Neuropsychological status of mitochondrial encephalomyopathies

We studied 15 patients suffering from mitochondrial encephalomyopathies (MEM) by a neuropsychological screening procedure. Eight of the patients were diagnosed as having progressive external ophthalmoplegia (PEO), four mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and three Kearns-Sayre syndrome (KSS). Based on test results covering memory, orientation, non-verbal intelligence, drawing, arithmetics, word list generation, trail making and digit span, only four patients were regarded as normal, two in the PEO and two in the KSS groups, while five patients were found to be demented (two patients in the PEO and three patients in the MELAS groups). Although memory problems were very common, it is concluded that no uniform pattern of neuropsychological deficits is seen in MEM, that MELAS patients apparently are severely handicapped cognitively, and that considerable mental deterioration may be seen even with normal computer-assisted tomography findings.     

Lack of apoptosis in mitochondrial encephalomyopathies

BACKGROUND/OBJECTIVE: Apoptosis, or programmed cell death, is an evolutionary conserved mechanism essential for morphogenesis and tissue homeostasis, but it plays an important role also in pathologic conditions, including neurologic disorders. Its execution pathway is critically regulated at the mitochondrial level. Evidence of apoptosis in muscle specimens was investigated in patients with genetically defined mitochondrial encephalomyopathies. METHODS: Thirty-three muscle biopsies from patients with genotypically different mitochondrial diseases (single and multiple deletions, A3243G/A8344G point mutations of the mitochondrial DNA) were studied. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) reaction was used as a marker of nuclear DNA fragmentation, as well as antibodies against pro- (Fas) or anti- (Bcl-2) apoptotic factors. Also, because one hallmark of apoptosis is morphologic, ultrastructural studies were performed on skeletal muscle from 18 of 33 patients, examining both phenotypically normal and ragged red fibers. RESULTS: In all muscle biopsies, no significant expression of either pro (Fas) and inhibiting (Bcl-2) apoptosis-related proteins was found, nor TUNEL positivity. This latter finding is confirmed by lack of morphologic evidence of apoptosis in all the fibers examined at the ultrastructural level. CONCLUSION: The authors' findings suggest that genetically determined defects of oxidative phosphorylation do not induce the apoptotic process and that apoptosis is not involved in the pathogenesis of mitochondrial disorders.     

Effectiveness of creatine monohydrate in mitochondrial encephalomyopathies

The mitochondrial encephalomyopathies are chronic progressive disorders affecting predominantly the neuromuscular system. Symptoms are induced by insufficient energy supply resulting from a deficiency of oxidative phosphorylation. We studied one male and four female patients with genetically proven mitochondrial encephalomyopathy. Their ages ranged from 7 to 19 years (two with Kearns-Sayre syndrome, one patient with neuronal muscle weakness, ataxia, and retinitis pigmentosa syndrome, and two patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes), using a retrospective study method. We studied the effect of creatine supplementation (0.08 g-0.35 g/kg body weight/day; 9 months to 4 years, 10 months) and measured skeletal muscle power analysis (bicycle ergometer). After creatine supplementation all patients demonstrated an increase in their maximum performance (W) (+4% - +30%; mean: +12.1%). These results indicate an improved aerobic oxidative function of mitochondria after creatine administration in patients with mitochondrial encephalomyopathies. Continuous physical exercise was improved to a greater extent than instantaneous activity.     

Superoxide dismutases of muscle in mitochondrial encephalomyopathies

Lmmunohistochemical analyses were made of the superoxide dismutases (Mn-SOD and CuiZn-SOD) in biopsied muscles from 7 patients with mitochondrial encephalomyopathies that included mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS), and chronic progressive external ophthalmoplegia (CPEO). Mn-SOD mainly was present in the subsarcolemmal region, but it also was found in a coarsely granular, reticular, or diffuse pattern of staining within the muscle fibers. These Mn-SOD-positive fibers corresponded almost completely to the ragged-red fibers. The immunoreaction for CuiZn-SOD was weakly positive in some of the muscle fibers positive for Mn-SOD. In CPEO, Mn-SOD-positive fibers predominantly showed decreased cytochrome c oxidase (COX) activity. In MELAS, Mn-SOD-positive fibers tended to be stained deeply for COX although a few were COX-negative. These findings suggest that Mn-SOD-positive fibers can be used to make a differential diagnosis between CPEO and MELAS and that in mitochondrial encephalomyopathies Mn-SOD in the raggedred fibers may protect against oxidative stress. © John Wiley & Sons, Inc.     

