When should MELAS (Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes) be the diagnosis? / Quando o diagnóstico deveria ser MELAS (Miopatia mitocondrial, encefalopatia, acidose lática, e episódios semelhantes a acidente vascular cerebral)?

ABSTRACTMitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes (MELAS) is a rare mitochondrial disorder. Diagnostic criteria for MELAS include typical manifestations of the disease: stroke-like episodes, encephalopathy, evidence of mitochondrial dysfunction (laboratorial or histological) and known mitochondrial DNA gene mutations. Clinical features of MELAS are not necessarily uniform in the early stages of the disease, and correlations between clinical manifestations and physiopathology have not been fully elucidated. It is estimated that point mutations in the tRNALeu(UUR) gene of the DNAmt, mainly A3243G, are responsible for more of 80% of MELAS cases. Morphological changes seen upon muscle biopsy in MELAS include a substantive proportion of ragged red fibers (RRF) and the presence of vessels with a strong reaction for succinate dehydrogenase. In this review, we discuss mainly diagnostic criterion, clinical and laboratory manifestations, brain images, histology and molecular findings as well as some differential diagnoses and current treatments.

RESUMOMiopatia mitocondrial, encefalopatia, acidose lática, e episódios semelhantes a acidente vascular cerebral (MELAS) é uma rara doença mitocondrial. Os critérios diagnósticos para MELAS incluem as manifestações típicas da doença: episódios semelhantes a acidente vascular cerebral, encefalopatia, evidência de disfunção mitocondrial (laboratorial ou histológica) e mutação conhecida em genes do DNA mitocondrial. Na fase inicial da doença, as manifestações clínicas podem não ser uniformes, e sua correlação com a fisiopatologia não está completamente elucidada. Estima-se que as mutações de ponto no gene tRNALeu(UUR) do DNAmt, principalmente a A3243G, sejam responsáveis por cerca de 80% dos casos de MELAS. As alterações morfológicas na biópsia muscular incluem uma grande proporção de fibras vermelhas rasgadas (RRF) e presença de vasos com forte reação para succinato desidrogenase. Nesta revisão, são discutidos os principais critérios diagnósticos, manifestações clínicas e laboratoriais, imagens cerebrais, padrões eletrofisiológicos, histológicos e alterações moleculares, bem como alguns dos diagnósticos diferenciais e tratamentos atuais.

Comportamiento de la mutación mtDNA A3243G en dos familas antioqueñas de pacientes diagnosticados con el síndrome MELAS / Behavior of the mtDNA mutation A3243 in two antioquian families of patients with melas syndrome

Introducción: mutaciones en mtDNA causan citopatias mitocondriales, la más común de ellases el síndrome MELAS; la transición A3243G en tRNA de leucina (tRNALeu) se presenta en 80% depacientes. La heteroplasmia, observada en citopatias mitocondriales, consiste en coexistenciade moléculas mutadas y normales en una célula, situación en la cual, dependiendo de su cantidad,afecta su función con expresión clínica variable.Objetivo: evaluar el comportamiento de la cantidad de heteroplasmia de la mutación 3243G ensu expresión clínica y en la dependencia de variantes nucleares.Pacientes y métodos: se buscaron mutaciones en el gen que codifica para el tRNA de leucinapor secuencia y por PCR-RFLP en 34 pacientes, y se tamizó en familiares de los portadores de lamutación. Se tipificaron cuatro Specific Population Allele (SPA) en pacientes y familiares con lamutación A3243G.Resultados: se halló la mutación A3243G en el tRNALeu en dos pacientes, luego de tamizar lamutación A3243G en ambas familias se evaluó la cantidad de mtDNA mutado (MDNA),encontrando que los casos índices de ambas familias presentaron la mayor cantidad de MDNA;en la primera familia se detectó la mutación en 15 miembros que presentaron diversos síntomas.En la segunda familia se detectó la mutación en un miembro con parálisis cerebral, en dos conmigraña y en uno asintomático.Conclusiones: la severidad de los síntomas se correlaciona con la cantidad de MDNA, se encontróademás correlación entre mtDNA mutado (MDNA) y el Índice de Ancestría Amerindio en cadaindividuo (IAA), indicando una posible influencia del contexto nuclear amerindio en lasegregación y replicación mitocondrial.

