The A to G transition at nt 3243 of the mitochondrial tRNALeu(UUR) may cause an MERRF syndrome.

OBJECTIVE--To verify the phenotype to genotype correlations of mitochondrial DNA (mtDNA) related disorders in an atypical maternally inherited encephalomyopathy. METHODS--Neuroradiological, morphological, biochemical, and molecular genetic analyses were performed on the affected members of a pedigree harbouring the heteroplasmic A to G transition at nucleotide 3243 of the mitochondrial tRNALeu(UUR), which is usually associated with the syndrome of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). RESULTS--The proband was affected by a fullblown syndrome of myoclonic epilepsy with ragged red fibres (MERRF), severe brain atrophy, and basal ganglia calcifications, without the MRI T2 hyperintense focal lesions which are pathognomonic of MELAS. Oligosymptomatic relatives were variably affected by lipomas, goitre, brain atrophy, and basal ganglia calcifications. Muscle biopsies in the proband and his mother showed a MELAS-like pattern with cytochrome c oxidase hyperreactive ragged red fibres and strongly succinate dehydrogenase reactive vessels. Quantification of the A3243G mutation disclosed 78% and 70% of mutated mtDNA in the muscle of the severely affected proband and of his oligosymptomatic mother respectively. Nucleotide sequencing of the mitochondrial tRNALeu(UUR) and tRNALys in the proband's muscle failed to show any additional nucleotide change which could account for the clinical oddity of this pedigree by modulating the expression of the primary pathogenic mutation. CONCLUSION--So far, MERRF has been associated with mutations of the mitochondrial tRNALys, and MELAS with mutations of the mitochondrial tRNALeu(UUR). Now MERRF may also be considered among the clinical syndromes associated with the A to G transition at nt 3243 of the tRNALeu(UUR).     

Alteration in the copy number of mitochondrial DNA in leukocytes of patients with mitochondrial encephalomyopathies

OBJECTIVES: We investigated whether mutation of mitochondrial DNA (mtDNA) affects the copy number of the mitochondrial genome in patients with mitochondrial myopathy encephalopathy with lactic acidosis and stroke-like episodes (MELAS) and those with myoclonic epilepsy with ragged-red fiber (MERRF) syndromes. MATERIALS AND METHODS: Forty-eight Taiwanese patients with MELAS syndrome and 20 patients with MERRF syndrome were recruited in this study. RESULTS: In relation to controls, the copy numbers of mtDNA in leukocytes of patients with MELAS or MERRF syndrome were significantly higher at a young age but lower at an advanced age. In addition, MELAS patients harboring higher proportions of mtDNA with A3243G transition had lower mtDNA copy numbers. The MELAS or MERRF patients with multi-system disorders had lower mtDNA copy numbers in leukocytes. Furthermore, higher proportions of mtDNA with 4977 bp deletion were found in leukocytes of MERRF patients with multi-system involvement. CONCLUSION: In leukocytes, alteration in the copy number of mtDNA is related to the proportion of mtDNA with a point mutation or large-scale deletion, which may serve as a biomarker in the pathogenesis and disease progression of MELAS and MERRF syndromes.     

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.     

Genetic, pathogenetic, and phenotypic implications of the mitochondrial A3243G tRNALeu(UUR) mutation

Mitochondrial disorders are frequently caused by mutations in mitochondrial genes and usually present as multisystem disease. One of the most frequent mitochondrial mutations is the A3,243G transition in the tRNALeu(UUR) gene. The phenotypic expression of the mutation is variable and comprises syndromic or non-syndromic mitochondrial disorders. Among the syndromic manifestations the mitochondrial encephalopathy, lactacidosis, and stroke-like episode (MELAS) syndrome is the most frequent. In single cases the A3,243G mutation may be associated with maternally inherited diabetes and deafness syndrome, myoclonic epilepsy and ragged-red fibers (MERRF) syndrome, MELAS/MERRF overlap syndrome, maternally inherited Leigh syndrome, chronic external ophthalmoplegia, or Kearns-Sayre syndrome. The wide phenotypic variability of the mutation is explained by the peculiarities of the mitochondrial DNA, such as heteroplasmy and mitotic segregation, resulting in different mutation loads in different tissues and family members. Moreover, there is some evidence that additional mtDNA sequence variations (polymorphisms, haplotypes) influence the phenotype of the A3,243G mutation. This review aims to give an overview on the actual knowledge about the genetic, pathogenetic, and phenotypic implications of the A3,243G mtDNA mutation.     

