Journal Article The phenotypic spectrum of COX20-associated mitochondrial disorder Get access Rui Ban, Rui Ban Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, ChinaInstitute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg 85764, Germany Present address: Department of Neurology, First Hospital of Tsinghua University, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Robert Kopajtich, Robert Kopajtich Institute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg 85764, GermanyInstitute of Human Genetics, School of Medicine, Technical University of Munich, Munich 81675, Germany Search for other works by this author on: Oxford Academic PubMed Google Scholar Junlan Lv, Junlan Lv Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Sarah L Stenton, Sarah L Stenton Institute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg 85764, GermanyInstitute of Human Genetics, School of Medicine, Technical University of Munich, Munich 81675, Germany Search for other works by this author on: Oxford Academic PubMed Google Scholar Masaru Shimura, Masaru Shimura Institute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg 85764, GermanyDepartment of Metabolism, Chiba Children’s Hospital, 260-0842 Chiba, Japan Search for other works by this author on: Oxford Academic PubMed Google Scholar Zhaoxia Wang, Zhaoxia Wang Department of Neurology, Peking University First Hospital, 100191 Beijing, China https://orcid.org/0000-0003-1742-9877 Search for other works by this author on: Oxford Academic PubMed Google Scholar Yun Yuan, Yun Yuan Department of Neurology, Peking University First Hospital, 100191 Beijing, China https://orcid.org/0000-0003-3282-9123 Search for other works by this author on: Oxford Academic PubMed Google Scholar Junling Wang, Junling Wang Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Xiaodi Han, Xiaodi Han Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Zhimei Liu, Zhimei Liu Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar ... Show more Qiang Shi, Qiang Shi Department of Neurology, Chinese PLA General Hospital, 100853 Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Chuanqiang Pu, Chuanqiang Pu Department of Neurology, Chinese PLA General Hospital, 100853 Beijing, China Search for other works by this author on: Oxford Academic PubMed Google Scholar Holger Prokisch, Holger Prokisch Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, ChinaInstitute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg 85764, GermanyInstitute of Human Genetics, School of Medicine, Technical University of Munich, Munich 81675, Germany Correspondence to: Holger Prokisch Helmholtz Zentrum München, Deutsches Forschungszentrum für Gesundheit und Umwelt Institut für Neurogenomik, Ingolstädter Landstr. 1 85764 Neuherberg, Germany E-mail: prokisch@helmholtz-muenchen.de https://orcid.org/0000-0003-2379-6286 Search for other works by this author on: Oxford Academic PubMed Google Scholar Fang Fang, Fang Fang Department of Neurology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, 100045, Beijing, China Correspondence may also be addressed to: Fang Fang Department of Neurology, Beijing Children’s Hospital Capital Medical University, National Center for Children’s Health No.56 Nanlishi Road, Xicheng District, 100045 Beijing, China E-mail: fangfang@bch.com.cn Search for other works by this author on: Oxford Academic PubMed Google Scholar Matthias Elstner Matthias Elstner Department of Neurology, School of Medicine, Technical University of Munich, Munich 81675, Germany https://orcid.org/0000-0002-9119-3455 Search for other works by this author on: Oxford Academic PubMed Google Scholar Brain, Volume 145, Issue 12, December 2022, Pages e125–e127, https://doi.org/10.1093/brain/awac344 Published: 22 September 2022 Article history Received: 25 August 2022 Accepted: 28 August 2022 Published: 22 September 2022 Corrected and typeset: 09 November 2022

Zusammenfassung Die Akutversorgung des Schlaganfalls in Deutschland hat ein sehr hohes Niveau, dargestellt durch die Stroke-Units. Die Erkrankung Schlaganfall hat eine Akutphase, gefolgt von einer chronischen Phase mit einem hohen und qualifizierten multi- und interprofessionellen Versorgungsbedarf. Die Deutsche Schlaganfall-Gesellschaft (DSG) hat 2020 eine Nachsorgekommission gegründet, mit dem Ziel der Darstellung der aktuellen Versorgungssituation und zur Erarbeitung von Vorschlägen für eine Verbesserung der Versorgung nach der Akutphase. In dieser Arbeit wird der Status quo ermittelt und Defizite benannt. Analysiert wurden Beiträge unterschiedlicher Beteiligter im deutschen Gesundheitswesen, dargestellt werden unterschiedliche Projekte einer Nachsorge. In Deutschland existiert kein anerkanntes strukturiertes Nachsorgekonzept für Patienten nach einem Schlaganfall. Die bestehende hausarztbasierte Versorgung ohne eine zukünftig stärkere und abgestimmte Integration der Neurologen erschwert eine leitlinien- und qualitätsgesteuerte Nachsorge. Aufgabenverteilungen sowie notwendige Ausbildungsstandards für ihre leitliniengerechte Erfüllung durch die Fachgruppen liegen nicht vor. Zu selten werden neben den medizinischen Domänen die physischen, sozialen und emotionalen Domänen durch ein multiprofessionelles Versorgungsteam beachtet. Zu diskutieren ist eine Weiterentwicklung eines regionalen Care-Management-Konzeptes. Evaluiert werden müssen die Ergebnisse und die Kosten eines Nachsorgekonzeptes vor einer breiten Anwendung.

