Duplications of mitochondrial DNA: implications for pathogenesis.

This paper describes the mapping data obtained on two patients in whom there was clear evidence for a rearrangement of mitochondrial DNA, using restriction enzyme analysis of DNA from whole blood and of polymerase chain reaction products. This suggested that a direct tandem duplication was present, and this was confirmed by sequence analysis of the junction fragment between duplicated segments. In each case the gene for cytochrome oxidase subunit I (MTCOX1) was interrupted, creating reading frames which, if transcribed and translated, would result in truncated versions of this peptide. Heteroplasmy and mosaicism for the abnormal mtDNA population were apparent. Preliminary data also suggest that high-molecular-weight rearrangements of the duplicated region are present in all tissues. The hypothesis that these duplicated genomes caused the phenotype was investigated by examining the distribution of duplicated genomes in various tissues using Southern hybridization and by RNA analysis. This included Northern blotting and cDNA sequencing. In order to investigate the origins of the duplicated mtDNAs, their distribution in different cells within a tissue was documented using the polymerase chain reaction.