CRISPR-Cas9 is the revolutionary gene-editing technology, discovered just a few years ago, that allows scientists to edit the DNA of any species with an unprecedented precision and efficiency. Today, thousands of researchers around the world are doing experiments with CRISPR, in the hope to cure us from genetic diseases and even deliver us designer babies. The first clinical trial to employ CRISPR-Cas9 is now underway in China, hoping to fight targeted cancers with modified immune cells.
The gene-editing method is based on the protective mechanism of bacteria against viruses. An RNA molecule carries segments of DNA from a previously encountered virus together with an enzyme (Cas9). Once the molecule encounters that same sequence of DNA, the enzyme gets activated and cuts it out. Researchers discovered that they can use this system to cut any DNA sequence at a precisely chosen location.
While the tool is touted for its precision, it is far from error free. Mutations do occur around the areas where the DNA has been cut and needs to be repaired. And sometimes CRISPR may hit unintended parts of the genome. Computer algorithms identify the most likely areas for these off-target mutations, which are later examined by researchers for deletions and insertions. However, whole-genome sequencing (WGS) – examining the entire DNA of living animals that had undergone gene editing – hadn’t been done.
In a recently published study in the journal Nature Methods, titled “Unexpected mutations after CRISPR–Cas9 editing in vivo” scientists used whole-genome sequencing to study the mutations that had occurred in the DNA of mice that had undergone CRISPR gene editing.