A case of overlap myoclonic epilepsy with ragged-red fibers-Leigh syndrome associated with mitochondrial DNA 8344A>G mutation / 中华神经科杂志

Overlap myoclonic epilepsy with ragged-red fibers (MERRF)-Leigh syndrome is a rare mitochondrial encephalomyopathy. A case of MERRF-Leigh syndrome associated with mitochondrial DNA 8344A>G (m.8344A>G) mutation was reported in this article. The patient has suffered from the disease since 15-year old with myoclonus, exercise intolerance, ataxia, limb weakness, dysphasia, dyspnea, blurred vision and hearing loss. Magnetic resonance imaging revealed lesions on right thalamus, bilateral medulla and lumbar spinal cord and atrophy of cervical spinal cord. Electromyography showed predominantly axonal damage of both sensory nerve and motor nerve. Histochemical analyses revealed ragged red fibers, ragged blue fibers, succinate dehydrogenase-stronghly reactive vessels and decreased cytochrome oxidase activity. Gene tests demonstrated a high level of m.8344A>G mutation and m. 14484T>C mutation. MERRF-Leigh overlap syndrome with m.8344A>G mutation was rare. Bulbar paralysis following myoclonus is the main clinical symptom.

Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes / myoclonus epilepsy with ragged-red fibers /Leigh overlap syndrome caused by mitochondrial DNA 8344A>G mutation / 北京大学学报(医学版)

OBJECTIVE@#Mitochondrial deoxyribonucleic acid (mtDNA) 8344 A>G (m.8344A>G) mutation is the common mutation associated with mitochondrial myoclonus epilepsy with ragged-red fibers (MERRF) syndrome. Herein we report a rare case with mitochondrial encephalopathy, lactic acidosis and stroke-like episodes/MERRF/Leigh (MELAS/MERRF/Leigh) overlap syndrome caused by m.8344A>G mutation.@*METHODS@#The clinical and imaging data of the patient were collected and an open muscle biopsy was carried out. We further employed molecular genetic analyses to detect mtDNA mutation in the proband and his mother. And then a clinical and neuroimaging follow-up was performed.@*RESULTS@#This patient was a 25-year-old male, who developed exercise intolerance since the age of 6. At age 10, he suffered from acute episodes of hemianopia, and cranial magnetic resonance imaging (MRI) showed occipital stroke-like lesions and cranial magnetic resonance spectroscopy (MRS) revealed a lactate peak corresponding to the lesion. After that the patient presented slowly progressive psychomotor decline. He had myoclonic seizures and cerebellar ataxia since the age of 12. At age 21, he was admitted to our hospital because of confusion and cranial MRI revealed symmetrical lesions in bilateral posterior putamen, thalami and midbrain. Then repeated MRI showed progression of original lesions and new frontal multiple stroke-like lesions. Symptomatic and rehabilitation treatment relieved his condition. Follow-up cranial MRI at age 24 showed the lesions in basal ganglia and thalami diminished, and the midbrain lesions even completely vanished. Muscle pathology indicated the presence of numerous scattered ragged-red fibers (RRF), suggestive of a mitochondrial disorder. Polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP) detected the m.8344A>G mutation of the MT-TK gene encoding mitochondrial transfer RNA for lysine in the patient's blood. Next generation sequencing (NGS) of the whole mitochondrial genome identified that the proportion of m.8344A>G was 90%, and no other mtDNA mutation was detected. Sanger sequencing further identified this mutation both in the proband and his mother's blood, although the mutation load was much lower in his mother's blood with approximately 10% heteroplasmy.@*CONCLUSION@#The present study is the first to describe a patient with m.8344A>G mutation in association with the MELAS/MERRF/Leigh overlap syndrome, which expands the phenotypic spectrum of the m.8344A>G mutation.

Myoclonus epilepsy with ragged-red fibers:a case report and literature review / 北京大学学报(医学版)

SUMMARY To demonstrate the clinical manifestation, diagnosis and treatment of myoclonus epilepsy with ragged-red-fibers ( MERRF) , a case of MERRF was presented with review of the literature. A 4-year-7-month-old girl was diagnosed with MERRF. She had tremor, fatigue and developmental delay for more than 2 years. Laboratory tests showed that the serum and urine lactic acid and pyruvic acid increased significantly. Electroencephalogram showed diffuse and focal spike slow wave and slow wave in right central and parietal regions. Electromyogram showed neurological damage. Gene mutational analysis showed mtDNA 8344 A>G mutation. The mutational rate was 78%. Mitochondrial disease MERRF syndrome was diagnosed. Cocktails therapy with vitamins B1, B6, B12, L-carnitine, and coenzyme Q10 was administra-ted to the patient. MERRF is a rare disease. The diagnosis can be made by gene mutational analysis. Cocktail therapy may slow down the deterioration of the disease. Gene therapy is still experimental.

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.

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.

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.

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.

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.

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.

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.