Investigators have identified a second individual who remained cognitively normal into his late 60s despite having the PSEN1 E280A mutation, which causes a familial version of early-onset Alzheimer’s disease (AD). The likely source of protection, a mutation in a gene called Reelin, is distinct from the protective mechanism identified in the first case of an individual who was protected from the effects of PSEN1 E280A. That case was reported in 2019.