CRISPR May Cause Many Off-Target Mutations

Image credit: Genome Research Limited

Image credit: Genome Research Limited

Questions are raised over the safety of the gene editing platform CRISPR-Cas9, as new research has revealed it may create a large number of unintended mutations

CRISPR has emerged as an efficient and more affordable way of editing genes in cells, and since its discovery has been widely adopted and tested in laboratories around the globe. It remains a highly promising technology but many scientists have doubts about the safety of the approach - querying whether the revolutionary system is accurate enough to avoid damaging off-target effects. 

Sequencing reveals accidental mutations

The bulk of the research has studied CRISPR using algorithms to identify regions of the genome which may have similarities to the sequence being targeted, and then testing these regions accordingly. A team of researchers has now instead utilised whole genome sequencing on mice which have undergone CRISPR treatment. 

"We feel it's critical that the scientific community consider the potential hazards of all off-target mutations caused by CRISPR, including single nucleotide mutations and mutations in non-coding regions of the genome. Researchers who aren't using whole genome sequencing to find off-target effects may be missing potentially important mutations"

Despite the previous predictive efforts, following a gene editing treatment two mice in the study were found to have 1,500 single-nucleotide mutations and over 100 sizeable deletions and insertions. These were importantly not in keeping with earlier predictions, and number vastly more than expected. 

Moving forward cautiously

Credit: National Institutes of Health (NIH)

Credit: National Institutes of Health (NIH)

This finding will have to be repeated on larger numbers of animals and cells to be confirmed further, but it certainly raises a red flag. With CRISPR now entering human clinical trials in China and the US it is a crucial finding to examine in fine detail. On a positive side note however, both mice in the study were apparently healthy with no ill effects after the therapy. This suggests that even with a myriad of off-target effects the likelihood of serious health effects may still be slim, With the development of more accurate and alternative versions of the CRISPR system this may become a negligible concern in the future. 

"We're physicians, and we know that every new therapy has some potential side effects—but we need to be aware of what they are. We hope our findings will encourage others to use whole-genome sequencing as a method to determine all the off-target effects of their CRISPR techniques and study different versions for the safest, most accurate editing"

 

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