Sporadic MERRF/MELAS overlap syndrome associated with the 3243 tRNALeu(UUR) mutation of mitochondrial DNA

We studied a patient with a mitochondrial encephalomyopathy characterized by the presence of all the cardinal features of both myoclonic epilepsy and ragged-red fibers (MERRF) and mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndromes. Muscle biopsy showed ragged-red fibers (RRF). Some RRF were cytochrome c oxidase (COX)-negative, while some others stained positive for COX. Muscle biochemistry revealed defects of complexes I and IV of the respiratory chain. Both muscle and blood mitochondrial DNA from the patient showed the presence of the mutation at nucleotide position 3243 in the tRNA^Leu(UUR) gene and the absence of point mutations related to MERRF syndrome. The proportions of mutant mtDNA were 70% in muscle and 30% in blood. The mutation was absent in blood from all maternal relatives, in hair follicles from the mother, and in muscle from one sister of the proband. Therefore, there was no evidence of maternal inheritance. © 1996 John Wiley & Sons, Inc.     

Ekbom's syndrome: Lipomas,ataxia, and neuropathy with MERRF

A 66-year-old woman with hereditary deafness and multiple symmetric lipomas presented with ataxia, slight myopathy, and neuropathy. Molecular genetic analysis of mitochondrial DNA revealed the adenine to guanine transition at position 8344 in the tRNA gene for lysine that has been associated with the myoclonic epilepsy and ragged red fiber (MERRF) syndrome. The deafness was transmitted by the patien's father and may have been an unrelated autosomal defect rather than a paternally transmitted mitochondrial point mutation. © 1994 John Wiley & Sons, Inc.     

CPEO and carnitine deficiency overlapping in MELAS syndrome

Mitochondrial myopathy, encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is one of the mitochondrial encephalomyopathies that has distinct clinical features including stroke-like episodes with migraine-like headache, nausea, vomiting, encephalopathy and lactic acidosis. We report a 27-year-old woman who presented with partial seizure, stroke-like episodes including hemiparesis, hemianopia and hemihypethesia, sensorineural hearing loss, migraine-like headache, and lactic acidosis. Brain computed tomographic scan showed encephalomalacia in the right parieto-occipital area and recent hypodensity in the left temporoparieto-occipital area with cortical atrophy. Muscle biopsy revealed ragged-red fibers and paracrystaline inclusions in the mitochondria. Genetic study revealed an A to G point mutation at nucleotide position (np) 3243 of mitochondrial DNA. External ophthalmoplegia and ptosis were also found during two exaggerated episodes in this patient. Therefore, the overlapping syndrome of chronic progressive external ophthalmoplegia in the MELAS syndrome is considered in this case. Furthermore, we also found carnitine deficiency in this patient and she was responsive well to steroid therapy. Muscle biopsy also revealed excessive lipid droplets deposits. Therefore, the carnitine defiency may occur in MELAS syndrome with the A to G point mutation at np 3243. We recommend the steroid or carnitine supplement therapy be applied to the MELAS syndrome with carnitine deficiency.     

MELAS syndrome associated with a tandem duplication in the D-loop of mitochondrial DNA

We describe a family with two cases of adult-onset mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome. Interestingly, the proband also had non-insulin dependent diabetes mellitus and hyperthyroidism. Endocrinological studies demonstrated a high titer of TSH receptor antibody in the proband and elevated levels in her maternal relatives. Analysis of mitochondrial DNA (mtDNA) showed an A-to-G transition at nucleotide position 3243 in the tRNA^Leu(UUR) gene (A3243G) in the three generations of the family. Furthermore, a previously described ~ 260 bp tandem duplication in the D-loop region of mtDNA was also found in the proband and her maternal relatives. To our knowledge, such kind of duplication has never before been reported in the MELAS syndrome. The proportions of mtDNA with the ~260 bp tandem duplication and A3243G point mutation were 12.5% and 82% in the muscle, respectively, and 1.6% and 35% in the blood cells, respectively, of the proband. We conclude that the hyperthyroidism in this MELAS patient may be related to the tandem duplication in the D-loop of mtDNA. This study further substantiates the importance of searching for additional genetic mutations in mitochondrial encephalomyopathic patients with new clinical phenotypes.     

