Identification of causative mutations in patients with Leigh syndrome and MERRF by mitochondrial DNA-targeted next-generation sequencing

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.

When should MERRF (myoclonus epilepsy associated with ragged-red fibers) be the diagnosis? / Quando o diagnóstico deveria ser MERRF (epilepsia mioclônica associada com fibras vermelhas rasgadas)?

Myoclonic epilepsy associated with ragged red fibers (MERRF) is a rare mitochondrial disorder. Diagnostic criteria for MERRF include typical manifestations of the disease: myoclonus, generalized epilepsy, cerebellar ataxia and ragged red fibers (RRF) on muscle biopsy. Clinical features of MERRF are not necessarily uniform in the early stages of the disease, and correlations between clinical manifestations and physiopathology have not been fully elucidated. It is estimated that point mutations in the tRNALys gene of the DNAmt, mainly A8344G, are responsible for almost 90% of MERRF cases. Morphological changes seen upon muscle biopsy in MERRF include a substantive proportion of RRF, muscle fibers showing a deficient activity of cytochrome c oxidase (COX) and the presence of vessels with a strong reaction for succinate dehydrogenase and COX deficiency. In this review, we discuss mainly clinical and laboratory manifestations, brain images, electrophysiological patterns, histology and molecular findings as well as some differential diagnoses and treatments.

Epilepsia mioclônica associada com fibras vermelhas rasgadas (MERRF) é uma rara doença mitocondrial. O critério diagnóstico para MERRF inclui as manifestações típicas da doença: mioclonia, epilepsia generalizada, ataxia cerebelar e fibras vermelhas rasgadas (RRF) na biópsia de músculo. Na fase inicial da doença, as manifestações clínicas podem não ser uniformes, e correlação entre as manifestações clínicas e fisiopatologia não estão completamente elucidadas. Estima-se que as mutações de ponto no gene tRNALys do DNAmt, principalmente a A8344G, sejam responsáveis por quase 90% dos casos de MERRF. As alterações morfológicas na biópsia muscular incluem uma grande proporção de RRF, fibras musculares com deficiência de atividade da citocromo c oxidase (COX) e presença de vasos com forte reação para succinato desidrogenase e deficiência da COX. Nesta revisão, são discutidas as principais manifestações clínicas e laboratoriais, imagens cerebrais, padrões eletrofisiológicos, histológicos e alterações moleculares, bem como, alguns dos diagnósticos diferenciais e tratamentos.

Annual Report on the External Quality Assessment of Diagnostic Genetics in Korea (2013) / 임상검사와정도관리

Quality control for genetic tests has become more important as the test volume and clinical demands increase dramatically. The diagnostic genetics subcommittee of the Korean Association of Quality Assurance for Clinical Laboratories performed two trials for cytogenetics and molecular genetics surveys in 2013. A total of 43 laboratories participated in the cytogenetic surveys, 30 laboratories participated in the fluorescent in situ hybridization surveys, and 122 laboratories participated in the molecular genetics surveys in 2013. Almost all of them showed acceptable results. However, some laboratories had unacceptable results for karyotype nomenclature, detection of complex cytogenetic abnormalities in hematologic neoplasms and constitutional anomalies. The molecular genetics surveys included various tests: Mycobacterium tuberculosis detection, hepatitis B and C virus detection and quantification, human papilloma virus genotyping, gene rearrangement tests for leukaemia and lymphomas, genetic tests for JAK2, fms-related tyrosine kinase 3, Nucleophosmin, cancer-associated genes (KRAS, EGFR and BRAF), hereditary breast and ovarian cancer genes (BRCA1 and BRCA2), Li-Fraumeni syndrome (TP53), Wilson disease (ATP7B), achondroplasia (FGFR3), Huntington disease, spinocerebellar ataxia, spinal and bulbar muscular atrophy, mitochondrial encephalopathy with lactic acidosis and stroke like episodes, myoclonic epilepsy associated with ragged-red fibers, Prader-Willi/Angelman syndrome, Duchenne muscular dystrophy, spinal muscular atrophy, Fragile X syndrome, non-syndromic hearing loss and deafness (GJB2), apolipoprotein E genotyping, methylenetetrahydrofolate reductase genotyping, ABO genotyping and DNA sequence analysis. Molecular genetic surveys showed excellent results for most of the participants. The external quality assessment program for genetic analysis in 2013 was proved to be helpful for continuous education and evaluation of quality improvement.

Genetics of Mitochondrial Myopathies

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.

