Of interest, the rare APOE ε3 Christchurch p. Arg136Ser mutation has recently been reported to delay onset of cognitive symptoms by 3 decades in a carrier of the Colombian PSEN1 p.Glu280Ala mutation.22,23 These findings could have implications for the role of APOE in the pathogenesis, treatment, and prevention of AD and highlight how much remains unknown about the complexities of interactions between different genetic risk factors and their influence on disease onset and survival. The gene discussed is PSEN1; the disease is Alzheimer disease.