Chronic Progressive External Ophthalmoplegia Is Associated with a Novel Mutation in the Mitochondrial tRNA(Asn) Gene

Chronic progressive external ophthalmoplegia (CPEO) is caused by a
decreased oxidative phosphorylation (OXPHOS) activity due to
large-scale deletions of the mitochondrial genome in 50 % of the
patients. The deletions encompass structural OXPHOS genes as well
as tRNA genes, required for their expression so that the
pathogenesis could be due to the deleted OXPHOS subunits or to an
impaired mitochondrial translation. We have analyzed the
mitochondrial genome of a patient presenting with CPEO for single
base substitutions and discovered a novel heteroplasmic mutation in
the tRNAAsn gene at position 5692 that converts a highly conserved
adenine into a guanine. This mutation is unique because it is
located at the transition of the anticodon loop to the anticodon
stem and it leads to an additional base pair, thus reducing the
number of loop-forming nucleotides from seven to five. Our findings
suggest that CPEO can be caused by a single base substition in a
mitochondrial tRNA gene so that the mitochondrial protein synthesis
becomes the rate limiting step in OXPHOS fidelity.