MERRF/MELAS overlap syndrome associated with 3243 tRNALeu(UUR) mutation of mitochondrial DNA

We report a case of myoclonus epilepsy associated with ragged-red fibers (MERRF)/mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) overlap syndrome with hearing loss, external ophthalmoplegia, and myoclonus epilepsy in addition to stroke-like episode and diabetes mellitus. Pathologically, there was degeneration in the dentate nuclei, substantia nigra, red nucleus, and subthalamic nucleus which has been reported as characteristic of MERRF, as well as necrotic lesions of various stages in the cerebral cortex, characteristic of MELAS. The gene study disclosed 3243 mutation in the tRNA^Leu(UUR) gene of mitochondrial DNA. This case is the first neuropathological report of MERRF/MELAS overlap syndrome verified by gene analyses.     

Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome: Report of a Chinese family with mitochondrial DNA point mutation in tRNALys gene

We report myoclonic epilepsy with ragged-red fibers (MERRF) syndrome in a Chinese family with confirmed mitochondrial DNA point mutation. Six members of the family including the grandmother, two siblings, and three grandchildren were affected. Among them, action myoclonus was seen in five; short stature, muscle weakness, and mental retardation in four; lactic acidosis, hearing impairment, and ataxia in two; and seizures in one. Muscle biopsy from two affected siblings revealed ragged-red fibers and abundant subsarcolemmal mitochondria with paracrystalline inclusions. Pedigree analysis suggests a maternal transmission. Analysis of mitochondrial DNA showed a point mutation from A to G at the 8344th nucleotide position located in the tRNA_Lys gene. To our knowledge, this is the first report of MERRF syndrome with such genetic defect from a Chinese family. The present and previous reports support the notion that mitochondrial DNA point mutation at the 8344th nucleotide position is the most common cause of MERRF syndrome. © 1994 John Wiley & Sons, Inc.     

MELAS syndrome: correlation between clinical features and molecular genetic analysis

The clinical manifestations and mitochondrial DNA (mtDNA) mutations in a Taiwanese family with a female proband exhibiting mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes syndrome are reported. Clinically, the proband had a stroke-like episode with right hemiparesis, hemianopsia and mental dysfunction as well as short stature, hearing impairments, and elevated lactate levels. Brain magnetic resonance images showed multiple increased signal intensities over the left frontal, parietal and temporal areas. There were no ragged-red fibers, but paracrystalline inclusion bodies were shown in the muscle biopsies under electron microscopic examination. A deficiency of NADH-CoQ reductase was also found in biochemical studies of the muscles. The family survey revealed no abnormal findings except for headache and episodic vomiting in her mother. The molecular analysis of mtDNA disclosed a mutation from A to G at the nucleotide pair 3243 of the mitochondrial transfer RNA^Leu gene in the blood, hair follicles and/or muscle of the maternal relatives. A characteristic finding of the MELAS family is variation of percentage of mutated mtDNA in various tissues and individuals. However, a higher proportion of mutated mtDNA was noted in the proband than that in the asymptomatic or oligosymptomatic family members. From the data, the variable clinical phenotypes in this MELAS family can be explained at least partly, by the different proportions of mutant mtDNA in the target tissues of the profound and maternal relatives.     

Autopsied case with MERRF/MELAS overlap syndrome accompanied by stroke‐like episodes localized to the precentral gyrus

We present an autopsied case with A8344G‐mutated myoclonus epilepsy with ragged red fibers (MERRF)/mitochondrial encephalomyopathy with lactic acidosis and stroke‐like episodes (MELAS) overlap syndrome accompanied by stroke‐like episodes localized to the precentral gyrus. A 16‐year‐old Japanese woman suddenly experienced repetitive consciousness disturbances with increased serum lactate and creatine kinase levels. Magnetic resonance imaging showed abnormal intensity of bilateral precentral gyrus. She was clinically diagnosed as having a mitochondrial disorder and the A8344G mutation was detected in mitochondrial DNA. At 17 years of age, she died from congestive heart failure secondary to a third episode of lactic acidosis. Neuropatho‐logically, multifocal laminar necrosis, which is responsible for stroke‐like episodes in MELAS, was seen in the frontal cortex including the precentral gyrus, but there was no neuronal loss and gliosis in the basal ganglia, cerebellum, and brainstem, which were compatible with MERRF. Hypertrophy of the vascular smooth muscle and choroidal epithelium were seen, and were strongly visualized by an anti‐mitochondrial antibody. Skeletal muscles showed uneven muscular diameters, increased central nuclei, and ragged red fibers (RRFs). Decreased cytochrome c oxidase (COX) activity and strongly succinate dehydrogenase (SDH)‐reactive blood vessels were also noted. Stroke‐like episodes in MERRF/MELAS overlap syndrome are thought to be rare in the frontal cortex including the precentral gyrus. Only two cases of MERRF/MELAS overlap syndrome with A8344G mutation, including this case, have shown stroke‐like episodes in the frontal lobes. Other than the A8344G mutation and frontal lobe involvement, they had a high degree of similarity in terms of presence of RRFs, gastrointestinal dysfunction, and lack of typical MERRF neuropathology. In conclusion, this is an important case describing the clinical spectrum associated with A8344G‐mutated MERRF/MELAS overlap syndrome.     

