PSEN1 and familial Alzheimer disease: The underlying nature of signaling alterations arising from the mutations in presenilin 1 or presenilin 2 genes that give rise to familial Alzheimer’s disease (FAD) in humans are unclear (Saura et al., 2004; Walker et al., 2005; Qi-Takahara et al., 2005; Kumar-Singh et al., 2006; Sambamurti et al., 2006; De Strooper, 2007; Hardy, 2007; Isoo et al., 2007; Shen and Kelleher, 2007; Wolfe et al., 2007).