RESUMEN
Folates enable the activation and transfer of one-carbon units for the biosynthesis of purines, thymidine and methionine. Antifolates are important immunosuppressive and anticancer agents. In proliferating lymphocytes and human cancers, mitochondrial folate enzymes are particularly strongly upregulated. This in part reflects the need for mitochondria to generate one-carbon units and export them to the cytosol for anabolic metabolism. The full range of uses of folate-bound one-carbon units in the mitochondrial compartment itself, however, has not been thoroughly explored. Here we show that loss of the catalytic activity of the mitochondrial folate enzyme serine hydroxymethyltransferase 2 (SHMT2), but not of other folate enzymes, leads to defective oxidative phosphorylation in human cells due to impaired mitochondrial translation. We find that SHMT2, presumably by generating mitochondrial 5,10-methylenetetrahydrofolate, provides methyl donors to produce the taurinomethyluridine base at the wobble position of select mitochondrial tRNAs. Mitochondrial ribosome profiling in SHMT2-knockout human cells reveals that the lack of this modified base causes defective translation, with preferential mitochondrial ribosome stalling at certain lysine (AAG) and leucine (UUG) codons. This results in the impaired expression of respiratory chain enzymes. Stalling at these specific codons also occurs in certain inborn errors of mitochondrial metabolism. Disruption of whole-cell folate metabolism, by either folate deficiency or antifolate treatment, also impairs the respiratory chain. In summary, mammalian mitochondria use folate-bound one-carbon units to methylate tRNA, and this modification is required for mitochondrial translation and thus oxidative phosphorylation.
Asunto(s)
Ácido Fólico/metabolismo , Mitocondrias/metabolismo , Biosíntesis de Proteínas , ARN de Transferencia/química , ARN de Transferencia/metabolismo , Aminohidrolasas/metabolismo , Biocatálisis , Proteínas Portadoras/metabolismo , Codón/genética , Transporte de Electrón , Antagonistas del Ácido Fólico/farmacología , Proteínas de Unión al GTP/metabolismo , Glicina Hidroximetiltransferasa/deficiencia , Glicina Hidroximetiltransferasa/metabolismo , Guanosina/metabolismo , Células HCT116 , Células HEK293 , Humanos , Leucina/genética , Lisina/genética , Metilación/efectos de los fármacos , Metilenotetrahidrofolato Deshidrogenasa (NADP)/metabolismo , Mitocondrias/efectos de los fármacos , Mitocondrias/enzimología , Enzimas Multifuncionales/metabolismo , Fosforilación Oxidativa/efectos de los fármacos , ARN de Transferencia/genética , Proteínas de Unión al ARN , Ribosomas/metabolismo , Sarcosina/metabolismo , Tetrahidrofolatos/metabolismo , Nucleótidos de Timina/biosíntesisRESUMEN
Respiratory chain complex I deficiency is the most frequently identified biochemical defect in childhood mitochondrial diseases. Clinical symptoms range from fatal infantile lactic acidosis to Leigh syndrome and other encephalomyopathies or cardiomyopathies. To date, disease-causing variants in genes coding for 27 complex I subunits, including 7 mitochondrial DNA genes, and in 11 genes encoding complex I assembly factors have been reported. Here, we describe rare biallelic variants in NDUFB8 encoding a complex I accessory subunit revealed by whole-exome sequencing in two individuals from two families. Both presented with a progressive course of disease with encephalo(cardio)myopathic features including muscular hypotonia, cardiac hypertrophy, respiratory failure, failure to thrive, and developmental delay. Blood lactate was elevated. Neuroimaging disclosed progressive changes in the basal ganglia and either brain stem or internal capsule. Biochemical analyses showed an isolated decrease in complex I enzymatic activity in muscle and fibroblasts. Complementation studies by expression of wild-type NDUFB8 in cells from affected individuals restored mitochondrial function, confirming NDUFB8 variants as the cause of complex I deficiency. Hereby we establish NDUFB8 as a relevant gene in childhood-onset mitochondrial disease.
Asunto(s)
Encefalopatías/genética , Complejo I de Transporte de Electrón/deficiencia , Enfermedad de Leigh/genética , Enfermedades Mitocondriales/genética , Mutación/genética , Secuencia de Aminoácidos , Encéfalo/diagnóstico por imagen , Encéfalo/patología , Complejo I de Transporte de Electrón/química , Complejo I de Transporte de Electrón/genética , Femenino , Fibroblastos/enzimología , Fibroblastos/patología , Humanos , Imagen por Resonancia Magnética , Masculino , Fosforilación Oxidativa , Linaje , Porinas/metabolismoRESUMEN
Isolated complex I deficiency is a common biochemical phenotype observed in pediatric mitochondrial disease and often arises as a consequence of pathogenic variants affecting one of the â¼65 genes encoding the complex I structural subunits or assembly factors. Such genetic heterogeneity means that application of next-generation sequencing technologies to undiagnosed cohorts has been a catalyst for genetic diagnosis and gene-disease associations. We describe the clinical and molecular genetic investigations of four unrelated children who presented with neuroradiological findings and/or elevated lactate levels, highly suggestive of an underlying mitochondrial diagnosis. Next-generation sequencing identified bi-allelic variants in NDUFA6, encoding a 15 kDa LYR-motif-containing complex I subunit that forms part of the Q-module. Functional investigations using subjects' fibroblast cell lines demonstrated complex I assembly defects, which were characterized in detail by mass-spectrometry-based complexome profiling. This confirmed a marked reduction in incorporated NDUFA6 and a concomitant reduction in other Q-module subunits, including NDUFAB1, NDUFA7, and NDUFA12. Lentiviral transduction of subjects' fibroblasts showed normalization of complex I. These data also support supercomplex formation, whereby the â¼830 kDa complex I intermediate (consisting of the P- and Q-modules) is in complex with assembled complex III and IV holoenzymes despite lacking the N-module. Interestingly, RNA-sequencing data provided evidence that the consensus RefSeq accession number does not correspond to the predominant transcript in clinically relevant tissues, prompting revision of the NDUFA6 RefSeq transcript and highlighting not only the importance of thorough variant interpretation but also the assessment of appropriate transcripts for analysis.
