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.     

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.     

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.     

MELAS综合征临床、影像、脑电图及基因特点分析

目的探讨MELAS综合征的临床症状、影像学和脑电图表现及基因突变特点,提高临床对疾病的认识。方法本研究共纳入MELAS综合征患者12例,收集其一般临床资料,分析其临床症状、颅脑影像学结果、脑电图表现及基因突变特点。结果 12例患者平均起病年龄28岁,临床主要表现为癫痫发作(66.7%)、卒中样发作(50.0%)、认知功能下降以及精神行为异常(41.7%)、糖尿病或糖耐量异常(41.7%)、听力损害(41.7%)等;影像学检查病灶呈长T1、长T2、DWI高信号改变,主要分布在枕、颞、顶叶,6例MRS检查中5例出现异常乳酸峰,8例脑电图检查主要表现为全脑弥漫性慢波或癫痫样放电,9例基因检测均为A3243G点杂合突变。结论MELAS综合征临床表现多样,颅脑影像学、脑电图检查特异性有限,MRS成像中异常乳酸峰可提示诊断,A3243G为最常见突变类型。     

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).     

MELAS- and kearns-sayre-type with myopathy and autoimmune polyendocrinopahy

A 35-year-old woman with features of Kearns-Sayre syndrome consisting of progressive ptosis, ophthalmoparesis, mitochondrial myopathy, and pigmentary retinopathy also had autoimmune polyglandular syndrome type I1 (Addison's disease, autoimmune insulin-dependent diabetes meuitus, Hashimoto's thyroiditis, and primary ovarian failure). There was no history of similarly affected relatives. Analysis of muscle mitochondrial DNA (mtDNA) revealed a 2,532-bp deletion of the type seen in Kearns-Sayre syndrome as well as a heteroplasmic A3243G mutation in the tRNA-Leu(UUR) gene of the type seen in mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). The patient's blood and her mother's blood harbored the A3243G mutation but not the deletion, and the maternal grandmother's blood had neither mutation. In muscle, the species of mtDNA harboring the deletion was exclusively associated with the species harboring the A3243G mutation, suggesting that the point mutation predisposed to the large-scale deletion. The mtDNA species with both mutations accounted for 88% of total muscle mtDNA. Other and as yet unrecognized point mutations in mtDNA might also be associated with, and possible causally related to, largescale mtDNA deletions.     

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.     

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.     

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.     

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.     

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.     

Wolff-Parkinson-White syndrome in Patients With MELAS

BACKGROUND: Tissues with high energy demands, such as the heart, are susceptible to the effects of mitochondrial DNA point mutations. OBJECTIVE: To investigate the frequency of Wolff-Parkinson-White (WPW) syndrome among a phenotypically and genotypically homogeneous cohort of patients with MELAS (mitochondrial encephalopathy, lactic acidosis, and strokelike episodes) and the A3243G mutation most commonly associated with MELAS syndrome. DESIGN: Survey. SETTING: The Pediatric Neuromuscular Disease Center at Columbia University. Patients Thirty patients with the A3243G mutation and MELAS syndrome enrolled in a clinical trial to assess the effect of dichloroacetate on neurologic symptoms. INTERVENTIONS: Medical histories and electrocardiograms were reviewed and DNA samples from fibroblasts, urine and cheek epithelial cells, leukocytes, and hair were analyzed to determine mitochondrial mutation abundance and estimate total mutation burden. RESULTS: Four of 30 patients (13%) had a clinical history of, or electrocardiographic findings consistent with, WPW syndrome. In 2 patients, WPW syndrome preceded MELAS syndrome by 15 and 21 years. The tissue burden of mutant mitochondria was similar in patients with (49.4%) and without (39.1%) WPW syndrome. CONCLUSIONS: The prevalence of WPW syndrome among patients with MELAS syndrome and the A3243G mutation appears much higher than in the normal population and may become manifest earlier than neurologic symptoms. Patients with WPW syndrome and neurologic abnormalities consistent with MELAS syndrome, such as seizures, deafness, short stature, and stroke, should be screened for the A3243G mutation. Moreover, patients with MELAS syndrome should be monitored for cardiac anomalies including cardiomyopathy and WPW syndrome.     

Common mitochondrial DNA and POLG1 mutations are rare in the Chinese patients with adult-onset ataxia on Taiwan

