation have survived 4 to 19 years. Two patients have presented with occasional epileptic seizures, and 1 patient has been seizure-free for 11 years. One patient with a heterozygous p.Q1236H mutation (but without mtDNA depletion in the liver) died suddenly 2 years after liver transplantation. In conclusion, the POLG1 mutation status and the age at presentation of valproate-induced liver failure can affect the prognosis after liver transplantation. A heterozygous POLG1 p.Q1236H mutation was related to valproate-induced liver failure without mtDNA depletion, whereas patients homozygous for POLG1 p.W748S and p.E1143G mutations had mtDNA depletion. An analysis of the POLG1 gene should be performed for all patients with suspected mitochondrial disease before the introduction of valproate therapy, and treatment with valproic acid should be avoided in these patients.
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Affiliation(s)
- Johanna Hynynen
- Institute of Clinical Medicine, Department of Pediatrics, University of Oulu, Oulu, Finland; Medical Research Center, Oulu University Hospital, University of Oulu, Oulu, Finland
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Stumpf JD, Copeland WC. MMS exposure promotes increased MtDNA mutagenesis in the presence of replication-defective disease-associated DNA polymerase γ variants. PLoS Genet 2014; 10:e1004748. [PMID: 25340760 PMCID: PMC4207668 DOI: 10.1371/journal.pgen.1004748] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 09/11/2014] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial DNA (mtDNA) encodes proteins essential for ATP production. Mutant variants of the mtDNA polymerase cause mutagenesis that contributes to aging, genetic diseases, and sensitivity to environmental agents. We interrogated mtDNA replication in Saccharomyces cerevisiae strains with disease-associated mutations affecting conserved regions of the mtDNA polymerase, Mip1, in the presence of the wild type Mip1. Mutant frequency arising from mtDNA base substitutions that confer erythromycin resistance and deletions between 21-nucleotide direct repeats was determined. Previously, increased mutagenesis was observed in strains encoding mutant variants that were insufficient to maintain mtDNA and that were not expected to reduce polymerase fidelity or exonuclease proofreading. Increased mutagenesis could be explained by mutant variants stalling the replication fork, thereby predisposing the template DNA to irreparable damage that is bypassed with poor fidelity. This hypothesis suggests that the exogenous base-alkylating agent, methyl methanesulfonate (MMS), would further increase mtDNA mutagenesis. Mitochondrial mutagenesis associated with MMS exposure was increased up to 30-fold in mip1 mutants containing disease-associated alterations that affect polymerase activity. Disrupting exonuclease activity of mutant variants was not associated with increased spontaneous mutagenesis compared with exonuclease-proficient alleles, suggesting that most or all of the mtDNA was replicated by wild type Mip1. A novel subset of C to G transversions was responsible for about half of the mutants arising after MMS exposure implicating error-prone bypass of methylated cytosines as the predominant mutational mechanism. Exposure to MMS does not disrupt exonuclease activity that suppresses deletions between 21-nucleotide direct repeats, suggesting the MMS-induce mutagenesis is not explained by inactivated exonuclease activity. Further, trace amounts of CdCl2 inhibit mtDNA replication but suppresses MMS-induced mutagenesis. These results suggest a novel mechanism wherein mutations that lead to hypermutation by DNA base-damaging agents and associate with mitochondrial disease may contribute to previously unexplained phenomena, such as the wide variation of age of disease onset and acquired mitochondrial toxicities. Thousands of mitochondrial DNA (mtDNA) per cell are necessary to maintain energy required for cellular survival in humans. Interfering with the mtDNA polymerase can result in mitochondrial diseases and mitochondrial toxicity. Therefore, it is important to explore new genetic and environmental mechanisms that alter the effectiveness and accuracy of mtDNA replication. This genetic study uses the budding yeast to demonstrate that heterozygous strains harboring disease-associated mutations in the mtDNA polymerase gene in the presence of a wild type copy of the mtDNA polymerase are associated with increased mtDNA point mutagenesis in the presence of methane methylsulfonate, a known base damaging agent. Further observations suggest that the inability of disease-associated variants to replicate mtDNA resulted in increased vulnerability to irreparable base damage that was likely to result in mutations when replicated. Also, this study showed that trace amounts of the environmental contaminant cadmium chloride impairs mtDNA replication but eliminates damage-induced mutagenesis in the remaining functional mitochondria. This interplay between disease-associated variant and wild type polymerase offers new insights on possible disease variation and implicates novel environmental consequences for compound heterozygous patients.