Asunto(s)
Complejo I de Transporte de Electrón/deficiencia , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales/genética , Mutación/genética , Alelos , Secuencia de Aminoácidos , Complejo I de Transporte de Electrón/genética , Femenino , Fibroblastos/patología , Heterogeneidad Genética , Humanos , Lactante , Masculino , Mitocondrias/genética , Fenotipo , Alineación de SecuenciaRESUMEN
Biogenesis of the mitochondrial oxidative phosphorylation system, which produces the bulk of ATP for almost all eukaryotic cells, depends on the translation of 13 mtDNA-encoded polypeptides by mitochondria-specific ribosomes in the mitochondrial matrix. These mitoribosomes are dual-origin ribonucleoprotein complexes, which contain mtDNA-encoded rRNAs and tRNAs and â¼80 nucleus-encoded proteins. An increasing number of gene mutations that impair mitoribosomal function and result in multiple OXPHOS deficiencies are being linked to human mitochondrial diseases. Using exome sequencing in two unrelated subjects presenting with sensorineural hearing impairment, mild developmental delay, hypoglycemia, and a combined OXPHOS deficiency, we identified mutations in the gene encoding the mitochondrial ribosomal protein S2, which has not previously been implicated in disease. Characterization of subjects' fibroblasts revealed a decrease in the steady-state amounts of mutant MRPS2, and this decrease was shown by complexome profiling to prevent the assembly of the small mitoribosomal subunit. In turn, mitochondrial translation was inhibited, resulting in a combined OXPHOS deficiency detectable in subjects' muscle and liver biopsies as well as in cultured skin fibroblasts. Reintroduction of wild-type MRPS2 restored mitochondrial translation and OXPHOS assembly. The combination of lactic acidemia, hypoglycemia, and sensorineural hearing loss, especially in the presence of a combined OXPHOS deficiency, should raise suspicion for a ribosomal-subunit-related mitochondrial defect, and clinical recognition could allow for a targeted diagnostic approach. The identification of MRPS2 as an additional gene related to mitochondrial disease further expands the genetic and phenotypic spectra of OXPHOS deficiencies caused by impaired mitochondrial translation.
Asunto(s)
Alelos , Pérdida Auditiva Sensorineural/genética , Hipoglucemia/genética , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales/genética , Mutación/genética , Proteínas Ribosómicas/genética , Secuencia de Aminoácidos , Preescolar , Análisis Mutacional de ADN , ADN Mitocondrial/genética , Femenino , Fibroblastos/metabolismo , Pérdida Auditiva Sensorineural/complicaciones , Humanos , Hipoglucemia/complicaciones , Lactante , Recién Nacido , Masculino , Enfermedades Mitocondriales/complicaciones , Proteínas Mitocondriales/química , Fosforilación Oxidativa , Subunidades de Proteína/genética , ARN Ribosómico/genética , Proteínas Ribosómicas/químicaRESUMEN
BACKGROUND: Childhood stroke is rare and can predispose to post-stroke epilepsy. The purpose of this study was to evaluate long-term quality of life (QoL) in patients with childhood stroke, focusing on epileptic aspects. METHOD: This involves a retrospective study of 98 patients with childhood stroke (pre- and neonatal strokes excluded), who had been inpatients between 1986 and 2003 for early rehabilitation. Data were obtained via interviews using a standardized questionnaire: QoL evaluation with KINDL, functional outcome with Barthel Index, and motor handicaps-assessment with modified Rankin Score. RESULTS: Forty-nine of 98 patients (31 males, mean follow-up 16 years, range 8-25 years) were included. Six patients passed away (three of sudden unexpected death in epilepsy). At least one epileptic seizure occurred in 27/49 patients (occurrence: 2 days-13 years.; mean 3.3 years.). Epilepsy manifested in 19/49 patients. No correlation was found between the development of epilepsy and the location or etiology of the stroke. The presence of functional independence was significantly higher in seizure-free patients and in patients without epilepsy. For the external assessment (filled in for the patient by the parent/caregiver), there was no significant difference in QoL in patients with and without epilepsy; however, in the in-person KINDL questionnaire a significantly lower QoL was noted in epilepsy patients compared with patients without epilepsy. CONCLUSION: One important finding in our study is that in the long-term course 39% of patients developed epilepsy after a childhood stroke. It occurred as late as 13 years after the acute episode and affected the QoL especially in cognitively less handicapped patients.
