Known causes of radiosensitive T– B– NK+ SCID include deficiencies of Artemis, DNA Ligase IV, DNA-dependent protein kinase catalytic subunit (DNA-PKcs), and Cernunnos–XRCC4-like factor (Cernunnos-XLF) (42), while ataxia-telangiectasia (AT) and Nijmegen breakage syndrome are counted among non-SCID forms of radiosensitive immunodeficiencies. This evidence concerns the gene LIG4 and ataxia telangiectasia.