Atypical MELAS associated with mitochondrial tRNA gene A8296G mutation

We report on a unique patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) presenting optic atrophy, cardiomyopathy, and bilateral striatal necrosis before stoke-like episodes became apparent. Skeletal muscle total mitochondrial DNA analysis identified a heteroplasmic A to G point mutation in the tRNA^Lys gene at position 8296. Skeletal muscle pathology revealed typical MELAS findings, including ragged-red fibers cytochrome c oxidase positive strongly succinate dehydrogenase-reactive blood vessels. Recent reports describe the 8296 mutation identified in patients with diabetes mellitus or myoclonus epilepsy with ragged-red fibers, not MELAS. We conclude that the 8296 mutation is likely to be pathogenic and that it may be not only a mutation responsible for diabetes mellitus or myoclonus epilepsy with ragged-red fibers but also for MELAS.     

Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation

The authors studied a 47-year-old patient who presented with an association of deafness, acute cerebral stroke-like episode, leukoencephalopathy, and extensive basal ganglia calcifications. Late onset and neuroradiologic findings were atypical for MELAS syndrome (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Strokelike episodes). A heteroplasmic G to A transition at nucleotide 4332 in the tRNA glutamine gene was identified in the patient's muscle mitochondrial DNA. The pathogenicity of the mutation was shown in single muscle fibers by the correlation between high mutation load and cytochrome c oxidase defect.     

MELAS phenotype associated with m.3302A>G mutation in mitochondrial tRNA gene

The m.3302A>G mutation in the mitochondrial tRNA^Leu(UUR) gene has been identified in only 12 patients from 6 families, all manifesting adult-onset slowly progressive myopathy with minor central nervous system involvement. An 11-year-old boy presented with progressive proximal-dominant muscle weakness from age 7 years. At age 10, he developed recurrent stroke-like episodes. Mitochondrial myopathy, encephalopathy, lactic acidosis, plus stroke-like episodes (MELAS) was diagnosed by clinical symptoms and muscle biopsy findings. Mitochondrial gene analysis revealed a heteroplasmic m.3302A>G mutation. Histological examination showed strongly SDH reactive blood vessels (SSVs), not present in previous cases with myopathies due to the m.3302A>G mutation. These findings broaden the phenotypic spectrum of this mutation.     

A novel tRNA(Val) mitochondrial DNA mutation causing MELAS

Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is the most common mitochondrial disease due to mitochondrial DNA (mtDNA) mutations. At least 15 distinct mtDNA mutations have been associated with MELAS, and about 80% of the cases are caused by the A3243G tRNA(Leu(UUR)) gene mutation. We report here a novel tRNA(Val) mutation in a 37-year-old woman with manifestations of MELAS, and compare her clinicopathological phenotype with other rare cases associated tRNA(Val) mutations.     

Autism associated with the mitochondrial DNA G8363A transfer RNA(Lys) mutation

We report a family with a heterogeneous group of neurologic disorders associated with the mitochondrial DNA G8363A transfer ribonucleic acid (RNA)Lys mutation. The phenotype of one child in the family was consistent with autism. During his second year of life, he lost previously acquired language skills and developed marked hyperactivity with toe-walking, abnormal reciprocal social interaction, stereotyped mannerisms, restricted interests, self-injurious behavior, and seizures. Brain magnetic resonance imaging (MRI) and repeated serum lactate studies were normal. His older sister developed signs of Leigh syndrome with progressive ataxia, myoclonus, seizures, and cognitive regression. Her laboratory studies revealed increased MRI T2-weighted signal in the putamen and posterior medulla, elevated lactate in serum and cerebrospinal fluid, and absence of cytochrome c oxidase staining in muscle histochemistry. Molecular analysis in her revealed the G8363A mutation of the mitochondrial transfer RNA(Lys) gene in blood (82% mutant mitochondrial DNA) and muscle (86%). The proportions of mutant mitochondrial DNA from her brother with autism were lower (blood 60%, muscle 61%). It is likely that the origin of his autism phenotype is the pathogenic G8363A mitochondrial DNA mutation. This observation suggests that certain mitochondrial point mutations could be the basis for autism in some individuals.     

A novel mutation in the mitochondrial tRNA(Phe) gene associated with mitochondrial myopathy

We report a novel heteroplasmic T-->C mutation at nt position 582 within the mitochondrial tRNA(Phe) gene of a 70-year-old woman with mitochondrial myopathy. No other family members were affected, suggesting that our patient was a sporadic case. The muscle showed frequent ragged red fibers and 43% cytochrome c oxidase deficient fibers. The mutation alters a conserved base pairing in the aminoacyl acceptor stem. The mutation load was 70% in muscle homogenate and varied from 0 to 95% in individual muscle fiber segments. Cytochrome c oxidase-negative fibers showed significantly higher levels of mutated mtDNA (>75%) than Cytochrome c oxidase-positive fibers (<55%). This mutation adds to the previously described four pathogenic mutations in the tRNA(Phe) gene.     