Asunto(s)
Epilepsia , Accidente Cerebrovascular , Niño , Epilepsia/etiología , Humanos , Recién Nacido , Masculino , Calidad de Vida , Estudios Retrospectivos , Convulsiones/complicaciones , Accidente Cerebrovascular/complicacionesRESUMEN
Complement component 1 Q subcomponent-binding protein (C1QBP; also known as p32) is a multi-compartmental protein whose precise function remains unknown. It is an evolutionary conserved multifunctional protein localized primarily in the mitochondrial matrix and has roles in inflammation and infection processes, mitochondrial ribosome biogenesis, and regulation of apoptosis and nuclear transcription. It has an N-terminal mitochondrial targeting peptide that is proteolytically processed after import into the mitochondrial matrix, where it forms a homotrimeric complex organized in a doughnut-shaped structure. Although C1QBP has been reported to exert pleiotropic effects on many cellular processes, we report here four individuals from unrelated families where biallelic mutations in C1QBP cause a defect in mitochondrial energy metabolism. Infants presented with cardiomyopathy accompanied by multisystemic involvement (liver, kidney, and brain), and children and adults presented with myopathy and progressive external ophthalmoplegia. Multiple mitochondrial respiratory-chain defects, associated with the accumulation of multiple deletions of mitochondrial DNA in the later-onset myopathic cases, were identified in all affected individuals. Steady-state C1QBP levels were decreased in all individuals' samples, leading to combined respiratory-chain enzyme deficiency of complexes I, III, and IV. C1qbp-/- mouse embryonic fibroblasts (MEFs) resembled the human disease phenotype by showing multiple defects in oxidative phosphorylation (OXPHOS). Complementation with wild-type, but not mutagenized, C1qbp restored OXPHOS protein levels and mitochondrial enzyme activities in C1qbp-/- MEFs. C1QBP deficiency represents an important mitochondrial disorder associated with a clinical spectrum ranging from infantile lactic acidosis to childhood (cardio)myopathy and late-onset progressive external ophthalmoplegia.
Asunto(s)
Cardiomiopatías/genética , Proteínas Portadoras/genética , Transporte de Electrón/fisiología , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales/genética , Mutación , Adulto , Edad de Inicio , Anciano , Alelos , Secuencia de Aminoácidos , Animales , Cardiomiopatías/complicaciones , Cardiomiopatías/patología , Proteínas Portadoras/química , Proteínas Portadoras/metabolismo , Células Cultivadas , Preescolar , Estudios de Cohortes , ADN Mitocondrial , Embrión de Mamíferos/metabolismo , Embrión de Mamíferos/patología , Femenino , Fibroblastos/metabolismo , Fibroblastos/patología , Humanos , Recién Nacido , Masculino , Ratones , Persona de Mediana Edad , Enfermedades Mitocondriales/complicaciones , Enfermedades Mitocondriales/patología , Proteínas Mitocondriales/química , Proteínas Mitocondriales/metabolismo , Fosforilación Oxidativa , Linaje , Conformación Proteica , Homología de Secuencia , Índice de Severidad de la Enfermedad , Adulto JovenRESUMEN
We have used whole-exome sequencing in ten individuals from four unrelated pedigrees to identify biallelic missense mutations in the nuclear-encoded mitochondrial inorganic pyrophosphatase (PPA2) that are associated with mitochondrial disease. These individuals show a range of severity, indicating that PPA2 mutations may cause a spectrum of mitochondrial disease phenotypes. Severe symptoms include seizures, lactic acidosis, cardiac arrhythmia, and death within days of birth. In the index family, presentation was milder and manifested as cardiac fibrosis and an exquisite sensitivity to alcohol, leading to sudden arrhythmic cardiac death in the second decade of life. Comparison of normal and mutant PPA2-containing mitochondria from fibroblasts showed that the activity of inorganic pyrophosphatase was significantly reduced in affected individuals. Recombinant PPA2 enzymes modeling hypomorphic missense mutations had decreased activity that correlated with disease severity. These findings confirm the pathogenicity of PPA2 mutations and suggest that PPA2 is a cardiomyopathy-associated protein, which has a greater physiological importance in mitochondrial function than previously recognized.
