The m.3244G>A mutation in mtDNA is another cause of progressive external ophthalmoplegia.

We sequenced all mitochondrial tRNA genes in a 61-year-old man with chronic progressive external ophthalmoplegia and mitochondrial myopathy but without mtDNA rearrangements, and identified a heteroplasmic m.3244G>A mutation in the tRNA(Leu(UUR)) gene. This mutation had been previously associated with the MELAS phenotype, but not described in any detail. The mutation load in muscle was 84% and COX-negative fibers harbored greater levels of mutant genomes than COX-positive fibers. The m.3244G>A mutation affects a highly conserved nucleotide in the dihydrouridine loop and has been associated with a wobble modification deficiency of the mutant tRNA.