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Abstract
PURPOSE OF REVIEW Barth syndrome (BTHS) is a mitochondrial disorder characterized by neutropenia, among other defects. As yet, the correlation between the mitochondrial defect in BTHS and the neutropenia observed in these patients is unclear. In this review, we hope to shed some light upon the correlation between the metabolic properties of neutrophil mitochondria and their susceptibility to the defects observed in BTHS. RECENT FINDINGS BTHS neutrophils avidly expose phosphatidyl serine, a phospholipid that is normally restrained to the inner leaflet of the plasma membrane. Although phosphatidyl serine exposure is usually considered to be a marker for apoptosis, BTHS neutrophils have no other apoptotic features and function normally. It has recently become clear that the respiratory chain in all BTHS tissues lacks super-complex organization, leading to inefficient electron transport. In neutrophils, the super-complex organization of the respiratory chain is disturbed by default, even in healthy individuals. Further disturbance in BTHS patients may lie at the basis of their neutropenia. SUMMARY It seems unlikely that neutropenia in BTHS is caused by apoptosis of the myeloid precursor cells or end-stage neutrophils. Instead, mitochondria-derived reactive oxygen species may act as signaling intermediates that trigger phosphatidyl serine exposure. This, in turn, appears to lead to increased clearance of neutrophils by tissue macrophages.
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Wonnapinij P, Chinnery PF, Samuels DC. The distribution of mitochondrial DNA heteroplasmy due to random genetic drift. Am J Hum Genet 2008; 83:582-93. [PMID: 18976726 DOI: 10.1016/j.ajhg.2008.10.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Revised: 10/08/2008] [Accepted: 10/14/2008] [Indexed: 11/16/2022] Open
Abstract
Cells containing pathogenic mutations in mitochondrial DNA (mtDNA) generally also contain the wild-type mtDNA, a condition called heteroplasmy. The amount of mutant mtDNA in a cell, called the heteroplasmy level, is an important factor in determining the amount of mitochondrial dysfunction and therefore the disease severity. mtDNA is inherited maternally, and there are large random shifts in heteroplasmy level between mother and offspring. Understanding the distribution in heteroplasmy levels across a group of offspring is an important step in understanding the inheritance of diseases caused by mtDNA mutations. Previously, our understanding of the heteroplasmy distribution has been limited to just the mean and variance of the distribution. Here we give equations, adapted from the work of Kimura on random genetic drift, for the full mtDNA heteroplasmy distribution. We describe how to use the Kimura distribution in mitochondrial genetics, and we test the Kimura distribution against human, mouse, and Drosophila data sets.
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Affiliation(s)
- Passorn Wonnapinij
- Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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53
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Sexton AC, Sahhar M, Thorburn DR, Metcalfe SA. Impact of a Genetic Diagnosis of a Mitochondrial Disorder 5–17 Years After the Death of an Affected Child. J Genet Couns 2008; 17:261-73. [DOI: 10.1007/s10897-007-9145-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Accepted: 12/05/2007] [Indexed: 11/25/2022]
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54
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NAKADA K, SATO A, HAYASHI JI. Reverse genetic studies of mitochondrial DNA-based diseases using a mouse model. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2008; 84:155-65. [PMID: 18941295 PMCID: PMC2858368 DOI: 10.2183/pjab.84.155] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 03/27/2008] [Indexed: 05/26/2023]
Abstract
In the situation that it would not be able to produce model animals for mitochondrial diseases caused by mitochondrial DNA (mtDNA) with pathogenic mutations, we succeeded in generating mice with pathogenic deletion mutant mtDNA (DeltamtDNA), named "mito-mice", by direct introduction of mitochondria with DeltamtDNA into mouse zygotes. In the mito-mice, accumulation of DeltamtDNA induced mitochondrial respiration defects in various tissues, resulting in mitochondrial disease phenotypes, such as low body weight, lactic acidosis, ischemia, myopathy, heart block, deafness, male infertility, and renal failure. Thus, mito-mice are the first model animal for mtDNA-based diseases, and the mice could be valuable for understanding precise pathogeneses and testing therapies of mitochondrial diseases. In the present review, we summarized reverse genetic studies using the mito-mice.(Communicated by Takao SEKIYA, M.J.A.).
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Affiliation(s)
- Kazuto NAKADA
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
| | - Akitsugu SATO
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
| | - Jun-Ichi HAYASHI
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
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55
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Brenner CA, Kubisch HM, Pierce KE. Role of the mitochondrial genome in assisted reproductive technologies and embryonic stem cell-based therapeutic cloning. Reprod Fertil Dev 2007; 16:743-51. [PMID: 15740697 DOI: 10.1071/rd04107] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2004] [Accepted: 10/19/2004] [Indexed: 11/23/2022] Open
Abstract
Mitochondria play a pivotal role in cellular metabolism and are important determinants of embryonic development. Mitochondrial function and biogenesis rely on an intricate coordination of regulation and expression of nuclear and mitochondrial genes. For example, several nucleus-derived transcription factors, such as mitochondrial transcription factor A, are required for mitochondrial DNA replication. Mitochondrial inheritance is strictly maternal while paternally-derived mitochondria are selectively eliminated during early embryonic cell divisions. However, there are reports from animals as well as human patients that paternal mitochondria can occasionally escape elimination, which in some cases has led to severe pathologies. The resulting existence of different mitochondrial genomes within the same cell has been termed mitochondrial heteroplasmy. The increasing use of invasive techniques in assisted reproduction in humans has raised concerns that one of the outcomes of such techniques is an increase in the incidence of mitochondrial heteroplasmy. Indeed, there is evidence that heteroplasmy is a direct consequence of ooplasm transfer, a technique that was used to 'rescue' oocytes from older women by injecting ooplasm from young oocytes. Mitochondria from donor and recipient were found in varying proportions in resulting children. Heteroplasmy is also a byproduct of nuclear transfer, as has been shown in studies on cloned sheep, cattle and monkeys. As therapeutic cloning will depend on nuclear transfer into oocytes and the subsequent generation of embryonic stem cells from resulting blastocysts, the prospect of mitochondrial heteroplasmy and its potential problems necessitate further studies in this area.
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56
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Acton BM, Lai I, Shang X, Jurisicova A, Casper RF. Neutral Mitochondrial Heteroplasmy Alters Physiological Function in Mice1. Biol Reprod 2007; 77:569-76. [PMID: 17554081 DOI: 10.1095/biolreprod.107.060806] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Cytoplasmic transfer is an assisted reproductive technique that involves the infusion of ooplasm from a donor oocyte into a recipient oocyte of inferior developmental competence. Although this technique has shown some success for couples with recurrent in vitro fertilization failure, it results in mitochondrial heteroplasmy in the offspring, defined as the presence of two different mitochondrial genomes in the same individual. Because the long-term health consequences of mitochondrial heteroplasmy are unknown, there is a need for appropriate animal models to evaluate any physiological changes of dual mtDNA genotypes. This longitudinal study was designed as a preliminary screen of basic physiological functions for heteroplasmic mice (NZB mtDNA on a BALB/cByJ background). The mice were tested for cardiovascular and metabolic function, hematological parameters, body mass analysis, ovarian reserve, and tissue histologic abnormalities over a period of 15 mo. Heteroplasmic mice developed systemic hypertension that corrected over time and was accompanied by cardiac changes consistent with pulmonary hypertension. In addition, heteroplasmic animals had increased body mass and fat mass compared with controls at all ages. Finally, these animals had abnormalities in electrolytes and hematological parameters. Our findings suggest that there are significant physiological differences between heteroplasmic and control mice. Because ooplasm transfer appears to be consistently associated with mitochondrial heteroplasmy, children conceived through ooplasm transfer should be closely followed to determine if they are at risk for any health problems.
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Affiliation(s)
- B M Acton
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Toronto, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5
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57
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Gardner JL, Craven L, Turnbull DM, Taylor RW. Experimental Strategies Towards Treating Mitochondrial DNA Disorders. Biosci Rep 2007; 27:139-50. [PMID: 17492502 DOI: 10.1007/s10540-007-9042-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
An extensive range of molecular defects have been identified in the human mitochondrial genome (mtDNA), causing a range of clinical phenotypes characterized by mitochondrial respiratory chain dysfunction. Sadly, given the complexities of mitochondrial genetics, there are no available cures for mtDNA disorders. In this review, we consider experimental, genetic-based strategies that have been or are being explored towards developing treatments, focussing on two specific areas which we are actively pursuing—assessing the benefit of exercise training for patients with mtDNA defects, and the prevention of mtDNA disease transmission.