Mitochondrial DNA mutations cause mitochondrialcytopathies. Among them Mitochondrial Encephalomyopathy,Lactic Acidosis, and Stroke-like episodes(MELA) is the commonest. The transition 3243A>G inthe Leucine tRNA is present in 80% of the patients.Heteroplasmy is observed in mitochondrialcytopathies, characterized by the coexistence of mutantand wild type molecules in a cell. Depending on thelevel of heteroplasmy, function and clinicalmanifestations might result affected.Objective: To test the degree of heteroplasmy of themutation 3243G on its expression (syntoms) andnuclear-variants dependence.Patients and methods: Mutations in the tRNALeu genewere sought in 34 patients by sequencing and PCR-RFLP.Four SPA (specific population alleles) were typed inpatients and their relatives carrying the mutation3243A>G.Results: The mutation 3243A>G in the Leucine tRNAgene was found in two patients. This mutation wasscreened in their relatives and the amount of mutantDNA (MDNA) was assessed. The index cases presentedwith the higher amounts of MDNA in both families. Infamily one, the mutation was detected in 14members, three of which presented with short stature,one with hearing loss, one with type 2 diabetes, 8 withmigraine and one healthy individual. In family two themutation was detected in one member with brainparalysis, two with migraine and one healthyindividual.Conclusions: Severity of the symptoms in patientsaffected with MELAS is correlated with the amount ofMDNA. Furthermore, it was found a correlationbetween MDNA and IAA, suggesting a possible effect ofamerind nuclear ontext in The mitochondrialsegregation and replication.

MELAS: clinical features, muscle biopsy and molecular genetics / MELAS: manifestações clínicas, biópsia muscular e estudo molecular

OBJECTIVE: The aim of the study was to analyze a series of Brazilian patients suffering from MELAS. METHOD: Ten patients with MELAS were studied with correlation between clinical findings, laboratorial data, electrophysiology, histochemical and molecular features. RESULTS: Blood lactate was increased in eight patients. Brain image studies revealed a stroke-like pattern in all patients. Muscle biopsy showed ralled-red fibers (RRF) in 90 percent of patients on modified Gomori-trichrome and in 100 percent on succinate dehydrogenase stains. Cytochrome c oxidase stain analysis indicated deficient activity in one patient and subsarcolemmal accumulation in seven patients. Strongly succinate dehydrogenase-reactive blood vessels (SSV) occurred in six patients. The molecular analysis of tRNA Leu(UUR) gene by PCR/RLFP and direct sequencing showed the A3243G mutation on mtDNA in 4 patients. CONCLUSION: The muscle biopsy often confirmed the MELAS diagnosis by presence of RRF and SSV. Molecular analysis of tRNA Leu(UUR) gene should not be the only diagnostic criteria for MELAS.

OBJETIVO: O objetivo deste estudo foi analisar uma série de pacientes brasileiros portadores de MELAS. MÉTODO: Dez pacientes com MELAS foram estudados com correlação entre manifestações clínicas, alterações laboratoriais, estudo eletrofisiológico, histoquímico e molecular. RESULTADOS: O nível de lactato sérico estava aumentado em 8 pacientes. O estudo das imagens do crânio revelou padrão semelhante ao de AVC isquêmico em todos os pacientes. A biópsia muscular mostrou fibras rajadas vermelhas (RRF) em 90 por cento dos pacientes na coloração pelo tricrômio de Gomori modificado e em 100 por cento na reação histoquímica pela desidrogenase succicínica (SDH). A análise da coloração pela citocromo c oxidase indicou atividade deficiente em um paciente e acúmulo subsarcolemal em sete pacientes. Vasos com forte reação para SDH (SSV) ocorreram em seis pacientes. O estudo molecular do gene tRNA Leu(UUR) por PCR/RLFP e seqüenciamento direto mostrou a mutação A3243G no DNAmt de 4 pacientes. CONCLUSÃO: A biópsia muscular frequentemente confirma o diagnóstico de MELAS pela presença de RRF e SSV. O estudo molecular do gene tRNA Leu(UUR) não deve ser o único critério diagnóstico para MELAS.

Characterization of 2-deoxy-D-glucose uptake in fibroblast cultures derived from patients with A3243G mitochondrial DNA mutation.

We investigated cellular glucose uptake of fibroblast cultures derived from seven patients with mitochondrial DNA (mtDNA) A3243G mutation and from six healthy controls with no mtDNA mutations. Heteroplasmy of fibroblast cultures were shifted by culturing for 5 days in galactose-containing medium. The proportion of mutant mtDNA decreased by 7.7% to 10% in three patient fibroblast cultures, whereas 2-deoxy-D-glucose uptake increased 1.8-2.1-fold at basal state, 1.9-2.3-fold in the presence of 60 ng/ml of insulin, and 1.8-2.1-fold in 100 ng/ml of insulin. No significant changes in level of heteroplasmy or glucose uptake were observed in the other patients samples and control samples. This study showed that alteration in the proportion of fibroblast mtDNA A3243G mutation content directly affected basal and insulin-stimulated glucose uptake.