Correlation between clinical and molecular features in two MELAS families.

We describe the clinical, morphological, biochemical presentation in two MELAS families, and correlate it with the distribution and proportion of mitochondrial DNA carrying the A to G transition at nt 3243. Family A was characterized by late onset MELAS in two members, CPEO in one, and mild CNS involvement in another. 20-61% of mtDNA of affected and unaffected individuals was mutated in muscle, 2-18% in blood. There was no obvious correlation between clinical picture and proportion of mutated mtDNA. In family B full MELAS syndrome appeared only in the third generation, but the mutation was also detected in muscle of asymptomatic individuals of the first and second generation. The proportion of mutated mtDNA in blood, and to a lesser extent in muscle, correlated with the severity of the clinical presentation. The MELAS mutation is consistently detected in all asymptomatic maternal relatives of MELAS patients. We conclude that different clinical presentations of mitochondrial encephalomyopathy may coexist in the same family, and correlation between clinical severity and molecular abnormality is not always recognizable. Presence of the MELAS mutation in muscle and blood is a necessary but not sufficient condition for the expression of the typical MELAS phenotype.     

线粒体脑肌病伴高乳酸血症和脑卒中样发作综合征一家系临床特征及线粒体基因A3243G位点点突变异质性水平

目的 调查1个疑似患有母系遗传性线粒体脑肌病伴高乳酸血症和脑卒中样发作(MELAS)综合征家系的临床表现、生物化学检测数据和影像学资料,并探索其与血细胞线粒体基因突变异质性水平的关联性.方法 收集先证者和11位其母系家系成员的一般情况、抽搐及脑卒中样发作等病史,检测家系成员的血常规和运动前后血浆乳酸水平等生化指标,并做头颅磁共振检查.用聚合酶链反应(PCR)-限制性内切酶片段长度多态和DNA测序法检测其成员是否存在线粒体基因组A3243G点突变,并用荧光实时定量PCR定量该突变的水平.结果 该家系部分成员存在抽搐、脑卒中样发作和高乳酸血症等MELAS综合征典型症状,以及身材矮小、运动不耐受和发热、偏头痛等非典型症状.发作期头颅磁共振成像符合MELAS综合征的典型特点,且普遍存在小脑萎缩.母系亲属均存在线粒体基因的A3243G位点点突变,突变异质性水平越高,症状越典型且严重.结论 该调查家系确诊母系遗传性MELAS综合征,其致病基因为线粒体A3243G点突变.外周血血细胞线粒体基因突变异质性水平与亲缘关系、抽搐早现性和血乳酸值等临床表型存在相关性.     

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.     

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.     

Hearing impairment is common in various phenotypes of the mitochondrial DNA A3243G mutation.

OBJECTIVE: To determine whether there are common symptoms within different phenotypes of the mitochondrial DNA A3243G mutation. DESIGN: A series of 52 adults with mitochondrial encephalomyopathies and their symptomatic relatives were screened for the A3243G mutation using restriction enzyme analysis. In addition to clinical examination, patients with the mutation underwent audiometry. RESULTS: The A3243G mutation was identified in 16 patients (10 index patients and 6 symptomatic relatives). Six of these patients presented with strokelike episodes and met the classical criteria of MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes), and one had MELAS/MERRF (myoclonic epilepsy with ragged-red fibers) overlap syndrome. Two patients presented with strokelike episodes but did not meet the classical criteria of MELAS. Predominant features of the 8 other patients were myopathy with hearing loss and diabetes mellitus (n = 1), chronic progressive external ophthalmoplegia (n = 1), diabetes mellitus with hearing loss (n = 1), painful muscle stiffness with hearing loss (n = 1), cardiomyopathy (n = 1), diabetes mellitus (n = 1), and hearing loss (n = 2). In 11 of 16 patients, hearing impairment was obvious on clinical examination. Furthermore, all 5 patients with normal hearing on clinical examination showed subclinical hearing loss; in 4, hearing loss was more pronounced than age-related hearing impairment and in 1, hearing loss can be age related as well. CONCLUSIONS: A variety of phenotypes represent the variable multisystemic involvement of the A3243G mutation. Less than half of the patients presented with MELAS. Hearing impairment, the most common symptom, was clinically or subclinically relevant in 15 (94%) of 16 patients.     

