We present evidence that although extrachromosomal marker (mar) elements are relatively stable during extended culture of mosaic patient-derived fibroblasts, instability during the reprogramming process led to the derivation of isogenic non-carrier hiPSC lines as well as mosaic carrier hiPSC lines. Because this mutation was initially identified as a complex genomic rearrangement (CGR), rather than as a karyotypic abnormality, it represents a cautionary indication that the precise structure of any genetic mutation should be clarified before moving forward with hiPSC-based studies.
