Chronic progressive external ophthalmoplegia: A new heteroplasmic tRNALeu(CUN) mutation of mitochondrial DNA

We sequenced all genes of mitochondrial tRNAs of a patient with chronic progressive external ophthalmoplegia with 5% ragged red fibres and 15% COX-negative fibres but without macrorearrangements of mitochondrial DNA (mtDNA). Direct sequencing showed a novel heteroplasmic G > A substitution in position 12316 of tRNALeu(CUN) gene. This change destroys a highly conserved G–C base coupling in tRNA TψC branch. By RFLP analysis we could demonstrate different degrees of heteroplasmy in different patient's tissues. This alteration, absent in a population of 110 patients with different encephalomyopathies, can be considered pathogenic: it is the tenth tRNALeu(CUN) pathogenic mutation described up to date.