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Affiliation(s)
- Julie L Gardner
- Mitochondrial Research Group, School of Neurology, Neurobiology and Psychiatry, The Medical School, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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58
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Jacobs L, Gerards M, Chinnery P, Dumoulin J, de Coo I, Geraedts J, Smeets H. mtDNA point mutations are present at various levels of heteroplasmy in human oocytes. Mol Hum Reprod 2007; 13:149-54. [PMID: 17259224 DOI: 10.1093/molehr/gal112] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Little is known about the load of mutations and polymorphisms in the mitochondrial DNA (mtDNA) of human oocytes and the possible effect these mutations may have during life. To investigate this, we optimised at the single cell level the recently developed method to screen the entire mtDNA for mainly heteroplasmic mutations by denaturing high performance liquid chromatography analysis. This method is sensitive (approximately 1% heteroplasmy detectable), specific and rapid. The entire mtDNA of 26 oocytes of 13 women was screened by this method. Ten different heteroplasmic mutations, of which only one was located in the D-loop and two were observed twice, were detected in seven oocytes with mutation loads ranging from <5% to 50%. From eight women >1 oocyte was received and in four of them heteroplasmic differences between oocytes of the same woman were observed. In one of these four, two homoplasmic D-loop variants were also detected. Additionally, four oocytes of a single woman were sequenced using the MitoChip (which lacks the D-loop region), but all sequences were identical. It is concluded that heteroplasmic mtDNA mutations are common in oocytes and that, depending on the position and mutation load, they might increase the risk of developing OXPHOS disease early or later in life.
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Affiliation(s)
- Lorraine Jacobs
- Department of Genetics and Cell Biology, University of Maastricht, The Netherlands
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59
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Au KM, Lau SC, Mak YF, Lai WM, Chow TC, Chen ML, Chiu MC, Chan AYW. Mitochondrial DNA deletion in a girl with Fanconi's syndrome. Pediatr Nephrol 2007; 22:136-40. [PMID: 16967281 DOI: 10.1007/s00467-006-0288-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 07/28/2006] [Accepted: 07/31/2006] [Indexed: 10/24/2022]
Abstract
We report a sporadic large-scale mitochondrial deletion in a paediatric patient with Fanconi's syndrome. Renal biopsy disclosed chronic interstitial nephritis. Ultrastructural examination of the renal tissue showed many giant atypical mitochondria. Histochemical stains revealed markedly reduced cytochrome c oxidase (COX). Genetic analysis disclosed a novel mitochondrial deletion of 7.3 kb in both peripheral blood and renal tissue. Mitochondrial diseases have heterogeneous clinical phenotypes; mutation analysis has proved to be an effective tool in confirming the diagnosis.
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Affiliation(s)
- Kam Ming Au
- Department of Pathology, Princess Margaret Hospital, Kwai Chung, Hong Kong SAR, China.
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60
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Giese A, Kirschner-Schwabe R, Blumchen K, Wronski L, Shalapour S, Prada J, Driever PH, Brauer M, Schuelke M, Henze G, Seeger K. Prenatal manifestation of pancytopenia in Pearson marrow-pancreas syndrome caused by a mitochondrial DNA deletion. Am J Med Genet A 2007; 143A:285-8. [PMID: 17219391 DOI: 10.1002/ajmg.a.31493] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Almut Giese
- Department of Pediatric Oncology/Hematology, Charité-Universitätsmedizin Berlin, Campus Virchow Klinikum, Berlin, Germany.
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61
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Hudson G, Chinnery PF. Mitochondrial DNA polymerase-gamma and human disease. Hum Mol Genet 2006; 15 Spec No 2:R244-52. [PMID: 16987890 DOI: 10.1093/hmg/ddl233] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The maintenance of mitochondrial DNA (mtDNA) is critically dependent upon polymerase-gamma (pol-gamma), encoded by the nuclear gene POLG. Over the last 5 years, it has become clear that mutations of POLG are a major cause of human disease. Secondary mtDNA defects characterize these disorders, with mtDNA depletion, multiple mtDNA deletions or multiple point mutations of mtDNA in clinically affected tissues. The secondary mtDNA defects cause cell and tissue-specific deficiencies of mitochondrial oxidative phosphorylation, leading to organ dysfunction and human disease. Functional genetic variants of POLG are present in up to approximately 0.5% of the general population, and pathogenic mutations have been described in most exons of the gene. Clinically, POLG mutations can present from early neonatal life to late middle age, with a spectrum of phenotypes that includes common neurological disorders such as migraine, epilepsy and Parkinsonism. Transgenic mice and biochemical studies of recombinant mutated proteins are helping to unravel mechanisms of pathogenesis, and patterns are beginning to emerge relating genotype to phenotype.
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Affiliation(s)
- Gavin Hudson
- Mitochondrial Research Group and Institute of Human Genetics, M41014, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
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62
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Schwartz S, Alazzouzi H, Perucho M. Mutational dynamics in human tumors confirm the neutral intrinsic instability of the mitochondrial D-loop poly-cytidine repeat. Genes Chromosomes Cancer 2006; 45:770-80. [PMID: 16708351 DOI: 10.1002/gcc.20340] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Somatic mutations at a mitochondrial noncoding polycytidine (C)(n) repeat (polyC) have been associated with tumor progression. We analyzed whether these alterations are due to the inherent mutability of repeated sequences. Insertion and deletion mutations were found in colon (n = 114), stomach (n = 105), endometrium (n = 53), breast (n = 45), lung (n = 35), and prostate (n = 20) tumors. The mutation frequency in colon, gastric, and endometrial tumors was 23, 17, and 11%, respectively, which paralleled the relative extent of microsatellite instability in long mononucleotide repeats observed in tumors with mismatch repair deficiency (colon > stomach > endometrium, relative ratio 10:8:4). Colon tumors with mutations of more than one nucleotide were more advanced in tumor progression. Further, two tumors showing a T > C mutation that restored the homopolymeric repeat, harbored sequential deletion mutations of up to 4 and 6 nucleotides. These results illustrate that the increased mutability of repeated mitochondrial sequences is dependent on the repetitive structure of the DNA molecule and suggest that mutations in the (C)(n) repeat, whether homoplasmic or not, and by extrapolation, mitochondrial mutations in general, are not the result of selective pressure during tumorigenesis. We also suggest that the (C)(n) repeat may be used as an universal molecular clock to estimate the relative mitotic history of tumors.
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Affiliation(s)
- Simó Schwartz
- Molecular Oncology and Aging Group, Centre d'Investigacions en Bioquimica i Biologia Molecular (CIBBIM), Hospital Universitari Vall d'Hebron, Centre Docent Universitat Autònoma de Barcelona, Spain.
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63
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Brown DT, Herbert M, Lamb VK, Chinnery PF, Taylor RW, Lightowlers RN, Craven L, Cree L, Gardner JL, Turnbull DM. Transmission of mitochondrial DNA disorders: possibilities for the future. Lancet 2006; 368:87-9. [PMID: 16815383 DOI: 10.1016/s0140-6736(06)68972-1] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- D T Brown
- Mitochondrial Research Group, School of Neurology, Neurobiology and Psychiatry, The Medical School, University of Newcastle upon Tyne, Newcastle NE2 4HH, UK
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Marchington DR, Scott-Brown M, Barlow DH, Poulton J. Mosaicism for mitochondrial DNA polymorphic variants in placenta has implications for the feasibility of prenatal diagnosis in mtDNA diseases. Eur J Hum Genet 2006; 14:816-23. [PMID: 16670690 DOI: 10.1038/sj.ejhg.5201618] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Women who have had a child with mitochondrial DNA (mtDNA) disease need to know the risk of recurrence, but this risk is difficult to estimate because mutant and wild-type (normal) mtDNA coexist in the same person (heteroplasmy). The possibility that a single sample may not reflect the whole organism both impedes prenatal diagnosis of most mtDNA diseases, and suggests radical alternative strategies such as nuclear transfer. We used naturally occurring mtDNA variants to investigate mtDNA segregation in placenta. Using large samples of control placenta, we demonstrated that the level of polymorphic heteroplasmic mtDNA variants is very similar in mother, cord blood and placenta. However, where placental samples were very small (< 10 mg) there was clear evidence of variation in the distribution of mtDNA polymorphic variants. We present the first evidence for variation in mutant load, that is, mosaicism for mtDNA polymorphic variants in placenta. This suggests that mtDNA mutants may segregate in placenta and that a single chorionic villous sample (CVS) may be unrepresentative of the whole placenta. Duplicates may be necessary where CVS are small. However, the close correlation of mutant load in maternal, fetal blood and placental mtDNA suggests that the average load in placenta does reflect the load of mutant mtDNA in the baby. Provided that segregation of neutral and pathogenic mtDNA mutants is similar in utero, our results are generally encouraging for developing prenatal diagnosis for mtDNA diseases. Identifying mtDNA segregation in human placenta suggests studies of relevance to placental evolution and to developmental biology.