OBJECTIVE:The cytochrome c oxidase assembly factor 7 (COA7) gene encodes a protein localized to mitochondria that is involved in the assembly of mitochondrial respiratory chain complex IV. Here, we report the clinical, genetic and biochemical analysis of a female patient with suspected mitochondrial disorder and novel variants in COA7, that presented with a considerably different phenotype and age of onset than the five COA7 patients reported to date.METHODS:We performed trio-exome sequencing in the affected patient and both parents. To verify the pathogenicity of the detected variants in COA7, mitochondrial enzyme activities and oxygen consumption rate were investigated in fibroblasts of the patient and her parents.RESULTS:A Chinese girl was referred at 9 months of age with a history of developmental delay and regression since 3 months of age. In the following months, she lost previously acquired skills and developed progressive spasticity of the lower extremities. Trio-exome sequencing revealed compound heterzygous variants in COA7 (c.511G > A/p.Ala171Thr and c.566A > G/p.Asn189Ser). Functional validation experiments revealed isolated complex IV deficiency and a significantly reduced mitochondrial respiration rate in patient-derived fibroblasts.INTERPRETATION:Hitherto, characteristic features of COA7 patients were described as slowly progressing neuropathy and spinocerebellar ataxia, starting at the toddler age and progressing into adulthood. In contrast, our patient was reported to show developmental delay from 3 months of age, which was found to be due to a rapidly progressive encephalopathy and brain atrophy seen at 9 months of age. Unexpectedly, the genetic investigation revealed a COA7-associated mitochondrial disease, which was confirmed functionally. Thus, this report broadens the genetic and clinical spectrum of this heterogeneous mitochondriopathy and highlights the value of the presented unbiased approach.

Background Progressive cavitating leukoencephalopathy (PCL) is thought to result from mutations in nuclear genes affecting mitochondrial function and energy metabolism. To date, mutations in two subunits of complex I, NDUFS1 and NDUFV1, have been reported to be related to PCL. Methods Patients underwent clinical examinations, brain MRI, skin biopsy and muscle biopsy. Whole-genome or whole-exome sequencing was performed on the index patients from two unrelated families with PCL. The effects of the mutations were examined through complementation of the NDUFV2 mutation by cDNA expression. Results The common clinical features of the patients in this study were recurring episodes of acute or subacute developmental regression that appeared in the first years of life, followed by gradual remissions and prolonged periods of stability. MRI showed leukoencephalopathy with multiple cavities. Three novel NDUFV2 missense mutations were identified in these families. Complex I deficiency was confirmed in affected individuals’ fibroblasts and a muscle biopsy. Functional and structural analyses revealed that these mutations affect the structural stability and function of the NDUFV2 protein, indicating that defective NDUFV2 function is responsible for the phenotypes in these individuals. Conclusions Here, we report the clinical presentations, neuroimaging and molecular and functional analyses of novel mutations in NDUFV2 in two sibling pairs of two Chinese families presenting with PCL. We hereby expand the knowledge on the clinical phenotypes associated with mutations in NDUFV2 and the genotypes causative for PCL.

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited mitochondrial disease. Most cases of MELAS are caused by the m.3243A > G variant in the MT-TL1 gene encoding tRNALeu (UUR) . However, the genetic cause in 10% of patients with MELAS is unknown. We investigated the pathogenicity of the novel mtDNA variant m.9396G > A/ MT-CO3 (p.E64K), which affects an extremely conserved amino acid in the CO3 subunit of mitochondrial respiratory chain (MRC) complex IV (CIV) in a patient with MELAS. Biochemical assays of a muscle biopsy confirmed remarkable CIV deficiency, and pathological examination showed ragged red fibers and generalized COX non-reactive muscle fibers. Transfer of the mutant mtDNA into cybrids impaired CIV assembly, followed by remarkable mitochondrial dysfunction and ROS production. Our findings highlight the pathogenicity of a novel m.9396G > A variant and extend the spectrum of pathogenic mtDNA variants.

