Sonlicromanol improves neuronal network dysfunction and transcriptome changes linked to m.3243A>G heteroplasmy in iPSC-derived neurons.

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is often caused by an adenine to guanine variant at m.3243 (m.3243A>G) of the MT-TL1 gene. To understand how this pathogenic variant affects the nervous system, we differentiated human induced pluripotent stem cells (iPSCs) into excitatory neurons with normal (low heteroplasmy) and impaired (high heteroplasmy) mitochondrial function from MELAS patients with the m.3243A>G pathogenic variant. We combined micro-electrode array (MEA) measurements with RNA sequencing (MEA-seq) and found reduced expression of genes involved in mitochondrial respiration and presynaptic function, as well as non-cell autonomous processes in co-cultured astrocytes. Finally, we show that the clinical phase II drug sonlicromanol can improve neuronal network activity when treatment is initiated early in development. This was intricately linked with changes in the neuronal transcriptome. Overall, we provide insight in transcriptomic changes in iPSC-derived neurons with high m.3243A>G heteroplasmy, and show the pathology is partially reversible by sonlicromanol.

Metformin delays neurological symptom onset in a mouse model of neuronal complex I deficiency.

Complex I (also known as NADH-ubiquinone oxidoreductase) deficiency is the most frequent mitochondrial disorder present in childhood. NADH-ubiquinone oxidoreductase iron-sulfur protein 3 (NDUFS3) is a catalytic subunit of the mitochondrial complex I; NDUFS3 is conserved from bacteria and essential for complex I function. Mutations affecting complex I, including in the Ndufs3 gene, cause fatal neurodegenerative diseases, such as Leigh syndrome. No treatment is available for these conditions. We developed and performed a detailed molecular characterization of a neuron-specific Ndufs3 conditional KO mouse model. We showed that deletion of Ndufs3 in forebrain neurons reduced complex I activity, altered brain energy metabolism, and increased locomotor activity with impaired motor coordination, balance, and stereotyped behavior. Metabolomics analyses showed an increase of glycolysis intermediates, suggesting an adaptive response to the complex I defect. Administration of metformin to these mice delayed the onset of the neurological symptoms but not of neuronal loss. This improvement was likely related to enhancement of glucose uptake and utilization, which are known effects of metformin in the brain. Despite reports that metformin inhibits complex I activity, our findings did not show worsening a complex I defect nor increases in lactic acid, suggesting that metformin should be further evaluated for use in patients with mitochondrial encephalopathies.

Mitochondrial DNA 10158T>C mutation in a patient with mitochondrial encephalomyopathy with lactic acidosis, and stroke-like episodes syndrome: A case-report and literature review (CARE-complaint).

RATIONALE: Mitochondrial encephalomyopathy with lactic acidosis and stroke- like episodes (MELAS) syndrome is caused by mitochondrial respiratory chain dysfunction and oxidative phosphorylation disorder. It is a rare clinical metabolic disease involved with multiple systems. PATIENT CONCERNS: A 22-year-old patient presented with limb convulsion accompanied by loss of consciousness, headache, partial blindness, blurred vision, and so on. DIAGNOSES: Brain magnetic resonance imaging showed a high-intensity area in bilateral occipital cortex, left parietal lobe and cerebellum on diffusion-weighted imaging. These focus did not distribute as vascular territory. The pathological examination of skeletal muscle revealed several succinate dehydrogenase reactive vessels with overreaction and increased content of lipid droplets in some muscle fibers. Genetic testing showed that the patient carried m.10158T>C mutation. INTERVENTIONS: She was provided with traditional arginine hydrochloride therapy and orally medication of coenzyme Q (10 mg). OUTCOMES: Mitochondrial DNA of blood and hair follicle of patient carried m.10158T>C mutation LESSONS:: For the suspected patients of MELAS syndrome, if the hot-spot mutation test is negative, more detection sites should be selected.

Fatal infantile mitochondrial encephalomyopathy, hypertrophic cardiomyopathy and optic atrophy associated with a homozygous OPA1 mutation.

BACKGROUND: Infantile-onset encephalopathy and hypertrophic cardiomyopathy caused by mitochondrial oxidative phosphorylation defects are genetically heterogeneous with defects involving both the mitochondrial and nuclear genomes. OBJECTIVE: To identify the causative genetic defect in two sisters presenting with lethal infantile encephalopathy, hypertrophic cardiomyopathy and optic atrophy. METHODS: We describe a comprehensive clinical, biochemical and molecular genetic investigation of two affected siblings from a consanguineous family. Molecular genetic analysis was done by a combined approach involving genome-wide autozygosity mapping and next-generation exome sequencing. Biochemical analysis was done by enzymatic analysis and Western blot. Evidence for mitochondrial DNA (mtDNA) instability was investigated using long-range and real-time PCR assays. Mitochondrial cristae morphology was assessed with transmission electron microscopy. RESULTS: Both affected sisters presented with a similar cluster of neurodevelopmental deficits marked by failure to thrive, generalised neuromuscular weakness and optic atrophy. The disease progression was ultimately fatal with severe encephalopathy and hypertrophic cardiomyopathy. Mitochondrial respiratory chain complex activities were globally decreased in skeletal muscle biopsies. They were found to be homozygous for a novel c.1601T>G (p.Leu534Arg) mutation in the OPA1 gene, which resulted in a marked loss of steady-state levels of the native OPA1 protein. We observed severe mtDNA depletion in DNA extracted from the patients' muscle biopsies. Mitochondrial morphology was consistent with abnormal mitochondrial membrane fusion. CONCLUSIONS: We have established, for the first time, a causal link between a pathogenic homozygous OPA1 mutation and human disease. The fatal multisystemic manifestations observed further extend the complex phenotype associated with pathogenic OPA1 mutations, in particular the previously unreported association with hypertrophic cardiomyopathy. Our findings further emphasise the vital role played by OPA1 in mitochondrial biogenesis and mtDNA maintenance.

