IGF1 and Alzheimer disease: Decreased serum levels of IGF-1 (Ramsey et al., 2004; Sonntag et al., 2005; Duron et al., 2014), and increased serum levels of TNF in AD patients (Perry et al., 2001; Holmes et al., 2009; Swardfager et al., 2010), might potentially impair hippocampal neurogenesis and/or neuroblast survival and differentiation.