Heterozygous and homozygous GADD45B knockout in human iPSCs results in high levels of DNA damage. (A) Pluripotency state of GADD45B^+/− and GADD45B^−/− iPSCs was assessed by real-time quantitative PCR and compared with validated healthy donor–derived human iPSCs expressing wild-type GADD45B. (B) GADD45B wild-type, GADD45B^+/−, and GADD45B^−/− iPSCs were irradiated with UV light for 5 minutes, incubated under cell culture conditions for 2 hours, and stained for intracellular γH2AX (phospho-Ser139). DNA damage in GADD45B wild-type and GADD45B heterozygous-knockout (C) or homozygous-knockout (D) iPSCs was quantified by the LORD-Q method. Cells were analyzed for mtDNA damage and nuclear DNA damage in the GAPDH and TP53 gene loci. All data are mean ± standard deviation derived from 3 independent experiments. *P ≤ .05, **P ≤ .01, ***P ≤ .001, Student t test.