Mitochondrial DNA deletions affect energy metabolism at tissue-specific and cell-specific threshold levels, but the pathophysiological mechanisms determining cell fate remain poorly understood. Chronic progressive external ophthalmoplegia (CPEO) is caused by mtDNA deletions and characterized by a mosaic distribution of muscle fibers with defective cytochrome oxidase (COX) activity, interspersed among fibers with retained functional respiratory chain. We used diagnostic histochemistry to distinguish COX-negative from COX-positive fibers in nine muscle biopsies from CPEO patients and performed laser capture microdissection (LCM) coupled to genome-wide gene expression analysis. To gain molecular insight into the pathogenesis, we applied network and pathway analysis to highlight molecular differences of the COX-positive and COX-negative fiber transcriptome. We then integrated our results with proteomics data that we previously obtained comparing COX-positive and COX-negative fiber sections from three other patients. By virtue of the combination of LCM and a multi-omics approach, we here provide a comprehensive resource to tackle the pathogenic changes leading to progressive respiratory chain deficiency and disease in mitochondrial deletion syndromes. Our data show that COX-negative fibers upregulate transcripts involved in translational elongation and protein synthesis. Furthermore, based on functional annotation analysis, we find that mitochondrial transcripts are the most enriched among those with significantly different expression between COX-positive and COX-negative fibers, indicating that our unbiased large-scale approach resolves the core of the pathogenic changes. Further enrichments include transcripts encoding LIM domain proteins, ubiquitin ligases, proteins involved in RNA turnover, and, interestingly, cell cycle arrest and cell death. These pathways may thus have a functional association to the molecular pathogenesis of the disease. Overall, the transcriptome and proteome show a low degree of correlation in CPEO patients, suggesting a relevant contribution of post-transcriptional mechanisms in shaping this disease phenotype.

Zusammenfassung Hintergrund Ungeachtet der großen gesamtgesellschaftlichen Bedeutung des Schlaganfalls sowie der Fortschritte in der Akutversorgung und Rehabilitation konnten bisher keine flächendeckenden Versorgungsstrukturen zur strukturierten ambulanten Nachsorge in Deutschland etabliert werden. Ziel der Arbeit und Methode Vor dem Hintergrund der bestehenden Versorgungslücken wurde im Mai 2020 die Kommission Schlaganfallnachsorge der Deutschen Schlaganfall-Gesellschaft (DSG) gegründet. Das Positionspapier diskutiert strukturelle Konzepte für zukünftige Versorgungsformen der Schlaganfallnachsorge. Ergebnisse und Diskussion Eine neurologische Betreuung sollte zentraler Bestandteil einer multidisziplinären, interprofessionellen und sektorenübergreifenden Behandlungsplanung sein. Strukturelle Konzepte zur Schlaganfallnachsorge müssen sowohl regionale Strukturunterschiede als auch den Aspekt der Qualitätssicherung berücksichtigen. Zertifizierungsprozesse und die angemessene Finanzierung von Nachsorgeregistern auf Landes- und Bundesebene können den Weg hierhin mittelfristig ebnen. Das Angebot zur strukturierten Schlaganfallnachsorge sollte allen Subgruppen von Schlaganfallpatienten offenstehen. Auch innovative Technologien können einen wichtigen Beitrag zur Schlaganfallnachsorge leisten. Die Einführung und Umsetzung einer strukturierten Schlaganfallnachsorge bedarf in jedem Fall einer ausreichenden Finanzierung und eigener finanzieller Anreize für die Leistungsträger. Die Vor- und Nachteile der spezifischen Versorgungs- und Finanzierungsmodelle müssen dabei kritisch gegeneinander abgewogen werden. Die Diskussion neuer Versorgungsformen zur Schlaganfallnachsorge erfährt gegenwärtig ein neues Momentum und eröffnet Perspektiven für eine Verbesserung der aktuell noch unzureichenden Versorgungslösung.