Asunto(s)
Muerte Súbita Cardíaca/etiología , Pirofosfatasa Inorgánica/deficiencia , Pirofosfatasa Inorgánica/genética , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales/deficiencia , Proteínas Mitocondriales/genética , Mutación Missense/genética , Acidosis Láctica/genética , Adolescente , Adulto , Secuencia de Aminoácidos , Animales , Arritmias Cardíacas/genética , Cardiomiopatías/enzimología , Cardiomiopatías/genética , Cardiomiopatías/patología , Cardiomiopatías/fisiopatología , Niño , Preescolar , Muerte Súbita Cardíaca/patología , Etanol/efectos adversos , Exoma/genética , Femenino , Fibroblastos/citología , Fibroblastos/patología , Fibrosis/enzimología , Fibrosis/genética , Fibrosis/patología , Humanos , Lactante , Recién Nacido , Pirofosfatasa Inorgánica/química , Pirofosfatasa Inorgánica/metabolismo , Masculino , Mitocondrias/enzimología , Mitocondrias/genética , Mitocondrias/patología , Enfermedades Mitocondriales/enzimología , Enfermedades Mitocondriales/patología , Enfermedades Mitocondriales/fisiopatología , Proteínas Mitocondriales/química , Proteínas Mitocondriales/metabolismo , Modelos Moleculares , Linaje , Fenotipo , Convulsiones , Adulto JovenRESUMEN
Among 131 children admitted to our institution for early phase rehabilitation after freshwater near-drowning (ND) between the year 1986 and 2000, 87 were in unresponsive wakefulness syndrome (UWS) for at least 4 weeks after the accidents. An anonymous questionnaire was sent to the families after 0.5 to 15.0 years (median: 4.6) and 48 mothers and 51 fathers of 55 of these 87 children were interviewed after 6.6 to 23.8 years (median: 13.8) of ND. At the time of the interviews, 8/55 children were able to perform daily living activities independently, 36/55 children were not able to do so (many of them suffered from chronic medical conditions like spasticity or disorders of swallowing), and 11/55 children had died. Health-related quality of life (HRQoL) was, however, similar to the normal population for mothers, and even higher for fathers. Furthermore, the ND accident had apparently not lead to a higher rate of separations of parents but had increased their likelihood to have further children. Feelings of guilt were highly prevalent (23/47 mothers, 20/47 fathers), and correlated with lower HRQoL of the respective parent. We found correlations between duty of supervision and feelings of guilt and between outcome and HRQoL for only the fathers. In conclusion, we found that after 4 weeks in UWS, the long-term neurological outcome of pediatric ND victims is often but not always poor. Despite often severe disabilities or death of the child during long-term care, parents surprisingly report little impact on their HRQoL, on the stability of their partnership or on their wish to have further children. Our findings may help parents and physicians to choose the best treatment for a child in UWS due to different etiologies striking the balance between rehabilitation and palliative care.
Asunto(s)
Ahogamiento Inminente/psicología , Padres/psicología , Estado Vegetativo Persistente/psicología , Calidad de Vida/psicología , Encuestas y Cuestionarios , Vigilia , Niño , Preescolar , Femenino , Culpa , Humanos , Lactante , Masculino , Ahogamiento Inminente/diagnóstico , Estado Vegetativo Persistente/diagnóstico , Factores de Tiempo , Resultado del TratamientoRESUMEN
OBJECTIVE: 3-Methylglutaconic aciduria, dystonia-deafness, hepatopathy, encephalopathy, Leigh-like syndrome (MEGDHEL) syndrome is caused by biallelic variants in SERAC1. METHODS: This multicenter study addressed the course of disease for each organ system. Metabolic, neuroradiological, and genetic findings are reported. RESULTS: Sixty-seven individuals (39 previously unreported) from 59 families were included (age range = 5 days-33.4 years, median age = 9 years). A total of 41 different SERAC1 variants were identified, including 20 that have not been reported before. With the exception of 2 families with a milder phenotype, all affected individuals showed a strikingly homogeneous phenotype and time course. Severe, reversible neonatal liver dysfunction and hypoglycemia were seen in >40% of all cases. Starting at a median age of 6 months, muscular hypotonia (91%) was seen, followed by progressive spasticity (82%, median onset = 15 months) and dystonia (82%, 18 months). The majority of affected individuals never learned to walk (68%). Seventy-nine percent suffered hearing loss, 58% never learned to speak, and nearly all had significant intellectual disability (88%). Magnetic resonance imaging features were accordingly homogenous, with bilateral basal ganglia involvement (98%); the characteristic "putaminal eye" was seen in 53%. The urinary marker 3-methylglutaconic aciduria was present in virtually all patients (98%). Supportive treatment focused on spasticity and drooling, and was effective in the individuals treated; hearing aids or cochlear implants did not improve communication skills. INTERPRETATION: MEGDHEL syndrome is a progressive deafness-dystonia syndrome with frequent and reversible neonatal liver involvement and a strikingly homogenous course of disease. Ann Neurol 2017;82:1004-1015.
Asunto(s)
Hidrolasas de Éster Carboxílico/genética , Trastornos Sordoceguera/diagnóstico por imagen , Trastornos Sordoceguera/genética , Progresión de la Enfermedad , Distonía/diagnóstico por imagen , Distonía/genética , Discapacidad Intelectual/diagnóstico por imagen , Discapacidad Intelectual/genética , Mutación/genética , Atrofia Óptica/diagnóstico por imagen , Atrofia Óptica/genética , Adolescente , Adulto , Secuencia de Aminoácidos , Niño , Preescolar , Estudios de Cohortes , Trastornos Sordoceguera/terapia , Distonía/terapia , Femenino , Humanos , Lactante , Recién Nacido , Discapacidad Intelectual/terapia , Masculino , Atrofia Óptica/terapia , Adulto JovenRESUMEN
The Warburg theory of cancer postulates that an important driver of tumorigenesis is insufficient respiration due to mitochondrial defects, and concomitant enhancement of lactate production due to increased aerobic glycolysis. We analysed 48 melanoma samples by immunohistochemistry and found that 38% of melanomas are characterized by areas of isolated or combined deficiencies of complexes of the oxidative phosphorylation (OXPHOS) system, whereby the incidence of OXPHOS-deficient areas is associated with an increased Breslow index; 62% of melanomas showed high expression of all OXPHOS complexes. Expression of carbonic anhydrase IX was low, indicating that melanomas generally are well-oxygenated. Expression of HIF-1α and MCT4 was high, which might be a consequence of increased lactate dehydrogenase A levels in melanomas. Our data indicate that there are two types of melanomas: one that features a classic Warburg effect, whereas the other one, despite being glycolytic, maintains a high level of OXPHOS complexes.