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Affiliation(s)
- Jeffrey D. Stumpf
- Mitochondrial DNA Replication Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIH, DHHS, Research Triangle Park, North Carolina, United States of America
| | - William C. Copeland
- Mitochondrial DNA Replication Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIH, DHHS, Research Triangle Park, North Carolina, United States of America
- * E-mail:
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Chattopadhyay K, Aldous C. A brief review on human mtDNA mutations and NRTI-associated mtDNA toxicity and mutations. Mitochondrial DNA A DNA Mapp Seq Anal 2014; 27:1685-7. [PMID: 25211089 DOI: 10.3109/19401736.2014.958728] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Mitochondrion is a cellular organelle that is present in most of the cells and is responsible for producing energy for the cell. Mitochondria have their own double-stranded DNA genome which is distinct from nuclear genome. The replication, recombination and repair of mtDNA are achieved by DNA polymerase-gamma which is encoded by POLG gene. Mutation in the mtDNA or POLG gene might lead to mitochondrial dysfunction and disease. Several mutations and polymorphisms in these regions have been associated to mitochondrial disorders. Nuceloside and nucelotide reverse transcriptase inhibitors (NRTIs) that form the basis of AIDS therapy have significantly increased the survival rate of HIV-infected individuals predisposing them to other side effects. One of the most common side effects of NRTI usage is mitochondrial toxicity leading to several mitochondrial disorders. Mutations in mtDNA have also been associated to the use of specific NRTIs leading to specific mitochondrial disorders. This review briefly summarizes the advances in mtDNA mutations and NRTI-caused mitochondrial toxicity and mutations.
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Affiliation(s)
- Koushik Chattopadhyay
- a Clinical Medicine Laboratory , School of Clinical Medicine, College of Health Sciences, University of KwaZulu-Natal , Durban , Republic of South Africa
| | - Colleen Aldous
- a Clinical Medicine Laboratory , School of Clinical Medicine, College of Health Sciences, University of KwaZulu-Natal , Durban , Republic of South Africa
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Abstract
Mitochondrial DNA is replicated by DNA polymerase γ in concert with accessory proteins such as the mitochondrial DNA helicase, single-stranded DNA binding protein, topoisomerase, and initiating factors. Defects in mitochondrial DNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mitochondrial DNA deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mitochondrial DNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mitochondrial DNA deletion disorders, such as progressive external ophthalmoplegia, ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy. This review focuses on our current knowledge of genetic defects of mitochondrial DNA replication (POLG, POLG2, C10orf2, and MGME1) that cause instability of mitochondrial DNA and mitochondrial disease.
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Affiliation(s)
- William C. Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
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Tzoulis C, Tran GT, Coxhead J, Bertelsen B, Lilleng PK, Balafkan N, Payne B, Miletic H, Chinnery PF, Bindoff LA. Molecular pathogenesis of polymerase γ-related neurodegeneration. Ann Neurol 2014; 76:66-81. [PMID: 24841123 PMCID: PMC4140551 DOI: 10.1002/ana.24185] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Revised: 05/17/2014] [Accepted: 05/18/2014] [Indexed: 12/20/2022]
Abstract
Objective Polymerase gamma (POLG) mutations are a common cause of mitochondrial disease and have also been linked to neurodegeneration and aging. We studied the molecular mechanisms underlying POLG-related neurodegeneration using postmortem tissue from a large number of patients. Methods Clinical information was available from all subjects. Formalin-fixed and frozen brain tissue from 15 patients and 23 controls was studied employing a combination of histopathology, immunohistochemistry, and molecular studies of microdissected neurons. Results The primary consequence of POLG mutation in neurons is mitochondrial DNA depletion. This was already present in infants with little evidence of neuronal loss or mitochondrial dysfunction. With longer disease duration, we found an additional, progressive accumulation of mitochondrial DNA deletions and point mutations accompanied by increasing numbers of complex I–deficient neurons. Progressive neurodegeneration primarily affected the cerebellar systems and dopaminergic cells of the substantia nigra. Superimposed on this chronic process were acute, focal cortical lesions that correlated with epileptogenic foci and that showed massive neuronal loss. Interpretation POLG mutations appear to compromise neuronal respiration via a combination of early and stable depletion and a progressive somatic mutagenesis of the mitochondrial genome. This leads to 2 distinct but overlapping biological processes: a chronic neurodegeneration reflected clinically by progressive ataxia and cognitive impairment, and an acute focal neuronal necrosis that appears to be related to the presence of epileptic seizures. Our findings offer an explanation of the acute-on-chronic clinical course of this common mitochondrial encephalopathy. ANN NEUROL 2014;76:66–81
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Affiliation(s)
- Charalampos Tzoulis
- Department of Neurology, Haukeland University Hospital, Bergen, Norway; Department of Clinical Medicine, University of Bergen, Bergen, Norway
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29
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Abstract
Human mitochondria harbor an essential, high copy number, 16,569 base pair, circular DNA genome that encodes 13 gene products required for electron transport and oxidative phosphorylation. Mutation of this genome can compromise cellular respiration, ultimately resulting in a variety of progressive metabolic diseases collectively known as 'mitochondrial diseases'. Mutagenesis of mtDNA and the persistence of mtDNA mutations in cells and tissues is a complex topic, involving the interplay of DNA replication, DNA damage and repair, purifying selection, organelle dynamics, mitophagy, and aging. We briefly review these general elements that affect maintenance of mtDNA, and we focus on nuclear genes encoding the mtDNA replication machinery that can perturb the genetic integrity of the mitochondrial genome.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC 27709, USA.
