RESUMEN
CHCHD10 is an amyotrophic lateral sclerosis/frontotemporal dementia gene that encodes a mitochondrial protein whose precise function is unclear. Here we show that Coiled-Coil-Helix-Coiled-Coil-Helix Domain Containing protein 10 interacts with the Stomatin-Like Protein 2 and participates in the stability of the prohibitin complex in the inner mitochondrial membrane. By using patient fibroblasts and mouse models expressing the same CHCHD10 variant (p.Ser59Leu), we show that Stomatin-Like Protein 2 forms aggregates with prohibitins, found in vivo in the hippocampus and as aggresome-like inclusions in spinal motor neurons of Chchd10S59L/+ mice. Affected cells and tissues display instability of the prohibitin complex, which participates at least in part in the activation of the OMA1 cascade with OPA1 processing leading to mitochondrial fragmentation, abnormal mitochondrial cristae morphogenesis and neuronal death found in spinal cord and the hippocampus of Chchd10S59L/+ animals. Destabilization of the prohibitin complex leads to the instability of the mitochondrial contact site and cristae organizing the system complex, probably by the disruption of OPA1-mitofilin interaction. Thus, Stomatin-Like Protein 2/prohibitin aggregates and destabilization of the prohibitin complex are critical in the sequence of events leading to motor neuron death in CHCHD10S59L-related disease.
Asunto(s)
Esclerosis Amiotrófica Lateral , Demencia Frontotemporal , Proteínas de la Membrana , Proteínas Mitocondriales , Animales , Ratones , Esclerosis Amiotrófica Lateral/genética , Esclerosis Amiotrófica Lateral/metabolismo , Demencia Frontotemporal/genética , Mitocondrias/metabolismo , Proteínas Mitocondriales/genética , Proteínas Mitocondriales/metabolismo , Neuronas Motoras/metabolismo , Prohibitinas , Factores de Transcripción/genética , Humanos , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismoRESUMEN
Several lines of recent evidence indicate that the amyloid precursor protein-derived C-terminal fragments (APP-CTFs) could correspond to an etiological trigger of Alzheimer's disease (AD) pathology. Altered mitochondrial homeostasis is considered an early event in AD development. However, the specific contribution of APP-CTFs to mitochondrial structure, function, and mitophagy defects remains to be established. Here, we demonstrate in neuroblastoma SH-SY5Y cells expressing either APP Swedish mutations, or the ß-secretase-derived APP-CTF fragment (C99) combined with ß- and γ-secretase inhibition, that APP-CTFs accumulation independently of Aß triggers excessive mitochondrial morphology alteration (i.e., size alteration and cristae disorganization) associated with enhanced mitochondrial reactive oxygen species production. APP-CTFs accumulation also elicit basal mitophagy failure illustrated by enhanced conversion of LC3, accumulation of LC3-I and/or LC3-II, non-degradation of SQSTM1/p62, inconsistent Parkin and PINK1 recruitment to mitochondria, enhanced levels of membrane and matrix mitochondrial proteins, and deficient fusion of mitochondria with lysosomes. We confirm the contribution of APP-CTFs accumulation to morphological mitochondria alteration and impaired basal mitophagy in vivo in young 3xTgAD transgenic mice treated with γ-secretase inhibitor as well as in adeno-associated-virus-C99 injected mice. Comparison of aged 2xTgAD and 3xTgAD mice indicates that, besides APP-CTFs, an additional contribution of Aß to late-stage mitophagy activation occurs. Importantly, we report on mitochondrial accumulation of APP-CTFs in human post-mortem sporadic AD brains correlating with mitophagy failure molecular signature. Since defective mitochondria homeostasis plays a pivotal role in AD pathogenesis, targeting mitochondrial dysfunctions and/or mitophagy by counteracting early APP-CTFs accumulation may represent relevant therapeutic interventions in AD.
