BDNF and Alzheimer disease: Since then, a reduction of BDNF protein and mRNA expression have been consistently reported in AD brain (Connor et al., 1997; Hock et al., 2000; Holsinger et al., 2000; Michalski et al., 2015; Buchman et al., 2016) as well as in serum (Laske et al., 2007; Ventriglia et al., 2013; Siuda et al., 2017).