The UK MRC Mitochondrial Disease Patient Cohort Study: clinical phenotypes associated with the m.3243A>G mutation--implications for diagnosis and management.

BACKGROUND: Population-based studies suggest the m.3243A>G mutation in MTTL1 is the most common disease-causing mtDNA mutation, with a carrier rate of 1 in 400 people. The m.3243A>G mutation is associated with several clinical syndromes including mitochondrial encephalopathy lactic acidosis and stroke-like episodes (MELAS), maternally inherited deafness and diabetes (MIDD) and progressive external ophthalmoplegia (PEO). Many patients affected by this mutation exhibit a clinical phenotype that does not fall within accepted criteria for the currently recognised classical mitochondrial syndromes. METHODS: We have defined the phenotypic spectrum associated with the m.3243A>G mtDNA mutation in 129 patients, from 83 unrelated families, recruited to the Mitochondrial Disease Patient Cohort Study UK. RESULTS: 10% of patients exhibited a classical MELAS phenotype, 30% had MIDD, 6% MELAS/MIDD, 2% MELAS/chronic PEO (CPEO) and 5% MIDD/CPEO overlap syndromes. 6% had PEO and other features of mitochondrial disease not consistent with another recognised syndrome. Isolated sensorineural hearing loss occurred in 3%. 28% of patients demonstrated a panoply of clinical features, which were not consistent with any of the classical syndromes associated with the m.3243A>G mutation. 9% of individuals harbouring the mutation were clinically asymptomatic. CONCLUSION: Following this study we propose guidelines for screening and for the management of confirmed cases.

Neonatal mitochondrial encephaloneuromyopathy due to a defect of mitochondrial protein synthesis.

Mitochondrial diseases are clinically and genetically heterogeneous disorders due to primary mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). We studied a male infant with severe congenital encephalopathy, peripheral neuropathy, and myopathy. The patient's lactic acidosis and biochemical defects of respiratory chain complexes I, III, and IV in muscle indicated that he had a mitochondrial disorder while parental consanguinity suggested autosomal recessive inheritance. Cultured fibroblasts from the patient showed a generalized defect of mitochondrial protein synthesis. Fusion of cells from the patient with 143B206 rho(0) cells devoid of mtDNA restored cytochrome c oxidase activity confirming the nDNA origin of the disease. Our studies indicate that the patient has a novel autosomal recessive defect of mitochondrial protein synthesis.

[Mitochondrial encephalopathy due to complex I deficiency. Brain tissue biopsy findings and clinical course following pharmacological]. / Encefalopatia mitocondrial por deficit del complejo I. Hallazgos en la biopsia cerebral y evolucion clinica tras tratamiento farmacologico.

INTRODUCTION: Mitochondrial encephalomyopathies belong to a heterogeneous group of diseases with a range of neurological symptoms caused by a dysfunction somewhere in the nervous system. They may arise from mutations of the mitochondrial DNA or nuclear DNA in the genes that code for the subunits of the respiratory chain. The results obtained from using different drugs to treat these diseases vary widely. CASE REPORT: A 33-year-old female with a history of migraine with aura, who was admitted to hospital because of epileptic seizures. Neuroimaging tests showed left-side occipital insult and a biopsy study of a sample of brain tissue revealed gliosis and vacuolisation of the white matter. Lactic acid levels in blood were normal. No ragged red fibres were seen in the muscle biopsy, but there was evidence of a complex I deficiency in the respiratory chain. After establishing treatment with coenzyme Q and riboflavin, the patient had no further episodes of neurological disorders. CONCLUSIONS: The absence of elevated levels of lactate, ragged red fibres in the muscle biopsy or the negative results for mutations in the genetic study do not rule out the possible existence of a mitochondrial disease. The gliosis and vacuolisation of the white matter with respect to the neurons that were found in the results of the brain tissue biopsy must lead us to consider a mitochondrial disease.

Additive effects of POLG1 and ANT1 mutations in a complex encephalomyopathy.

