Consequently, disruption of NHEJ proteins (Ku, DNA-PKcs, XLF, LIG4, and Artemis) often results in defects in DSB repair, radiation sensitivity, and severe combined immunodeficiency (SCID) (Li et al, 1995; Gu et al, 1997; Moshous et al, 2003; Buck et al, 2006). Here, NHEJ1 is linked to severe combined immunodeficiency.