<p>The CRISPR-Cas9 system has enabled researchers to precisely modify/edit the sequence of a genome. A typical editing experiment consists of two steps: (i) editing cultured cells and (ii) selection of clones, which are presumed to be isogenic, with and without the intended edit. The application of the CRISPR-Cas9 system may result in off-target edits, while cloning would reveal culture-acquired mutations. We analyzed the extent of the former and of the latter by whole genome sequencing (WGS) involving separate genomic loci in three experiments conducted by three independent laboratories. In all experiments we hardly found any off-target edits, while we detected hundreds to thousands of single nucleotide mutations unique to each clone after relatively short culture of 10-20 passages. Notably, clones also differed in copy number alterations that were several kb to several mb in size, representing the largest source of genomic divergence among clones. </p><p>This study in dbGaP includes data from experiments carried out by investigators at the Oklahoma Medical Research Foundation and Baylor College of Medicine (OMRF/BCM) involving an iPSC line derived from fibroblasts of a female patient (line c7) carrying a constitutional heterozygous variant (chr1:1,464,679 C>T; GRCh37) in exon 15 of the ATPase family, AAA domain containing 3A (ATAD3A) gene. The parental line was edited by introducing a double stranded break at the variant allele to correct the variant by homology directed repair. Two unedited control clones (clone7 and clone8) and one edited clone (SC20) were selected for WGS. </p>

Clonally Selected Lines after CRISPR/Cas Editing are not Isogenic