Increased radiosensitivity has been found in cells from patients with DDR or DNA-repair disorders such as Ataxia Telangiectasia (defect in ATM), Nijmegen Breakage Syndrome (defect in NBS1), Fanconi anemia, defective Artemis, DNA ligase I and DNA ligase IV [33]. The gene discussed is LIG4; the disease is ataxia telangiectasia.