MtDNA instability is associated with a wide spectrum of clinical presentations, from dominant or recessive progressive external ophthalmoplegia (PEO) to juvenile-onset spino-cerebellar ataxia and epilepsy (SCAE) or infantile Alpers-Huttenlocher syndrome. We present here the clinical and molecular features of a patient with a clinical presentation characterized initially by PEO with mtDNA multiple deletions lately evolving into a severe neurological syndrome, which included sensory and cerebellar ataxia, peripheral neuropathy, parkinsonism, and depression. This complex phenotype is the result of mutations in two distinct proteins, ANT1 and PolgammaA, which cause additive, deleterious effects on mtDNA maintenance and integrity.

A novel mutation in the mitochondrial tRNA Asn gene associated with a lethal disease.

We describe a lethal mitochondrial disease in a 10-month-old child who presented with encephalomyopathy. Histochemical and electron microscopy examinations of skeletal muscle biopsy revealed abnormal mitochondria associated with a combined deficiency of complexes I and IV. After excluding mitochondrial DNA deletions and depletion, direct sequencing was used to screen for mutation in all transfer RNA (tRNA) genes. A T-to-C substitution at position 5693 in the tRNA(Asn) gene was found in blood and muscle. Microdissection of muscle biopsy and its analysis revealed the highest level of this mutation in cytochrome c oxidase (COX)-negative fibres. We suggest that this novel mutation would affect the anticodon loop structure of the tRNA(Asn) and cause a fatal mitochondrial disease.

Human mitochondrial diseases associated with tRNA wobble modification deficiency.

A growing number of mutations in mitochondrial (mt) tRNA genes have been found to associate with human mitochondrial diseases. Our previous analysis of mutant mt tRNAs isolated from cells derived from patients with mitochondrial diseases revealed the lack of a post-transcriptional taurine-modification at the anticodon wobble uridine in two mt tRNAs bearing typical pathogenic mutations: mt tRNA(Leu(UUR)) with either the MELAS 3243 or 3271 mutation and mt tRNA(Lys) with the MERRF 8344 mutation. We here summarize our recent studies that clarify the molecular basis of the defective mitochondrial translation caused by this wobble modification deficiency. The MERRF mt tRNA(Lys) lacking the wobble modification cannot translate either of its codons (AAA and AAG), while the translational activity of MELAS mt tRNA(Leu(UUR)) lacking wobble modification is more depressed in decoding of UUG codon than UUA codon. These findings suggest that the wobble modification deficiency plays a primary role in the molecular pathogenesis of the MELAS and MERRF mitochondrial diseases.

Clinical phenotype, prognosis and mitochondrial DNA mutation load in mitochondrial encephalomyopathies.

We studied 42 individuals, including 8 patients with either complete or partial syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), 8 patients with either complete or partial syndrome of myoclonic epilepsy with ragged-red fibers (MERRF) and 26 maternal family members who carried either the A3243G or A8344G mutation of mitochondrial DNA (mtDNA). Clinical manifestations and prognosis were followed up in the patients harboring the A3243G or A8344G mutation. The relationship between clinical features and proportions of mutant mtDNAs in muscle biopsies, blood cells and/or hair follicles was studied. In the 8 regularly followed patients with the A3243G mutation, 4 died within 1 month to 7 years due to status epilepticus and/or recurrent stroke-like episodes. Two patients developed marked mental deterioration and 2 remained stationary. All of the patients harboring the A8344G mutation were stable or deteriorated slightly, except for 1 patient who died due to brain herniation after putaminal hemorrhage. The A3243G and A8344G mtDNA mutations were heteroplasmic in the muscle biopsies, blood cells and hair follicles of both the probands and their maternal family members. The mean proportion of A3243G mutant mtDNA in the muscle biopsies of the patients with MELAS syndrome (68.5 +/- 21.3%, range 33-92%) was significantly higher than that of the asymptomatic family members (37.1 +/- 12.6%, range 0-51%). The average proportions of A8344G mutant mtDNA in the muscle biopsies (90.1 +/- 3.9%, range 89-95%) and hair follicles (93.9 +/- 6.4%, range 84-99%) of the patients with MERRF syndrome were also significantly higher than those of the asymptomatic family members (muscle: 40.3 +/- 39.5%, range 1-80%; hair follicles: 51.0 +/- 44.5%, range 0.1-82%). We concluded that measurement of the proportion of mutant mtDNA in muscle biopsies may provide useful information in the identification of symptomatic patients with mitochondrial encephalomyopathies. For patients with the A3243G mutation, the prognosis was related to status epilepticus and the number of recurrent stroke-like episodes and was much worse than for patients with the A8344G mutation of mtDNA, who had stable or slowly deteriorating clinical courses.

[Mitochondrial encephalopathies]. / Encefalomiopatías mitocondriales.

OBJECTIVE: We carry out a review of the current basic genetic, biochemical, clinical, diagnostic and therapeutic aspects of mitochondrial cytopathies due to deficiencies in the mitochondrial respiratory chain complexes, which appear clinically during childhood and/or adolescence. DEVELOPMENT: The clinical description has been divided into two groups: mitochondrial cytopathies secondary to alterations of mitochondrial DNA (mtDNA) and mitochondrial cytopathies secondary to alterations of the nuclear DNA (nDNA); we also consider about the importance of such conditions at this age.