Mitochondrial base editor DdCBE causes substantial DNA off-target editing in nuclear genome of embryos

Mitochondrial DNA (mtDNA) is encapsulated by the organelle membrane 1 forming the barrier for the access of CRISPR-based gene-editing tools to the mtDNA. Furthermore, mitochondrial genome lacks similar repair systems for the protection of nuclear genome from DNA damage after induction of double-strand break by programmable nuclease such as ZFN, TALEN etc., which results in the elimination of target mtDNA 2 , 3 , 4 , 5 instead of mutation installation on mtDNA in contrast to the outcome of indel formation on nuclear DNA 6 . Recent studies positioned DdCBE as a promising technology to install targeted mutations or introduce transmissible mutations of base conversion in mammalian mtDNA 7 , 8 , 9 , 10 rather than eliminate them with previous ZF- or TALE-based nuclease 2 , 3 , 4 , 5 . Thus, DdCBE has the potential to model mitochondrial disease mutations, correct pathogenic variants, and expand our knowledge of mitochondrial biology. However, it is worth mentioning that these studies have found that DdCBE can cause low-frequent off-target events on mtDNA 9 , 10 . As indicated, the off-target profile of DdCBE remained to be comprehensively investigated by additional research for their systematic effect on mtDNA as well as nuclear genome.