ATM and ataxia telangiectasia: Ataxia-telangiectasia-mutated (ATM) is an attractive therapeutic target as constitutional loss of ATM in ataxia-telangiectasia (A-T) patients causes profound sensitivity to DNA damaging agents that induce double-strand breaks (e.g. ionizing radiation).1,2 ATM is the major signalling kinase involved in the initiation of double-strand break (DSB) repair by homologous recombination (HR) and activated by exposed DNA double-stranded ends.3 ATM can trigger cell cycle checkpoints (G1/S and intra-S phase) to ensure fidelity of DNA repair and cell survival.4