In AD, earliest disease onset ages are recorded in PSEN1 mutation carriers, in whom the disease starts on average 8.4 years earlier than in APP mutation carriers (average 42.9 vs. 51.3 years) and 14.2 years earlier than in PSEN2 mutation carriers (average 57.1 years) (Fig. 1). This evidence concerns the gene PSEN2 and Alzheimer disease.