Off target sites of the CRISPR CAS babies

Sure, we don’t know the genome of the Chinese couple (which would be mandatory for any prediction) . And we know only one confirmed off target site that has 5! mismatches

At least I would expect more than 1 off target site.. So we are could check several online services that include the human genome..


CRISPOR finds one region with 2 mismatches (intergenic) and 13 with 3 mismatches (7 intergenic hits, 5x introns (ST8SIA6, CTD-2532D12.5, CNTN5, C2D3, RABGAP1) and 1x exon of ACACA). This doesn’t match the reported off target sequence above, nor any reported de novo mutations (COL4A, CCDC170, NUCB2, GCDH, FTL).


Cas-OFFinder identifies 5 regions with 2 mismatches (1x intergenic, 2x sites in LIMCH1, 1x intergenic, 1 in BPIFC).

CCtop (yes, was waiting for that name)

COS finds only one intergenic region with 3 mismatches.


has the best explanation of what it does but cannot search from sgRNA to off-target as many other online tools.


is spotting 1 intergenic region with 2 mismatches,  3 with 3 mismatches (2 intergenic, 1 in RP11-238K6.1).

Taken together, this is largely random guess-work, making any prediction  in humans questionable.