Asunto(s)
Melanoma/metabolismo , Neoplasias Cutáneas/metabolismo , Antígenos de Neoplasias/metabolismo , Anhidrasa Carbónica IX/metabolismo , Perfilación de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Glucólisis , Humanos , Hipoxia , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Inmunohistoquímica , Melanocitos , Mitocondrias/metabolismo , Transportadores de Ácidos Monocarboxílicos/metabolismo , Proteínas Musculares/metabolismo , Fosforilación Oxidativa , Oxígeno/química , Fenotipo , FosforilaciónRESUMEN
Unexplained global developmental delay and epilepsy in childhood pose a major socioeconomic burden. Progress in defining the molecular bases does not often translate into effective treatment. Notable exceptions include certain inborn errors of metabolism amenable to dietary intervention. CAD encodes a multifunctional enzyme involved in de novo pyrimidine biosynthesis. Alternatively, pyrimidines can be recycled from uridine. Exome sequencing in three families identified biallelic CAD mutations in four children with global developmental delay, epileptic encephalopathy, and anaemia with anisopoikilocytosis. Two died aged 4 and 5 years after a neurodegenerative disease course. Supplementation of the two surviving children with oral uridine led to immediate cessation of seizures in both. A 4-year-old female, previously in a minimally conscious state, began to communicate and walk with assistance after 9 weeks of treatment. A 3-year-old female likewise showed developmental progress. Blood smears normalized and anaemia resolved. We establish CAD as a gene confidently implicated in this neurometabolic disorder, characterized by co-occurrence of global developmental delay, dyserythropoietic anaemia and seizures. While the natural disease course can be lethal in early childhood, our findings support the efficacy of uridine supplementation, rendering CAD deficiency a treatable neurometabolic disorder and therefore a potential condition for future (genetic) newborn screening.
Asunto(s)
Aspartato Carbamoiltransferasa/genética , Carbamoil-Fosfato Sintasa (Glutamina-Hidrolizante)/genética , Dihidroorotasa/genética , Mutación/genética , Espasmos Infantiles/tratamiento farmacológico , Espasmos Infantiles/genética , Uridina/uso terapéutico , Anemia/complicaciones , Anemia/tratamiento farmacológico , Anemia/genética , Encéfalo/diagnóstico por imagen , Niño , Preescolar , Análisis Mutacional de ADN , Discapacidades del Desarrollo/complicaciones , Discapacidades del Desarrollo/genética , Femenino , Humanos , Lactante , Imagen por Resonancia Magnética , Masculino , Espasmos Infantiles/complicaciones , Espasmos Infantiles/diagnóstico por imagenRESUMEN
Mitochondrial protein synthesis involves an intricate interplay between mitochondrial DNA encoded RNAs and nuclear DNA encoded proteins, such as ribosomal proteins and aminoacyl-tRNA synthases. Eukaryotic cells contain 17 mitochondria-specific aminoacyl-tRNA synthases. WARS2 encodes mitochondrial tryptophanyl-tRNA synthase (mtTrpRS), a homodimeric class Ic enzyme (mitochondrial tryptophan-tRNA ligase; EC 6.1.1.2). Here, we report six individuals from five families presenting with either severe neonatal onset lactic acidosis, encephalomyopathy and early death or a later onset, more attenuated course of disease with predominating intellectual disability. Respiratory chain enzymes were usually normal in muscle and fibroblasts, while a severe combined respiratory chain deficiency was found in the liver of a severely affected individual. Exome sequencing revealed rare biallelic variants in WARS2 in all affected individuals. An increase of uncharged mitochondrial tRNATrp and a decrease of mtTrpRS protein content were found in fibroblasts of affected individuals. We hereby define the clinical, neuroradiological, and metabolic phenotype of WARS2 defects. This confidently implicates that mutations in WARS2 cause mitochondrial disease with a broad spectrum of clinical presentation.
