Table 1.

Summary of reported on- and off-target mutation frequencies of single and dual CRISPR-Cas9 systems

Investigators	Platform	Reported on-targeting (%)	Reported off-targeting (%)
Shalem et al., 2014 [39]	Single Cas platform	~100	0–15b
Wang et al., 2014 [41]	Single Cas platform	97	0–29.5c
Koike-Yusa et al., 2014 [42]	Single Cas platform	12.7	~0.7d
Tsai et al., 2014 [46]	Dual Cas platform	3–40	0
Ran et al., 2013 [48]	Dual Cas platform	40a	0
Guilinger et al., 2014 [47]	Dual Cas platform	8–22	0

^aOn-target mutation frequencies of up to 40% were observed in target sequences when the distance between the Cas9 nickase pairs were between −4 and +20 bp.

^b9 of 12 sgRNAs showed minimal (~0–3%) modification of predicted off-target sites. 3 of 12 sgRNAs showed modification (~15% or higher) on at least 1 of their off-target sites.

^c0–2.5% cleavage of 12 of the 13 predicted off-target sites, 29.5% cleavage of 1 of the 13 predicted off-target sites.

^dCleavage analysis of 275 potential off-target sites for the Pigga site 2 sgRNA revealed only 2 of those potential off-target sites were cleaved and both were in noncoding regions (2/275*100 = ~0.7%).