For the first time, biologists are trying to get the CRISPR gene-editing machinery directly into mature human sperm, rather than into fertilised embryos. The work is still at an early stage but could lead to a new way to prevent inherited diseases.

Around half a dozen teams have used the CRISPR genome-editing method to alter the DNA of human embryos but it is still far from clear whether this approach is safe . One issue is that the embryo …