An infant with a mitochondrial A3243G mutation demonstrating the MELAS phenotype

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a syndrome associated with mitochondrial DNA mutations such as A3243G, the most common mutation. Ragged-red fibers and strongly succinate dehydrogenase-reactive blood vessels in the muscle are diagnostic pathologic features of MELAS. In general, the first typical attack of MELAS occurs in children at school age; it is rare for stroke-like episodes to occur in early infancy. This report describes a 4-month-old male harboring A3243G, whose phenotype at onset was consistent with that of MELAS in infancy. The patient was admitted because of disturbances of consciousness and ventilatory insufficiency. Remarkable lactic acidosis was observed. MRI revealed several bilateral lesions. Periodic lateralized epileptic discharges on the EEG suggested regional lesions. Biopsied muscle displayed scattered ragged-red fibers and succinate dehydrogenase-reactive blood vessels; over 90% of muscle mitochondrial DNA had A3243G. This case suggests that MELAS can develop in early infancy with its typical clinical presentation. The high percentage of A3243G may contribute to the early onset of the MELAS phenotype in this patient.     

mtDNA A3243G MELAS mutation is not associated with multigenerational female migraine

The authors searched for mitochondrial DNA (mtDNA) A3243G mutation in peripheral blood leukocytes from female migraine patients with pure matrilinear history of migraine along two or three generations. The current study was designed to exclude any male transmission of the disease. The mutation was absent in all patients. We conclude that mtDNA A3243G mutation does not contribute to the pathogenesis of pure matrilinear multigenerational migraine with or without aura.     

MERRF/MELAS overlap syndrome in a family with A3243G mtDNA mutation

Four members of a family were found to carry the A3243G mtDNA mutation. Clinical features varied from typical MELAS to myoclonic epilepsy to simple deafness without neurological signs. Several other members of the family had symptoms consistent with a mitochondrial disease. Muscle biopsy in 3 of the 4 patients showed the most prominent mitochondrial alterations with partial deficiency of cytochrome c oxidase in the case with the mildest phenotype. Mitochondrial DNA analysis detected a variable percentage of A3243G mutation, roughly correlating with the phenotype. The interesting feature of the family lies in the great intrafamilial variability of the severity of clinical expression, encompassing MELAS and MERRF features, associated with the A3243G mtDNA mutation. A search for the most common mtDNA mutations is recommended in all patients featuring incomplete MELAS or MERRF syndromes and in all familial cases presenting minimal clinical signs.     

MELAS mitochondrial DNA mutation A3243G reduces glutamate transport in cybrids cell lines

MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is commonly associated with the A3243G mitochondrial DNA (mtDNA) mutation encoding the transfer RNA of leucine (UUR) (tRNA ^Leu(UUR)). The pathogenetic mechanisms of this mutation are not completely understood. Neuronal functions are particularly vulnerable to alterations in oxidative phosphorylation, which may affect the function of the neurotransmitter glutamate, leading to excitotoxicity. In order to investigate the possible effects of A3243G upon glutamate homeostasis, we assessed glutamate uptake in osteosarcoma-derived cytoplasmic hybrids (cybrids) expressing high levels of this mutation. High-affinity Na⁺-dependent glutamate uptake was assessed as radioactive [³H]-glutamate influx mediated by specific excitatory amino acid transporters (EAATs). The maximal rate (V_max) of Na⁺-dependent glutamate uptake was significantly reduced in all the mutant clones. Although the defect did not relate to either the mutant load or magnitude of oxidative phosphorylation defect, we found an inverse relationship between A3243G mutation load and mitochondrial ATP synthesis, without any evidence of increased cellular or mitochondrial free radical production in these A3243G clones. These data suggest that a defect of glutamate transport in MELAS neurons may be due to decreased energy production and might be involved in mediating the pathogenic effects of the A3243G mtDNA mutation.     

