PURPOSE: Mitochondrial diseases are clinically and genetically heterogeneous disorders, which make their exact diagnosis and classification difficult. The purpose of this study was to identify pathogenic mitochondrial DNA (mtDNA) mutations in 2 Korean families with myoclonic epilepsy with ragged-red fibers (MERRF) and Leigh syndrome, respectively. MATERIALS AND METHODS: Whole mtDNAs were sequenced by the method of mtDNA-targeted next-generation sequencing (NGS). RESULTS: Two causative mtDNA mutations were identified from the NGS data. An m.8344A>G mutation in the tRNA-Lys gene (MT-TK ) was detected in a MERRF patient (family ID: MT132), and an m.9176T>C (p.Leu217Pro) mutation in the mitochondrial ATP6 gene (MT-ATP6) was detected in a Leigh syndrome patient (family ID: MT130). Both mutations, which have been reported several times before in affected individuals, were not found in the control samples. CONCLUSION: This study suggests that mtDNA-targeted NGS will be helpful for the molecular diagnosis of genetically heterogeneous mitochondrial diseases with complex phenotypes.
Classification ; Diagnosis ; DNA, Mitochondrial ; Humans ; Leigh Disease* ; MERRF Syndrome* ; Mitochondrial Diseases ; Phenotype

Mitochondrion is an intracellular organelle with its own genome. Its function in cellular metabolism is indispensable that mitochondrial dysfunction gives rise to multisystemic failure. The manifestation is most prominent with tissues of high energy demand such as muscle and nerve. Mitochondrial myopathies occur not only by mutations in mitochondrial genome, but also by defects in nuclear genes or secondarily by toxic insult on mitochondrial replication. Currently curative treatment modality does not exist and symptomatic treatment remains mainstay. Administration of L-arginine holds great promise according to the recent reports. Advances in mitochondrial RNA import might enable a new therapeutic strategy.
Arginine ; Genome ; Genome, Mitochondrial ; MELAS Syndrome ; MERRF Syndrome ; Mitochondria ; Mitochondrial Myopathies ; Muscles ; Ophthalmoplegia, Chronic Progressive External ; Organelles ; RNA

We describe a unique patient with progressive external ophthalmoplegia, intestinal pseudo-obstruction, and neurogenic bladder. Genetic study in this patient shows point mutation at T8356C, the locus known as that of myoclonic epilepsy with ragged-red fibers. To the best of our knowledge, this is the first report of a mitochondrial syndrome consisting of intestinal pseudo-obstruction, neurogenic bladder, and progressive external ophthalmoplegia, point mutation at T8356C. We suggest that this could comprise a new mitochondrial disease rather than a new variant of mitochondrial neurogastrointestinal encephalomyopathy.
Humans ; Intestinal Pseudo-Obstruction* ; MERRF Syndrome ; Mitochondrial Diseases* ; Ophthalmoplegia, Chronic Progressive External ; Point Mutation* ; Urinary Bladder, Neurogenic*

Anticonvulsants ; therapeutic use ; Clonazepam ; therapeutic use ; Female ; Humans ; Levetiracetam ; therapeutic use ; MERRF Syndrome ; drug therapy ; Male ; Myoclonus ; drug therapy

Adult ; DNA, Mitochondrial ; genetics ; Electroencephalography ; Humans ; MERRF Syndrome ; genetics ; Male ; Mitochondrial Myopathies ; genetics ; Mutation ; RNA, Transfer, Asn ; genetics

An A to G mutation at nucleotide 3243 or 8344 of the mitochondrial genome has been associated with insulin dependent diabetes mellitus(IDDM) and noninsulin dependent diabetes mellitus(NIDDM) in some patients whose family members are frequently affected in maternally inherited fashion. The hypothesis is entertained that defective oxidative phosphorylation system(OXPHOS) caused by mitochondrial DNA mutations would hamper the insulin secretion from pancreas beta islet cells, which requires large amount of ATP energy. Recently, a number of study have been reported to examine the frequecy of these mutations in diabetic populations. In this study, efforts have been directed to investigate the frequency of MELAS tRNALeu(3243) and MERRF tRNALys(8344) mutations in 53 Korean IDDM patients. Total genomic DNA extracted from patients' lymphocytes have been amplified using two sets of mitochondrial specific primers to cover the regions of nt 3243 or 8344. PCR-RFLP anlaysis using Apa I for MELAS(3243) or Ban II for MERRF(8344) were utilized to screen the presence of these mutations in 53 IDDM patients. Two positive controls have been directly sequenced to confirm the presence of these mutations. The results showed that none of IDDM patients(0/53) screened carried these mutations. In conclusion, mitochondrial DNA mutations of MELAS(3243) or MERRF(8344) may be very rare causative factor in developing IDDM, though a large number of IDDM patients are needed to be screened.
Adenosine Triphosphate ; Diabetes Mellitus, Type 1* ; DNA ; DNA, Mitochondrial* ; Genome, Mitochondrial ; Humans ; Insulin ; Islets of Langerhans ; Lymphocytes ; Mass Screening* ; MELAS Syndrome* ; MERRF Syndrome* ; Oxidative Phosphorylation ; Pancreas ; RNA, Transfer*

