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Serial MRIs of the brain revealed severe but evanescent cerebral cortical abnormalities.A left temporal brain biopsy was performed to exclude encephalitis.Light microscopy revealed a diffuse fibrillary gliosis with abundant reactive gemistocytes,focal evidence of ischemic neuronal injury, and edema.Electron microscopy revealed bizarre enlarged mitochondria and changes consistent with cellular edema.Succinate dehydrogenase staining was strongly reactive within cerebral blood vessels and within neurons.A point mutation was subsequently found at no 3243 of the mitochondrial tRNA Leu(UUR)gene in peripheral leukocytes and in brain,confirming the clinical diagnosis of MELAS.Quantitation revealed that 82%of brain mitochondria carried the disease mutation,indicating that most,if not all,tissues were affected.Our findings suggest that strokelike episodes in MELAS result from defects in neuronal metabolism,as well as in cerebral vasculature. |
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