| | - Matthew J Longley
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC 27709, USA
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30
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Siciliano G, Pasquali L, Mancuso M, Murri L. Molecular diagnostics and mitochondrial dysfunction: a future perspective. Expert Rev Mol Diagn 2014; 8:531-49. [DOI: 10.1586/14737159.8.4.531] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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31
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Rouzier C, Chaussenot A, Serre V, Fragaki K, Bannwarth S, Ait-El-Mkadem S, Attarian S, Kaphan E, Cano A, Delmont E, Sacconi S, Mousson de Camaret B, Rio M, Lebre AS, Jardel C, Deschamps R, Richelme C, Pouget J, Chabrol B, Paquis-Flucklinger V. Quantitative multiplex PCR of short fluorescent fragments for the detection of large intragenic POLG rearrangements in a large French cohort. Eur J Hum Genet 2013; 22:542-50. [PMID: 23921535 DOI: 10.1038/ejhg.2013.171] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2012] [Revised: 05/21/2013] [Accepted: 06/19/2013] [Indexed: 01/03/2023] Open
Abstract
Polymerase gamma (POLG) is the gene most commonly involved in mitochondrial disorders with mitochondrial DNA instability and causes a wide range of diseases with recessive or dominant transmission. More than 170 mutations have been reported. Most of them are missense mutations, although nonsense mutations, splice-site mutations, small deletions and insertions have also been identified. However, to date, only one large-scale rearrangement has been described in a child with Alpers syndrome. Below, we report a large cohort of 160 patients with clinical, molecular and/or biochemical presentation suggestive of POLG deficiency. Using sequencing, we identified POLG variants in 22 patients (18 kindreds) including five novel pathogenic mutations. Two patients with novel mutations had unusual clinical presentation: the first exhibited an isolated ataxic neuropathy and the second was a child who presented with endocrine signs. We completed the sequencing step by quantitative multiplex PCR of short fluorescent fragments (QMPSF) analysis in 37 patients with either only one POLG heterozygous variant or a family history suggesting a dominant transmission. We identified a large intragenic deletion encompassing part of intron 21 and exon 22 of POLG in a child with refractory epilepsia partialis continua. In conclusion, we describe the first large French cohort of patients with POLG mutations, expanding the wide clinical and molecular spectrum observed in POLG disease. We confirm that large deletions in the POLG gene are rare events and we highlight the importance of QMPSF in patients with a single heterozygous POLG mutation, particularly in severe infantile phenotypes.
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Affiliation(s)
- Cécile Rouzier
- 1] Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France [2] IRCAN, CNRS UMR 7284/INSERM U1081/UNS, School of Medicine, Nice Sophia-Antipolis University, Nice, France
| | - Annabelle Chaussenot
- Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France
| | - Valérie Serre
- Jacques Monod Institute, CNRS-University Paris Diderot, Sorbonne, Paris, France
| | - Konstantina Fragaki
- 1] Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France [2] IRCAN, CNRS UMR 7284/INSERM U1081/UNS, School of Medicine, Nice Sophia-Antipolis University, Nice, France
| | - Sylvie Bannwarth
- 1] Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France [2] IRCAN, CNRS UMR 7284/INSERM U1081/UNS, School of Medicine, Nice Sophia-Antipolis University, Nice, France
| | - Samira Ait-El-Mkadem
- 1] Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France [2] IRCAN, CNRS UMR 7284/INSERM U1081/UNS, School of Medicine, Nice Sophia-Antipolis University, Nice, France
| | - Shahram Attarian
- Department of Neurology, Timone Hospital, Marseille Teaching Hospital, Marseille, France
| | - Elsa Kaphan
- Department of Neurology, Timone Hospital, Marseille Teaching Hospital, Marseille, France
| | - Aline Cano
- Department of Neuropediatrics, Timone Hospital, Marseille Teaching Hospital, Marseille, France
| | - Emilien Delmont
- Department of Neurology, Nice Teaching Hospital, Nice, France
| | - Sabrina Sacconi
- Department of Neurology, Nice Teaching Hospital, Nice, France
| | | | - Marlène Rio
- Department of Medical Genetics, Necker Hospital, Paris Teaching Hospital, Paris, France
| | - Anne-Sophie Lebre
- Department of Medical Genetics, Necker Hospital, Paris Teaching Hospital, Paris, France
| | - Claude Jardel
- Department of Molecular and Chromosomal Genetics, Pitié-Salpétrière Hospital, Paris Teaching Hospital, Paris, France
| | - Romain Deschamps
- Department of Neuromuscular disorders, Fort-de-France Teaching Hospital, Martinique, France
| | - Christian Richelme
- Department of Pediatrics, Lenval Hospital, Nice Teaching Hospital, Nice, France
| | - Jean Pouget
- Department of Neurology, Timone Hospital, Marseille Teaching Hospital, Marseille, France
| | - Brigitte Chabrol
- Department of Neuropediatrics, Timone Hospital, Marseille Teaching Hospital, Marseille, France
| | - Véronique Paquis-Flucklinger
- 1] Department of Medical Genetics, National Centre for Mitochondrial diseases, Nice Teaching Hospital, Nice, France [2] IRCAN, CNRS UMR 7284/INSERM U1081/UNS, School of Medicine, Nice Sophia-Antipolis University, Nice, France
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Nanau RM, Neuman MG. Adverse drug reactions induced by valproic acid. Clin Biochem 2013; 46:1323-38. [PMID: 23792104 DOI: 10.1016/j.clinbiochem.2013.06.012] [Citation(s) in RCA: 188] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/11/2013] [Accepted: 06/12/2013] [Indexed: 12/11/2022]
Abstract
Valproic acid is a widely-used first-generation antiepileptic drug, prescribed predominantly in epilepsy and psychiatric disorders. VPA has good efficacy and pharmacoeconomic profiles, as well as a relatively favorable safety profile. However, adverse drug reactions have been reported in relation with valproic acid use, either as monotherapy or polytherapy with other antiepileptic drugs or antipsychotic drugs. This systematic review discusses valproic acid adverse drug reactions, in terms of hepatotoxicity, mitochondrial toxicity, hyperammonemic encephalopathy, hypersensitivity syndrome reactions, neurological toxicity, metabolic and endocrine adverse events, and teratogenicity.
