THE CLINICAL FEATURES AND PATHOGENESIS IN MITOCHONDRIAL DNA MUTATION : BASIC STUDY FOR GENE THERAPY

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Mitochondrial DNA (mtDNA) mutations are associated with various disease. Recent studies have shown that there is a close association between the nt 3243 of t RNA^<Leu(UUR)> gene (A3243G mutation) and maternally inherited diabetes mellitus (DM). Multiorgan involvement has been suggested. As a test of exocrine pancreatic function, we performed a bentiromide test using benzoyl-tyrosyl-p-aminobenzoic acid (PABA). % recovery of PABA decreased at a range 19-68% (cf normal 81.9 8.5% ; DM 77.0 12.6%). The percentage of mutant mtDNA ranged from 6-63%. This result indicated that exocrine pancreatic dysfunction may be associated with the A3243G mutation. We have calculated the prevalence of spontaneous abortion in 379 women who delivered children in our hospital. The prevalence of spontaneous abortion was 14.4% (spontaneous abortion/total pregnancy=96/717). In our study, the prevalence of spontaneous abortion was higher in the population with the mutation than that of general population (25.0 vs 13.4%). In the basic study, we used C_2C_<12> myoblast treated with ethidium bromide 250 ng/ml for 10 days in medium. The cell line C2C12 was treated with EB for 10 days, and total RNA extract from cells from the cells. After 10 days incubation with EB, no mtRNA was detectable in C_2C_<12> cells, but the contents of beta-actin were not affected. After 60% confluent, we changed medium to 2% horse serum, 50 mug/ml uridine and 0.1 mg/ml pyruvate. Differentiation to myotubes in C_2C_<12> cells with EB was remarkably impaired. We also study the effect of EB in differentiated C_2C_<12> myotubes on insulin stimulated glucose transport. C_2C_<12> myotubes were treated with EB 3 days, and 2-deoxyglucose transport was measured. Insulin-stimulated glucose transport activity was decreased in C_2C_<12> myotubes treated with EB.In conclusion, we observed variable clinical symptoms in the patients and lacking of mtDNA induced a impaired muscle differentiation and its function in culture cells.