A NOVEL MITOCHONDRIAL TRANSFER-RNA ISOLEUCINE GENE MUTATION CAUSING CHRONIC PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA

We report a sporadic case of chronic progressive external ophthalmople gia that developed during childhood and was associated with ragged-red and cytochrome c oxidase (COX)-negative fibers in skeletal muscle. Se quencing of all the mitochondrial transfer RNA (tRNA) genes identified a single potentially pathogenic mutation-a T to C transition at posit ion 4274 in the tRNA(Ile) gene. This mutation was not present in skele tal muscle from 79 controls, and the level of the mutation in COX-nega tive fibers was significantly greater than the level in COX-positive f ibers.