Peripheral and central BDNF levels are reduced in MS (Connor et al., 1997; Baker et al., 2010; Laske et al., 2010; Pereira et al., 2013), and are associated with signs of depression and anxiety due to reduced release of synaptic proteins and neurotransmitters (monoamines and opioids) (Egan et al., 2003; Hariri et al., 2003; Vaynman et al., 2006). This evidence concerns the gene BDNF and major depressive disorder.