In this work, we have expanded the use of mtZFNs through significant
design enhancements that permit targeting of pathogenic
mitochondrial genomes in cybrid cells. When targeted to pathogenic
mtDNA harbouring a point mutation or large-scale deletion, mtZFN
expression produces a heteroplasmy shift towards wild-type mtDNA
through selective degradation of mutant mtDNA. Moreover, a
decrease in the mutant mtDNA load results in phenotypic rescue of
the severe bioenergetic dysfunction associated with high levels of
partially deleted mtDNA. Thus, we provide a robust method for sitespecific
editing of mtDNA in patient-derived cybrid cells, with future
therapeutic potential.