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Affiliation(s)
- David R Marchington
- Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Oxford OX3 9DU, UK
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65
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Sato A, Nakada K, Hayashi JI. Mitochondrial dynamics and aging: Mitochondrial interaction preventing individuals from expression of respiratory deficiency caused by mutant mtDNA. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:473-81. [PMID: 16624428 DOI: 10.1016/j.bbamcr.2006.03.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Revised: 02/24/2006] [Accepted: 03/01/2006] [Indexed: 01/13/2023]
Abstract
In mammalian cells, there is an extensive and continuous exchange of mitochondrial DNA (mtDNA) and its products between mitochondria. This mitochondrial complementation prevents individuals from expression of respiration deficiency caused by mutant mtDNAs. Thus, the presence of mitochondrial complementation does not support the generally accepted mitochondrial theory of aging, which proposes that accumulation of somatic mutations in mtDNA is responsible for age-associated mitochondrial dysfunction. Moreover, the presence of mitochondrial complementation enables gene therapy for mitochondrial diseases using nuclear transplantation of zygotes.
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Affiliation(s)
- Akitsugu Sato
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan
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66
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Frederiksen AL, Andersen PH, Kyvik KO, Jeppesen TD, Vissing J, Schwartz M. Tissue specific distribution of the 3243A->G mtDNA mutation. J Med Genet 2006; 43:671-7. [PMID: 16490799 PMCID: PMC2564591 DOI: 10.1136/jmg.2005.039339] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
BACKGROUND The 3243A-->G is a common pathogenic mitochondrial DNA (mtDNA) point mutation causing a variety of different phenotypes. Segregation of this mutation to different tissues during embryonic life and postnatally is still enigmatic. OBJECTIVE To investigate the tissue distribution of this mutation. METHODS In 65 individuals from nine families segregating the 3243A-->G mutation, the mutation load (% mutated mtDNA) was determined in various tissues. Mutation load was measured in two to four cell types--blood leucocytes, buccal cells, skeletal muscle cells, and urine epithelial cells (UEC)--derived from all three embryogenic germ layers. RESULTS There was a significant correlation among mutation loads in the four tissues (r = 0.80-0.89, p<0.0001). With blood serving as reference, the mutation load was increased by 16% in buccal mucosa, by 31% in UEC, and by 37% in muscle. There were significant differences between the mitotic tissues blood, buccal mucosa, and UEC (p<0.0001), but no difference between UEC and muscle. Using the present data as a cross sectional investigation, a negative correlation of age with the mutation load was found in blood, while the mutation load in muscle did not change with time; 75% of the children presented with higher mutation loads than their mothers in mitotic tissues but not in the post-mitotic muscle. CONCLUSIONS There appears to be a uniform distribution of mutant mtDNA throughout the three germ layers in embryogenesis. The significant differences between mutation loads of the individual tissue types indicate tissue specific segregation of the 3243A-->G mtDNA later in embryogenesis.
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67
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Thouas GA, Trounson AO, Jones GM. Developmental effects of sublethal mitochondrial injury in mouse oocytes. Biol Reprod 2006; 74:969-77. [PMID: 16452460 DOI: 10.1095/biolreprod.105.048611] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Mitochondrial dysfunction may be acquired or inherited by oocytes without detectable morphological abnormalities. This pathology may account for some examples of unexplained pregnancy loss in women following transfer of morphologically normal in vitro fertilization (IVF) embryos. The present study was intended to determine whether sublethal mitochondrial injury in mouse oocytes before IVF negatively affects pre- and postimplantation development, and to further define the latency of developmental compromise in relation to aberrant mitochondrial metabolism. Mature mouse oocytes were loaded with the mitochondrial fluorophore rhodamine-123 and photosensitized for 20 sec, a duration previously found to permit preimplantation embryo development to the blastocyst stage and so deemed "sublethal." This treatment resulted in some aberrations in cytoplasmic patterning of organelles, but did not inhibit zygote mitochondrial metabolism. Blastocyst development following IVF was not significantly inhibited following sublethal oocyte photosensitization; however, a decrease in trophectoderm cell numbers was observed relative to untreated controls. Following intrauterine transfer, blastocysts derived from sublethally photosensitized oocytes implanted but later aborted at a higher rate, formed fetuses with lower average weights, and, in rare cases, formed abnormal fetuses relative to controls. Photosensitization for more prolonged durations resulted in failed fertilization (2 min) and rapid oocyte degeneration (10 min). Therefore, photosensitization duration and the consequent degree of mitochondrial dysfunction are negatively related to the onset of developmental compromise. Acquired low-level mitochondrial injury is heritable by the resultant embryos and can cause postimplantation developmental compromise that may be relevant to some clinically observed outcomes following human assisted reproduction strategies, including reduced birth weights for gestational age. Future strategies for the detection and prevention of mitochondrial dysfunction may assist in improving outcomes for some clinically infertile women.
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Affiliation(s)
- George A Thouas
- Monash Immunology and Stem Cell Laboratories (MISCL), Monash University, Clayton, Victoria 3800, Australia.
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68
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Abstract
BACKGROUND Mitochondrial respiratory chain disorders are the most prevalent group of inherited neurometabolic diseases. They present with central and peripheral neurological features usually in association with other organ involvement including the eye, the heart, the liver, and kidneys, diabetes mellitus and sensorineural deafness. Current treatment is largely supportive and the disorders progress relentlessly causing significant morbidity and premature death. Vitamin supplements, pharmacological agents and exercise therapy have been used in isolated cases and small clinical trials, but the efficacy of these interventions is unclear. OBJECTIVES To determine whether there is objective evidence to support the use of current treatments for mitochondrial disease. SEARCH STRATEGY We searched the Cochrane Neuromuscular Disease Group trials register (searched September 2003), the Cochrane Central Register of Controlled Trials, MEDLINE (January 1966 to October 3 2003), EMBASE (January 1980 to October 3 2003) and the European Neuromuscular Centre (ENMC) clinical trials register, and contacted experts in the field. SELECTION CRITERIA We included randomised controlled trials (including crossover studies) and quasi-randomised trials comparing pharmacological treatments, and non-pharmacological treatments (vitamins and food supplements), and physical training in individuals with mitochondrial disorders. The primary outcome measures included an improvement in muscle strength and/or endurance, or neurological clinical features. Secondary outcome measures included quality of life assessments, biochemical markers of disease and negative outcomes. DATA COLLECTION AND ANALYSIS Details of the number of randomised patients, treatment, study design, study category, allocation concealment and patient characteristics were extracted. Analysis was based on intention to treat data. We planned to use meta-analysis, but this did not prove necessary. MAIN RESULTS Six hundred and seventy-eight abstracts were reviewed, and six fulfilled the entry criteria. Two trials studied the effects of co-enzyme Q10 (ubiquinone), one reporting a subjective improvement and a significant increase in a global scale of muscle strength, but the other trial did not show any benefit. Two trials used creatine, with one reporting improved measures of muscle strength and post-exercise lactate, but the other reported no benefit. One trial of dichloroacetate showed an improvement in secondary outcome measures of mitochondrial metabolism, and one trial using dimethylglycine showed no significant effect. AUTHORS' CONCLUSIONS There is currently no clear evidence supporting the use of any intervention in mitochondrial disorders. Further research is needed to establish the role of a wide range of therapeutic approaches.
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Affiliation(s)
- P Chinnery
- University of Newcastle upon Tyne, Department of Neurology, Medical School, Framlington Place, Newcastle Upon Tyne, UK, NE24 4HH.