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Affiliation(s)
- Radu M Nanau
- Department of Pharmacology and Toxicology, Faculty of Medicine, University of Toronto, In Vitro Drug Safety and Biotechnology, Toronto, Ontario, Canada
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Stumpf JD, Saneto RP, Copeland WC. Clinical and molecular features of POLG-related mitochondrial disease. Cold Spring Harb Perspect Biol 2013; 5:a011395. [PMID: 23545419 DOI: 10.1101/cshperspect.a011395] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The inability to replicate mitochondrial genomes (mtDNA) by the mitochondrial DNA polymerase (pol γ) leads to a subset of mitochondrial diseases. Many mutations in POLG, the gene that encodes pol γ, have been associated with mitochondrial diseases such as myocerebrohepatopathy spectrum (MCHS) disorders, Alpers-Huttenlocher syndrome, myoclonic epilepsy myopathy sensory ataxia (MEMSA), ataxia neuropathy spectrum (ANS), and progressive external ophthalmoplegia (PEO). This chapter explores five important topics in POLG-related disease: (1) clinical symptoms that identify and distinguish POLG-related diseases, (2) molecular characterization of defects in polymerase activity by POLG disease variants, (3) the importance of holoenzyme formation in disease presentation, (4) the role of pol γ exonuclease activity and mutagenesis in disease and aging, and (5) novel approaches to therapy and avoidance of toxicity based on primary research in pol γ replication.
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Affiliation(s)
- Jeffrey D Stumpf
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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Crovetto F, Lattuada D, Rossi G, Mangano S, Somigliana E, Bolis G, Fedele L. A role for mitochondria in gestational diabetes mellitus? Gynecol Endocrinol 2013; 29:259-62. [PMID: 23167811 DOI: 10.3109/09513590.2012.736556] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mitochondrial activity is critical for maintenance of correct glucose homeostasis and alteration in mitochondrial content or function may progressively lead to the development of insulin resistance. Evidence on the possible role of mitochondria in the pathogenesis of gestational diabetes mellitus (GDM) is conversely scanty and inconsistent. The aim was to evaluated mitochondrial DNA (mtDNA) content in peripheral blood of pregnant women with GDM. We selected 25 pregnant women affected by GDM and 50 controls with physiological pregnancies. A blood sample was collected at 32-36 weeks' gestation, stored and thawed simultaneously. The mtDNA content was determined utilizing a quantitative real-time polymerase chain reaction by the Taqman method, using a genomic control and a target gene. Results are expressed as copy number per nuclear DNA. The median (interquartile range) mtDNA content in GDM and controls was 122 (107-198) and 170 (129-196), respectively (p = 0.039). The mtDNA content was also correlated to GDM treatment, self-blood glucose monitoring and newborns' weight, but these analyses failed to document any statistically significant association. Attenuated mitochondrial function may play a role in the development of GDM. Further experiments are required to definitely clarify whether this defect represents a primary event in the pathogenesis of the disease.
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Affiliation(s)
- Francesca Crovetto
- Department of Obstetrics and Gynecology, Fondazione IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milan, Italy.
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Abstract
Alpers-Huttenlocher syndrome is an uncommon mitochondrial disease most often associated with mutations in the mitochondrial DNA replicase, polymerase-γ. Alterations in enzyme activity result in reduced levels or deletions in mitochondrial DNA. Phenotypic manifestations occur when the functional content of mitochondrial DNA reaches a critical nadir. The tempo of disease progression and onset varies among patients, even in identical genotypes. The classic clinical triad of seizures, liver degeneration, and progressive developmental regression helps define the disorder, but a wide range of clinical expression occurs. The majority of patients are healthy before disease onset, and seizures herald the disorder in most patients. Seizures can rapidly progress to medical intractability, with frequent episodes of epilepsia partialis continua or status epilepticus. Liver involvement may precede or occur after seizure onset. Regardless, eventual liver failure is common. Both the tempo of disease progression and range of organ involvement vary from patient to patient, and are only partly explained by pathogenic effects of genetic mutations. Diagnosis involves the constellation of organ involvement, not the sequence of signs. This disorder is relentlessly progressive and ultimately fatal.