Asunto(s)
Enfermedad de Alzheimer/patología , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Encéfalo/patología , Mitocondrias/patología , Mitocondrias/ultraestructura , Mitofagia/genética , Anciano , Anciano de 80 o más Años , Enfermedad de Alzheimer/metabolismo , Secretasas de la Proteína Precursora del Amiloide/antagonistas & inhibidores , Secretasas de la Proteína Precursora del Amiloide/metabolismo , Animales , Ácido Aspártico Endopeptidasas/antagonistas & inhibidores , Ácido Aspártico Endopeptidasas/metabolismo , Autopsia , Línea Celular , Femenino , Humanos , Potencial de la Membrana Mitocondrial , Ratones , Mitocondrias/metabolismo , Fragmentos de Péptidos/genética , Fragmentos de Péptidos/metabolismo , Especies Reactivas de Oxígeno/metabolismoRESUMEN
Whole mitochondrial DNA (mtDNA) sequencing is now systematically used in clinical laboratories to screen patients with a phenotype suggestive of mitochondrial disease. Next Generation Sequencing (NGS) has significantly increased the number of identified pathogenic mtDNA variants. Simultaneously, the number of variants of unknown significance (VUS) has increased even more, thus challenging their interpretation. Correct classification of the variants' pathogenicity is essential for optimal patient management, including treatment and genetic counseling. Here, we used single muscle fiber studies to characterize eight heteroplasmic mtDNA variants, among which were three novel variants. By applying the pathogenicity scoring system, we classified four variants as "definitely pathogenic" (m.590A>G, m.9166T>C, m.12293G>A, and m.15958A>T). Two variants remain "possibly pathogenic" (m.4327T>C and m.5672T>C) but should these be reported in a different family, they would be reclassified as "definitely pathogenic." We also illustrate the contribution of single-fiber studies to the diagnostic approach in patients harboring pathogenic variants with low level heteroplasmy.
Asunto(s)
ADN Mitocondrial/genética , Enfermedades Mitocondriales/genética , Adolescente , Adulto , Anciano , Femenino , Heteroplasmia , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , Patrón de Herencia , Masculino , Persona de Mediana Edad , Conformación de Ácido Nucleico , Análisis de Secuencia de ADNRESUMEN
MDH2 encodes mitochondrial malate dehydrogenase (MDH), which is essential for the conversion of malate to oxaloacetate as part of the proper functioning of the Krebs cycle. We report bi-allelic pathogenic mutations in MDH2 in three unrelated subjects presenting with early-onset generalized hypotonia, psychomotor delay, refractory epilepsy, and elevated lactate in the blood and cerebrospinal fluid. Functional studies in fibroblasts from affected subjects showed both an apparently complete loss of MDH2 levels and MDH2 enzymatic activity close to null. Metabolomics analyses demonstrated a significant concomitant accumulation of the MDH substrate, malate, and fumarate, its immediate precursor in the Krebs cycle, in affected subjects' fibroblasts. Lentiviral complementation with wild-type MDH2 cDNA restored MDH2 levels and mitochondrial MDH activity. Additionally, introduction of the three missense mutations from the affected subjects into Saccharomyces cerevisiae provided functional evidence to support their pathogenicity. Disruption of the Krebs cycle is a hallmark of cancer, and MDH2 has been recently identified as a novel pheochromocytoma and paraganglioma susceptibility gene. We show that loss-of-function mutations in MDH2 are also associated with severe neurological clinical presentations in children.
Asunto(s)
Encefalopatías/genética , Ciclo del Ácido Cítrico , Malato Deshidrogenasa/genética , Mutación , Edad de Inicio , Alelos , Secuencia de Aminoácidos , Niño , Preescolar , Ciclo del Ácido Cítrico/genética , Fibroblastos/enzimología , Fibroblastos/metabolismo , Fumaratos/metabolismo , Prueba de Complementación Genética , Humanos , Lactante , Recién Nacido , Malato Deshidrogenasa/química , Malato Deshidrogenasa/metabolismo , Malatos/metabolismo , Masculino , Metabolómica , Modelos MolecularesRESUMEN
Wolfram syndrome (WS) is a progressive neurodegenerative disease characterized by early-onset optic atrophy and diabetes mellitus, which can be associated with more extensive central nervous system and endocrine complications. The majority of patients harbour pathogenic WFS1 mutations, but recessive mutations in a second gene, CISD2, have been described in a small number of families with Wolfram syndrome type 2 (WFS2). The defining diagnostic criteria for WFS2 also consist of optic atrophy and diabetes mellitus, but unlike WFS1, this phenotypic subgroup has been associated with peptic ulcer disease and an increased bleeding tendency. Here, we report on a novel homozygous CISD2 mutation (c.215A > G; p.Asn72Ser) in a Moroccan patient with an overlapping phenotype suggesting that Wolfram syndrome type 1 and type 2 form a continuous clinical spectrum with genetic heterogeneity. The present study provides strong evidence that this particular CISD2 mutation disturbs cellular Ca2+ homeostasis with enhanced Ca2+ flux from the ER to mitochondria and cytosolic Ca2+ abnormalities in patient-derived fibroblasts. This Ca2+ dysregulation was associated with increased ER-mitochondria contact, a swollen ER lumen and a hyperfused mitochondrial network in the absence of overt ER stress. Although there was no marked alteration in mitochondrial bioenergetics under basal conditions, culture of patient-derived fibroblasts in glucose-free galactose medium revealed a respiratory chain defect in complexes I and II, and a trend towards decreased ATP levels. Our results provide important novel insight into the potential disease mechanisms underlying the neurodegenerative consequences of CISD2 mutations and the subsequent development of multisystemic disease.
