The CRISPR/Cas9 gene editing system may cause nearly undetectable genetic damage, British researchers have warned.
The findings deal a blow to hopes that the technology could lead a medical revolution by allowing the editing of stem cells to treat diseases such as sickle cell disease.
Reporting in Nature Biotechnology, scientists say that standard DNA tests will not detect the genetic damage.
The work at the Wellcome Trust Sanger Institute, Cambridge, UK, involved a systematic study in mouse and human cells of the effects of gene editing.
The study found extensive mutations from the technique, often at some distance from the target site. These involved DNA deletions and insertions.
This could lead to important genes being switched on and off, the researchers warn.
Researcher Professor Allan Bradley said: "This is the first systematic assessment of unexpected events resulting from CRISPR/Cas9 editing in therapeutically relevant cells, and we found that changes in the DNA have been seriously underestimated before now.
“It is important that anyone thinking of using this technology for gene therapy proceeds with caution, and looks very carefully to check for possible harmful effects.”
Fellow researcher Michael Kosicki said: “My initial experiment used CRISPR/Cas9 as a tool to study gene activity, however it became clear that something unexpected was happening.
“Once we realised the extent of the genetic rearrangements we studied it systematically, looking at different genes and different therapeutically relevant cell lines, and showed that the CRISPR/Cas9 effects held true.”
Other scientists said the findings suggested a great deal more work would be needed before the technique can be used clinically.
An independent expert, Professor Maria Jasin, of Memorial Slone Kettering Cancer Centre, New York, said: “This study is the first to assess the repertoire of genomic damage arising at a CRISPR/Cas9 cleavage site. While it is not known if genomic sites in other cell lines will be affected in the same way, this study shows that further research and specific testing is needed before CRISPR/Cas9 is used clinically.”
Source: Kosicki, M., Tomberg, K. and Bradley, A., 2018. Repair of double-strand breaks induced by CRISPR–Cas9 leads to large deletions and complex rearrangements. Nature Biotechnology.
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