Pseudo-infarto cerebral como primera manifestación de un MELAS tardío / Stroke-like as the first debut late onset MELAS

MELAS is an acronym for the convergence of mitochondrial myopathy, encephalopathy lactic acidosis and stroke like episodes. It was described by Pavlakis et al. in 1984.This is a genetic disease caused by mutations in the maternal mitochondrial genome, affecting the adenosine triphosphate (ATP) synthesis. The mutations have heteroplasmic loads on different tissues, which could specially involve those highly energy-dependent such as muscles, brain and CNS tissues. We describe a 33 year old female presenting migraine headaches associated to stroke-like episodes, related to an infection. Neurological manifestations include language and visual disturbances. The magnetic resonance imaging (MRI) showed low-intensity areas, predominantly in the temporal, parietal and occipital left lobes. She further presented a status epilepticus. The complementary study shows elevated basal and post exercise lactic acidosis, ragged red fibers in the muscle biopsy, and the mutation of A3243G in the mitochondrial genome. Her asymptomatic mother and sister showed ragged red fibers in muscle biopsy. The patient showed clinical and radiological features improvement, maintaining non epileptic slow focal occipital discharges in the electroencephalogram. The assumption is that this mitochondrial disorder could be more frequent than detected in our medium, given that a significant number of women could be just asymptomatic bearers (Like the patient's mother and sister). This pathology should always be assessed in patients less than 40 years of age with strokes, regardless whether they have family history with the disease.

MELAS es un acrónimo inglés que define la convergencia de miopatía mitocondrial, encefalopatía, acidosis láctica y episodios de pseudo-infarto cerebral, descrita por Pavlakis et al, en 1984. Es una enfermedad mitocondrial originada por mutaciones en el genoma mitocondrial materno. Se afectan las funciones aeróbicas como consecuencia del déficit que se produce en la generación de adenosina trifosfato (ATP). El compromiso de los distintos tejidos es variable, debido a la heteroplasmia de la mutación, aunque preferentemente se suelen dañar el tejido muscular y el sistema nervioso central, tejidos con mayores requerimientos energéticos. Presentamos una paciente de 33 años que inicia su enfermedad con un síndrome jaquecoso, seguido de un episodio de pseudo infarto cerebral, en relación a un cuadro infeccioso. Clínicamente, evolucionó con alteraciones visuales y del lenguaje que eran concordantes con las áreas de hipointensidad en ambas cortezas temporales y en la corteza del lóbulo parietal y occipital izquierdo, vistas en la Resonancia Magnética. Varios días después de su ingreso cursó con un estatus epiléptico. Su estudio demostró aumento de la lactoacidemia de reposo (39,7) y de esfuerzo (89,4). En la biopsia muscular se observó la presencia de fibras rojas raídas, al igual que en su madre y hermana menor, ambas asintomáticas. El análisis genético demostró la presencia de la mutación A3243G del genoma mitocondrial, estimada en un 26 por ciento del total. La paciente mejoró espontánea y completamente en lo clínico y radiológico, sólo mantuvo una actividad lenta occipital izquierda, de carácter no epiléptico. Se presume que esta alteración mitocondrial podría ser más frecuente de lo detectado en nuestro medio, porque numerosas mujeres podrían ser sólo portadoras asintomáticas (como la madre y hermana de la paciente). Es una patología que debiera investigarse siempre en los accidentes vasculares de jóvenes menores de 40 años, aunque no tengan antecedentes familiar.

A MELAS syndrome family harboring two mutations in mitochondrial genome

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a genetically heterogeneous mitochondrial disorder with variable clinical symptoms. Here, from the sequencing of the entire mitochondrial genome, we report a Korean MELAS family harboring two homoplasmic missense mutations, which were reported 9957T>C (Phe251Leu) transition mutation in the cytochrome c oxidase subunit 3 (COX3) gene and a novel 13849A>C (Asn505His) transversion mutation in the NADH dehydrogenase subunit 5 (ND5) gene. Neither of these mutations was found in 205 normal controls. Both mutations were identified from the proband and his mother, but not his father. The patients showed cataract symptom in addition to MELAS phenotype. We believe that the 9957T>C mutation is pathogenic, however, the 13849A>C mutation is of unclear significance. It is likely that the 13849A>C mutation might function as the secondary mutation which increase the expressivity of overlapping phenotypes of MELAS and cataract. This study also demonstrates the importance of full sequencing of mtDNA for the molecular genetic understanding of mitochondrial disorders.