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69
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White HE, Durston VJ, Seller A, Fratter C, Harvey JF, Cross NCP. Accurate detection and quantitation of heteroplasmic mitochondrial point mutations by pyrosequencing. ACTA ACUST UNITED AC 2006; 9:190-9. [PMID: 16225398 DOI: 10.1089/gte.2005.9.190] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Disease-causing mutations in mitochondrial DNA (mtDNA) are typically heteroplasmic and therefore interpretation of genetic tests for mitochondrial disorders can be problematic. Detection of low level heteroplasmy is technically demanding and it is often difficult to discriminate between the absence of a mutation or the failure of a technique to detect the mutation in a particular tissue. The reliable measurement of heteroplasmy in different tissues may help identify individuals who are at risk of developing specific complications and allow improved prognostic advice for patients and family members. We have evaluated Pyrosequencing technology for the detection and estimation of heteroplasmy for six mitochondrial point mutations associated with the following diseases: Leber's hereditary optical neuropathy (LHON), G3460A, G11778A, and T14484C; mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), A3243G; myoclonus epilepsy with ragged red fibers (MERRF), A8344G, and neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP)/Leighs: T8993G/C. Results obtained from the Pyrosequencing assays for 50 patients with presumptive mitochondrial disease were compared to those obtained using the commonly used diagnostic technique of polymerase chain reaction (PCR) and restriction enzyme digestion. The Pyrosequencing assays provided accurate genotyping and quantitative determination of mutational load with a sensitivity and specificity of 100%. The MELAS A3243G mutation was detected reliably at a level of 1% heteroplasmy. We conclude that Pyrosequencing is a rapid and robust method for detecting heteroplasmic mitochondrial point mutations.
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Affiliation(s)
- Helen E White
- National Genetics Reference Laboratory (Wessex), Salisbury District Hospital, Odstock, Salisbury, Wiltshire, United Kingdom.
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Sato A, Kono T, Nakada K, Ishikawa K, Inoue SI, Yonekawa H, Hayashi JI. Gene therapy for progeny of mito-mice carrying pathogenic mtDNA by nuclear transplantation. Proc Natl Acad Sci U S A 2005; 102:16765-70. [PMID: 16275929 PMCID: PMC1283814 DOI: 10.1073/pnas.0506197102] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pathogenic mutations in mtDNAs have been shown to be responsible for expression of respiration defects and resultant expression of mitochondrial diseases. This study directly addressed the issue of gene therapy of mitochondrial diseases by using nuclear transplantation of zygotes of transmitochondria mice (mito-mice). Mito-mice expressed respiration defects and mitochondrial diseases due to accumulation of mtDNA carrying a large-scale deletion (DeltamtDNA). Second polar bodies were used as biopsy samples for diagnosis of mtDNA genotypes of mito-mouse zygotes. Nuclear transplantation was carried out from mito-mouse zygotes to enucleated normal zygotes and was shown to rescue all of the F(0) progeny from expression of respiration defects throughout their lives. This procedure should be applicable to patients with mitochondrial diseases for preventing their children from developing the diseases.
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Affiliation(s)
- Akitsugu Sato
- Graduate School of Life and Environmental Sciences, Center for Tsukuba Advanced Research Alliance, University of Tsukuba, Ibaraki 305-8572, Japan
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71
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Toivonen JM, Manjiry S, Touraille S, Alziari S, O'Dell KMC, Jacobs HT. Gene dosage and selective expression modify phenotype in a Drosophila model of human mitochondrial disease. Mitochondrion 2005; 3:83-96. [PMID: 16120347 DOI: 10.1016/s1567-7249(03)00077-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2003] [Revised: 06/03/2003] [Accepted: 06/04/2003] [Indexed: 11/22/2022]
Abstract
Human mitochondrial disease manifests with a wide range of clinical phenotypes of varying severity. To create a model for these disorders, we have manipulated the Drosophila gene technical knockout, encoding mitoribosomal protein S12. Various permutations of endogenous and transgenic alleles create a range of phenotypes, varying from larval developmental arrest through to mild neurological defects in the adult, and also mimic threshold effects associated with human mtDNA disease. Nuclear genetic background influences mutant phenotype by a compensatory mechanism affecting mitochondrial RNA levels. Selective expression of the wild-type allele indicates critical times and cell-types in development, in which mitochondrial protein synthesis deficiency leads to specific phenotypic outcomes.
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Affiliation(s)
- Janne M Toivonen
- Institute of Medical Technology and Tampere University Hospital, 33014 Tampere, Finland
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72
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Jacobs LJAM, de Wert G, Geraedts JPM, de Coo IFM, Smeets HJM. The transmission of OXPHOS disease and methods to prevent this. Hum Reprod Update 2005; 12:119-36. [PMID: 16199488 DOI: 10.1093/humupd/dmi042] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Diseases owing to defects of oxidative phosphorylation (OXPHOS) affect approximately 1 in 8,000 individuals. Clinical manifestations can be extremely variable and range from single-affected tissues to multisystemic syndromes. In general, tissues with a high energy demand, like brain, heart and muscle, are affected. The OXPHOS system is under dual genetic control, and mutations in both nuclear and mitochondrial genes can cause OXPHOS diseases. The expression and segregation of mitochondrial DNA (mtDNA) mutations is different from nuclear gene defects. The mtDNA mutations can be either homoplasmic or heteroplasmic and in the latter case disease becomes manifest when the mutation exceeds a tissue-specific threshold. This mutation load can vary between tissues and often an exact correlation between mutation load and phenotypic expression is lacking. The transmission of mtDNA mutations is exclusively maternal, but the mutation load between embryos can vary tremendously because of a segregational bottleneck. Diseases by nuclear gene mutations show a normal Mendelian inheritance pattern and often have a more constant clinical manifestation. Given the prevalence and severity of OXPHOS disorders and the lack of adequate therapy, existing and new methods for the prevention of transmission of OXPHOS disorders, like prenatal diagnosis (PND), preimplantation genetic diagnosis (PGD), cytoplasmic transfer (CT) and nuclear transfer (NT), are technically and ethically evaluated.
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Affiliation(s)
- L J A M Jacobs
- Department of Genetics and Cell Biology, University of Maastricht, 6200 MD Maastricht, The Netherlands
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73
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Bayona-Bafaluy MP, Blits B, Battersby BJ, Shoubridge EA, Moraes CT. Rapid directional shift of mitochondrial DNA heteroplasmy in animal tissues by a mitochondrially targeted restriction endonuclease. Proc Natl Acad Sci U S A 2005; 102:14392-7. [PMID: 16179392 PMCID: PMC1242285 DOI: 10.1073/pnas.0502896102] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Frequently, mtDNA with pathogenic mutations coexist with wild-type genomes (mtDNA heteroplasmy). Mitochondrial dysfunction and disease ensue only when the proportion of mutated mtDNAs is high, thus a reduction in this proportion should provide an effective therapy for these disorders. We developed a system to decrease specific mtDNA haplotypes by expressing a mitochondrially targeted restriction endonuclease, ApaLI, in cells of heteroplasmic mice. These mice have two mtDNA haplotypes, of which only one contains an ApaLI site. After transfection of cultured hepatocytes with mitochondrially targeted ApaLI, we found a rapid, directional, and complete shift in mtDNA heteroplasmy (2-6 h). We tested the efficacy of this approach in vivo, by using recombinant viral vectors expressing the mitochondrially targeted ApaLI. We observed a significant shift in mtDNA heteroplasmy in muscle and brain transduced with recombinant viruses. This strategy could prevent disease onset or reverse clinical symptoms in patients harboring certain heteroplasmic pathogenic mutations in mtDNA.
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Affiliation(s)
- Maria Pilar Bayona-Bafaluy
- Department of Neurology and Cell Biologyalysis, University of Miami Miller School of Medicine, Miami, FL 33136, USA
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74
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Abstract
The human mitochondrial genome is extremely small compared with the nuclear genome, and mitochondrial genetics presents unique clinical and experimental challenges. Despite the diminutive size of the mitochondrial genome, mitochondrial DNA (mtDNA) mutations are an important cause of inherited disease. Recent years have witnessed considerable progress in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer. However, many challenges remain, including the prevention and treatment of these diseases. This review explores the advances that have been made and the areas in which future progress is likely.
