When designing such an experiment, it is also important to consider the inherent variability between patients as well as in the processes of both reprogramming of somatic cells to iPSCs and differentiation into particular cell types. It has been suggested that at least part of this heterogeneity results from an “epigenetic memory” of the DNA methylation signature of the cell type from which the iPSCs were derived (Kim et al. 2010), which may impact upon the phenotypes observed, or the ability to differentiate into particular lineages (Bar-Nur et al. 2011). Reassuringly however, recent studies looking at the origin of heterogeneity within 25 iPSC lines have demonstrated that, at least at the transcriptional level, the majority of variation is due to genetic background as opposed to any epigenetic contribution (Rouhani et al. 2014). In order to account for such inherent variability, it is necessary to analyse multiple (typically at least three) patients, each with independent iPSC derivations, clonally derived lines and differentiation experiment, which rapidly increases the number of samples that need to be analysed (Fig. 2). The number of each
