The majority of DNA repair defects that are most associated with immunodeficiencies are due to defects in 3 repair pathways: DSBR, MMR (such as LIG4 deficiency, ataxia telangiectasia, and Nijmegen Breakage syndrome) and BER (UNG deficiency). The gene discussed is LIG4; the disease is hyperinsulinemic hypoglycemia, familial, 4.