Familial Mitochondrial Encephalomyopathy with Stroke-like Episodes and Episodic Disturbances of Consciousness: A Study of Pedigree Including Three Generations with Multisystemic Abnormalities

Abstract: We report here two cases in a family with pleomorphic clinical features which include mitochondrial myopathy, encephalopathy, stroke-like episodes, episodic disturbances of consciousness and other multisystemic abnormalities. The other signs observed in multisystemic abnormalities were ophthalmoplegia, short stature, diabetes mellitus, diabetes insipidus, renal dysfunction, optic atrophy, retinal degeneration, impairment of hearing and mental retardation or deterioration. A symptomatological variation was observed in cases in the same family. It is suggested that these widely varying symptoms may be expressions caused by a common biochemical defect which involves different tissuesin different individuals in the family. The syndromes observed in the present cases were compared with other possibly-related mitochondrial encephalomyopathies.     

Progressive myoclonus epilepsies: an electroclinical, biochemical, morphological and molecular genetic study of 17 cases

Electroclinical, morphological, biochemical and molecular genetic data from 17 patients affected by progressive myoclonus epilepsies (PME) are reported. Twelve patients were characterized by prominent action myoclonus, sporadic seizures, mild ataxia, lack of dementia and persistence of normal EEG background activity; three patients showed a more rapid worsening of symptomatology, characterized by early mental impairment, massive and action myoclonus, cerebellar signs and tonic clonic seizures; in these patients EEG background activity was slow, even in early stages of the disease. In two patients, previously classified as cryptogenetic PME, a mitochondrial aetiology was recognized by the presence of ragged red fibers in muscle biopsy and by a reduction of the respiratory chains enzymes. Molecular genetical investigation of mtDNA demonstrated the reported heteroplasmic point mutation at nt 8344 of mtDNA in the two MERRF patients, while it was negative in all of the others.     

MELAS: clinical phenotype and morphological brain abnormalities

We describe the clinical and neuropathological findings of three unrelated autopsy cases of MELAS harboring the A3243G transition in the mitochondrial DNA (mtDNA). Using immunohistochemical techniques, we studied the expression of several subunits of the respiratory chain in various brain regions from the same cases. In all three cases there was a reduced immunocytochemical staining for mtDNA-encoded subunits of the respiratory chain, confirming the presence of a defective mitochondrial protein synthesis in this disease. Mitochondrial abnormalities were mostly confined to multiple areas of different size and shape, in agreement with the focal character of the brain pathology in MELAS, and were most prominent in the cerebral cortex, providing a morphological contribution to the explanation of the cognitive regression of the patients. Immunoreactivity for mtDNA-encoded subunits was reduced in the walls of many pial and intracerebral arterioles of different brain regions but there was no clear correlation between territories of affected vessels and distribution of the histological and immunohistochemical lesions. Cerebral focal lesions in MELAS might have a metabolic nature and several pathogenetic mechanisms might be involved in the genesis of stroke-like episodes when there is a local increased ATP demand.     

Functional respiratory chain studies in mitochondrial cytopathies. Support for mitochondrial DNA heteroplasmy in myoclonus epilepsy and ragged red fibers (MERRF) syndrome

Summary Mitochondrial respiratory chain function was investigated with polarographic and enzymatic studies, and correlated with immunoblot studies using a battery of probes against respiratory chain holocomplexes in a series of patients with myoclonus epilepsy and ragged red fibers (MERRF) syndrome. State III respiration rates in intact skeletal muscle mitochondria were normal in two cases, suggested site I deficiency in one case and a midrespiratory defect in another. Immunological studies of complex I showed reduced levels of several subunits with the apparent absence of two bands (which at 45 and 42 kDa, coincide with the predicted electrophoretic mobility of the ND5 gene product) in one case. Complex I, III and IV composition was normal in the other three cases indicating no major disruption of complex assembly. A differing severity of skeletal muscle respiratory chain impairment in a group of unrelated patients with severe cerebral clinical involvement is best explained by uneven tissue distribution between brain and muscle of a heteroplasmic mtDNA mutation. The relationship between MERRF and mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) encephalopathies is reappraised by extension of this hypothesis.     

