According to the neurotrophin hypothesis, the imbalance of neurotrophins and their receptors during aging plays a critical role in abnormal Aβ accumulation, cholinergic and synaptic dysfunction, and hence, neurodegeneration in sporadic AD (Zhou 2016; Costantini et al. 2006; Cattaneo and Calissano 2012). Here, BDNF is linked to Alzheimer disease.