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Vasta V, Merritt JL, Saneto RP, Hahn SH. Next-generation sequencing for mitochondrial diseases: a wide diagnostic spectrum. Pediatr Int 2012; 54:585-601. [PMID: 22494076 DOI: 10.1111/j.1442-200x.2012.03644.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The current diagnostic approach for mitochondrial disorders requires invasive procedures such as muscle biopsy and multiple biochemical testing but the results are often inconclusive. Clinical sequencing tests are available only for a limited number of genes. Recently, massively parallel sequencing has become a powerful tool for testing genetically heterogeneous conditions such as mitochondrial disorders. METHODS Targeted next-generation sequencing was performed on 26 patients with known or suspected mitochondrial disorders using in-solution capture for the exons of 908 known and candidate nuclear genes and an Illumina genome analyzer. RESULTS None of the 18 patients with various abnormal respiratory chain complex (RCC) activities had molecular defects in either subunits or assembly factors of mitochondrial RCC enzymes except a reference control sample with known mutations in SURF1. Instead, several variants in known pathogenic genes including CPT2, POLG, PDSS1, UBE3A, SDHD, and a few potentially pathogenic variants in candidate genes such as MTO1 or SCL7A13 were identified. CONCLUSIONS Sequencing only nuclear genes for RCC subunits and assembly factors may not provide the diagnostic answers for suspected patients with mitochondrial disorders. The present findings indicate that the diagnostic spectrum of mitochondrial disorders is much broader than previously thought, which could potentially lead to misdiagnosis and/or inappropriate treatment. Overall analytic sensitivity and precision appear acceptable for clinical testing. Despite the limitations in finding mutations in all patients, the present findings underscore the considerable clinical benefits of targeted next-generation sequencing and serve as a prototype for extending the clinical evaluation in this clinically heterogeneous patient group.
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Affiliation(s)
- Valeria Vasta
- University of Washington School of Medicine, Seattle Children's Research Institute, C9S, 1900 9th Avenue, Seattle, WA 98101, USA
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Abstract
Mitochondrial DNA (mtDNA) is replicated by the DNA polymerase g in concert with accessory proteins such as the mtDNA helicase, single stranded DNA binding protein, topoisomerase, and initiating factors. Nucleotide precursors for mtDNA replication arise from the mitochondrial salvage pathway originating from transport of nucleosides, or alternatively from cytoplasmic reduction of ribonucleotides. Defects in mtDNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mtDNA deletions, point mutations, or depletion which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mtDNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders, such as progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). This review focuses on our current knowledge of genetic defects of mtDNA replication (POLG, POLG2, C10orf2) and nucleotide metabolism (TYMP, TK2, DGOUK, and RRM2B) that cause instability of mtDNA and mitochondrial disease.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Durham, North Carolina 27709, USA.
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Zhang L, Chan SSL, Wolff DJ. Mitochondrial disorders of DNA polymerase γ dysfunction: from anatomic to molecular pathology diagnosis. Arch Pathol Lab Med 2011. [PMID: 21732785 DOI: 10.1043/2010-0356-rar.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
CONTEXT Primary mitochondrial dysfunction is one of the most common causes of inherited disorders predominantly involving the neuromuscular system. Advances in the molecular study of mitochondrial DNA have changed our vision and our approach to primary mitochondrial disorders. Many of the mitochondrial disorders are caused by mutations in nuclear genes and are inherited in an autosomal recessive pattern. Among the autosomal inherited mitochondrial disorders, those related to DNA polymerase γ dysfunction are the most common and the best studied. Understanding the molecular mechanisms and being familiar with the recent advances in laboratory diagnosis of this group of mitochondrial disorders are essential for pathologists to interpret abnormal histopathology and laboratory results and to suggest further studies for a definitive diagnosis. OBJECTIVES To help pathologists better understand the common clinical syndromes originating from mutations in DNA polymerase γ and its associated proteins and use the stepwise approach of clinical, laboratory, and pathologic diagnosis of these syndromes. DATA SOURCES Review of pertinent published literature and relevant Internet databases. CONCLUSIONS Mitochondrial disorders are now better recognized with the development of molecular tests for clinical diagnosis. A cooperative effort among primary physicians, diagnostic pathologists, geneticists, and molecular biologists with expertise in mitochondrial disorders is required to reach a definitive diagnosis.
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Affiliation(s)
- Linsheng Zhang
- Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.
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Biochemical analysis of the G517V POLG variant reveals wild-type like activity. Mitochondrion 2011; 11:929-34. [PMID: 21856450 DOI: 10.1016/j.mito.2011.08.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 07/13/2011] [Accepted: 08/04/2011] [Indexed: 11/22/2022]
Abstract
The c.1550g→t mutation in the POLG gene causing the G517V substitution has been reported by many groups to be associated with a variety of mitochondrial diseases, including autosomal dominant and recessive forms of ataxia neuropathy, myopathy and microcephaly, progressive external ophthalmoplegia, diabetes, strokes, hypotonia, and epilepsy. However, the variable disease presentation and age of onset raises suspicion of its pathogenicity. Because of the varied reported associated symptoms and request from physicians to address the consequence of this mutation, we have carried out the biochemical analysis of the purified recombinant human DNA polymerase γ protein harboring the G517V substitution. These analyses revealed that the G517V mutant enzyme retained 80-90% of wild-type DNA polymerase activity, in addition to its functional interaction with the p55 accessory subunit. DNA binding by the mutant was also only slightly lower than the wild-type enzyme. Our data suggest that the G517V mutation by itself in pol γ most likely does not have a role in mitochondrial disorders.
