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EN
Genomes are subject to a number of exogenous or endogenous DNA-damaging agents that cause DNA double-strand breaks (DSBs). These critical DNA lesions can result in cell death or a wide variety of genetic alterations, including deletions, translocations, loss of heterozygosity, chromosome loss, or chromosome fusions, which enhance genome instability and can trigger carcinogenesis. The cells have developed an efficient mechanism to cope with DNA damages by evolving the DNA repair machinery. There are 2 major DSB repair mechanisms: nonhomologous end joining (NHEJ) and homologous recombination (HR). One element of the repair machinery is the MRN complex, consisting of MRE11, RAD50 and NBN (previously described as NBS1), which is involved in DNA replication, DNA repair, and signaling to the cell cycle checkpoints. A number of kinases, like ATM (ataxia-telangiectasia mutated), ATR (ataxia-telangiectasia and Rad-3-related), and DNA PKcs (DNA protein kinase catalytic subunit), phosphorylate various protein targets in order to repair the damage. If the damage cannot be repaired, they direct the cell to apoptosis. The MRN complex as well as repair kinases are also involved in telomere maintenance and genome stability. The dysfunction of particular elements involved in the repair mechanisms leads to genome instability disorders, like ataxia telangiectasia (A-T), A-T-like disorder (ATLD) and Nijmegen breakage syndrome (NBS). The mutated genes responsible for these disorders code for proteins that play key roles in the process of DNA repair. Here we present a detailed review of current knowledge on the MRN complex, kinases engaged in DNA repair, and genome instability disorders.
EN
The results of brain MRI are presented in 22 patients with documented Nijmegen breakage syndrome (NBS), aged from 1 and 9/12 to 20 years. T1-, PD or FLAIR and T2-weighted SE/TSE images in three planes were obtained. Twenty-one patients showed microcephaly. Decreased size of frontal lobes and narrow frontal horns of the lateral ventricles was observed in all cases. In 6 patients agenesis of the posterior part of the corpus callosum was found as well as colpocephaly and temporal horn dilatation. In 2 patients callosal hypoplasia was accompanied by other anomalies: abnormal cerebrospinal fluid spaces. Sinusitis was present in all patients as a result of primary immunodeficiency. As in ataxia teleangiectasia and other breakage syndromes, NBS patients show inherited malignancy susceptibility and hypersensitivity to X and g radiation. Because of that computed tomography is contraindicated in these patients and MRI should be the method of choice in diagnostic imaging.
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