Adrenal insufficiency in a child with MELAS syndrome

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) are established subgroups of mitochondrial encephalomyopathy. m.3243A > G a common point mutation is detected in tRNA in majority of patients with MELAS phenotype whereas m.8344A > G point mutation in tRNA is observed, in MERRF phenotype. Adrenal insufficiency has not been reported in mitochondrial disease, except in Kearns-Sayre Syndrome (KSS), which is a mitochondrial deletion syndrome. We report an unusual presentation in a five year old boy who presented with clinical phenotype of MELAS and was found to have m.8344A > G mutation in tRNA. Addison disease was identified due to hyperpigmentation of lips and gums present from early childhood. This is the first report describing adrenal insufficiency in a child with MELAS phenotype.     

Genotype to phenotype correlations in mitochondrial encephalomyopathies associated with the A3243G mutation of mitochondrial DNA

We studied 22 subjects carrying the A3243G point mutation of human mitochondrial DNA (mtDNA). In 14 cases the clinical phenotype was characterized by mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), while 8 patients had chronic progressive external ophthalmoplegia (CPEO). The proportion of A3243G heteroplasmy in muscle was determined by two methods: densitometry on a diagnostic restriction-fragment length polymorphism and solid-phase mini-sequencing. We found a highly significant inverse correlation between the percentage of A3243G mutation and the specific activity of complex 1, the respiratory complex with the highest number of mtDNA-encoded subunits, suggesting a direct effect of the mutation on mtDNA translation. No correlation was observed between the percentage of mutated mtDNA and the presence or absence of specific clinical features, such as stroke, ophthalmoplegia and diabetes mellitus. However, in the MELAS group the percentage of mutated mtDNA molecules was strongly correlated with the age of onset, while no such correlation was found in the CPEO group, suggesting a different time-dependent evolution of the mutation in the two groups. Finally, in contrast with other mtDNA mutations associated with ragged-red fibres (RRF), in both MELAS³²⁴³ and CPE0³²⁴³ we observed a high proportion of RRF that were positive to the histochemical reaction to cytochromec oxidase, a morphological feature that seems to be specific for the neuromuscular phenotypes associated with mutations affecting the tRNA^Leu(UUR) gene.     

线粒体基因G13513A突变导致的线粒体脑肌病六例临床表型分析

目的 报告6例mtDNA G13513A点突变引起的线粒体脑肌病患者的临床、影像学特点,总结mtDNA G13513A突变所致的线粒体病的临床表型.方法 对35例mtDNA常见突变(包括大片段缺失及A3243G、T3271C、A8344G、T8993G/C点突变)检查为阴性的线粒体脑肌病患者,用线粒体DNA全长测序和(或)聚合酶链反应-限制性片段长度多态法检测mtDNA G13513A点突变,分析阳性患者的临床特点,复习文献报道的mtDNA G13513A所致线粒体病的病例.结果 35例患者中有6例存在mtDNA G13513A突变.该6例患者均出现偏盲、轻偏瘫或偏身感觉障碍等卒中样发作表现,其中3例成人发病者以卒中样发作为主要症状,伴随癫痫、头痛、身材矮小、神经性耳聋等,头颅MRI显示以顶-枕-颢叶受累为主的大片病灶,符合成人型线粒体脑肌病伴高乳酸血症和卒中样发作(MELAS)的临床和影像学特点;3例青少年发病者除卒中样发作外,还有构音障碍、共济失调、眼外肌瘫痪等脑干受累的症状,MRI检查可见枕-颞叶大脑皮质非对称性病灶,以及双侧基底节和脑干的对称性病灶,符合青少年型MELAS-Leigh叠加综合征的临床和影像学特点.肌肉病理检查在5例患者发现不整红边纤维.经复习文献,发现mtDNA G13513A突变患者还存在婴幼儿型Leigh或Leigh样综合征表型.结论 mtDNA G13513A点突变是线粒体脑肌病较常见的致病性突变,主要导致Leigh综合征、MELAS-Leigh叠加综合征或MELAS综合征,其临床表型具有年龄依赖性.