Apoptosis is suspended in muscle of mitochondrial encephalomyopathies

Over the past few years, many studies have been done on the apoptotic involvement in muscle fiber degeneration in various myopathies, but the occurrence of apoptosis in muscles of mitochondrial encephalomyopathies is still controversial. To confirm whether apoptotic processes are truly related to muscle fiber degeneration in mitochondrial encephalomyopathies, we performed the TUNEL method not only at the light microscopic (LM) but also at the electron microscopic (EM) level for muscles of five MELAS, five CPEO and five MERRF patients and five control muscles. Immunohistochemical studies of Bcl-2, Bax, cytochrome c, Apaf-1, activated caspase-3 and human inhibitor of apoptosis protein XIAP, and immunoblotting of Apaf-1 and XIAP were also carried out. In LM-TUNEL, MELAS, CPEO and MERRF patients had only very small numbers of TUNEL-positive myonuclei: 0.13+/-0.10%, 0.15+/-0.14% and 0.04+/-0.09%, respectively. Almost all of them were seen in ragged-red fibers (RRFs). EM-TUNEL showed no significant increase of DNA fragmentation in RRFs despite mild peripheral chromatin condensation. However, Bax and Apaf-1 expression and cytochrome c release from mitochondria were seen in RRFs. Caspase-3 activation was confirmed in 9.0+/-3.7%, 12.0+/-4.4% and 12.4+/-3.8% of RRFs in MELAS, CPEO and MERRF, respectively, but not in control muscles. Almost all RRFs showed sarcoplasmic expression of XIAP. Thus, there is a possibility that, although apoptotic reactions started in muscles of mitochondrial encephalomyopathies, their execution is rarely completed. Sarcoplasmic expression of XIAP probably leads to the suspension of the apoptotic process in mitochondrial encephalomyopathies.     

Myostatin expression in muscular dystrophies and mitochondrial encephalomyopathies

The demonstration that myostatin may negatively regulate muscle mass in adult individuals has raised the possibility of targeting the myostatin pathway in order to increase muscle growth in a variety of muscle degenerative and wasting conditions. In this regard, blockade of endogenous myostatin results in anatomic, biochemical, and physiologic improvement in the dystrophic phenotype in the mdx mouse. Moreover, myostatin messenger ribonucleic acid levels are decreased in the regenerated muscle of these mice, suggesting that myostatin may also be involved in the pathogenesis of the disease. To gain further insight into the possible role of myostatin in muscle degenerative diseases, the present work investigates the expression of muscle myostatin in children with muscular dystrophies and mitochondrial encephalomyopathies. No differences in the pattern of myostatin expression were evident in any case, even in those patients with prominent muscular atrophy. These findings suggest that muscle loss that can be observed in muscle degenerative diseases does not depend on changes in myostatin expression.     

Treatment of mitochondrial encephalomyopathies with a xanthine oxidase inhibitor

Five females with mitochondrial encephalomyopathies were treated for 3 to 7 years with a xanthine oxidase inhibitor (allopurinol, oral route, 20 mg/kg/day, in 2 or 3 doses daily). Clinical course was monitored in all patients. In addition, various metabolic variables, namely blood lactic acid, blood adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate were monitored, as well as energy charge. Data obtained were compared with data for an age-matched control group of 10 healthy children. Four of the five patients manifested clinical improvement, and the remaining patient exhibited slower disease progression. Three of the four patients who exhibited clinical improvement also had normalization of blood lactic acid level. All five patients had an increase in blood adenosine triphosphate levels and a decline in blood adenosine monophosphate; four of the five manifested a decline in blood adenosine diphosphate and increased energy charge. Mean blood adenosine triphosphate was significantly increased with respect to pretreatment levels and with respect to the control group; mean energy charge displayed an increase, though this was not statistically significant. In one patient, reduction of the allopurinol dose to 10 mg/kg/day was followed by a decline in both blood adenosine triphosphate level and energy charge, and by clinical worsening. In conclusion, the xanthine oxidase inhibitor allopurinol appears to have had beneficial effects in these patients in terms of both energy metabolism and clinical course.     

Correlative multidisciplinary approach to the study of mitochondrial encephalomyopathies

Mitochondrial encephalomyopathies can be caused by defects in the mitochondrial respiratory complexes. The clinical phenotypes are quite protean but in many instances a characteristic or suggestive clinical presentation permits a tentative bedside diagnosis. The diagnosis can be verified by laboratory investigations. The major laboratory hallmarks of mitochondrial encephalomyopathies include: ragged red fibers on muscle biopsy, a specific defect or deficiency in a mitochondrial respiratory enzyme complex, mtDNA abnormalities, reduced anaerobic threshold by bicycle ergometry, impaired cellular energy state by MRS and characteristic brain imaging abnormalities. Monitoring of some of these parameters along with the clinical phenotype will aid in the evaluation of therapeutic trials.     

