[A case of mitochondrial encephalomyopathy--Mitochondrial myopathy, encephalopathy, lactic acidosis and strokelike episodes (MELAS)].
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Acidosis, Lactic↗
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[Mitochondrial encephalomyopathies].
Mitochondrial encephalomyopathies include various syndromes involving both muscles and the nervous system. They are characterized by morphological and/or functional mitochondrial abnormalities. Relevant histological modifications in muscle are ragged-red fibers with or without cytochrome C oxidase (COX) activity. Neuropathological alterations in the brain are not specific. They consist of spongiosis with or without preferential involvement of territories of "system degeneration", neuronal loss, focal necrosis, capillary proliferation and mineral deposits. Their topographic patterns are characteristic of each syndrome. Mitochondrial encephalomyopathies are due to defects in mitochondrial DNA, sporadic, with maternal inheritance or defects in nuclear DNA with mendelian inheritance. The first group is more frequent including MERRF, MELAS, KEARNS-SAYRE, and some LEIGH syndromes. LEIGH syndrome is also the most frequent in the second group. However, in accordance with the progress in molecular genetics, these syndromes might be reclassified.
Humans↗
Correlative multidisciplinary approach to the study of mitochondrial encephalomyopathies.
Mitochondrial encephalomyopathies can be caused by defects in the mitochondrial respiratory complexes. The clinical phenotypes are quite protean but in many instances a characteristic or suggestive clinical presentation permits a tentative bedside diagnosis. The diagnosis can be verified by laboratory investigations. The major laboratory hallmarks of mitochondrial encephalomyopathies include: ragged red fibers on muscle biopsy, a specific defect or deficiency in a mitochondrial respiratory enzyme complex, mtDNA abnormalities, reduced anaerobic threshold by bicycle ergometry, impaired cellular energy state by MRS and characteristic brain imaging abnormalities. Monitoring of some of these parameters along with the clinical phenotype will aid in the evaluation of therapeutic trials.
Brain Diseases↗
Electrophysiological analysis of cognitive slowing in subjects with mitochondrial encephalomyopathy.
Mitochondrial encephalomyopathies (MEs) are multisystemic inherited disorders affecting tissues with high energy requirement such as the muscle, retina and central nervous system. Progressive external ophthalmoplegia and myopathy are the most common features in adults, and cognitive impairment is rare. In many neurodegenerative disorders, ERPs have been effectively performed to record cognitive slowing on tasks with different amount of information. To analyze the evidence for possible cognitive slowing, a standard auditory oddball paradigm with a button-press response was applied. Participants were 11 non-demented patients affected by mitochondrial encephalomyopathy and 14 age-matched normal controls. This hypothesis was tested using two tasks of different difficulty (pure tone vs. phonetic stimuli). Reaction time (RT), performance (P) and event-related potentials (ERPs) were measured. RT and P were not significantly different between the groups. Patients showed significantly increased N2 latency and reduced P3 amplitude on both tasks. No difference was found in pure tone and phonetic task conditions. Results were interpreted as electrophysiological signs of cognitive slowing--particularly in relation to stimulus evaluation--irrespective of sensory problems, response selection and cognitive load. These findings suggest that in ME patients, there may be a possible dysfunction of neural mechanisms underlying cognitive events and ERP generation.
Acoustic Stimulation↗
Growth hormone therapy may benefit protein metabolism in mitochondrial encephalomyopathy.
Mitochondrial encephalomyopathy is a genetic disorder for which there is at present no cure. Conventional treatment regimes may not be effective in preventing weight loss and muscle wasting in many patients. Recombinant human GH has been shown to have anabolic effects on protein metabolism and to reduce muscle wasting in various diseases. We have treated a patient known to have myoclonus, epilepsy with ragged red fibres (MERRF) with a high protein diet for 1 month followed by a high protein diet and GH therapy for 1 month. To assess the benefit of these treatments the patient underwent whole body protein turnover, myometric and body composition studies at baseline, following the high protein diet (100 g/day) and following GH therapy. Whole body protein synthesis (and protein breakdown) increased following a high protein intake and was further enhanced by treatment with GH and in a high protein diet. Body composition did not change significantly following treatment with either the high protein diet or GH but there was an improvement in muscle performance following GH treatment. Mitochondrial encephalomyopathy, a wasting disorder, may be a disease in which the known protein anabolic effect of GH may have a therapeutic benefit.
Body Composition↗
[Comments on anesthesia procedures in mitochondrial encephalomyopathy].