Random mitotic segregation of mitochondrial DNA in MELAS syndrome

We describe the heterogeneity of clinical features and molecular genetic characteristics of the probands and other members in two families with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome. A point mutation at the 3243rd nucleotide position of mtDNA was found only in some of the maternal lineage members of the two families. Furthermore, the proportions of mutant mtDNA were varied and found only in some tissues of the individuals. Intriguingly, in some subjects, the mutant mtDNA was found in blood cells or hair follicles but was absent in muscles. The data do not support the notion of a selective advantage of wild-type mtDNA to rapidly replicating cells. We suggest that a rapid replicative segregation may occur in early embryogenesis.     

The Ramsay Hunt syndrome revisited: Mediterranean myoclonus versus mitochondrial encephalomyopathy with ragged-red fibers and Baltic myoclonus

Among progressive myoclonus epilepsies (PME), the nosography of the Ramsay Hunt syndrome (RHS) has been much debated. The authors report on a homogeneous group of 43 patients originating from around the western Mediterranean, with a large number of northern African subjects, who were followed up for a mean period of 11.6 years. Onset is between 6 and 17 years (mean: 11.2) and the transmission appears to be recessive. The clinical features include: action myoclonus, generalized epileptic seizures, mild cerebellar signs and lack of dementia. EEG features include normal background activity, spontaneous fast generalized spike-wave discharges, photosensitivity, lack of activation during nREM sleep and vertex/rolandic spikes during REM sleep. The prognosis is variable, even within families, but the progression seems to be slow in a majority of patients. This condition can be distinguished from mitochondrial encephalomyopathy and is less severe than Baltic myoclonus. The authors propose that this form of PME, formerly reported as RHS, be more properly described as Mediterranean myoclonus.     

Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy,Lactic Acidosis,and Stroke-Like Episodes (MELAS)

BackgroundEpileptic seizures in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) are heterogeneous with no pathognomonic features. We reviewed epilepsy characteristics and clinical outcome exclusively in a pediatric population.MethodsTwenty-two children and adolescents (13 males) with confirmed mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes due to mitochondrial DNA A3243G mutation and epilepsy were recruited. Clinical data including seizure semiology, treatment response, neuroimaging findings, and electroencephalography were analyzed. We also examined the effect of the age at seizure onset and initial symptoms on the clinical variables.ResultsSeizure semiology and electroencephalography abnormalities showed no syndrome-specific findings. Focal seizures occurred in 21 of 22 subjects (95.5%), whereas generalized seizures developed in seven of 22 subjects (31.8%). Twenty of 22 subjects (90.9%) achieved partial to complete reduction of clinical seizures for more than one year with a combination of more than two antiepileptic drugs. The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group, although there were no significant differences in the initial symptoms. The subjects with severe epileptic conditions tended to have more severe clinical dysfunction and more severe organ involvement.ConclusionsBoth focal and generalized seizures occurred in patients with MELAS. Epilepsy in this population is drug resistant, but a certain degree of clinical seizure reduction was achievable with antiepileptic drugs, with more favorable outcomes than historically expected. Close observation and active epilepsy treatment of individuals with MELAS episodes and earlier seizure onset might improve the prognosis.     

