Reversion of an A-T iPSC line proved to be a valuable accident. However, the fact that an iPSC line derived from an A-T subject reverted at all provides a cautionary tale for those culturing gene variants in stem cells. Clearly, variations occur randomly in culture. As an example (Figure S2B), two different sublines prepared from the same individual exhibited 1,034 SNP variations from source cells independent of the ATM gene reversion. This rate of variation predicts that as many as 4 × 106 bp may vary between these lines across the entire genome. Clearly it is important that a gene variation of interest be monitored over growth of iPSC cultures, just as it is important to monitor cultures for evidence of cross-contamination (Yu et al., 2015). These results demonstrate that iPSC cultures must be evaluated continuously to ensure that the cells appropriately represent the genetic model being investigated.