Mitochondrial encephalomyopathies (MEMP) are rare diseases caused by a disturbance of the mitochondrial chain of respiration. This prevents pyruvate from being completely integrated into the tricarboxylic acid (Krebs') cycle, and hence there is an accumulation of lactate. Histologically this is marked by the appearance of "ragged red fibres" in the light microscope which, in the electron microscope, are eventually recognised as typical accumulations of pathological mitochondria. The clinical pattern can vary greatly and ranges from ophthalmoplegia via mainly myopathic to encephalopathic forms. The pattern of signs and symptoms enables subclassification into three main syndromes (10): The Kearns-Sayre syndrome (KSS), "myoclonus epilepsy with ragged red fibres syndrome" (MERRF) and "mitochondrial myopathy, encephalopathy, lactic acidosis and strokelike episodes syndrome" (MELAS). Intermediate types, however, are frequent. Furthermore, quite a large number of other syndromes such as the "Toni-Fanconi-Debré syndrome" can be classified among the group of mitochondrial encephalomyopathies.--The patient must be classified as a risk patient. Disturbances of cardiac conduction may require a transient or permanent pacemaker. Increase in oxygen requirement must be avoided to prevent increase in lactate levels and development of lactate acidosis. The severity of the myopathy makes it necessary to exercise caution in the use of benzodiazepines and long-term relaxants. When using local anaesthetics one should consider both their negative dromotropism and the resulting reduction of the epileptic threshold. There is a relative contraindication for spinal and epidural anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)
Anesthesia, General↗
Mitochondrial encephalomyopathies.
Mitochondrial encephalomyopathies are neurodegenerative disorders characterized by ragged-red myopathy and encephalopathy, which are recognized with increasing frequency. This article presents the clinical features; pertinent historical, biochemical, and genetic aspects; evaluation; and treatment of mitochondrial encephalomyopathies of childhood and the adult years.
Central Nervous System Diseases↗
Mitochondrial encephalomyopathy.
Mitochondrial encephalomyopathy is a disease based on multisystemic mitochondrial dysfunction. Pathologic, biochemical and molecular genetic approaches to the disease have revealed the complex features of the phenotype and its relationship to the genotype. Last decade's great success of the mtDNA study must move research of the disease into the next phase.
DNA, Mitochondrial↗
[Mitochondrial encephalomyopathies].
Mitochondrial Encephalomyopathies are primary disorders of energy metabolism recently described. They are the result of mitochondrial abnormalities with a wide spectrum of syndromes implying a multisystemic but predominantly muscular and cerebral involvement. Biochemical, histological, imagiologic and clinical features of the three well known mitochondrial syndromes (MERRF, MELAS and KSS) are described, as well as the mitochondrial genetics and maternal inheritance pattern.
Energy Metabolism↗
Mitochondrial encephalomyopathies.
Mitochondrial encephalomyopathies are diseases caused by defective oxidative phosphorylation (OXPHOS), and affect the nervous system and/or skeletal muscle. They have emerged as a major entity among the neurometabolic diseases of childhood with an incidence of 1 in 11,000 children, and also have a high prevalence in adults. The first pathogenic mutation of human mitochondrial DNA (mtDNA) was discovered in 1988. Since then more than 100 mutations of mtDNA have been reported, including point mutations of genes encoding transfer RNA, ribosomal RNA, and proteins, as well as large-scale deletions. The first nuclear-DNA gene mutation causing OXPHOS disease was described in 1995. Mutations in nuclear genes may affect the respiratory chain by various mechanisms. Pathogenic mutations of nuclear-DNA-encoded subunits of complex I and II have been demonstrated as have mutations of respiratory chain assembly proteins. Several nuclear genes associated with mtDNA maintenance have been found to be associated with mitochondrial disorders since mutations in these genes predispose to multiple mtDNA deletions and/or reduced copy number of mtDNA. The genotype-phenotype correlation is not yet entirely clear, but new animal models will enhance our ability to study the pathophysiology of OXPHOS disorders.
Animals↗
A mutation in the tRNA(Leu)(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies.
Mitochondrial encephalomyopathies are usually divided into three distinct clinical subgroups: (1) mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS); (2) myoclonus epilepsy associated with ragged-red fibres (MERRF); and (3) chronic progressive external ophthalmoplegia (CPEO) including Kearns-Sayre syndrome. Large deletions of human mitochondrial DNA and a transition mutation at the mitochondrial transfer RNALys gene give rise to CPEO including Kearns-Sayre syndrome and MERRF, respectively. Here we report an A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNA(Leu)(UUR) that is specific to patients with MELAS. Because this mutation creates an ApaI restriction site, we could perform a simple molecular diagnostic test for the disease. The mutation was present in 26 out of 31 independent MELAS patients and 1 out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested. Southern blot analysis confirmed that the mutant DNA always coexists with the wild-type DNA (heteroplasmy).
Base Sequence↗
Apoptosis in mitochondrial encephalomyopathies with mitochondrial DNA mutations: a potential pathogenic mechanism.