BACKGROUND AND PURPOSE: Spinocerebellar ataxia (SCA) is a heterogeneous group of neurodegenerative disorders with common features of adult-onset cerebellar ataxia. Many patients with clinically suspected SCA are subsequently diagnosed with common SCA gene mutations. Previous reports suggest some common mitochondrial DNA (mtDNA) point mutations and mitochondrial DNA polymerase gene (POLG1) mutations might be additional underlying genetic causes of cerebellar ataxia. We tested whether mtDNA point mutations A3243G, A8344G, T8993G, and T8993C, or POLG1 mutations W748S and A467T are found in patients with adult-onset ataxia who did not have common SCA mutations. METHODS: Four hundred seventy-six unrelated patients with suspected SCA underwent genetic testing for SCA 1, 2, 3, 6, 7, 8, 10, 12, 17, and DRPLA gene mutations. After excluding these SCA mutations and patients with paternal transmission history, 265 patients were tested for mtDNA mutations A3243G, A8344G, T8993G, T8993C, and POLG1 W748S and A467T mutations. RESULTS: No mtDNA A3243G, A8344G, T8993G, T8993C, or POLG1 W748S and A467T mutation was detected in any of the 265 ataxia patients, suggesting that the upper limit of the 95% confidence interval for the prevalence of these mitochondrial mutations in Chinese patients with adult-onset non-SCA ataxia is no higher than 1.1%. CONCLUSIONS: The mtDNA mutations A3243G, A8344G, T8993G, T8993C, or POLG1 W748S and A467T are very rare causes of adult-onset ataxia in Taiwan. Routine screening for these mutations in ataxia patients with Chinese origin is of limited clinical value.     

"MELAS" (A3243G) mutation of mitochondrial DNA: a study of the relationships between the clinical phenotype in 19 patients and morphological and molecular data

Nineteen patients were found to harbor the mitochondrial DNA A3243G mutation associated with MELAS syndrome (Mitochondrial myopathy, Encephalopathy, Lactic Acidosis and Stroke-like episodes). Eight of them had presented with stroke-like episodes and therefore had a clinical diagnosis of MELAS syndrome. The other 11 patients had no strokes and presented with generally less severe multisystemic disease. In the two groups, we compared muscle morphology, biochemical activities of muscle respiratory chain, and genetic characteristics: proportion and tissue distribution of the mutation, sequence of the 22 transfer RNA genes of the mitochondrial DNA. The proportion of mutant mtDNA in muscle was always greater than in blood. The number of patients in the two groups was too low to reach significant values. However, the patients with a MELAS syndrome presented with more severe respiratory chain abnormalities and with a proportion of the A3243G mutation that was both higher and more uniformly distributed among tissues. For symptoms others than stroke-like episodes, we did not observe any correlation with the level of mutant mtDNA in muscle. The analysis of the 22 tRNA sequences did not show differences between the two groups, and no co-inherited modifying tRNA genes could explain the variability of severity in our patients.     

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.     

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.     

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.     

Neuroimaging characteristics in mitochondrial encephalopathies associated with the m.3243A>G MTTL1 mutation

Stroke-like lesions (SLL) are common radiological findings in patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (SLE; MELAS) harboring the m.3243A>G MTTL1 mutation. Imaging patterns in the m.3243A>G mutation carriers with encephalopathies lacking SLE have not been systematically examined to date. The aim of this study was to analyze brain imaging findings in encephalopathies associated with the m.3243A>G mutation irrespective of the presence or absence of SLE. Brain MRI and cranial CT scans from 11 m.3243A>G mutation carriers with encephalopathies were analyzed by two neuroradiologists in consensus. We evaluated stroke-like lesions (SLL), deep grey matter (DGM) changes on T1- and T2-weighted MR images, calcification on CT, brain atrophy, and white matter (WM) changes. SLL were present in all patients showing the full MELAS phenotype with SLE (4/11). Seven patients did not show SLE. DGM changes with T1 hyperintensity and T2 hypointensity were a distinctive finding in most patients (7/11) and present in the majority of m.3243A>G mutation carriers lacking SLE (5/7). DGM changes were also seen in half of our MELAS patients with SLL (2/4), though less pronounced. Brain atrophy was a prominent finding in general and accentuated in the cerebellum. In contrast, WM changes were rather mild and more prevalent and pronounced in MELAS. Our data stress that the distinction between MELAS with SLE and m.3243A>G mutation carriers lacking SLE is rather artificial. In clinical practice, mitochondrial disorders associated with the m.3243A>G mutation should be taken into consideration in encephalopathies with DGM changes, even when SLE and SLL are lacking.     

External ophthalmoplegia with severe progressive multiorgan involvement associated with the mtDNA A3243G mutation

BACKGROUND: Chronic progressive external ophthalmoplegia (CPEO) may be related to primary nuclear DNA or mitochondrial (mt)DNA mutations. The A3243G mtDNA point mutation most frequently causes mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, but also has been associated with other phenotypes including CPEO, migraine, seizure, diabetes, and sensorineural hearing loss. CASE DESCRIPTION: We report a 38-year-old white man with seizures and progressive difficulties of infantile origin including CPEO, sensorineural hearing loss, cataracts, migraines, multiple endocrinopathy, myopathy, and cardiomyopathy. Moderate hearing loss in association with CPEO, diabetes mellitus, or migraines were noted in the proband's maternal grandmother, great aunt, mother, and three sisters, suggesting either an autosomal dominant or maternal inheritance. Detailed histological and biochemical analysis of the proband's biopsied muscle specimen revealed severe abnormalities compatible with a mitochondrial disease. MtDNA analysis excluded large-scale deletions, but revealed a heteroplasmic A to G transition at nt3243 in 56.4% and 27.4% of molecules in muscle and white blood cells, respectively. CONCLUSION: We discuss possible causes of this intrafamilial heterogeneity of phenotypes associated with the A3243G mtDNA 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.