Asunto(s)
Envejecimiento Prematuro/genética , Pérdida Auditiva Sensorineural/genética , Proteínas de la Membrana/genética , Enfermedades Mitocondriales/genética , Atrofia Óptica/genética , Calcio/metabolismo , Retículo Endoplásmico/genética , Retículo Endoplásmico/metabolismo , Homeostasis , Humanos , Masculino , Proteínas de la Membrana/metabolismo , Persona de Mediana Edad , Mitocondrias/genética , Mitocondrias/metabolismo , Linaje , Síndrome de Wolfram/genéticaRESUMEN
The genetic causes of Leigh syndrome are heterogeneous, with a poor genotype-phenotype correlation. To date, more than 50 nuclear genes cause nuclear gene-encoded Leigh syndrome. NDUFS6 encodes a 13 kiloDaltons subunit, which is part of the peripheral arm of complex I and is localized in the iron-sulfur fraction. Only a few patients were reported with proven NDUFS6 pathogenic variants and all presented with severe neonatal lactic acidemia and complex I deficiency, leading to death in the first days of life. Here, we present a patient harboring two NDUFS6 variants with a phenotype compatible with Leigh syndrome. Although most of previous reports suggested that NDUFS6 pathogenic variants invariably lead to early neonatal death, this report shows that the clinical spectrum could be larger. We found a severe decrease of NDUFS6 protein level in patient's fibroblasts associated with a complex I assembly defect in patient's muscle and fibroblasts. These data confirm the importance of NDUFS6 and the Zn-finger domain for a correct assembly of complex I.
Asunto(s)
Enfermedad de Leigh/genética , NADH Deshidrogenasa/genética , Acidosis Láctica/genética , Núcleo Celular/genética , Complejo I de Transporte de Electrón/química , Complejo I de Transporte de Electrón/genética , Fibroblastos/enzimología , Estudios de Asociación Genética , Humanos , Lactante , Enfermedad de Leigh/diagnóstico por imagen , Enfermedad de Leigh/enzimología , Masculino , Mitocondrias/genética , Músculos/enzimología , NADH Deshidrogenasa/metabolismo , Dominios Proteicos/genética , Análisis de Secuencia de ADNRESUMEN
Recently, we provided genetic basis showing that mitochondrial dysfunction can trigger motor neuron degeneration, through identification of CHCHD10 encoding a mitochondrial protein. We reported patients, carrying the p.Ser59Leu heterozygous mutation in CHCHD10, from a large family with a mitochondrial myopathy associated with motor neuron disease (MND). Rapidly, our group and others reported CHCHD10 mutations in amyotrophic lateral sclerosis (ALS), frontotemporal dementia-ALS and other neurodegenerative diseases. Here, we generated knock-in (KI) mice, carrying the p.Ser59Leu mutation, that mimic the mitochondrial myopathy with mtDNA instability displayed by the patients from our original family. Before 14 months of age, all KI mice developed a fatal mitochondrial cardiomyopathy associated with enhanced mitophagy. CHCHD10S59L/+ mice also displayed neuromuscular junction (NMJ) and motor neuron degeneration with hyper-fragmentation of the motor end plate and moderate but significant motor neuron loss in lumbar spinal cord at the end stage of the disease. At this stage, we observed TDP-43 cytoplasmic aggregates in spinal neurons. We also showed that motor neurons differentiated from human iPSC carrying the p.Ser59Leu mutation were much more sensitive to Staurosporine or glutamate-induced caspase activation than control cells. These data confirm that mitochondrial deficiency associated with CHCHD10 mutations can be at the origin of MND. CHCHD10 is highly expressed in the NMJ post-synaptic part. Importantly, the fragmentation of the motor end plate was associated with abnormal CHCHD10 expression that was also observed closed to NMJs which were morphologically normal. Furthermore, we found OXPHOS deficiency in muscle of CHCHD10S59L/+ mice at 3 months of age in the absence of neuron loss in spinal cord. Our data show that the pathological effects of the p.Ser59Leu mutation target muscle prior to NMJ and motor neurons. They likely lead to OXPHOS deficiency, loss of cristae junctions and destabilization of internal membrane structure within mitochondria at motor end plate of NMJ, impairing neurotransmission. These data are in favor with a key role for muscle in MND associated with CHCHD10 mutations.