Mitochondrial encephalomyopathies caused by mitochondrial DNA (mtDNA) defects are a genetically and phenotypically heterogeneous group of disorders. The site, percentage and distribution of mutations do not explain the overall clinical heterogeneity that is found. Apoptosis (programmed cell death) is an evolutionarily conserved mechanism that is essential for tissue development and homeostasis. Dysregulation of apoptosis has been implicated in the pathogenesis of various human diseases, such as cancer and autoimmune and neurodegenerative disorders. Recent in vitro evidence has indicated the central role of mitochondria in the apoptotic process. We investigated the occurrence of apoptosis in muscle biopsies of 36 patients carrying different mtDNA mutations and four patients with inclusion body myositis and mitochondrial abnormalities. Apoptotic features, mainly localized in cytochrome c oxidase-negative fibres, were observed in muscle fibres of patients carrying a high percentage of single mtDNA deletions (>40%) and of tRNA point mutations (>70%). By contrast, no apoptotic changes were observed in inclusion body myositis and in patients carrying mutations of mtDNA structural genes. Our study suggests that apoptosis is not simply a means whereby cells with dysfunctional mitochondria are eliminated, but that it seems to play a role in the pathogenesis of mitochondrial disorders associated with mtDNA defects affecting mitochondrial protein synthesis. The imbalance and relative abundances of nuclear-encoded and mtDNA-encoded subunits may favour cytochrome c inactivation and release. Cytochrome c, together with respiratory chain dysfunction, could activate apoptotic pathways that, in turn, inhibit the rate of mitochondrial translation and the importation of nuclear-encoded mitochondrial protein precursors. This vicious circle may amplify the biochemical defects and tissue damage and contribute to the modulation of clinical features.
Adolescent↗
Mitochondrial encephalomyopathies.
Mitochondrial diseases are uniquely interesting from a genetic point of view because mitochondria contain their own DNA (mtDNA) and are capable of synthesizing a small but vital set of proteins, all of which are components of respiratory chain complexes. Numerous mutations in mtDNA have been described in the past 5 years, and, it is, therefore, important for the clinician to keep in mind both some characteristic clinical presentations and, more importantly, some basic principles of "mitochondrial genetics," including heteroplasmy, the threshold effect, mitotic segregation, and maternal inheritance. The vast majority of mitochondrial proteins are encoded by nuclear DNA (nDNA) and have to be imported from the cytoplasm into mitochondria through a complex translocation machinery, which is also under the control of the nuclear genome. In addition, nDNA encodes several factors that control mtDNA replication, transcription, and translocation. Mitochondrial diseases due to mutations in nDNA are transmitted as mendelian traits and fall into three categories: (1) alterations of mitochondrial proteins; (2) alterations of mitochondrial protein importation; and (3) alterations of intergenomic communication. The first group of disorders can be further classified on the basis of the biochemical area affected, including defects of transport, defects of substrate utilization, defects of the Krebs cycle, defects of oxidation/phosphorylation coupling, and defects of the respiratory chain. The second group includes only few well-documented disorders but will certainly expand in the near future. The third group includes two conditions, an autosomal dominant form of progressive external ophthalmoplegia associated with multiple mtDNA deletions, and a quantitative defect of mtDNA (mtDNA depletion) causing severe infantile myopathy or hepatopathy.
Chromosome Deletion↗
[Mitochondrial encephalomyopathies and mitochondrial DNA].
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DNA, Mitochondrial↗
Effectiveness of creatine monohydrate in mitochondrial encephalomyopathies.
The mitochondrial encephalomyopathies are chronic progressive disorders affecting predominantly the neuromuscular system. Symptoms are induced by insufficient energy supply resulting from a deficiency of oxidative phosphorylation. We studied one male and four female patients with genetically proven mitochondrial encephalomyopathy. Their ages ranged from 7 to 19 years (two with Kearns-Sayre syndrome, one patient with neuronal muscle weakness, ataxia, and retinitis pigmentosa syndrome, and two patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes), using a retrospective study method. We studied the effect of creatine supplementation (0.08 g-0.35 g/kg body weight/day; 9 months to 4 years, 10 months) and measured skeletal muscle power analysis (bicycle ergometer). After creatine supplementation all patients demonstrated an increase in their maximum performance (W) (+4% - +30%; mean: +12.1%). These results indicate an improved aerobic oxidative function of mitochondria after creatine administration in patients with mitochondrial encephalomyopathies. Continuous physical exercise was improved to a greater extent than instantaneous activity.
Adolescent↗
99mTc-HMPAO brain single photon emission computerized tomography in mitochondrial encephalomyopathies.
