Manipulating the Genome of Human Embryos: Some Unforeseen Effects

In recent years scientists have developed powerful tools to create specific breaks in DNA sequences. They can then either repair those breaks or introduce new DNA into the sequence at the site of the break. These are called genome editing techniques. Two main techniques at present are the CRISPR-Cas9 system and zinc-finger nucleases. In principle, researchers can modify any part of the genome. They have achieved intended modifications in experiments with human and animal cells and also with mouse embryos. But the specific alterations do not always occur and there are also unintended effects.

The techniques are not as precise as they are sometimes made out to be, so there is every reason for caution in their application, especially in connection with the manipulation of human cells or human embryos. But over and beyond technical issues is the pressing ethical concern: should researchers cross the line into genetically manipulating human embryos?  

Knowing that scientists in China were performing these experiments, two groups of researchers and others published comments in Science and Nature in March 2015 warning about...