PSEN1 c.839A>C (p.Glu280Ala) [86], of European origin, is the largest family in the world with familial Alzheimer’s disease and living nearby is a family with the PSEN1 variant c.1247 T>C (p.Ile416Thr) [87] that originated in Africa. This evidence concerns the gene PSEN1 and early-onset autosomal dominant Alzheimer disease.