Objective Mitochondrial disorder is one of the important factors in young stroke patients.To understand the clinical, pathological and molecular genetics features of Mitochondrial encephalomyopathies with lactic acidosis and stroke like episodes(MELAS).Methods Fifteen young stroke patients who were accordant with MELAS by biopsied skeletal muscle pathologies were analysed and related reports were reviewed. The clinical presentations,the findings of their biochemistry tests, the neuroimagings and the pathology of biopsied muscles were summarized. The hotspot mutations of mtDNA have been analyzed after PCR. For the patients without hotspot mutations, the sequential analyses of the entire mtDNA have been performed.Results All the patients have headache, stroke like episodes or seizures with the lesions in the cortex, especially in occipital and parietal lobes. The results of the MRI reveal some common features. Their biochemistry tests show the increase of blood lactic acid and the ratio of lactic acid to pyruvic acid and a slight increase of creatase. The biopsied muscles show the RRF andCOX/SDH blue-dyed fibers with the observation of the accumulation of mitochondria and intramitochondrial inclusions by electric microscopy. Mitochondrial DNA analysis revealed that eleven patients were caused by mutations in leucine tRNA1 gene, while CO3*9469C/T, ATP8*8489A/G,CO1*6253T/C was supposed as the causative mutation of three patients, alternatively. But there was not any mtDNA mutation identified in a patient.Conclusion MELAS is one of important diseases among young stroke patients which can be diagnosed by pathological study of biopsied muscles. The leucine tRNA1 gene is the most frequent causative gene.