Clinical Spectrum and Prognostic Factors of Acute Necrotizing Encephalopathy in Children

This study was conducted to investigate the etiology, the clinical characteristics and prognosis of acute necrotizing encephalopathy (ANE) in Korean children. Six children (1 yr to 7 yr) patients with ANE were enrolled. They were diagnosed by clinical and radiological characteristics and their clinical data were retrospectively analyzed. In a search of clinically plausible causes, brain MRI in all patients, mitochondrial DNA studies for mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) and myoclonus epilepsy and ragged red fibers (MERRF) in four patients, and genomic typing on HLA DRB/HLA DQB genes in three patients were performed. All had precedent illnesses and the main initial symptoms included mental change (83%), seizures (50%), and focal deficits (50%). MRI revealed increased T2 signal density in the bilateral thalami and/or the brainstem in all patients. Mitochodrial DNA studies for MELAS and MERRF were negative in those children and HLA-DRB1*1401, HLA-DRB3*0202, and HLA-DQB1*0502 seemed to be significant. A high dose steroid was given to all patients, which seemed to be partly effective except for 2 patients. In conclusion, ANE is relatively rare, but can result in serious neurological complication in children. Early detection and appropriate treatment may lead to a better neurological outcome.

Mutational analysis of whole mitochondrial DNA in patients with MELAS and MERRF diseases

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.

Congenital muscular dystrophy: part I: a review of phenotypical and diagnostic aspects / Distrofia muscular congênita: parte I: revisão dos aspectos fenotípicos e diagnósticos

The congenital muscular dystrophies (CMDs) are a group of genetically and clinically heterogeneous hereditary myopathies with preferentially autosomal recessive inheritance, that are characterized by congenital hypotonia, delayed motor development and early onset of progressive muscle weakness associated with dystrophic pattern on muscle biopsy. The clinical course is broadly variable and can comprise the involvement of the brain and eyes. From 1994, a great development in the knowledge of the molecular basis has occurred and the classification of CMDs has to be continuously up dated. We initially present the main clinical and diagnostic data concerning the CMDs related to changes in the complex dystrophin-associated glycoproteins-extracellular matrix: CMD with merosin deficiency (CMD1A), collagen VI related CMDs (Ullrich CMD and Bethlem myopathy), CMDs with abnormal glycosylation of alpha-dystroglycan (Fukuyama CMD, Muscle-eye-brain disease, Walker-Warburg syndrome, CMD1C, CMD1D), and the much rarer CMD with integrin deficiency. Finally, we present other forms of CMDs not related with the dystrophin/glycoproteins/extracellular matrix complex (rigid spine syndrome, CMD1B, CMD with lamin A/C deficiency), and some apparently specific clinical forms not yet associated with a known molecular mechanism. The second part of this review concerning the pathogenesis and therapeutic perspectives of the different subtypes of CMD will be described in a next number.

As distrofias musculares congênitas (DMCs) são miopatias hereditárias geralmente, porém não exclusivamente, de herança autossômica recessiva, que apresentam grande heterogeneidade genética e clínica. São caracterizadas por hipotonia muscular congênita, atraso do desenvolvimento motor e fraqueza muscular de início precoce associada a padrão distrófico na biópsia muscular. O quadro clínico, de gravidade variável, pode também incluir anormalidades oculares e do sistema nervoso central. A partir de 1994, os conhecimentos sobre genética e biologia molecular das DMCs progrediram rapidamente, sendo a classificação continuamente atualizada. Nesta revisão apresentaremos os principais aspectos clínicos e diagnósticos dos subtipos mais comuns de DMC associados com alterações do complexo distrofina-glicoproteínas associadas-matriz extracelular que são DMC com deficiência de merosina (DMC tipo 1A), DMCs relacionadas com alterações do colágeno VI (DMC tipo Ullrich e miopatia de Bethlem), DMCs com anormalidades de gliocosilação da alfa-distroglicana (DMC Fukuyama, DMC "Muscle-eye-brain" ou MEB, síndrome de Walker-Warburg, DMC tipo 1C, DMC tipo 1D), além da raríssima DMC com deficiência de integrina. Outras formas mais raras de DMC, não relacionadas com o complexo distrofina-glicoproteínas associadas-matriz extracelular também serão apresentadas (DMC com espinha rígida, DMC tipo 1B, DMC com deficiência de lamina A/C) e, finalmente, algumas formas clínicas com fenótipo aparentemente específico que ainda não estão associadas com um defeito molecular definido. A patogenia e as perspectivas terapêuticas dos principais subtipos de DMC serão apresentados em um próximo número, na segunda parte desta revisão.