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75
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Tejerizo-García A, Hernández-Hernández L, Henríquez A, González-Rodríguez S, Ruiz M, Alcántara R, Martínez del Val M, Lanchares J, Tejerizo-López L. Enfermedades mitocondriales y gestación. CLINICA E INVESTIGACION EN GINECOLOGIA Y OBSTETRICIA 2005. [DOI: 10.1016/s0210-573x(05)73478-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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76
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Thorburn DR, Sugiana C, Salemi R, Kirby DM, Worgan L, Ohtake A, Ryan MT. Biochemical and molecular diagnosis of mitochondrial respiratory chain disorders. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1659:121-8. [PMID: 15576043 DOI: 10.1016/j.bbabio.2004.08.006] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Revised: 08/16/2004] [Accepted: 08/16/2004] [Indexed: 12/25/2022]
Abstract
Biochemical diagnosis of mitochondrial respiratory chain disorders requires caution to avoid misdiagnosis of secondary enzyme defects, and can be improved by the use of conservative diagnostic criteria. Pathogenic mutations causing mitochondrial disorders have now been identified in more than 30 mitochondrial DNA (mtDNA) genes encoding respiratory chain subunits, ribosomal- and t-RNAs. mtDNA mutations appear to be responsible for most adult patients with mitochondrial disease and approximately a quarter of paediatric patients. A family history suggesting maternal inheritance is the exception rather than the norm for children with mtDNA mutations, many of whom have de novo mutations. Prenatal diagnosis and pre-implantation genetic diagnosis can be offered to some women at risk of transmitting a mtDNA mutation, particularly those at lower recurrence risk. Mutations in more than 30 nuclear genes, including those encoding for respiratory chain subunits and assembly factors, have now been shown to cause mitochondrial disorders, creating difficulties in prioritising which genes should be studied by mutation analysis in individual patients. A number of approaches offer promise to guide the choice of candidate genes, including Blue Native-PAGE immunoblotting and microarray expression analysis.
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Affiliation(s)
- David R Thorburn
- Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria 3052 Australia.
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77
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Jacobs LJAM, de Coo IFM, Nijland JG, Galjaard RJH, Los FJ, Schoonderwoerd K, Niermeijer MF, Geraedts JPM, Scholte HR, Smeets HJM. Transmission and prenatal diagnosis of the T9176C mitochondrial DNA mutation. Mol Hum Reprod 2005; 11:223-8. [PMID: 15709156 DOI: 10.1093/molehr/gah152] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
A family presented with three affected children with Leigh syndrome, a progressive neurodegenerative disorder. Analysis of the OXPHOS complexes in muscle of two affected patients showed an increase in activity of pyruvate dehydrogenase and a decrease of complex V activity. Mutation analysis revealed the T9176C mutation in the mtATPase 6 gene (OMIM 516060) and the mutation load was above 90% in the patients. Unaffected maternal relatives were tested for carrier-ship and one of them, with a mutation load of 55% in blood, was pregnant with her first child. The possibility of prenatal diagnosis was evaluated. The main problem was the lack of data on genotype-phenotype associations for the T9176C mutation and on variation of the mutation percentage in tissues and in time. Therefore, multiple tissues of affected and unaffected carriers were analysed. Eventually, prenatal diagnosis was offered with understanding by the couple that there could be considerable uncertainty in the interpretation of the results. Prenatal diagnosis was carried out twice on cultured and uncultured chorion villi and amniotic fluid cells. The result was a mutation percentage just below the assumed threshold of expression (90%). The couple decided to continue the pregnancy and an apparently healthy child was born with an as yet unclear prognosis. This is the first prenatal diagnosis for a carrier of the T9176C mutation. Prenatal diagnosis for this mutation is technically reliable, but the prognostic predictions are not straightforward.
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Affiliation(s)
- L J A M Jacobs
- Department of Genetics and Cell Biology, Research Institute GROW, University of Maastricht, Maastricht, The Netherlands
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78
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Wong LJC, Boles RG. Mitochondrial DNA analysis in clinical laboratory diagnostics. Clin Chim Acta 2005; 354:1-20. [PMID: 15748595 DOI: 10.1016/j.cccn.2004.11.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 10/22/2004] [Accepted: 11/03/2004] [Indexed: 11/25/2022]
Abstract
Mitochondrial disorders are increasingly being diagnosed, especially among patients with multiple, seemingly unrelated, neuromuscular and multi-sytem disorders. The genetics are complex, in particular as the primary mutation can be either on the nuclear or the mitochondrial DNA (mtDNA). mtDNA mutations are often maternally inherited, but can be sporadic or secondary to autosomally inherited mutations in nuclear genes that regulate mtDNA biosynthesis. mtDNA mutations demonstrate extreme variable expressivity in terms of clinical manifestations and severity, even within a family. Disease is often episodic. Several well-defined clinical syndromes associated with specific mutations are described, yet the genotype-phenotype correlation is fair at best and most patients do not fit within any defined syndrome and have rare or novel mutations. In most patients, mutant and wild-type mtDNA coexist ("heteroplasmy"), although homoplasmic mtDNA mutations also are known. "Standard" mtDNA clinical diagnostics usually consists of a PCR-based assay to detect a small number of relatively common point mutations and Southern blotting (or PCR) for large (>500 bp) rearrangements. In selected cases testing negative, additional analyses can include real-time PCR for mtDNA depletion, and full mtDNA genome screening for the detection of rare and novel point mutations by a variety of methods. Prenatal diagnosis is problematic in most cases.
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Affiliation(s)
- Lee-Jun C Wong
- Institute for Molecular and Human Genetics, Georgetown University Medical Center, 3800 Reservoir Road, NW, M4000, Washington, DC 20007, USA
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79
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Komlósi K, Kellermayer R, Maász A, Havasi V, Hollódy K, Vincze O, Merkli H, Pál E, Melegh B. Maternally inherited deafness and unusual phenotypic manifestations associated with A3243G mitochondrial DNA mutation. Pathol Oncol Res 2005; 11:82-6. [PMID: 15999151 DOI: 10.1007/bf02893371] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Accepted: 05/15/2005] [Indexed: 11/30/2022]
Abstract
The mitochondrial DNA A3243G transition is a fairly common mutation which often associates with a MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes) phenotype, however, a broad variety in the associated clinical picture has also been described. The patient reported here developed a generalized seizure at age 12, which was followed by bilateral hearing loss and occasional fatigue. The maternal inheritance pattern of hearing loss pointed to a possible mitochondrial origin, which was confirmed by molecular analysis of the mitochondrial DNA, revealing a heteroplasmic A3243G transition. Interestingly, muscle biopsy showed ragged-red fibers in the proband, which is unusual in the deafness-associated forms of this mitochondrial disorder. In addition to hearing impairment in four generations of the family, fatal cerebral embolization in the mother and fatal heart attack in the maternal grandmother (both at age 33) also occurred. On the contrary, diabetes, which usually accompanies the hearing loss variant, was specifically absent in all generations. The unusual manifestations associated with this mutation somewhat differentiate this family from the already known variants.
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Affiliation(s)
- Katalin Komlósi
- Department of Medical Genetics and Child Development, University of Pécs, Pécs, H-7624, Hungary
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80
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Chinnery PF, DiMauro S, Shanske S, Schon EA, Zeviani M, Mariotti C, Carrara F, Lombes A, Laforet P, Ogier H, Jaksch M, Lochmüller H, Horvath R, Deschauer M, Thorburn DR, Bindoff LA, Poulton J, Taylor RW, Matthews JNS, Turnbull DM. Risk of developing a mitochondrial DNA deletion disorder. Lancet 2004; 364:592-6. [PMID: 15313359 DOI: 10.1016/s0140-6736(04)16851-7] [Citation(s) in RCA: 156] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
BACKGROUND Pathogenic mitochondrial DNA (mtDNA) mutations are found in at least one in 8000 individuals. No effective treatment for mtDNA disorders is available, making disease prevention important. Many patients with mtDNA disease harbour a single pathogenic mtDNA deletion, but the risk factors for new cases and disease recurrence are not known. METHODS We did a multicentre study of 226 families in which a single mtDNA deletion had been identified in the proband, including patients with chronic progressive external ophthalmoplegia, Kearns Sayre syndrome, or Pearson's syndrome. We studied the relation between maternal age and the risk of unaffected mothers having an affected child, and determined the recurrence risks among the siblings and offspring of affected individuals. FINDINGS We noted no relation between maternal age and the risk of unaffected mothers having children with an mtDNA deletion disorder. None of the 251 siblings of the index cases developed clinical features of mtDNA disease. Risk of recurrence among the offspring of affected women was 4.11% (95% CI 0.86-11.54, or one in 117 to one in nine births). Only one of the mothers who had an affected child had a duplication of mtDNA in skeletal muscle. INTERPRETATION Unlike nuclear chromosomal rearrangements, incidence of mtDNA deletion disorders does not increase with maternal age, and unaffected mothers are unlikely to have more than one affected child. Affected women were previously thought to have a negligible chance of having clinically affected offspring, but the actual risk is, on average, about one in 24 births.