Absence of maternal A3243G mtDNA mutation and reversible hyperglycemia in a patient with MELAS syndrome

We report the unusual features of a female patient who had MELAS-specific A3243G mutation in mitochondrial DNA (mtDNA) and diabetes mellitus (DM). The patient showed mitochondrial myopathy, encephalopathy, lactic acidosis, and deafness but lacked the stroke-like episode. Acute hyperglycemia was noted after one attack of status epilepticus. Molecular genetic analysis demonstrated a heteroplasmic A3243G point mutation in the mtDNAs of muscle, blood cells and hair follicles. Glucagon stimulation test exhibited marked depression of pancreatic beta-cell function. However, in a further study neither this mutation, nor MELAS syndrome or DM, was found in all of her maternal relatives. A series of follow-up studies for beta-cell function also showed gradual improvement. The pedigree study led us to believe that this A3243G mutation arose from the germ line cells or occurred later in somatic tissues of the patient. We also suggest that the A3243G mutation of mtDNA may elicit the pathogenesis of a subtype of DM. Nevertheless, environmental stress may be another important factor for provocation of the disease.     

Neuroradiological features of six kindreds with MELAS tRNALeu A3243G point mutation: implications for pathogenesis

OBJECTIVE—To determinethe neuroradiological abnormalities associated with subjectscarrying the mitochondrial myopathy, encephalopathy, lacticacidosis, and strokelike episodes (MELAS) tRNA^Leu(UUR)A3243G point mutation
METHODS—Mitochondrialgenetic analysis was performed on 24 subjects from six kindreds withthe MELAS tRNA^Leu(UUR) A3243G point mutation. Cerebral CTand MRI were performed on 24 patients and 15 patients respectively.Previous neuroradiological investigations including cerebral CT fromfour deceased members of the families were also reviewed. Histologicalexamination of postmortem specimens of two patients within the kindredswas performed.
RESULTS—The commonestradiological finding was basal ganglia calcification. Otherabnormalities included focal lesions and cerebellar and cerebralatrophy. Basal ganglia calcification was progressive, symmetric, andasymptomatic. Histologically, basal ganglia calcification in onepatient was found to be in the pericapillary regions of the globuspallidus, with no neuronal involvement. Focal lesions most commonlyinvolved the grey matter of the parietal and occipital lobes andcerebellum. Histopathological examination suggested that these were dueto cellular rather than vascular dysfunction. Enlargement of the fourthventricle was the first sign of cerebellar atrophy. Cerebral andcerebellar atrophy were only present with severe disease.
CONCLUSIONS—Theseradiological findings, when considered in the context of the clinicaland pathological findings, seem to reflect two major disease processes:an intermittent abrupt loss of function associated with cell injuryfrom which there is at least partial recovery and a slowly progressivedegenerative process causing basal ganglia calcification, and cerebraland cerebellar atrophy. The clinical and radiological featuresresulting from these processes are distinctive and provide insight intothe consequences of mitochondrial dysfunction on the brain.

     

A3243G mitochondrial mutation associated with polymicrogyria

The mitochondrial transfer ribonucleic acid for leucine is encoded by nucleotides 3230-3304. A-to-G transition at nucleotide 3243 can cause maternally transmitted diabetes mellitus-deafness syndrome, and MELAS syndrome. MELAS syndrome is a rare disorder of mitochondrial energy production, and is an acronym for myopathy, encephalopathy, lactic acidosis, and stroke-like episodes. Cortical malformations are heterogeneous and result from abnormal cell proliferation/apoptosis, migration, and/or differentiation of neuroepithelial cells. They are an important and relatively common cause of intractable epilepsy and neurodevelopmental disorders. The association between these A3243G mutations and cortical malformation has never before been reported. Here a 14-year-old female with A3243G mutation and polymicrogyria is described and possible aetiologies of this association are discussed.     

