DNA, Mitochondrial ; genetics ; Humans ; MELAS Syndrome ; diagnosis ; diagnostic imaging ; genetics ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Mutation ; genetics

Mitochondrial diseases are maternally inherited heterogeneous disorders that are primarily caused by mitochondrial DNA (mtDNA) mutations. Depending on the ratio of mutant to wild-type mtDNA, known as heteroplasmy, mitochondrial defects can result in a wide spectrum of clinical manifestations. Mitochondria-targeted endonucleases provide an alternative avenue for treating mitochondrial disorders via targeted destruction of the mutant mtDNA and induction of heteroplasmic shifting. Here, we generated mitochondrial disease patient-specific induced pluripotent stem cells (MiPSCs) that harbored a high proportion of m.3243A>G mtDNA mutations and caused mitochondrial encephalomyopathy and stroke-like episodes (MELAS). We engineered mitochondrial-targeted transcription activator-like effector nucleases (mitoTALENs) and successfully eliminated the m.3243A>G mutation in MiPSCs. Off-target mutagenesis was not detected in the targeted MiPSC clones. Utilizing a dual fluorescence iPSC reporter cell line expressing a 3243G mutant mtDNA sequence in the nuclear genome, mitoTALENs displayed a significantly limited ability to target the nuclear genome compared with nuclear-localized TALENs. Moreover, genetically rescued MiPSCs displayed normal mitochondrial respiration and energy production. Moreover, neuronal progenitor cells differentiated from the rescued MiPSCs also demonstrated normal metabolic profiles. Furthermore, we successfully achieved reduction in the human m.3243A>G mtDNA mutation in porcine oocytes via injection of mitoTALEN mRNA. Our study shows the great potential for using mitoTALENs for specific targeting of mutant mtDNA both in iPSCs and mammalian oocytes, which not only provides a new avenue for studying mitochondrial biology and disease but also suggests a potential therapeutic approach for the treatment of mitochondrial disease, as well as the prevention of germline transmission of mutant mtDNA.
Animals ; DNA, Mitochondrial ; genetics ; Humans ; Induced Pluripotent Stem Cells ; cytology ; metabolism ; MELAS Syndrome ; genetics ; Male ; Mice ; Microsatellite Repeats ; genetics ; Mitochondria ; genetics ; metabolism ; Mutation ; genetics

OBJECTIVEMitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a progressive, multisystem affected mitochondrial disease associated with a number of disease-related defective genes. MELAS has unpredictable presentations and clinical course, and it can be commonly misdiagnosed as encephalitis, cerebral infarction, or brain neoplasms. This review aimed to update the diagnosis progress in MELAS, which may provide better understanding of the disease nature and help make the right diagnosis as well.

DATA SOURCESThe data used in this review came from published peer review articles from October 1984 to October 2014, which were obtained from PubMed. The search term is "MELAS".

STUDY SELECTIONInformation selected from those reported studies is mainly based on the progress on clinical features, blood biochemistry, neuroimaging, muscle biopsy, and genetics in diagnosing MELAS.

RESULTSMELAS has a wide heterogeneity in genetics and clinical manifestations. The relationship between mutations and phenotypes remains unclear. Advanced serial functional magnetic resonance imaging (MRI) can provide directional information on this disease. Muscle biopsy has meaningful value in diagnosing MELAS, which shows the presence of ragged red fibers and mosaic appearance of cytochrome oxidase negative fibers. Genetic studies have reported that approximately 80% of MELAS cases are caused by the mutation m.3243A>G of the mitochondrial transfer RNA (Leu (UUR)) gene (MT-TL1).

CONCLUSIONSMELAS involves multiple systems with variable clinical symptoms and recurrent episodes. The prognosis of MELAS patients depends on timely diagnosis. Therefore, overall diagnosis of MELAS should be based on the maternal inheritance family history, clinical manifestation, and findings from serial MRI, muscle biopsy, and genetics.

Humans ; MELAS Syndrome ; diagnosis ; genetics ; Magnetic Resonance Imaging

OBJECTIVETo delineate the characteristics of the clinical manifestation, pathology of skeletal muscle and gene mutations of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episode (MELAS) in children.

METHODThe clinical manifestation, laboratorial data, brain images, muscle pathology and mitochondrial gene mutations were analyzed in 24 patients with MELAS who were diagnosed in Department of Pediatrics, Peking University First Hospital. Their prognosis was evaluated by following up.

