A recent attempt by Chinese scientists to modify human embryos showed serious problems with that strategy. From the paper [1]: "...the efficiency of homologous

A recent attempt by Chinese scientists to modify human embryos showed serious problems with that strategy. From the paper [1]: "...the efficiency of homologous recombination directed repair...was low and the edited embryos were mosaic. Off-target cleavage was also apparent... Furthermore, the endogenous delta-globin gene (HBD), which is homologous to HBB, competed with exogenous donor oligos to act as the repair template, leading to untoward mutations. Our data also indicated that repair of the HBB locus in these embryos occurred preferentially through the non-crossover HDR pathway. Taken together, our work highlights the pressing need to further improve the fidelity and specificity of the CRISPR/Cas9 platform, a prerequisite for any clinical applications of CRSIPR/Cas9-mediated editing." Maybe we'll find a system that's better or we'll modify Cas9 somehow to stop these off-target effects, but for now it's not really viable. [1] http://link.springer.com/article/10.1007%2Fs13238-015-0153-5 http://link.springer.com/article/10.1007%2Fs13238-015-0153-5