Asunto(s)
Esclerosis Amiotrófica Lateral/metabolismo , Demencia Frontotemporal/metabolismo , Mitocondrias/patología , Neuronas Motoras/metabolismo , Unión Neuromuscular/metabolismo , Esclerosis Amiotrófica Lateral/genética , Animales , Muerte Celular/genética , Proteínas de Unión al ADN/metabolismo , Demencia Frontotemporal/genética , Ratones Transgénicos , Proteínas Mitocondriales/metabolismo , Degeneración Nerviosa/genética , Degeneración Nerviosa/patología , FenotipoRESUMEN
Following the involvement of CHCHD10 in FrontoTemporal-Dementia-Amyotrophic Lateral Sclerosis (FTD-ALS) clinical spectrum, a founder mutation (p.Gly66Val) in the same gene was identified in Finnish families with late-onset spinal motor neuronopathy (SMAJ). SMAJ is a slowly progressive form of spinal muscular atrophy with a life expectancy within normal range. In order to understand why the p.Ser59Leu mutation, responsible for severe FTD-ALS, and the p.Gly66Val mutation could lead to different levels of severity, we compared their effects in patient cells. Unlike affected individuals bearing the p.Ser59Leu mutation, patients presenting with SMAJ phenotype have neither mitochondrial myopathy nor mtDNA instability. The expression of CHCHD10S59L mutant allele leads to disassembly of mitochondrial contact site and cristae organizing system (MICOS) with mitochondrial dysfunction and loss of cristae in patient fibroblasts. We also show that G66V fibroblasts do not display the loss of MICOS complex integrity and mitochondrial damage found in S59L cells. However, S59L and G66V fibroblasts show comparable accumulation of phosphorylated mitochondrial TDP-43 suggesting that the severity of phenotype and mitochondrial damage do not depend on mitochondrial TDP-43 localization. The expression of the CHCHD10G66V allele is responsible for mitochondrial network fragmentation and decreased sensitivity towards apoptotic stimuli, but with a less severe effect than that found in cells expressing the CHCHD10S59L allele. Taken together, our data show that cellular phenotypes associated with p.Ser59Leu and p.Gly66Val mutations in CHCHD10 are different; loss of MICOS complex integrity and mitochondrial dysfunction, but not TDP-43 mitochondrial localization, being likely essential to develop a severe motor neuron disease.
Asunto(s)
Esclerosis Amiotrófica Lateral/genética , Esclerosis Amiotrófica Lateral/patología , Proteínas de Unión al ADN/genética , Demencia Frontotemporal/genética , Demencia Frontotemporal/patología , Mitocondrias/genética , Mitocondrias/patología , Proteínas Mitocondriales/genética , Adulto , Proteínas de Unión al ADN/análisis , Femenino , Células HEK293 , Células HeLa , Humanos , Masculino , Proteínas de la Membrana/análisis , Proteínas de la Membrana/genética , Persona de Mediana Edad , Mitocondrias/ultraestructura , Enfermedades Mitocondriales/genética , Enfermedades Mitocondriales/patología , Proteínas Mitocondriales/análisis , Mutación/genética , Proteínas de Saccharomyces cerevisiae/análisis , Proteínas de Saccharomyces cerevisiae/genética , Índice de Severidad de la EnfermedadRESUMEN
BACKGROUND: Since the advent of next generation sequencing (NGS), several studies have tried to evaluate the relevance of targeted gene panel sequencing and whole exome sequencing for molecular diagnosis of mitochondrial diseases. The comparison between these different strategies is extremely difficult. A recent study analysed a cohort of patients affected by a mitochondrial disease using a NGS approach based on a targeted gene panel including 132 genes. This strategy led to identify the causative mutations in 15.2% of cases. The number of novel genes responsible for respiratory chain deficiency increases very rapidly. METHODS: In order to determine the impact of larger panels used as a first screening strategy on molecular diagnosis success, we analysed a cohort of 80 patients affected by a mitochondrial disease with a first mitochondrial DNA (mtDNA) NGS screening and secondarily a targeted mitochondrial panel of 281 nuclear genes. RESULTS: Pathogenic mtDNA abnormalities were identified in 4.1% (1/24) of children and 25% (14/56) of adult patients. The remaining 65 patients were analysed with our targeted mitochondrial panel and this approach enabled us to achieve an identification rate of 21.7% (5/23) in children versus 7.1% (3/42) in adults. CONCLUSIONS: Our results confirm that larger gene panels do not improve diagnostic yield of mitochondrial diseases due to (i) their very high genetic heterogeneity, (ii) the ongoing discovery of novel genes and (iii) mutations in genes apparently not related to mitochondrial function that lead to secondary respiratory chain deficiency.
