BDNF and Alzheimer disease: In patients with AD, the precursor form of BDNF and mature BDNF or its mRNA are decreased in the parietal cortex and hippocampus in the early stage of the disease (Phillips et al., 1991; Holsinger et al., 2000; Michalski and Fahnestock, 2003; Peng et al., 2005).