The Clinical And Genetic Analysis Of Heteroplasmic 3243A>G Mutation In Mitochondrial TRNA^Leu（UUR） Gene Among 6 Chinese Patients With MELAS

Mitochondrion is prevalent in eukaryote cells and can produce energy through oxidative phosphorylation. While during the transmission of electrons and protons, the appearance of electrons and protons leakage are detrimental to mitochondrial complexes, and result in the defects of respiratory chain. Then, a decline of ATP production in high energy dependent organs such as brain, skeletal muscle, cardiac and cochlea would lead to the dysfunction among these tissues, and thereby causing the abnormal in clinical expression, including mitochondrial myopathy and mitochondrial encephalomyopathies with lactic acidosis and stroke-like episodes (MELAS). In particular, MELAS is one of the most common mitochondrial disease, and up to 80% of the cases are caused by m.3243A>G in tRNALeu(UUR) gene.In present study, the physical tests including audition and blood-sugar content of 6 probands and maternal members who were from The Second Affiliated Hospital of Zhejiang University were analyzed. The MRI and MRS about brain imaging of 6 probands were studied. Histochemical methods such as modified Gomori, haematine et al were used to test muscle slice. Mitochondrial genomes were sequenced, and the heteroplasmic proportion of tRNALeu(UUR) gene m.3243A>G mutation was analyzed by restriction endonuclease Apa I and Pyrosequencing. Two patients with MELAS/Leigh syndrome had no m.3243 A>G mutation, and then mitochondrial genome DNAthat from muscle were sequenced, and two nuclear genes-POLG1 and SURF1 were screened to explore whether there existed pathologic mutation.Muscle slice gave a point that RRFs were be existence, and crystal-like inclusion body was observed through electron microscope. Mesencephalon, occipital lobe and bitamporal disorders were pointed out by MRI.In this study,4 patients with MELAS carried m.3243A>G heteroplasmic mutation, ranging from 29%-59%, and had an observation that the correlation between heteroplasmy and severity of clinical phenotype. One of the two patients who had no m.3243A>G mutation carried m.13094T>C heteroplasmic mutation in blood and homoplasmic mutation in muscle. The other had no any pathologic mutation but m.11084A>G which had been reported to have a contribution to MELAS/Leigh syndrome.More nuclear genes that lead to Leigh syndrome are screened to discover the pathologic mechanism among the subjects who were negative for the presence of m.3243A>G mutation.