Furthermore, BLM treatment caused a fivefold (10 days) and threefold (21 days) increase in ATM phosphorylation (Fig. 1B; Appendix Fig. S1f), and a 40% (10 days) and 30% (21 days) increase in the amount of γH.2AX positive cells (Fig. 1D) compared with PBS-treated WT mice. This evidence concerns the gene ATM and Bloom syndrome.