Analysis of DNA repair factors has revealed that depletion of breast cancer DNA repair factor BRCA1 is associated with Alzheimer disease (AD). BRCA1 dysfunction is known to have a role in breast cancer, and Elsa Suberbielle and colleagues have now shown that BRCA1 levels are low in the brains of people with AD and of mice that are transgenic for the human amyloid precursor protein. In mice, BRCA1 depletion caused cognitive and learning deficits, but not neuronal death. Neuronal activity seemed to regulate BRCA1 levels, and accumulation of amyloid-β depleted BRCA1 levels.