线粒体脑肌病的临床、病理及影像学特点

目的探讨线粒体脑肌病(ME)的临床、病理及影像学特点。方法回顾性分析20例ME患者的临床资料。结果本组中,慢性进行性眼外肌麻痹(CPEO)7例;肌阵挛性癫痫伴破碎红纤维(MERRF)6例;线粒体脑肌病伴乳酸中毒以及卒中样发作(MELAS)5例;Leigh综合征(LS)2例。临床表现为眼睑下垂7例(35%),肢体无力12例(60%),癫痫10例(50%),卒中样发作5例(25%)和精神智能障碍9例(45%)。8例患者血肌酸激酶升高;7例患者行血乳酸水平检查,均不同程度增高。EMG显示肌源性损害8例,神经源性损害4例,周围神经损害2例,正常6例。头颅MRI表现为脑萎缩、脑白质变性和不符合血管分布的卒中样改变。骨骼肌病理可见破碎红纤维(RRF)和SDH染色肌间小血管强染(SSV);细胞色素C氧化酶(COX)酶活性减低或缺失。电镜下线粒体结构和/或数量异常。结论 ME临床表现复杂多样,多有骨骼肌和脑受累。RRF和SSV是ME主要病理表现。     

Muscle coenzyme Q10 in mitochondrial encephalomyopathies.

Coenzyme Q₁₀ (CoQ) content was measured in isolated muscle mitochondria from 25 patients with mitochondrial encephalomyopathies (MEM), most of whom had mitochondrial DNA mutations. The CoQ level was significantly lower in MEM patients than in controls. CoQ levels varied widely from patient to patient, especially in those with chronic progressive external ophthalmoplegia including Kearns-Sayre syndrome, which may explain, at least in part, the variable response of patients to CoQ administration.     

The neuropsychological features of mitochondrial myopathies and encephalomyopathies.

Detailed testing of higher cerebral function was performed in 36 patients with mitochondrial myopathies and encephalomyopathies. Fourteen of these patients were thought to be cognitively impaired on clinical grounds. The assessments included tests of general intellectual ability and focal tests of memory, language, and perception. Twenty-one (58%) of the 36 patients who were tested had evidence of general intellectual deterioration, with focal cognitive deficits of variable degree. Of the remaining 15 patients in whom there was no evidence of general intellectual decline, five displayed focal cognitive deficits. In only 10 patients was there evidence of cerebral dysfunction. The range and extent of cognitive deficits in mitochondrial myopathies are greater than predicted by their clinical presentations.     

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.     

反复发热头痛的线粒体脑肌病患者病理及影像学分析

目的：探讨以反复发热、头痛为主要临床表现的线粒体脑肌病患者的病理及影像学特征。方法选取1例临床确诊的线粒体脑肌病伴高乳酸血症和卒中样发作（mitochondrial encephalomyopathy ，lactic acidosis ，and strokelike episode ， MELAS）患者，调查其发病情况、家族史、病理及影像学特征进行研究。结果该患者18岁起病，2a病程，临床主要表现为反复出现的发热、头痛，类似轻型病毒性脑炎表现。磁共振平扫及血管成像（MRA）发现枕叶异常信号，呈此消彼长的变化特征；乳酸测定发现空腹乳酸明显增高。左侧肱二头肌开放式肌肉活检：光镜下可见大量破碎红纤维。结论临床上貌似病毒性脑炎的年轻患者应注意和MELAS相鉴别，磁共振和开放式肌肉活检是确诊该病的关键措施。     

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.     

Resistance to ischaemic nerve-fibre block in diabetes mellitus and in mitochondrial encephalomyopathies

Thermal thresholds were measured during ischaemic compression block in the left forearms of 26 healthy subjects, 10 patients with diabetes mellitus and 6 patients suffering from different kinds of mitochondrial disorders. Cold and warm thresholds in the 6 patients with deficiencies in the respiratory chain increased earlier than in normals. When cold perception was impaired, cold stimuli were perceived as warmth and pinprick perception attenuated. In diabetics cold thresholds were less elevated during ischaemic block than in controls. This was paralleled by tingling paraesthesiae in all groups. The findings show that higher resistance to ischaemic nerve-fibre block in diabetes mellitus is not exclusively based on increased anaerobic metabolism.