A new mtDNA mutation in the tRNA(Leu(UUR)) gene associated with ocular myopathy

We studied a patient with ptosis, ophthalmoparesis, and exercise intoleranc e who showed in her muscle biopsy ragged-red fibers and combined defects of the complexes I and IV of the mitochondrial respiratory chain, Molecular a nalysis revealed a T3273C transition in the mitochondrial DNA tRNA(Leu(UUR) ) gene. The mutation was heteroplasmic and very abundant in muscle from the proposita, less abundant in her other tissues studied, and still less abun dant in blood from her maternal relatives. Single muscle fiber analysis sho wed significantly higher levels of mutant genomes in ragged-red fibers than in normal fibers. The T3273C mutation affects a strictly conserved base pa ir in the anticodon stem and was not found in controls, thus satisfying the accepted criteria for pathogenicity. (C) 2001 Elsevier Science B.V. All ri ghts reserved.