Asunto(s)
Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales/genética , Proteínas Nucleares/genética , Análisis de Secuencia de ADN/métodos , Anciano , Preescolar , Femenino , Heterogeneidad Genética , Variación Genética , Humanos , Lactante , Recién Nacido , Masculino , Persona de Mediana EdadRESUMEN
The eukaryotic initiation factor 5A (eIF5A), which is highly conserved throughout evolution, has the unique characteristic of post-translational activation through hypusination. This modification is catalyzed by two enzymatic steps involving deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Notably, eIF5A may be involved in regulating the lifespan of Drosophila during long-term hypoxia. Therefore, we investigated the possibility of a link between eIF5A hypusination and cellular resistance to hypoxia/anoxia. Pharmacologic targeting of DHPS by N1-guanyl-1,7-diaminoheptane (GC7) or RNA interference-mediated inhibition of DHPS or DOHH induced tolerance to anoxia in immortalized mouse renal proximal cells. Furthermore, GC7 treatment of cells reversibly induced a metabolic shift toward glycolysis as well as mitochondrial remodeling and led to downregulated expression and activity of respiratory chain complexes, features characteristic of mitochondrial silencing. GC7 treatment also attenuated anoxia-induced generation of reactive oxygen species in these cells and in normoxic conditions, decreased the mitochondrial oxygen consumption rate of cultured cells and mice. In rats, intraperitoneal injection of GC7 substantially reduced renal levels of hypusinated eIF5A and protected against ischemia-reperfusion-induced renal injury. Finally, in the preclinical pig kidney transplant model, intravenous injection of GC7 before kidney removal significantly improved graft function recovery and late graft function and reduced interstitial fibrosis after transplant. This unconventional signaling pathway offers an innovative therapeutic target for treating hypoxic-ischemic human diseases and organ transplantation.
Asunto(s)
Muerte Celular/efectos de los fármacos , Trasplante de Riñón , Lisina/análogos & derivados , Mitocondrias/efectos de los fármacos , Mitocondrias/fisiología , Factores de Iniciación de Péptidos/efectos de los fármacos , Proteínas de Unión al ARN/efectos de los fármacos , Animales , Hipoxia de la Célula/efectos de los fármacos , Células Cultivadas , Femenino , Lisina/farmacología , Masculino , Ratones , Ratones Endogámicos C57BL , Oxigenasas de Función Mixta , Ratas , Ratas Wistar , Porcinos , Resultado del Tratamiento , Factor 5A Eucariótico de Iniciación de TraducciónRESUMEN
Patients carrying Acyl-CoA dehydrogenase 9 (ACAD9) mutations reported to date mainly present with severe hypertrophic cardiomyopathy and isolated complex I (CI) dysfunction. Here we report a novel ACAD9 mutation in a young girl presenting with severe hypertrophic cardiomyopathy, isolated CI deficiency and interestingly multiple respiratory chain complexes assembly defects. We show that ACAD9 analysis has to be performed in first intention in patients presenting with cardiac hypertrophy even in the presence of multiple assembly defects.