线粒体DNA A3243G点突变在成年患者中的临床特点

目的 探讨mtDNA A3243G点突变在成年患者的临床表现特点.方法 对发病年龄在18岁以上的36例患者的临床资料进行分析(5个家系28例,散发8例),其中23例行mtDNAA3243G点突变检查(5个家系15例,散发8例),14例行头颅影像学检查,10例进行了骨骼肌病理检查.结果 5个家系的28例患者中出现糖尿病17例(60.7%)、耳聋16例(57.1%)、卒中样发作9例(32.1%),三者可以并存或单独出现,少见表现包括心肌病和肾脏损害.23例mtDNA A3243G点突变患者中线粒体脑肌病伴随乳酸血症和卒中样发作(MELAS)14例(61.0%),其主要表现为认知功能障碍、言语障碍和头痛;其余9例包括无症状的基因突变携带者3例(13.0%)、线粒体糖尿病和(或)神经性耳聋2例(8.7%)、自主神经功能异常2例(8.7%)、糖尿病伴不孕症1例(4.3%)和心肌病1例(4.3%).14例MELAS患者的头颅影像学检查显示以枕叶和颞叶受累为主,额叶最少;10例肌肉病理检查发现9例存在不整红边纤维.mtDNA A3243G点突变比例均值在MELAS患者为28.75%±13.69%,非MELAS患者为25.08%±11.54%,两者差异没有统计学意义.结论 mtDNAA3243G点突变在成年患者主要累及中枢神经、胰岛以及听神经.认知功能障碍、言语障碍和头痛是成年MELAS的主要临床表现.家族中多例患者出现糖尿病和耳聋,提示该突变并非MELAS突变,应当关注mtDNA A3243G点突变家系中非MELAS患者的存在.     

MELAS with the mitochondrial DNA 3243 point mutation: a neuropathological study

We performed a neuropathological examination of the central nervous system from seven autopsied patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). Five of the seven cases were confirmed to have the mitochondrial DNA (mtDNA) 3243 point mutation. In addition to the changes reported previously, diffuse atrophy of the cerebral and cerebellar cortices, diffuse gliosis of cerebral and cerebellar white matter, and cactus formation of Purkinje cells were observed. Electron microscopy revealed accumulation of mitochondria in the cactus formations. These lesions are common in MELAS with the mtDNA 3243 point mutation, but cannot be explained solely by mitochondrial angiopathy, and suggest that intrinsic mitochondrial malfunction contributes to neuronal damage in MELAS pathology. Moreover, the pathological changes observed in the cerebellum suggest that cerebellar function should be evaluated more carefully at the clinical level. Received: 3 December 1998 / Accepted: 21 April 1999     

Polymorphism of epilepsy associated with the A3243G mutation of mitochondrial DNA (MELAS): reasons for delayed diagnosis

INTRODUCTION: Mitochondrial disease is a potential diagnosis in patients with epilepsy beginning in childhood or adolescence with a typical polymorphic presentation and preponderant occipital lobe seizures. Diagnosis may however be delayed in some patients with long-standing disease, particularly when cardinal mitochondrial symptoms are missing; clinical manifestations may be dissociated over time leading to genetic diagnostic tests being prescribed long after disease onset. OBSERVATION: We report the case of a 17 year old woman in whom the diagnosis of lipothymic episodes, migraine, idiopathic photo-sensitive generalized epilepsy, and partial occipital epilepsy complicated by occipital epileptic status were successively proposed because of the initial clinical presentation and the slow disease course. Eleven years after disease onset the diagnosis of progressive myoclonic epilepsy was made due to the occurrence of myoclonic jerks with giant SEPs associated with a cerebellar syndrome, deterioration of psychomotor performances and diffuse slowing of EEG activity with pseudo-periodic bursts of delta waves. Genetic analysis showed an A3243G mutation of mitochondrial DNA, usually correlated with the MELAS phenotype, while the clinical presentation of progressive myoclonic epilepsy was more suggestive of MERRF. CONCLUSION: Although each of the symptoms successively observed in this patient has been reported in MELAS, the slow course of the disease, which is unusual in this mutation, the absence of stroke-like episodes, and the polymorphism of the epilepsy all contributed to delayed final diagnosis.     

Mitochondrial 3243 A-->G mutation (MELAS mutation) associated with painful muscle stiffness.

The mitochondrial mutation A-->G at nucleotide position 3243 is associated with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and other mitochondrial encephalomyopathies. We found this mutation in a 61-year-old patient who developed at the age of 54 a myopathy with painful muscle stiffness as the predominant symptom. Additionally hypacusis, a mild hemisensory syndrome and impaired glucose tolerance were present. Muscle histopathology showed few ragged red fibers. The mutation was detected heteroplasmatically in DNA from muscle and blood. So far painful muscle stiffness has not been a known phenotype of the 3243 mutation.     

