BDNF signaling is crucial for the action of essentially all AD drugs (Autry and Monteggia, 2012; Castrén and Antila, 2017; Duman and Monteggia, 2006), but this effect has been assumed to be indirectly mediated by other proteins such as 5HTT or NMDA receptors. This evidence concerns the gene SLC6A4 and Alzheimer disease.