According to the recently published reports about mitochondrial diseasbl the clinical manifestations are more various than expected. There have been no clinical studies covering whole spectrum of mitochond7iral disease except a few case reports in our country. The authors performed this studies to understand the various clinical and laboratory findings of mitochondrial disease and the usefulness of current tools for the diagnosis of mitochondrial diseases. We reviewed retrospectively the clinical, laboratory and pathologic findings of mitochondrial disease. The diagnosis of mitochondrial disease was based on clinical manifestations, 'ragged-red fiber' in Gomori stainging, and/or abnormal mitochondrial morphologies on electron microscopy. Twenty one patients were diagnosed as mitochondrial disease. Their clinical diagnosis included 7 MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes); 3 MERRF (myoclonic epilepsy with ragged red fibers); 2 KSS (Kearns-Sayre syndrome); 7 CPEO (chronic progressive external ophthalmoplegia); and 2 mitochondrial myopathy. The usefulness of electrodiagnostic studies, such as EMG, NCV and FEG, were limited in some patients. The muscle biopsy showed ragged red fibers in 10 of 15 sampled examined. Eleven patients had abnormal serum lactic acid level. The authors found that the mitochondrial disease revealed broad clinical spectrum and clinically available diagnostic tests, such as serum lactate and light microscopic examination showed limited value. Therefore, to evaluate the mitochondrial dysfunction with systemic involvement may be desirable to depend on sensitive and specific methods including succinate dehydrogenase (SDH) staining, electron microscopy and biologic studies of mitochondrial DNA.
Acidosis, Lactic ; Biopsy ; Diagnosis ; Diagnostic Tests, Routine ; DNA, Mitochondrial ; Epilepsy ; Humans ; Lactic Acid ; MELAS Syndrome ; MERRF Syndrome ; Microscopy, Electron ; Mitochondrial Diseases* ; Mitochondrial Myopathies ; Muscular Diseases ; Ophthalmoplegia, Chronic Progressive External ; Retrospective Studies ; Succinate Dehydrogenase

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

Myoclonus epilepsy and ragged-red fiber (MERRF) syndrome is one of the common etiologies of progressive myoclonus epilepsy. The clinical features of MERRF syndrome are myoclonus, seizure, dementia, ataxia, neuropathy, myopathy, deafness, and lipouta. The patients with MERRF syndrome have a point mutation in mitochondrial DNA at 8344 or 8356 nucleotide. We are reporting a patient who developed myoclonus and seizure at the age of eighteen. He later showed cerebellar ataxia, peripheral neuropathy, and cognitive dysfunction. Skeletal muscle biopsy failed to demonstrate ragged-red fibers. He was diagnosed as MERRF syndrome by the mitochondrial DNA analysis. He had 86% mutant mitochondrial genomes (A-)G(8%) mutation) in leukocytes, and his asymptomatic mother had 66%. The absence of ragged-red fibers does not rule out the possibility of MERRF syndrome. Demonstration of mitochondrial DNA mutation is the most convincing method for establishing the diagnosis of MERRF.
Ataxia ; Biopsy ; Cerebellar Ataxia ; Deafness ; Dementia ; Diagnosis ; DNA, Mitochondrial ; Epilepsies, Myoclonic* ; Genome, Mitochondrial ; Humans ; Leukocytes ; MERRF Syndrome ; Mothers ; Muscle, Skeletal ; Muscular Diseases ; Myoclonic Epilepsies, Progressive ; Myoclonus* ; Peripheral Nervous System Diseases ; Point Mutation ; Seizures

PURPOSE: Myoclonic epilepsy with ragged red fiber (MERRF) syndrome is a disease of the mitochondrial encephalomyopathies, characterized by progressive myoclonus (action), epilepsy, cerebellar ataxia, intention tremor, muscle weakness, progressive dementia, sensorineural hearing loss and optic atrophy. Its inheritance is maternally inherited mitochondrial mutation, and its pathologic finding is characterized by ragged red fibers (RRF). Biochemically its defects are diverse. This study was undertaken to investigate the pattern of mitochondrial mutation and characterize the clinical features in Korean patients with MERRF. METHODS: We collected 3 clinically suspected MERRF patients from 2 Korean families who have progressive myoclonus, epilepsy, cerebellar ataxia, intention tremor, muscle weakness, progressive dementia etc. We reviewed their clinical findings, electrophysiologic studies, radiologic findings and pathologic findings, retrospectively. Of the 2 patients (case 1 and case 3) who had undergone muscle biopsy, case 1 showed RRF in modified Gomori trichrome staining, increased mitochondrial number and abnormal inclusion body in EM. To examine the pattern of mitochondrial mutation of these patients, molecular study was carried out in 3 patients, 2 mothers, 2 fathers, and 4 siblings. Their genomic DNAs were isolated from peripheral leukocytes, subsequent PCR-direct nucleotide sequencing and Ban II digestion were followed. RESULTS: All mutations in our cases were A to G point mutations in the tRNALys gene at position 8344. CONCLUSION: We confirmed clinically suspected MERRF patients as MERRF and their mothers and siblings as carriers, on the basis of molecular genetic analysis. This study suggests that the molecular genetic analysis can be utilized to diagnose MERRF patients easily and confirm carriers, especially at the presymptomatic stage before the characteristic pathologic changes appear.
Biopsy ; Cerebellar Ataxia ; Dementia ; Diagnosis* ; Digestion ; DNA ; Epilepsies, Myoclonic* ; Epilepsy ; Fathers ; Hearing Loss, Sensorineural ; Humans ; Inclusion Bodies ; Leukocytes ; MERRF Syndrome ; Mitochondrial Encephalomyopathies ; Molecular Biology* ; Mothers ; Muscle Weakness ; Myoclonus ; Optic Atrophy ; Point Mutation ; Retrospective Studies ; RNA, Transfer, Lys ; Siblings ; Tremor ; Wills