Primary immunodeficiency syndromes associated with defective DNA double-strand break repair.

Damaging DNA double-strand breaks (DNA-DSBs) following ionizing radiation (IR) exposure, potentially lead to cell death or carcinogenesis. Non-homologous end-joining (NHEJ) is the main repair pathway employed by vertebrate cells to repair such damage. Many repair pathway proteins have been identified. The creation of many diverse lymphocyte receptors to identify potential pathogens has evolved by breaking and randomly re-sorting the gene segments coding for antigen receptors. Subsequent DNA-DSB repair utilizes the NHEJ proteins. Individuals with defective repair pathways are increasingly recognized with radiosensitivity and immunodeficiency. Patients with defects in ataxia-telangiectasia mutated, nibrin, MRE11, Rad50, Artemis, DNA ligase IV and Cernunnos-XRCC4-like factor have been identified. Most exhibit immunodeficiency, with a spectrum of presentation and overlap between conditions. Conventional treatment with immunoglobulin replacement or haematopoietic stem cell transplantation (HSCT) can be effective. A greater understanding of the molecular defect will enable better, tailored therapies to improve survival.