Phenotypes and mitochondrial DNA substitutions in families with A3243G mutation

OBJECTIVE: To clarify the relationship between mitochondrial DNA (mtDNA) sequence variations and phenotypes in patients with A3243G mutation. MATERIALS AND METHODS: We studied whole mtDNA sequences in two families with A3243G mutation and characteristic clinical features. Two brothers in Family 1 had shown thiamine deficiency and mitochondrial myopathy without central nervous system involvement. In Family 2, a 16-year-old woman showed the symptoms of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Her mother had had diabetes mellitus and died at the age of 42. The proportion of A3243G mtDNA in blood was 87 and 89% in the patients of Family 1, and 25% in the patient and less than 5% in the mother of Family 2. RESULTS: The mtDNA analysis revealed the following homoplasmic substitutions: T1520C and C12153T found only in Family 1, and A15954G found only in Family 2. These substitutions were not detected in seven other MELAS patients or in 50 controls. CONCLUSION: These substitutions might be specific to these families and could be one of the factors that modulate their clinical features together with the A3243G mutation.     

A study of familial MELAS: evaluation of A3243G mutation, clinical phenotype, and magnetic resonance spectroscopy-monitored progression

The clinical manifestations of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS syndrome) are nonspecific and can easily be misdiagnosed. Magnetic resonance spectroscopy (MRS)-based detection of lactate in the brain has been found to be of diagnostic help in MELAS syndrome, however, the issue of whether MRS features vary by stage remains unresolved. We assessed the causative mutation and radiological features of a family of MELAS. Four of the family members harbored the A3243G mutation, probably of maternal inheritance. However, the clinical phenotypic expression was different in these patients. MRS showed a lactate peak, decreased N-acetylaspartate, choline, and creatine, which became more pronounced with progression of the disease, demonstrating that brain-MRS-based detection of lactate may be a suitable way to monitor the progression and treatment of MELAS.     

Oxidative phosphorylation defect in the brains of carriers of the tRNAleu(UUR) A3243G mutation in a MELAS pedigree

MELAS is a mitochondrial encephalomyopathy characterized clinically by recurrent stroke-like episodes, seizures, sensorineural deafness, dementia, hypertrophic cardiomyopathy, and short stature. The majority of patients are heteroplasmic for a mutation (A3243G) in the tRNAleu(UUR) gene in mitochondrial DNA (mtDNA). In cells cultured in vitro, the mutation produces a severe mitochondrial translation defect only when the proportion of mutant mtDNAs exceeds 95% of total mtDNAs. However, most patients are symptomatic well below this threshold, a paradox that remains unexplained. We studied the relationship between the level of heteroplasmy for the mutant mtDNA and the clinical and biochemical abnormalities in a large pedigree that included 8 individuals carrying the A3243G mutation, 4 of whom were asymptomatic. Unexpectedly, we found that brain lactate, a sensitive indicator of oxidative phosphorylation dysfunction, was linearly related to the proportion of mutant mtDNAs in all individuals carrying the mutation, whether they were symptomatic or not. There was no evidence for threshold expression of the metabolic defect. These results suggest that marked tissue-specific differences may exist in the pathogenic expression of the A3243G mutation and explain why a neurological phenotype can be observed at relatively low levels of heteroplasmy.     

Maternally inherited cardiomyopathy: A new phenotype associated with the A to G at nt.3243 of mitochondrial DNA (MELAS mutation)

The A to G transition at nt.3243 of the tRNA^Leu(UUR) gene of mtDNA, commonly associated with MELAS, was detected in several members of a family affected by a maternally inherited form of hypertrophic cardiomyopathy. These findings suggest adding cardiomyopathy in the list of phenotypes associated with the 3243 mutation. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 221–225, 1997.     

Ubiquinone and nicotinamide treatment of patients with the 3243A-->G mtDNA mutation

The efficacy and safety of ubiquinone (Q10) and nicotinamide were evaluated in a 6-month open-label trial in patients with the 3243A-->G mitochondrial DNA mutation. Blood lactate and pyruvate concentrations decreased, but there was little clinical improvement. Q10 and nicotinamide were well tolerated, but two patients died suddenly and unexpectedly during the trial. These deaths may have been unrelated to treatment. The unpredictable course of the disease makes evaluation of the clinical response difficult.