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81
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Kwon SJ, Park SS, Kim JM, Ahn TB, Kim SH, Kim J, Lee SH, Ha CK, Ahn MY, Jeon BS. Investigation of common mitochondrial point mutations in Korea. Ann N Y Acad Sci 2004; 1011:339-44. [PMID: 15126311 DOI: 10.1007/978-3-662-41088-2_34] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Between 1997 and 2002, 65 patients with suspected mitochondrial diseases were screened for the mitochondrial point mutations A3243G, T3271C, A8344G, and T8356C. Among these patients, 15 were found to have one of these mutations: 12 with A3243G and 3 with A8344G. The phenotypes of A3243G and A8344G mutations were MELAS and MERRF, respectively. Many asymptomatic family members had the same mutations. In this report, detailed clinical and laboratory findings are presented.
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Affiliation(s)
- Seon-Joo Kwon
- Department of Neurology, Seoul National University Medical Research Center, Clinical Research Institute, Seoul, Korea
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82
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83
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KWON SEONJOO, PARK SUNGSUP, KIM JONGMIN, AHN TAEBEOM, KIM SEUNGHYUN, KIM JUHAN, LEE SUNGHYUN, HA CHOONGKUN, AHN MOOYOUNG, JEON BEOMS. Investigation of Common Mitochondrial Point Mutations in Korea. Ann N Y Acad Sci 2004. [DOI: 10.1196/annals.1293.034] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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84
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Sills ES, Takeuchi T, Tucker MJ, Palermo GD. Genetic and epigenetic modifications associated with human ooplasm donation and mitochondrial heteroplasmy – considerations for interpreting studies of heritability and reproductive outcome. Med Hypotheses 2004; 62:612-7. [PMID: 15050116 DOI: 10.1016/j.mehy.2003.10.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2003] [Accepted: 10/20/2003] [Indexed: 11/23/2022]
Abstract
The mitochondrial heteroplasmy present in offspring from IVF and human ooplasm donation is troublesome and merits further exploration in a debate that is already complex and controversial. Improving the understanding of mitochondrial genomics in this context is important because mitochondriopathies can impact crucial cellular processes in renal, cardiovascular, central nervous, and endocrine systems. Relevant epigenetic consequences of mitochondrial heteroplasmy include associated abnormalities in mitochondrial translation products. Furthermore, as transmission and inheritance patterns of mtDNA are species-specific, it remains to be proven if findings derived from animal studies are applicable to human offspring. As an alternative to gamete research and proteomics based on animal experimentation, continued molecular characterization of the de novo human mitochondriopathies is posed to offer further insights regarding mitochondrial heteroplasmy. In this context, because knowledge of human mitochondrial genetics remains limited and the risks associated with ooplasm donation cannot be quantified, we do not favor its use for our patients at present. However, the small number of infants already conceived from this experimental approach warrant careful longitudinal evaluation. In particular, observational study of the few children born after ooplasm donation could provide opportunities to assess human mtDNA transmission and inheritance. Such findings could help identify features distinguishing natural mtDNA heteroplasmy from heteroplasmy observed after ooplasm donation. Future investigations should also quantify the degree any such heteroplasmy can exist innocuously. Disclosure of mtDNA mutations potentially affecting children conceived from IVF and ooplasm donation must be included during patient education at centers contemplating such treatment.
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Affiliation(s)
- E Scott Sills
- Cornell Institute for Reproductive Medicine and Infertility, Weill Medical College of Cornell University, New York-Presbyterian Hospital, New York, USA.
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85
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Racine AC, Blanchot G, Le Vaillant C, Boog G. Grossesse chez une patiente atteinte de cytopathie mitochondriale. ACTA ACUST UNITED AC 2004; 33:131-9. [PMID: 15052179 DOI: 10.1016/s0368-2315(04)96412-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report a case of a pregnant woman with a mitochondrial disorder affecting the energy-generating pathway of oxidative phosphorylation which was suggested when the patient presented the progressive clinical phenotype of a proximal tubular renal insufficiency, a muscular weakness of extremities, a bilateral optic neuropathy and a brain magnetic resonance imaging suggesting diffuse leucoencephalopathy. Her diagnosis was made on the basis of abnormal mitochondria on a muscle biopsy and of spectrophotometric deficiencies of the complexes I, II+III and IV of the respiratory chain. No specific molecular mutation could be detected. Her pregnancy was complicated by a severe preeclampsia, an insulin requiring gestational diabetes and a worrying renal failure which precipitated the premature delivery by cesarean section at 30 weeks gestation. The clinical course of the female neonate weighing 1030 grams was uneventful. At two Years of age she showed no sign of mitochondrial disease. But the postpartum course of the mother was complicated by seizures and a terminal renal failure leading presently to dialysis, but requiring a kidney transplantation in the near future.
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Affiliation(s)
- A-C Racine
- Service d'Obstétrique et de Médecine Foetale, Hôpital Mère et Enfant, CHU, Quai Moncousu, 44093 Nantes Cedex 1
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86
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McFarland R, Kirby DM, Fowler KJ, Ohtake A, Ryan MT, Amor DJ, Fletcher JM, Dixon JW, Collins FA, Turnbull DM, Taylor RW, Thorburn DR. De novo mutations in the mitochondrial ND3 gene as a cause of infantile mitochondrial encephalopathy and complex I deficiency. Ann Neurol 2004; 55:58-64. [PMID: 14705112 DOI: 10.1002/ana.10787] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Both nuclear and mitochondrial DNA mutations can cause energy generation disorders. Respiratory chain complex I deficiency is the most common energy generation disorder and a frequent cause of infantile mitochondrial encephalopathies such as Leigh's disease and lethal infantile mitochondrial disease. Most such cases have been assumed to be caused by nuclear gene defects, but recently an increasing number have been shown to be caused by mutations in the mitochondrially encoded complex I subunit genes ND4, ND5, and ND6. We report the first four cases of infantile mitochondrial encephalopathies caused by mutations in the ND3 subunit gene. Three unrelated children have the same novel heteroplasmic mutation (T10158C), only the second mutation reported in ND3, and one has the previously identified T10191C mutation. Both mutations cause disproportionately greater reductions in enzyme activity than in the amount of fully assembled complex I, suggesting the ND3 subunit plays an unknown but important role in electron transport, proton pumping, or ubiquinone binding. Three cases appear to have a de novo mutation, with no mutation detected in maternal relatives. Mitochondrial DNA disease may be considerably more prevalent in the pediatric population than currently predicted and should be considered in patients with infantile mitochondrial encephalopathies and complex I deficiency.
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Affiliation(s)
- Robert McFarland
- Mitochondrial Research Group, School of Neurology, Neurobiology and Psychiatry, University of Newcastle upon Tyne, United Kingdom
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87
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Abstract
Mitochondrial disorders are among the most common inherited metabolic diseases and the issue of treatment arises on a regular basis. There is no established treatment for mitochondrial disorders and current management is largely supportive, but recent advances in our understanding of the pathophysiology provide hope for novel treatments. Patients with mitochondrial myopathy due to mutations of mitochondrial DNA (mtDNA) may benefit from treatments that move normal mitochondrial genomes from the muscle satellite cells into skeletal muscle, but there are concerns about the long-term effects of this approach. A greater understanding of the pathophysiology of a number of nuclear genetic mitochondrial disorders suggests new avenues for treatment (such as copper-histidine in children with SCO2 gene mutations, and strategies modifying intra-mitochondrial nucleoside pools in the various disorders of mtDNA maintenance). A number of different strategies are also being explored at the molecular level, including the use of antigenomic molecules to mutated mtDNA and the allotropic expression of mutated mtDNA genes within the cell nucleus. Nuclear transfer techniques also provide hope for women at risk of transmitting pathogenic mtDNA mutations.
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Affiliation(s)
- Patrick F Chinnery
- Department of Neurology, Medical School, Framlington Place, The University of Newcastle upon Tyne, NE2 4HH, UK.