Screening for MELAS mutations in young patients with stroke of undetermined origin

PURPOSE: It has been suggested that mitochondrial disease may be responsible for a substantial proportion of strokes of indetermined origin. We have preliminarily screened for MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) mutations in young patients with cryptogenic strokes. METHOD: The mitochondrial mutations A3243G and T3271C were investigated in 38 subjects aged less than 46 years. Group 1: 15 patients with cryptogenic strokes; Group 2: 3 patients with diagnosis of MELAS syndrome, including stroke-like episodes; Group 3: 20 healthy subjects. RESULTS: The A3243G mutation was absent in all subjects in Groups 1 and 3 but was present in all subjects in Group 2. CONCLUSION: Our results do not support screening for these mutations to diagnose oligosymptomatic forms of MELAS in cryptogenic strokes in the absence of other features of the syndrome. We suggest that clinical findings should guide mitochondrial genetic testing.

PROPÓSITO: Foi sugerido que mitocondriopatias possam ser responsáveis por uma proporção substancial de acidentes vasculares cerebrais de etiologia indeterminada. Realizamos um estudo preliminar de pesquisa de mutações relacionadas à síndrome de MELAS (encefalomiopatia mitocondrial, acidose lática e episódios "stroke-like") em pacientes jovens com acidentes vasculares cerebrais criptogênicos. MÉTODO: As mutações mitocondriais A3243G e T3271C em 38 indivíduos com menos de 46 anos. Grupo 1: 15 pacientes com acidentes vasculares cerebrais criptogênicos; Grupo 2: 3 pacientes com diagnóstico de síndrome de MELAS, incluindo episódios "stroke-like"; Grupo 3: 20 voluntários saudáveis. RESULTADOS: A mutação A3243G esteve ausente em todos os indivíduos dos Grupos 1 e 3 mas esteve presente em todos os indivíduos do Grupo 2. CONCLUSÃO: Nossos resultados sugerem que não há utilidade em pesquisar estas mutações para diagnosticar formas oligossintomáticas de MELAS em acidentes vasculares cerebrais criptogênicos na ausência de características da síndrome. Sugerimos que o quadro clínico deva guiar a solicitação de pesquisas de mutações relacionadas a mitocondriopatias nestes pacientes.

Precipitation of stroke-like event by chickenpox in a child with MELAS syndrome.

The mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS) is a rare congenital disorder of mitochondrial DNA (mtDNA). Herein we report a case of MELAS, whose second stroke-like episode was provoked by chickenpox. A point mutation at nucleotide (nt) 3243 in mtDNA supported the diagnosis of MELAS in this case. History of myopathy, the presence of lesions that did not conform to accepted distributions of vascular territories on cranial magnetic resonance imaging (MRI), normal result of cranial magnetic resonance angiography, hyperintensity on diffusion weighted MRI and apparent diffusion coefficient mapping indicating the presence of vasogenic edema in the fresh stroke-like lesion, and mitochondrial DNA analysis helped to exclude the diagnosis of ischemic cerebral infarction which can also be induced by chickenpox.

Histochemical and Molecular Genetic Study of MELAS and MERRF in Korean Patients

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episode (MELAS) and myoclonic epilepsy and raggedred fibers (MERRF) are rare disorders caused by point mutation of the tRNA gene of the mitochondrial genome. To understand the pathogenetic mechanism of MELAS and MERRF, we studied four patients. Serially sectioned frozen muscle specimens with a battery of histochemical stains were reviewed under light microscope and ultrastructural changes were observed under electron microscope. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was performed and the tRNA genes were sequenced to confirm mutations. In two patients with MELAS, strongly succinyl dehydrogenase positive blood vessels (SSVs) and many cytochrome oxidase (COX) positive raggedred fibers (RRFs) were observed, and A3243G mutations were found from the muscle samples. In two patients with MERRF, neither SSV nor COX positive RRFs were seen and A8344G mutations were found from both muscle and blood samples. In the two MERRF families, the identical mutation was observed among family members. The failure to detect the mutation in blood samples of the MELAS suggests a low mutant load in blood cells. The histochemical methods including COX stain are useful for the confirmation and differentiation of mitochondrial diseases. Also, molecular biological study using muscle sample seems essential for the confirmation of the mtDNA mutation.