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40
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Euro L, Farnum GA, Palin E, Suomalainen A, Kaguni LS. Clustering of Alpers disease mutations and catalytic defects in biochemical variants reveal new features of molecular mechanism of the human mitochondrial replicase, Pol γ. Nucleic Acids Res 2011; 39:9072-84. [PMID: 21824913 PMCID: PMC3241644 DOI: 10.1093/nar/gkr618] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutations in Pol γ represent a major cause of human mitochondrial diseases, especially those affecting the nervous system in adults and in children. Recessive mutations in Pol γ represent nearly half of those reported to date, and they are nearly uniformly distributed along the length of the POLG1 gene (Human DNA Polymerase gamma Mutation Database); the majority of them are linked to the most severe form of POLG syndrome, Alpers–Huttenlocher syndrome. In this report, we assess the structure–function relationships for recessive disease mutations by reviewing existing biochemical data on site-directed mutagenesis of the human, Drosophila and yeast Pol γs, and their homologs from the family A DNA polymerase group. We do so in the context of a molecular model of Pol γ in complex with primer–template DNA, which we have developed based upon the recently solved crystal structure of the apoenzyme form. We present evidence that recessive mutations cluster within five distinct functional modules in the catalytic core of Pol γ. Our results suggest that cluster prediction can be used as a diagnosis-supporting tool to evaluate the pathogenic role of new Pol γ variants.
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Affiliation(s)
- Liliya Euro
- Research Programs Unit, Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland
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41
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Pronicka E, Weglewska-Jurkiewicz A, Pronicki M, Sykut-Cegielska J, Kowalski P, Pajdowska M, Jankowska I, Kotulska K, Kalicinski P, Jakobkiewicz-Banecka J, Wegrzyn G. Drug-resistant epilepsia and fulminant valproate liver toxicity. Alpers-Huttenlocher syndrome in two children confirmed post mortem by identification of p.W748S mutation in POLG gene. Med Sci Monit 2011; 17:CR203-9. [PMID: 21455106 PMCID: PMC3539522 DOI: 10.12659/msm.881716] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Background POLG (polymerase gamma) gene mutations lead to a variety of neurological disorders, including Alpers-Huttenlocher syndrome (AHS). The diagnostic triad of AHS is: resistant epilepsy, liver impairment triggered by sodium valproate (VA), and mitochondrial DNA depletion. Material/Methods A cohort of 28 children with mitochondrial encephalopathy and liver failure was qualified for retrospective study of mitochondrial DNA depletion and POLG mutations. Results The p.W748S POLG gene mutation was revealed in 2 children, the only ones in the cohort who fulfilled the AHS criteria. Depletion of mtDNA (16% of control value) was confirmed post mortem in available liver tissue and was not detected in the muscle. The disease started with drug-resistant seizures, failure to thrive and developmental regression at the ages of 7 and 18 months, respectively. Irreversible liver failure developed after VA administration. Co-existence of epilepsy, VA liver toxicity, lactic acidemia and muscle respiratory chain dysfunction led finally to the diagnosis of mitochondrial disorder (and AHS suspicion). Conclusions Our results confirm, for the first time, the occurrence of a pathology caused by POLG gene mutation(s) in the Polish population. POLG mutation screening and mtDNA depletion assessment should be included in differential diagnosis of drug-resistant epilepsy associated with a hepatopathy.
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Affiliation(s)
- Ewa Pronicka
- Department of Metabolic Diseases, Endocrinology and Diabetology, Children's Memorial Health Institute Warsaw, Poland.
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Zhang L, Chan SSL, Wolff DJ. Mitochondrial disorders of DNA polymerase γ dysfunction: from anatomic to molecular pathology diagnosis. Arch Pathol Lab Med 2011; 135:925-34. [PMID: 21732785 PMCID: PMC3158670 DOI: 10.5858/2010-0356-rar.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
CONTEXT Primary mitochondrial dysfunction is one of the most common causes of inherited disorders predominantly involving the neuromuscular system. Advances in the molecular study of mitochondrial DNA have changed our vision and our approach to primary mitochondrial disorders. Many of the mitochondrial disorders are caused by mutations in nuclear genes and are inherited in an autosomal recessive pattern. Among the autosomal inherited mitochondrial disorders, those related to DNA polymerase γ dysfunction are the most common and the best studied. Understanding the molecular mechanisms and being familiar with the recent advances in laboratory diagnosis of this group of mitochondrial disorders are essential for pathologists to interpret abnormal histopathology and laboratory results and to suggest further studies for a definitive diagnosis. OBJECTIVES To help pathologists better understand the common clinical syndromes originating from mutations in DNA polymerase γ and its associated proteins and use the stepwise approach of clinical, laboratory, and pathologic diagnosis of these syndromes. DATA SOURCES Review of pertinent published literature and relevant Internet databases. CONCLUSIONS Mitochondrial disorders are now better recognized with the development of molecular tests for clinical diagnosis. A cooperative effort among primary physicians, diagnostic pathologists, geneticists, and molecular biologists with expertise in mitochondrial disorders is required to reach a definitive diagnosis.
