CHEK1 and Friedreich ataxia: With this aim in mind, we conducted 2 experiments in which FA-like CD34+ cells were incubated with a specific inhibitor of CHEK-1 (SB-2118078) that prevents the MMC-mediated accumulation of FA cells in the G2/M phase of the cell cycle and also the phosphorylation of CHEK-1 in FA cells (Supplemental Figure 5, A and B, respectively).