Reprint of “The clinical impact of deficiency in DNA non-homologousend-joining”

DNA non-homologous end-joining (NHEJ) is the major DNA double strand break (DSB) repair pathway inmammalian cells. Defects in NHEJ proteins confer marked radiosensitivity in cell lines and mice models,since radiation potently induces DSBs. The process of V(D)J recombination functions during the devel-opment of the immune response, and involves the introduction and rejoining of programmed DSBs togenerate an array of diverse T and B cells. NHEJ rejoins these programmed DSBs. Consequently, NHEJdeficiency confers (severe) combined immunodeficiency – (S)CID – due to a failure to carry out V(D)Jrecombination efficiently. NHEJ also functions in class switch recombination, another step enhancing Tand B cell diversity. Prompted by these findings, a search for radiosensitivity amongst (S)CID patientsrevealed a radiosensitive sub-class, defined as RS-SCID. Mutations in NHEJ genes, defining human syn-dromes deficient in DNA ligase IV (LIG4 Syndrome), XLF-Cernunnos, Artemis or DNA-PKcs, have beenidentified in such patients. Mutations in XRCC4 or Ku70,80 in patients have not been identified. RS-SCIDpatients frequently display additional characteristics including microcephaly, dysmorphic facial featuresand growth delay. Here, we overview the clinical spectrum of RS-SCID patients and discuss our currentunderstanding of the underlying biology

Immune diversity and genomic stability: opposite goals but similar paths

DNA damage response mechanisms serve to protect cells from exogenous and endogenous DNA damaging agents with the aim of maintaining genomic stability. In contrast, the generation of an efficient immune response requires the creation of a repertoire of distinct immunoglobulin and T cell receptor genes able to recognise the huge array of antigens that may be encountered in a lifetime. Surprisingly, cells have exploited the same mechanisms used to maintain genomic integrity to create genetic diversity during immune development. Here, we review the damage response mechanisms operating on DNA double strand breaks and their function during development of the immune response. We discuss disorders that are associated with immunodeficiency and defective responses to the presence of DNA double strand breaks