CRISPR/Cas9 is one of the newest genome editing tools. It can alter sections of DNA in cells by cutting at specific points and introducing changes at that location. Scientists at the Wellcome Sanger Institute carried out a full systematic study in both mouse and human cells and discovered that CRISPR/Cas9 frequently caused extensive mutations, but at a greater distance from the target site.

Published in the journal Nature Biotechnology, the study found that CRISPR/Cas9 gene editing can cause greater genetic damage in cells than was previously thought. The researchers found that many of the cells had large genetic rearrangements such as DNA deletions and insertions.

These results create safety implications for gene therapies using CRISPR/Cas9 in the future as the unexpected damage could lead to dangerous changes in some cells. In addition, some of these changes were too far away from the target site to be seen with standard genotyping methods. The researchers stressed that standard tests for detecting DNA changes miss finding this genetic damage, and that caution and specific testing will be required for any potential gene therapies.