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Affiliation(s)
- Linsheng Zhang
- Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.
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43
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Mousson de Camaret B, Chassagne M, Mayençon M, Padet S, Crehalet H, Clerc-Renaud P, Rouvet I, Zabot MT, Rivier F, Sarda P, des Portes V, Bozon D. POLG exon 22 skipping induced by different mechanisms in two unrelated cases of Alpers syndrome. Mitochondrion 2011; 11:223-7. [DOI: 10.1016/j.mito.2010.07.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 06/29/2010] [Accepted: 07/23/2010] [Indexed: 11/16/2022]
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44
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Stewart JD, Horvath R, Baruffini E, Ferrero I, Bulst S, Watkins PB, Fontana RJ, Day CP, Chinnery PF. Polymerase γ gene POLG determines the risk of sodium valproate-induced liver toxicity. Hepatology 2010; 52:1791-6. [PMID: 21038416 PMCID: PMC3841971 DOI: 10.1002/hep.23891] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
UNLABELLED Sodium valproate (VPA) is widely used throughout the world to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy. VPA toxicity is an uncommon but potentially fatal cause of idiosyncratic liver injury. Rare mutations in POLG, which codes for the mitochondrial DNA polymerase γ (polγ), cause Alpers-Huttenlocher syndrome (AHS). AHS is a neurometabolic disorder associated with an increased risk of developing fatal VPA hepatotoxicity. We therefore set out to determine whether common genetic variants in POLG explain why some otherwise healthy individuals develop VPA hepatotoxicity. We carried out a prospective study of subjects enrolled in the Drug Induced Liver Injury Network (DILIN) from 2004 to 2008 through five US centers. POLG was sequenced and the functional consequences of VPA and novel POLG variants were evaluated in primary human cell lines and the yeast model system Saccharomyces cerevisiae. Heterozygous genetic variation in POLG was strongly associated with VPA-induced liver toxicity (odds ratio = 23.6, 95% confidence interval [CI] = 8.4-65.8, P = 5.1 × 10⁻⁷). This was principally due to the p.Q1236H substitution which compromised polγ function in yeast. Therapeutic doses of VPA inhibited human cellular proliferation and high doses caused nonapoptotic cell death, which was not mediated through mitochondrial DNA depletion, mutation, or a defect of fatty acid metabolism. CONCLUSION These findings implicate impaired liver regeneration in VPA toxicity and show that prospective genetic testing of POLG will identify individuals at high risk of this potentially fatal consequence of treatment.
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Affiliation(s)
- Joanna D Stewart
- Mitochondrial Research Group, Institute of Human Genetics, Newcastle University, UK
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45
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Rinaldi T, Dallabona C, Ferrero I, Frontali L, Bolotin-Fukuhara M. Mitochondrial diseases and the role of the yeast models. FEMS Yeast Res 2010; 10:1006-22. [PMID: 20946356 DOI: 10.1111/j.1567-1364.2010.00685.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Nowadays, mitochondrial diseases are recognized and studied with much attention and they cannot be considered anymore as 'rare diseases'. Yeast has been an instrumental organism to understand the genetic and molecular aspects of the many roles of mitochondria within the cells. Thanks to the general conservation of mitochondrial genes and pathways between human and yeast, it can also be used to model some diseases. In this review, we focus on the most recent topics, exemplifying those for which yeast models have been especially valuable.
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Affiliation(s)
- Teresa Rinaldi
- Department of Cell and Developmental Biology, Pasteur Institute-Cenci Bolognetti Foundation, Sapienza University of Rome, Rome, Italy
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46
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Mitochondrial DNA replication and disease: insights from DNA polymerase γ mutations. Cell Mol Life Sci 2010; 68:219-33. [PMID: 20927567 DOI: 10.1007/s00018-010-0530-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Revised: 08/31/2010] [Accepted: 09/02/2010] [Indexed: 10/19/2022]
Abstract
DNA polymerase γ (pol γ), encoded by POLG, is responsible for replicating human mitochondrial DNA. About 150 mutations in the human POLG have been identified in patients with mitochondrial diseases such as Alpers syndrome, progressive external ophthalmoplegia, and ataxia-neuropathy syndromes. Because many of the mutations are described in single citations with no genotypic family history, it is important to ascertain which mutations cause or contribute to mitochondrial disease. The vast majority of data about POLG mutations has been generated from biochemical characterizations of recombinant pol γ. However, recently, the study of mitochondrial dysfunction in Saccharomyces cerevisiae and mouse models provides important in vivo evidence for the role of POLG mutations in disease. Also, the published 3D-structure of the human pol γ assists in explaining some of the biochemical and genetic properties of the mutants. This review summarizes the current evidence that identifies and explains disease-causing POLG mutations.