A novel mutation (8342G-->A) in the mitochondrial tRNA(Lys) gene associated with progressive external ophthalmoplegia and myoclonus

We describe a patient who suffered from impaired ocular motility from age 10 years and at 16 years developed ptosis, proximal weakness and progressive fatigability. At 35 years she developed massive myoclonic jerks, and head and distal tremor. A muscle biopsy showed a high percentage of cytochrome c oxidase negative fibers but no ragged-red fibers. A novel heteroplasmic mutation (8342G-->A) was found in the mitochondrial transfer RNA(Lys) gene by single-strand conformation polymorphism screening, followed by sequence and restriction fragment length polymorphism analysis. Approximately 80% of muscle mitochondrial DNA (mtDNA) harbored the mutation, while the mutation was absent in lymphocyte DNA of the proband, as well as of her mother, daughter and a maternal aunt. However, the pathogenicity of the mutation was confirmed by restriction fragment length polymorphism analysis of single muscle fibers, which revealed a significantly greater level of mutant mtDNA in cytochrome c oxidase negative over cytochrome c oxidase positive fibers.     

New phenotypic diversity associated with the mitochondrial tRNA(SerUCN) gene mutation

We performed detailed clinical, histopathological, biochemical, in vitro translation and molecular genetic analysis in patients from two unrelated families harbouring the tRNA(SerUCN) 7472C-insertion mutation. Proband 1 developed a progressive neurodegenerative phenotype characterised by myoclonus, epilepsy, cerebellar ataxia and progressive hearing loss. Proband 2 had a comparatively benign phenotype characterised by isolated myopathy with exercise intolerance. Both patients had the 7472C-insertion mutation in identical proportions and they exhibited a similar muscle biochemical and histopathological phenotype. However, proband 2 also had a previously unreported homoplasmic A to C transition at nucleotide position 7472 in the tRNA(SerUCN) gene. This change lengthens further the homopolymeric C run already expanded by the 7472C-insertion. These data extend the phenotypic range associated with the 7472C-insertion to include isolated skeletal myopathy, as well as a MERRF-like phenotype.     

A novel mutation in the mitochondrial tRNA(TYr) gene associated with exercise intolerance

The authors report a novel A5874G mutation in the mitochondrial tRNA tyrosine (tRNA(TYr)) gene associated with exercise intolerance, limb weakness, and complex III deficiency. The mutation was absent in blood from the patient and all maternal family members, indicating that it may be a spontaneous somatic mutation in muscle. This is the first point mutation in the tRNA(TYr) gene associated with human disease and is further evidence that exercise intolerance associated with complex III deficiency is genetically heterogeneous.     

MELAS syndrome with mitochondrial tRNA(Leu(UUR)) gene mutation in a Chinese family.

The clinical features of a patient in a Chinese family with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS syndrome) are reported. The study revealed that hearing and visual impairments and miscarriages may be early clinical presentations in MELAS. A heteroplasmic A to G transition in the tRNA(Leu(UUR)) gene was noted at the nucleotide pair 3243 in the mitochondrial DNA of muscle, blood, and hair follicles of the proband and his maternal relatives. Quantitative analysis of the mutated mitochondrial DNA revealed variable proportions in different tissues and subjects of maternal lineage in the family. Muscle tissue contained a higher proportion of the mutant mitochondria than other tissues examined. The function of the reproductive system of the proband seems to be impaired. In one clinically healthy sibling, the 3243rd point mutation was found in sperm mitochondrial DNA, although sperm motility was not affected. It seems that biochemical defects in mitochondrial respiration and oxidative phosphorylation are tissue specific expressions of the 3243rd point mutation in the mitochondrial DNA of the affected target tissues.     

A new mitochondrial DNA mutation (A3288G) in the tRNA(Leu(UUR)) gene associated with familial myopathy.

We describe a family with a maternally inherited mitochondrial myopathy and an A3288G mutation in the tRNA(Leu(UUR)) gene. The proband had muscle cramping and mild weakness while her brother had long-standing limb and respiratory muscle weakness and her daughter had elevated serum CK. The mutation, which was nearly homoplasmic in muscle and heteroplasmic in blood, affects the TpsiC loop at a conserved site and was not found in 107 controls. This report confirms the frequent association of tRNA(Leu(UUR)) mutations with respiratory muscle involvement and bolsters the concept that tRNA(Leu(UUR)) is a hotspot for mtDNA mutations.     

