PSEN1 and familial Alzheimer disease: The data do not support significant changes in adult hippocampal neurogenesis in fAD, yet they suggest some trends toward (1) reduced neurogenesis in fAD, supporting previous work on early-onset AD (Crews et al., 2010); (2) a disease-associated reduction in neurogenesis, despite younger NSC niches; and (3) mutation-specific effects, such as the reduced impact of the PSEN1 M139V mutation on Notch cleavage compared with other mutations.