Asunto(s)
Acil-CoA Deshidrogenasas/genética , Cardiomiopatía Hipertrófica/genética , Cardiomiopatía Hipertrófica/metabolismo , Complejo I de Transporte de Electrón/deficiencia , Mutación , Acil-CoA Deshidrogenasa/genética , Acil-CoA Deshidrogenasas/sangre , Niño , Transporte de Electrón , Complejo I de Transporte de Electrón/sangre , Complejo I de Transporte de Electrón/genética , Complejo I de Transporte de Electrón/metabolismo , Femenino , Humanos , LactanteRESUMEN
INTRODUCTION: Acyl-coenzyme A dehydrogenase 9 (ACAD9) has a role in mitochondrial complex I (CI) assembly. Only a few patients who carry ACAD9 mutations have been reported. They mainly present with severe hypertrophic cardiomyopathy, although a minority have only mild isolated myopathy. Although the secondary factors influencing disease severity have not been elucidated, conservation of CI assembly and residual enzymatic activity have been suggested as explanations for the mild phenotypes associated with ACAD9 mutations. METHODS: We report a novel homozygous ACAD9 mutation (c.1240C>T; p.Arg414Cys) in a 34-year-old woman who presented with non-progressive myopathy. RESULTS: We show that this ACAD9 mutation led to a severe defect in CI assembly in the patient's muscle. Furthermore, the impact of CI deficiency is confirmed by accumulation of mitochondrial DNA deletions. CONCLUSION: Our data suggest that a major defect of CI assembly is not responsible for a severe phenotype. Muscle Nerve 55: 919-922, 2017.
Asunto(s)
Acil-CoA Deshidrogenasas/metabolismo , Acil-CoA Deshidrogenasas/genética , Adulto , Consanguinidad , Análisis Mutacional de ADN , ADN Mitocondrial/genética , Complejo I de Transporte de Electrón/genética , Complejo I de Transporte de Electrón/metabolismo , Femenino , Humanos , Enfermedades Musculares/genética , Enfermedades Musculares/patología , Mutación/genéticaRESUMEN
BACKGROUND: Coenzyme Q10 (CoQ10 or ubiquinone) deficiency can be due either to mutations in genes involved in CoQ10 biosynthesis pathway, or to mutations in genes unrelated to CoQ10 biosynthesis. CoQ10 defect is the only oxidative phosphorylation disorder that can be clinically improved after oral CoQ10 supplementation. Thus, early diagnosis, first evoked by mitochondrial respiratory chain (MRC) spectrophotometric analysis, then confirmed by direct measurement of CoQ10 levels, is of critical importance to prevent irreversible damage in organs such as the kidney and the central nervous system. It is widely reported that CoQ10 deficient patients present decreased quinone-dependent activities (segments I + III or G3P + III and II + III) while MRC activities of complexes I, II, III, IV and V are normal. We previously suggested that CoQ10 defect may be associated with a deficiency of CoQ10-independent MRC complexes. The aim of this study was to verify this hypothesis in order to improve the diagnosis of this disease. RESULTS: To determine whether CoQ10 defect could be associated with MRC deficiency, we quantified CoQ10 by LC-MSMS in a cohort of 18 patients presenting CoQ10-dependent deficiency associated with MRC defect. We found decreased levels of CoQ10 in eight patients out of 18 (45 %), thus confirming CoQ10 disease. CONCLUSIONS: Our study shows that CoQ10 defect can be associated with MRC deficiency. This could be of major importance in clinical practice for the diagnosis of a disease that can be improved by CoQ10 supplementation.
Asunto(s)
Ataxia/genética , Transporte de Electrón/genética , Enfermedades Mitocondriales/genética , Debilidad Muscular/genética , Mutación , Ubiquinona/análogos & derivados , Ubiquinona/deficiencia , Adolescente , Adulto , Anciano , Ataxia/diagnóstico , Ataxia/metabolismo , Biopsia , Células Cultivadas , Niño , Preescolar , Cromatografía Liquida , Femenino , Fibroblastos/enzimología , Humanos , Lactante , Masculino , Persona de Mediana Edad , Enfermedades Mitocondriales/diagnóstico , Enfermedades Mitocondriales/metabolismo , Debilidad Muscular/diagnóstico , Debilidad Muscular/metabolismo , Músculos/patología , Espectrofotometría/métodos , Espectrometría de Masas en Tándem/métodos , Ubiquinona/biosíntesis , Ubiquinona/genética , Ubiquinona/metabolismo , Adulto JovenRESUMEN
