A NEW MITOCHONDRIAL TRNA(MET) GENE MUTATION IN A PATIENT WITH DYSTROPHIC MUSCLE AND EXERCISE INTOLERANCE

A 30-year-old woman with a novel heteroplasmic U4409C mtDNA mutation i n the tRNA(Met) gene presented with growth retardation, muscle weaknes s, severe exercise intolerance, and lactic acidosis. Muscle biopsy sho wed unusually severe dystrophic features. The mutation was not present in maternal relatives or 25 healthy subjects. Single-fiber PCR-RFLP a nalysis of mtDNA showed higher proportion of the mutation in COX-negat ive than in COX-positive muscle fibers.