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88
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Chapter 30 Mitochondrial disorders. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/s1567-424x(09)70366-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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89
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Abstract
Disorders of mitochondrial oxidative phosphorylation (OXPHOS) are renowned for their variability in clinical features and genetic causes. This makes it difficult to determine their true prevalence, but recent studies have documented a minimum birth prevalence of 13.1/100000 or 1/7634 for oxidative phosphorylation disorders with onset at any age. This clearly remains an underestimate but it indicates that oxidative phosphorylation disorders can be regarded as the most common group of inborn errors of metabolism. Pathogenic mutations causing human oxidative phosphorylation disorders have now been identified in more than 30 of the 37 mitochondrial DNA genes and in more than 30 nuclear genes. Most of the nuclear gene defects cause autosomal recessive diseases, but autosomal dominant and X-linked disorders also occur. It is likely that at least another 30, and perhaps over 100, nuclear-encoded oxidative phosphorylation disorders await identification. Oxidative phosphorylation genetics are complex and there appear to be a number of common misconceptions about mitochondrial DNA mutations that may impede optimal investigation and management of patients. In our experience, mitochondrial DNA mutations are not a negligible cause of OXPHOS disorders in children but account for 20-25% of cases. Similarly, a family history suggesting maternal inheritance is the exception rather than the norm for children with mitochondrial DNA mutations, many of whom have de novo mutations. Only some mitochondrial DNA mutations disappear from cultured cells, so deficient enzyme activity in fibroblasts does not imply the presence of a nuclear defect. Finally, it is still widely thought that there are very few reproductive options that can be offered to women at risk of transmitting a mitochondrial DNA mutation. While a cautious approach is needed, there is now a consensus that prenatal diagnosis should be offered to some women, particularly those at lower recurrence risk. Preimplantation genetic diagnosis can also be an option.
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Affiliation(s)
- D R Thorburn
- The Murdoch Children's Research Institute and Genetic Health Services Victoria, Royal Children's Hospital, and Department of Paediatrics, University of Melbourne, Melbourne, Australia.
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90
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Knerr I, Metzler M, Niemeyer CM, Holter W, Gerecke A, Baumann I, Trollmann R, Repp R. Hematologic features and clinical course of an infant with Pearson syndrome caused by a novel deletion of mitochondrial DNA. J Pediatr Hematol Oncol 2003; 25:948-51. [PMID: 14663277 DOI: 10.1097/00043426-200312000-00008] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE Pearson bone marrow-pancreas syndrome (PS) is a rare, usually fatal mitochondrial disorder involving the hematopoietic system in early infancy. Due to the diversity of clinical symptoms, the diagnosis can be difficult. The authors describe a boy with severe hypoplastic anemia in whom extensive clinical, biochemical, and morphologic findings led to the diagnosis of PS, and molecular analysis revealed a novel deletion of mitochondrial DNA from nucleotide position 10.371 to 14.607. METHODS The patient is a 2-year-old boy who presented at age 5 months with hypoplastic macrocytic anemia. His first months of life and the family history were uneventful. Extensive pretransfusion evaluations did not reveal a metabolic, infectious, or hematologic-neoplastic etiology, and he had no evidence of exocrine pancreatic insufficiency. However, a second bone marrow aspirate at age 7 months showed a reduced cell number, vacuolated erythroblasts and myeloblasts, and ringed sideroblasts, so PS was suspected. RESULTS Additional molecular analysis from the boy's blood leukocytes revealed a deletion of mitochondrial DNA from nucleotide position 10.371 to 14.607, which was absent in his mother's blood cells, consistent with a sporadic mutation as commonly seen in PS. The muscle histology and the respiratory chain enzymes were normal. CONCLUSIONS Mitochondriopathies should be considered in children with persistent non-neuromuscular symptoms such as unexplained refractory anemia. Due to the often-fatal course of PS, the rapid detection of mitochondrial DNA deletions is imperative for diagnosis and family counseling.
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Affiliation(s)
- Ina Knerr
- Department of Pediatrics, University of Erlangen-Nuremberg, Germany.
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91
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Abstract
Following the discovery in the early 1960s that mitochondria contain their own DNA (mtDNA), there were two major advances, both in the 1980s: the human mtDNA sequence was published in 1981, and in 1988 the first pathogenic mtDNA mutations were identified. The floodgates were opened, and the 1990s became the decade of the mitochondrial genome. There has been a change of emphasis in the first few years of the new millennium, away from the "magic circle" of mtDNA and back to the nuclear genome. Various nuclear genes have been identified that are fundamentally important for mitochondrial homeostasis, and when these genes are disrupted, they cause autosomally inherited mitochondrial disease. Moreover, mitochondrial dysfunction plays an important role in the pathophysiology of several well established nuclear genetic disorders, such as dominant optic atrophy (mutations in OPA1), Friedreich's ataxia (FRDA), hereditary spastic paraplegia (SPG7), and Wilson's disease (ATP7B). The next major challenge is to define the more subtle interactions between nuclear and mitochondrial genes in health and disease.
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Affiliation(s)
- P F Chinnery
- Department of Neurology, The University of Newcastle upon Tyne, Newcastle upon Tyne, UK.
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92
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Sinnathuray AR, Raut V, Awa A, Magee A, Toner JG. A review of cochlear implantation in mitochondrial sensorineural hearing loss. Otol Neurotol 2003; 24:418-26. [PMID: 12806294 DOI: 10.1097/00129492-200305000-00012] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE Mitochondrial sensorineural hearing loss (SNHL) may be nonsyndromic (occurring in isolation), associated with the A1555G mutation in the MTRNR1 gene. Mitochondrial SNHL may also be syndromic, associated with the A3243G point mutation in the MTTL1 gene. In syndromic cases-mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS), maternally inherited diabetes and deafness, Kearns-Sayre syndrome, and chronic progressive external ophthalmoplegia-the SNHL compounds already existing disabilities. The genetic basis for mitochondrial SNHL and postulated sites of pathologic changes are discussed. DATA SOURCES Sources used were relevant clinical and basic science publications. STUDY SELECTION A search of the entire databases of Medline and Web of Science, using various subject headings and free-text terms, was used to identify patients with mitochondrial disease having cochlear implants. DATA EXTRACTION The data from publications were critically reviewed and tabulated to assess implantation outcomes. DATA SYNTHESIS The data were not amenable to formal meta-analysis or valid data summarization, other than descriptive statistics. CONCLUSIONS There is an increasing awareness of the prevalence of mitochondrial SNHL and its progressive nature. High-risk candidates warrant genetic testing and family screening. Correlating the data for mitochondrial SNHL as a treatable entity is important, and the authors present an overview of these patients successfully rehabilitated by cochlear implantation.
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Affiliation(s)
- A R Sinnathuray
- Department of Otolaryngology, Belfast City Hospital, Queen's University, Belfast at the Belfast City Hospital, UK.
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93
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Chretien D, Bénit P, Chol M, Lebon S, Rötig A, Munnich A, Rustin P. Assay of mitochondrial respiratory chain complex I in human lymphocytes and cultured skin fibroblasts. Biochem Biophys Res Commun 2003; 301:222-4. [PMID: 12535666 DOI: 10.1016/s0006-291x(02)03016-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Respiratory chain complex I (NADH:ubiquinone oxidoreductase) deficiency is one of the most frequent causes of mitochondrial disease in humans. The activity of this complex can be confidently measured in most tissue samples, but not in cultured skin fibroblasts or circulating lymphocytes. Highly contaminating non-mitochondrial NADH-quinone oxidoreductase activity in fibroblasts and the limited access of substrates to complex I in lymphocytes hinder its measurement in permeabilized cells. Complex I assay in these cells requires the isolation of mitochondria, which in turn necessitates large quantities of cells and is not feasible when studying circulating lymphocytes. Here we report a simple method to measure complex I activity in a minute amount of either cell type. The procedure strongly reduces contaminating NADH:quinone oxidoreductase activity and permits measuring high rates of rotenone-sensitive complex I activity thanks to effective cell permeabilization.
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Affiliation(s)
- Dominique Chretien
- Unité de Recherches sur les Handicaps Génétiques de l'Enfant (INSERM U393), 2éme Etage, Hôpital Necker-Enfants Malades, 149, rue de Sèvres, 75743 Paris cedex 15, France
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94
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Niers L, van den Heuvel L, Trijbels F, Sengers R, Smeitink J. Prerequisites and strategies for prenatal diagnosis of respiratory chain deficiency in chorionic villi. J Inherit Metab Dis 2003; 26:647-58. [PMID: 14707513 DOI: 10.1023/b:boli.0000005605.57420.b4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Prenatal diagnosis for respiratory chain deficiencies is a complex procedure that requires a thorough diagnostic work-up of the index patient. This includes confirmation of the clinical and metabolic evaluations through histological and enzymatic examinations of tissue biopsies. Prenatal diagnosis currently relies on biochemical assays of respiratory chain complexes in chorionic villi or amniocytes and is possible by mutation analysis of nuclear genes in a limited but increasing proportion of cases. Based on a recent survey of prenatal diagnosis in families with complex I and complex IV deficiencies, performed at Nijmegen Centre for Mitochondrial Disorders (NCMD), prerequisites and strategies for performing prenatal diagnosis have been developed to increase reliability. Biochemical investigations in chorionic villi can be done reliably if the respiratory chain enzyme deficiency is expressed in both skeletal muscle and skin fibroblasts to rule out tissue specificity. No mitochondrial DNA defects must be suspected or established. The NCMD does not offer prenatal diagnosis until all the prerequisites have been confirmed. We expect prenatal diagnosis at the molecular level to become more feasible in time as the mutational spectrum broadens with advances in medical research.