Mitochondrial DNA instability disorders are responsible for a large clinical spectrum, among which amyotrophic lateral sclerosis-like symptoms and frontotemporal dementia are extremely rare. We report a large family with a late-onset phenotype including motor neuron disease, cognitive decline resembling frontotemporal dementia, cerebellar ataxia and myopathy. In all patients, muscle biopsy showed ragged-red and cytochrome c oxidase-negative fibres with combined respiratory chain deficiency and abnormal assembly of complex V. The multiple mitochondrial DNA deletions found in skeletal muscle revealed a mitochondrial DNA instability disorder. Patient fibroblasts present with respiratory chain deficiency, mitochondrial ultrastructural alterations and fragmentation of the mitochondrial network. Interestingly, expression of matrix-targeted photoactivatable GFP showed that mitochondrial fusion was not inhibited in patient fibroblasts. Using whole-exome sequencing we identified a missense mutation (c.176C>T; p.Ser59Leu) in the CHCHD10 gene that encodes a coiled-coil helix coiled-coil helix protein, whose function is unknown. We show that CHCHD10 is a mitochondrial protein located in the intermembrane space and enriched at cristae junctions. Overexpression of a CHCHD10 mutant allele in HeLa cells led to fragmentation of the mitochondrial network and ultrastructural major abnormalities including loss, disorganization and dilatation of cristae. The observation of a frontotemporal dementia-amyotrophic lateral sclerosis phenotype in a mitochondrial disease led us to analyse CHCHD10 in a cohort of 21 families with pathologically proven frontotemporal dementia-amyotrophic lateral sclerosis. We identified the same missense p.Ser59Leu mutation in one of these families. This work opens a novel field to explore the pathogenesis of the frontotemporal dementia-amyotrophic lateral sclerosis clinical spectrum by showing that mitochondrial disease may be at the origin of some of these phenotypes.
Asunto(s)
Esclerosis Amiotrófica Lateral/etiología , ADN Mitocondrial/genética , Demencia Frontotemporal/etiología , Mitocondrias/patología , Enfermedades Mitocondriales/complicaciones , Proteínas Mitocondriales/genética , Edad de Inicio , Anciano , Alelos , Esclerosis Amiotrófica Lateral/genética , Esclerosis Amiotrófica Lateral/fisiopatología , Exoma/genética , Femenino , Demencia Frontotemporal/genética , Demencia Frontotemporal/fisiopatología , Células HeLa , Humanos , Masculino , Persona de Mediana Edad , Mitocondrias/genética , Enfermedades Mitocondriales/genética , Mutación Missense , Linaje , FenotipoRESUMEN
BACKGROUND: Mitochondrial DNA (mtDNA) diseases are rare disorders whose prevalence is estimated around 1 in 5000. Patients are usually tested only for deletions and for common mutations of mtDNA which account for 5-40% of cases, depending on the study. However, the prevalence of rare mtDNA mutations is not known. METHODS: We analysed the whole mtDNA in a cohort of 743 patients suspected of manifesting a mitochondrial disease, after excluding deletions and common mutations. Both heteroplasmic and homoplasmic variants were identified using two complementary strategies (Surveyor and MitoChip). Multiple correspondence analyses followed by hierarchical ascendant cluster process were used to explore relationships between clinical spectrum, age at onset and localisation of mutations. RESULTS: 7.4% of deleterious mutations and 22.4% of novel putative mutations were identified. Pathogenic heteroplasmic mutations were more frequent than homoplasmic mutations (4.6% vs 2.8%). Patients carrying deleterious mutations showed symptoms before 16 years of age in 67% of cases. Early onset disease (<1 year) was significantly associated with mutations in protein coding genes (mainly in complex I) while late onset disorders (>16 years) were associated with mutations in tRNA genes. MTND5 and MTND6 genes were identified as 'hotspots' of mutations, with Leigh syndrome accounting for the large majority of associated phenotypes. CONCLUSIONS: Rare mitochondrial DNA mutations probably account for more than 7.4% of patients with respiratory chain deficiency. This study shows that a comprehensive analysis of mtDNA is essential, and should include young children, for an accurate diagnosis that is now accessible with the development of next generation sequencing technology.
