 Four (ataxia-telangiectasia, ataxia-telangiectasia-like disorder, Nijmegen breakage syndrome and Alzheimer's disease) are defective in genes involved in repairing DNA double-strand breaks.Overall, it seems that oxidative stress is a major cause of genomic instability in the brain.A particular neurological disease arises when a pathway that normally prevents oxidative stress is deficient, or a DNA repair pathway that normally repairs damage caused by oxidative stress is deficient.