New research finds one copy of a protective genetic variant, APOE3 Christchurch, delayed onset of Alzheimer’s disease for 27 members of a ~6,000-person family in Colombia at high risk for early-onset Alzheimer’s in their 40s due to carrying the ‘Paisa’ (Presenilin-1 E280A) mutation. This work builds on a 2019 case report of a woman in this family who had two copies of the Christchurch variant and delayed Alzheimer’s into her 70s. The new findings are the first to show that one copy of the variant confers some level of protection and increases the researchers’ confidence that this genetic pathway should be targeted for therapeutics.