RESUMO
Myoclonic epilepsy associated with ragged red fibers (MERRF) is a rare mitochondrial disorder. Diagnostic criteria for MERRF include typical manifestations of the disease: myoclonus, generalized epilepsy, cerebellar ataxia and ragged red fibers (RRF) on muscle biopsy. Clinical features of MERRF 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 tRNALys gene of the DNAmt, mainly A8344G, are responsible for almost 90% of MERRF cases. Morphological changes seen upon muscle biopsy in MERRF include a substantive proportion of RRF, muscle fibers showing a deficient activity of cytochrome c oxidase (COX) and the presence of vessels with a strong reaction for succinate dehydrogenase and COX deficiency. In this review, we discuss mainly clinical and laboratory manifestations, brain images, electrophysiological patterns, histology and molecular findings as well as some differential diagnoses and treatments.
Assuntos
Síndrome MERRF/diagnóstico , Diagnóstico Diferencial , Humanos , Síndrome MERRF/tratamento farmacológico , Síndrome MERRF/genéticaRESUMO
Myoclonic epilepsy associated with ragged red fibers (MERRF) is a rare mitochondrial disorder. Diagnostic criteria for MERRF include typical manifestations of the disease: myoclonus, generalized epilepsy, cerebellar ataxia and ragged red fibers (RRF) on muscle biopsy. Clinical features of MERRF 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 tRNALys gene of the DNAmt, mainly A8344G, are responsible for almost 90% of MERRF cases. Morphological changes seen upon muscle biopsy in MERRF include a substantive proportion of RRF, muscle fibers showing a deficient activity of cytochrome c oxidase (COX) and the presence of vessels with a strong reaction for succinate dehydrogenase and COX deficiency. In this review, we discuss mainly clinical and laboratory manifestations, brain images, electrophysiological patterns, histology and molecular findings as well as some differential diagnoses and treatments.
Epilepsia mioclônica associada com fibras vermelhas rasgadas (MERRF) é uma rara doença mitocondrial. O critério diagnóstico para MERRF inclui as manifestações típicas da doença: mioclonia, epilepsia generalizada, ataxia cerebelar e fibras vermelhas rasgadas (RRF) na biópsia de músculo. Na fase inicial da doença, as manifestações clínicas podem não ser uniformes, e correlação entre as manifestações clínicas e fisiopatologia não estão completamente elucidadas. Estima-se que as mutações de ponto no gene tRNALys do DNAmt, principalmente a A8344G, sejam responsáveis por quase 90% dos casos de MERRF. As alterações morfológicas na biópsia muscular incluem uma grande proporção de RRF, fibras musculares com deficiência de atividade da citocromo c oxidase (COX) e presença de vasos com forte reação para succinato desidrogenase e deficiência da COX. Nesta revisão, são discutidas as principais manifestações clínicas e laboratoriais, imagens cerebrais, padrões eletrofisiológicos, histológicos e alterações moleculares, bem como, alguns dos diagnósticos diferenciais e tratamentos.
Assuntos
Humanos , Síndrome MERRF/diagnóstico , Diagnóstico Diferencial , Síndrome MERRF/tratamento farmacológico , Síndrome MERRF/genéticaRESUMO
Myoclonic epilepsy with ragged red fibers (MERRF) is a mitochondrial disease that is characterized by myoclonic epilepsy with ragged red fibers (RRF) in muscle biopsies. The aim of this study was to analyze Brazilian patients with MERRF. Six patients with MERRF were studied and correlations between clinical findings, laboratory data, electrophysiology, histology and molecular features were examined. We found that blood lactate was increased in four patients. Electroencephalogram studies revealed generalized epileptiform discharges in five patients and generalized photoparoxysmal responses during intermittent photic stimulation in two patients. Muscle biopsies showed RRF in all patients using modified Gomori-trichrome and succinate dehydrogenase stains. Cytochrome c oxidase (COX) stain analysis indicated deficient activity in five patients and subsarcolemmal accumulation in one patient. Molecular analysis of the tRNA(Lys) gene with PCR/RFLP and direct sequencing showed the A8344G mutation of mtDNA in five patients. The presence of RRFs and COX deficiencies in muscle biopsies often confirmed the MERRF diagnosis. We conclude that molecular analysis of the tRNA(Lys) gene is an important criterion to help confirm the MERRF diagnosis. Furthermore, based on the findings of this study, we suggest a revision of the main characteristics of this disease.