RESULTSymptoms of central nervous system such as stroke-like episodes, vomiting, convulsion and headache were present in all the 24 cases. Nine cases had the symptoms of myopathy. Twenty cases had developmental delay. Short stature, being thin and hairy was very common in these cases. Serum lactate level increased in all the cases, pyruvate increased in 17 cases. Elevated CSF lactate was found in 2 cases. Magnetic resonance imaging (MRI) was performed on 24 cases, out of them 23 were abnormal. The lesions mainly involved cerebral lobes. Occipital lobe was the most common site of lesions. Computed tomography (CT) was performed on 13 cases, low density lesions were present in 10 cases, basal ganglia calcifications in 5 cases. Muscle biopsy was performed on 8 cases, ragged-red fibers (RRF) were found in 4/8 cases, and abnormal accumulation of mitochondria were found in 3/8 cases. The mtDNA gene mutational analysis showed A3243G mutation in these patients. The mutation rates varied from 11.6% to 75.0%. The same mutation were found in 4/5 mothers who had the genetic tests, and the mutation rates of the mothers varied from 15.0% to 23.6%. The clinical information of 11 cases was available through recent following up. Three cases died, the others had some degrees of mental retardation.

CONCLUSIONChildren with MELAS had various clinical manifestations. Central nervous system and skeletal muscle were usually involved. Short stature and hypertrichosis were common signs. The prognosis of this disease was disappointing. mtDNA A3243G was the most common mutation in MELAS. Fully understanding the characteristics of its clinical manifestation, laboratory tests, brain image, muscle pathology and molecular features can be helpful to the early diagnosis and treatment.

Acidosis, Lactic ; blood ; Adolescent ; Brain ; diagnostic imaging ; pathology ; Child ; Child, Preschool ; DNA Mutational Analysis ; DNA, Mitochondrial ; genetics ; Electroencephalography ; Female ; Follow-Up Studies ; Humans ; Infant ; MELAS Syndrome ; diagnosis ; genetics ; pathology ; Magnetic Resonance Imaging ; Male ; Muscle, Skeletal ; diagnostic imaging ; pathology ; Point Mutation ; Pyruvic Acid ; blood ; Stroke ; diagnostic imaging ; genetics ; pathology ; Syndrome ; Tomography, X-Ray Computed

Mitochondrial diseases are clinically and genetically heterogeneous disorders, which make the exact diagnosis and classification difficult. The purpose of this study was to identify pathogenic mtDNA mutations in 61 Korean unrelated families (or isolated patients) with MELAS or MERRF. In particular, the mtDNA sequences were completely determined for 49 patients. From the mutational analysis of mtDNA obtained from blood, 5 confirmed pathogenic mutations were identified in 17 families, and 4 unreported pathogenically suspected mutations were identified in 4 families. The m.3243A>G in the tRNA(Leu(UUR)) was predominantly observed in 10 MELAS families, and followed by m.8344A>G in the tRNA(Lys) of 4 MERRF families. Most pathogenic mutations showed heteroplasmy, and the rates were considerably different within the familial members. Patients with a higher rate of mutations showed a tendency of having more severe clinical phenotypes, but not in all cases. This study will be helpful for the molecular diagnosis of mitochondrial diseases, as well as establishment of mtDNA database in Koreans.
Adolescent ; Adult ; Amino Acid Sequence ; Asian Continental Ancestry Group/genetics ; Base Sequence ; DNA Mutational Analysis ; DNA, Mitochondrial/analysis/*genetics ; Female ; Humans ; MELAS Syndrome/diagnosis/*genetics ; MERRF Syndrome/diagnosis/*genetics ; Male ; Middle Aged ; Molecular Diagnostic Techniques ; Pedigree ; Polymorphism, Single Nucleotide ; Sequence Homology ; Young Adult

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a genetically heterogeneous mitochondrial disorder with variable clinical symptoms. Here, from the sequencing of the entire mitochondrial genome, we report a Korean MELAS family harboring two homoplasmic missense mutations, which were reported 9957T>C (Phe251Leu) transition mutation in the cytochrome c oxidase subunit 3 (COX3) gene and a novel 13849A>C (Asn505His) transversion mutation in the NADH dehydrogenase subunit 5 (ND5) gene. Neither of these mutations was found in 205 normal controls. Both mutations were identified from the proband and his mother, but not his father. The patients showed cataract symptom in addition to MELAS phenotype. We believe that the 9957T>C mutation is pathogenic, however, the 13849A>C mutation is of unclear significance. It is likely that the 13849A>C mutation might function as the secondary mutation which increase the expressivity of overlapping phenotypes of MELAS and cataract. This study also demonstrates the importance of full sequencing of mtDNA for the molecular genetic understanding of mitochondrial disorders.
Adult ; Asian Continental Ancestry Group ; DNA Mutational Analysis ; DNA, Mitochondrial/analysis/*genetics ; Electron Transport Complex I/*genetics ; Electron Transport Complex IV/*genetics ; Female ; Humans ; Korea ; MELAS Syndrome/*genetics ; Male ; Middle Aged ; Mitochondrial Proteins/*genetics ; *Mutation, Missense ; Pedigree ; Polymorphism, Genetic

Adult ; DNA, Mitochondrial ; genetics ; Female ; Humans ; MELAS Syndrome ; genetics ; pathology ; Male ; Middle Aged ; Muscles ; pathology ; Mutation

OBJECTIVETo discuss the clinical characteristics associated with mitochondrial DNA A3243G mutation.

