Upon activation of the repair mechanism, ATR phosphorylates checkpoint kinase 1 (CHK1), halting the cell cycle, initiating the non-homologous end joining (NHEJ) repair process via phosphorylation of MRE11, and activating the Fanconi anaemia (FA) pathway, thereby promoting homologous recombination (HR) repair of DNA damage (Figure 3(b)).126–128. This evidence concerns the gene CHEK1 and Friedreich ataxia.