Weeks after the pioneers of gene-editing techniques warned against germline editing, or the modification of the genome in human embryos, Chinese scientists have confirmed that they indeed tried it out, but with very poor results. Though the Chinese scientists were working on non-viable embryos—embryos that undergo the first stage of development but can’t result in live birth—in vitro, and were testing if they could eliminate a potentially fatal, gene-borne blood disorder, ß-thalassaemia, the outcry against the attempt has been prompt and vocal. However, that the experiment failed, and precisely in a manner of which the geneticist community and the ethicists were apprehensive of, perhaps served the naysayers’ purpose the best. For one, the modification was only apparent in four of the 85 test embryos, and in all four, certain cells overrode the modification to revert to the original gene, leaving these embryos genetic mosaics. In all four, there was collateral damage—mutations were left behind as the cells tried to override the edited sequence. In all other cases, the embryo died or the modification was entirely obliterated.
While the envisaged benefits of germline editing—ending debilitating and fatal genetic conditions is one—are many, the Chinese research has shown that it is by no means a fail-safe technology, at least as of yet. In fact, given that any viable modification would be inheritable, germline editing poses searching ethical questions. The exact consequences can perhaps never be comprehensively understood as how the body responds to a modification at the cellular level remains unclear, as evidenced by the genetic mosaics the Chinese study created.