A new, brief study in mice from the Vinit Mahajan lab argues CRISPR can have very large numbers of off-target sites. Their paper is entitled “Unexpected mutations after CRISPR–Cas9 editing in vivo” and was published in Nature Methods.This work has garnered a lot of attention in the media. Let’s take a journal club review kind of approach to this pub.
In this paper there were two major reported findings. First, the number of reported CRISPR-associated mutations in the two mice studied (versus one control) were high, over a thousand overall and a small number were predicted to be functionally important in the sense of being disruptive to gene expression. Second, many of the off-target sites were not ones that would readily be anticipated in advance based on widely used computational predictive approaches and were not particularly similar to gRNA sequences. In the two mice the off-target sites strongly overlapped suggesting a non-random phenomenon. Continue reading “Journal club review of new CRISPR ‘lots of off-target activity’ mouse paper”