FISH in interphase cells confirmed that 9p24.1-carrier hiPSCs from both the proband (DL3363) and mother (DL5459) showed evidence of cells with two (left) or three (right) chr 9 signals (within the DAPI-positive nuclei) (Figure 3A). Moreover, additional FISH images demonstrated overlap of the chr 9 signal with the mar element, indicating that the mar is likely the source of the chr 9 DUP/TRP sequence (Figure 3C). The percentage of mosaicism in two genotype-positive hiPSCs, one with high mar and one with low mar mosaicism, by G-banding karyotype analysis at p12 (DL3363 C1, 10%; DL5459 C5, 55%), was comparable with the level of mosaicism determined by FISH at p12 (DL3363 C1, 6.5%; DL5459 C5, 49.0%), despite being tested 6–12 months apart (Figure 3B and Table S3).