Abstract：

Objective To report 6 Chinese patients with mitochondrial encephalomyopathy caused by mitochondrial DNA(mtDNA)G13513A mutation and discuss the mitochondrial phenotype associated with this mutation based on the data of our patient series as well as the reports by others.Methods Direct sequencing of polymerase chain reaction(PCR)products or PCR-RFLP analysis Was performed to screen mtDNA G13513A mutation in 35 cases with mitoehondrial encephalomyopathy.who carried no mtDNA common mutations(1arge 8eale deletion,A3243G,T3271 C,A8344G,or T8993G/C).The clinical features,MRI changes were retrospectively collected and analyzed.Published studies of all patients with mtDNA G13513A mutation were also reviewed.Results Six patients were identified carrying mtDNA G13513A mutation.All patients presented stroke-like episodes with hemianopsia.hemiparesis or hemiparesthesia.Three adult patients presented clinical and radiological features of adult-onset mitochondrial myopathy,encephalopathy,lactic acidosis,and stroke-like episodes(MELAS),including stroke-like episodes,epilepsy,headache,short stature,sensorineural deafness,multifocal lesions on parietal,occipital and temporal lobes on cranial MRI scans.Three iuvenile.onset patients presented the clinical and brain MRI features of MELAS-Leigh syndrome(LS)overlap syndrome.In addition to the stroke-like episodes,they also showed brain stem lesions with dysarthria,ataxia,and ophthalmopJegia. Brain MRI revealed asymmetrical lesions in the cortex of the oecipital and temporal lobes,as well as symmetrical lesions in the bilateral basal ganglia and brainstem.Muslce biopsy showed ragged redfibem in 5 patients.The infant-onset LS or Leigh-like syndrome with mtDNA G135 13A was described in the English literature.Conclusions mtDNA G13513A mutation is a common pathogenic mutmion for mitochondrial encephalomyopathy,which can result in Leigh syndrome,MELAS-LS overlap syndrome and adult MELAS.The onset of various phenotypes is relatively age-dependent.     

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.     

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.     

Heterogeneous phenotypic manifestations of maternally inherited deafness associated with the mitochondrial A3243G mutation. Case report

The A3243G mutation is one of the most frequent mutations of mitochondrial DNA. The phenotypic expression of the A3243G mutation is variable and causes a wide range of syndromic and non-syndromic clinical disorders. Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome is the most frequent syndromic manifestation of the A3243G mutation. Stroke-like episodes seem to be the dominant feature of MELAS. We have investigated the case of a family with A3243G mutation, in which a dominant symptom in three generations was the maternally inherited hearing loss with absence of stroke-like episodes. Besides deafness, we found also other clinical features such as myopathy, neuropathy, migraine, ataxia, short stature, diabetes mellitus, and cardiomyopathy.     

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.     

Tissue mosaicism in the skeletal muscle and sural nerve biopsies in the MELAS syndrome

We describe a clinically full-blown MELAS patient, who had an A3243G point mutation of mitochondrial DNA (mtDNA) in muscle and blood cells, and his family members. From the proband two muscle biopsies from the vastus lateralis muscle were analysed; one had typical ragged red fibers and focal cytochrome c oxidase deficiency and the other was completely normal. He also had a peripheral neuropathy confirmed by nerve conduction velocity and sural nerve biopsy studies. Axonal degeneration, relative loss of large myelinated fibers and paracrystalline inclusion bodies in the Schwann cells were noted. Intriguingly, the A3243G mutation of mtDNA was not found in the sural nerve biopsy. Therefore, we conclude that tissue mosaicism is present in the muscle fibers and that the mtDNA mutation may not be detected in the nerve involved as proved by pathology. We also suggest that the involvement of specific tissues in patients with mitochondrial diseases should be further determined by single fiber mtDNA analysis.     

