BDNF and major depressive disorder: Given the regulatory or activity dependent secretions of the BDNF is severely reduced (about 30%) in Met BDNF carriers (Chen et al., 2004; Egan et al., 2003), and the majority of BDNF protein is released from the regulated secretory pathway in neurons (Egan et al., 2003), it has been theorized that Met carriers are at greater risk of depression and other psychiatric disorders given low BDNF is considered a risk factor (Groves, 2007).