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Predicting the contribution of novel POLG mutations to human disease through analysis in yeast model. Mitochondrion 2010; 11:182-90. [PMID: 20883824 DOI: 10.1016/j.mito.2010.09.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 09/17/2010] [Accepted: 09/20/2010] [Indexed: 11/24/2022]
Abstract
The yeast Saccharomyces cerevisiae was used to validate the pathogenic significance of eight human mutations in the gene encoding for the mitochondrial DNA polymerase gamma, namely G303R, S305R, R386H, R574W, P625R, D930N, K947R and P1073L, among which three are novel and four are of unclear pathological significance. Mitochondrial DNA extended and point mutability as well as dominance/recessivity of each mutation has been evaluated. The analysis in yeast revealed that two mutations, S305R and R386H, cannot be the sole cause of pathology observed in patients. These data led us to search for a second mutation in compound with S305R and we found a mutation, P1073L, missed in the first genetic analysis. Finally, a significant rescue of extended mutability has been observed for several dominant mutations by treatment with mitochondrial antioxidants.
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Wong LJC, Naviaux RK, Brunetti-Pierri N, Zhang Q, Schmitt ES, Truong C, Milone M, Cohen BH, Wical B, Ganesh J, Basinger AA, Burton BK, Swoboda K, Gilbert DL, Vanderver A, Saneto RP, Maranda B, Arnold G, Abdenur JE, Waters PJ, Copeland WC. Molecular and clinical genetics of mitochondrial diseases due to POLG mutations. Hum Mutat 2010; 29:E150-72. [PMID: 18546365 DOI: 10.1002/humu.20824] [Citation(s) in RCA: 209] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mutations in the POLG gene have emerged as one of the most common causes of inherited mitochondrial disease in children and adults. They are responsible for a heterogeneous group of at least 6 major phenotypes of neurodegenerative disease that include: 1) childhood Myocerebrohepatopathy Spectrum disorders (MCHS), 2) Alpers syndrome, 3) Ataxia Neuropathy Spectrum (ANS) disorders, 4) Myoclonus Epilepsy Myopathy Sensory Ataxia (MEMSA), 5) autosomal recessive Progressive External Ophthalmoplegia (arPEO), and 6) autosomal dominant Progressive External Ophthalmoplegia (adPEO). Due to the clinical heterogeneity, time-dependent evolution of symptoms, overlapping phenotypes, and inconsistencies in muscle pathology findings, definitive diagnosis relies on the molecular finding of deleterious mutations. We sequenced the exons and flanking intron region from approximately 350 patients displaying a phenotype consistent with POLG related mitochondrial disease and found informative mutations in 61 (17%). Two mutant alleles were identified in 31 unrelated index patients with autosomal recessive POLG-related disorders. Among them, 20 (67%) had Alpers syndrome, 4 (13%) had arPEO, and 3 (10%) had ANS. In addition, 30 patients carrying one altered POLG allele were found. A total of 25 novel alterations were identified, including 6 null mutations. We describe the predicted structural/functional and clinical importance of the previously unreported missense variants and discuss their likelihood of being pathogenic. In conclusion, sequence analysis allows the identification of mutations responsible for POLG-related disorders and, in most of the autosomal recessive cases where two mutant alleles are found in trans, finding deleterious mutations can provide an unequivocal diagnosis of the disease.
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Affiliation(s)
- Lee-Jun C Wong
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.
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Jarrett SG, Lewin AS, Boulton ME. The importance of mitochondria in age-related and inherited eye disorders. Ophthalmic Res 2010; 44:179-90. [PMID: 20829642 PMCID: PMC2952187 DOI: 10.1159/000316480] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Mitochondria are critical for ocular function as they represent the major source of a cell's supply of energy and play an important role in cell differentiation and survival. Mitochondrial dysfunction can occur as a result of inherited mitochondrial mutations (e.g. Leber's hereditary optic neuropathy and chronic progressive external ophthalmoplegia) or stochastic oxidative damage which leads to cumulative mitochondrial damage and is an important factor in age-related disorders (e.g. age-related macular degeneration, cataract and diabetic retinopathy). Mitochondrial DNA (mtDNA) instability is an important factor in mitochondrial impairment culminating in age-related changes and pathology, and in all regions of the eye mtDNA damage is increased as a consequence of aging and age-related disease. It is now apparent that the mitochondrial genome is a weak link in the defenses of ocular cells since it is susceptible to oxidative damage and it lacks some of the systems that protect the nuclear genome, such as nucleotide excision repair. Accumulation of mitochondrial mutations leads to cellular dysfunction and increased susceptibility to adverse events which contribute to the pathogenesis of numerous sporadic and chronic disorders in the eye.
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Affiliation(s)
- Stuart G. Jarrett
- Department of Molecular and Biomedical Pharmacology, College of Medicine, University of Kentucky, Lexington, Ky., USA
| | - Alfred S. Lewin
- Department of Molecular Genetics, University of Florida, Gainesville, Fla., USA
| | - Michael E. Boulton
- Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, Fla., USA
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50
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Saneto RP, Naviaux RK. Polymerase gamma disease through the ages. ACTA ACUST UNITED AC 2010; 16:163-74. [DOI: 10.1002/ddrr.105] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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