PROGRESSIVE MYOCLONUS EPILEPSY AND MITOCHONDRIAL MYOPATHY ASSOCIATED WITH MUTATIONS IN THE TRNA(SER(UCN)) GENE

We report seven unrelated families with mitochdonrial tRNA(Ser(UCN)) g ene mutations at three different loci. A novel G7497A mutation is foun d in two families, both of which present with progressive myopathy, ra gged-red fibers, lactic acidosis, and deficiency of respiratory chain complexes I and IV. This mutation presumably affects the tertiary tRNA (Ser(UCN)) dihydrouridine interaction. Mutations 7472 insC and T7512C, found in three and two families, respectively, are associated with my oclonus epilepsy, dearness, ataxia, cognitive impairment, and complex IV deficiency. No ragged-red fibers or ultrastructural abnormalities a re seen. It is interesting that 6 of our 7 index patients are apparent ly homoplasmic, indicating a minor pathogenetic power of the tRNA(Ser( UCN)) mutations.