Asunto(s)
Aminoacil-ARNt Sintetasas/genética , Variación Genética , Discapacidad Intelectual/genética , Enfermedades Mitocondriales/genética , Encefalomiopatías Mitocondriales/genética , Secuencia de Aminoácidos , Aminoacil-ARNt Sintetasas/metabolismo , Exoma/genética , Femenino , Humanos , Recién Nacido , Discapacidad Intelectual/enzimología , Masculino , Enfermedades Mitocondriales/enzimología , Encefalomiopatías Mitocondriales/enzimología , Encefalomiopatías Mitocondriales/patología , Modelos Moleculares , Mutación , Linaje , Fenotipo , Embarazo , Alineación de Secuencia , Secuenciación del ExomaRESUMEN
F-box and leucine-rich repeat protein 4 (FBXL4) is a mitochondrial protein whose exact function is not yet known. However, cellular studies have suggested that it plays significant roles in mitochondrial bioenergetics, mitochondrial DNA (mtDNA) maintenance, and mitochondrial dynamics. Biallelic pathogenic variants in FBXL4 are associated with an encephalopathic mtDNA maintenance defect syndrome that is a multisystem disease characterized by lactic acidemia, developmental delay, and hypotonia. Other features are feeding difficulties, growth failure, microcephaly, hyperammonemia, seizures, hypertrophic cardiomyopathy, elevated liver transaminases, recurrent infections, variable distinctive facial features, white matter abnormalities and cerebral atrophy found in neuroimaging, combined deficiencies of multiple electron transport complexes, and mtDNA depletion. Since its initial description in 2013, 36 different pathogenic variants in FBXL4 were reported in 50 affected individuals. In this report, we present 37 additional affected individuals and 11 previously unreported pathogenic variants. We summarize the clinical features of all 87 individuals with FBXL4-related mtDNA maintenance defect, review FBXL4 structure and function, map the 47 pathogenic variants onto the gene structure to assess the variants distribution, and investigate the genotype-phenotype correlation. Finally, we provide future directions to understand the disease mechanism and identify treatment strategies.
Asunto(s)
ADN Mitocondrial/genética , Proteínas F-Box/genética , Estudios de Asociación Genética , Encefalomiopatías Mitocondriales/genética , Ubiquitina-Proteína Ligasas/genética , Acidosis Láctica/genética , Cardiomiopatía Hipertrófica/genética , Predisposición Genética a la Enfermedad , Humanos , Estimación de Kaplan-Meier , Mitocondrias/genética , Encefalomiopatías Mitocondriales/epidemiología , Encefalomiopatías Mitocondriales/patología , Proteínas Mitocondriales/genética , Hipotonía Muscular/genética , Mutación , Fosforilación Oxidativa , Proteoma/genéticaRESUMEN
Mitochondrial diseases often exhibit tissue-specific pathologies, but this phenomenon is poorly understood. Here we present regulation of mitochondrial translation by the Mitochondrial Translation Optimization Factor 1, MTO1, as a novel player in this scenario. We demonstrate that MTO1 mediates tRNA modification and controls mitochondrial translation rate in a highly tissue-specific manner associated with tissue-specific OXPHOS defects. Activation of mitochondrial proteases, aberrant translation products, as well as defects in OXPHOS complex assembly observed in MTO1 deficient mice further imply that MTO1 impacts translation fidelity. In our mouse model, MTO1-related OXPHOS deficiency can be bypassed by feeding a ketogenic diet. This therapeutic intervention is independent of the MTO1-mediated tRNA modification and involves balancing of mitochondrial and cellular secondary stress responses. Our results thereby establish mammalian MTO1 as a novel factor in the tissue-specific regulation of OXPHOS and fine tuning of mitochondrial translation accuracy.
Asunto(s)
Proteínas Portadoras/metabolismo , Enfermedades Mitocondriales/tratamiento farmacológico , Enfermedades Mitocondriales/metabolismo , Fosforilación Oxidativa , Biosíntesis de Proteínas , ARN de Transferencia/metabolismo , Secuencia de Aminoácidos , Animales , Proteínas Portadoras/química , Proteínas Portadoras/genética , Dieta Cetogénica , Fibroblastos/metabolismo , Humanos , Ratones , Mitocondrias/metabolismo , Enfermedades Mitocondriales/genética , Proteínas Mitocondriales , Datos de Secuencia Molecular , Especificidad de Órganos , ARN de Transferencia/genética , Proteínas de Unión al ARN , Alineación de SecuenciaRESUMEN
BACKGROUND: Mitochondria are dynamic organelles which undergo continuous fission and fusion to maintain their diverse cellular functions. Components of the fission machinery are partly shared between mitochondria and peroxisomes, and inherited defects in two such components (dynamin-related protein (DRP1) and ganglioside-induced differentiation-associated protein 1 (GDAP1)) have been associated with human disease. Deficiency of a third component (mitochondrial fission factor, MFF) was recently reported in one index patient, rendering MFF another candidate disease gene within the expanding field of mitochondrial and peroxisomal dynamics. Here we investigated three new patients from two families with pathogenic mutations in MFF. METHODS: The patients underwent clinical examination, brain MRI, and biochemical, cytological and molecular analyses, including exome sequencing. RESULTS: The patients became symptomatic within the first year of life, exhibiting seizures, developmental delay and acquired microcephaly. Dysphagia, spasticity and optic and peripheral neuropathy developed subsequently. Brain MRI showed Leigh-like patterns with bilateral changes of the basal ganglia and subthalamic nucleus, suggestive of impaired mitochondrial energy metabolism. However, activities of mitochondrial respiratory chain complexes were found to be normal in skeletal muscle. Exome sequencing revealed three different biallelic loss-of-function variants in MFF in both index cases. Western blot studies of patient-derived fibroblasts indicated normal content of mitochondria and peroxisomes, whereas immunofluorescence staining revealed elongated mitochondria and peroxisomes. Furthermore, increased mitochondrial branching and an abnormal distribution of fission-mediating DRP1 were observed. CONCLUSIONS: Our findings establish MFF loss of function as a cause of disturbed mitochondrial and peroxisomal dynamics associated with early-onset Leigh-like basal ganglia disease. We suggest that, even if laboratory findings are not indicative of mitochondrial or peroxisomal dysfunction, the co-occurrence of optic and/or peripheral neuropathy with seizures warrants genetic testing for MFF mutations.
