This is also corroborated by the existence of familiar forms of AD resulting from mutations in the APP gene, as well as in presenilin 1 (PS1 or PSEN1) and presenilin 2 (PS2 or PSEN2) genes, coding for these two proteins participating in the γ-secretase complex which are essential for its activity [16,46]. The gene discussed is APP; the disease is Alzheimer disease.