Leigh syndrome (LS) is one of the most common mitochondrial diseases in children, for which at least 90 causative genes have been identified. However, many LS patients have no genetic diagnosis, indicating that more disease-related genes remain to be identified. In this study, we identified a novel variant, m.3955G > A, in mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1 (MT-ND1) in two unrelated LS patients, manifesting as infancy-onset frequent seizures, neurodegeneration, elevated lactate levels, and bilateral symmetrical lesions in the brainstem, basal ganglia, and thalamus. Transfer of the mutant mtDNA with m.3955G > A into cybrids disturbed the MT-ND1 expression and CI assembly, followed by remarkable mitochondrial dysfunction, reactive oxygen species production, and mitochondrial membrane potential reduction. Our findings demonstrated the pathogenicity of the novel m.3955G > A variant, and extend the spectrum of pathogenic mtDNA variants.

Dementia with Lewy bodies (DLB) patients frequently experience well formed recurrent complex visual hallucinations (RCVH). This is associated with reduced blood flow or hypometabolism on imaging of the primary visual cortex. To understand these associations in DLB we used pathological and biochemical analysis of the primary visual cortex to identify changes that could underpin RCVH. Alpha-synuclein or neurofibrillary tangle pathology in primary visual cortex was essentially absent. Neurone density or volume within the primary visual cortex in DLB was also unchanged using unbiased stereology. Microarray analysis, however, demonstrated changes in neuropeptide gene expression and other markers, indicating altered GABAergic neuronal function. Calcium binding protein and GAD65/67 immunohistochemistry showed preserved interneurone populations indicating possible interneurone dysfunction. This was demonstrated by loss of post synaptic GABA receptor markers including gephyrin, GABARAP, and Kif5A, indicating reduced GABAergic synaptic activity. Glutamatergic neuronal signalling was also altered with vesicular glutamate transporter protein and PSD-95 expression being reduced. Changes to the primary visual cortex in DLB indicate that reduced GABAergic transmission may contribute to RCVH in DLB and treatment using targeted GABAergic modulation or similar approaches using glutamatergic modification may be beneficial.

Taqman q-RT-PCR Assay Details used in determination of mRNA relative levels in primary visual cortex. Assay ID, specific assay identifier; Gene Name, mRNA target of assay. (DOC 41 kb)

Dizziness and imbalance frequently affect the elderly and contribute to falls and frailty. In many geriatric patients, clinical testing uncovers a dysfunction of the vestibular system, but no specific etiology can be identified. Neuropathological studies have demonstrated age-related degeneration of peripheral and central vestibular neurons, but the molecular mechanisms are poorly understood. In contrast, recent studies into age-related hearing loss strongly implicate mitochondrial dysfunction, oxidative stress and apoptotic cell death of cochlear hair cells. While some data suggest that analogous biological pathomechanisms may underlie vestibular dysfunction, actual proof is missing. In this review, we summarize the available data on the molecular causes of vestibular dysfunction.

Neurodegenerative Disease Pathology in the Occipital Lobe in (A) Control and (B) Alzheimer’s disease cases. Representative staining for α-synuclein, Aβ (4G8), and hyperphosphorylated tau (AT8) in primary visual cortex (BA17), secondary visual cortex (BA18), and lateral occipital cortex (BA37) in A) elderly normal control or in B) AD individuals. An absence of α-synuclein pathology was seen in BA17 in either AD or controls cases. Similarly, an absence of AT8 (hyperphosphorylated tau) staining was seen in BA17 in controls, but increasing levels were seen in BA17, BA18 and BA37 in AD. Aβ (4G8 antibody) pathology was present in all cortical regions examined with high levels seen in BA17 in AD cases and in other cortical regions examined. Photomicrographs were taken at x2.5 magnification (upper rows) or at x40 magnification (lower rows) with scale bars at 1000 μm (upper rows) or 50 μm (lower rows). (ZIP 1315 kb)