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ADN Mitocondrial/genética , Enfermedades Mitocondriales/genética , Mutación , Adolescente , Adulto , Edad de Inicio , Anciano , Niño , Preescolar , Femenino , Humanos , Lactante , Recién Nacido , Masculino , Persona de Mediana Edad , Enfermedades Mitocondriales/diagnóstico , Enfermedades Mitocondriales/epidemiología , Fenotipo , Prevalencia , Adulto JovenRESUMEN
OBJECTIVE: The objective of this study was to evaluate the implementation of NGS within the French mitochondrial network, MitoDiag, from targeted gene panels to whole exome sequencing (WES) or whole genome sequencing (WGS) focusing on mitochondrial nuclear-encoded genes. METHODS: Over 2000 patients suspected of Primary Mitochondrial Diseases (PMD) were sequenced by either targeted gene panels, WES or WGS within MitoDiag. We described the clinical, biochemical, and molecular data of 397 genetically confirmed patients, comprising 294 children and 103 adults, carrying pathogenic or likely pathogenic variants in nuclear-encoded genes. RESULTS: The cohort exhibited a large genetic heterogeneity, with the identification of 172 distinct genes and 253 novel variants. Among children, a notable prevalence of pathogenic variants in genes associated with oxidative phosphorylation (OXPHOS) functions and mitochondrial translation was observed. In adults, pathogenic variants were primarily identified in genes linked to mtDNA maintenance. Additionally, a substantial proportion of patients (54% (42/78) and 48% (13/27) in children and adults, respectively), undergoing WES or WGS testing displayed PMD mimics, representing pathologies that clinically resemble mitochondrial diseases. INTERPRETATION: We reported the largest French cohort of patients suspected of PMD with pathogenic variants in nuclear genes. We have emphasized the clinical complexity of PMD and the challenges associated with recognizing and distinguishing them from other pathologies, particularly neuromuscular disorders. We confirmed that WES/WGS, instead of panel approach, was more valuable to identify the genetic basis in patients with "possible" PMD and we provided a genetic testing flowchart to guide physicians in their diagnostic strategy.
Asunto(s)
Enfermedades Mitocondriales , Humanos , Enfermedades Mitocondriales/genética , Enfermedades Mitocondriales/diagnóstico , Francia , Niño , Adulto , Masculino , Femenino , Adolescente , Persona de Mediana Edad , Preescolar , Estudios de Cohortes , Adulto Joven , Lactante , Secuenciación del Exoma , Anciano , Secuenciación Completa del Genoma , ADN Mitocondrial/genética , Diagnóstico DiferencialRESUMEN
MFN2 and OPA1 genes encode two dynamin-like GTPase proteins involved in the fusion of the mitochondrial membrane. They have been associated with Charcot-Marie-Tooth disease type 2A and autosomal dominant optic atrophy, respectively. We report a large family with optic atrophy beginning in early childhood, associated with axonal neuropathy and mitochondrial myopathy in adult life. The clinical presentation looks like the autosomal dominant optic atrophy 'plus' phenotype linked to OPA1 mutations but is associated with a novel MFN2 missense mutation (c.629A>T, p.D210V). Multiple mitochondrial DNA deletions were found in skeletal muscle and this observation makes MFN2 a novel gene associated with 'mitochondrial DNA breakage' syndrome. Contrary to previous studies in patients with Charcot-Marie-Tooth disease type 2A, fibroblasts carrying the MFN2 mutation present with a respiratory chain deficiency, a fragmentation of the mitochondrial network and a significant reduction of MFN2 protein expression. Furthermore, we show for the first time that impaired mitochondrial fusion is responsible for a deficiency to repair stress-induced mitochondrial DNA damage. It is likely that defect in mitochondrial DNA repair is due to variability in repair protein content across the mitochondrial population and is at least partially responsible for mitochondrial DNA instability.
Asunto(s)
ADN Mitocondrial/genética , GTP Fosfohidrolasas/genética , Miopatías Mitocondriales/genética , Proteínas Mitocondriales/genética , Atrofia Óptica/genética , Adolescente , Adulto , Niño , Daño del ADN , ADN Mitocondrial/metabolismo , Femenino , GTP Fosfohidrolasas/metabolismo , Humanos , Masculino , Persona de Mediana Edad , Miopatías Mitocondriales/complicaciones , Miopatías Mitocondriales/metabolismo , Proteínas Mitocondriales/metabolismo , Mutación Missense , Atrofia Óptica/complicaciones , Atrofia Óptica/metabolismo , LinajeRESUMEN
Isolated complex III defect is a relatively rare cause of mitochondrial disorder. New genes involved were identified in the last two decades, with only a few cases described for each deficiency. UQCRC2, which encodes ubiquinol-cytochrome c reductase core protein 2, is one of the eleven structural subunits of complex III. We report seven French patients with UQCRC2 deficiency to complete the phenotype reported so far. We highlight the similarities with neoglucogenesis defect during decompensations - hypoglycaemias, liver failure and lactic acidosis - and point out the rapid improvement with glucose fluid infusion, which is a remarkable feature for a mitochondrial disorder. Finally, we discuss the relevance of coenzyme Q10 supplementation in this defect.