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Enfermedades de los Ganglios Basales/genética , Proteínas de la Membrana/genética , Proteínas Mitocondriales/genética , Atrofia Óptica/genética , Enfermedades del Sistema Nervioso Periférico/genética , Enfermedades de los Ganglios Basales/diagnóstico por imagen , Enfermedades de los Ganglios Basales/fisiopatología , Encefalopatías/genética , Encefalopatías/fisiopatología , Preescolar , Exoma , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , Lactante , Imagen por Resonancia Magnética , Masculino , Mitocondrias/genética , Mitocondrias/patología , Proteínas del Tejido Nervioso , Atrofia Óptica/diagnóstico por imagen , Atrofia Óptica/fisiopatología , Enfermedades del Sistema Nervioso Periférico/diagnóstico por imagen , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Peroxisomas/genética , Peroxisomas/patologíaRESUMEN
Whole-exome sequencing and autozygosity mapping studies, independently performed in subjects with defective combined mitochondrial OXPHOS-enzyme deficiencies, identified a total of nine disease-segregating FBXL4 mutations in seven unrelated mitochondrial disease families, composed of six singletons and three siblings. All subjects manifested early-onset lactic acidemia, hypotonia, and developmental delay caused by severe encephalomyopathy consistently associated with progressive cerebral atrophy and variable involvement of the white matter, deep gray nuclei, and brainstem structures. A wide range of other multisystem features were variably seen, including dysmorphism, skeletal abnormalities, poor growth, gastrointestinal dysmotility, renal tubular acidosis, seizures, and episodic metabolic failure. Mitochondrial respiratory chain deficiency was present in muscle or fibroblasts of all tested individuals, together with markedly reduced oxygen consumption rate and hyperfragmentation of the mitochondrial network in cultured cells. In muscle and fibroblasts from several subjects, substantially decreased mtDNA content was observed. FBXL4 is a member of the F-box family of proteins, some of which are involved in phosphorylation-dependent ubiquitination and/or G protein receptor coupling. We also demonstrate that FBXL4 is targeted to mitochondria and localizes in the intermembrane space, where it participates in an approximately 400 kDa protein complex. These data strongly support a role for FBXL4 in controlling bioenergetic homeostasis and mtDNA maintenance. FBXL4 mutations are a recurrent cause of mitochondrial encephalomyopathy onset in early infancy.
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Predisposición Genética a la Enfermedad , Encefalomiopatías Mitocondriales/genética , Proteínas Mitocondriales/genética , Mutación/genética , Edad de Inicio , Niño , Preescolar , Cromosomas Humanos Par 6/genética , ADN Complementario/genética , Proteínas F-Box/química , Proteínas F-Box/genética , Femenino , Fibroblastos/metabolismo , Fibroblastos/patología , Genes Recesivos/genética , Células HEK293 , Humanos , Lactante , Recién Nacido , Masculino , Mitocondrias/metabolismo , Encefalomiopatías Mitocondriales/epidemiología , Músculo Esquelético/patología , Proteínas Mutantes/metabolismo , Fosforilación Oxidativa , Linaje , Transporte de Proteínas , Fracciones Subcelulares/metabolismo , Síndrome , Ubiquitina-Proteína Ligasas/química , Ubiquitina-Proteína Ligasas/genéticaRESUMEN
BACKGROUND: Severe methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn defect disturbing the remethylation of homocysteine to methionine (<200 reported cases). This retrospective study evaluates clinical, biochemical genetic and in vitro enzymatic data in a cohort of 33 patients. METHODS: Clinical, biochemical and treatment data was obtained from physicians by using a questionnaire. MTHFR activity was measured in primary fibroblasts; genomic DNA was extracted from cultured fibroblasts. RESULTS: Thirty-three patients (mean age at follow-up 11.4 years; four deceased; median age at first presentation 5 weeks; 17 females) were included. Patients with very low (<1.5%) mean control values of enzyme activity (n = 14) presented earlier and with a pattern of feeding problems, encephalopathy, muscular hypotonia, neurocognitive impairment, apnoea, hydrocephalus, microcephaly and epilepsy. Patients with higher (>1.7-34.8%) residual enzyme activity had mainly psychiatric symptoms, mental retardation, myelopathy, ataxia and spasticity. Treatment with various combinations of betaine, methionine, folate and cobalamin improved the biochemical and clinical phenotype. During the disease course, patients with very low enzyme activity showed a progression of feeding problems, neurological symptoms, mental retardation, and psychiatric disease while in patients with higher residual enzyme activity, myelopathy, ataxia and spasticity increased. All other symptoms remained stable or improved in both groups upon treatment as did brain imaging in some cases. No clear genotype-phenotype correlation was obvious. DISCUSSION: MTHFR deficiency is a severe disease primarily affecting the central nervous system. Age at presentation and clinical pattern are correlated with residual enzyme activity. Treatment alleviates biochemical abnormalities and clinical symptoms partially.
