The Guardian view on adjusting DNA: a new world | Editorial

A hope that embryos could be purged of a genetic disease has been fulfilled in part. However, we are some way off reimplanting modified embryos into their mothers - for all the right reasons

The news that a team of scientists from America and Korea have corrected a genetic defect in single-cell embryos is tremendous. In the short term it affirms the revolutionary principles of the gene editing technique known as Crispr - or, formally, Crispr-Cas9 . In the medium term it holds out the prospect - if the law changes - of eliminating some single-gene defects from entire families, since embryos treated in this way will no longer transmit the defective form of the gene. In the long term, the prospects for widespread genetic manipulation of humans are chilling as well as exhilarating.

Crispr makes it possible to manipulate a genome in the way that we can alter the words in a word processor. Very small identifying stretches of DNA around a defective gene can be targeted and then deliberately broken. The hope is that when the cell repairs the break, it does so without the original error. When the DNA is copied at the next cell division, only a functioning version of the gene is reproduced. When this is done early enough, at the embryo stage, the change does not last only for the patient's lifetime, but is transmitted to all their descendants, too.

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