METHODSClinical manifestations as well as results of brain CT and/or MRI scanning, blood level of lactic acid and muscle biopsy results of 25 mitochondrial encephalomyopathies patients whose A3243G mutations were analyzed.

RESULTSAlthough all of the 25 patients carried mtDNA A3243G point mutation, their clinical manifestations varied greatly. Among them, there were 19 cases of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), 2 cases of encephalopathies which could not be classified into any specific type, 2 cases of floppy infants, one case of Kearns-Sayer syndrome (KSS) and one case of mitochondrial entero-myopathy. Most patients showed abnormal cranial radiological findings and ragged-red-fibers on muscle biopsies. Elevation of blood lactic acid was notably found in all of the 25 patients.

CONCLUSIONSSignificant variations in clinical manifestation and brain images are the prominent features in patients with A3243G mutation. Mitochondrial diseases should be considered in patients with multiple organ involvement and elevated serum lactic acid mtDNA mutation examination is necessary for the diagnosis of mitochondrial diseases.

Adolescent ; Adult ; Child ; Child, Preschool ; DNA, Mitochondrial ; genetics ; Female ; Humans ; Infant ; Kearns-Sayre Syndrome ; blood ; genetics ; Lactic Acid ; blood ; MELAS Syndrome ; blood ; genetics ; Male ; Mitochondrial Encephalomyopathies ; blood ; genetics ; Muscle Hypotonia ; blood ; genetics ; Phenotype ; Point Mutation

The importance of quality control for dramatically growing genetic tests continues to be emphasized with increasing clinical demands. Diagnostic genetics subcommitee of KSQACP performed two trials for cytogenetic study in 2002. Cytogenetic surveys were performed by 33 laboratories and answered correctly in most laboratories except some problems in nomenclature and analysis for mosaicism and cytogenetics of neoplasia. The molecular genetic test surveys include M. tuberculosis, HCV, HBV, leukemia/lymphoma, ABO genotyping, ApoE genotyping, spinocerebellar ataxia (SCA), spinal muscular atrophy (SMA), and mitochondrial encephalomyopathy, lactic acidosis, and stroke like episodes (MELAS). HBV, SCA, SMA, MELAS tests were the first challenge of the genetic survey. Molecular genetic survey showed excellent results in most participants, however, ABO genotyping tests should be improved by new methods in a few laboratories. External quality assessment program for diagnostic genetics could be helpful to give participants many chances of continuous education and of interesting case materials.
Acidosis, Lactic ; Apolipoproteins E ; Cytogenetics ; Education ; Genetics* ; Korea* ; MELAS Syndrome ; Mitochondrial Encephalomyopathies ; Molecular Biology ; Mosaicism ; Muscular Atrophy, Spinal ; Quality Control ; Spinocerebellar Ataxias ; Stroke ; Tuberculosis

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) and myoclonic epilepsy and raggedred fibers (MERRF) are rare disorders caused by point mutation of the tRNA gene of the mitochondrial genome. To understand the pathogenetic mechanism of MELAS and MERRF, we studied four patients. Serially sectioned frozen muscle specimens with a battery of histochemical stains were reviewed under light microscope and ultrastructural changes were observed under electron microscope. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was performed and the tRNA genes were sequenced to confirm mutations. In two patients with MELAS, strongly succinyl dehydrogenase positive blood vessels (SSVs) and many cytochrome oxidase (COX) positive raggedred fibers (RRFs) were observed, and A3243G mutations were found from the muscle samples. In two patients with MERRF, neither SSV nor COX positive RRFs were seen and A8344G mutations were found from both muscle and blood samples. In the two MERRF families, the identical mutation was observed among family members. The failure to detect the mutation in blood samples of the MELAS suggests a low mutant load in blood cells. The histochemical methods including COX stain are useful for the confirmation and differentiation of mitochondrial diseases. Also, molecular biological study using muscle sample seems essential for the confirmation of the mtDNA mutation.
Adolescent ; Adult ; Electron Transport Complex IV/metabolism ; Female ; Humans ; Korea ; MELAS Syndrome/*genetics/metabolism/*pathology ; MERRF Syndrome/*genetics/metabolism/*pathology ; Male ; Pedigree ; Polymerase Chain Reaction/methods ; Polymorphism, Restriction Fragment Length ; RNA, Transfer ; Sequence Analysis, DNA