Unraveling the potential of CRISPR-Cas9 for gene therapy

The molecular machinery from the prokaryotic clustered regularly interspaced short palindromic repeats (CRISPR)-Cas immune system has broadly been repurposed for genome editing in eukaryotes. In particular, the sequence-specific Cas9 endonuclease can be flexibly harnessed for the genesis of precise double-stranded DNA breaks, using single guide RNAs that are readily programmable. The endogenous DNA repair machinery subsequently generates genome modifications, either by random insertion or deletions using non-homologous end joining (NHEJ), or designed integration of mutations or genetic material using homology-directed repair (HDR) templates. This technology has opened new avenues for the investigation of genetic diseases in general, and for gene therapy applications in particular.