Acquired alterations in mitochondrial DNA are believed to play a pathogenic role in Parkinson's disease. In particular, accumulation of mitochondrial DNA deletions has been observed in substantia nigra pars compacta dopaminergic neurons from patients with Parkinson's disease and aged individuals. Also, mutations in mitochondrial DNA polymerase gamma result in multiple mitochondrial DNA deletions that can be associated with levodopa-responsive parkinsonism and severe substantia nigra pars compacta dopaminergic neurodegeneration. However, whether mitochondrial DNA deletions play a causative role in the demise of dopaminergic neurons remains unknown. Here we assessed the potential pathogenic effects of mitochondrial DNA deletions on the dopaminergic nigrostriatal system by using mutant mice possessing a proofreading-deficient form of mitochondrial DNA polymerase gamma (POLGD257A), which results in a time-dependent accumulation of mitochondrial DNA deletions in several tissues, including the brain. In these animals, we assessed the occurrence of mitochondrial DNA deletions within individual substantia nigra pars compacta dopaminergic neurons, by laser capture microdissection and quantitative real-time polymerase chain reaction, and determined the potential deleterious effects of such mitochondrial DNA alterations on mitochondrial function and dopaminergic neuronal integrity, by cytochrome c oxidase histochemistry and quantitative morphology. Nigral dopaminergic neurons from POLGD257A mice accumulate mitochondrial DNA deletions to a similar extent (∼40-60%) as patients with Parkinson's disease and aged individuals. Despite such high levels of mitochondrial DNA deletions, the majority of substantia nigra pars compacta dopaminergic neurons from these animals did not exhibit mitochondrial dysfunction or degeneration. Only a few individual substantia nigra pars compacta neurons appeared as cytochrome c oxidase-negative, which exhibited higher levels of mitochondrial DNA deletions than cytochrome c oxidase-positive cells (60.38±3.92% versus 45.18±2.83%). Survival of dopaminergic neurons in POLGD257A mice was associated with increased mitochondrial DNA copy number, enhanced mitochondrial cristae network, improved mitochondrial respiration, decreased exacerbation of mitochondria-derived reactive oxygen species, greater striatal dopamine levels and resistance to parkinsonian mitochondrial neurotoxins. These results indicate that primary accumulation of mitochondrial DNA deletions within substantia nigra pars compacta dopaminergic neurons, at an extent similar to that observed in patients with Parkinson's disease, do not kill dopaminergic neurons but trigger neuroprotective compensatory mechanisms at a mitochondrial level that may account for the high pathogenic threshold of mitochondrial DNA deletions in these cells.

Alpha-synuclein (α-Syn) accumulation/aggregation and mitochondrial dysfunction play prominent roles in the pathology of Parkinson's disease. We have previously shown that postmortem human dopaminergic neurons from PD brains accumulate high levels of mitochondrial DNA (mtDNA) deletions. We now addressed the question, whether alterations in a component of the mitochondrial import machinery--TOM40--might contribute to the mitochondrial dysfunction and damage in PD. For this purpose, we studied levels of TOM40, mtDNA deletions, oxidative damage, energy production, and complexes of the respiratory chain in brain homogenates as well as in single neurons, using laser-capture-microdissection in transgenic mice overexpressing human wildtype α-Syn. Additionally, we used lentivirus-mediated stereotactic delivery of a component of this import machinery into mouse brain as a novel therapeutic strategy. We report here that TOM40 is significantly reduced in the brain of PD patients and in α-Syn transgenic mice. TOM40 deficits were associated with increased mtDNA deletions and oxidative DNA damage, and with decreased energy production and altered levels of complex I proteins in α-Syn transgenic mice. Lentiviral-mediated overexpression of Tom40 in α-Syn-transgenic mice brains ameliorated energy deficits as well as oxidative burden. Our results suggest that alterations in the mitochondrial protein transport machinery might contribute to mitochondrial impairment in α-Synucleinopathies.

Mitochondrial dysfunction has been strongly implicated in the pathogenesis of Parkinson's disease (PD) and Alzheimer's disease (AD), but its relation to protein aggregation is unclear. PD is characterized by synuclein aggregation (i.e., Lewy body [LB] formation). In AD, the abnormal accumulation of tau protein forms neurofibrillary tangles. In this study, we laser-dissected LB-positive and -negative neurons from the substantia nigra of postmortem PD brains, and tau-positive and -negative hippocampal neurons from AD brains. We quantified mitochondrial DNA deletions in relation to the cellular phenotype and in comparison with age-matched controls. Deletion levels were highest in LB-positive neurons of PD brains (40.5 ± 16.8%), followed by LB-negative neurons of PD cases (31.8 ± 14.4%) and control subjects (25.6 ± 17.5%; analysis of variance p < 0.005). In hippocampal neurons, deletion levels were 25%-30%, independent of disease status and neurofibrillary tangles. The presented findings imply increased mitochondrial DNA damage in LB-positive midbrain neurons, but do not support a direct causative link of respiratory chain dysfunction and protein aggregation.