A mitochondrial tRNA(Lys) gene mutation (T8316C) in a patient with mitochondrial myopathy, lactic acidosis, and stroke-like episodes

We studied a patient with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes who had morphologically and biochemically abnormal muscle mitochondria. Molecular analysis revealed a T8316C transition in the mitochondrial DNA tRNA(Lys) gene. The mutation was homoplasmic in muscle from the proposita, heteroplasmic in her blood, and still less abundant in blood from her asymptomatic maternal relatives. The T8316C mutation affects a highly conserved base pair and was not found in controls, thus satisfying the accepted criteria for pathogenicity. Our data document the genetic heterogeneity in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome, underlining that the same syndrome may be associated with mutations of different genes.     

Pure myopathy associated with a novel mitochondrial tRNA gene mutation

The authors describe a 47-year-old man who presented with proximal muscle weakness, myalgia, elevated creatine kinase, and features of a pure myopathic syndrome in whom they have identified a novel mutation in the mitochondrial tRNA(Ala) gene. This 5591G>A transition is heteroplasmic, segregates with cytochrome c oxidase deficiency in single muscle fibers, and fulfills recognized criteria for pathogenicity. This case exemplifies the wide-ranging clinical spectrum of mitochondrial disease presentations.     

A novel mutation in the mitochondrial DNA tRNA Leu (UUR) gene associated with late-onset ocular myopathy

We identified a novel G3283A transition in the mitochondrial DNA tRNA(Leu (UUR)) gene in a patient with ptosis, ophthalmoparesis and hyporeflexia. Muscle biopsy showed cytochrome oxidase positive ragged-red fibers, and defects of complexes I, III and IV of the mitochondrial respiratory chain. The mutation was heteroplasmic in muscle of the proband, being absent in her blood. Ragged-red fibers harbored greater levels of mutant genomes than normal fibers. The G3283A mutation affects a strictly conserved base pair in the TPsiC stem of the gene and was not found in controls, thus satisfying the accepted criteria for pathogenicity.     

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.     

A novel mitochondrial DNA tRNA(Ile) (A4267G) mutation in a sporadic patient with mitochondrial myopathy

We describe a novel mutation in the mitochondrial tRNA(Ile) gene, an A to G transition at nucleotide position 4267, in a 37-year-old woman with myopathy, ataxia and sensorineural hearing loss. The A4267G mutation was heteroplasmic in several of the proband's tissues and single fibre analysis revealed significantly higher levels of mutated mitochondrial DNA in cytochrome c oxidase-deficient fibres than cytochrome c oxidase-positive fibres. It is predicted to disrupt a highly conserved base pair within the aminoacyl acceptor stem of the tRNA causing functional impairment, and as such fulfils all the accepted criteria for pathogenicity. Moreover, we were unable to detect the A4267G mutation in lymphocytes, buccal epithelia and hair of the patient's mother and two siblings, implying that the A4267G transition represents a sporadic, germline mutation.     

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.     

Clinical features of A3243G mitochondrial tRNA mutation

Mitochondrial cytopathy is a heterogeneous group of disorders with a wide range of clinical features. To evaluate the incidence and clinical heterogeneity of A3243G mitochondrial tRNA mutation in the Korean population, we evaluated patients who were clinically suggestive of having mitochondrial encephalomyopathy. Eighty-five patients were included in this study. All showed clinical features of mitochondrial encephalomyopathy and had three or more of the following clinical manifestations: (1) psychomotor regression, (2) hyperlacticacidemia, (3) recurrent stoke-like episodes, (4) idiopathic cardiomyopathy, (5) sensoryneural hearing loss, (6) diabetes mellitus, (7) myopathy, (8) renal disease and (9) relatives with known mitochondrial disease. The patients were clinically classified as MELAS, MERRF, Leigh syndrome, Kearns-Sayre syndrome, chronic progressive external ophthalmoplegia and uncertain. Of the 85 patients, 19 had the A3243G mutation (22.3%). Thirty-one patients showed typical clinical characteristics of MELAS. Fourteen of those 31 patients had A3243G mutation (45.1%). Four patients harboring A3243G mutations showed atypical and heterogeneous clinical features, unlike MELAS. This study revealed the frequent occurrence of A3243G mutation in Korean patients with mitochondrial disorders and their clinical features can be heterogeneous. It will be helpful to screen the presence of A3243G mutation for the genetic diagnosis of mitochondrial encephalomyopathy in Korea.     

MELAS associated with a mutation in the valine transfer RNA gene of mitochondrial DNA

We describe a patient with the mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) phenotype in whom initial investigations in skeletal muscle failed to show any histochemical or biochemical defect. Subsequent analyis of the mitochondrial genome identified a new heteroplasmic mutation in the valine transfer RNA gene, the first described in this region.