PSEN1 and Alzheimer disease: The Christchurch variant rs121918393 (APOEChc: CGC > aGC, p.Arg[R]136Ser[S]) [19–21] and the Jacksonville variant rs199768005 (APOEJax: GTG > GaG, p.Val[V]236Glu[E]) [22, 23] have been identified as protective variants against AD in Caucasians, with the APOEChc variant apparently reducing the effects of the pathogenic PSEN1 variant (GAA > GcA, p.Glu[E]280Ala[A]), which is a highly penetrant and causative mutation for dominantly inherited AD [20, 21].