 However, XRCC1 mediated MMEJ repair is directly mutagenic, so in this case, over-expression, rather than under-expression, apparently leads to cancer.Reduction of mutagenic XRCC1 mediated MMEJ repair leads to reduced progression of cancer.Oxidative stress is increased in the brain during ischemic stroke leading to an increased burden on stress resistance mechanisms, including those for repairing oxidatively damaged DNA.