Interestingly, impairment of DNA ligase IV (LIG4), nibrin (NBS1), or aprataxin (APTX) activity as a result of genes’ deleterious mutation leads to severe disorders in DNA damage response known as LIG4 syndrome, Nijmegen breakage syndrome (NBS), and Ataxia oculomotor apraxia-1 (Chun and Gatti, 2004; Chrzanowska et al., 2012; Altmann and Gennery, 2016). The gene discussed is APTX; the disease is LIG4 syndrome.