Multiple Symmetric Lipomatosis with Peripheral Neuropathy: A case report

Multiple symmetric lipomatosis is a rare disorder characterized by massive fatty deposits arranged symmetrically around the neck, shoulder, abdomen and back. It is typically associated with high alcohol consumption and a high prevalence of peripheral neuropathy. The pathogenesis of the syndrome is still unknown, but mitochondrial abnormality or metabolic abnormalities are occasionally found in the affected patients. In our patient, clinical and electrophysiologic signs of a generalized peripheral sensorimotor neuropathy and a multiple bilateral lumbosacral radiculopathy were observed. Sural nerve biopsy demonstrated many small unmyelinated fibers with complete loss of axoplasm and a extensive loss of myelinated fibers. Lipoma biopsy demonstrated non-capsulated mature adipose cells in the subcutaneous tissue. Serum lipid studies were normal. MERRF point mutation of mitochondrial DNA were negative in blood. We reported a case of multiple symmetric lipomatosis and peripheral polyneuropathy with the review of literature.

Mitochondrial Intestinal Pseudo-Obstruction with Neurogenic Bladder Syndrome: Point Mutation at T8356C: A New Mitochondrial Disease?

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.

Neurological mitochondrial cytopathies.

The mitochondrial cytopathies are genetically and phenotypically heterogeneous group of disorders caused by structural and functional abnormalities in mitochondria. To the best of our knowledge, there are very few studies published from India till date. Selected and confirmed fourteen cases of neurological mitochondrial cytopathies with different clinical syndromes admitted between 1997 and 2000 are being reported. There were 8 male and 6 female patients. The mean age was 24.42+/-11.18 years (range 4-40 years). Twelve patients could be categorized into well-defined syndromes, while two belonged to undefined group. In the defined syndrome categories, three patients had MELAS (mitochondrial encephalopathy, lactic acidosis and stroke like episodes), three had MERRF (myoclonic epilepsy and ragged red fibre myopathy), three cases had KSS (Kearns-Sayre Syndrome) and three were diagnosed to be suffering from mitochondrial myopathy. In the uncategorized group, one case presented with paroxysmal kinesogenic dystonia and the other manifested with generalized chorea alone. Serum lactic acid level was significantly increased in all the patients (fasting 28.96+/-4.59 mg%, post exercise 41.02+/-4.93 mg%). Muscle biopsy was done in all cases. Succinic dehydrogenase staining of muscle tissue showed subsarcolemmal accumulation of mitochondria in 12 cases. Mitochondrial DNA study could be performed in one case only and it did not reveal any mutation at nucleotides 3243 and 8344. MRI brain showed multiple infarcts in MELAS, hyperintensities in putaminal areas in chorea and bilateral cerebellar atrophy in MERRF.

Histochemical and Molecular Genetic Study of MELAS and MERRF in Korean Patients

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.

Seizures in myoclonic epilepsy with ragged-red fibers detected by DNA analysis: a case report.

A 19-year-old Thai woman presented with progressive ataxia and generalized tonic-clonic seizures. Later on, she developed status epilepticus. Blood was tested by molecular DNA analysis which showed A8344G mitochondrial DNA mutation associated with myoclonic epilepsy with ragged-red fibers (MERRF). We confirmed this finding in other members of this family. This is an interesting case report in Thailand of MERRF identified to have A-->G transition mutation at nucleotide 8344 of mitochondrial tRNA(lys) gene without ragged-red fibers from histopathologic studies of muscle. Molecular genetic analysis in suspicious cases of mitochondrial disorders is necessary for proper management and genetic counseling.

cytopathies mitochondriales: etude clinique

Mitochondrial myopathy is a group of multisytemic disease, variable in the age at onset, frequency, clinical data, evolution and prognosis. It results from nuclear or mitochondrial DNA mutation or from defective interaction between nuclear and mitochondrial DNA. The transmission of this mitochondrial myopathy is exlusively maternal. Sometimes the mutationns are born in the maternal ovule, or early in the embryonal life. The diagnosis is suspected on clinical manifestations and is confirmed by existence of ragged - red - fibers in the muscular biopsy, and especially, by molecular study which discovers the mutation of mitochondrial DNA. The treatment is often disappointing, however some specific measures are necessary to improve the quality of patients life

Molecular Genetic Diagnosis in Korean Patients with Myoclonic Epilepsy with Ragged Red Fiber (MERRF) Syndrome

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.

Molecular Genetic Diagnosis in Korean Patients with Myoclonic Epilepsy with Ragged Red Fiber (MERRF) Syndrome

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.

Screening for Mitochondrial DNA Mutations of MELAS tRNA Leu(3243), MERRF tRNA Lys(8344) in Korean IDDM Patients / 대한소아내분비학회지

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.

A Case of Myoclonus Epilepsy and Ragged-red Fiber Syndrome

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.

Clinical Manifestations of Mitochondrial Diseases

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.