We recently discovered two copies of the rare APOE3 Christchurch (APOE3ch [Arg136→Ser]) mutation, located in the ApoE protein’s low-density lipoprotein receptor (LDLR) binding region, in an amyloid-β42 (Aβ42)-overproducing presenilin 1 (PSEN1) E280A mutation carrier from the world’s largest autosomal dominant AD (ADAD) kindred who did not develop mild cognitive impairment (MCI) until her 70s, nearly three decades after her kindred’s mean age at MCI onset5. The gene discussed is PSEN1; the disease is Cognitive impairment.