This process initially involves the activation of either the serine/threonine protein kinases ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3-related or DNA-dependent protein kinase catalytic subunit, subsequently leading to the phosphorylation of histone H2AX at S139 (γH2AX)7–11. Here, ATM is linked to ataxia telangiectasia.