Analysis of the tissue distribution and inheritance of heteroplasmic mitochondrial DNA point mutation by denaturing gradient gel electrophoresis in merrf syndrome

MERRF (Myoclonic Epilepsy and Ragged-Red Fibres) syndrome is one of the maternally inherited diseases for which a mitochondrial DNA (mtDNA) point mutation has recently been identified. The mutation is always heteroplasmic, that is normal and mutant mtDNA coexist within the same individual. We studied mtDNA heteroplasmy in two families with MERRF syndrome, using a denaturing gradient gel electrophoresis technique that avoids the errors in the evaluation of wild/mutant mtDNA ratios caused by restriction enzyme cutting in the situation of amplification of a heteroplasmic DNA. In two patients, the proportion of muscle mutant mtDNA was in agreement with the severity of muscle mitochondrial proliferation, energy defect and fibre type I predominance. In nine patients from three generations of one family, mutant mtDNA proportion in leukocytes was in relative agreement with the clinical severity of the disease. Transmission of mutant mtDNA through these three generations did not show any tendency toward homoplasmy. Homogeneity of the mutant mtDNA proportion among different tissues from one patient was demonstrated in brain, liver, muscle and heart but a possibility of divergence of the mutant mtDNA proportion during mitosis was documented in cultured skin fibroblasts.     

Content of mutant mitochondrial DNA and organ dysfunction in a patient with a MELAS subgroup of mitochondrial encephalomyopathies

A point mutation of mitochondrial tRNA^Leu(UUR) gene is responsible for a MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) subgroup of mitochondrial encephalomyopathies. In most cases, the mutant mitochondrial DNA (mtDNA) coexists with normal mtDNA in a heteroplasmic manner. In order to quantify the content of mutant mtDNA, we developed a quantitative method of PCR. Using this method, the distribution of the mutant mtDNA was examined in 32 different tissues among 18 autopsied organs from a patient with MELAS, who had shown hypophyseal dysfunction. The percentage of the mutant mtDNA at nucleotide number 3243 in each tissue was ranged between 22% and 95%. The content of the mutant mtDNA was at the highest (95%) in the hypophysis and higher in the cerebral cortex than in the white matter. This study shows a possible correlation of tissue dysfunction with accumulation of the mutant mtDNA within the brain.     

Mitochondrial encephalomyopathy (MELAS): pathological study and successful therapy with coenzyme Q10 and idebenone

Two patients with mitochondrial myopathy, encephalopathy, lactic acidosis and strokelike episodes (MELAS) in one family are reported. Pathological examination of case 1 showed ragged-red fibers, with 7% of the fibers being unstained by cytochrome c oxidase stain, peripheral nerve damage, multiple areas of softening in the cerebrum and midbrain, and spongy changes in the cerebrum, optic nerve and pons. Electron microscopic examination revealed abnormal accumulations of mitochondria in the skeletal muscle, smooth muscle and cardiac muscle. The activity of cytochrome c oxidase in the brain and liver showed a tendency to decrease. In case 2 (maternal aunt of case 1), muscular weakness and peripheral nerve damage improved by treatment with coenzyme Q₁₀. By adding idebenone to the coenzyme Q₁₀ therapy, the EEG and Wechsler's Adult Intelligence Scale (WAIS) improved. Furthermore, in the cerebral spinal fluid (CSF), the protein, lactate, and pyruvate decreased, and the monoamines and monoamine metabolites increased.     

Molecular neuropathology of MELAS: level of heteroplasmy in individual neurones and evidence of extensive vascular involvement

Mitochondrial DNA (mtDNA) disease is an important genetic cause of neurological disability. A variety of different clinical features are observed and one of the most common phenotypes is MELAS (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis and Stroke-like episodes). The majority of patients with MELAS have the 3243A>G mtDNA mutation. The neuropathology is dominated by multifocal infarct-like lesions in the posterior cortex, thought to underlie the stroke-like episodes seen in patients. To investigate the relationship between mtDNA mutation load, mitochondrial dysfunction and neuropathological features in MELAS, we studied individual neurones from several brain regions of two individuals with the 3243A>G mutation using dual cytochrome c oxidase (COX) and succinate dehydrogenase (SDH) histochemistry, and Polymerase Chain Reaction Restriction Fragment Lenght Polymorphism (PCR-RFLP) analysis. We found a low number of COX-deficient neurones in all brain regions. There appeared to be no correlation between the threshold level for the 3243A>G mutation to cause COX deficiency within single neurones and the degree of pathology in affected brain regions. The most severe COX deficiency associated with the highest proportion of mutated mtDNA was present in the walls of the leptomeningeal and cortical blood vessels in all brain regions. We conclude that vascular mitochondrial dysfunction is important in the pathogenesis of the stroke-like episodes in MELAS patients. As migraine is a commonly encountered feature in MELAS, we propose that coupling of the vascular mitochondrial dysfunction with cortical spreading depression (CSD) might underlie the selective distribution of ischaemic lesions in the posterior cortex in these patients.