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.     

Clinical and genetic features in two families with MELAS and the T3271C mutation in mitochondrial DNA

The majority of patients with MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes) have the A3243G point mutation. The much rarer T3271C mutation has been reported predominantly in Japanese subjects. Our objective was to better define the clinical phenotype and mutation load in patients with MELAS and the T3271C mutation in mitochondrial DNA. We present clinical and molecular genetic data in two pedigrees with the T3271C mutation. The age at onset was 8 years in one proband and 14 years in the other. Both patients had migrainelike headache, seizures, and strokelike episodes. Mutation loads were quantified in multiple tissues from the patients and from family members by polymerase chain reaction-restriction fragment length polymorphism analysis. The symptoms in both probands were typical of MELAS, and, contrary to previous reports, onset was early. Hearing loss was less common than in typical MELAS, and ragged red fibers were absent. The proportion of mutant genomes was consistently and markedly greater in DNA from urinary sediment than from blood. In the mother of one proband, mutant genomes were detected only in DNA from hair follicles and cheek mucosa The phenotype of patients with the T3271C mutation might not be as distinct as that of the A3243G mutation, as previously described. Our data also suggest that urine is a better source of DNA than blood for diagnosis and that multiple tissues should be studied in maternal relatives, especially when the mutation cannot be detected in blood.     

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes correlates with heteroplasmic mutations of mitochondrial DNA 3243 A single-case genealogy analysis

BACKGROUND: Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a common syndrome of mitochondrial diseases caused primarily by a mutation from adenine to guanine at mitochondrial DNA 3243. However, the correlation between heteroplasmic mutations and clinical characteristics of hereditary MELAS syndrome is unclear. OBJECTIVE: To survey the clinical behaviors, biochemical outcomes, and imaging data in a patient with suspected MELAS syndrome by maternal inheritance, and to investigate the correlation with heteroplasmic mutations of hemocyte mitochondrial DNA. DESIGN, TIME AND SETTING: A case analysis based on hereditary family surgery was performed in the Enliang Hospital of Anshan, Taian County, and biochemical tests and gene diagnosis were erformed at the Department of Laboratory and Institute of Neurology, the First Affiliated Hospital of China Medical University, between March and September 2009. ARTICIPANTS: A 22-year-old female patient with MELAS syndrome was diagnosed in the First Affiliated Hospital of China Medical University in January, 2009. She had five males and seven females in her maternal family. METHODS: We obtained stroke and convulsion history in the patient and her family, as well as erforming routine blood tests, plasma lactic acid levels before and after movement, and magnetic resonance of the head. A mutation at m.3243A > G was verified using polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing, and quantitated using real-time polymerase chain reaction. MAIN OUTCOME MEASURES: Correlation of clinical behaviors and biochemical outcomes, as well as imaging data with heteroplasmic mutations in family members with typical and atypical MELAS syndrome. RESULTS: Some family members had typical symptoms of convulsion, stroke, and MELAS syndrome, as well as atypical symptoms of microsomia, movement intolerance, febrile, and migraine. Magnetic resonance of the head was consistent with typical imaging data of MELAS syndrome during attacks, and family members showed cerebellar atrophy. A heteroplasmic mutation of mitochondrial DNA 3243 occurred in all family members, although higher levels caused severe typical symptoms. The age of first-onset convulsion was negatively correlated with level of heteroplasmic mutation (r= -0.852, P< 0.05), but lactic acid was positively correlated with mutation levels (before movement, r= 0.945, P< 0.001; after movement, r= 0.945, P< 0.001). CONCLUSION: MELAS syndrome was diagnosed in this family by maternal inheritance, and the etiological factor was a mutation of mitochondrial A3243G. The level of heteroplasmic mutation correlated with anticipated convulsion and lactic acid levels.