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Homocistinuria/enzimología , Homocistinuria/genética , Metilenotetrahidrofolato Reductasa (NADPH2)/deficiencia , Metilenotetrahidrofolato Reductasa (NADPH2)/genética , Espasticidad Muscular/enzimología , Espasticidad Muscular/genética , Ataxia/genética , Betaína/uso terapéutico , Niño , Femenino , Ácido Fólico/uso terapéutico , Estudios de Asociación Genética/métodos , Homocistinuria/tratamiento farmacológico , Humanos , Discapacidad Intelectual/genética , Masculino , Metionina/uso terapéutico , Espasticidad Muscular/tratamiento farmacológico , Mutación/genética , Fenotipo , Trastornos Psicóticos/tratamiento farmacológico , Trastornos Psicóticos/enzimología , Trastornos Psicóticos/genética , Estudios Retrospectivos , Enfermedades de la Médula Espinal/genética , Vitamina B 12/uso terapéuticoRESUMEN
Exome sequencing of an individual with congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy, and lactic acidosis, all typical symptoms of Sengers syndrome, discovered two nonsense mutations in the gene encoding mitochondrial acylglycerol kinase (AGK). Mutation screening of AGK in further individuals with congenital cataracts and cardiomyopathy identified numerous loss-of-function mutations in an additional eight families, confirming the causal nature of AGK deficiency in Sengers syndrome. The loss of AGK led to a decrease of the adenine nucleotide translocator in the inner mitochondrial membrane in muscle, consistent with a role of AGK in driving the assembly of the translocator as a result of its effects on phospholipid metabolism in mitochondria.
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Cardiomiopatías/enzimología , Catarata/enzimología , Codón sin Sentido , Mitocondrias/enzimología , Proteínas Mitocondriales/deficiencia , Fosfotransferasas (Aceptor de Grupo Alcohol)/deficiencia , Adulto , Alelos , Cardiomiopatías/genética , Catarata/genética , Niño , Exoma , Femenino , Heterocigoto , Humanos , Lactante , Recién Nacido , Masculino , Mitocondrias/genética , Translocasas Mitocondriales de ADP y ATP/genética , Proteínas Mitocondriales/genética , Músculos/metabolismo , Fenotipo , Fosfolípidos/metabolismo , Fosfotransferasas (Aceptor de Grupo Alcohol)/genética , Adulto JovenRESUMEN
The mitochondrial pyruvate oxidation route is a tightly regulated process, which is essential for aerobic cellular energy production. Disruption of this pathway may lead to severe neurometabolic disorders with onset in early childhood. A frequent finding in these patients is acute and chronic lactic acidemia, which is caused by increased conversion of pyruvate via the enzyme lactate dehydrogenase. Under stable clinical conditions, this process may remain well compensated and does not require specific therapy. However, especially in situations with altered energy demands, such as febrile infections or longer periods of fasting, children with mitochondrial disorders have a high risk of metabolic decompensation with exacerbation of hyperlactatemia and severe metabolic acidosis. Unfortunately, no controlled studies regarding therapy of this critical condition are available and clinical outcome is often unfavorable. Therefore, the aim of this review was to formulate expert-based suggestions for treatment of these patients, including dietary recommendations, buffering strategies and specific drug therapy. However, it is important to keep in mind that a specific therapy for the underlying metabolic cause in children with mitochondrial diseases is usually not available and symptomatic therapy especially of severe lactic acidosis has its ethical limitations.
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Acidosis Láctica/tratamiento farmacológico , Acidosis Láctica/fisiopatología , Hipotermia/tratamiento farmacológico , Enfermedades Mitocondriales/metabolismo , Ácido Pirúvico/metabolismo , Niño , Preescolar , Manejo de la Enfermedad , Humanos , Oxidación-ReducciónRESUMEN
Inherited disorders of mitochondrial energy metabolism form a large and heterogeneous group of metabolic diseases. More than 250 gene defects have been reported to date and this number continues to grow. Mitochondrial diseases can be grouped into (1) disorders of oxidative phosphorylation (OXPHOS) subunits and their assembly factors, (2) defects of mitochondrial DNA, RNA and protein synthesis, (3) defects in the substrate-generating upstream reactions of OXPHOS, (4) defects in relevant cofactors and (5) defects in mitochondrial homeostasis. Deficiency of more than one respiratory chain enzyme is a common finding. Combined defects are found in 49 % of the known disease-causing genes of mitochondrial energy metabolism and in 57 % of patients with OXPHOS defects identified in our diagnostic centre. Combined defects of complexes I, III, IV and V are typically due to deficiency of mitochondrial DNA replication, RNA metabolism or translation. Defects in cofactors can result in combined defects of various combinations, and defects of mitochondrial homeostasis can result in a generalised decrease of all OXPHOS enzymes. Noteworthy, identification of combined defects can be complicated by different degrees of severity of each affected enzyme. Furthermore, even defects of single respiratory chain enzymes can result in combined defects due to aberrant formation of respiratory chain supercomplexes. Combined OXPHOS defects have a great variety of clinical manifestations in terms of onset, course severity and tissue involvement. They can present as classical encephalomyopathy but also with hepatopathy, nephropathy, haematologic findings and Perrault syndrome in a subset of disorders.