In AD, total BDNF levels are decreased and the TrkB-TC:TrkB-FL ratio is increased in hippocampal and cortical post-mortem samples from AD patients (Phillips et al., 1991; Connor et al., 1997; Allen et al., 1999; Ferrer et al., 1999; Holsinger et al., 2000). This evidence concerns the gene NTRK2 and Alzheimer disease.