BACKGROUND: Mitochondrial encephalomyopathies are heterogeneous diseases with common clinical features of muscle and/or the central nervous system. Although molecular and histological diagnoses have been established, imaging modalities for the functioning evaluation of these patients are still obscure. In this study, we tried to use 99mTc-HMPAO brain SPECT images to analyze various mitochondrial encephalomyopathies. METHODS: We examined 99mTc-HMPAO Brain SPECT studies of 15 patients with various types of mitochondrial encephalomyopathy (3 Leber's hereditary optic neuropathy (LHON), 4 Kearns-Sayre syndrome (KSS), 4 mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), 3 myoclonic epilepsy and ragged-red fiber disease (MERRF), and 1 Leigh syndrome), diagnosed by molecular studies. RESULTS: The results of our studies show obviously decreased radiotracer accumulation in the parieto-temporal regions after stroke-like episodes in patients with MELAS and MERRF: Relatively diminished brain perfusion in patients with KSS is noted, probably secondary to severe encephalomyopathy or subdural effusion. However, there seems to be no significant correlation between the clinical manifestations and the imaging findings in LHON and Leigh. CONCLUSIONS: 99mTc-HMPAO Brain SPECT is useful in the diagnosing and assessment of the progress of MERRF, MELAS and KSS. However, its role in LHON and Leigh syndrome seems to be debatable.
Adult↗
[A case of mitochondrial encephalomyopathy (MELAS)].
Mitochondrial encephalomyopathy is a hereditary syndrome showing impairment of muscle and the central nervous system. In this disorder, the following three syndromes have been identified on the basis of characteristic symptoms: Kearns-Sayre syndrome (KSS), mitochondrial encephalomyopathy with lactic acidosis, and stroke-like episodes (MELAS), and myotonic epilepsy with ragged-red fibers (MERRF). In this report, we describe a case of mitochondrial encephalomyopathy with renal disease. A 25-year-old man was referred to our hospital in May, 1992 for evaluation of long-standing proteinuria. He had a small stature, exotropia and no pretibial edema. No mental retardation was observed. Urinary protein excretion was 2.0 g/day and urine sugar was negative. Laboratory examination revealed a serum urea nitrogen 19 mg/dl, and a creatinine value of 1.5 mg/dl. Creatinine clearance was 45.8 ml/min. His serum and spinal fluid lactate value were elevated. Biopsied muscle showed an absence of ragged-red fibers, and the presence of an A-to-G point mutation at nucleotide pari 3243 in the mitochondrial tRNA(Leu(UUR)) in peripheral blood leucocytes. He was thought to have MELAS. On the renal biopsy specimens, light microscopic examinations showed minor glomerular abnormalities with two glomerular collapses and tubulo-interstitial damage. Electron microscopic examinations showed partial thickening of the glomerular basement membrane. We report here this rare case of MELAS with renal disease, and also review seventeen cases of mitochondrial encephalopathy associated with renal disease. The existence of a relationship between mitochondrial disorder and renal damage remains obscure.
Adult↗
Progressive sensorineural hearing loss in children with mitochondrial encephalomyopathies.
OBJECTIVE: Mitochondrial disorders are responsible for a variety of neurological syndromes. Specific mitochondrial DNA mutations have been identified recently in some of these rare disorders. Clinical symptoms may occur in different organs to various extent; often they are associated with progressive hearing loss. The aims of this study were to determine incidence, onset, and characteristics of hearing loss in children with mitochondrial encephalomyopathies and to investigate a possible correlation between the degree of hearing loss and neurological symptoms. In addition, we investigated the prognostic value of hearing loss as a predictor of the disease. STUDY DESIGN: From August 1992 to September 1998, 29 patients ranging in age from 5 to 23 years (mean years) were studied. These children were hospitalized for diagnostic purposes in the neuropediatric department. METHODS: The mitochondrial disorder was diagnosed by clinical and laboratory testings, including analysis of the mtDNA. Audiological evaluation consisted of measurements of pure-tone and speech audiometry, tympanometry, and acoustic refle- threshold testing, auditory brainstem response, and evoked as well as distortion-product otoacoustic emissions. RESULTS: A sensorineural hearing loss was identified in 12 children. Three of these were diagnosed as having classic Kearns-Sayre syndrome; five as having multisystem KSS; two as having the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); one as having KSS-MELAS overlap syndrome; and one as having Friedreich ataxia. Longitudinal testing was performed in seven children, and in all of them a progression of the hearing loss could be demonstrated. Audiological test results in all 12 children suggested cochlear as well as retrocochlear origin of the hearing loss presenting independently from the severity of hearing impairment. No correlation between the characteristics and degrees of hearing loss and the number and severity of clinical neurological symptoms could be found. CONCLUSIONS: The present study demonstrated a high incidence (42%) of sensorineural hearing loss in children with mitochondrial encephalomyopathies. The progressive nature of the hearing impairment was confirmed by a significant correlation between the duration in years and severity of hearing loss in the children. The hearing loss does not have a prognostic value for the progression of the disorder. Based on our findings, we recommend regular audiometric examinations in patients with mitochondrial disorders.
Acoustic Impedance Tests↗