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Affiliation(s)
- L Niers
- Department of Paediatrics, Nijmegen Centre for Mitochondrial Disorders, The Netherlands
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95
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Abstract
In eukaryotic cells, mitochondria are the major site of ATP production, which is achieved through the electron-transport chain and oxidative phosphorylation, according to the energy demand. Mitochondria contain their own genome (mitochondrial DNA, mtDNA) on which a limited number of genes are encoded. In the human sperm, mitochondria helically wrap the midpiece of the tail and supply the energy for the driving force of motility. While various mutations in mtDNA in somatic cells are found to be associated with a wide spectrum of diseases, it is also reported that the abnormal mtDNA causes astenozoospermia and male infertility. At fertilization, the paternal mitochondria and mtDNA are rapidly degraded early in embryogenesis, thus, only maternal mtDNA is transmitted to the descendant. We briefly review here the basic characteristics of mtDNA and its maternal transmission during fertilization, as well as male infertility. (Reprod Med Biol 2002; 1: 41-47).
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Affiliation(s)
| | | | | | - Tadashi Mabuchi
- Biochemistry, Yamanashi Medical University, Nakakoma, Yamanashi, Japan
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96
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Hancock DK, Schwarz FP, Song F, Wong LJC, Levin BC. Design and Use of a Peptide Nucleic Acid for Detection of the Heteroplasmic Low-Frequency Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS) Mutation in Human Mitochondrial DNA. Clin Chem 2002. [DOI: 10.1093/clinchem/48.12.2155] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Abstract
Background: Most pathogenic human mitochondrial DNA (mtDNA) mutations are heteroplasmic (i.e., mutant and wild-type mtDNA coexist in the same individual) and are difficult to detect when their concentration is a small proportion of that of wild-type mtDNA molecules. We describe a simple methodology to detect low proportions of the single base pair heteroplasmic mutation, A3243G, that has been associated with the disease mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) in total DNA extracted from blood.
Methods: Three peptide nucleic acids (PNAs) were designed to bind to the wild-type mtDNA in the region of nucleotide position 3243, thus blocking PCR amplification of the wild-type mtDNA while permitting the mutant DNA to become the dominant product and readily discernable. DNA was obtained from both apparently healthy and MELAS individuals. Optimum PCR temperatures were based on the measured ultraviolet thermal stability of the DNA/PNA duplexes. The presence or absence of the mutation was determined by sequencing.
Results: In the absence of PNAs, the heteroplasmic mutation was either difficult to detect or undetectable by PCR and sequencing. Only PNA 3 successfully inhibited amplification of the wild-type mtDNA while allowing the mutant mtDNA to amplify. In the presence of PNA 3, we were able to detect the heteroplasmic mutation when its concentration was as low as 0.1% of the concentration of the wild-type sequence.
Conclusion: This methodology permits easy detection of low concentrations of the MELAS A3243G mutation in blood by standard PCR and sequencing methods.
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Affiliation(s)
- Diane K Hancock
- Biotechnology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Frederick P Schwarz
- Biotechnology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Fenhong Song
- University of Maryland Biotechnology Institute, Center for Advanced Research in Biotechnology, Rockville, MD 20850
| | - Lee-Jun C Wong
- Institute for Molecular and Human Genetics, Georgetown University Medical Center, Washington, DC 20007
| | - Barbara C Levin
- Biotechnology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
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97
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Chinnery PF. Inheritance of mitochondrial disorders. Mitochondrion 2002; 2:149-55. [PMID: 16120317 DOI: 10.1016/s1567-7249(02)00046-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 06/20/2002] [Accepted: 06/24/2002] [Indexed: 11/22/2022]
Abstract
Over the last decade there have been major advances in our understanding of the genetic basis of mitochondrial disease, enabling genetic counseling for patients with autosomal dominant and autosomal recessive disorders. Genetic counseling for patients with mitochondrial DNA (mtDNA) mutations is less well established. Approximately one-third of adults with a mtDNA disorder are sporadic cases, usually due to a single deletion of mtDNA. About two-thirds of adults with mtDNA disease harbor a maternally transmitted point mutation. The recurrence risks are well documented for homoplasmic mtDNA mutations causing Leber hereditary optic neuropathy, but the situation is less clear for families with heteroplasmic mtDNA disorders. Two large studies have shown that for some heteroplasmic point mutations there appears to be a relationship between the percentage level of mutant mtDNA in a mother's blood and her risk of having clinically affected offspring. The situation is less clear for other point mutations, some of which may cause sporadic disease. Recent evidence has cast light on the general principles behind the transmission of heteroplasmic mtDNA point mutations, which may be important for genetic counseling in the future.
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Affiliation(s)
- Patrick F Chinnery
- Department of Neurology, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
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98
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Abstract
Mitochondrial disorders are caused by deficient respiratory chain function, resulting in a complex series of pathophysiological events. Genetic counselling is complicated because the respiratory chain subunits are encoded by both nuclear and mitochondrial DNA genes. Only a minority of the nuclear genes involved in mitochondrial function have been identified, and even fewer are associated with human mitochondrial disease. Mutations in mitochondrial DNA are particularly challenging because of the complexities of mitochondrial genetics: the mitochondrial DNA is strictly maternally inherited; there are 10(3)-10(4) copies of mitochondrial DNA in somatic cells; affected individuals often have a mixture of normal and mutated mitochondrial DNA (mitochondrial DNA heteroplasmy), the level of mutated mitochondrial DNA (the mitochondrial DNA mutation load) may vary widely between different maternally related individuals, between tissues and with time; a particular minimal threshold of mutated mitochondrial DNA is required to impair respiratory chain function; and there is not always a good correlation between mutant load and phenotype.
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Affiliation(s)
- Caroline Graff
- Karolinska Institute, Department of Medical Nutrition and Biosciences, Novum, Huddinge University Hospital, Stockholm, Sweden
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99
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Hafezparast M, Ahmad-Annuar A, Wood NW, Tabrizi SJ, Fisher EMC. Mouse models for neurological disease. Lancet Neurol 2002; 1:215-24. [PMID: 12849454 DOI: 10.1016/s1474-4422(02)00100-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The mouse has many advantages over human beings for the study of genetics, including the unique property that genetic manipulation can be routinely carried out in the mouse genome. Most importantly, mice and human beings share the same mammalian genes, have many similar biochemical pathways, and have the same diseases. In the minority of cases where these features do not apply, we can still often gain new insights into mouse and human biology. In addition to existing mouse models, several major programmes have been set up to generate new mouse models of disease. Alongside these efforts are new initiatives for the clinical, behavioural, and physiological testing of mice. Molecular genetics has had a major influence on our understanding of the causes of neurological disorders in human beings, and much of this has come from work in mice.
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Affiliation(s)
- Majid Hafezparast
- Department of Neurodegenerative Disease, National Hospital for Neurology and Neurosurgery, London, UK
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100
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Wright R, Boggs J. Learning cell biology as a team: a project-based approach to upper-division cell biology. CELL BIOLOGY EDUCATION 2002; 1:145-53. [PMID: 12669105 PMCID: PMC149487 DOI: 10.1187/cbe.02-03-0006] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2002] [Revised: 07/22/2002] [Accepted: 07/29/2002] [Indexed: 12/17/2022]
Abstract
To help students develop successful strategies for learning how to learn and communicate complex information in cell biology, we developed a quarter-long cell biology class based on team projects. Each team researches a particular human disease and presents information about the cellular structure or process affected by the disease, the cellular and molecular biology of the disease, and recent research focused on understanding the cellular mechanisms of the disease process. To support effective teamwork and to help students develop collaboration skills useful for their future careers, we provide training in working in small groups. A final poster presentation, held in a public forum, summarizes what students have learned throughout the quarter. Although student satisfaction with the course is similar to that of standard lecture-based classes, a project-based class offers unique benefits to both the student and the instructor.
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Affiliation(s)
- Robin Wright
- Department of Zoology, University of Washington, Seattle, Washington 98195, USA.
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